Filtered Local Shading in the Wavelet

Many global illumination algorithms generate directionally-and positionally-varying radiance data that then need to be somehow re-sampled and used for nal shading. This operation should lter all light over the incident hemisphere through the BRDF to generate an accurate image. This can be done analytically for simple BRDFs, such as Lambertian or Phong-like BRDFs, but becomes more diicult in the presence of a general BRDF. This paper presents an eecient method to calculate the reeected light in a given direction, ltering over all incident light directions. The method exploits wavelet representations of incident light and of the BRDF to compute the total relfected light in a given direction. For eeciency the incident light is restricted to a Haar transformed representation, while the BRDF can be represented and compressed with any appropriate basis. The method can be used with any system that can generate projections of incident light elds onto Haar wavelet bases.