CS562 References

Collapse All
Expand All
Toggle All

• References:
  • Ambient Occlusion: Ambient Occlusion techniques calculate, in real-time, the occlusion of lighting environment under/near objects.

    • Practical Realtime Strategies for Accurate Indirect Occlusion Abstract 2016 Jorge Jimenez, Xian-Chun Wu, Angelo Pesce, Adrian Jarabo Ambient occlusion is ubiquitous in games and other real-time applications to approximate global illumination effects. However there is no analytic solution to ambient occlusion integral for arbitrary scenes, and using general numerical integration algorithms is too slow, so approximations used in practice often are empirically made to look pleasing even if they don’t accurately solve the AO integral. In this work we introduce a new formulation of ambient occlusion, GTAO, which is able to match a ground truth reference in half a millisecond on current console hardware. This is done by using an alternative formulation of the ambient occlusion equation, and an efficient implementation which distributes computation using spatio-temporal filtering. We then extend GTAO with a novel technique that takes into account near-field global illumination, which is lost when using ambient occlusion alone. Finally, we introduce a technique for specular occlusion, GTSO, symmetric to ambient occlusion which allows to compute realistic specular reflections from probe-based illumination. Our techniques are efficient, give results close to the ray-traced ground truth, and have been integrated in recent AAA console titles.

    • Scalable Ambient Obscurance Abstract 2012 Morgan McGuire, Michael Mara, and David Luebke This paper presents a set of architecture-aware performance and integration improvements for a recent screen-space ambient obscurance algorithm. These improvements collectively produce a 7× performance increase at 2560 × 1600, generalize the algorithm to both forward and deferred renderers, and eliminate the radius- and scene-dependence of the previous algorithm to provide a hard real-time guarantee of fixed execution time. The optimizations build on three strategies: pre-filter the depth buffer to maximize memory hierarchy efficiency; reduce total bandwidth by carefully reconstructing positions and normals at high precision from a depth buffer; and exploit low-level intra- and inter-thread techniques for parallel, floating-point architectures.

    • The Alchemy Screen-Space Ambient Obscurance Algorithm Abstract 2011 Morgan McGuire, Brian Osman, Michael Bukowski, Padraic Hennessy Ambient obscurance (AO) produces perceptually important illumination effects such as darkened corners, cracks, and wrinkles; prox- imity darkening; and contact shadows. We present the AO algorithm from the Alchemy engine used at Vicarious Visions in com- mercial games. It is based on a new derivation of screen-space obscurance for robustness, and the insight that a falloff function can cancel terms in a visibility integral to favor efficient operations. Alchemy creates contact shadows that conform to surfaces, captures obscurance from geometry of varying scale, and provides four intuitive appearance parameters: world-space radius and bias, and aesthetic intensity and contrast.

    • Volumetric Obscurance Abstract 2010 Bradford James Loos, Peter-Pike Sloan Obscurance and Ambient Occlusion (AO) are popular techniques in both film and games that model how ambient light is shadowed. While it is largely a solved problem for static scenes, for dynamic scenes it is still difficult to compute at interactive rates. Recent attempts to compute AO in screen space for dynamic scenes either have poor performance or suffer from under-sampling problems. We formulate the problem as a 3D volumetric integral, which maps more naturally to graphics hardware. This integral can be solved using line samples to improve the under-sampling problems that plague other techniques. Following the idea of line integrals to its logical conclusion, we show results using area samples that use a simple statistical model of the depth buffer that allows us to use a single sample. We also discuss strategies for generating point, line, and area sample patterns along with ways to incorporate the surface normal into the volume obscurance calculation.

    • A Simple and Practical Approach to SSAO Abstract 2010 José María Mendez Global illumination (GI) is a term used in computer graphics to refer to all lighting phenomena caused by interaction between surfaces (light rebounding off them, refracting, or getting blocked), for example: color bleeding, caustics, and shadows. Many times the term GI is used to refer only to color bleeding and realistic ambient lighting. Direct illumination – light that comes directly from a light source – is easily computed in real-time with today´s hardware, but we can´t say the same about GI because we need to gather information about nearby surfaces for every surface in the scene and the complexity of this quickly gets out of control. However, there are some approximations to GI that are easier to manage. When light travels through a scene, rebounding off surfaces, there are some places that have a smaller chance of getting hit with light: corners, tight gaps between objects, creases, etc. This results in those areas being darker than their surroundings.

    • Approximating Dynamic Global Illumination in Image Space Abstract 2009 Tobias Ritschel, Thorsten Grosch, Hans-Peter Seidel Physically plausible illumination at real-time framerates is often achieved using approximations. One popular example is ambient occlusion (AO), for which very simple and efficient implementations are used extensively in production. Recent methods approximate AO between nearby geometry in screen space (SSAO). The key observation described in this paper is, that screen-space occlusion methods can be used to compute many more types of effects than just occlusion, such as directional shadows and indirect color bleeding. The proposed generalization has only a small overhead compared to classic SSAO, approximates direct and one-bounce light transport in screen space, can be combined with other methods that simulate transport for macro structures and is visually equivalent to SSAO in the worst case without introducing new artifacts. Since our method works in screen space, it does not depend on the geometric complexity. Plausible directional occlusion and indirect lighting effects can be displayed for large and fully dynamic scenes at real-time frame rates.

    • Screen Space Ambient Occlusion Abstract 2008 Louis Bavoil, Miguel Sainz Ambient occlusion is a lighting model that approximates the amount of light reaching a point on a diffuse surface based on its directly visible occluders. It is commonly used to add a global illumination look to rendered images. This ambient occlusion algorithm operates on the depth buffer of the scene being rendered and associated per-pixel normals. For multiple directions defined in image space around the current pixel, the algorithm samples the depth buffer, computes a horizon angle for each sample, and integrates the ambient occlusion for the current direction based on the tangent plane, the horizon angle and a weighting function. This whitepaper includes a brief introduction to the algorithm and its parameters. For more details, please refer to [Bavoil and Sainz 08a] and [Bavoil and Sainz 08b].

    • Image-Space Horizon-Based Ambient Occlusion Abstract 2008 Louis Bavoil, Miguel Sainz Siggraph 2008 presentation (47 slides)

    • Image-Space Horizon-Based Ambient Occlusion Abstract 2008 Louis Bavoil, Miguel Sainz, Rouslan Dimitrov Ambient occlusion is a lighting model that approximates the amount of light reaching a point on a diffuse surface based on its directly visible occluders. It gives perceptual clues of curvature and spatial proximity. Like [Mittring 2007] and [Shanmugam and Arikan 2007], we propose a real-time ambient occlusion computation as a postprocessing pass mainly based on a depth image from the eye’s point of view. This approach requires no scene- dependent precomputations and is applicable to dynamic scenes. Our proposed method does not have the overocclusion issue from [Shanmugam and Arikan 2007] and samples inside the radius of influence, unlike [Mittring 2007].

    • Hardware Accelerated Ambient Occlusion Techniques on GPUs Abstract 2007 Perumaal Shanmugam, Okan Arikan We introduce a visually pleasant ambient occlusion approximation running on real-time graphics hardware. Our method is a multi-pass algorithm that separates the ambient occlusion problem into highfrequency, detailed ambient occlusion and low-frequency, distant ambient occlusion domains, both capable of running independently and in parallel. The high-frequency detailed approach uses an image-space method to approximate the ambient occlusion due to nearby occluders caused by high surface detail. The low-frequency approach uses the intrinsic properties of a modern GPU to greatly reduce the search area for large and distant occluders with the help of a low-detail approximated version of the occluder geometry. Our method utilizes the highly parallel, stream processors (GPUs) to perform real-time visually pleasant ambient occlusion. We show that our ambient occlusion approximation works on a wide variety of applications such as molecular data visualization, dynamic deformable animated models, highly detailed geometry. Our algorithm demonstrates scalability and is well-suited for the current and upcoming graphics hardware.

    • A Practical Analytic Single Scattering Model for Real Time Rendering Abstract 2004 Bo Sun, Ravi Ramamoorthi, Srinivasa G. Narasimhan, Shree K. Nayar We consider real-time rendering of scenes in participating media, capturing the effects of light scattering in fog, mist and haze. While a number of sophisticated approaches based on Monte Carlo and finite element simulation have been developed, those methods do not work at interactive rates. The most common real-time methods are essentially simple variants of the OpenGL fog model. While easy to use and specify, that model excludes many important qualitative effects like glows around light sources, the impact of volumetric scat- tering on the appearance of surfaces such as the diffusing of glossy highlights, and the appearance under complex lighting such as environment maps. In this paper, we present an alternative physically based approach that captures these effects while maintaining real-time performance and the ease-of-use of the OpenGL fog model. Our method is based on an explicit analytic integration of the single scattering light transport equations for an isotropic point light source in a homogeneous participating medium. We can implement the model in modern programmable graphics hardware using a few small numerical lookup tables stored as texture maps. Our model can also be easily adapted to generate the appearances of materials with arbitrary BRDFs, environment map lighting, and precomputed radiance transfer methods, in the presence of participating media. Hence, our techniques can be widely used in real-time rendering.

    • Practical Realtime Strategies for Accurate Indirect Occlusion Abstract 2000 Jorge Jimenez, Xian-Chun Wu, Angelo Pesce, Adrian Jarabo Ambient occlusion is ubiquitous in games and other real-time applications to approximate global illumination effects. However there is no analytic solution to ambient occlusion integral for arbitrary scenes, and using general numerical integration algorithms is too slow, so approximations used in practice often are empirically made to look pleasing even if they don’t accurately solve the AO integral. In this work we introduce a new formulation of ambient occlusion, GTAO, which is able to match a ground truth reference in half a millisecond on current console hardware. This is done by using an alternative formulation of the ambient occlusion equation, and an efficient implementation which distributes computation using spatio-temporal filtering. We then extend GTAO with a novel technique that takes into account near-field global illumination, which is lost when using ambient occlusion alone. Finally, we introduce a technique for specular occlusion, GTSO, symmetric to ambient occlusion which allows to compute realistic specular reflections from probe-based illumination. Our techniques are efficient, give results close to the ray-traced ground truth, and have been integrated in recent AAA console titles.

  • Anti-Aliasing: Theory and practice to eliminate aliasing artifacts

    • SMAA: Enhanced Subpixel Morphological Antialiasing Abstract 2012 Jorge Jimenez, Jose I. Echevarria, Tiago Sousa, Diego Gutierrez We present a new image-based, post-processing antialiasing technique, which offers practical solutions to the common, open problems of existing filter-based real-time antialiasing algorithms. Some of the new features include local contrast analysis for more reliable edge detection, and a simple and effective way to handle sharp geometric features and diagonal lines. This, along with our accelerated and accurate pattern classification allows for a better reconstruction of silhouettes. Our method shows for the first time how to combine morphological antialiasing (MLAA) with additional multi/supersampling strategies (MSAA, SSAA) for accurate subpixel features, and how to couple it with temporal reprojection; always preserving the sharpness of the image. All these solutions combine synergies making for a very robust technique, yielding results of better overall quality than previous approaches while more closely converging to MSAA/SSAA references but maintaining extremely fast execution times. Additionally, we propose different presets to better fit the available resources or particular needs of each scenario.

    • A Reconstruction Filter for Plausible Motion Blur Abstract 2012 Morgan McGuire, Padraic Hennessy, Michael Bukowski, Brian Osman This paper describes a novel filter for simulating motion blur phenomena in real time by applying ideas from offline stochastic reconstruction. The filter operates as a 2D post-process on a conventional framebuffer augmented with a screen-space velocity buffer. We demonstrate results on video game scenes rendered and reconstructed in real-time on NVIDIA GeForce 480 and Xbox 360 platforms, and show that the same filter can be applied to cinematic post-processing of offline-rendered images and real photographs. The technique is fast and robust enough that we deployed it in a production game engine used at Vicarious Visions.

    • FXAA Abstract 2009 Timothy Lottes This sample presents a high performance and high quality screen-space software approximation to anti-aliasing called FXAA

    • Rendering Anti-Aliased Line Segments Abstract 2005 Keen-Hon Wong, Xin Ouyang, Chi-Wan Lim, Tiow-Seng Tan, Jurg Nievergelt Bridging the modeling and rendering gap between the existing triangle and point primitives, we explore the use of line segments as a new primitive to represent and render 3D models. Our main contribution extends the anti-aliasing theory in texture mapping to anti-aliased line segment rendering, and presents an approximation algorithm to render high quality anti-aliased opaque and transparent line segments in 3D models. This anti- aliasing technique is empirically validated by building a software pipeline to render models of any combination of the three types of modeling primitives: triangles, line segments and points. Our experiment shows that models comprising line segments are generally more efficient and effective for high quality rendering as compared to their corresponding pure point models.

    • Advanced Visual Effects with Direct3D Abstract 2004 Mike Burrows, Sim Dietrich, David Gosselin, Kev Gee, Jeff Grills, Shawn Hargreaves, Richard Huddy, Gary McTaggart, Jason Mitchell, Ashutosh Rege and Matthias Wloka A 50 slide presentation.

    • Hardware Accelerated Motion Blur Generation Abstract 2003 Clement Shimizu, Amit Shesh, Baoquan Chen Motion blur occurs in photography by the motion of objects during the finite exposure time that the camera shutter remains open for to record the image on film. The traditional method of rendering a motion blur with a computer is to render the scene at many discrete time instances in every frame. In this paper, we present an efficient motion blur generation method that leverages modern commodity graphics hardware. Our method avoids rendering the entire complex scene many times per frame. It first renders the scene into a texture, next renders the optic flow, created based on object transformation, to a vector field texture. The scene texture is finally efficiently blurred according to the vector field using texturemapping hardware to do a piecewise iterative line integral convolution. Though our method uses vertex velocities to calculate image pixel velocities, the line integral convolution is performed on an image, making our method largely independent of scene complexity.

    • Discontinuity Edge Overdraw Abstract 2001 Pedro V. Sander, Hugues Hoppe, John Snyder, Steven J. Gortler Aliasing is an important problem when rendering triangle meshes. Efficient antialiasing techniques such as mipmapping greatly improve the filtering of textures defined over a mesh. A major component of the remaining aliasing occurs along discontinuity edges such as silhouettes, creases, and material boundaries. Framebuffer supersampling is a simple remedy, but 2x2 super- sampling leaves behind significant temporal artifacts, while greater supersampling demands even more fill-rate and memory. We present an alternative that focuses effort on discontinuity edges by overdrawing such edges as antialiased lines. Although the idea is simple, several subtleties arise. Visible silhouette edges must be detected efficiently. Discontinuity edges need consistent orientations. They must be blended as they approach the silhouette to avoid popping. Unfortunately, edge blending results in blurriness. Our technique balances these two competing objectives of temporal smoothness and spatial sharpness. Finally, the best results are obtained when discontinuity edges are sorted by depth. Our approach proves surprisingly effective at reducing temporal artifacts commonly referred to as "crawling jaggies", with little added cost.

    • The Aliasing problem in Computer-Generated Shaded Images Abstract 1997 Franklin Crow Certain defects, such as jagged edges and disappearing detail, have long been an annoyance in digitally generated shaded images. Although increasing the resolution or defocusing the display can attenuate them, an understanding of these defects leads to more effective methods. This paper explains the observed defects in terms of the aliasing phenomenon inherent in sampled signals and discusses prerdtering as a recognized cure. A method for evaluating filters is presented, the application of prefiltering to hidden-surface algorithms is discussed, and an implementation of a filtering tiler is shown accompanied by examples of its effectiveness.

    • An Efficient Antialiasing Technique Abstract 1991 Xiaolin Wu An intuitive concept of antialiasing is developed into very efficient antialiased line and circle generators that require even less amount of integer arithmetic than Bresenham's line and circle algorithms. Unlike its predecessors, the new antialiasing technique is derived in spatial domain (raster plane) under a subjectively meaningful error measure to preserve the dynamics of curve and object boundaries. A formal analysis of the new antialiasing technique in frequency domain is also conducted. It is shown that our antialiasing technique computes the same antialiased images as Fujimoto-Iwata's algorithm but at a fraction of the latter's computational cost. The simplicities of the new antialiased line and circle generators also mean they are easy hardware implementations.

    • Stochastic Sampling in Computer Graphics Abstract 1986 Robert L. Cook Ray tracing, ray casting, and other forms of point sampling are important techniques in computer graphics, but their usefulness has been undermined by aliasing artifacts. In this paper it is shown that these artifacts are not an inherent part of point sampling, but a consequence of using regularly spaced samples. If the samples occur at appropriate non-uniformly spaced locations, frequencies above the Nyquist limit do not alias, but instead appear as noise of the correct average intensity. This noise is much less objectionable to our visual system than aliasing. In ray tracing, the rays can be sarcastically distributed to perform a Monte Carlo evaluation of integrals in the rendering equation. This is called distributed ray tracing and can be used to simulate motion blur, depth of field, penumbrae, gloss, and translucency.

    • Digital Filtering Tutorial, Part II Abstract 1983 Alvy Ray Smith The Sampling Theorem assumes samples are taken at a niform rate. We continue to assume a given input is sampled uniformly -- at the pixels -- and that the output is sampled uniformly -- also at the pixels. So we can still use the Sampling Theorem, for example, to reconstruct the original input from its samples. In case of magnification and minification scaling the abscissa x by a constant factor), the spacing of the input samples is changed by the scaling but the spacing remains uniform. In this memo, however, a less restricted class of mappings is considered which, in general, does not preserve input sample spacing uniformity. A good illustration of such a mapping is f(x) = (ax+b)/(cx+d) which occurs in perspective [2]. We shall show in this memo that the simplifications obtained for magnification and minification do not go through for general mappings, including, unfortunately, perspective. Then we shall discuss some practical filters which are useful for the case where the Sampling Theorem does hold: for scaling, translation, and rotation. The filters include the Catmull-Rom and B-spline cubic spline basis functions and the sine function made finite with a variety of window functions: Bartlett, Hamming, Hanning, Blackman, Lanczos, Kaiser, etc.

    • Digital Filtering Tutorial for Computer Graphics Abstract 1983 Alvy Ray Smith Digital sampling and filtering in both space and time are intrinsic to computer graphics. The pixels of a framebuffer representation of a picture are regularly placed samples in 2-dimensional screen space. Inappropriate application of sampling theory (or no application at all) results in the artifact called"jaggies". The frames of a film representation of a movement are regularly placed samples in time. The artifact here is called "strobing". Spatial filtering, called "antialiasing", is used to soften the jaggies. Temporal filtering, called "motion blur", removes strobing of edges and backward spinning stagecoach wheels. The purpose of this memo is to review the principles of digital sampling and filtering theory in the context of computer graphics. In particular, it is a rewording of the classical results in terms with which I am comfortable. Hopefully other computer graphicists will also find the restatement helpful.

  • Bidirectional Reflectance Distribution Function: Micro-facet and other surface reflection models; Alternatives to Phong Lighting.
    • Physically Based Lighting: Siggraph 2013 course

      • Real Shading in Unreal Engine 4 Abstract 2013 Brian Karis 38 slides

      • Real Shading in Unreal Engine 4 Abstract 2013 Brian Karis

      • Physically Based Lighting at Pixar Abstract 2013 Christophe Hery, Ryusuke Villemin 67 slides

      • Physically Based Lighting at Pixar Abstract 2013 Christophe Hery, Ryusuke Villemin For Monsters University and more recently for The Blue Umbrella, the lighting pipeline at Pixar was completely rewritten and switched to a physically based and ray-traced system. Although ray-tracing was already used in some cases—in the movie Cars for example—we were still using point lights, shadow maps, ad hoc shading models, etc. Over the years, the original pipeline has gotten more and more complex, with thousands of lights and shader tweaking in every shot. The idea was to let the computer handle all this complexity, freeing the lighter to concentrate on the artistic side.

      • Open Shading Language in Disney's OZ The Great and Powerful Abstract 2013 Adam Martinez 31 slides

      • Getting more Physical in Call of Duty BLACK OPS Abstract 2013 Dimitar Lazarov We started pursuing Physically Based Lighting during the development of Call of Duty: Black Ops. The details were presented at SIGGRAPH 2011 as part of the Advances in Real-Time Rendering course [11]. Here we’ll give a brief recap of the important bits relevant for this course and then describe the improvements we did during the development of Call of Duty: Black Ops II.

      • Getting more Physical in Call of Duty BLACK OPS Abstract 2013 Dimitar Laxarov 35 slides

      • Everything You Always Wanted to Know About mia_material Abstract 2013 Hakan “Zap” Andersson As the original author of the popular mental ray shader mia_material, I will herein discuss its background, development history, features, and even its failures.

      • Everything You Always Wanted to Know About mia_material Abstract 2013 Zap Andersson 46 slides

      • Crafting a Next-Gen Material Pipeline for The Order: 1886 Abstract 2013 David Neubelt, Matt Pettineo The Order: 1886 is an upcoming third-person action-adventure game for the PlayStation 4. When we first started pre-production for the project, the word “filmic” was often used to describe the cinematic feel that we wanted to achieve with the game’s visuals. Things like cinematic lighting, grungy streets, and highly detailed characters were identified as key elements in creating a convincing portrayal of 19th-century London. It was decided very early in the project that utilizing a physically based shading model would be a key component of achieving the look we wanted for the game. A Cook-Torrance-like microfacet BRDF was adopted as the default specular BRDF for our materials, and energy conservation was enforced throughout the rendering pipeline. We also implemented several alternative BRDFs for skin, hair, fabrics, and anisotropic materials.

      • Crafting a Next-Gen Material Pipeline for The Order: 1886 Abstract 2013 David Neubelt, Matt Pettineo 74 slides

      • Crafting Physically Motivated Shading Models for Game Development Abstract 2013 Naty Hoffman 66 slides

      • Background: Physics and Math of Shading Abstract 2013 Naty Hoffman 78 slides

      • Background: Physics and Math of Shading Abstract 2013 Naty Hoffman In this section of the course notes, we will go over the fundamentals behind physically based shading models, starting with a qualitative description of the underlying physics, followed by a quantitative description of the relevant mathematical models, and finally discussing how these mathematical models can be implemented for shading.

      • Physically-Based Shading at Disney Abstract 2012 Brent Burley Following our success with physically-based hair shading on Tangled [27], we began considering physically- based shading models for a broader range of materials. With the physically-based hair model, we were able to achieve a great degree of visual richness while maintaining artistic control. However, it proved challenging to integrate the lighting of the hair with the rest of the scene which had still used tradi- tional “ad-hoc” shading models and punctual lights. For subsequent films we wanted to increase the richness of all of our materials while making lighting responses more consistent between materials and environments and also wanted to improve artist productivity through the use of simplified controls.

      • Crafting Physically Motivated Shading Models for Game Development Abstract 2010 Naty Hoffman In this section of the course notes, we discuss the design of shading models that are both physically based and appropriate for game development use.

    • Sampling the GGX Distribution of Visible Normals Abstract 2018 Eric Heitz Importance sampling microfacet bidirectional scattering distribution functions (BSDFs) using their distribution of visible normals (VNDF) yields significant variance reduction in Monte Carlo rendering. In this article, we describe an efficient and exact sampling routine for the VNDF of the GGX microfacet distribution. This routine leverages the property that GGX is the distribution of normals of a truncated ellipsoid, and sampling the GGX VNDF is equivalent to sampling the 2D projection of this truncated ellipsoid. To do that, we simplify the problem by using the linear transformation that maps the truncated ellipsoid to a hemisphere. Since linear transformations preserve the uniformity of projected areas, sampling in the hemisphere configuration and transforming the samples back to the ellipsoid configuration yields valid samples from the GGX VNDF.

    • A Comprehensive Framework for Rendering Layered Materials Abstract 2014 Jakob, d'Eon, Jakob, Marschner We present a general and practical method for computing BSDFs of layered materials. Its ingredients are transport-theoretical models of isotropic or anisotropic scattering layers and smooth or rough boundaries of conductors and dielectrics. Following expansion into a directional basis that supports arbitrary composition, we are able to efficiently and accurately synthesize BSDFs for a great variety of layered structures. Reflectance models created by our system correctly account for multiple scattering within and between layers, and in the context of a rendering system they are efficient to evaluate and support texturing and exact importance sampling. Although our approach essentially involves tabulating reflectance functions in a Fourier basis, the generated models are compact to store due to the inherent sparsity of our representation, and are accurate even for narrowly peaked functions. While methods for rendering general layered surfaces have been investigated in the past, ours is the first system that supports arbitrary layer structures while remaining both efficient and accurate.

    • Thinking in Layers - Modelling with Layered Surfaces Abstract 2011 Andrea Weidlich, Alexander Wilkie This course serves as a guide on the considerable potential of layered surface models that are available in many commercial products.The key advantage of using such layered materials over traditional, more general shading language constructs is that the end result is automatically highly physically plausible because they simulate real materials more precisely. However, this does not mean that these models cannot be used for artistic purposes. In particular, we demonstrate on simple layered surface models how a surprisingly large number of interesting and important surface types can be efficiently represented. We also show how handy such an approach is for the eventual end user, whose main concern is the ease with which one can describe object appearance based only on a few intuitive parameters. We first discuss layered surface models in general and the constraints of modelling object appearance in a physically plausible fashion by explaining basic material properties. We then demonstrate the techniques that can be used to analyse such materials, both for high quality offline rendering as well as in a real-time setting before we give examples of the surface types that can be described in this way and demonstrate how we create them in our company.

    • Crafting Physically Motivated Shading Models for Game Development Abstract 2010 Naty Hoffman Talk Outline Motivation and Infrastructure Making an Ad-hoc Game Shading Model Physically Plausible Environmental And Ambient Light Fine-Tuning and Future Directions

    • An Overview of BRDF Models Abstract 2008 Rosana Montes, Carlos Ureña This paper is focused on the Bidirectional Reflectance Distribution Function (BRDF) in the context of algorithms for computational production of realistic synthetic images. We provide a review of most relevant analytical BRDF models proposed in the literature which have been used for realistic rendering. We also show different approaches used for obtaining efficient models from acquired reflectance data, and the related function fitting techniques, suitable for using that data in efficient rendering algorithms. We consider the algorithms for computation of BRDF integrals, by using Monte-Carlo based numerical integration. In this context, we review known techniques to design efficient BRDF sampling schemes for both analytical and measured BRDF models.

    • Microfacet Models for Refraction through Rough Surfaces Abstract 2007 Walter, Marschner, Li, Torrance Microfacet models have proven very successful for modeling light reflection from rough surfaces. In this paper we review microfacet theory and demonstrate how it can be extended to simulate transmission through rough surfaces such as etched glass. We compare the resulting transmission model to measured data from several real surfaces and discuss appropriate choices for the microfacet distribution and shadowing-masking functions. Since rendering transmission through media requires tracking light that crosses at least two interfaces, good importance sampling is a practical necessity. Therefore, we also describe efficient schemes for sampling the microfacet models and the corresponding probability density functions.

    • Arbitrarily layered micro-facet surfaces Abstract 2007 Andrea Weidlich and Alexander Wilkie. In this paper we present a method to combine several micro-facet based surface layers into a single unified, expressive BRDF model that is easy to use. The restriction to micro-facet based layers constitutes no loss of generality, since both perfectly specular and perfectly diffuse surfaces can be seen as limit cases of the micro-facet approach. Such multi-layered surfaces can be used to re-create the appearance of a wide range of different materials, and yield good results without having to perform explicit sub–surface scattering computations. This is achieved through suitable approximations and simplifications of the scattering within the simulated layered surface, while still taking absorption and total internal reflection into account. We also discuss the corresponding probability distribution function that is needed for sampling purposes, and investigate how the flexibility of this new approach is best put to use.

    • An Inexpensive BRDF Model for Physically-based Rendering Abstract 2003 Christophe Schlick A new BRDF model is presented which can be viewed as an kind of intermediary model between empirism and theory. Main results of physics are observed (energy conservation, reciprocity rule, microfacet theory) and numerous phenomena involved in light reflection are accounted for, in a physically plausible way (incoherent and coherent reflection, spectrum modifications, anisotropy, self-shadowing, multiple surface and subsurface reflection, differences between homogeneous and heterogeneous materials). The model has been especially intended for computer graphics applications and therefore includes two main features: simplicity (a small number of intuitively understandable parameters controls the model) and efficiency (the formulation provides adequation to Monte-Carlo rendering techniques and/or hardware implementations).

    • BRDF models and their use in Global Illumination Algorithms Abstract 2000 Kalos 42 slides

    • An Anisotropic Phong BRDF Model Abstract 2000 Michael Ashikhmin, Peter Shirley We present a BRDF model that combines several advantages of the various empirical models currently in use. In particular, it has intuitive parameters, is anisotropic, conserves energy, is reciprocal, has an appropriate non-Lambertian diffuse term, and is well-suited for use in Monte Carlo renderers.

    • Compact Metallic Reflectance Models Abstract 1999 Neumann, Neumann, Szirmay-Kalos The paper presents simple, physically plausible, but not physically based reflectance models for metals and other specular materials. So far there has been no metallic BRDF model that is easy to compute, suitable for fast importance sampling and is physically plausible. This gap is filled by appropriate modifications of the Phong, Blinn and the Ward models. The Phong and the Blinn models are known not to have metallic characteristics. On the other hand, this paper also shows that the Cook-Torrance and the Ward models are not physically plausible, because of their behavior at grazing angles. We also compare the previous and the newly proposed models. Finally, the generated images demonstrate how the metallic impression can be provided by the new models.

    • Models of Light Reflection for Computer Synthesized Pictures Abstract 1997 James F. Blinn In the production of computer generated pictures of three dimensional objects, one stage of the calculation is the determination of the intensity of a given object once its visibility has been established. This is typically done by modeling the surface as a perfect diffuser, sometimes with a specular component added for the simulation of hilights. This paper presents a more accurate function for the generation of hilights which is based on some experimental measurements of how light reflects from real surfaces. It differs from previous models in that the intensity of the hilight changes with the direction of the light source. Also the position and shape of the hilights is somewhat different from that generated by simpler models. Finally, the hilight function generates different results when simulating metallic vs. nonmetallic surfaces. Many of the effects so generated are somewhat subtle and are apparent only during movie sequences. Some representative still frames from such movies are included.

    • An Anisotropic Phong Light Reflection Model Abstract 1997 Michael Ashikhmin, Peter Shirley We present a new BRDF model that attempts to combine the advantages of the various empirical models currently in use. In particular, it has intuitive parameters, is anisotropic, energy-conserving, reciprocal, has an appropriate non- Lambertian diffuse term, and is easy to use in a Monte Carlo framework.

    • Using the Modified Phong Reflectance Model for Physically Based Rendering Abstract 1994 Eric P. Lafortune and Yves D. Willems This text discusses a few aspects of reflectance models in physically based rendering: The first section presents the definition of the bidirectional reflection distribution function (brdf) of a surface and its physical properties. On a more practical level, the next section discusses models to represent brdfs and their desired properties in general for Monte Carlo algorithms. The third section goes into details about a specific reflectance model, the modified Phong brdf, with its definition, its properties and its use. We show how this model can be correctly integrated in importance sampling schemes for physically based Monte Carlo rendering algorithms. The fourth section is devoted to alternative parameter spaces in which reflectance models can be sampled, either deterministically or stochastically. The last section discusses an important implementational issue, more specifically the problem of verifying the implementation of a reflectance model.

    • Generalization of Lambert's Reflectance Model Abstract 1994 Michael Oren, Shree K. Nayar Lambert's model for body reflection is widely used in computer graphics. It is used extensively by rendering techniques such as radiosity and ray tracing. For several real-world objects, however, Lambert's model can prove to be a very inaccurate approximation to the body reflectance. While the brightness of a Lambertian surface is independent of viewing direction, that of a rough surface increases as the viewing direction approaches the light source direction. In this paper, a comprehensive model is developed that predicts body reflectance from rough surfaces. The surface is modeled as a collection of Lambertian facets. It is shown that such a surface is inherently non-Lambertian due to the foreshortening of the surface facets. Further, the model accounts for complex geometric and radiometric phenomena such as masking, shadowing, and interreflections between facets. Several experiments have been conducted on samples of rough diffuse surfaces, such as, plaster, sand, clay, and cloth. All these surfaces demonstrate significant deviation from Lambertian behavior. The reflectance measurements obtained are in strong agreement with the reflectance predicted by the model.

    • Measuring and Modeling Anisotropic Reflection Abstract 1992 Gregory Ward A new device for measuring the spatial reflectance distributions of surfaces is introduced, along with a new mathematical model of anisotropic reflectance. The reflectance model presented is both simple and accurate, permitting efficient reflectance data reduction and reproduction. The validity of the model is substantiated with comparisons to complete measurements of surface reflectance functions gathered with the novel reflectometry device. This new device uses imaging technology to capture the entire hemisphere of reflected directions simultaneously, which greatly accelerates the reflectance data gathering process, making it possible to measure dozens of surfaces in the time that it used to take to do one. Example measurements and simulations are shown, and a table of fitted parameters for several surfaces is presented.

    • Making Shaders More Physically Plausible Abstract 1992 Robert Lewis There is a need to develop shaders that not only "look good", but are more physically plausible. From physical and geometric considerations, we review the derivation of a shading equation expressing reflected radiance in terms of incident radiance and the bidirectional reflectance distribution function (BRDF). We then examine the connection between this equation and conventional shaders used in computer graphics. Imposing the additional physical constraints of energy conservation and Helmholtz reciprocity allows us to create variations of the conventional shaders that are more physically plausible.

    • A Reflectance Model for Computer Graphics Abstract 1982 Robert L. Cook, Kenneth E. Torrance A new reflectance model for rendering computer synthesized images is presented. The model accounts for the relative brightness of different materials and light sources in the same scene. It describes the directional distribution of the reflected light and a color shift that occurs as the reflectance changes with incidence angle. A method for obtaining the spectral energy distribution of the light reflected from an object made of a specific real material is presented, and a procedure for accurately reproducing the color associated with the spectral energy distribution is discussed. The model is applied to the simulation of a metal and a plastic.

    • Surface Reflection Models Abstract Frank Losasso One of the fundamental topics in lighting is how the light interacts with the environment. The academic community has researched several models over the last century, but for the most part, we are still stuck with the most basic of models. The reason for this is for the most part the lack of computational power, making it difficult to use more truthful models in real-time. The goal of this paper is to investigate the viability of some of the more sophisticated surface reflection models that have been created, giving developers a sense as to how much computational power needs to be used to create better looking surfaces. Traditionally, the most used method of finding the color of a pixel has been through Gouraud interpolation of Lambert's Cosine Law at the vertices. This lighting model is extremely cheap to compute and is amenable to fixed function pipelines. With the advent of GPUs, Phong interpolation has become a viable option. This model has allowed for innovations like bump mapping giving more realism to modern virtual worlds. The underlying assumptions however are still the same; the surfaces are Lambertian. Unfortunately, this has the side effect of making most of the computer generated images look very much alike, and very different from the real world. The Lambertian surface assumption works great for some materials (like plastic), which means that different models must be used if other materials are to be represented faithfully. And this is what we will investigate over the next few pages.

    • Reflection Models, and Physically-Based Illumination Models Abstract A 17 slide presentation.

    • An Introduction to BRDF-Based Lighting Abstract Chris Wynn The introduction of modern GPUs such as the GeForce 256 and GeForce2 GTS has opened the door for creating stunningly photorealistc interactive 3D content. While the realization of realtime computer-generated images indistinguishable from photographs remains as yet unreached, one piece of machinery that will play an important role in realizing interactive photorealism is the notion of a Bi-directional Reflectance Distribution Function (BRDF) and BRDF-based lighting techniques. The purpose of this tutorial is to provide a working knowledge of the concepts and basic mathematics necessary to appreciate BRDFs and to provide some exposure to the terminology used when discussing BRDFs and BRDF-based lighting techniques. If you are already familiar with BRDFs, this paper will be a review; however, if you are new to BRDFs, this paper will provide a good starting point for understanding many reflectance-based lighting techniques.

  • Deferred Shading: A multi-pass technique which forms the basis for all modern rendering pipelines.

    • Forward+: Bringing Deferred Lighting to the Next Level Abstract 20012 Harada, McKee, and Yang This paper presents Forward+, a method of rendering many lights by culling and storing only lights that contribute to the pixel. Forward+ is an extension to traditional forward rendering. Light culling, implemented using the compute capability of the GPU, is added to the pipeline to create lists of lights; that list is passed to the final rendering shader, which can access all information about the lights. Although Forward+ increases workload to the final shader, it theoretically requires less memory traffic compared to compute-based deferred lighting. Furthermore, it removes the major drawback of deferred techniques, which is a restriction of materials and lighting models. Experiments are performed to compare the performance of Forward+ and deferred lighting.

    • Deferred Attribute Interpolation for Memory-Efficient Deferred Shading Abstract 2015 Christoph Schied, Carsten Dachsbacher In this work we present a novel approach to deferred shading suitable for high resolution displays and high visibility sampling rates. We reduce the memory costs of deferred shading by substituting the geometry buffer with a visibility buffer that stores references into a triangle buffer. The triangle buffer is populated dynamically with all visible triangles which is compatible with the use of tessellation. Stored triangles are represented by a sample point and screen-space partial derivatives. This representation allows for efficient attribute interpolation during shading and gives shaders knowledge about the partial derivatives of all attributes. We show that the size of the visibility buffer can be further decreased by storing a linked list of visibility samples per pixel. For high-resolution displays we propose an extension of our algorithm to perform shading at reduced frequency, allowing us to reduce the sampling rate for computationally expensive, but low-frequency signals such as indirect illumination.

    • Light Pre-Pass: Deferred Lighting: Latest Development Abstract 2009 Wolfgang Engel An 18 slice set.

    • Inferred Lighting: Fast dynamic lighting and shadows for opaque and translucent objects Abstract 2009 Scott Kircher, Alan Lawrance This paper presents a three phase pipeline for real-time rendering that provides fast dynamic light calculations while enabling greater material flexibility than deferred shading. This method, called inferred lighting, allows lighting calculations to occur at a significantly lower resolution than the final output and is compatible with hardware multisample antialiasing (MSAA). In addition, inferred lighting introduces a novel method of computing lighting and shadows for translucent objects (alpha polygons) that unifies the pipeline for processing lit alpha polygons with that of opaque polygons. The key to our method is a discontinuity sensitive filtering algorithm that enables material shaders to "infer" their lighting values from a light buffer sampled at a different resolution. This paper also discusses specific implementation issues of inferred lighting on DirectX 10, Xbox 360, and PlayStation 3 hardware.

    • Deferred Rendering in Killzone 2 Abstract 2009 Michal Valient A 55 slide set.

    • Non-interleaved Deferred Shading of Interleaved Sample Patterns Abstract 2006 Segovia, Iehl, Mitanchey, Péroche This paper presents a novel and fast technique to combine interleaved sampling and deferred shading on a GPU. The core idea of this paper is quite simple. Interleaved sample patterns are computed in a non-interleaved deferred shading process. The geometric buffer (G-buffer) which contains all of the pixel information is actually split into several separate and distinct sub-buffers. To achieve such a result in a fast way, a massive two-pass swizzling copy is used to convert between these two buffer organizations. Once split, the sub-buffers can then be accessed to perform any fragment operation as it is done with a standard deferred shading rendering pipeline. By combining interleaved sampling and deferred shading, real time rendering of global illumination effects can be therefore easily achieved. Instead of evaluating each light contribution on the whole geometric buffer, each shading computation is coherently restricted to a smaller subset a fragments using the sub-buffers. Therefore, each screen pixel in a regular n m pattern will have its own small set of light contributions. Doing so, the consumed fillrate is considerably decreased and the provided rendering quality remains close to the quality obtained with a non-interleaved approach. The implementation of this rendering pipeline is finally straightforward and it can be easily integrated in any existing real-time rendering package already using deferred shading.

    • Deferred Shading Tutorial Abstract 2005 Policarpo, Fonseca The authors of this article proposed a rendering technique that produces 3D images that favor the recognition of shapes and patterns, since shapes can be readily understood if certain geometric properties are enhanced. In order to optimize the enhancement process, geometric properties of the surfaces are preserved as Geometric-Buffers G-buffers). So, by using G-buffers as intermediate results, artificial enhancement processes are separated from geometric processes (projection and hidden surface removal) and physical processes (shading and texture mapping), and performed as a post-processing pass

    • Illumination for Real-Time Rendering of Large Architectural Environments Abstract 2005 Markus Fahlen A Master's Thesis. This thesis explores efficient techniques for high quality real-time rendering of large architectural environments using affordable graphics hardware, as applied to illumination, including window reflections, shadows, and "bump mapping". For each of these fields, the thesis investigates existing methods and intends to provide adequate solutions. The focus lies on the use of new features found in current graphics hardware, making use of new OpenGL extensions and functionality found in Shader Model 3.0 vertex and pixel shaders and the OpenGL 2.0 core. The thesis strives to achieve maximum image quality, while maintaining acceptable performance at an affordable cost. The thesis shows the feasibility of using deferred shading on current hardware and applies high dynamic range rendering with the intent to increase realism. Furthermore, the thesis explains how to use environment mapping to simulate true planar reflections as well as incorporates relevant image post-processing effects. Finally, a shadow mapping solution is provided for the future integration of dynamic geometry.

    • Deferred Shading Abstract 2004 Shawn Hargreaves A 32 slide presentation from a Game Developers conference. It contains a nice, but brief outline of deferred shading with some nice pictures but not much detail.

    • 6800 Leagues Under the Sea: Deferred Shading Abstract 2004 Shawn Hargreaves, Mark Harris A 44 slide presentation by Nvidia about deferred shading, and its use with many other effects: lighting, shadows, AA, ...

    • The Triangle Processor and Normal Vector Shader: A VLSI System for High Performance Graphics Abstract 1988 Michael Deering, Stephanie Winner, Bic Schediwy, Chris Duffy, Nell Hunt Note: This, the origin of the deferred shading concept, is mostly concerned with the hardware architecture needed render triangles quickly. Buried within that, is the idea that geometry should be rendered once, and the pixel shading should be done on only visible pixels later. Current affordable architectures for high-speed display of shaded 3D objects operate orders of magnitude too slowly. Recent advances in floating point chip technology have out-paced polygon fill time, making the memory access bottleneck between the drawing processor and the frame buffer the most significant factor to be accelerated. Massively parallel VLSI systems have the potential to by pass this bottleneck , but to date only at very high cost. We describe a new more affordable VLSI solution. A pipeline of triangle processors rasterizes the geometry, then a further pipeline of shading processors applies Phong shading with multiple light sources. The triangle processor pipeline performs 100 billion additions per second, and the shading pipeline performs two billion multiplies per second. This allows 3D graphics systems to be built capable of displaying more than one million triangles per second. We show the results of an anti-aliasing technique, and discuss extensions to texture mapping, shadows, and environment maps.

  • Environment Maps: The mathematics of sphere parameterizations for environment maps

    • A Survey of Efficient Representations for Independent Unit Vectors Abstract 2014 Cigolle, Donow, Evangelakos, Mara, McGuire, Meyer The bandwidth cost and memory footprint of vector buffers are limiting factors for GPU rendering in many applications. This article surveys time- and space-efficient representations for the important case of non-register, in-core, statistically independent unit vectors, with emphasis on GPU encoding and decoding. These representations are appropriate for unit vectors in a geometry buffer or attribute stream—where no correlation between adjacent vectors is easily available—or for those in a normal map where quality higher than that of DXN is required. We do not address out-of-core and register storage vectors because they favor minimum-space and maximum-speed alternatives, respectively. We evaluate precision and its qualitative impact across these techniques and give CPU reference implementations. For those methods with good quality and reasonable performance, we provide optimized GLSL GPU implementations of encoding and decoding.

    • The Tennis-ball Map: A Low-Distortion Sampling-Efficient Parameterization of the Sphere Abstract 2011 Gary Herron We introduce a parameterization of the sphere, called the tennis-ball parameterization, which exhibits properties highly desirable for computer graphics applications which need to represent values over a sphere, for instance spherical images for view-independent reflections maps and omni-directional shadow maps. We are particularly interested in using such maps in applications requiring high frame-rate real-time rendering of dynamic scenes. We use some carefully selected metrics to compare the tennisball parameterization to a number of other parameterizations found in traditional computer graphics, as well as several found in applied mathematics and sciences. Under the restrictions implied by view-independence and the high frame rate of real-time applications, we will show that the tennis-ball map exhibits some greatly improved characteristics compared to the other parameterizations.

    • Practical Implementation of Dual Paraboloid Shadow Maps Abstract 2006 Brian Osman, Mike Bukowski, Chris McEvoy \ In this paper, we present refinements to dual paraboloid shadow mapping algorithm from Brabec, et. al. This work makes the algorithm practical for broader use in video games. We give solutions for the tessellation constraints on shadow casters and receivers present in the original work. We also discuss heuristics for splitting plane placement and pitfalls in filtering.

    • Dual Paraboloid Mapping In the Vertex Shader Abstract 2006 Jason Zink I had heard about "dual-paraboloid mapping" some time ago and always wanted to look into how the algorithm worked. The name itself begs to be investigated, and the paraboloid mapping could be applied to environment maps as well as shadow maps so it seemed like a good idea to look into it. When I recently found some spare time to read up on it I found several different academic papers on the topic explaining the theory behind the algorithm. However, after several rounds with Google I realized that there weren't many good resources on how to implement the mapping scheme. So I decided that I would investigate the topic and try to provide an easy to understand guide to the theory as well as a reference to the implementation of paraboloid mapping in the modern programmable rendering pipeline. The implementation is written in DirectX 9 HLSL. The effect files that are developed in this exercise are provided with the article and may be used in whatever manner you desire.

    • Shadow Mapping for Hemispherical and Omnidirectional Light Sources Abstract 2002 Stefan Brabec, Thomas Annen, Hans-Peter Seidel \ In this paper we present a shadow mapping technique for hemispherical and omnidirectional light sources using dual-paraboloid mapping. In contrast to the traditional perspective projection this parameterization has the benefit that only a minimal number of rendering passes is needed during generation of the shadow maps, making the method suitable for dynamic environments and real time applications. By utilizing programmable features available on state-of-the-art graphics cards we show how the algorithm can be efficiently mapped to hardware.

    • Parameterized Environment Maps Abstract 2001 Hakura, Snyder, Lengyel Static environment maps fail to capture local reflections including effects like selfreflections and parallax in the reflected imagery. We instead propose parameterized environment maps (PEMs), a set of per-view environment maps which accurately reproduce local reflections at each viewpoint as computed by an offline ray tracer. Even with a small set of viewpoint samples, PEMs support plausible movement away from and between the pre-rendered viewpoint samples while maintaining local reflections. They also make use of environment maps supported in graphics hardware to provide real-time exploration of the pre-rendered space. In addition to parameterization by viewpoint, our notion of PEMe xtends to general, multidimensional parameterizations of the scene, including relative motions of objects and lighting changes. Our contributions include a technique for inferring environment maps providing a close match to ray-traced imagery. We also explicitly infer and encode all MIPMAP levels of the PEMs to achieve higher accuracy. We propose layered environment maps that separate local and distant reflected geometry. We explore several types of environment maps including finite spheres, ellipsoids, and boxes that better approximate the environmental geometry. We demonstrate results showing faithful local reflections in an interactive viewer.

    • A Unified Approach to Prefiltered Environment Maps Abstract 2000 Kautz, Vazquez, Heidrich, Seidel Different methods for prefiltered environment maps have been proposed, each of which has different advantages and disadvantages. We present a general notation for prefiltered environment maps, which will be used to classify and compare the existing methods. Based on that knowledge we develop three new algorithms: 1. A fast hierarchical prefiltering method that can be utilized for all previously proposed prefiltered environment maps. 2. A technique for hardware-accelerated prefiltering of environment maps that achieves interactive rates even on low-end workstations. 3. Anisotropic environment maps using the Banks model.

    • View-independent Environment Maps Abstract 1998 Wolfgang Heidrich, Hans-Peter Seidel Environment maps are widely used for approximating reflections in hardware-accelerated rendering applications. Unfortunately, the parameterizations for environment maps used in today's graphics hardware severely undersample certain directions, and can thus not be used from multiple viewing directions. Other parameterizations exist, but require operations that would be too expensive for hardware imple- mentations. In this paper we introduce an inexpensive new parameterization for environment maps that allows us to reuse the environment map for any given viewing direction. We describe how, under certain restrictions, these maps can be used today in standard OpenGL implementations. Furthermore, we explore how OpenGL could be extended to support this kind of environment map more directly.

  • Global Illumination: Realtime approximations of indirect illumination, area lights and such.

    • Real-time Global Illumination by Precomputed Local Reconstruction from Sparse Radiance Probes Abstract 2017 Ari Silvennoinen, Jaakko Lehtinen We present a direct-to-indirect transport technique that enables accurate realtime rendering of indirect illumination in mostly static scenes of complexity on par with modern games while supporting fully dynamic lights, cameras and diffuse surface materials. Our key contribution is an algorithm for reconstructing the incident radiance field from a sparse set of local samples — radiance probes — by incorporating mutual visibility into the reconstruction filter. To compute global illumination, we factorize the direct-to-indirect transport operator into global and local parts, sample the global transport with sparse radiance probes at real-time, and use the sampled radiance field as input to our precomputed local reconstruction operator to obtain indirect radiance. In contrast to previous methods aiming to encode the global directto-indirect transport operator, our precomputed data is local in the sense that it needs no long-range interactions between probes and receivers, and every receiver depends only on a small, constant number of nearby radiance probes, aiding compression, storage, and iterative workflows. While not as accurate, we demonstrate that our method can also be used for rendering indirect illumination on glossy surfaces, and approximating global illumination in scenes with large-scale dynamic geometry.

    • Real-Time Global Illumination using Precomputed Light Field Probes Abstract 2017 Morgan McGuire, Mike Mara, Derek Nowrouzezahrai, David Luebke We introduce a new data structure and algorithms that employ it to compute real-time global illumination from static environments. Light field probes encode a scene’s full light field and internal visibility. They extend current radiance and irradiance probe structures with per-texel visibility information similar to a G-buffer and variance shadow map. We apply ideas from screen-space and voxel cone tracing techniques to this data structure to efficiently sample radiance on world space rays, with correct visibility information, directly within pixel and compute shaders. From these primitives, we then design two GPU algorithms to efficiently gather real-time, viewer-dependent global illumination onto both static and dynamic objects. These algorithms make different tradeoffs between performance and accuracy. Supplemental GLSL source code is included.

    • Real-Time Diffuse Global Illumination Using Radiance Hints Abstract 2011 Georgios Papaioannou GPU-based interactive global illumination techniques are receiving an increasing interest from both the research and the industrial community as real-time graphics applications strive for visually rich and realistic dynamic three-dimensional environments. This paper presents a fast new diffuse global illumination method that generates a sparse set of low-cost radiance field evaluation points (radiance hints) and computes an arbitrary number of diffuse inter-reflections within a given volume. The proposed approximate technique combines ideas from exiting grid-based radiance caching techniques with reflective shadow maps as well as a stochastic scheme for visibility calculations, in order to achieve high frame rates for multiple light bounces.

    • Real-Time Bidirectional Path Tracing via Rasterization Supplemental Material Abstract 2011 Tokuyosh, Ogaki Supplemental Material

    • Real-Time Bidirectional Path Tracing via Rasterization Abstract 2011 Tokuyosh, Ogak Global illumination drastically improves visual realism of interactive applications. Although many interactive techniques are available, they have some limitations or employ coarse approximations. For example, general instant radiosity often has numerical error, because the sampling strategy fails in some cases. This problem can be reduced by a bidirectional sampling strategy that is often used in off-line rendering. However, it has been complicated to implement in real-time applications. This paper presents a simple real-time global illumination system based on bidirectional path tracing. The proposed system approximates bidirectional path tracing by using rasterization on a commodity DirectX11 capable GPU. Moreover, for glossy surfaces, a simple and efficient artifact suppression technique is also introduced.

    • Interactive Indirect Illumination Using Voxel Cone Tracing Abstract 2011 Crassin, Neyret, Sainz, Green, Eisemann Indirect illumination is an important element for realistic image synthesis, but its computation is expensive and highly dependent on the complexity of the scene and of the BRDF of the involved surfaces. While off-line computation and pre-baking can be acceptable for some cases, many applications (games, simulators, etc.) require real-time or interactive approaches to evaluate indirect illumination. We present a novel algorithm to compute indirect lighting in real-time that avoids costly precomputation steps and is not restricted to low-frequency illumination. It is based on a hierarchical voxel octree representation generated and updated on the fly from a regular scene mesh coupled with an approximate voxel cone tracing that allows for a fast estimation of the visibility and incoming energy. Our approach can manage two light bounces for both Lambertian and glossy materials at interactive framerates (25-70FPS). It exhibits an almost scene-independent performance and can handle complex scenes with dynamic content thanks to an interactive octree-voxelization scheme. In addition, we demonstrate that our voxel cone tracing can be used to efficiently estimate Ambient Occlusion,

    • Cascaded Light Propagation Volumes for Real-Time Indirect Illumination Abstract 2010 Anton Kaplanyan, Carsten Dachsbacher This paper introduces a new scalable technique for approximating indirect illumination in fully dynamic scenes for real-time applications, such as video games. We use lattices and spherical harmonics to represent the spatial and angular distribution of light in the scene. Our technique does not require any precomputation and handles large scenes with nested lattices. It is primarily targeted at rendering single-bounce indirect illumination with occlusion, but can be extended to handle multiple bounces and participating media. We demonstrate that our method produces plausible results even when running on current game console hardware with a budget of only a few milliseconds for performing all computation steps for indirect lighting. We evaluate our technique and show it in combination with a variety of popular real-time rendering techniques.

    • Light Propagation Volumes in CryEngine 3 Abstract 2009 Anton Kaplanyan This chapter introduces a new technique for approximating the first bounce of diffuse global illumination in real-time. As diffuse global illumination is very computationally intensive, it is usually implemented only as static precomputed solutions thus negatively affecting game production time. In this chapter we present a completely dynamic solution using spherical harmonics (SH) radiance volumes for light field finite-element approximation, point-based injective volumetric rendering and a new iterative radiance propagation approach. Our implementation proves that it is possible to use this solution efficiently even with current generation of console hardware (Microsoft Xbox 360, Sony PlayStation 3). Because this technique does not require any preprocessing stages and fully supports dynamic lighting, objects, materials and view points, it is possible to harmoniously integrate it into an engine as complex as the cross-platform engine CryEngine 3 with a large set of graphics technologies without requiring additional production time. Additional applications and combinations with existing techniques are dicussed in details in this chapter.

    • Hardware-Accelerated Global Illumination by Image Space Photon Mapping Abstract 2009 McGuire, Luebke We describe an extension to photon mapping that recasts the most expensive steps of the algorithm - the initial and final photon bounces - as image-space operations amenable to GPU acceleration. This enables global illumination for real-time applications as well as accelerating it for offline rendering. Image Space Photon Mapping (ISPM) rasterizes a light-space bounce map of emitted photons surviving initial-bounce Russian roulette sampling on a GPU. It then traces photons conventionally on the CPU. Traditional photon mapping estimates final radiance by gathering photons from a k-d tree. ISPM instead scatters indirect illumination by rasterizing an array of photon volumes. Each volume bounds a filter kernel based on the a priori probability density of each photon path. These two steps exploit the fact that initial path segments from point lights and final ones into a pinhole camera each have a common center of projection. An optional step uses joint bilateral upsampling of irradiance to reduce the fill requirements of rasterizing photon volumes. ISPM preserves the accurate and physically-based nature of photon mapping, supports arbitrary BSDFs, and captures both high- and low-frequency illumination effects such as caustics and diffuse color interreflection. An implementation on a consumer GPU and 8-core CPU renders highquality global illumination at up to 26 Hz at HD (1920X1080) resolution, for complex scenes containing moving objects and lights.

    • Instant Radiosity An Approach for Real-Time Global Illumination Abstract 2008 Kinkelin, Liensberger We give an overview of Instant Radiosity, an approach for global illumination which has recently become suitable for real-time rendering of complex scenes on PCs exploiting current 3D hardware. We give an introduction to global illumination, present other approaches for the solution of this problem and dig deeper into Instant Radiosity including recent extensions and optimizations. We also provide some of our own ideas for practical implementations.

    • Imperfect Shadow Maps for Efficient Computation of Indirect Illumination Abstract 2008 Ritschel, Grosch, Kim, Seidel, Dachsbacher, Kautz Video: http://youtu.be/Pdp3rfyFF14 We present a method for interactive computation of indirect illumination in large and fully dynamic scenes based on approximate visibility queries. While the high-frequency nature of direct lighting requires accurate visibility, indirect illumination mostly consists of smooth gradations, which tend to mask errors due to incorrect visibility. We exploit this by approximating visibility for indirect illumination with imperfect shadow map-low-resolution shadow maps rendered from a crude point-based representation of the scene. These are used in conjunction with a global illumination algorithm based on virtual point lights enabling indirect illumination of dynamic scenes at real-time frame rates. We demonstrate that imperfect shadow maps are a valid approximation to visibility, which makes the simulation of global illumination an order of magnitude faster than using accurate visibility.

    • Interactive Global Illumination Based on Coherent Surface Shadow Maps Abstract 2007 Tobias Ritschel, Thorsten Grosch, Jan Kautz, Hans-Peter Seidel Interactive rendering of global illumination effects is a challenging problem. While precomputed radiance transfer (PRT) is able to render such effects in real time the geometry is generally assumed static. This work proposes to replace the precomputed lighting response used in PRT by precomputed depth. Precomputing depth has the same cost as precomputing visibility, but allows visibility tests for moving objects at runtime using simple shadow mapping. For this purpose, a compression scheme for a high number of coherent surface shadow maps (CSSMs) covering the entire scene surface is developed. CSSMs allow visibility tests between all surface points against all points in the scene. We demonstrate the effectiveness of CSSM-based visibility using a novel combination of the lightcuts algorithm and hierarchical radiosity, which can be efficiently implemented on the GPU. We demonstrate interactive n-bounce diffuse global illumination, with a final glossy bounce and many high frequency effects: general BRDFs, texture and normal maps, and local or distant lighting of arbitrary shape and distribution – all evaluated per-pixel. Furthermore, all parameters can vary freely over time – the only requirement is rigid geometry.

    • Splatting Indirect Illumination Abstract 2006 Dachsbacher, Stamminger In this paper we present a novel method for plausible real-time rendering of indirect illumination effects for diffuse and non-diffuse surfaces. The scene geometry causing indirect illumination is captured by an extended shadow map, as proposed in previous work, and secondary light sources are distributed on directly lit surfaces. One novelty is the rendering of these secondary lights' contribution by splatting in a deferred shading process, which decouples rendering time from scene complexity. An importance sampling strategy, implemented entirely on the GPU, allows efficient selection of secondary light sources. Adapting the light's splat shape to surface glossiness also allows efficient rendering of caustics. Unlike previous approaches the approximated indirect lighting does barely exhibit coarse artifacts - even under unfavorable viewing and lighting conditions. We describe an implementation on contemporary graphics hardware, show a comparison to previous approaches, and present adaptation to and results in game-typical applications.

    • Reflective Shadow Maps Abstract 2005 Carsten Dachsbacher, Marc Stamminger In this paper we present "reflective shadow maps", an algorithm for interactive rendering of plausible indirect illumination. A reflective shadow map is an extension to a standard shadow map, where every pixel is considered as an indirect light source. The illumination due to these indirect lights is evaluated on-the-fly using adaptive sampling in a fragment shader. By using screen-space interpolation of the indirect lighting, we achieve interactive rates, even for complex scenes. Since we mainly work in screen space, the additional effort is largely independent of scene complexity. The resulting indirect light is approximate, but leads to plausible results and is suited for dynamic scenes. We describe an implementation on current graphics hardware and show results achieved with our approach.

    • Lightcuts: A Scalable Approach to Illumination Abstract 2005 Bruce Walter, Sebastian Fernandez, Adam Arbree, Kavita Bala, Michael Donikian, Donald P. Greenberg Lightcuts is a scalable framework for computing realistic illumination. It handles arbitrary geometry, non-diffuse materials, and illumination from a wide variety of sources including point lights, area lights, HDR environment maps, sun/sky models, and indirect illumination. At its core is a new algorithm for accurately approximating illumination from many point lights with a strongly sublinear cost. We show how a group of lights can be cheaply approximated while bounding the maximum approximation error. A binary light tree and perceptual metric are then used to adaptively partition the lights into groups to control the error vs. cost tradeoff. We also introduce reconstruction cuts that exploit spatial coherence to accelerate the generation of anti-aliased images with complex illumination. Results are demonstrated for five complex scenes and show that lightcuts can accurately approximate hundreds of thousands of point lights using only a few hundred shadow rays. Reconstruction cuts can reduce the number of shadow rays to tens.

    • Fast, Realistic Lighting for Video Games Abstract 2003 Andrey Iones, Anton Krupkin, Mateu Sbert, Sergey Zhukov A novel, view-independent technology produces natural-looking lighting effects faster than radiosity and ray tracing. The approach is suited for 3D real-time interactive applications and production rendering.

    • Efficient Illumination by High Dynamic Range Images Abstract 2003 Thomas Kollig, Alexander Keller We present an algorithm for determining quadrature rules for computing the direct illumination of predominantly diffuse objects by high dynamic range images. The new method precisely reproduces fine shadow detail, is much more efficient as compared to Monte Carlo integration, and does not require any manual intervention

    • Hardware-Accelerated Global Illumination by Image Space Photon Mapping Abstract 2000 Morgan McGuire, David Luebke We describe an extension to photon mapping that recasts the most expensive steps of the algorithm - the initial and final photon bounces - as image-space operations amenable to GPU acceleration. This enables global illumination for real-time applications as well as accelerating it for offline rendering. Image Space Photon Mapping (ISPM) rasterizes a light-space bounce map of emitted photons surviving initial-bounce Russian roulette sampling on a GPU. It then traces photons conventionally on the CPU. Traditional photon mapping estimates final radiance by gathering photons from k-d tree. ISPM instead scatters indirect illumination by rasterizing an array of photon volumes. Each volume bounds a filter kernel based on the a priori probability density of each photon path. These two steps exploit the fact that initial path segments from point lights and final ones into a pinhole camera each have a common center of projection. An optional step uses joint bilateral upsampling of irradiance to reduce the fill requirements of rasterizing photon volumes. ISPM preserves the accurate and physically-based nature of photon mapping, supports arbitrary BSDFs, and captures both high- and low-frequency illumination effects such as caustics and diffuse color interreflection. An implementation on a consumer GPU and 8-core CPU renders highquality global illumination at up to 26 Hz at HD (1920x1080) resolution, for complex scenes containing moving objects and lights.

    • Instant Radiosity Abstract 1997 Alexander Keller We present a fundamental procedure for instant rendering from the radiance equation. Operating directly on the textured scene description, the very efficient and simple algorithm produces photorealistic images without any finite element kernel or solution discretization of the underlying integral equation. Rendering rates of a few seconds are obtained by exploiting graphics hardware, the deterministic technique of the quasi-random walk for the solution of the global illumination problem, and the new method of jittered low discrepancy sampling.

  • High Dynamic Range: Tone mapping HDR images to LDR devices, and related post-processing effects.

    • Realtime HDR Rendering Abstract 2007 Christian Luksch High dynamic range rendering in realtime graphics has increased the visual quality of realtime scenes essentially. There are several techniques of HDR-Rendering. This work summarizes the theoretical background and results of previous works. A ready-to-use HDR rendering library has been developed that integrates seamlessly into the open source graphics engine Ogre3D. Further a comparison that show the advantages and disadvantages of different techniques in a realtime rendered scene has been made.

    • Real-Time HDR Image Based Lighting Abstract 2007 Jorg, Frishert This report presents the work done on the final project for the course of Image Based Rendering. A real-time application has been implemented with the purpose of demonstrating the capabilities of nowadays GPU's power within the scope of Image Based Rendering and Lighting. The built application has a full High Dynamic Range (HDR) pipeline and it deals with issues like tone mapping, automatic scene exposure, vignette effect and blooming (to increase the high dynamic effect). Furthermore, some materials were used to demonstrate the potentiality of Image Based Lighting.

    • High Dynamic Range Imaging: Theory and Practice Abstract 2006 A Siggraph 2006 Course presentation by multiple authors consisting of 320 slides. Current display devices have a limited range of contrast and colors that can be displayed, which is one of the main reasons that most image and video acquisition, processing and display techniques use no more than eight bits per color channel. This course outlines recent advances in high dynamic range imaging (HDRI) - from capture to display - that lift this restriction thereby enabling images to represent the color gamut and dynamic range of the original scene rather than the limited subspace imposed by current monitor technology.

    • Perceptual Evaluation of Tone Mapping Operators with Real-World Scenes Abstract 2005 Akiko Yoshida, Volker Blanz, Karol Myszkowski and Hans-Peter Seidel A number of successful tone mapping operators for contrast compression have been proposed due to the need to visualize high dynamic range (HDR) images on low dynamic range devices. They were inspired by fields as diverse as image processing, photographic practice, and modeling of the human visual systems (HVS). The variety of approaches calls for a systematic perceptual evaluation of their performance.

    • Perceptual Effects in Real-time Tone Mapping Abstract 2005 Hans-Peter Seidel, Karol Myszkowski, Grzegorz Krawczyk Tremendous progress in the development and accessibility of high dynamic range (HDR) technology that has happened just recently results in fast proliferation of HDR synthetic image sequences and captured HDR video. When properly processed, such HDR data can lead to very convincing and realistic results even when presented on traditional low dynamic range LDR) display devices. This requires real-time local contrast compression tone mapping) with simultaneous modeling of important in HDR image perception effects such as visual acuity, glare, day and night vision. We propose a unified model to include all those effects into a common computational framework, which enables an efficient implementation on currently available graphics hardware. We develop a post processing module which can be added as the final stage of any real-time rendering system, game engine, or digital video player, which enhances the realism and believability of displayed image streams.

    • High Dynamic Range Imaging Abstract 2004 Paul Debevec, Erik Reinhard, Greg Ward, Sumanta Pattanaik A Siggraph 2004 Course presentation by multiple authors consisting of 276 slides. Current display devices can display only a limited range of contrast and colors, which is one of the main reasons that most image acquisition, processing, and display techniques use no more than eight bits per color channel. This course outlines recent advances in high-dynamic-range imaging, from capture to display, that remove this restriction, thereby enabling images to represent the color gamut and dynamic range of the original scene rather than the limited subspace imposed by current monitor technology.

    • High Dynamic Range Images Abstract 2003 Timo Jyrinki This paper describes some of the principles in the computation and displaying of High Dynamic Range images. Various methods have been developed in computing High Dynamic Range images in higher precision and virtually unlimited range, and displaying the images on low-dynamic-range devices, such as CRT/LCD monitors.

    • Tone Reproduction and Physically Based Spectral Rendering Abstract 2002 Kate Devlin, Alan Chalmers, Alexander Wilkie, Werner Purgathofer The ultimate aim of realistic graphics is the creation of images that provoke the same responses that a viewer would have to a real scene. This STAR addresses two related key problem areas in this effort which are located at opposite ends of the rendering pipeline, namely the data structures used to describe light during the actual rendering process, and the issue of displaying such radiant intensities in a meaningful way. This STAR report will review the work to date on spectral rendering and tone reproduction techniques. It will include an investigation into the need for spectral imagery synthesis methods and accurate tone reproduction, and a discussion of major approaches to physically correct rendering and key tone mapping algorithms.

    • RADEON(TM) 9700 Shading Abstract 2002 Jason L. Mitchell In this supplement to Chapter 3 in the bound course notes, we will outline the shading capabilities of the new RADEON(TM) 9700 graphics processor and illustrate its power with a series of examples.

    • Image-Based Lighting Abstract 2002 Paul Debevec This tutorial shows how image-based lighting can illuminate synthetic objects with measurements of real light, making objects appear as if they're actually in a real-world scene.

    • A Tone Mapping Algorithm for High Contrast Images Abstract 2002 Michael Ashikhmin A new method is presented that takes as an input a high dynamic range image and maps it into a limited range of luminance values reproducible by a display device. There is significant evidence that a similar operation is performed by early stages of human visual system HVS). Our approach follows functionality of HVS without attempting to construct its sophisticated model. The operation is performed in three steps. First, we estimate local adaptation luminance at each point in the image. Then, a simple function is applied to these values to compress them into the required display range. Since important image details can be lost during this process, we then re-introduce details in the final pass over the image.

    • Pixel Shading with DirectX 8.1 and the ATI RADEONTM 8500 Abstract 2002 Jason L. Mitchell Programmable shaders are a powerful way to describe the interaction of surfaces with light, as evidenced by the success of programmable shading models like RenderMan and others. In these notes, we will outline the structure of the programming model and present some illustrative examples. In the companion notes distributed at SIGGRAPH, we will show implementations of the common example shaders used throughout this course (bumped cubic environment mapping, McCool BRDF and parametrized volumetric wood) as well as a new programming model which goes beyond ps.1.4.

    • Real-Time High-Dynamic Range Texture Mapping Abstract 2001 Jonathan Cohen, Chris Tchou, Tim Hawkins, and Paul Debevec This paper presents a technique for representing and displaying high dynamic-range texture maps (HDRTMs) using current graphics hardware. Dynamic range in real-world environments often far exceeds the range representable in 8-bit per-channel texture maps. The increased realism afforded by a high-dynamic range representation provides improved fidelity and expressiveness for interactive visualization of image-based models. Our technique allows for real-time rendering of scenes with arbitrary dynamic range, limited only by available texture memory.

    • Photographic Tone Reproduction for Digital Images Abstract 2001 Erik Reinhard, Michael Stark, Peter Shirley, James Ferwerda A classic photographic task is the mapping of the potentially high dynamic range of real world luminances to the low dynamic range of the photographic print. This tone reproduction problem is also faced by computer graphics practitioners who map digital images to a low dynamic range print or screen. The work presented in this paper leverages the time-tested techniques of photographic practice to develop a new tone reproduction operator. In particular, we use and extend the techniques developed by Ansel Adams to deal with digital images. The resulting algorithm is simple and produces good results for a wide variety of images

    • Interactive Tone Mapping Abstract 2000 Fredo Durand and Julie Dorsey Tone mapping and visual adaptation are crucial for the generation of static, photorealistic images. A largely unexplored problem is the simulation of adaptation and its changes over time on the visual appearance of a scene. In applications such as driving simulators, these changes must be modeled in order to reproduce the visibility conditions of real-world situations. In this paper, we address the practical issues of interactive tone mapping and propose a simple model of visual adaptation.

  • Image Based Lighting: Using an HDR image as the source of lighting in a scene.

    • GPU-Based Importance Sampling Abstract 2006 Mark Colbert, Jaroslav Kivánek We present a technique for image-based lighting of glossy objects using a Monte Carlo quadrature that requires minimal precomputation and operates within a single GPU shader, thereby fitting easily into almost any production pipeline requiring real-time dynamically changing materials or lighting.

  • Light Effects: Volumetric lighting, Caustics, Sub-surface scattering, etc...
    • Caustics: Light patterns caused by refraction and (somtimes) reflection.

      • Fast Real-time Caustics from Height Fields Abstract 2009 Cem Yuksel. John Keyser Caustics are crucial in water rendering, yet they are often neglected in real-time applications due to the demanding computational requirements of the general purpose caustics computation methods. In this paper we present a two-pass algorithm for caustics computation that is extremely fast and produces high quality results. Our algorithm is targeted for commonly used height field representations of water and a planar caustic-receiving surface. The underlying theory of our approach is presented along with implementation details and pseudo codes.

      • Hierarchical Caustic Maps Abstract 2008 Chris Wyman Interactive applications typically rely on local models for lighting, occasionally augmented by GPU-friendly methods for approximating global illumination. Caustic mapping ap- proximates the specular focusing of light using a light-space image, akin to a shadow map, which is projected onto the scene during final rendering. Unfortunately, existing caus- tic map implementations must choose between quality and speed. Quickly generated maps use few photons and look extremely blurry, while sharper maps created from millions of photons only render at a few frames per second. This paper introduces a number of hierarchical enhancements to caustic mapping that allow real-time rendering with high quality caustic maps, even when using maps from multiple light sources. These techniques utilize the geometry process- ing stage of recent GPUs to avoid processing every photon and to render a pyramidal caustic map that allows photon splats of varying diameters without the increased costs in- herent in rasterizing large splats.

      • Caustics Mapping: An Image-space Technique for Real-time Caustics Abstract 2007 Shah, Konttinen, Pattanaik In this paper, we present a simple and practical technique for real-time rendering of caustics from reflective and refractive objects. Our algorithm, conceptually similar to shadow mapping, consists of two main parts: creation of a caustic map texture, and utilization of the map to render caustics onto non-shiny surfaces. Our approach avoids performing any expensive geometric tests, such as ray-object intersection, and involves no pre-computation; both of which are common features in previous work. The algorithm is well suited for the standard rasterization pipeline and runs entirely on the graphics hardware.

    • Subsurface Scattering: Realtime lighting approximations for skin and other semi-transparent materials.

      • Screen-Space Perceptual Rendering of Human Skin Abstract 2009 Jimenez, Sundstedt, Gutierrez We propose a novel skin shader which translates the simulation of subsurface scattering from texture space to a screen-space diffusion approximation. It naturally scales well while maintaining a perceptually plausible result. This technique allows us to ensure real-time performance even when several characters may appear on screen at the same time. The visual realism of the resulting images is validated using a subjective psychophysical preference experiment. Our results show that, independent of distance and light position, the images rendered using our novel shader have as high visual realism as a previously developed physically-based shader.

      • Realistic Shading of Human Skin in Real time Abstract 2004 Florian Struck, Christian-A. Bohn, Sebastian Schmidt, Volker Helzle The demand for realistic human characters is driven by interactive application developers worldwide. The look of 3D models in real time graphics is efficiently improved by powerful shader techniques. Today a common technique consists of a simple lighting model combined with textures, which have precalculated illumination included. In this paper we will give an overview of the most recent techniques in skin shading. We present a multifaceted implementation of shading techniques by efficiently combining various approaches. Therefore we will explain physical and anatomical backgrounds and refer to relevant papers. In our opinion, this work is a valuable reference to assist shader developers in their implementations and adaptions on recent and future graphic hardware.

      • Mental Ray Fast Subsurface Scattering Tutorial Abstract 2004 Subsurface scattering skin shader tutorial for Mental Ray.

      • Skin in the "Dawn" Demo Abstract 2003 Curtis Beeson, Kevin Bjorke In particular, the chapter describes the skin shader used in NVIDIA's "Dawn" real-time demo, which was featured at the SIGGRAPH 2003 Electronic Theater. While the intent of this particular chapter was to describe how programmable hardware could be used to simulate human skin, the flexibility offered by programmable hardware has many ramifications.

      • A Rapid Hierarchical Rendering Technique for Translucent Materials Abstract 2002 Henrik Wann Jensen, Juan Buhler This paper introduces an efficient two-pass rendering technique for translucent materials. We decouple the computation of irradiance at the surface from the evaluation of scattering inside the material. This is done by splitting the evaluation into two passes, where the first pass consists of computing the irradiance at selected points on the surface. The second pass uses a rapid hierarchical integration technique to evaluate a diffusion approximation based on the irradiance samples. This approach is substantially faster than previous methods for rendering translucent materials, and it has the advantage that it integrates seamlessly with both scanline rendering and global illumination methods. We show several images and animations from our implementation that demonstrate that the approach is both fast and robust, making it suitable for rendering translucent materials in production.

    • Volumetric Lighting: Simulating light rays passing through a scattering medium.

      • Voxelized Shadow Volumes Abstract 2011 Chris Wyman Video: http://homepage.cs.uiowa.edu/~cwyman/publications/files/voxelShadowVols/voxelizedShadowVolumes.DivX.avi Efficient shadowing algorithms have been sought for decades, but most shadow research focuses on quickly identifying shadows on surfaces. This paper introduces a novel algorithm to efficiently sample light visibility at points inside a volume. These voxelized shadow volumes (VSVs) extend shadow maps to allow efficient, si- multaneous queries of visibility along view rays, or can alternately be seen as a discretized shadow volume. We voxelize the scene into a binary, epipolar-space grid where we apply a fast parallel scan to identify shadowed voxels. Using a view-dependent grid, our GPU implementation looks up 128 visibility samples along any eye ray with a single texture fetch. We demonstrate our algorithm in the context of interactive shadows in homogeneous, single-scattering participating media.

      • Real Time Volumetric Shadows using Polygonal Light Volumes Abstract 2010 Markus Billeter, Erik Sintorn, Ulf Assarsson This paper presents a more efficient way of computing single scattering effects in homogeneous participating media for real-time purposes than the currently popular ray-marching based algorithms. These effects include halos around light sources, volumetric shadows and crepuscular rays. By displacing the vertices of a base mesh with the depths from a standard shadow map, we construct a polygonal mesh that encloses the volume of space that is directly illuminated by a light source. Using this volume we can calculate the airlight contribution for each pixel by considering only points along the eye-ray where shadow-transitions occur. Unlike previous ray-marching methods, our method calculates the exact airlight contribution, with respect to the shadow map resolution, at real time frame rates.

      • Epipolar Sampling for Shadows and Crepuscular Rays in Participating Media with Single Scattering Abstract 2010 Thomas Engelhardt, Carsten Dachsbacher Scattering in participating media, such as fog or haze, generates volumetric lighting effects known as crepuscular or god rays. Ren- dering such effects greatly enhances the realism in virtual scenes, but is inherently costly as scattering events occur at every point in space and thus it requires costly integration of the light scattered towards the observer. This is typically done using ray marching which is too expensive for every pixel on the screen for interactive applications. We propose a rendering technique for textured light sources in single-scattering media, that draws from the concept of epipolar geometry to place samples in image space: the inscattered light varies orthogonally to crepuscular rays, but mostly smoothly along these rays. These are epipolar lines of a plane of light rays that projects onto one line on the image plane. Our method sam- ples sparsely along epipolar lines and interpolates between sam- ples where adequate, but preserves high frequency details that are caused by shadowing of light rays. We show that our method is very simple to implement on the GPU, yields high quality images, and achieves high frame rates.

      • Volume Light Abstract 2008 Nvidia Volume Light technique can be considered a simple approximation of real world light scattering effect. Small particles, sprayed in the air, interact with light beams and produce different effects like rainbows or sun shafts. Volumetric effects, are traditionally considered to be computational heavy, but can be approximated in realtime. In most cases a convincing look can be achieved by a good looking effect that integrates seamlessly into the scene. Thus, volumetric light is going to be a visual effect, rather than a physically correct simulation.

      • GPU Gems 3: Chapter 13. Volumetric Light Scattering as a Post-Process Abstract 2007 Kenny Mitchell In this chapter, we present a simple post-process method that produces the effect of volumetric light scattering due to shadows in the atmosphere. We improve an existing analytic model of daylight scattering to include the effect of volumetric occlusion, and we present its implementation in a pixel shader. The demo, which is included on the DVD accompanying this book, shows the technique can be applied to any animating image of arbitrary scene complexity.

      • A Practical Analytic Single Scattering Model for Real Time Rendering∗ Abstract 2005 Bo Sun, Ravi Ramamoorthi, Srinivasa G. Narasimhan, Shree K. Nayar We consider real-time rendering of scenes in participating media, capturing the effects of light scattering in fog, mist and haze. While a number of sophisticated approaches based on Monte Carlo and fi- nite element simulation have been developed, those methods do not work at interactive rates. The most common real-time methods are essentially simple variants of the OpenGL fog model. While easy to use and specify, that model excludes many important qualitative effects like glows around light sources, the impact of volumetric scattering on the appearance of surfaces such as the diffusing of glossy highlights, and the appearance under complex lighting such as environment maps. In this paper, we present an alternative physically based approach that captures these effects while maintaining realtime performance and the ease-of-use of the OpenGL fog model. Our method is based on an explicit analytic integration of the single scattering light transport equations for an isotropic point light source in a homogeneous participating medium. We can implement the model in modern programmable graphics hardware using a few small numerical lookup tables stored as texture maps. Our model can also be easily adapted to generate the appearances of materials with arbitrary BRDFs, environment map lighting, and precomputed radiance transfer methods, in the presence of participating media. Hence, our techniques can be widely used in real-time rendering.

      • Light Shafts Abstract 2004 Jason Mitchell A 44 slide set.

    • Real-Time Rough Refraction Abstract 2011 de Rousiers, Bousseau, Subr, Holzschuch, Ramamoorthi We present an algorithm to render objects of transparent materials with rough surfaces in real-time, under distant illumination. Rough surfaces cause wide scattering as light enters and exits objects, which significantly complicates the rendering of such materials. We present two contributions to approximate the successive scattering events at interfaces, due to rough refraction : First, an approximation of the Bidirectional Transmittance Distribution Function (BTDF), using spherical Gaussians, suitable for real-time estimation of environment lighting using pre-convolution; second, a combination of cone tracing and macro-geometry filtering to effi- ciently integrate the scattered rays at the exiting interface of the object. We demonstrate the quality of our approximation by comparison against stochastic raytracing

    • Practical Post-Process Depth of Field Abstract 2006 Hammon, Ward In this chapter we describe a depth-of-field (DoF) algorithm particularly suited for first-person games. At Infinity Ward, we pride ourselves on immersing players in a rich cinematic experience. Consistent with this goal, we developed a technique for Call of Duty 4: Modern Warfare that provides depth of field's key qualitative features in both the foreground and the background with minimal impact on total system performance or engine architecture. Our technique requires Shader Model 2.0 hardware.

  • Modeling: Techniques for modeling dynamic objects: fire, rain, water...

    • Rendering Snowing Scene on GPU Abstract 2010 Jun Zhang, Xingquan Cai, Jinhong Li As the part of natural sceneries, snow scene is a familiar natural phenomenon in the north of China. In this paper, we present a new method to render snow scene on GPU based particle system. We simulate the whirling snowflakes in the sky and the snow deposition effect. Our method processes the birth and death of snow particles via index on CPU and uses a pair of Floating Point Textures on GPU to store the dynamic attributes of snow particles. Our method also updates the dynamic attributes of snow particles, and renders the system on GPU. We also provide a method based height field and establish some deposition rules to simulate the snow deposition. Finally, our experiments prove that our method is feasible and high performance. Our method can be used in computer animation, games, special movie effects, etc.

    • Real-time Procedural Volumetric Fire Abstract 2007 Alfred R. Fuller, Hari Krishnan, Karim Mahrous, Bernd Hamann, Kenneth I. Joy We present a method for generating procedural volumetric fire in real time. By combining curve-based volumetric free-form deformation, hardware-accelerated volumetric rendering and Improved Perlin Noise or M-Noise we are able to render a vibrant and uniquely animated volumetric fire that supports bi-directional environmental macro-level interactivity. Our system is easily customizable by content artists. The fire is animated both on the macro and micro levels. Macro changes are controlled either by a prescripted sequence of movements, or by a realistic particle simulation that takes into account movement, wind, high-energy particle dispersion and thermal buoyancy. Micro fire effects such as individual flame shape, location, and flicker are generated in a pixel shader using three- to four-dimensional Improved Perlin Noise or M-Noise (depending on hardware limitations and performance requirements). Our method supports efficient collision detection, which, when combined with a sufficiently intelligent particle simulation, enables real-time bi-directional interaction between the fire and its environment. The result is a three-dimensional procedural fire that is easily designed and animated by content artists, supports dynamic interaction, and can be rendered in real time.

    • Fur (using Shells and Fins) Abstract 2007 Sarah Tariq This sample illustrates the use of a new feature of DirectX 10, the Geometry Shader, to create new geometry on the fly. The sample uses the shells and fins technique to render fur on arbitrary triangle meshes. Fins are rendered by creating new geometry per frame along the silhouette edges of a mesh. Before DirectX 10 this required adding degenerate triangles to the mesh at every edge but now fins can be generated efficiently using the Geometry Shader.

    • A Parametric Model for Oriented, Navigable Surfaces in Virtual Environments Abstract 2006 Wang, Kearney This paper introduces a parametric model of oriented, navigable surfaces in virtual environments. An oriented, navigable surface in 3D space is modeled as a ribbon which has a central axis and can be twisted around the central axis. The axis is represented with a cubic spline curve and is approximately arc-length parameterized. The prole of the ribbon along the axis is described by a slant function. With the representation of the ribbon axis and the ribbon pro- le, a point on the ribbon surface can be expressed as a function of two parameters: the arc length along the axis and the offset from the axis. The parametric model of a ribbon naturally forms a local ribbon coordinate system which provides a frame of reference for behavior code. In order to provide an uniform, continuous frame of reference for an agent to navigate through connected ribbons, we unite the ribbons to form a ribbon called a path.

    • Using Vertex Texture Displacement for Realistic Water Rendering Abstract 2005 Yuri Kryachko Water surfaces are common in computer graphics, especially in games. They are a critical element that can significantly improve the level of realism in a scene. But depicting them realistically is a hard problem, because of the high visual complexity present in the motion of water surfaces, as well as in the way light interacts with water. This chapter describes techniques developed for rendering realistic depictions of the ocean for the game Pacific Fighters. Modern graphics hardware provides a number of useful features with DirectX Shader Model 3.0 that can be used to aid the rendering of water surfaces. This chapter will discuss how one of these features, vertex texturing, can be used to increase the realism of rendered water surfaces. Figure 18-1 shows some sample results. In addition, we also use branching in order to improve the performance of our vertex programs.

    • Realistic real-time rain rendering Abstract 2005 Pierre Rousseau, Vincent Jolivet, Djamchid Ghazanfarpour Real-time rendering of virtual weather conditions has been investigated in many papers. Inserting fog or snow in a scene is rather straightforward. Rain is one of the most encountered natural phenomena, but its rendering often lacks realism. In this paper, we propose a realistic real-time rain rendering method using programmable graphics hardware. In order to simulate the refraction of the scene inside a raindrop, the scene is captured to a texture which is distorted according to optical properties of raindrops. This texture is mapped onto each raindrop. Our method also takes into account retinal persistence, and interaction with light sources.

    • Curved PN Triangles Abstract 2001 Vlachos, Peters, Boyd, Mitchell To improve the visual quality of existing triangle-based art in real-time entertainment, such as computer games, we propose replacing flat triangles with curved patches and higher-order normal variation. At the hardware level, based only on the three vertices and three vertex normals of a given flat triangle, we substitute the geometry of a three-sided cubic Bézier patch for the triangle’s flat geometry, and a quadratically varying normal for Gouraud shading. These curved point-normal triangles, or PN triangles, require minimal or no change to existing authoring tools and hardware designs while providing a smoother, though not necessarily everywhere tangent continuous, silhouette and more organic shapes.

  • Non-PhotoRealistic Rendering: Toon shading, Edge enhancement, Hatch Shading

    • Non-Photorealistic Real-Time Edge Rendering using Non-Duplicate Parallel Detection and Capping Abstract 2010 Dwight House Non-photorealistic rendering (NPR) provides distinctly different information to the viewer when compared with photorealistic rendering. Examples of NPR range from visually pleasing toon and watercolor styles to the highly precise and informative technical illustration styles. One of the most important structures that can be found in many different NPR styles is the humble edge. It can define boundaries, amplify structure, highlight importance, and is an essential component of several artistic styles. Their utility has inspired research on realtime edge detection and rendering techniques since the early days of computer graphics. There are dozens of diverse methods to achieve real-time edge detection and rendering. In this thesis, a survey of major edge detection methods is presented. The methods in the survey are divided into four distinct categories. Next, Morgan McGuire and John F. Hugh's "Hardware-Determined Edge Features" method is described in detail. It forms the basis for the author's exploration of, and contributions to, edge detection. Then, the author details his attempts to correct the problems with McGuire and Hughes' method. A few alternative methods are explored that take advantage of OpenCL, a new GPU computation technology. Finally, the effectiveness of the contributions are analyzed and compared.

    • Highlight Lines for Conveying Shape Abstract 2007 Doug DeCarlo, Szymon Rusinkiewicz Recent work has shown that sparse lines defined on 3D shapes, including occluding contours and suggestive contours, are effective at conveying shape. We introduce two new families of lines called suggestive highlights and principal highlights, based on definitions related to suggestive contours and geometric creases. We show that when these are drawn in white on a gray background they are naturally interpreted as highlight lines, and complement contours and suggestive contours. We provide object-space definitions and algorithms for extracting these lines, explore several stylization possibilities, and compare the lines to ridges and valleys of intensity in diffuse-shaded images.

    • Real-Time Rendering of Cartoon Smoke and Clouds Abstract 2006 Morgan McGuire, Andi Fein We describe an algorithm for rendering animated smoke particle systems in a cartoon style. This style includes outlines and celshading. For efficient self-shadowing effects, we introduce nailboard shadow volumes that create complex shadows from few polygons. Including shadows, the renderer draws only three polygons per particle and entirely avoids the latency of depth buffer readback. We combine the renderer with a fast simulator that generates the phenomenology of real smoke but has artistically controllable parameters. Together they produces real-time interactive smoke animations at over 30 fps. Thus our algorithm is well-suited to applications where interactive performance and expressive power are preferred to realism; for example, video games and rapid development of animation.

    • Real-Time Pencil Rendering Abstract 2006 Hyunjun Lee, Sungtae Kwon, Seungyong Lee This paper presents a real-time technique for rendering 3D meshes in the pencil drawing style. We analyze the characteristics of pencil drawing and incorporate them into the rendering process, which is fully implemented on a GPU. For object contours, we propose a multiple contour drawing technique that imitates trial-and-errors of human in contour drawing. For interior shading, we present a simple approach for mapping oriented textures onto an object surface. To improve the quality of pencil rendering, we generate and map pencil textures that reflect the properties of graphite pencils and paper. We show several rendering examples that demonstrate the high performance of the proposed technique in terms of speed and quality.

    • Real-Time Pen-and-Ink Illustration of Landscapes Abstract 2006 Liviu Coconu, Oliver Deussen, Hans-Christian Hege Non-photorealistic rendering has been proven to be particularly efficient in conveying and transmitting selected visual information. Our paper presents a NPR rendering pipeline that supports pen-andink illustration for, but not limited to, complex landscape scenes in real time. This encompasses a simplification framework using clustering which enables new approaches to efficient and coherent rendering of stylized silhouettes, hatching and abstract shading. Silhouette stylization is performed in image-space. This avoids explicit computation of connected lines. Further, coherent hatching of the tree foliage is performed using an approximate view-dependent parameterization computed on-the-fly within the same simplification framework. All NPR algorithms are integrated with photorealistic rendering, allowing seamless transition and combination between a variety of photorealistic and non-photorealistic drawing styles.

    • Illustrative Rendering in Team Fortress 2 Abstract 2006 Jason Mitchell, Moby Francke, Dhabih Eng We present a set of artistic choices and novel real-time shading techniques which support each other to enable the unique rendering style of the game Team Fortress 2. Grounded in the conventions of early 20th century commercial illustration, the look of Team Fortress 2 is the result of tight collaboration between artists and engineers. In this paper, we will discuss the way in which the art direction and technology choices combine to support artistic goals and gameplay constraints. In addition to achieving a compelling style, the shading techniques are designed to quickly convey geometric information using rim highlights as well as variation in luminance and hue, so that game players are consistently able to visually "read" the scene and identify other players in a variety of lighting conditions.

    • Real-Time Halftoning: Fast and Simple Stylized Shading Abstract 2004 Bert Freudenberg, Maic Masuch, Thomas Strothotte This gem introduces halftoning as a way for implementing non-photorealistic rendering styles for computer games. The technique uses only the conventional multi-texturing pipeline on common hardware. We show how to create halftone screens for images that resemble pen-and-ink drawing styles and how to implement fast halftone rendering with modest pixel shading hardware.

    • IMPaSTo: A Realistic, Interactive Model for Paint Abstract 2004 William Baxter, Jeremy Wendt, Ming C. Lin We present a paint model for use in interactive painting systems that captures a wide range of styles similar to oils or acrylics. The model includes both a numerical simulation to recreate the physical flow of paint and an optical model to mimic the paint appearance. Our physical model for paint is based on a conservative advection scheme that simulates the basic dynamics of paint, augmented with heuristics that model the remaining key properties needed for painting. We allow one active wet layer, and an unlimited number of dry layers, with each layer being represented as a height-field. We represent paintings in terms of paint pigments rather than RGB colors, allowing us to relight paintings under any full-spectrum illuminant. We also incorporate an interactive implementation of the Kubelka-Munk diffuse reflectance model, and use a novel eightcomponent color space for greater color accuracy. We have integrated our paint model into a prototype painting system, with both our physical simulation and rendering algorithms running as fragment programs on the graphics hardware. The system demonstrates the model's effectiveness in rendering a variety of painting styles from semi-transparent glazes, to scumbling, to thick impasto.

    • Estimating Curvatures and Their Derivatives on Triangle Meshes Abstract 2004 Rusinkiewicz The computation of curvature and other differential properties of surfaces is essential for many techniques in analysis and rendering. We present a finite-differences approach for estimating curvatures on irregular triangle meshes that may be thought of as an extension of a common method for estimating per-vertex normals. The technique is efficient in space and time, and results in significantly fewer outlier estimates while more broadly offering accuracy comparable to existing methods. It generalizes naturally to computing derivatives of curvature and higher-order surface differentials.

    • Non-Photorealistic Rendering Techniques for Motion in Computer Games Abstract 2004 Michael Haller, Christian Hanl, Jeremiah Diephuis Still images can portray motion by using a stylized technique. Most of these techniques are commonly used for dynamic images as well (e.g., for cartoons). Typically, an artist abstracts the motion of a specific scene or animation to illustrate movement. Depicting motion in real-time environments is no less essential, and therefore a similar approach is desirable. Our approach is focused on three methods to stylize motion: squash-and-stretch, multiple images, and motion lines. A discussion of these methods for depicting motion in dynamic images and an implementation are presented in this paper. Finally, we discuss the results and conclude with the outlook for further development.

    • Pen-and-ink textures for real-time rendering Abstract 2003 Jennifer Fung, Oleg Veryovka Simulation of a pen-and-ink illustration style in a realtime rendering system is a challenging computer graphics problem. Tonal art maps (TAMs) were recently suggested as a solution to this problem. Unfortunately, only the hatching aspect of pen-and-ink media was addressed thus far. We extend the TAM approach and enable representation of arbitrary textures. We generate TAM images by distributing stroke primitives according to a probability density function. This function is derived from the input image and varies depending on the TAM's scale and tone levels. The resulting depiction of textures approximates various styles of pen-and-ink illustrations such as outlining, stippling, and hatching.

    • Hatching Stroke Styles & Pointillism Abstract 2003 Kevin Buchin, Maike Walther Hatching is a common technique used in Non-Photorealistic Rendering (NPR). For hatching, series of strokes are combined into textures. These compositions of strokes can convey the surface form through stroke orientation, the surface material through stroke arrangement and style, and the effect of light on the surface through stroke density. Up until now an important issue of real-time hatching techniques has been how to employ the limited programmability of the graphics hardware currently available. Pixel programmability has now reached a state where we can shift the focus to adding more flexibility to the hatching scheme and combining hatching with other techniques for creating new effects. We present a hatching scheme and some extensions to it, namely interactively changing the stroke style, and hatching with specular highlights. As an application, we show how we integrate hand drawings into a scene taking into account the effect of lighting. Finally, we show how to choose a color for each stroke depending on the background color, which can be used for a pointillistic style.

    • Non-Photorealistic Rendering Abstract 2002 Anna Vilanova Rendering in computer graphics means the process by which a virtual scene is converted into an image. Pioneer work in computer graphics was done to achieve photorealism. The goal was to create synthetic images that can be mistaken by photographs. It is rather absurd that a field of study is named after what it is not. Stanislaw Ulam said once that "The study of non-linear physics is like the study of non-elephant biology". Non-photorealistic rendering is the means of generate imaging that does not aspire to realism. It is difficult to express what exactly it is, therefore it is easier to express what it is not. Photorealism has a lot of applications (special ef- Figure 1: Van Gogh, The Starry Night(June 1889) fects, design visualization and so on). But simulating reality is not as important as creating the illusion of reality in the mind of the observer. There are several motivations for generating images that does not pretend to simulate reality.

    • Fine Tone Control in Hardware Hatching Abstract 2002 Matthew Webb, Emil Praun, Adam Finkelstein, Hugues Hoppe Recent advances in NPR have enabled real-time rendering of 3D models shaded with hatching strokes for use in interactive applications. The key challenges in real-time hatching are to convey tone by dynamically adjusting stroke density, while controlling stroke size and maintaining frame-to-frame coherence. In this paper, we introduce two new real-time hatching schemes that leverage recent advances in texture mapping hardware. Both schemes provide enhanced control of tone, thereby avoiding blending or aliasing artifacts present in previous systems. The first scheme, which relies on volume rendering hardware, admits the use of color. The second scheme, which uses pixel shaders, allows per-pixel lighting operations such as texture modulation. Both schemes run at interactive rates on inexpensive PC graphics cards.

    • Real-Time Halftoning: A Primitive For Non-Photorealistic Shading Abstract 2002 Bert Freudenberg, Maic Masuch, Thomas Strothotte We introduce halftoning as a general primitive for real-time non-photorealistic shading. It is capable of producing a variety of rendering styles, ranging from engraving with lighting-dependent line width to pen-and-ink style drawings using prioritized stroke textures. Since monitor resolution is limited we employ a smooth threshold function that provides stroke antialiasing. By applying the halftone screen in texture space and evaluating the threshold function for each pixel we can influence the shading on a pixel-by-pixel basis. This enables many effects to be used, including indication mapping and individual stroke lighting. Our real-time halftoning method is a drop-in replacement for conventional multitexturing and runs on commodity hardware. Thus, it is easy to integrate in existing applications, as we demonstrate with an artistically rendered level in a game engine.

    • Non-Photorealistic Rendering Techniques for Real-Time Character Animation Abstract 2002 Jerome Thoma In this thesis, we present the results of an investigation into the use of nonphotorealistic rendering techniques for real-time character animation. So far, most non-photorealistic rendering methods have only been applied to simple, static scenes. In the context of real-time character animation, a number of special technical issues arise that put much higher requirements on the rendering algorithms. Based on established techniques, we examine and extend a number of different non-photorealistic rendering techniques and integrate them into a real-time animation system. We analyse the results with respect to a number of different criteria and develop ideas for extending and refining the presented techniques. Furthermore, we motivate our work by putting it into the context of computer depiction and related fields such as fine arts and psychology.

    • Real-Time Hatching Abstract 2001 Emil Praun, Hugues Hoppe, Matthew Webb, Adam Finkelstein Drawing surfaces using hatching strokes simultaneously conveys material, tone, and form. We present a system for real-time rendering of hatching strokes over arbitrary surfaces, in a variety of non-photorealistic styles. During an automatic preprocess, we construct a sequence of mip-mapped hatch images corresponding to different tones, collectively called a tonal art map. Strokes within the hatch images are scaled to attain appropriate stroke size and density at all resolutions, and are organized to maintain coherence across scales and tones. At runtime, hardware multitexturing blends the hatch images over the rendered faces to locally vary tone while maintaining both spatial and temporal coherence. In order to render strokes over arbitrary surfaces, we build a lapped texture parametrization where the overlapping patches align to a curvaturebased direction field. By exploiting modern texture-mapping hardware, our scheme convincingly renders hatching strokes in real-time on a variety of complex surfaces.

    • Hardware-Determined Feature Edges Abstract 2000 Morgan McGuire, John F. Hughes Algorithms that detect silhouettes, creases, and other edge based features often perform per-edge and per-face mesh computations using global adjacency information. These are unsuitable for hardware-pipeline implementation, where programmability is at the vertex and pixel level and only local information is available. Card and Mitchell and Gooch have suggested that adjacency information could be packed into a vertex data structure; we describe the details of converting global/per-edge computations into local/per-vertex computations on a related edge mesh. Using this trick, we describe a feature-edge detection algorithm that runs entirely in hardware, and show how to use it to create thick screen-space contours with end-caps that join adjacent thick line segments. The end-cap technique favors speed over quality and produces artifacts for some meshes. We present two parameterizations for mapping stroke textures onto these thick line's tessellation-independent screen space method that is better suited to still images, and an object space method better suited to animation. As additional applications, we show how to create fins for fur rendering and how to extrude contours in world-space to create the sides of a shadow volume directly on the GPU. The edge mesh is about nine times larger than the original mesh when stored at 16-bit precision and is constructed through a linear time pre-processing step. As long as topology remains fixed, the edge mesh can be animated as if it were a vertex mesh.

    • Introduction to 3D Non-Photorealistic Rendering: Silhouettes and Outlines Abstract 2000 Aaron Hertzmann In these notes, we survey some of the basic tools used for non-photorealistic rendering of 3D scenes. We will primarily focus on detecting outlines of object shape: silhouettes, boundaries, and creases. (Hatching and shading, which are also very important for communicating shape, are discussed elsewhere in the course notes.) The algorithms in this section can be divided into algorithms that operate in the image space (2D), and algorithms that operate in world space (3D).

    • Art-Based Rendering of Fur, Grass, and Trees Abstract 1999 Michael A. Kowalski, Lee Markosian, J.D. Northrup, Lubomir Bourdevy, Ronen Barzelz, Loring S. Holden, John F. Hughes Artists and illustrators can evoke the complexity of fur or vegetation with relatively few well-placed strokes. We present an algorithm that uses strokes to render 3D computer graphics scenes in a stylized manner suggesting the complexity of the scene without representing it explicitly. The basic algorithm is customizable to produce a range of effects including fur, grass and trees, as we demonstrate in this paper and accompanying video. The algorithm is implemented within a broader framework that supports procedural stroke-based textures on polyhedral models. It renders moderately complex scenes at multiple frames per second on current graphics workstations, and provides some interframe coherence.

    • Real-Time Nonphotorealistic Rendering Abstract 1997 Lee Markosian, Michael A. Kowalski, Samuel J. Trychin, Lubomir, D. Bourdev, Daniel Goldstein, John F. Hughes Nonphotorealistic rendering (NPR) can help make comprehensible but simple pictures of complicated objects by employing an economy of line. But current nonphotorealistic rendering is primarily a batch process. This paper presents a real-time nonphotorealistic renderer that deliberately trades accuracy and detail for speed. Our renderer uses a method for determining visible lines and surfaces which is a modification of Appel's hidden-line algorithm, with improvements which are based on the topology of singular maps of a surface into the plane. The method we describe for determining visibility has the potential to be used in any NPR system that requires a description of visible lines or surfaces in the scene. The major contribution of this paper is thus to describe a tool which can significantly improve the performance of these systems.We demonstrate the systemwith several nonphotorealistic rendering styles, all of which operate on complex models at interactive frame rates.

  • Procedural Textures: Wood ...

    • Simulating the structure and texture of solid wood Abstract 2016 Albert Julius Liu, Zhao Dong, Milos Hasan, Steve Marschner Wood is an important decorative material prized for its unique appearance. It is commonly rendered using artistically authored 2D color and bump textures, which reproduces color patterns on flat surfaces well. But the dramatic anisotropic specular figure caused by wood fibers, common in curly maple and other species, is harder to achieve. While suitable BRDF models exist, the texture parameter maps for these wood BRDFs are difficult to author—good results have been shown with elaborate measurements for small flat samples, but these models are not much used in practice. Furthermore, mapping 2D image textures onto 3D objects leads to distortion and inconsistencies. Procedural volumetric textures solve these geometric problems, but existing methods produce much lower quality than image textures. This paper aims to bring the best of all these techniques together: we present a comprehensive volumetric simulation of wood appearance, including growth rings, color variation, pores, rays, and growth distortions. The fiber directions required for anisotropic specular figure follow naturally from the distortions. Our results rival the quality of textures based on photographs, but with the consistency and convenience of a volumetric model. Our model is modular, with components that are intuitive to control, fast to compute, and require minimal storage.

    • Procedural wood textures Abstract 2015 Existing bidirectional reflectance distribution function (BRDF) models are capable of capturing the distinctive highlights produced by the fibrous nature of wood. However, capturing parameter textures for even a single specimen remains a laborious process requiring specialized equipment. In this paper we take a procedural approach to generating parameters for the wood BSDF. We characterize the elements of trees that are important for the appearance of wood, discuss techniques appropriate for representing those features, and present a complete procedural wood shader capable of reproducing the growth patterns responsible for the distinctive appearance of highly prized “figured” wood. Our procedural wood shader is random-access, 3D, modular, and is fast enough to generate a preview for design.

    • Measuring and Modeling the Appearance of Finished Wood Abstract 2005 Stephen R. Marschner, Stephen H. Westin, Adam Arbree, Jonathan T. Moon Wood coated with transparent finish has a beautiful and distinctive appearance that is familiar to everyone. Woods with unusual grain patterns, such as tiger, burl, and birdseye figures, have a strikingly unusual directional reflectance that is prized for decorative applications. With new, high resolution measurements of spatially varying BRDFs, we show that this distinctive appearance is due to light scattering that does not conform to the usual notion of anisotropic surface reflection. The behavior can be explained by scattering from the matrix of wood fibers below the surface, resulting in a subsurface highlight that occurs on a cone with an out-of-plane axis. We propose a new shading model component to handle reflection from subsurface fibers, which is combined with the standard diffuse and specular components to make a complete shading model. Rendered results from fits of our model to the measurement data demonstrate that this new model captures the distinctive appearance of wood.

    • Generating Textures of New Zealand Native Wood Abstract 2002 Jack Wang This report explores algorithms for computer generated textures simulating New Zealand native wood, we out line procedural texturing algorithms like Perlin noise and turbulence, techniques like texture generation, texture mapping and Ray tracing. The main goal of this research is to study New Zealand native wood in depth and to gather sufficient information to be able to generate realistic and detailed 3D texture for New Zealand native woods. In particular this work shows the development of texture for Kauri out of New Zealand’s most famous native trees, and with Rimu.

  • Ray Tracing: All things ray tracing.
    • Path Guiding: The latest techniques for optimizing path tracing.

      • Variance-Aware Path Guiding Abstract 2020 Alexander Rath, Pascal Grittmann, Sebastian Herholz, Petr Vévoda, Philipp Slusallek, Jaroslav Křivánek Path guiding is a promising tool to improve the performance of path tracing algorithms. However, not much research has investigated what target densities a guiding method should strive to learn for optimal performance. Instead, most previous work pursues the zero-variance goal: The local decisions are guided under the assumption that all other decisions along the random walk will be sampled perfectly. In practice, however, many decisions are poorly guided, or not guided at all. Furthermore, learned distributions are often marginalized, e.g., by neglecting the BSDF. We present a generic procedure to derive theoretically optimal target densities for local path guiding. These densities account for variance in nested estimators, and marginalize provably well over, e.g., the BSDF. We apply our theory in two state-of-the-art rendering applications: a path guiding solution for unidirectional path tracing [Müller et al. 2017] and a guiding method for light source selection for the many lights problem [Vévoda et al. 2018]. In both cases, we observe significant improvements, especially on glossy surfaces. The implementations for both applications consist of trivial modifications to the original code base, without introducing any additional overhead.

      • Spatiotemporal reservoir resampling for real-time ray tracing with dynamic direct lighting -- Supplemental document Abstract 2020 Benedikt Bitterli, Chris Wyman, Matt Pharr, Peter Shirley, Aaron Lefohn, Wojciech Jarosz Supplemental document.

      • Spatiotemporal reservoir resampling for real-time ray tracing with dynamic direct lighting Abstract 2020 Benedikt Bitterli, Chris Wyman, Matt Pharr, Peter Shirley, Aaron Lefohn, Wojciech Jarosz Efficiently rendering direct lighting from millions of dynamic light sources using Monte Carlo integration remains a challenging problem, even for off-line rendering systems. We introduce a new algorithm—ReSTIR—that renders such lighting interactively, at high quality, and without needing to maintain complex data structures. We repeatedly resample a set of candidate light samples and apply further spatial and temporal resampling to leverage information from relevant nearby samples. We derive an unbiased Monte Carlo estimator for this approach, and show that it achieves equal-error 6×-60× faster than state-of-the-art methods. A biased estimator reduces noise further and is 35×-65× faster, at the cost of some energy loss. We implemented our approach on the GPU, rendering complex scenes containing up to 3.4 million dynamic, emissive triangles in under 50 ms per frame while tracing at most 8 rays per pixel.

    • Denoising and Guiding: From Siggraph 2021: Neural Networks for optimizing path tracing and denoising.

      • Weakly Supervised Contrastive Learning in Path Manifold for Monte Carlo Image Reconstruction Abstract 2021 Cho, Huo, Yoon Image-space auxiliary features such as surface normal have significantly contributed to the recent success of Monte Carlo (MC) reconstruction networks. However, path-space features, another essential piece of light propagation, have not yet been sufficiently explored. Due to the curse of dimensionality, information flow between a regression loss and high-dimensional path-space features is sparse, leading to difficult training and inefficient usage of pathspace features in a typical reconstruction framework. This paper introduces a contrastive manifold learning framework to utilize path-space features effectively. The proposed framework employs weakly-supervised learning that converts reference pixel colors to dense pseudo labels for light paths. A convolutional path-embedding network then induces a low-dimensional manifold of paths by iteratively clustering intra-class embeddings, while discriminating inter-class embeddings using gradient descent. The proposed framework facilitates path-space exploration of reconstruction networks by extracting low-dimensional yet meaningful embeddings within the features. We apply our framework to the recent image- and sample-space models and demonstrate considerable improvements, especially on the sample space. The source code is available at https://github.com/Mephisto405/WCMC.

      • Real-time Neural Radiance Caching for Path Tracing Abstract 2021 Müller, Rousselle, Novák, Keller We present a real-time neural radiance caching method for path-traced global illumination. Our system is designed to handle fully dynamic scenes, and makes no assumptions about the lighting, geometry, and materials. The data-driven nature of our approach sidesteps many difficulties of caching algorithms, such as locating, interpolating, and updating cache points. Since pretraining neural networks to handle novel, dynamic scenes is a formidable generalization challenge, we do away with pretraining and instead achieve generalization via adaptation, i.e. we opt for training the radiance cache while rendering. We employ self-training to provide low-noise training targets and simulate infinite-bounce transport by merely iterating few-bounce training updates. The updates and cache queries incur a mild overhead—about 2.6ms on full HD resolution—thanks to a streaming implementation of the neural network that fully exploits modern hardware. We demonstrate significant noise reduction at the cost of little induced bias, and report state-of-the-art, real-time performance on a number of challenging scenarios

      • Interactive Monte Carlo Denoising Using Affinity of Neural Features Abstract 2021 Işik, Mullia, Fisher, Eisenmann, Gharbi, High-quality denoising of Monte Carlo low-sample renderings remains a critical challenge for practical interactive ray tracing. We present a new learning-based denoiser that achieves state-of-the-art quality and runs at interactive rates. Our model processes individual path-traced samples with a lightweight neural network to extract per-pixel feature vectors. The rest of our pipeline operates in pixel space. We define a novel pairwise affinity over the features in a pixel neighborhood, from which we assemble dilated spatial kernels to filter the noisy radiance. Our denoiser is temporally stable thanks to two mechanisms. First, we keep a running average of the noisy radiance and intermediate features, using a per-pixel recursive filter with learned weights. Second, we use a small temporal kernel based on the pairwise affinity between features of consecutive frames. Our experiments show our new affinities lead to higher quality outputs than techniques with comparable computational costs, and better high-frequency details than kernel-predicting approaches. Our model matches or outperfoms state-ofthe-art offline denoisers in the low-sample count regime (2–8 samples per pixel), and runs at interactive frame rates at 1080p resolution.

      • Hierarchical Neural Reconstruction for Path Guiding Using Hybrid Path and Photon Samples Abstract 2021 Zhu, Xu, Sun, Kuznetsov, Meyer, Jensen, Su, Ramamoorthi Path guiding is a promising technique to reduce the variance of path tracing. Although existing online path guiding algorithms can eventually learn good sampling distributions given a large amount of time and samples, the speed of learning becomes a major bottleneck. In this paper, we accelerate the learning of sampling distributions by training a light-weight neural network offline to reconstruct from sparse samples. Uniquely, we design our neural network to directly operate convolutions on a sparse quadtree, which regresses a highquality hierarchical sampling distribution. Our approach can reconstruct reasonably accurate sampling distributions faster, allowing for efficient path guiding and rendering. In contrast to the recent offline neural path guiding techniques that reconstruct low-resolution 2D images for sampling, our novel hierarchical framework enables more fine-grained directional sampling with less memory usage, effectively advancing the practicality and efficiency of neural path guiding. In addition, we take advantage of hybrid bidirectional samples including both path samples and photons, as we have found this more robust to different light transport scenarios compared to using only one type of sample as in previous work. Experiments on diverse testing scenes demonstrate that our approach often improves rendering results with better visual quality and lower errors. Our framework can also provide the proper balance of speed, memory cost, and robustness.\

      • Spatiotemporal reservoir resampling for real-time ray tracing with dynamic direct lighting Abstract 2020 Bitterli, Wyman, Pharr, Shirley, Lefohn, Jarosz, Efficiently rendering direct lighting from millions of dynamic light sources using Monte Carlo integration remains a challenging problem, even for off-line rendering systems. We introduce a new algorithm—ReSTIR—that renders such lighting interactively, at high quality, and without needing to maintain complex data structures. We repeatedly resample a set of candidate light samples and apply further spatial and temporal resampling to leverage information from relevant nearby samples. We derive an unbiased Monte Carlo estimator for this approach, and show that it achieves equal-error 6×-60× faster than state-of-the-art methods. A biased estimator reduces noise further and is 35×-65× faster, at the cost of some energy loss. We implemented our approach on the GPU, rendering complex scenes containing up to 3.4 million dynamic, emissive triangles in under 50 ms per frame while tracing at most 8 rays per pixel.

      • Neural Temporal Adaptive Sampling and Denoising Abstract 2020 Munkberg, Salvi, Patney, Lefohn Despite recent advances in Monte Carlo path tracing at interactive rates, denoised image sequences generated with few samples per-pixel often yield temporally unstable results and loss of high-frequency details. We present a novel adaptive rendering method that increases temporal stability and image fidelity of low sample count path tracing by distributing samples via spatio-temporal joint optimization of sampling and denoising. Adding temporal optimization to the sample predictor enables it to learn spatio-temporal sampling strategies such as placing more samples in disoccluded regions, tracking specular highlights, etc; adding temporal feedback to the denoiser boosts the effective input sample count and increases temporal stability. The temporal approach also allows us to remove the initial uniform sampling step typically present in adaptive sampling algorithms. The sample predictor and denoiser are deep neural networks that we co-train end-to-end over multiple consecutive frames. Our approach is scalable, allowing trade-off between quality and performance, and runs at near real-time rates while achieving significantly better image quality and temporal stability than previous methods.

      • Sample-based Monte Carlo Denoising using a Kernel-Splatting Network Abstract 2019 Gharbi, Li, Aittala, Lehtinen, Durand Denoising has proven to be useful to efficiently generate high-quality Monte Carlo renderings. Traditional pixel-based denoisers exploit summary statistics of a pixel’s sample distributions, which discards much of the samples’ information and limits their denoising power. On the other hand, samplebased techniques tend to be slow and have difficulties handling general transport scenarios. We present the first convolutional network that can learn to denoise Monte Carlo renderings directly from the samples. Learning the mapping between samples and images creates new challenges for the network architecture design: the order of the samples is arbitrary, and they should be treated in a permutation invariant manner. To address these challenges, we develop a novel kernel-predicting architecture that splats individual samples onto nearby pixels. Splatting is a natural solution to situations such as motion blur, depth-of-field and many light transport paths, where it is easier to predict which pixels a sample contributes to, rather than a gather approach that needs to figure out, for each pixel, which samples (or nearby pixels) are relevant. Compared to previous state-of-the-art methods, ours is robust to the severe noise of low-sample count images (e.g. 8 samples per pixel) and yields higher-quality results both visually and numerically. Our approach retains the generality and efficiency of pixel-space methods while enjoying the expressiveness and accuracy of the more complex sample-based approaches.

      • Kernel-Predicting Convolutional Networks for Denoising Monte Carlo Renderings Abstract 2017 Bako, Vogels, Mcwilliams, Meyer, Novák, Harvill, Sen, Derose, Rousselle Regression-based algorithms have shown to be good at denoising Monte Carlo (MC) renderings by leveraging its inexpensive by-products (e.g., feature buffers). However, when using higher-order models to handle complex cases, these techniques often overt to noise in the input. For this reason, supervised learning methods have been proposed that train on a large collection of reference examples, but they use explicit filters that limit their denoising ability. To address these problems, we propose a novel, supervised learning approach that allows the filtering kernel to be more complex and general by leveraging a deep convolutional neural network (CNN) architecture. In one embodiment of our framework, the CNN directly predicts the final denoised pixel value as a highly non-linear combination of the input features. In a second approach, we introduce a novel, kernel-prediction network which uses the CNN to estimate the local weighting kernels used to compute each denoised pixel from its neighbors. We train and evaluate our networks on production data and observe improvements over state-of-theart MC denoisers, showing that our methods generalize well to a variety of scenes. We conclude by analyzing various components of our architecture and identify areas of further research in deep learning for MC denoising.

    • Ray Tracing Gems II Abstract 2021 Adam Marrs, Peter Shirley, Ingo Wald In 2018, real-time ray tracing arrived in consumer GPU hardware and swiftly established itself as a key component of how images would be generated moving forward. Now, three years later, the second iteration of this hardware is available, mainstream game consoles support ray tracing, and cross-platform API standards have been established to drive even wider adoption. Developers and researchers have been busy inventing (and reinventing) algorithms to take advantage of the new possibilities created by these advancements. The “gems” of knowledge discovered during this process are what you will fnd in the pages that follow.

    • Ray Tracing Gems Abstract 2020 Eric Haines, Tomas Akenine-Möller High-Quality and Real-Time Rendering with DXR and Other APIs

    • Continuous Multiple Importance Sampling Abstract 2020 Rex West, Iliyan Georgiev, Adrien Gruson, Toshiya Hachisuka Multiple importance sampling (MIS) is a provably good way to combine a finite set of sampling techniques to reduce variance in Monte Carlo integral estimation. However, there exist integration problems for which a continuum of sampling techniques is available. To handle such cases we establish a continuous MIS (CMIS) formulation as a generalization of MIS to uncountably infinite sets of techniques. Our formulation is equipped with a base estimator that is coupled with a provably optimal balance heuristic and a practical stochastic MIS (SMIS) estimator that makes CMIS accessible to a broad range of problems. To illustrate the effectiveness and utility of our framework, we apply it to three different light transport applications, showing improved performance over the prior state-of-the-art techniques.

    • Understanding the Masking-Shadowing Function in Microfacet-Based BRDFs Abstract 2014 Eric Heitz We provide a new presentation of the masking-shadowing functions (or geometric attenuation factors) in microfacet-based BRDFs and answer some common questions about their applications. Our main motivation is to define a correct (geometrically indicated), physically based masking function for application in microfacet models, as well as the properties that function should exhibit. Indeed, several different masking functions are often presented in the literature and making the right choice is not always obvious. We start by showing that physically based masking functions are constrained by the projected area of the visible microsurface onto the outgoing direction. We use this property to derive the distribution of visible normals from the microsurface, whose normalization factor is the masking function. We then show how the common form of microfacet-based BRDFs emerges from this distribution. As a consequence, the masking function is related to the correct normalization of microfacetbased BRDFs. However, while the correct masking function satisfies these normalization constraints, its explicit form is can only be determined for a given microsurface profile. Our derivation emphasizes that under the assumptions of their respective microsurface profiles, both Smith’s function and the V-cavity masking function are correct. However, we show that the V-cavity microsurface yields results that miss the effect of occlusion, making it analogous to the shading of a normal map instead of a displacement map. This observation explains why the V-cavity model yields incorrect glossy highlights at grazing view angles. We also review other common masking functions, which are not associated with a microsurface profile and thus are not physically based. The insights gained from these observations motivate new research directions in the field of microfacet theory. For instance, we show that masking functions are stretch invariant and we show how this property can be used to derive the masking function for anisotropic microsurfaces in a straightforward way. We also discuss future work such as the incorporation of multiple scattering on the microsurface into BRDF models.

    • Importance Sampling Microfacet-Based BSDFs using the Distribution of Visible Normals -- supplemental material Abstract 2014 E. Heitz, E. d’Eon We present a new approach to microfacet-based BSDF importance sampling. Previously proposed sampling schemes for popular analytic BSDFs typically begin by choosing a microfacet normal at random in a way that is independent of direction of incident light. To sample the full BSDF using these normals requires arbitrarily large sample weights leading to possible fireflies. Additionally, at grazing angles nearly half of the sampled normals face away from the incident ray and must be rejected, making the sampling scheme inefficient. Instead, we show how to use the distribution of visible normals directly to generate samples, where normals are weighted by their projection factor toward the incident direction. In this way, no backfacing normals are sampled and the sample weights contain only the shadowing factor of outgoing rays (and additionally a Fresnel term for conductors). Arbitrarily large sample weights are avoided and variance is reduced. Since the BSDF depends on the microsurface model, we describe our sampling algorithm for two models: the V-cavity and the Smith models. We demonstrate results for both isotropic and anisotropic rough conductors and dielectrics with Beckmann and GGX distributions.

    • Importance Sampling Microfacet-Based BSDFs using the Distribution of Visible Normals Abstract 2014 E. Heitz, E. d’Eon We present a new approach to microfacet-based BSDF importance sampling. Previously proposed sampling schemes for popular analytic BSDFs typically begin by choosing a microfacet normal at random in a way that is independent of direction of incident light. To sample the full BSDF using these normals requires arbitrarily large sample weights leading to possible fireflies. Additionally, at grazing angles nearly half of the sampled normals face away from the incident ray and must be rejected, making the sampling scheme inefficient. Instead, we show how to use the distribution of visible normals directly to generate samples, where normals are weighted by their projection factor toward the incident direction. In this way, no backfacing normals are sampled and the sample weights contain only the shadowing factor of outgoing rays (and additionally a Fresnel term for conductors). Arbitrarily large sample weights are avoided and variance is reduced. Since the BSDF depends on the microsurface model, we describe our sampling algorithm for two models: the V-cavity and the Smith models. We demonstrate results for both isotropic and anisotropic rough conductors and dielectrics with Beckmann and GGX distributions.

    • GPU Ray Marching of Distance Fields Abstract 2012 Lukasz Jaroslaw Tomczak Computer Graphics since its existence has been striving to visualize its representations of surfaces and objects to accurately match their real life counterparts. We investigate the correctness of the ambient occlusion effect produced with the use of a distance to the closest surface metric. This value is obtained from a signed distance function/field. We evaluate the robustness of the method as well as its ease of use. We also test how this applies to a polygon mesh converted into a 3D texture of distance values and included into our scenes. For rendering images we use our GPU implementation of ray marching in the form of sphere tracing and we compare the results to the ones produced by a ray tracing framework.

    • Adaptive Rendering with Non-Local Means Filtering Abstract 2012 Fabrice Rousselle, Claude Knaus, Matthias Zwicker We propose a novel approach for image space adaptive sampling and filtering in Monte Carlo rendering. We use an iterative scheme composed of three steps. First, we adaptively distribute samples in the image plane. Second, we denoise the image using a non-linear filter. Third, we estimate the residual per-pixel error of the filtered rendering, and the error estimate guides the sample distribution in the next iteration. The effectiveness of our approach hinges on the use of a state of the art image denoising technique, which we extend to an adaptive rendering framework. A key idea is to split the Monte Carlo samples into two buffers. This improves denoising performance and facilitates variance and error estimation. Our method relies only on the Monte Carlo samples, allowing us to handle arbitrary light transport and lens effects. In addition, it is robust to high noise levels and complex image content. We compare our approach to a state of the art adaptive rendering technique based on adaptive bandwidth selection and demonstrate substantial improvements in terms of both numerical error and visual quality. Our framework is easy to implement on top of standard Monte Carlo renderers and it incurs little computational overhead.

    • A Survey of Importance Sampling Applications in Unbiased Physically Based Rendering Abstract 2011 Dietger van Antwerpen In this survey, we will discuss the application of importance sampling to the field of unbiased physically based rendering. Unbiased rendering algorithms are based on the Monte Carlo method. In this context, importance sampling techniques are used to reduce the variance of the Monte Carlo estimate. Importance sampling has played an important role in the develop- ment of the field of unbiased rendering and has let to three major rendering algorithms: Path Tracing (PT), Bidirectional Path Tracing (BDPT) and Metropolis Light Transport (MLT). In our discussion, we will focus on these algorithms, discussing them in detail. Furthermore, we will more briefly discuss important extensions to these algorithms, based on importance sampling.

    • Unbiased physically based rendering on the GPU Abstract 2010 Dietger van Antwerpen Since the introduction of General-Purpose GPU computing, there has been a significant increase in ray traversal performance on the GPU. While CPU’s perform reasonably well on coherent rays with similar origin and direction, on current hardware the GPU vastly outperforms the CPU when it comes to incoherent rays, required for unbiased rendering. A number of path tracers have been implemented on the GPU, pulling unbiased physically based rendering to the GPU. However, since the introduction of the path tracing algorithm, the field of unbiased physically based rendering has made significant advances. Notorious improvements are BiDirectional Path Tracing and the Metropolis Light Transport algorithm. As of now little effort has been made to implement these more advanced algorithms on the GPU. The goal of this thesis is to find efficient GPU implementations for unbiased physically based rendering methods. The CUDA framework is used for the GPU implementation. To justify the attempts for moving the sampling algorithm to the GPU, a hybrid architecture is investigated first, implementing the sampling algorithm on the CPU while using the GPU as a ray traversal and intersection co-processor. Results show that today’s CPU’s are not well suited for this architecture, making the CPU memory bandwidth a large bottleneck. We therefore propose three streaming GPU-only rendering algorithms: a Path Tracer (PT), a BiDirectional Path Tracer (BDPT) and an Energy Redistribution Path Tracer (ERPT). The streaming PT uses compaction to remove all terminated paths from the stream, leaving a continuous stream of active samples. New paths are regenerated in large batches at the end of the stream, thereby exploiting primary ray coherence during traversal. A streaming BDPT is obtained by using a recursive reformulation of the Multiple Importance Sampling computations. This requires only storage for a single light and eye vertex in memory at any time during sample evaluation, making the method’s memory-footprint independent of the maximum path length and allowing high SIMT efficiency. We propose an alternative mutation strategy for the ERPT method, further improving the convergence of the algorithm. Using this strategy, a GPU implementation of the ERPT method is presented. By sharing mutation chains between all threads within a GPU warp, efficiency and memory coherence is retained. Finally, the performance of these methods is evaluated and it is shown that the convergence characteristics of the original methods are preserved in our GPU implementations.

    • Importance Sampling for Production Rendering Abstract 2010 Colbert, Premoze, Francois \ Importance sampling provides a practical, production-proven method for integrating diffuse and glossy surface reflections with arbitrary image-based environment or area lighting constructs. Here, functions are evaluated at random points across a domain to produce an estimate of an integral. When using a large number of sample points, the method produces a very accurate result of the integral and provides a strong basis for simulating complex problems such as light transport. Frequently, using the necessary number of samples to reach the exact result is too computationally expensive and fewer samples are evaluated at the cost of visual noise, or variance, within the image. Importance sampling offers a means to reduce the variance by skewing the samples toward regions of the illumination integral that provide the most energy. For instance, the direction of specular reflection or a bright light source within an environment more likely represent the final value of the integral than a random sample. The variance can be reduced more efficiently by combining multiple components of the illumination integral, such as the lighting and material function, to determine where to sample, which is the principle of Multiple Importance Sampling (MIS). As an alternative to the noise in importance sampling, Filtered Importance Sampling (FIS) can provide fast integration, where the lighting environment look-ups are prefiltered to give a smoother result with a significantly smaller number of samples. Importance sampling, MIS and FIS have various practical implications. In thi`s quarter-day course, we cover the necessary background for using Monte Carlo-based techniques for direct lighting and explain how various visual effects companies use these shading methods in their production pipelines.

    • Incremental calculation of weighted mean and variance Abstract 2009 Tony Finch In these notes I explain how to derive formulae for numerically stable calculation of the mean and standard deviation, which are also suitable for incremental on-line calculation. I then generalize these formulae to weighted means and standard deviations. I unpick the difficulties that arise when generalizing further to normalized weights. Finally I show that the exponentially weighted moving average is a special case of the incremental normalized weighted mean formula, and derive a formula for the exponentially weighted moving standard deviation.

    • Bidirectional Path Tracing Abstract 2009 Mikkel Adamsen In this report we present the bidirectional path tracing method. Bidirectional path tracing combines the ideas of shooting and gathering light to create photorealistic images. We discuss, how the well known path tracing algorithm and the light tracing algortihm are subsets of the bidirectional path tracing algorithm. Finally we will show tests that shows how bidirectional path tracing can decrease the noise, in rendered images, in curtain scenes.

    • Ray tracing implicit surfaces on the GPU Abstract 2008 Gábor Liktor In this paper we examine the methods of rendering implicit surfaces with a per-pixel approach. Ray tracing the implicit model directly has several benefits as opposed to processing tessellated meshes, but also invokes new kinds of problems. The main challenge is efficiently finding the first ray-surface intersection point where the surface is not given in an explicit form. Our implementation uses the sphere tracing algorithm to attack this problem and runs on the GPU to achieve high frame rates. We also discuss secondary issues like shading and texturing implicit models.

    • Two Stage Importance Sampling for Direct Lighting Abstract 2006 David Cline, Parris K. Egbert, Justin F. Talbot, David L. Cardon We describe an importance sampling method to generate samples based on the product of a BRDF and an environment map or large light source. The method works by creating a hierarchical partition of the light source based on the BRDF function for each primary (eye) ray in a ray tracer. This partition, along with a summed area table of the light source, form an approximation to the product function that is suitable for importance sampling. The partition is used to guide a sample warping algorithm to transform a uniform distribution of points so that they approximate the product distribution. The technique is unbiased, requires little precomputation, and we demonstrate that it works well for a variety of BRDF types. Further, we present an adaptive method which allocates varying numbers of samples to different image pixels to reduce shadow artifacts.

    • Energy Redistribution Path Tracing Abstract 2005 David Cline, Justin Talbot, Parris Egbert We present Energy Redistribution (ER) sampling as an unbiased method to solve correlated integral problems. ER sampling is a hybrid algorithm that uses Metropolis sampling-like mutation strategies in a standard Monte Carlo integration setting, rather than resorting to an intermediate probability distribution step. In the context of global illumination, we present Energy Redistribution Path Tracing (ERPT). Beginning with an inital set of light samples taken from a path tracer, ERPT uses path mutations to redistribute the energy of the samples over the image plane to reduce variance. The result is a global illumination algorithm that is conceptually simpler than Metropolis Light Transport (MLT) while retaining its most powerful feature, path mutation. We compare images generated with the new technique to standard path tracing and MLT.

    • A Simplified Path Tracing Architecture Abstract 2004 Boulos While the basic path tracing algorithm was developed for simple surfaces and well-defined luminaires, modern scenes contain complex luminaires, surfaces and participating media. This has resulted in add-ons for the path tracing algorithm. We rethink the path tracing architecture in the context of this complexity, and show that an even simpler architecture than classical path tracing works well. This consists of using simple directional sampling without shadow rays, and treating participating media as probabilistic surfaces.

    • Structured Importance Sampling of Environment Maps Abstract 2003 Agarwal, Ramamoorthi, Belongie, Jensen We introduce structured importance sampling, a new technique for efficiently rendering scenes illuminated by distant natural illumination given in an environment map. Our method handles occlusion, high-frequency lighting, and is significantly faster than alternative methods based on Monte Carlo sampling. We achieve this speedup as a result of several ideas. First, we present a new metric for stratifying and sampling an environment map taking into account both the illumination intensity as well as the expected variance due to occlusion within the scene. We then present a novel hierarchical stratification algorithm that uses our metric to automatically stratify the environment map into regular strata. This approach enables a number of rendering optimizations, such as pre-integrating the illumination within each stratum to eliminate noise at the cost of adding bias, and sorting the strata to reduce the number of sample rays. We have rendered several scenes illuminated by natural lighting, and our results indicate that structured importance sampling is better than the best previous Monte Carlo techniques, requiring one to two orders of magnitude fewer samples for the same image quality.

    • Metropolis Light Transport Abstract 2000 Eric Veach, Leonidas J. Guibas We present a new Monte Carlo method for solving the light transport problem, inspired by the Metropolis sampling method in computational physics. To render an image, we generate a sequence of light transport paths by randomly mutating a single current path (e.g. adding a new vertex to the path). Each mutation is accepted or rejected with a carefully chosen probability, to ensure that paths are sampled according to the contribution they make to the ideal image. We then estimate this image by sampling many paths, and recording their locations on the image plane. Our algorithm is unbiased, handles general geometric and scattering models, uses little storage, and can be orders of magnitude more efficient than previous unbiased approaches. It performs especially well on problems that are usually considered difficult, e.g. those involving bright indirect light, small geometric holes, or glossy surfaces. Furthermore, it is competitive with previous unbiased algorithms even for relatively simple scenes. The key advantage of the Metropolis approach is that the path space is explored locally, by favoring mutations that make small changes to the current path. This has several consequences. First, the average cost per sample is small (typically only one or two rays). Second, once an important path is found, the nearby paths are explored as well, thus amortizing the expense of finding such paths over many samples. Third, the mutation set is easily extended. By constructing mutations that preserve certain properties of the path (e.g. which light source is used) while changing others, we can exploit various kinds of coherence in the scene. It is often possible to handle difficult lighting problems efficiently by designing a specialized mutation in this way.

    • Efficient Simulation of Light Transport in Scenes with Participating Media using Photon Maps Abstract 1998 Jensen, Christensen This paper presents a new method for computing global illumination in scenes with participating media. The method is based on bidirectional Monte Carlo ray tracing and uses photon maps to increase efficiency and reduce noise. We remove previous restrictions limiting the photon map method to surfaces by introducing a volume photon map containing photons in participating media. We also derive a new radiance estimate for photons in the volume photon map. The method is fast and simple, but also general enough to handle nonhomogeneous media and anisotropic scattering. It can efficiently simulate effects such as multiple volume scattering, color bleeding between volumes and surfaces, and volume caustics (light reflected from or transmitted through specular surfaces and then scattered by a medium). The photon map is decoupled from the geometric representation of the scene, making the method capable of simulat- ing global illumination in scenes containing complex objects. These objects do not need to be tessellated; they can be instanced, or even represented by an implicit function. Since the method is based on a bidirectional simulation, it automatically adapts to illumination and view. Furthermore, because the use of photon maps reduces noise and aliasing, the method is suitable for rendering of animations.

    • Robust Monte Carlo Methods for Light Transport Simulation Abstract 1997 Eric Veach Light transport algorithms generate realistic images by simulating the emission and scatter- ing of light in an artificial environment. Applications include lighting design, architecture, and computer animation, while related engineering disciplines include neutron transport and radiative heat transfer. The main challenge with these algorithms is the high complexity of the geometric, scattering, and illumination models that are typically used. In this disserta- tion, we develop new Monte Carlo techniques that greatly extend the range of input models for which light transport simulations are practical. Our contributions include new theoreti- cal models, statistical methods, and rendering algorithms. We start by developing a rigorous theoretical basis for bidirectional light transport al- gorithms (those that combine direct and adjoint techniques). First, we propose a linear op- erator formulation that does not depend on any assumptions about the physical validity of the input scene. We show how to obtain mathematically correct results using a variety of bidirectional techniques. Next we derive a different formulation, such that for any physi- cally valid input scene, the transport operators are symmetric. This symmetry is important for both theory and implementations, and is based on a new reciprocity condition that we derive for transmissive materials. Finally, we show how light transport can be formulated as an integral over a space of paths. This framework allows new sampling and integration tech- niques to be applied, such as the Metropolis sampling algorithm. We also use this model to investigate the limitations of unbiased Monte Carlo methods, and to show that certain kinds of paths cannot be sampled. Our statistical contributions include a new technique called multiple importance sam- pling, which can greatly increase the robustness of Monte Carlo integration. It uses more than one sampling technique to evaluate an integral, and then combines these samples in a vii way that is provably close to optimal. This leads to estimators that have low variance for a broad class of integrands. We also describe a new variance reduction technique called efficiency-optimized Russian roulette. Finally, we link these ideas together to obtain new Monte Carlo light transport algo- rithms. Bidirectional path tracing uses a family of different path sampling techniques that generate some path vertices starting from a light source, and some starting from a sensor. We show that when these techniques are combined using multiple importance sampling, a large range of difficult lighting effects can be handled efficiently. The algorithm is unbiased, handles arbitrary geometry and materials, and is relatively simple to implement. The second algorithm we describe is Metropolis light transport, inspired by the Me- tropolis sampling method from computational physics. Paths are generated by following a random walk through path space, such that the probability density of visiting each path is proportional to the contribution it makes to the ideal image. The resulting algorithm is un- biased, uses little storage, handles arbitrary geometry and materials, and can be orders of magnitude more efficient than previous unbiased approaches. It performs especially well on problems that are usually considered difficult, e.g. those involving bright indirect light, small geometric holes, or glossy surfaces. To our knowledge, this is the first application of the Metropolis method to transport problems of any kind.

    • Sphere tracing: a geometric method for the antialiased ray tracing of implicit surfaces Abstract 1996 John C. Hart \ Sphere tracing is a new technique for rendering implicit surfaces that uses geometric distance. Sphere tracing marches along the ray toward its first intersection in steps guaranteed not to penetrate the implicit surface. It is particularly adept at rendering pathological surfaces. Creased and rough implicit surfaces are defined by functions with discontinuous or undefined derivatives. Sphere tracing requires only a bound on the magnitude of the derivative, robustly avoiding problems where the derivative jumps or vanishes. It is an efficient direct visualization system for the design and investigation of new implicit models. Sphere tracing efficiently approximates cone tracing, supporting symbolic-prefiltered antialiasing. Signed distance functions for a variety of primitives and operations are derived.

    • Sphere tracing: a geometric method for the antialiased ray tracing of implicit surfaces Abstract 1996 John C. Hart Sphere tracing is a new technique for ren- dering implicit surfaces that uses geomet- ric distance. Sphere tracing marches along the ray toward its first intersection in steps guaranteed not to penetrate the implicit surface. It is particularly adept at render- ing pathological surfaces. Creased and rough implicit surfaces are defined by functions with discontinuous or undefined derivatives. Sphere tracing requires only a bound on the magnitude of the deriva- tive, robustly avoiding problems where the derivative jumps or vanishes. It is an efficient direct visualization system for the design and investigation of new implicit models. Sphere tracing efficiently approx- imates cone tracing, supporting symbolic- prefiltered antialiasing. Signed distance functions for a variety of primitives and operations are derived.

    • Sphere Tracing: A Geometric Method for the Antialiased Ray Tracing of Implicit Surfaces Abstract 1994 John C. Hart Sphere tracing is a new technique for rendering implicit surfaces using geometric distance. Distance-based models are common in computer-aided geometric design and in the modeling of articulated figures. Given a function returning the distance to an object, sphere tracing marches along the ray toward its first intersection in steps guaranteed not to penetrate the implicit surface. Sphere tracing is particularly adept at rendering pathological surfaces. Creased and rough implicit surfaces are defined by functions with discontinuous or undefined derivatives. Current root finding techniques such as L-G surfaces and interval analysis require periodic evaluation of the derivative, and their behavior is dependent on the behavior of the derivative. Sphere tracing requires only a bound on the magnitude of the derivative, robustly avoiding problems where the derivative jumps or vanishes. This robustness and scope support sphere tracing as an efficient direct visualization system for the design and investigation of new implicit models. Furthermore, sphere tracing efficiently approximates cone tracing, supporting symbolicprefiltered antialiasing. Signed distance functions for a variety of primitives and operations are derived and appear independently as appendices, specifically the natural quadrics and torus, superquadrics, Bezier-based generalized cylinders and offset surfaces, constructive solid geometry, pseudonorm and Gaussian blends, taper, twist and hypertexture.

    • Sphere Tracing: A Geometric Method for the Antialiased Ray Tracing of Implicit Surfaces Abstract 1994 John C. Hart \ Sphere tracing is a new technique for rendering implicit surfaces using geometric distance. Distance-based models are common in computer-aided geometric design and in the modeling of articulated figures. Given a function returning the distance to an object, sphere tracing marches along the ray toward its first intersection in steps guaranteed not to penetrate the implicit surface. Sphere tracing is particularly adept at rendering pathological surfaces. Creased and rough implicit surfaces are defined by functions with discontinuous or undefined derivatives. Current root finding techniques such as L-G surfaces and interval analysis require periodic evaluation of the derivative, and their behavior is dependent on the behavior of the derivative. Sphere tracing requires only a bound on the magnitude of the derivative, robustly avoiding problems where the derivative jumps or vanishes. This robustness and scope support sphere tracing as an efficient direct visualization system for the design and investigation of new implicit models. Furthermore, sphere tracing efficiently approximates cone tracing, supporting symbolic- prefiltered antialiasing. Signed distance functions for a variety of primitives and operations are derived and appear independently as appendices, specifically the natural quadrics and torus, superquadrics, Bezier-based generalized cylinders and offset surfaces, constructive solid geometry, pseudonorm and Gaussian blends, taper, twist and hypertexture.

    • Bi-Directional Path Tracing Abstract 1993 Lafortune, Willems In this paper we present a new Monte Carlo rendering algorithm that seamlessly integrates the ideas of shooting and gathering power to create photorealistic images. The algorithm can be explained as a generalisation of the well-known path tracing algorithm. Test results show that it performs significantly better for typical indoor scenes where indirect lighting is important.

    • Ray Tracing Deterministic 3-D Fractals Abstract 1989 John C. Hart, Daniel J. Sandin, Louis H. Kauffman As shown in 1982, Julia sets of quadratic functions as well as many other deterministic fractals exist in spaces of higher dimensionality than the complex plane. Originally a boundary-tracking algorithm was used to view these structures but required a large amount of storage space to operate. By ray tracing these objects, the storage facilities of a graphics work- station frame buffer are sufficient. A short discussion of a specific set of 3-D deterministic fractals precedes a full description of a ray-tracing algorithm applied to these objects. A comparison with the boundary- tracking method and applications to other 3-D deter- ministic fractals are also included.

    • The Rendering Equation Abstract 1986 James Kajiya We present an integral equation which generallzes a variety of known rendering algorithms. In the course of discussing a monte carlo solution we also present a new form of variance reduction, called Hierarchical sampling and give a number of elaborations shows that it may be an efficient new technique for a wide variety of monte carlo procedures. The resulting renderlng algorithm extends the range of optical phenomena which can be effectively simulated.

  • Summed Area Tables: --

    • Fast Summed-Area Table Generation and its Applications Abstract 2005 Justin Hensley, Thorsten Scheuermann, Greg Coombe, Montek Singh,Anselmo Lastra We introduce a technique to rapidly generate summed-area tables using graphics hardware. Summed area tables, originally introduced by Crow, provide a way to filter arbitrarily large rectangular regions of an image in a constant amount of time. Our algorithm for generating summed-area tables, similar to a technique used in scientific computing called recursive doubling, allows the generation of a summed-area table in O(log n) time. We also describe a technique to mitigate the precision requirements of summed-area tables. The ability to calculate and use summed-area tables at interactive rates enables numerous interesting rendering effects. We present several possible applications. First, the use of summed-area tables allows real-time rendering of interactive, glossy environmental reflections. Second, we present glossy planar reflections with varying blurriness dependent on a reflected object’s distance to the reflector. Third, we show a technique that uses a summed-area table to render glossy transparent objects. The final application demonstrates an interactive depth-of-field effect using summedarea tables.

    • Summed-Area Tables Area Tables And Their Application to Dynamic Glossy Environment Reflections Abstract 2004 Thorsten Scheuermann Rendering dynamic reflections with per-pixel glossiness using dual-paraboloid maps and summed-area tables

    • Optimizing Parallel Reduction in CUDA Abstract 0 Mark Harris Slide set -- No abstract.

  • Shadow Algorithms: Mostly point-light base shadow-maps and enhancements for soft/anti-aliased shadows, and better use of limited resolution.
    • Filtered Shadow Maps: For soft shadows(penumbras) and anti-aliasing.

      • Beyond Hard Shadows: Moment Shadow Maps for Single Scattering, Soft Shadows and Translucent Occluders Abstract 2016 Peters, Münstermann, Wetzstein, Klein Building upon previous works, we transfer the recently proposed moment shadow mapping to three new applications. Like variance shadow maps and convolution shadow maps, moment shadow maps can be filtered directly. Classically, this is used to filter hard shadows but previous works explore other applications. Prefiltered single scattering uses convolution shadow maps to render single scattering in homogenous participating media, variance soft shadow mapping uses variance shadow maps for approximate soft shadows and Fourier opacity mapping uses convolution shadow maps for translucent occluders. We combine these three techniques with moment shadow mapping to arrive at better heuristics with less computational overhead.

      • Moment Shadow Mapping Abstract 2015 Peters, Klein We present moment shadow mapping, a novel technique for fast, filtered hard shadows. Like variance shadow mapping it allows for the application of all kinds of efficient texture filtering and antialiasing to its moment shadow map. However it is designed to provide a substantially higher quality. Moment shadow maps store four moments of the depth within the filter kernel. Using this information, our efficient algorithm computes the sharpest possible lower bound as approximation to the shadow intensity. The choice to compute such a bound using four moments is based upon an automated evaluation of thousands of alternatives and thus known to be optimal. To reduce memory and bandwidth requirements we present an optimized quantization scheme to allow 16-bit quantization of moment shadow maps. Our evaluation demonstrates that moment shadow mapping produces high quality results with a single shadow map sample per fragment using 64 bits per shadow map texel.

      • Exponential Soft Shadow Mapping Abstract 2013 Li Shen, Jieqing Feng, Baoguang Yang In this paper we present an image-based algorithm to render visually plausible anti-aliased soft shadows in real time. Our technique employs a new shadow pre-filtering method based on an extended exponential shadow map- ping theory. The algorithm achieves faithful contact shadows by adopting an optimal approximation to exponential shadow reconstruction function. Benefiting from a novel overflow free summed area table tile grid data structure, numerical stability is guaranteed and error filtering response is avoided. By integrating an adaptive anisotropic filtering method, the proposed algorithm can produce high quality smooth shadows both in large penumbra areas and in high frequency sharp transitions, meanwhile guarantee cheap memory consumption and high performance.

      • Layered Variance Shadow Maps Abstract 2008 Lauritzen,McCool Shadow maps are commonly used in real-time rendering, but they cannot be filtered linearly like standard color, resulting in severe aliasing. Variance shadow maps resolve this problem by representing the depth distribution using moments, which can be linearly filtered. However, variance shadow maps suffer from "light bleeding"" artifacts and require high-precision texture filtering hardware. We introduce layered variance shadow maps, which provide simultaneous solutions to both of these limitations. By partitioning the shadow map depth range into multiple layers, we eliminate all light bleeding between different layers. Using more layers increases the quality of the shadows at the expense of additional storage. Because each of these layers covers a reduced depth range, they can be stored in lower precision than would be required with typical variance shadow maps, enabling their use on a much wider range of graphics hardware. We also describe an iterative optimization algorithm to automatically position layers so as to maximize the utility of each. Our algorithm is easy to implement on current graphics hardware and provides an efficient, scalable solution to the problem of shadow map filtering.

      • Exponential Shadow Maps Abstract 2008 Annen, Mertens, Seidel, Flerackers, Kautz Rendering high-quality shadows in real-time is a challenging problem. Shadow mapping has proved to be an efficient solution, as it scales well for complex scenes. However, it suffers from aliasing problems. Filtering the shadow map alleviates aliasing, but unfortunately, native hardware-accelerated filtering cannot be applied, as the shadow test has to take place beforehand. We introduce a simple approach to shadow map filtering, by approximating the shadow test using an exponential function. This enables us to pre-filter the shadow map, which in turn allows for high quality hardware-accelerated filtering. Compared to previous filtering techniques, our technique is faster, consumes less memory and produces less artifacts.

      • Convolution Shadow Maps Abstract 2007 Annen, Mertens, Bekaert, Seidel, Kautz We present Convolution Shadow Maps, a novel shadow representation that affords efficient arbitrary linear filtering of shadows. Traditional shadow mapping is inherently non-linear w.r.t. the stored depth values, due to the binary shadow test. We linearize the problem by approximating shadow test as a weighted summation of basis terms. We demonstrate the usefulness of this representation, and show that hardware-accelerated anti-aliasing techniques, such as tri-linear filtering, can be applied naturally to Convolution Shadow Maps. Our approach can be implemented very efficiently in current generation graphics hardware, and offers real-time frame rates.

      • Variance Shadow Maps Abstract 2006 William Donnelly, Andrew Lauritzen Shadow maps are a widely used shadowing technique in real time graphics. One major drawback of their use is that they cannot be filtered in the same way as color textures, typically leading to severe aliasing. This paper introduces variance shadow maps, a new real time shadowing algorithm. Instead of storing a single depth value, we store the mean and mean squared of a distribution of depths, from which we can efficiently compute the variance over any filter region. Using the variance, we derive an upper bound on the fraction of a shaded fragment that is occluded. We show that this bound often provides a good approximation to the true occlusion, and can be used as an approximate value for rendering. Our algorithm is simple to implement on current graphics processors and solves the problem of shadow map aliasing with minimal additional storage and computation.

      • Percentage-Closer Soft Shadows Abstract 2005 Randima Fernando One of the fundamental problems in computer graphics is generating accurate soft shadows from area light sources. Soft shadows provide valuable cues about the relationships between objects, becoming sharper as objects contact each other and more blurry (softer) the further they are apart. This sketch presents a new method, called Percentage-Closer Soft Shadows (PCSS), for generating perceptually accurate soft shadows. Based on shadow mapping Williams 1978 and percentage-closer filtering (PCF) Reeves et al. 1987, PCSS has these key characteristics: Generates perceptually accurate soft shadows Uses a single light source sample (one shadow map Requires no pre-processing, post-processing, or additional geometry Seamlessly replaces a traditional shadow map query This combination makes it uniquely suitable for a wide range of applications, from next-generation games to DCC/CAD applications. Because it uses just a single sample and requires no special processing steps, the technique easily replaces existing shadow mapping shader code in an application while producing much more compelling images. The only required change is to replace the typical shadow mapping pixel shader with a PCSS shader.

      • Rendering Antialiased Shadows with Depth Maps (PCF) Abstract 2000 William T. Reeves, David H. Salesin, Robert L. Cook We present a solution to the aliasing problem for shadow algorithms that use depth maps. The solution is based on a new filtering technique called percentage closer filtering. In addition to antialiasing, the improved algorithm provides soft shadow boundaries that resemble penumbrae. We describe the new algorithm in detail, demonstrate the effects of its parameters, and analyze its performance.

    • Shadow Rendering Techniques for Real-Time Applications Abstract 2008 Sean Shypula Shadows, subtle though they may be, provide a number of visual cues as to the layout and orientation of a scene and its light sources that would otherwise be difficult or impossible to convey. Shadows, which play a vital role in computer graphics, have been a highly active area of research from the publication of the first seminal papers in the late 1970's all the way to the current day. This research provides an overview of the techniques that have been developed for rendering shadows in real-time applications. The two most widely used techniques for rendering hard-edged shadows are presented and discussed in detail. Additionally, several approaches to rendering soft-edged and physically based shadows are discussed, and an implementation of several of these techniques is presented in order to compare their performance and behavior in real-world applications

    • Resolution-Matched Shadow Maps Abstract 2007 Aaron E. Lefohn, Shubhabrata Sengupta, John D. Owens This article presents resolution-matched shadow maps (RMSM), a modified adaptive shadow map (ASM) algorithm, that is practical for interactive rendering of dynamic scenes. Adaptive shadow maps, which build a quadtree of shadow samples to match the projected resolution of each shadow texel in eye space, offer a robust solution to projective and perspective aliasing in shadow maps. However, their use for interactive dynamic scenes is plagued by an expensive iterative edge-finding algorithm that takes a highly variable amount of time per frame and is not guaranteed to converge to a correct solution. This article introduces a simplified algorithm that is up to ten times faster than ASMs, has more predictable performance, and delivers more accurate shadows. Our main contribution is the observation that it is more efficient to forgo the iterative refinement analysis in favor of generating all shadow texels requested by the pixels in the eye-space image. The practicality of this approach is based on the insight that, for surfaces continuously visible from the eye, adjacent eye-space pixels map to adjacent shadow texels in quadtree shadow space. This means that the number of contiguous regions of shadow texels (which can be efficiently generated with a rasterizer) is proportional to the number of continuously visible surfaces in the scene. Moreover, these regions can be coalesced to further reduce the number of render passes required to shadow an image. The secondary contribution of this paper is demonstrating the design and use of data-parallel algorithms inseparably mixed with traditional graphics programming to implement a novel interactive rendering algorithm. For the scenes described in this paper, we achieve 60-80 frames per second on static scenes and 20-60 frames per second on dynamic scenes for 512^2 and 1024^2 images with a maximum effective shadow resolution of 32,768^2 texels.

    • Pixel-Correct Shadow Maps with Temporal Reprojection and Shadow Test Confidence Abstract 2007 Daniel Scherze, Stefan Jeschke, Michael Wimmer Shadow mapping suffers from spatial aliasing (visible as blocky shadows) as well as temporal aliasing (visible as flickering). Several methods have already been proposed for reducing such artifacts, but so far none is able to provide satisfying results in real time. This paper extends shadow mapping by reusing information of previously rasterized images, stored efficiently in a so-called history buffer. This buffer is updated in every frame and then used for the shadow calculation. In combination with a special confidence-based method for the history buffer update (based on the current shadow map), temporal and spatial aliasing can be completely removed. The algorithm converges in about 10 to 60 frames and during convergence, shadow borders are sharpened over time. Consequently, in case of real-time frame rates, the temporal shadow adaption is practically imperceptible. The method is simple to implement and is as fast as uniform shadow mapping, incurring only the minor speed hit of the history buffer update. It works together with advanced filtering methods like percentage closer filtering and more advanced shadow mapping techniques like perspective or light space perspective shadow maps

    • Cascaded Shadow Maps Abstract 2007 NVIDIA Shadow maps are a very popular technique to obtain realistic shadows in game engines. When trying to use them for large spaces, shadow maps get harder to tune and will be more prone to exhibit surface acne and aliasing. Cascaded Shadow maps (CSM) is a know approach that helps to fix the aliasing problem by providing higher resolution of the depth texture near the viewer and lower resolution far away. This is done by splitting the camera view frustum and creating a separate depth-map for each partition in an attempt to make the screen error constant.

    • Efficient Physically-Based Shadow Algorithms Abstract 2006 Samuli Laine This research focuses on developing efficient algorithms for computing shadows in computer-generated images. A distinctive feature of the shadow algorithms presented in this thesis is that they produce correct, physically based results, instead of giving approximations whose quality is often hard to ensure or evaluate.

    • Parallel-Split Shadow Maps for Large-scale Virtual Environments Abstract 2006 Fan Zhang, Hanqiu Sun, Leilei Xu, Lee Kit Lun Shadowing effects dramatically enhance the realism of virtual environments by providing useful visual cues. Shadow mapping is an efficient algorithm for real-time shadow rendering, which is extensively adopted in real-time applications by its generality and efficiency. However, shadow mapping usually suffers from the inherent aliasing errors due to the image-based nature. In this paper, we present the Parallel-Split Shadow Maps (PSSMs) scheme, which splits the view frustum into different parts by using the planes parallel to the view plane and then generates multiple smaller shadow maps for the split parts. A fast and robust split strategy based on the analysis of shadow map aliasing has been proposed, which produces a moderate aliasing distribution over the whole depth range. By applying the geometry approximation procedure to each of the split parts instead of the whole scene, the tighter bounding shapes of visible objects enhance the utilization of the shadow map resolution. Hardware-acceleration is used to remove the extra rendering passes when synthesizing the scene-shadows. Our approach is intuitive to implement without using complex data structures, with real-time performance for dynamic and large-scale virtual environments.

    • Shadow in Games Abstract 2005 Xin Li Shadows increase the visual realism, reduce the "floating effect" by consolidating spatial relationships between objects, reveal geometrical information (locations and angles) of the light sources and therefore provide a better 3D cue. Shadows are also important to game plays. For instance, a player object should be able to hide in a dark area by changing its color and the environmental light intensity. Shadows are traditionally handled by using empirical add-on algorithms, including scanline-based, two-pass Weiler-Atherton, shadow volume, two-pass Z-buffer, ray tracing and radiosity. These approaches are able of creating realistic shadows, but often too slow to be practical for real-time applications. However, there are more and more reasons to speculate that, as hardware marches onwards with nowadays speed, those algorithms will be supported by graphic acceleration chips to produce higher and higher quality shadows.

    • SDK White Paper: Soft Shadows Abstract 2004 Nvidia This paper describes how Shader Model 3.0's conditional branching accelerates the computation of soft shadows. Note that you are not generating true soft-shadows, but rather approximating soft shadows by softening the boundaries of traditional hard shadows. The technique described in this paper performs a small amount of computation to estimate if the current pixel is in the approximated soft-shadow region. If the pixel is completely in shadow, or completely out of shadow, the shader exits early. Otherwise, additional work is performed to produce a more accurate estimate of the shadow's intensity at the current pixel. Using conditional branching to perform this additional work only when needed gains considerable performance over techniques that don't use branching.

    • Light Space Perspective Shadow Maps Abstract 2004 Michael Wimmer, Daniel Scherzer, Werner Purgathofer In this paper, we present a new shadow mapping technique that improves upon the quality of perspective and uniform shadow maps. Our technique uses a perspective transform specified in light space which allows treating all lights as directional lights and does not change the direction of the light sources. This gives all the benefits of the perspective mapping but avoids the problems inherent in perspective shadow mapping like singularities in post-perspective space, missed shadow casters etc. Furthermore, we show that both uniform and perspective shadow maps distribute the perspective aliasing error that occurs in shadow mapping unequally over the available depth range. We therefore propose a transform that equalizes this error and gives equally pleasing results for near and far viewing distances. Our method is simple to implement, requires no scene analysis and is therefore as fast as uniform shadow mapping.

    • GPU Gems Chapter 14: Perspective Shadow Maps: Care and Feeding Abstract 2004 Simon Kozlov Shadow generation has always been a big problem in real-time 3D graphics. Determining whether a point is in shadow is not a trivial operation for modern GPUs, particularly because GPUs work in terms of rasterizing polygons instead of ray tracing. Today's shadows should be completely dynamic. Almost every object in the scene should cast and receive shadows, there should be self-shadowing, and every object should have soft shadows. Only two algorithms can satisfy these requirements: shadow volumes (or stencil shadows) and shadow mapping. The difference between the algorithms for shadow volumes and shadow mapping comes down to object space versus image space:

    • Real-Time Soft Shadows Using a Single Light Sample Abstract 2003 Nvidia We present a real-time rendering algorithm that generates soft shadows of dynamic scenes using a single light sample. As a depth-map algorithm it can handle arbitrary shadowed surfaces. The shadow-casting surfaces, however, should satisfy a few geometric properties to prevent artifacts. Our algorithm is based on a bivariate attenuation function, whose result modulates the intensity of a light causing shadows. The first argument specifies the distance of the occluding point to the shadowed point; the second argument measures how deep the shadowed point is inside the shadow. The attenuation function can be implemented using dependent texture accesses; the complete implementation of the algorithm can be accelerated by todays graphics hardware. We outline the implementation, and discuss details of artifact prevention and filtering.

    • Perspective Shadow Maps Abstract 2002 Marc Stamminger, George Drettakis Shadow maps are probably the most widely used means for the generation of shadows, despite their well known aliasing problems. In this paper we introduce perspective shadow maps, which are generated in normalized device coordinate space, i.e., after perspective transformation. This results in important reduction of shadow map aliasing with almost no overhead. We correctly treat light source transformations and show how to include all objects which cast shadows in the transformed space. Perspective shadow maps can directly replace standard shadow maps for interactive hardware accelerated rendering as well as in high-quality, offline renderers.

    • Adaptive Shadow Maps Abstract 2001 Randima Fernando, Sebastian Fernandez, Kavita Bala, Donald P. Greenberg ASMs are based on the observation that a high-quality shadow map need not be of uniform high resolution; only regions that contain shadow boundaries need to be sampled densely. In those regions, the resolution of the shadow map should be at least as high as the corresponding region in the eye view to avoid aliasing artifacts. An ASM hierarchically subdivides an ordinary shadow map, providing higher resolutions in visually important regions. Like a conventional shadow map, an ASM takes as input a set of transformed eye view points and allows shadow queries on this set, returning true if a particular point is lit and false otherwise. In software systems, ASMs can seamlessly replace conventional shadow maps.

    • A Survey of Shadow Algorithms Abstract 1997 Andrew Woo, Pierre Poulin, Alain Fournier Shadows are essential to realistic and visually appealing images, but they are difficult to compute in most display environments. This survey will characterize the various types of shadows, describe most existing shadow algorithms, and for each one discuss their complexities, their advantages and their shortcomings. The types of shadows examined are hard shadows, soft shadows, shadows of transparent objects, and shadows for complex modeling primitives. For each type, we examine shadow algorithms within various rendering techniques. The goal of the survey is to provide readers with enough background and insight on the various methods to allow them to choose the algorithm best suited to their needs. It is also hoped that our analysis will help identify the areas that need more research, and point to possible solutions.

  • Spherical Harmonics: A Polynomial basis for low frequency spherical functions used to represent diffuse illumination.

    • Stupid Spherical Harmonics (SH) Tricks Abstract 2008 Peter-Pike Sloan This paper provides a brief overview of spherical harmonics (SH) and discusses several ways they can be used in interactive graphics and problems that might arise. In particular it focuses on the following issues: How to evaluate lighting models efficiently using SH, what “ringing” is and what you can do about it, efficient evaluation of SH products and where they might be used.

    • Spherical Harmonic Lighting: The Gritty Details Abstract 2003 Robin Green Spherical Harmonic lighting (SH lighting) is a technique for calculating the lighting on 3D models from area light sources that allows us to capture, relight and display global illumination style images in real time. It was introduced in a paper at Siggraph 2002 by Sloan, Kautz and Snyder as a technique for ultra realistic lighting of models. Looking a little closer at it's derivation we can show that it is in fact a toolbox of interrelated techniques that the games community can use to good effect.

    • An Efficient Representation for Irradiance Environment Maps Abstract 2000 Ramamoorthi, Hanrahan We consider the rendering of diffuse objects under distant illumination, as specified by an environment map. Using an analytic expression for the irradiance in terms of spherical harmonic coefficients of the lighting, we show that one needs to compute and use only 9 coefficients, corresponding to the lowest-frequency modes of the illumination, in order to achieve average errors of only 1%. In other words, the irradiance is insensitive to high frequencies in the lighting, and is well approximated using only 9 parameters. In fact, we show that the irradiance can be procedurally represented simply as a quadratic polynomial in the cartesian components of the surface normal, and give explicit formulae. These observations lead to a simple and efficient procedural rendering algorithm amenable to hardware implementation, a prefiltering method up to three orders of magnitude faster than previous techniques, and new representations for lighting design and image-based rendering.

  • Parallax/bump/displacement mapping: Using texture maps for simulating surface detail on smooth polygons.

    • Linear Efficient Antialiased Displacement and Reflectance Mapping Abstract 2013 Jonathan Dupuy, Eric Heitz, Jean-Claude, Pierre Poulin, Fabrice Neyret, Victor Ostromoukhov We present Linear Efficient Antialiased Displacement and Reflectance (LEADR) mapping, a reflectance filtering technique for displacement mapped surfaces. Similarly to LEAN mapping, it employs two mipmapped texture maps, which store the first two moments of the displacement gradients. During rendering, the projection of this data over a pixel is used to compute a noncentered anisotropic Beckmann distribution using only simple, linear filtering operations. The distribution is then injected in a new, physically based, rough surface microfacet BRDF model, that includes masking and shadowing effects for both diffuse and specular reflection under directional, point, and environment lighting. Furthermore, our method is compatible with animation and deformation, making it extremely general and flexible. Combined with an adaptive meshing scheme, LEADR mapping provides the very first seamless and hardware-accelerated multi-resolution representation for surfaces. In order to demonstrate its effectiveness, we render highly detailed production models in real time on a commodity GPU, with quality matching supersampled ground-truth images.

    • Quadtree Displacement Mapping with Height Blending Abstract 2009 Michal Drobot GDC09 Slide set: 119 slides

    • GPU Gems 3 - Chapter 18: Relaxed Cone Stepping for Relief Mapping Abstract 2009 Fabio Policarpo, Manuel M. Oliveira The presence of geometric details on object surfaces dramatically changes the way light interacts with these surfaces. Although synthesizing realistic pictures requires simulating this interaction as faithfully as possible, explicitly modeling all the small details tends to be impractical. To address these issues, an image-based technique called relief mapping has recently been introduced for adding per-fragment details onto arbitrary polygonal models (Policarpo et al. 2005). The technique has been further extended to render correct silhouettes (Oliveira and Policarpo 2005) and to handle non-height-field surface details (Policarpo and Oliveira 2006). In all its variations, the ray-height-field intersection is performed using a binary search, which refines the result produced by some linear search procedure. While the binary search converges very fast, the linear search (required to avoid missing large structures) is prone to aliasing, by possibly missing some thin structures, as is evident in Figure 18-1a. Several space-leaping techniques have since been proposed to accelerate the ray-height-field intersection and to minimize the occurrence of aliasing (Donnelly 2005, Dummer 2006, Baboud and Decoret 2006). Cone step mapping (CSM) (Dummer 2006) provides a clever solution to accelerate the intersection calculation for the average case and avoids skipping height-field structures by using some precomputed data (a cone map).

    • LEAN Mapping Abstract 2008 Marc Olano, Dan Baker We introduce Linear Efficient Antialiased Normal (LEAN) Map- ping, a method for real-time filtering of specular highlights in bump and normal maps. The method evaluates bumps as part of a shading computation in the tangent space of the polygonal surface rather than in the tangent space of the individual bumps. By operat- ing in a common tangent space, we are able to store information on the distribution of bump normals in a linearly-filterable form compatible with standard MIP and anisotropic filtering hardware. The necessary textures can be computed in a preprocess or generated in real-time on the GPU for time-varying normal maps. The method effectively captures the bloom in highlight shape as bumps become too small to see, and will even transform bump ridges into anisotropic shading. Unlike even more expensive methods, several layers can be combined cheaply during surface rendering, with perpixel blending. Though the method is based on a modified Ward shading model, we show how to map between its parameters and those of a standard Blinn-Phong model for compatibility with existing art assets and pipelines, and demonstrate that both models produce equivalent results at the largest MIP levels.

    • Pyramidal Displacement Mapping: A GPU based Artifacts-Free Ray Tracing through an Image Pyramid Abstract 2007 Oh, Ki, Lee Displacement mapping enables us to details to polygonal meshes. We present a real-time artifacts-free inverse displacement mapping method using per-pixel ray tracing through an image pyramid on the GPU. In each pixel, we make a ray and trace the ray through a displacement map to find an intersection. To skip empty-regions safely, we use the quad-tree image pyramid of a displacement map in top-down order. For magnification we estimate an intersection between a ray and a bi-linearly interpolated displacement. For minification we perform a mipmap-like prefiltering to improve quality of result images and rendering performance. Results show that our method produces correct images even at steep grazing angles. Rendering speed of test scenes were over hundreds of frames per second and less influence to the resolution of the map. Our method is simple enough to add to existing virtual reality systems easily.

    • Accurate Per-Pixel Displacement Mapping using a Pyramid Structure Abstract 2007 Hyunwoo Ki, Kyoungsu O We present a per-pixel displacement mapping method that provides high accuracy as well as real-time performance. This arises from the observation that we can safely skip empty regions by moving a ray to the maximum height value. We store this bounding information in the image pyramid of a heighfield texture. In our method, a ray along view direction advances hierarchically via this pyramid structure. This method, called pyramidal displacement mapping, guarantees finding the correct intersections on any heightfield and viewing conditions. This article explains implementation details with more accessible illustrations and descriptions for 3D application developers. Additionally, we introduce a new LOD technique to improve rendering performance and quality.

    • Practical Parallax Occlusion Mapping For Highly Detailed Surface Rendering Abstract 2006 Natalya Tatarchuk A set of 70 slides from a Siggraph'2006 presentation.

    • Practical Parallax Occlusion Mapping For Highly Detailed Surface Rendering Abstract 2006 Natalya Tatarchuk 3D Application Research Group ATI Research A 69 slide presentation about parallax maps.

    • Dynamic Parallax Occlusion Mapping with Approximate Soft Shadows Abstract 2006 Natalya Tatarchuk This paper presents a per-pixel ray tracing algorithm with dynamic lighting of surfaces in real-time on the GPU. First, we propose a method for increased precision of the critical rayheight field intersection and adaptive height field sampling. We achieve higher quality results than the existing inverse displacement mapping algorithms. Second, soft shadows are computed by estimating light visibility for the displaced surfaces. Third, we describe an adaptive level-of-detail system which uses the information supplied by the graphics hardware during rendering to automatically manage shader complexity. This LOD scheme maintains smooth transitions between the full displacement computation and a simplified representation at a lower level of detail without visual artifacts. The algorithm performs well for animated objects and supports dynamic rendering of height fields for a variety of interesting displacement effects. The presented method is scalable for a range of consumer grade GPU products. It exhibits a low memory footprint and can be easily integrated into existing art pipelines for games and effects rendering.

    • Displacement Mapping on the GPU - State of the Art Abstract 2006 Szirmay-Kalos, Umenhoffer This paper reviews the latest developments of displacement mapping algorithms implemented on the vertex, geometry, and fragment shaders of graphics cards. Displacement mapping algorithms are classified as per-vertex and per-pixel methods. Per-pixel approaches are further categorized as safe algorithms that aim at correct solutions in all cases, to unsafe techniques that may fail in extreme cases but are usually much faster than safe algorithms, and to combined methods that exploit the robustness of safe and the speed of unsafe techniques. We discuss the possible roles of vertex, geometry, and fragment shaders to implement these algorithms. Then the particular GPU based bump, parallax, relief, sphere, horizon mapping, cone stepping, local ray tracing, pyramidal and view-dependent displacement mapping methods, as well as their numerous variations are reviewed providing also implementation details of the shader programs. We present these methods using uniform notations and also point out when different authors called similar concepts differently. In addition to basic displacement mapping, self-shadowing and silhouette processing are also reviewed. Based on our experiences gained having re-implemented these methods, their performance and quality are compared, and the advantages and disadvantages are fairly presented.

    • Cone Step Mapping: An Iterative Ray-Heightfield Intersection Algorithm Abstract 2006 Jonathan Dummer This paper presents Cone Step Mapping (CSM), a new approach to the Ray-Heightfield Intersection problem. CSM uses preprocessed information about the heightfield to dynamically adjust step sizes along the ray when finding the first intersection. It is an iterative method that is unconditionally stable, without the need to tune algorithm parameters. This method is suitable for real-time rendering and has been implemented using the OpenGL Shading Language (GLSL) on a GeForce 6600.

    • Practical Parallax Occlusion Mapping with Approximate Soft Shadows for Detailed Surface Rendering Abstract 2006 This chapter presents a per-pixel ray tracing algorithm with dynamic lighting of surfaces in real-time on the GPU. First, we will describe a method for increased precision of the critical ray-height field intersection and adaptive height field sampling. We achieve higher quality results than the existing inverse displacement mapping algorithms. Second, soft shadows are computed by estimating light visibility for the displaced surfaces. Third, we describe an adaptive level-of-detail system which uses the information supplied by the graphics hardware during rendering to automatically manage shader complexity. This LOD scheme maintains smooth transitions between the full displacement computation and a simplified representation at a lower level of detail without visual artifacts. Finally, algorithm limitations will be discussed along with the practical considerations for integration into game pipelines. Specific attention will be given to the art asset authoring, providing guidelines, tips and concerns. The algorithm performs well for animated objects and supports dynamic rendering of height fields for a variety of interesting displacement effects. The presented method is scalable for a range of consumer grade GPU products. It exhibits a low memory footprint and can be easily integrated into existing art pipelines for games and effects rendering.

    • Parallax Mapping with Offset Limiting: A Per-Pixel Approximation of Uneven Surfaces Abstract 2004 Terry Welsh This paper describes parallax mapping and an enhancement that makes it more practical for general use. Parallax mapping is a method for approximating the correct appearance of uneven surfaces by modifying the texture coordinate for each pixel. Parallax is exhibited when areas of a surface appear to move relative to one another as the view position changes. This can be observed on any surface that is not flat. Parallax can be simulated well by constructing a complete geometric model of a surface, but it can be computationally expensive to draw all the necessary polygons. The method presented here requires no extra polygons and approximates surface parallax using surface height data.

    • View-Dependent Displacement Mapping Abstract 2003 Lifeng Wang, Xi Wang, Xin Tong, Stephen Lin, Shimin Hu, Baining Guo, Heung-Yeung Shum Significant visual effects arise from surface mesostructure, such as fine-scale shadowing, occlusion and silhouettes. To efficiently render its detailed appearance, we introduce a technique called view-dependent displacement mapping VDM) that models surface displacements along the viewing direction. Unlike traditional displacement mapping, VDM allows for efficient rendering of self-shadows, occlusions and silhouettes without increasing the complexity of the underlying surface mesh. VDM is based on per-pixel processing, and with hardware acceleration it can render mesostructure with rich visual appearance in real time.

    • Synthetic Object Rendering Abstract 1998 Paul Debevec We present a method that uses measured scene radiance and global illumination in order to add new objects to light-based models with correct lighting. The method uses a high dynamic range imagebased model of the scene, rather than synthetic light sources, to illuminate the newobjects. To compute the illumination, the scene is considered as three components: the distant scene, the local scene, and the synthetic objects. The distant scene is assumed to be photometrically unaffected by the objects, obviating the need for reflectance model information. The local scene is endowed with estimated reflectance model information so that it can catch shadows and receive reflected light from the new objects. Renderings are created with a standard global illumination method by simulating the interaction of light amongst the three components. A differential rendering technique allows for good results to be obtained when only an estimate of the local scene reflectance properties is known. We apply the general method to the problem of rendering synthetic objects into real scenes. The light-based model is constructed from an approximate geometric model of the scene and by using a light probe to measure the incident illumination at the location of the synthetic objects. The global illumination solution is then composited into a photograph of the scene using the differential rendering technique. We conclude by discussing the relevance of the technique to recovering surface reflectance properties in uncontrolled lighting situations. Applications of the method include visual effects, interior design, and architectural visualization.

    • Shade Trees Abstract 1984 Robert L. Cook Shading is an important part of computer imagery, but shaders have been based on fixed models to which all surfaces must conform. As computer imagery becomes more sophisticated, surfaces have more complex shading characteristics and thus require a less rigid shading model. This paper presents a flexible tree-structured shading model that can represent a wide range of shading characteristics. The model provides an easy means for specifying complex shading characteristics. It is also efficient because it can tailor the shading calculations to each type of surface.

  • new: New papers, not yet categorized.
    • Empty