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Color vision is useful because it helps us identify objects and their properties. We choose to eat a yellow banana rather than a green banana because color informs us about ripeness. Yet the information about an object conveyed by the spectral properties of light reflected from it is ambiguous: the reflected light depends both on the object's surface reflectance and on the illuminant. Because surface properties and illuminant are confounded in the light reaching the eye, color can only be useful only if visual processing separates these two physical effects to produce a psychological representation that depends primarily on object surface properties. To the extent that the visual system does so, it is referred to as color constant. Much of the research in my lab is directed at understanding the extent to which humans vision exhibits color constancy and how this constancy comes about.
David Brainard: 16 July, 2006