Global Illumination Animation with Random Radiance Representation

László Szirmay-Kalos, György Antal, Balázs Benedek
Department of Control Engineering and Information Technology, Technical University of Budapest,
Budapest, Magyar Tudósok krt. 2, H-1117, HUNGARY


This paper proposes a non-diffuse global illumination algorithm that is fast enough to be appropriate for interactive walkthroughs and general animations. To meet the severe performance requirements, we heavily exploit coherence both in time and space, and use randomization to reduce the time and storage complexity. To speed up convergence and to support animation, the approximation of the radiance is stored in object space as well. However, in order to reduce the high memory requirements of such representations and to reduce finite-element artifacts, we use just a random approximation, which fluctuates around the real radiance function. The direction dependent radiance approximation is represented in a compact way, by four random variables per patch. The key of performance is then to make the error, i.e. the variance of this compact approximation as small as possible. In addition to main part separation, we apply a novel sampling scheme inspired by the Metropolis method to achieve this goal. In this algorithm light transfers are computed by both local and global methods using ray bundles and with the support of the graphics hardware. We conclude that both local and global approaches fail to efficiently compute all types of transfers, thus cannot be used alone. However, with the aid of multiple importance sampling, the merits of the two light transfer methods can be combined resulting in an algorithm that is robust and fast enough for animations. On the other hand, ray bundles, especially global ones, can update the illumination quickly when objects move, since they can efficiently identify which light paths became invalid.

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