Color-imaging primaries and gamut as prescribed by the human visual system

Abstract

Image reproduction from one medium to another suffers from differences in size and shape of color gamut, as well as from strong metamerism when spectral compositions of light from corresponding pixels are very different. The present purpose is to suggest primaries, and their resulting color gamuts, for any form of display or hardcopy providing color images to be viewed by normal human vision. Both optimum primaries and optimum color gamuts, appropriate to images produced by either additive or subtractive color mixture, are here defined by the prime colors of the normal human observer. In the case of additive color mixture, the optimum primaries are spectral lights near 450 nm, 533 nm, and 611 nm; these wavelengths mark the peaks of the three spectral sensitivities of the normal human visual system. With subtractive color mixture, the suggested `primaries' are lights composed of incident light reflected from broader components of spectral reflectance, still peaked (or averaged) near the same three wavelengths. These additive primaries provide (1) maximum visual efficiency (brightest image per unit power output) and (2) a color gamut appreciably larger than those of the CIE Standard Observers. In addition, for subtractive color mixture, the optimum `primaries' lead (3) to `preferred' coloration of imaged objects, (4) to optimum constancy of hue and chroma of each pixel, against variation of the spectral power distribution of the illumination, and (5) to strong reduction of metamerism.