Direct estimation of lightness of surface colors.

Abstract

Achromatic and chromatic lightness and darkness of an array of 104 reflecting surfaces were scaled by the method of magnitude estimation. Samples subtended a visual angle of 4° and were viewed under both artificial light and daylight. The dominant wavelengths of the chromatic samples were blue 470, green 553, yellow 574, and red 622 nm. For each hue, the subjective attributes of both lightness and darkness were judged at five levels of colorimetric purity Pc. Both lightness and darkness increased as a power function of the luminous reflectance of the neutral grays and the pigmented surfaces. The lowest exponents, from 0.5 to 0.74, were found among the most and the least saturated samples. Exponents of about 1.0 were obtained for both lightness and darkness functions for the neutral grays, for two Pc levels of red, for one Pc level of green, and one of blue, under both artificial light and daylight. For the yellows, the exponents were close to 1.0 at all purity levels under daylight only. All other samples gave exponents less than one.