ABSTRACT
The two fundamental techniques for using environment maps with more general reflection models are Decomposition: The reflection model is decomposed into simpler contri-
butions, which can be treated separately. For example, a reflection model may be separated into a diffuse and a specular term, where the specular term is represented as a mirror reflection using an environment map and is multiplied with an viewing-angle-dependent Fresnel term. More generally, we could use a factorized model for the non-mirror terms of the BRDF. This approach has the disadvantage, mentioned above, that we are not actually using the same representation of the illumination for both parts of the reflectance.
