A New Change of Variables for Efficient BRDF Representation

Szymon Rusinkiewicz

We describe an idea for making decomposition of Bidirectional Reflectance Distribution Functions into basis functions more efficient, by performing a change-of-variables transformation on the BRDFs. In particular, we propose a reparameterization of the BRDF as a function of the halfangle (i.e. the angle halfway between the directions of incidence and reflection) and a difference angle instead of the usual parameterization in terms of angles of incidence and reflection. Because features in common BRDFs, including specular and retroreflective peaks, are aligned with the transformed coordinate axes, the change of basis reduces storage requirements for a large class of BRDFs. We present results derived from analytic BRDFs and measured data.