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Sr. Research Scientist

Associate Professor of
Computer Science


E-Mail Address:
chris.wyman (at) acm.org
chris.wyman (at) ieee.org

Connect Via:
LinkedIn

Chris Wyman's Web Page

(I have left the University as of July 1, 2014. For updates, visit my personal page or my NVIDIA page.)

This material presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therin are retained by the authors or other copyright holders. In particular, please refer to the ACM and IEEE Copyright Policies.
Research Funding From: ARL, DARPA, NIH, RDECOM, Rockwell Collins
In-Kind Donations From: AMD, NVIDIA, S3
Other Resources: Aim@Shape, Keenan Crane, Light Romance, Paul Debevec, Stanford.


Hang Dou, Yajie Yan, Ethan Kerzner, Zeng Dai, and Chris Wyman. "Adaptive Depth Bias for Shadow Maps." ACM Symposium on Interactive 3D Graphics and Games. (March 2014)

Files: [ Preprint (17 MB) ]

Abstract:

Shadow aliasing due to limited storage precision has been plaguing discrete shadowing algorithms for decades. We present a simple method to eliminate false self-shadowing through adaptive depth bias. Unlike existing methods which simply set the weight of the bias based on surface slope or utilize the second nearest surface, we evaluate the bound of bias for each fragment and compute the optimal bias within the bound. Our method introduces small overhead, preserves more shadow details than widely used constant bias and slope scale bias and works for common 2D shadow maps as well as 3D binary shadow volumes.



Chris Wyman and Zeng Dai. "Imperfect Voxelized Shadow Volumes." ACM/EG Symposium on High Performance Graphics. (July 2013)

Files: [ Preprint (7.6 MB) ] [ Video (58 MB) ]
High Resolution Figures: [ Fig 1, Fig 2, Fig 4, Fig 6, Fig 7, Fig 8, Fig 10, Fig 11, Fig 12, Fig 13 ]


Preliminary version to appear as a talk at SIGGRAPH 2013: [ Extended Abstract (2.1 MB) ]

Abstract:

Voxelized shadow volumes provide a discretized view-dependent representation of shadow volumes, but are limited to point or directional lights. We extend them to allow dynamic volumetric visibility from area light sources using imperfect shadow volumes. We show a coarser visibility sampling suffices for area lights. Combining this coarser resolution with a parallel shadow volume construction enables interactive rendering of dynamic volumetric shadows from area lights in homogeneous single-scattering media, at under 4x the cost of hard volumetric shadows.



Chris Wyman, Peter-Pike Sloan, and Peter Shirley. "Simple Analytic Approximations to the CIE XYZ Color Matching Functions." Journal of Computer Graphics Techniques 2(2). (July 2013)

Files: [ Paper (1.3 MB) ]

Abstract:

We provide three analytical fits to the CIE x, y, and z color matching curves, commonly used in predictive and spectral renderers as an intermediate between light spectra and RGB colors. Any can replace the standard CIE curves, which come tabulated. Using tabulated curves can introduce typos, encourage crude simplifying approximations, or add opportunities to download curves from sources featuring inconsistent or incorrect data. Our analytic fits are simple to implement and verify. While fitting introduces error, our fits introduce less than the variance between the human subject data aggregated into the CIE standard. Additionally, common rendering approximations, such as coarse spectral binning, introduce significantly more error. We provide simple, analytic fits in Equations 2 and 3, but even our more accurate fit in Equation 4 only requires 10 lines of code.



Hang Dou, Christian Bauer, Chris Wyman, and Reinhard Beichel. "Efficient Rendering of Anatomical Tree Structures Using Geometry Proxy." IEEE International Symposium on Biomedical Imaging. (April 2013)

Files: [ Paper (2.5 MB) ]

Abstract:

Rendering tubular structures efficiently is crucial for studying anatomical tree-like structures, such as vessels and airways. Most existing methods are based on surface reconstruction, resulting in complex meshes, which slows the rendering performance as the tree complexity increases. In this paper, we present an approach to render tubular tree structures using geometry proxy. We generate low complexity proxy meshes on the fly and shade the meshes as tubular objects consisting of truncated cones and spheres. Unlike surface reconstruction, our method requires no precomputation and produces appealing imagery with faster rendering performance.



Chris Wyman. "Voxelized Shadow Volumes." ACM/EG Symposium on High Performance Graphics, 33-40. (August 2011)

Files: [ Paper (7.8 MB) ] [ Local PDF ] [ Video (43 MB) ] [ Slides (5 MB) ]
High Resolution Figures: [ Fig 1, Fig 6, Fig 10, Fig 13, Fig 14, Fig 15, Extra 1, Extra 2 ]
Demo: [ README, Windows Executable & Code (64 MB), More Scenes (154 MB) ]


Preliminary version presented as a sketch at SIGGRAPH Asia 2010: [ Extended Abstract (1.4 MB) ]

Abstract:

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, simultaneous 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.



Paul Rosen, Voicu Popescu, Kyle Hayward, and Chris Wyman. "Non-Pinhole Approximations for Interactive Rendering." IEEE Computer Graphics and Applications 31(6), 68-83. (Nov/Dec 2011)

Files: [ Preprint (1 MB) ] [ Video (96 MB) ]

Abstract:

Depth images have been used to approximate scene geometry in a variety of interactive 3-D graphics applications. In previous work, images were constructed using orthographic or perspective projection which limits approximation quality to what is visible along a single view direction or from a single viewpoint. This paper shows that images constructed with non-pinhole cameras improve approximation quality at little additional cost provided that the non-pinhole camera offers fast projection. For such a camera, the fundamental operation of ray depth-image intersection proceeds efficiently by searching along the one-dimensional projection of the ray onto the image. In the context of two-camera configurations, our work extends epipolar geometry constraints to non-pinholes. We demonstrate the advantages of non-pinhole depth images in the context of reflections, refractions, relief texture mapping, and ambient occlusion.



Thomas Hansen, Juan Pablo Hourcade, Alberto Segre, Chris Hlady, Philip Polgreen, and Chris Wyman. "Interactive Visualization of Hopsital Contact Network Data on Multi-touch Displays." Proceedings of the 2010 Mexican Workshop on Human Computer Interaction, 15-22. (November 2010)

Files: [ PDF (400 kB) ]

Abstract:

Hospital infections cost the lives of more than 100,000 people in the United States every year. Understanding how infections spread in hospitals is critical to reducing this problem. To help in this endeavor, we developed an interactive, multi-touch hospital contact-network visualization and disease spread simulation. The system visually animates healthcare workers as they move through a hospital building based on a very large, real world dataset of electronic medical record login sessions. Users control the visualization and infection spread simulation by direct manipulation using multi-touch interactions and on screen controls. Through our implementation, we explore how infection control experts might use visual analytics and multi-touch user interfaces to explore such large datasets. We share the feedback gathered from three domain experts, who tested our application and suggested additional use cases for similar systems or potential datasets.



Greg Nichols, Rajeev Penmatsa, and Chris Wyman. "Interactive, Multiresolution Image-Space Rendering for Dynamic Area Lighting." Computer Graphics Forum 29(4), 1279-1288. (June 2010)

Files: [ PDF (7.3 MB) ] [ Video (96 MB) ] [ Tech Report (4.2 MB) ]

Preliminary version presented at ACM I3D 2010: [ poster PDF (530kB) ]

Abstract:

Area lights add tremendous realism, but rendering them interactively proves challenging. Integrating visibility is costly, even with current shadowing techniques, and existing methods frequently ignore illumination variations at unoccluded points due to changing radiance over the light's surface. We extend recent image-space work that reduces costs by gathering illumination in a multiresolution fashion, rendering varying frequencies at corresponding resolutions. To compute visibility, we eschew shadow maps and inestead rely on a course screen-space voxelization, which effectively provides a cheap layered depth image for binary visibility queries via ray marching. Our technique requires no precomputation and runs at interactive rates, allowing scenes with large area lights, including dynamic content such as video screens.



Voicu Popescu, Paul Rosen, Laura Arns, Xavier Tricoche, Chris Wyman, and Christoph Hoffmann. "The General Pinhole Camera: Effective and Efficient Non-Uniform Sampling for Visualization." IEEE Transactions on Visualization and Computer Graphics, 16(5), 777-790. (September/October 2010)

Files: [ Preprint ]

Abstract:

We introduce the general pinhole camera (GPC), defined by a center of projection (i.e. the pinhole), an image plane, and a set of sampling locations in the image plane. We demonstrate the advantages of the GPC in the contexts of remote visualization, of focus plus context visualization, and of extreme antialiasing, which all greatly benefit from the sampling flexibility afforded by the GPC. For remote visualization we describe a GPC that allows zooming-in at the client without the need for transferring additional data from the server. For focus plus context visualization we describe a GPC with multiple regions of interest that are magnified while preserving sampling rate continuity to the surrounding areas. For extreme antialiasing we describe a GPC variant that allows supersampling locally with a very high number of color samples per output pixel (e.g. 1024x), supersampling levels that are out of reach for conventional approaches that supersample the entire image. The GPC supports many types of data, including surface geometry, volumetric, and image data, as well as many rendering modes, including highly view-dependent effects such as volume rendering. Finally GPC visualization is efficientGPC images are rendered and resampled with the help of graphics hardware at interactive rates.



Greg Nichols and Chris Wyman. "Interactive Indirect Illumination Using Adaptive Multiresolution Splatting." IEEE Transactions on Visualization and Computer Graphics 16(5), 729-741. (September/October 2010)

Files: [ Preprint ]

Extends our ACM I3D 2009 paper: "Multiresolution Splatting for Indirect Illumination"

Abstract:

Global illumination provides a visual richness not achievable with the direct illumination models used by most interactive applications. To generate global effects, numerous approximations attempt to reduce global illumination costs to levels feasible in interactive contexts. One such approximation, reflective shadow maps, samples a shadow map to identify secondary light sources whose contributions are splatted into eye-space. This splatting introduces significant overdraw that is usually reduced by artificially shrinking each splat's radius of influence. This paper introduces a new, multi-resolution approach for interactively splatting indirect illumination. Instead of reducing GPU fill rate by reducing splat size, we reduce fill rate by rendering splats into a multi-resolution buffer. This takes advantage of the low-frequency nature of diffuse and glossy indirect lighting, allowing rendering of indirect contributions at low resolution where lighting changes slowly and at high resolution near discontinuities. Because this multi-resolution rendering occurs on a per-splat basis, we can significantly reduce fill rate without arbitrarily clipping splat contributions below a given threshold---those regions simply are rendered at a coarse resolution.



Chris Wyman, Greg Nichols, and Jeremy Shopf. "Fast, Stencil-Based Multiresolution Splatting for Indirect Illumination." GPU Pro: Advanced Rendering Techniques, Chapter 4.1, 199-214. Edited by Wolfgang Engel. AK Peters, 2010. ISBN: 978-1-56881-472-8.

(University of Iowa Library, Call No: T385 .G6885 2010)
(OCLC Accession No: 473119083)

Demo: [ Visual Studio 2008 Project (52 MB) ]



Greg Nichols, Jeremy Shopf, and Chris Wyman. "Hierarchical Image-Space Radiosity for Interactive Global Illumination." Computer Graphics Forum 28(4), 1141-1149. (June 2009)

Files: [ Paper (1.4 MB) ] [ Video (36 MB) ] [ Slides (4 MB) ]

Abstract:

We introduce image-space radiosity and a hierarchical variant as a method for interactively approximating diffuse indirect illumination in fully dynamic scenes. As oft observed, diffuse indirect illumination contains mainly low-frequency details that do not require independent computations at every pixel. Prior work leverages this to reduce computation costs by clustering and caching samples in world or object space. This often involves scene preprocessing, complex data structures for caching, or wasted computations outside the view frustum. We instead propose clustering computations in image space, allowing the use of cheap hardware mipmapping and implicit quadtrees to allow coarser illumination computations. We build on a recently introduced multiresolution splatting technique combined with an image-space lightcut algorithm to intelligently choose virtual point lights for an interactive, one-bounce instant radiosity solution. Intelligently selecting point lights from our reflective shadow map enables temporally coherent illumination similar to results using more than 4096 regularly-sampled VPLs.



Greg Nichols and Chris Wyman. "Multiresolution Splatting for Indirect Illumination." ACM Symposium on Interactive 3D Graphics and Games, 83-90. (February 2009)

Files: [ Paper PDF (10 MB) ] [ Local PDF ] [ Slides (20 MB) ] [ Video (34 MB) ]
Demo: [ Windows Executable & Code (55 MB), README]

Abstract:

Global illumination provides a visual richness not achievable with the direct illumination models used by most interactive applications. To generate global effects, numerous approximations attempt to reduce global illumination costs to levels feasible in interactive contexts. One such approximation, reflective shadow maps, samples a shadow map to identify secondary light sources whose contributions are splatted into eye-space. This splatting introduces significant overdraw that is usually reduced by artificially shrinking each splat's radius of influence. This paper introduces a new, multi-resolution approach for interactively splatting indirect illumination. Instead of reducing GPU fill rate by reducing splat size, we reduce fill rate by rendering splats into a multi-resolution buffer. This takes advantage of the low-frequency nature of diffuse and glossy indirect lighting, allowing rendering of indirect contributions at low resolution where lighting changes slowly and at high resolution near discontinuities. Because this multi-resolution rendering occurs on a per-splat basis, we can significantly reduce fill rate without arbitrarily clipping splat contributions below a given threshold---those regions simply are rendered at a coarse resolution.



Chris Wyman and Greg Nichols. "Adaptive Caustic Maps Using Deferred Shading." Computer Graphics Forum 28(2), 309-318. (April 2009)

Files: [ Paper (2 MB) ] [ Slides (2 MB) ] [ Videos (1), (2), (3), (4), (5) (20-40 MB) ]
Demo: [ Windows Executable & Code (67 MB), README]

Abstract:

Caustic maps provide an interactive image-space method to render caustics, the focusing of light via reflection and refraction. Unfortunately, caustic mapping suffers problems similar to shadow mapping: aliasing from poor sampling and map projection as well as temporal incoherency from frame-to-frame sampling variations. To reduce these problems, researchers have suggested methods ranging from caustic blurring to building a multiresolution caustic map. Yet these all require a fixed photon sampling, precluding the use of importance-based photon densities. This paper introduces adaptive caustic maps, which allow dynamic photon sampling using a hierarchical renderer enabled by a new deferred shading technique. Alone, deferred shading speeds rendering of refractive geometry up to 25% and with adaptive sampling speeds caustic rendering up to 200%. These benefits are particularly noticable for complex geometry or using millions of photons. While developed for a GPU rasterizer, adaptive caustic map creation can be performed by any renderer that individually traces photons, e.g., a GPU ray tracer.



Chris Wyman and Shaun Ramsey. "A Hybrid Method for Interactive Shadows in Homogeneous Media." ShaderX7: Advanced Rendering Techniques, 331-344. Edited by Wolfgang Engel. Charles River Media, 2009. ISBN: 1-58450-598-2.

(University of Iowa Library, Call No: QA76.76.C672 S487 2009)
(OCLC Accession No: 234444097)



Chris Wyman and Shaun Ramsey. "Interactive Volumetric Shadows in Participating Media with Single-Scattering." IEEE Symposium on Interactive Ray Tracing, 87-92. (August 2008)

Files: [ Paper (22 MB) ] [ Slides (963 kB) ] [ Videos (1), (2), (3) (13-25 MB) ]
Files: [ Appendix A ] [ Appendix B ] [ GLSL Shader from Appendix A ]
Demo: [ Windows Executable & Code (31.6 MB), README ]

Abstract:

Scattering effects arising from participating media, such as smoke, haze, and fog, dramatically add to perceived realism in renderings. As shadows affect illumination throughout an environment, they significantly diminish scattering effects in umbral regions. Unlike surface shadowing, accurate volumetric shadows require simultaneously integrating illumination, scattering, and attenuation throughout the volume, which proves challenging for interactive applications. We propose a method for rendering volumetric shadows in homogeneous single scattering media that combines shadow volume and ray marching techniques, which eliminates performance deficiencies inherent in both. We extend this approach to interactively render shadows from textured lights and show results under two scattering models.



Chris Wyman. "Hierarchical Caustic Maps." ACM Symposium on Interactive 3D Graphics and Games, 163-171. (February 2008)

Files: [ Paper PDF (19 MB) ] [ Local PDF ]
Files: [ Talk (2.4 MB) ] [ Videos (1), (2), (3), (4) (30-40 MB)]
Code: [ A limited implementation is in the demo for "Adaptive Caustic Maps" ]

Abstract:

Interactive applications typically rely on local models for lighting, occasionally augmented by GPU-friendly methods for approximating global illumination. Caustic mapping approximates 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 caustic 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 processing 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 inherent in large splats.



Chris Wyman and Carsten Dachsbacher. "Reducing Noise in Image-Space Caustics with Variable-Sized Splatting." Journal of Graphics Tools, 13(1), 1-17 (January 2008).

Files: [ Tech Report (1.0 MB) ] [ Videos (1), (2), (3) (10-20 MB) ]
Demo: [ Windows (21 MB), additional models (44 MB), README ]

Abstract:

Interactivity requires tradeoffs to achieve the right balance between rendering quality and speed. In practice, today's applications restrict lighting to mainly direct illumination, sometimes augmented by precomputed transfer techniques for diffuse global effects. Dynamic high-frequency specular effects, such as caustics, are largely lacking due to the high costs for recomputation each frame. Recent work has introduced a variety of related caustics approximations that interactively render light-space photons into a photon buffer, gather them into a caustic map, and project this map onto the scene similar to shadow mapping. While the process is simple and straightforward, the discretization of light into a finite number of uniformly-distributed photons leads to undersampling and aliasing artifacts. This paper examines two techniques for reducing these artifacts using varying sized photon splats. Conceptually, these are similar to the variable-radius $k$-nearest neighbor search used in photon mapping, allowing noise reduction in areas of low photon density while maintaining crisp caustics at focal points. Our techniques improve image quality at a modest cost that is significantly cheaper than supersampling the photon buffer.



Qi Mo, Voicu Popescu, and Chris Wyman. "The Soft Shadow Occlusion Camera." Proceedings of Pacific Graphics, 189-198. (October 2007)

Files: [ Paper (18.6 MB) ] [ Videos (1), (2), (3) (2-5 MB) ]

Preliminary version presented at MIDGRAPH 2006: [ poster PDF (52 kB)].

Abstract:

A fundamental challenge for existing shadow map based algorithms is dealing with partially illuminated surfaces. A conventional shadow map built with a pinhole camera only provides a binary visibility sorting of the scene, and this all-or-nothing approach to visibility does not capture penumbral regions. We present an interactive soft shadow algorithm based on a variant of the depth discontinuity occlusion camera, a non-pinhole camera with rays that reach around blockers to sample normally hidden surfaces. Our soft shadow occlusion camera (SSOC) classifies a fragment on a continuum from fully visible to fully hidden, as seen from the light. The SSOC is used directly in fragment illumination computation without building an explicit ``soft shadow map.'' This method renders plausible soft shadows at interactive speeds under fully dynamic conditions.



Scott Davis and Chris Wyman. "Interactive Refractions with Total Internal Reflection." Proceedings of Graphics Interface, 185-190. (May 2007)

Files: [ Paper PDF (8 MB) ] [ Local PDF ]
Files: [ Slides (7.0 MB) ] [ Video (4.9 MB) ]

Abstract:

A requirement for rendering realistic images interactively is efficiently simulating material properties. Recent techniques have improved the quality for interactively rendering dielectric materials, but have mostly neglected a phenomenon associated with refraction, namely, total internal reflection. We present an algorithm to approximate total internal reflection on commodity graphics hardware using a ray-depth map intersection technique that is interactive and requires no precomputation. Our results compare favorably with ray traced images and improve upon approaches that avoid total internal reflection.



Chris Wyman. "Interactive Refractions and Caustics Using Image-Space Techniques," in ShaderX5: Advanced Rendering Techniques, 359-371. Edited by Wolfgang Engel. Charles River Media, 2007. ISBN: 1-58450-499-4.

(University of Iowa Library, Call No: T385 .S38 2007)
(OCLC Accession No: 74459039)



Chris Wyman and Scott Davis. "Interactive Image-Space Techniques for Approximating Caustics." ACM Symposium on Interactive 3D Graphics and Games, 153-160. (March 2006)

Files: [ Paper PDF (710 kB) ] [ Local PDF ]
Files: [ Slides ] [ Video (33.2 MB) ]
Demo: [ Windows (12.4 MB), README ]

Abstract:

Interactive applications require simplifications to lighting, geometry, and material properties that preclude many effects encountered in the physical world. Until recently only the most simplistic reflections and refractions could be performed interactively, but state-of-the-art research has lifted some restrictions on such materials. This paper builds upon this work, but examines reflection and refraction from the light's viewpoint to achieve interactive caustics from point sources. Our technique emits photons from the light and stores the results in image-space, similar to a shadow map. We then examine various techniques for gathering these photons, comparing their advantages and disadvantages for rendering caustics. These approaches run interactively on modern GPUs, work in conjunction with existing techniques for rendering specular materials, and produce images competitive with offline renderings using comparable numbers of photons.



Chris Wyman, Steven Parker, Peter Shirley, and Charles Hansen. "Interactive Display of Isosurfaces with Global Illumination." IEEE Transactions on Visualization and Computer Graphics 12(2), 186-196. (March/April 2006)

Files: [ Paper (3.6 MB) ] [ Video (41.5 MB) ]

Abstract:

In many applications, volumetric datasets are examined by displaying isosurfaces, surfaces where data, or some function of the data, takes on a given value. Interactive applications typically use local lighting models to render such surfaces. This work introduces a method to precompute or lazily compute global illumination to improve interactive isosurface renderings. The precomputed illumination resides in a separate volume and includes direct light, shadows, and interreflections. Using this volume, interactive globally illuminated renderings of isosurfaces becomes feasible while still allowing dynamic manipulation of viewpoint and isovalue.



Dave Edwards, Solomon Boulos, Jared Johnson, Peter Shirley, Michael Ashikhmin, Michael Stark, and Chris Wyman. "The Halfway Vector Disk for BRDF Modeling." ACM Transactions on Graphics 25(1), 1-18. (January 2006)

Files: [ Paper PDF (479 kB) ]

Abstract:

We present a mathematical framework for enforcing energy conservation in a BRDF by specifying halfway vector distributions in simple two-dimensional domains. Energy-conserving BRDFs can produce plausible rendered images with accurate reflectance behavior, especially near grazing angles. Using our framework, we create an empirical BRDF that allows easy specification of diffuse, specular, and retroreflective materials. We also present a second BRDF model that is useful for data fitting; although it does not preserve energy, it uses the same halfway vector domain as the first model. We show that this data-fitting BRDF can be used to match measured data extremely well using only a small set of parameters. We believe that this is an improvement over table-based lookups and factored versions of BRDF data.

Chris Wyman. "Interactive Image-Space Refraction of Nearby Geometry." Proceedings of GRAPHITE, 205-211. (December 2005)

Files: [ Paper PDF (700 kB) ] [ Local PDF ]
Files: [ Slides (1.1 MB) ] [ Video (29.5 MB) ]
Code: [ An implementation is in the demo for "Adaptive Caustic Maps" ]

Abstract:

Interactive applications often strive for realism, but framerate constraints usually limit realistic effects to those that run efficiently in graphics hardware. One effect largely ignored in interactive applications is refraction. We build upon a simple, image-space approach to refraction that easily runs on modern graphics cards. This image-space approach requires two passes on a GPU, and allows refraction of distant environments through two interfaces. Our works explores extensions allowing the refraction of nearby opaque objects, at the cost of one additional pass to render nearby geometry to texture and a more complex fragment shader for computing refracted color. Like all image-based algorithms, aliasing can occur in certain circumstances, especially when a few texels are magnified to cover a sizable portion of screen space. However, our plausible refractions should suffice for many applications.

Chris Wyman. "An Approximate Image-Space Approach for Interactive Refraction." ACM Transactions on Graphics 24(3), 1050-1053. (August 2005)

Files: [ Paper PDF (6.0 MB) ] [ Local PDF ]
Files: [ Slides (2.6 MB) ] [ Videos (1), (2), (3) (7-13 MB) ]
Demo: [ Windows (17.7 MB), README, Cg Shaders vertex, fragment ]

Abstract:

Many interactive applications strive for realistic renderings, but framerate constraints usually limit realism to effects that run efficiently in graphics hardware. One effect largely ignored in such applications is refraction. We introduce a simple, image-space approach to refractions that easily runs on modern graphics cards. Our method requires two passes on a GPU, and allows refraction of a distant environment through two interfaces, compared to current interactive techniques that are restricted to a single interface. Like all image-based algorithms, aliasing can occur in certain circumstances, but the plausible refractions generated with our approach should suffice for many applications.



Chris Wyman, Charles Hansen, and Peter Shirley. "Interactive Caustics Using Local Precomputed Irradiance." Proceedings of the Pacific Graphics, 143-151. (October 2004)

Files: [ Paper (538 kB) ] [ Slides (480 kB) ] [ Video (6.5 MB) ]

Abstract:

Bright patterns of light focused via reflective or refractive objects onto matte surfaces are called ``caustics''. We present a method for rendering dynamic scenes with moving caustics at interactive rates. This technique requires some simplifying assumptions about caustic behavior allowing us to consider it a local spatial property which we sample in a pre-processing stage. Storing the caustic locally limits caustic rendering to a simple lookup. We examine a number of ways to represent this data, allowing us to trade between accuracy, storage, run time, and precomputation time.



Chris Wyman. "Fast Local Approximation to Global Illumination." PhD Thesis, University of Utah, Salt Lake City, Utah. (August 2004)
(OCLC Accession No: 56020105)

Files: [ Dissertation (4.0 MB) ] [ Slides (1.4 MB) ]
Files: [ C++ Spherical Harmonic Rotation Class ]

Abstract:

Interactive global illumination remains an elusive goal in rendering, as energy from every portion of the scene contributes to the final image. Integrating over a complex scene, with a polygon count in the millions or more, proves difficulty even for static techniques. Interactive with such complex environments while maintaining high quality rendering generally requires recomputing the paths of countless photons using a small number of CPUs.

This dissertation examines a simplified approach to interactive global illumination. Observing that local illumination computations can be performed interactively even on fairly simple graphics accelerators, a reduction of global illumination problems to local problems would allow interactive rendering. A number of techniques are suggested that simplify global illumination to specific global illumination effects (e.g., diffuse interreflection, soft shadows, and caustics), which can individually be sampled at a local level. Rendering these simplified global illumination effects reduces to a few lookups, which can easily be done at interactive rates. While some tradeoffs exist between rendering speed, rendering quality, and memory consumption, these techniques show that approximating global illumination locally allows interactivity while still maintaining significant realism.

Chris Wyman and Charles Hansen. "Penumbra Maps: Approximate Soft Shadows in Real-Time." Proceedings of the Eurographics Symposium on Rendering, 202-207. (June 2003)

Files: [ Paper (2.3 MB) ] [ Slides (370 KB) ] [ Video (14 MB) ], [ Example Images ]

Abstract:

Generating soft shadows quickly is difficult. Few techniques have enough flexibility to interactively render soft shadows in scenes with arbitrarily complex occluders and receivers. This paper introduces the penumbra map, which extends current shadow map techniques to interactively approximate soft shadows. Using object silhouette edges, as seen from the center of an area light, a map is generated containing approximate penumbral regions. Rendering requires two lookups, one into each the penumbra and shadow maps. Penumbra maps allow arbitrary dynamic models to easily shadow themselves and other nearby complex objects with plausible penumbrae.



Chris Wyman, Charles Hansen, and Peter Shirley. "Interactive Raytraced Caustics." Tech Report, School of Computing, University of Utah, UUCS-03-009.

Files: [ Tech Report (33.8 MB) ] [ Local Copy (4.6 MB) ]

Abstract:

In computer graphics, bright patterns of light focused onto matte surfaces are called ``caustics''. We present a method for rendering dynamic scenes with moving caustics at interactive rates. This technique requires some simplifying assumptions about caustic behavior allowing us to consider it a local spatial property which we sample in a pre-processing stage. Storing the caustic locally limits caustic rendering to a simple lookup. We examine a number of ways to represent this data, allowing us to trade between accuracy, storage, run time, and precomputation time.

Early versions of many of these papers are available as technical reports. Please see:
Last Modified: Wednesday, June 12, 2013
Some Creative Commons licensed images used, thanks to: (1) (2) (3) (4)
Current and prior research funding from:

Resources and in-kind support from: