Optical properties (bidirectional reflection distribution functions) of velvet

Abstract

A detailed investigation has been made of the unusual characteristics of the angular distribution of surface scattering from velvet in the visual region. We present a novel method in which samples of velvet fabric are wrapped around a right-circular cylinder so that reemitted radiance can be measured by a digital CCD camera. This setup makes it relatively simple to acquire a large set of bidirectional reflection distribution function (BRDF) samples. The study reveals that, apart from the grazing specular lobe and an anisotropic backscattering peak near 50 degrees , the overall BRDF's are rather uniform across the whole angular span of observation. Attempts are made to relate these scattering characteristics to the physical and the geometrical structure of velvet.

A microfacet-based BRDF generator

“…We can call this arrangement milliscale geometry in contrast with microgeometry formed by the thin fibers themselves. Similar geometry was credited as the major reason for velvet anisotropic reflection behavior by Lu et al [11]. Strictly speaking, our model does not take into account visibility issues due to this higher-order arrangement of microfacets.…”

“…Because retroreflection is one of the most pronounced reflection properties of velvet [11], we used the correlated form of shadowing term (Equation 14) to generate both this and slanted fiber (see below) velvet BRDFs. Contrary to Westin et al we ignore the tips of the fibers due to their very small area.…”

Principles of appearance acquisition and representation

“…An alternative approach is to eliminated the hemispherical reflector and to use curved material samples instead of a planar one [MWLT00,LKK98]. For isotropic materials, one can use a sphere.…”

Measuring bidirectional texture reflectance with a kaleidoscope

“…[Lu et al 1998] arranges a sample patch onto a known cylinder. [Marschner et al 1999] relaxes the sample geometry restriction by utilizing a range scanner, and improves acquisition flexibility by allowing for free positioning of the capture camera.…”