Approximation of Glossy Reflection with Prefiltered Environment Maps

A method is presented that can render glossy reflections with arbitrary isotropic bidirectional reflectance distribution functions (BRDFs) at interactive rates using texture mapping. This method is based on the well-known environment map technique for specular reflections. Our approach uses a singleor multilobe representation of bidirectional reflectance distribution functions, where the shape of each radially symmetric lobe is also a function of view elevation. This approximate representation can be computed efficiently using local greedy fitting techniques. Each lobe is used to filter specular environment maps during a preprocessing step, resulting in a three-dimensional environment map. For many BRDFs, simplifications using lower-dimensional approximations, coarse sampling with respect to view elevation, and small numbers of lobes can still result in a convincing approximation to the true surface reflectance.