Adaptation and chromatic discrimination

Abstract

Many careful measurements have been made of the variation of chromatic discrimination over color space. In an elegant set of experiments MacAdam derived a set of ellipses which plot the stimuli equally discriminable from various loci in the CIE chromaticity diagram. The pattern of variation of the ellipses is complex. New measurements have been made with the observer's state of adaptation rigorously controlled during the measurements. Two special adaptation regimes were employed. In one the observer was adapted throughout the measurements to one point in color space, e.g., an equal energy white while the location of the stimuli to be discriminated varied over color space. In the second regime the observer was adapted to the locus at which discrimination was measured. The pattern of results obtained in these conditions, expressed as discrimination ellipses, differ markedly from one another and from those of MacAdam. The new results are more orderly than previous ones and can be related by simple principles