Physically-based Analysis and Rendering of Bidirectional Texture Functions Data

Abstract

In order to draw a photorealistic surface, Bidirectional Texture Function (BTF), a 6D texture function which extends Bidirectional Reflectance Distribution Function (BRDF) to include the self-shadowing, self-occlusion and inter-reflection effects, has been used frequently in recent years. Its main drawback is its massive data size. To solve this, the Spatial Bidirectional Reflectance Function (SBRDF) techniques compress BTFs into reflectance model parameters. However, SBRDF cannot produce the self-shadowing and self-occlusion effects in real-world surface geometry. This work is aimed to this drawback. We investigate how self-shadowing and self-occlusion affect the surface appearance by additional physically-based analysis and rely on two physical phenomena to separate self-shadowing and self-occlusion into two independent effects. First, self-shadowing is view independent. Second, self-occlusion is independent of lighting direction changes. After these analyses, we add self-shadowing and self-occlusion to SBRDF to achieve rendering quality that is much closer to the original uncompressed BTF data.