Generating Reeected Directions from Brdf Data

Monte-Carlo path tracing algorithms for computer graphics require that given an incident light ray at a surface an outgoing direction can be computed with a distribution given by the magnitude of the bidirectional reeectance distribution function (BRDF). For analytic reeectance functions this can be done using various techniques including inverting the function, or tabulating some representation of the inverse. However, measured BRDF data sets are too large for this to be practical. We present a method to generate reeection rays distributed according to the magnitude of the BRDF. The method relies on a wavelet-based representation of the BRDF. This representation is eecient and compact, allowing large, anisotropic measured BRDF data sets to be represented with a few thousand coeecients. In particular, we exploit the wavelet representation to quickly compute integrals over ranges of the BRDF.