An Anisotropic Phong BRDF Model
Michael Ashikhmin, Peter Shirley · Journal of Graphics Tools · 2000
We present a BRDF model that combines several advantages of the various empirical models currently in use. In particular, it has intuitive parameters, is anisotropic, conserves energy, is reciprocal, has an appropriate non-Lambertian diffuse term, and is well-suited for use in Monte Carlo renderers.