Spatially Varying BRDF Map Filtering

Abstract

In recent years, the use of spatially varying bidirectional reflectance distribution function (SVBRDF) textures has been steadily increasing in real-time rendering. To reduce aliasing, it is necessary to prefilter SVBRDF textures before rendering. A comprehensive filtering algorithm is proposed that considers the contribution of each component of the SVBRDF texels. First, the weight of each texel is defined as the sum of the luminance of its diffuse albedo and specular albedo. Next, the model of mixture of von Mises-Fisher (vMF) is examined and weighting mechanism is added to it. Finally, by heuristically choosing the initial values for the <italic>k</italic>-means algorithm, an improved method for calculating SVBRDF Mipmap in a bottom-up fashion is proposed. To evaluate the algorithm, 4 SVBRDF materials with different microscopic normal distributions are crafted by hand. When rendering complex SVBRDF materials, the proposed method could achieve an RMSE value 25.5% lower than that of the reference algorithm. When changing the number of fitted lobes, the proposed algorithm can obtain a better result with 2 vMF lobes than previous methods with 4 lobes.