Level-of-detail representation of bidirectional texture functions for real-time rendering

This paper presents a new technique for rendering bidirectional texture functions (BTFs) at different levels of detail (LODs). Our method first decomposes each BTF image into multiple subbands with a Laplacian pyramid. Each vector of Laplacian coefficients of a texel at the same level is regarded as a Laplacian bidirectional reflectance distribution function (BRDF). These vectors are then further compressed by applying principal components analysis (PCA). At the rendering stage, the LOD parameter for each pixel is calculated according to the distance from the viewpoint to the surface. Our rendering algorithm uses this parameter to determine how many levels of BTF Laplacian pyramid are required for rendering. Under the same sampling resolution, a BTF gradually transits to a BRDF as the camera moves away from the surface. Our method precomputes this transition and uses it for multiresolution BTF rendering. Our Laplacian pyramid representation allows real-time anti-aliased rendering of BTFs using graphics hardware. In addition to provide visually satisfactory multiresolution rendering for BTFs, our method has a comparable compression rate to the available single-resolution BTF compression techniques.