Specular and diffuse reflectance in microfacet models

In this paper we consider diffuse reflectance from surfaces modelled as distributions of specular microfacets. We show how the relative contributions of specular and diffuse reflectance can be found analytically for such microfacet models using Fresnel theory. This removes the need for ad hoc specular and diffuse reflectance coefficients, ensuring the conservation of energy and only allowing physically plausible mixtures of the two components. We show how the amount of light that can be diffusely reflected is dependent on the angle of incidence and physical properties of the surface.