Uniform color scales*

Judgments of relative magnitudes of color differences exhibited by 128 selected nearest-neighbor pairs of 59 colored tiles were recorded by 49 to 76 observers, all of whom had normal color vision. Scale values that represent the perceived magnitudes of the color differences were obtained by statistical analysis of their reports. From colorimetric specifications of the tiles, formulas have been devised that define a three-dimensional euclidean space in which the distances between the points that represent the colors correlate reasonably well with the reported magnitudes of the perceived color differences. Lattice points of a regular rhombohedral crystal in that space have been used to specify about 500 colors that are being made for distribution by the Optical Society. Because of the manner of selection of those colors, each except the most saturated of the chosen colors will exhibit equal magnitudes of color difference from 12 others. About 2500 equally noticeable color differences can be exhibited by suitable arrangements of those colors. Each except the most saturated of the colors can be arranged in six different series. Each of those series exhibits from three to ten color differences, all of equal magnitude. Such a series of colors, which exhibits equal color differences is known as a uniform color scale. Provision of a set of colors with which the maximum possible number and variety of uniform color scales can be constructed was the goal of the Optical Society Committee on Uniform Color Scales, of which this is a report.