The BRDF Model This model was introduced by He, Torrance, Sillion and Greenberg at Siggraph in 1991. The model relies on wave-optics, more precisely on the Beckman-Kirchoff theory and is known to be very difficult to use or to implement. In this post, we provide our implementation as well as some details about the model itself, which is not that complex to implement, at least in its unpolarized version! In the supplemental material of our paper we compare our new BRDF Model with the unpolarized version of the He et al.