Measuring bidirectional reflectance distribution function

Patent Granted The bidirectional reflectance distribution function (BRDF; f_{\text{r}}(\omega_{\text{i}},\, \omega_{\text{r}}) ) is a function of four real variables that defines how light is reflected at an opaque surface. It is employed both in the optics of real-world light, in computer graphics algorithms, and in computer vision algorithms. The function takes an incoming light direction, \omega_{\text{i}}, and outgoing direction, \omega_{\text{r}} (taken in a coordinate system where the surface normal \mathbf n lies along the z-axis), and returns the ratio of reflected radiance exiting along \omega_{\text{r}} to the irradiance incident on the surface from direction \omega_{\text{i}}.