Circularly polarized spherical illumination reflectometry

Abstract

Figure 1: Renderings under environmental illumination of subjects with spatially varying reflectance acquired using circularly polarized spherical illumination. AbstractWe present a novel method for surface reflectometry from a few observations of a scene under a single uniform spherical field of circularly polarized illumination. The method is based on a novel analysis of the Stokes reflectance field of circularly polarized spherical illumination and yields per-pixel estimates of diffuse albedo, specular albedo, index of refraction, and specular roughness of isotropic BRDFs. To infer these reflectance parameters, we measure the Stokes parameters of the reflected light at each pixel by taking four photographs of the scene, consisting of three photographs with differently oriented linear polarizers in front of the camera, and one additional photograph with a circular polarizer. The method only assumes knowledge of surface orientation, for which we make a few additional photometric measurements. We verify our method with three different lighting setups, ranging from specialized to off-theshelf hardware, which project either discrete or continuous fields of spherical illumination. Our technique offers several benefits: it estimates a more detailed model of per-pixel surface reflectance parameters than previous work, it requires a relatively small number of measurements, it is applicable to a wide range of material types, and it is completely viewpoint independent.

Estimating dual-scale properties of glossy surfaces from step-edge lighting

“…Our work fits into what we believe is a "sweet spot" in the space of appearance capture techniques: our method recovers both BRDF and mesostructure (as in prior work [Gardner et al 2003;Georghiades 2003;Ghosh et al 2009;Ghosh et al 2010]), but adopts a simplified frequency spectrum model for the latter and a simple capture system using a single reflected image of a step-edge illuminant displayed on an LCD screen (along with a couple of images to calibrate the setup beforehand). Without an exact measurement of the mesostructure, we use a statistical approach to recover microscale properties.…”

“…On the other hand, mesostructure also exhibits visible texture at different frequency scales, and thus requires a more detailed description than the invisible microfacets. Prior work has acquired complete normal maps to provide this detail [Chen et al 2006;Francken et al 2008a;Francken et al 2008b;Ghosh et al 2009;Ghosh et al 2010], but many real-world surfaces-including certain paints, metals, plastics, and ceramics-have the following properties, which allow a simple statistical description to suffice:…”

Decomposition of reflection and scattering by multiple-weighted measurements

“…Wolff and Boult [4] utilized linear polarization to remove the specular reflection component of the observed image. Many researchers also used linear or circular polarization [16][17][18][19]. Both of the methods based on color and polarization can be combined since both are in complementary relationship [20][21][22][23][24].…”

“…Techniques based on circular polarization can separate specular reflection [4,19] and single scattering [32,34] from other components. The nature of circular polarization is that right-handed (or left-handed) circularly polarized light cannot transmit through a left-handed (or right-handed) circular polarizer.…”

Estimating dual-scale properties of glossy surfaces from step-edge lighting

“…With the assumption of homogeneity, surfaces can be described by a single reflectance function that can be estimated from images [Yu et al 1999] or rapidly acquired by handheld devices [Dong et al 2010;X-Rite 2011], but the resulting surfaces always look too featureless, because surfaces with no visible texture are rare. Good, detailed appearance can be * e-mail:cpwang@cs.cornell.edu † e-mail:snavely@cs.cornell.edu ‡ e-mail:srm@cs.cornell.edu achieved by measuring high-resolution parameter maps for particular samples [Gardner et al 2003;Ghosh et al 2009;Ghosh et al 2010], but these methods are considerably less convenient-too much work to add subtle texture to a basically homogeneous surface.…”