Trichromatic opponent color classification

Stimuli varying in intensity and chromaticity, presented on numerous backgr ounds, were classified into red/green, blue/yellow and white/black opponent color categories. These measurements revealed the shapes of the boundaries that separate opponent colors in three-dimensional color space. Opponent c olor classification boundaries were generally not planar, but their shapes could be summarized by a piecewise linear model in which increment and decr ement color signals are combined with different weights at two stages to pr oduce opponent color sensations. The effect of background light on classifi cation was largely explained by separate gain changes in increment and decr ement cone signals. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.