Techniques for BRDF evaluation

Abstract

Bidirectional reflectance distribution functions (BRDFs) describe how light interacts with a point on a surface. To propose a new BRDF formulation or to compare different reflectance representations, it is necessary to confront the results obtained with those functions against previous work or measured data. Despite the importance of using reliable techniques to evaluate a BRDF, there is a lack of works in the literature that gathers and compares those. This paper proposes a compilation of techniques used to evaluate BRDF representations along with their formal definitions. Those techniques were classified into three different groups—comparison functions, rendered images, and plots—and, to illustrate their use, three classical and widely adopted models and one state-of-the-art BRDF representation were evaluated regarding their capacity to preserve the appearance of measured materials. Based on our research regarding comparison functions, a stable and robust BRDF evaluation technique is proposed. It has been observed during both literature review and experiments that each group of techniques provides complementary information about the evaluated BRDFs, which suggests that at least one model from each category should be adopted during the choice of criteria to evaluate a BRDF.