Report CW 197, 19 pages, Departement Computerwetenschappen, KU Leuven, Celestijnenlaan 200A, 3001 Heverlee, Belgium, November 1994.
This text discusses a few aspects of re ectance models in physically based rendering: The first section presents the de nition of the bidirectional reflection distribution function (brdf) of a surface and its physical properties. On a more practical level, the next section discusses models to represent brdfs and their desired properties in general for Monte Carlo algorithms. The third section goes into details about a specific reflectance model, the modified Phong brdf, with its definition, its properties and its use. We show how this model can be correctly integrated in importance sampling schemes for physically based Monte Carlo rendering algorithms. The fourth section is devoted to alternative parameter spaces in which reflectance models can be sampled, either deterministically or stochastically. The last section discusses an important implementational issue, more specifically the problem of verifying the implementation of a reflectance model.