Introduction

When a physical object is illuminated by some spectral power distribution (e.g. daylight or tungsten lamp), a modified spectral power distribution is emitted according to the reflectance properties of the object. This reflected stimulus enters the eye and is perceived as an “object color.” It is possible for two objects with different reflectance properties to produce the same object color sensation under the action of one illuminant, but to produce visibly different object color sensations under the action of a different illuminant. This is concept of “metamerism,” (more specifically known as “illuminant metamerism” in the color science literature). This journal article presents a mathematical procedure to generate the reflectance profiles of a pair of objects that will theoretically produce the same color sensation under an arbitrary number of sequentially applied illuminants.

Abstract

This paper extends matrix-R operations, developed by Cohen and Kappauf in 1982, 1985 and by Cohen in 1988, to create generalized metameric object color stimuli, here termed multiple metamers, that remain metameric with respect to several different illuminants. As discussed in prior literature, matrix-R operations resolve any radiometric function (specifying a color stimulus) into a fundamental color stimulus and a residual or metameric black, as hypothesized by Gunter Wyszecki in 1953. The fundamental is sensed by the visual system while the residual is ignored. Metameric color stimuli comprise the same fundamental but different residuals. Thus, matrix-R operations easily construct metameric suites under an equal-energy source or under any other illuminant whose physical specification is incorporated into the radiometric function of the color stimulus entering the visual system. In the present article, matrix-R operations are extended to create metameric stimuli that theoretically remain metameric with respect to an arbitrary number of sequential illuminants. While the stimuli remain metamers under different illuminants, the color sensation evoked with respect to one illuminant is generally different from the color sensation evoked with respect to another illuminant. Examples demonstrate multiple metamers with respect to CIE standard illuminants A and C and with respect to four artificial illuminants. In principle, extended matrix-R operations create multiple metamers with respect different observers, or with respect to any combination of observers and illuminants.

Link to PDF

The PDF of this journal article can be found here: Multiple Metamers: Preserving Color Matches under Diverse Illuminants, Burns, Cohen, and Kuznetsov, 1989