An unstructured lumigraph based approach to the SVBRDF estimation problem

Appearance preservation aims to estimate reflectance functions to model the way real materials interact with light. These functions are especially useful in digital preservation of heritage and realistic rendering, as they reproduce the appearance of real materials in virtual scenes. This work proposes an image-based process that aims to preserve the appearance of surfaces whose reflectance properties are spatially variant. During image acquisition, this process considers the whole environment as a source of light over the area to be preserved and, assuming the environment is static, it does not require controlled environments. To achieve this goal, the scene geometry and relative camera positions are approximated from a set of HDR images taken inside the real scene, using a combination of structure from motion and multiview stereo methods. Based on this data, a set of unstructured lumigraphs is traced, on-demand, inside the reconstructed scene. The color information retrieved from these lumigraphs is then used to estimate a linear combination of basis BRDFs for a grid of points in the surface area, defining thus its SVBRDF. This paper details the proposed method and presents the results obtained using real and synthetic settings. It shows that considering the whole environment as a source of light is a viable approach to obtain reliable results and to enable more flexible acquisition setups. (C) 2020 Elsevier Ltd. All rights reserved.