Chris Wyman. "Fast Local Approximation to Global Illumination." PhD Thesis, University of Utah, Salt Lake City, Utah, August 2004.
Dissertation: [pdf (4.0 MB), pdf (40 MB)], Defense Talk: [pdf (1.4 MB)], SH Rotation Code: [C++ 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 2003 Eurographics Symposium on Rendering, 202-207.
Paper: [pdf (2.3 MB)], Video: [DivX 5 (14 MB)], Talk: [pdf (370 KB)]

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.
Paper: [pdf (33.8 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.