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Single-Shot Reflectance Measurement from Polarized Color Gradient Illumination
Single-Shot Reflectance Measurement from Polarized Color Gradient Illumination
ICCP 2015
Graham Fyffe     Paul Debevec
USC Institute for Creative Technologies


 


Introduction:

As the physical and digital worlds converge, there is an increasing need for creating digital models of people and objects. A digital model typically consists of geometric information, indicating the shape of the object's surfaces, and reflectance information, indicating how each part of the object reflects light. Acquiring the geometry of an object can be done in many ways, from laser scanning, to structured light, to passive photogrammetry, the latter of which can be performed from photos all shot at the same instant. Acquiring the reflectance of an object - the coloration of each surface, which parts are diffuse, which parts are shiny, and high-resolution surface detail - typically involves photographing the object under a series of lighting conditions and fitting the observations to a reflectance model. With the reflectance captured, the digital model can be digitally rendered as if lit by the light of any desired environment, making the object a useful digital asset.

Single-shot scanning techniques, where the acquisition takes place at a single brief moment of time, make model acquisition more efficient and much easier to apply to dynamic subjects such as facial performances. However, since the subject is lit by just one lighting condition, not much about the object's reflectance can be captured beyond its appearance under diffuse illumination. Far more useful would be to have, at each surface point, a measurement of the subject's diffuse color, its specular component, and a highresolution measurement of its surface normal.

In this paper, we present a novel single-shot scanning technique which uses a color polarized illumination setup to record precisely these measurements. The subject is placed in a sphere of red, green, and blue LEDS, with horizontallyoriented and vertically-oriented linear polarizers distributed throughout. With this setup, different gradient directions of light are produced on the different polarizations of the color channels, and the subject is photographed with a set of cameras some of which are polarized horizontally and some of which are polarized vertically. We leverage the fact that for dielectric materials including skin, the specular reflection component preserves the polarization, and the diffuse component depolarizes the light. These lighting conditions and cameras allow the diffuse color, specular intensity, and photometric surface orientation to be estimated at each pixel location on the object, yielding a single-shot scanning technique for both geometry and reflectance. We demonstrate the technique with two experimental setups: one using two DSLR cameras and a polarizing beam splitter to record reflectance from a single viewpoint, and a multi-view setup with a set of DSLR cameras placed around the subject with differently oriented polarization filters.


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