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How much does illuminant color affect unasserted colors?

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Abstract

After adapting to a new illumination, does the light coming from a surface (as opposed to the surface color) appear the same as before the illumination changed? Many answers have been proposed over the past century but all have been unsatisfactory. The hardest measurement problem is to provide a comparison stimulus that is unaffected by the adaptation being tested. My subjects used a mental standard. Under 4000K, 6500K, and 10000K adaptation (the extremes and average of daylight) they produced on a CRT unique hues with a constant saturation (memorized during training). The hardest evaluation problem is how to determine theoretical invariant chromaticity shifts for comparison with the data. Like most previous investigators, I used light sources rather than actual surfaces and illuminants. Using a new technique I determined the chromaticities that surfaces would have under the test illuminants. Using Cohen’s basis vectors, I derived theoretical reflectances that under 6500K would produce the chromaticities that the subject chose as unique hues. The chromaticities of those same reflectances under 4000K and 10000K are theoretical points representing invariant appearance of the light coming from the surfaces. Even for this small range of illuminants there were systematic departures from invariance.

© 1991 Optical Society of America

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