The D-BRDF model as a basis for BRDF acquisition

Real world materials exhibit characteristic surface reflectance, such as glossy or specular highlights, and anisotropy that need to be modeled accurately for realistic rendering applications. The surface reflectance of a material is formalized by the notion of the Bidirectional Reflectance Distribution Function (BRDF). The acquisition of real world BRDF data, particularly with image-based techniques, has been a very active area of research over the last few years. Independent of the acquisition process, the acquired data is generally not used directly due to its large size, the noise present in the measurement process, and missing data for certain incident and exitant directions. Instead, the data is usually either fitted to an analytical model or projected into a suitable basis as a post-process. Recently, Ghosh et al. [2007] have proposed an alternative approach where the BRDF data is optically projected into a suitable basis function directly during the capture process. This speeds up acquisition time to one or two minutes compared to a few hours required by traditional approaches. They develop a set of basis functions for this purpose that are similar to the spherical harmonics basis and are orthonormal over the zone of directions that can be simultaneously covered with their optical setup.