Diffuse reflection [intensity reflectance model]

An intensity reflectance model is proposed for diffuse reflection originating from subsurface multiple scattering within inhomogeneous dielectric materials. One of the most common assumptions in computer vision from inhomogeneous dielectrics is Lambertian. The proposed model utilizes the subsurface intensity distribution predicted by modeling subsurface multiple scattering based upon radiative transfer theory. For an optically smooth surface boundary this subsurface intensity distribution becomes altered by Fresnel attenuation upon refraction into air, making it become significantly non-Lambertian. This resulting intensity distribution serves as a reflection law for individual optically smooth microfacets that compose an opaque rough surface, producing a physical unification of diffuse reflection with the Torrance-Sparrow specular reflection model. Experimental results that verify the accuracy of the model are presented. A relatively simple formula that approximates closely the true behaviour of diffuse reflection and can be used in place of a Lambertian term is presented. The non-Lambertian nature of the diffuse component becomes most significant near occluding contours and sometimes produces a previously unnoticed intensity effect that can aid in their detection