Abstract

The color constancy problem is one of calculating reflectance values for surfaces under differing illuminants. Retinex theory (e.g., Land, 1986) states that relative receptor responses are used to recover surface reflectance after they have been normalized with respect to the responses of neighboring receptor responses. Specifically, a number of paths to the pixel in question are randomly chosen and the logarithm of the ratio of the pixel receptor's response to the geometric mean of the receptor responses over a large number of paths is used as the lightness value for the pixel in question. Symbolically (1) where r(x,k) is the response of receptor x (to pixel x) of class k (where k is either the short wavelength, medium wavelength, or long wavelength cone), G(p,k) is the geometric mean of all of the receptor responses of class k covered by the random paths p, and l(x,k) is the resulting lightness value for receptor x (to pixel x) of class k. By normalizing the lightness value to the geometric mean of the neighboring receptor responses the change of the lightness value in response to overall spectral changes in illumination is minimized.

© 1987 Optical Society of America