Chromaticity contrast, luminance contrast, and legibility of text

— The purpose of this investigation was to determine if color differences can improve legibility and compensate for insufficient luminance contrast. Several authors previously have answered this question positively on the basis of performance experiments. We argue that a valid answer cannot be given unless subjective data are used. In four experiments, subjective ratings were collected pertaining to multicolor CRT text displays. The displays were systematically varied with respect to both luminance contrast and chromaticity contrast. The results indicate that chromaticity contrast and luminance contrast are additive only under specific conditions. Chromaticity contrast cannot improve legibility if an acceptable level of luminance contrast is present. Generally, chromaticity contrast cannot be substituted for luminance contrast.