Color Differences

Abstract

Analogous to Mercator charts and other kinds of maps of the world that misrepresent the ratios of distances, the chromaticity diagram does not represent perceptually equal color differences by equal distances between points that represent equally luminous colors. The noticeability of color differences was not considered — very few data were available — when the chromaticity diagram was devised and adopted. However, as soon as it came into use, anomalies were encountered in interpreting the configurations of points on the diagram. Inconsistencies between distances and perceived magnitudes of color differences were evident. The analogy with geographical maps was quickly noted and suggestions were made to change the representation so that equal distances would represent equally noticeable color differences. The hoped-for chromaticity diagram with such properties came to be called “uniform”. The search for it has extended over 50 years and seems no nearer its goal than at the beginning. Much of the accumulated evidence indicates that the goal is unattainable — that a flat diagram cannot represent equal color differences by equal distances any more than a flat map of the world can represent equal geographical distances by equal distances on the map. Nevertheless, useful methods have been devised for evaluating color differences in terms of chromaticity differences.