Irradiance Filtering for Monte Carlo Ray Tracing

Janne Kontkanen, Jussi Räsänen and Alexander Keller
in proceedings of MC2QMC 2004


Stochastic ray tracing algorithms generate photo-realistic images by simulating the global illumination. Typically a rather long computation time is required for decreasing the visible noise to an acceptable level. In this paper we propose a spatially variant low-pass filter for reducing this noise. We analyze the theoretical background of the method and present an efficient implementation that enables the use of a comparatively small number of samples while producing high quality images. Our algorithm can be used to accelerate path tracing and final gathering in photon mapping. We compared the method to irradiance caching and according to the results, our algorithm renders images of similar or better quality up to five times faster.



Some heads on an infinite plate. This scene consists of >0.9M triangles, and is lit by a physically based sun/skylight-model using full global illumination.
Helicopter in a hangar lit by sunlight. For comparison, it took nearly nine times more indirect illumination ray-casts to render this scene with irradiance caching aiming at similar quality. The full set of images is included in the article. (Model courtesy of Eetu Martola)

Janne Kontkanen, 4.5.2006