Saturation of light mixtures as a function of chromatic and achromatic excitation in the visual system

Summary The saturation of mixtures of white and chromatic lights may be measured by magnitude estimation as a function of the proportion of chromatic light in the mixture. When the intensity of the white light is kept constant, and the intensity of the chromatic light is varied, the psychophysical saturation curves change in a regular way: With higher chromatic intensity, they become less convex, and finally turn concave. Therefore it is possible to measure a whole class of stimulus-response curves representing the relation of chromatic light proportion to saturation. In this paper, a hyperbolic function is developed to describe this class of curves. The function is based upon the assumption that the data-processing system of human color vision evaluates the proportion of chromatic and achromatic excitation to produce subjective saturation. This assumption is in accordance with the known constancy of color perception under natural viewing conditions. The experimental data are approximated just as well, and in some cases better, by the hyperbolic function than by the commonly used power function.