Faster Photon Map Global Illumination

Abstract

The photon map method is an extension of ray tracing that makes it able to efciently compute caustics and soft indirect illumination on surfaces and in participating media. This paper describes a method to further speed up the computation of soft indirect illumination (diffuse-diffuse light transport such as color bleeding) on surfaces. The speed- up is based on the observation that the many look-ups in the global photon map during nal gathering can be simplied by precomputing local irradiance values at the photon positions. Our tests indicate that the calculation of soft indirect illumination during rendering, which is the most time-consuming part, can be sped up by a factor of 5n7 in typical scenes at the expense of 1) a precomputation that takes about 2%n5% of the time saved during rendering and 2) a 28% increase of memory use.