The generic framework of metamerism implies that the number of sensors is smaller than the dimension of the stimulus. The metameric black paradigm was introduced by Wyszecki [Farbe 2, 39 (1953)] and developed by Cohen and Kappauf [Am. J. Psychol. 95, 537 (1982)]. Within a multireceptor and multiprimary scheme, we investigate how far the choice of illumination can isolate a photoreceptor response. The spectral profiles of the fundamental metamers that correspond to a collection of (x,y) values over the chromaticity diagram are shown. When the luminance is set at a fixed value, the relative excitation of the melanopsin cells and of the rods elicited by the fundamental metamers varies over the chromaticity diagram. The range of excitation of the melanopsin cells and of the rods that could be achieved at a given chromaticity, by manipulating the metameric black content, is examined. When only the melanopsin excitation is manipulated, the range of melanopsin excitation that can be achieved is rather limited. On the chromaticity diagram, the largest range of variation of the rods and the melanopsin cells excitation is obtained for (x,y) chromaticity coordinates near (1/3,1/3). Extension of Cohen's procedure to rod and cone metamers is proposed. The higher the number of spectral bands, the wider the choice of metameric lights.
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