OctreeBTFs – A compact, seamless and distortion-free reflectance representation

Abstract

Conventional reflectance acquisition techniques rely on the reconstruction of a closed surface geometry and a subsequent surface parametrization that is required to store the reflectance data parametrized over the surface. Among the main drawbacks of this approach is the need for a suitable surface parametrization which is particularly challenging for inaccuracies in the reconstruction or holes occurring due to missing observations. An inappropriate parametrization, in turn, leads to artifacts such as distortion effects and visible seams which severely decrease the visual quality of the digitized object appearance. Furthermore, standard reflectance representations are either compact and less expressive or not compact and expressive. In this paper, we introduce a compact, accurate, seamless and distortion-free volumetric reflectance representation to address these issues. This novel representation named OctreeBTFs is based on storing surface reflectance in terms of Apparent BRDFs in a grid structure that is adapted to the underlying object geometry. The local coordinate systems required to store and render the local reflectance behavior of anisotropic surface reflectance characteristics are computed based on a novel, biologically inspired local approach, instead of computing them based on the texture coordinates obtained from the uv-parameterization. The resulting octree-based data structure results in a more compact BTF representation that can be rendered in real-time with multiple light sources. Finally, our data structure can also be applied to other reflectance representations or to store other information such as physical properties.