Atdn: Toward a uniform color space†

To derive a uniform chromaticity space for small color differences, we applied compressive intensity-response functions of the form ρ = In/(σ + In) to each of the four color signals from the T (red vs. green) and D (blue vs. yellow) mechanisms of the ATD vector model for color vision. The values of σ and n for each response were optimized by computer iteration to provide reasonably uniform color spaces (ATDN) for describing the color-discrimination data of MacAdam [J. Opt. Soc. Am. 32, 246-274 (1942)] and Pointer [J. Opt. Soc. Am. 64, 750–759 (1974)]. To determine how well ATDN accounts for large color differences, we transformed the coordinates of the Munsell renotation system to ATDN space. Origin-bound radial lines and origin-centered circles in ATDN are about equivalent to those of CIELAB in approximating iso-hue and iso-sat-uration contours of the Munsell system. A computer program written in BASIC that can be used to transform 1931 CIE X, Y, Z values to points in ATDN space is included as an appendix.