Bidirectional Scattering Surface Reflectance Distribution Function
The Bidirectional Scattering Surface Reflectance Distribution Function ( BSSRDF , dt .: Bidirectional surface scattering reflectance distribution function ) is a function for describing the reflection behavior of a material with volume scattering .
In contrast to the BRDF , the reflection of a light beam at a given point depends not only on the angle of incidence and also on the viewing angle, but also on the point at which the light beam entered the material. This adds two or three additional dimensions to the BRDF.
In the area of 3D computer graphics , the BSSRDF is only of theoretical importance. In practice, it is replaced by a simplified model in which a phase function with an absorption and scattering coefficient is specified for the entire material .