Appearance Preserving Prefiltering for Rendering Complex Scenes

Complex materials and lighting conditions can produce remarkably high-quality renderings with photorealism. However, efficiently rendering them remains challenging due to the high complexity of physically based light transport simulation. To improve the efficiency of rendering complex scenes, one common approach is using prefiltering techniques to precompute simplified material or lighting models. But usually these prefiltered models cannot preserve their original appearance accurately, leading to undesired rendering results.In this dissertation, we present a series of novel appearance preserving prefiltering techniques. Our goal is to compute prefiltered material and lighting models that have smaller storage sizes and enable efficient rendering of complex scenes. Images rendered using the prefiltered model should closely resemble the overall appearance given by the original model.Our first work addresses the challenge of prefiltering volumetric scattering models. We present a joint optimization of multiple material scattering parameters, i.e., single-scattering albedos and phase functions, to accurately prefilter heterogeneous and anisotropic media. Our method leads to significantly better accuracy compared to traditional linear downsampling and offers several orders of magnitude storage reduction.Our second work focuses on prefiltering the reflectance of a displacement-mapped surface. We represent the prefiltered surface reflectance model as a spatially varying bidirectional reflectance distribution function (SVBRDF) at a reduced resolution. To express our appearance preserving SVBRDF efficiently, we decompose it into a spatially varying normal distribution function (SVNDF) and a novel scaling function that accurately captures micro-scale changes of shadowing, masking, and interreflection effects. The scaling function can further be computed by an efficient factorization. Our prefiltering method generalizes well to different types of surfaces and enables anti-aliased level-of-detail rendering.Finally, our last work turns to the challenge caused by complex lighting conditions. Given a scene with many polygonal area lights, we prefilter all the lights into a sparse 3D grid of spherical harmonic (SH) lighting coefficients and gradients, allowing interpolating SH coefficients accurately at any intermediate point. This enables scaling real-time precomputed radiance transfer (PRT) to hundreds of area lights. Our method builds on a novel analytic formula for SH gradients, which may benefit many other applications beyond rendering