Abstract: Many global illumination algorithms generate directionally- and positionally-varying radiance data that then need to be somehow re-sampled and used for final shading. This operation should filter 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 diffictilt in the presence of a general BRDF. This paper presents an efficient method to calculate the reflected light in a given direction by filtering over all incident light directions. The method exploits wavelet representations of incident light and of the BRDF to compute the total reflected light in a given direction. For efficiency 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 fields onto Haar wavelet bases.