Abstract

The dichromatic reflection model is widely used to describe empirical properties of color signals reflected from inhomogeneous materials. This model assumes that light is reflected by two independent mechanisms of the specular (or interface) reflection and the diffuse (or subsurface) reflection. However, there are relatively few experimental results to evaluate the adequacy of the model. We describe new measurements of the spectral power distributions of lights reflected from inhomogeneous objects in a variety of geometric conditions. We use a principal component decomposition of these observed spectra to test the adequacy of the model. If the model is correct, and furthermore the spectral composition of the specular component of light is the same as the spectral composition of the incident light, it is possible to estimate the spectral power distribution of the light from sensor data. We show that the estimation problem is reduced to finding the common spectral information from the measurements from two or more surfaces. From experiments we conclude that the dichromatic model is adequate for describing color signals from some inhomogeneous materials. Furthermore, we present an algorithm for estimating the illuminant spectral power distribution. The feasibility of this estimation is evaluated using several test objects. (12 min)

© 1988 Optical Society of America