Cues and strategies for color constancy: perceptual scission, image junctions and transformational color matching.

The identification of objects, illuminants, and transparencies are probably the most important perceptual functions of color. This paper examines the effects of perceptual scission, image junctions, color adaptation, and color correlations on identification. Simulations of natural illuminants, materials, and filters were used in a forced-choice procedure to simultaneously measure thresholds for identifying filters and objects across illuminants, and discrimination thresholds within illuminants. In the vast majority of the cases, if observers could discriminate within illuminants they could identify across illuminants. Since results were similar for identical color distributions, whether transparency cues like X-junctions were present or not, the primary cues for color identification were systematic color shifts across illuminants. These color shifts can be well described by three-parameter affine transformations, and the parameters can be derived from differences and ratios of mean chromaticities. A strategy based on post-transformation color matching predicts generally accurate identification despite perceptible color shifts, and also provides plausible reasons for those few conditions where identification thresholds are significantly higher than discrimination thresholds.