Adaptive Sampling of Area Light Sources in Ray Tracing Including Diffuse Interreflection

Ray tracing algorithms that sample both the light received directly from light sources and the light received indirectly by diffuse reflection from other patches, can accurately render the global illumination in a scene and can display complex scenes with accurate shadowing. A drawback of these algorithms, however, is the high cost for sampling the direct light which is done by shadow ray testing. Although several strategies are available to reduce the number of shadow rays, still a large number of rays will be needed, in particular to sample large area light sources. An adaptive sampling strategy is proposed that reduces the number of shadow rays by using statistical information from the sampling process and by applying information from a radiosity preprocessing. A further reduction in shadow rays is obtained by applying shadow pattern coherence, i.e. reusing the adaptive sampling pattern for neighboring sampling points.