A BRDF postprocess to integrate porosity on rendered surfaces

The behavior of light interacting with materials is a crucial factor in achieving a high degree of realism in image synthesis. Local illumination processes, describing the interactions between a point of the surface and a shading ray, are evaluated by Bidirectional Reflectance Distribution Functions (BRDFs). Current theoretical BRDFs use surface models restricted to roughness only, sometimes at different scales. In this paper, we present a more complete surface micro-geometry description, suitable for some common surface defects, including porosity and micro-cracks; both of them are crucial surface features since they strongly influence light reflection properties. These new features are modeled by holes inserted in the surface profile, depending on two parameters: the proportion of surface covered by the defects and the mean geometric characteristic of these defects. In order to preserve the advantages and characteristics of existing BRDFs, a postprocessing method is adopted (we integrate our technique into existing models, instead of defining a completely new one). Beyond providing graphical results closely matching real behaviors, this method moreover opens the way to various important new considerations in computer graphics (for example, changes of appearance due to the degree of humidity).