Large color differences among achromatic colors

Abstract

Small color differences between simple achromatic stimuli have been understood for more than a century: extensive detection and discrimination data, including the Weber fraction, coexists with successful theories based on signal detection. Larger color differences and complex stimuli, which are more important in engineering applications, are less well understood. We have been investigating these stimuli using priming in a visual search task as our measure of color difference. The task, which depends on perceived color identity of patterns similar in complexity to letters, provides stable data with thresholds much larger than either the MacAdam ellipses or the Weber fraction. The results show evidence of stimulus categorization based on luminance with the categories anchored to the background luminance.