Testing new variants of the Beckmann–Kirchhoff model against radiance data

In this paper, we explore whether the Fresnel term can be used to improve the predictions of the Beckmann–Kirchhoff (B-K) model for moderately rough surfaces. Our aim in developing this model is to describe subsurface scattering effects for surfaces of intermediate roughness. We use the BRDF measurements from the CUReT database to compare the predictions of the Fresnel correction process with a number of alternative models. The models studied are the Vernold–Harvey modification of the B-K model, and the three variants of the Kirchhoff scatter theory developed by Beckmann, Ogilvy, and Nieto-Garcia. The main conclusions from our experiments with 24 surface samples using these variants of the B-K model and the phenomenological model of Oren–Nayar are as follows. First, the Vernold–Harvey modification provides consistently accurate predictions for very-rough surfaces. Second, our new Fresnel correction provides the most accurate predictions for all of the moderately rough surfaces studied. Finally, the Oren–Nayar model fails to fit the data for most of the surface samples under our study.