Metameric color stimuli, fundamental metamers, and Wyszecki's metameric blacks

In 1953, Wyszecki described radiometric functions as composed of two components--a fundamental color-stimulus function and a metameric black function. The present paper discusses procedures for accomplishing the decomposition or resolution of any visual stimulus into these components. These methods rest on the fact that the color-stimulus space is a space of three dimensions and the metameric black space is orthogonal to it. Introduced and given specific attention here is the particular procedure wherein the stimulus-energy vector is premultiplied by A(A'A)-1A', A being any matrix of experimentally established color-mixture data with three linearly independent columns (primaries). This computation provides the fundamental metamer (as we shall call it) of the visual stimulus being analyzed. The difference between the stimulus-energy distribution and the fundamental metameric function provides the metameric black function. Examples of both types of functions are given and discussed.