[SWH+95a]
Cornell University Program of Computer Graphics 

Global illumination via density estimation.Peter Shirley, Bretton Wade, Philip Hubbard, David Zareski, Bruce Walter, and Donald P. Greenberg.In Eurographics Rendering Workshop 1995. Eurographics, June 1995. This paper presents a new globalillumination algorithm for highly complex static environments containing both diffuse and nondiffuse surfaces. The algorithm accounts for all types of surface reflection, accommodates textured surfaces, and supports coarsegrained parallelism. A key to this method is a novel decomposition of the problem into a sequence of three looselycoupled phases. The first phase consists of Monte Carlo particle tracing in which powercarrying particles are emitted from each luminaire, and tracked through the environment until they are absorbed. A list of particle ``hit points'' is kept for each surface. In the second phase, called the ``densityestimation'' phase, the stored hit points are used to construct an approximate irradiance function for each surface. In the final phase, called the ``meshing'' phase, each surface irradiance function is approximated by a piecewiselinear function. Display output can be either Gouraudshaded polygonal elements for interactive walkthroughs, or raytraced pixels for higherquality still frames. The method is modular, relatively easy to implement, has low memory overhead, and has produced viewindependent display meshes for models larger than the ones that have been processed by previous methods. Such solutions could improve the stateoftheart in architectural simulations, immersive environments, and other virtual reality applications.
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