Two-dimensional BRDF estimation from polarisation

This paper presents a novel technique for reflectance function (BRDF) estimation, which uses polarisation information and photometric stereo. The first stage of the technique is standard and involves the acquisition of polarisation information (angle and degree of polarisation) using a linear polariser and a digital camera. This yields a field of ambiguous surface normal estimates for an arbitrarily shaped object. A photometric stereo algorithm is then used with three different light source directions to disambiguate the surface normals. Next, the proposed algorithm constructs a 3D histogram of the surface normals and pixel brightnesses. A surface, representing the BRDF, is then fitted to the histogram data using simulated annealing optimisation. The result is a set of Cartesian triples that relate the surface normals to the observed pixel brightnesses. Unlike most previous techniques for BRDF estimation, the technique is image-based and does not require sophisticated equipment or intrusive light sources. Although the technique is restricted to smooth and slightly rough dielectric objects, no prior knowledge about the surface geometry is assumed.