Wavelet Basis Functions for Precomputed Radiance Transfer

Precomputed Radiance Transfer (PRT) aims at computing global illumination effects such as soft shadows and object interreflection in realtime. This is accomplished by precomputing the factors of the Rendering Equation and projecting them into a suitable basis which allows to combine them efficiently at runtime. Several basis function have been proposed for PRT. Recently, Haar wavelets have been employed which provide superior results, especially for high frequency effects. In this report, the computation of the triple product integral of lighting, BRDF and visibility in the Haar basis is detailed and an efficient implementation of this algorithm is presented. The influence of the input signal resolution and of nonlinear approximations of the basis representation of the input signals on the quality of the renderings is examined.