Color constancy
how humans perceive color
Color constancy is a feature of the human color perception system which ensures that the perceived color of objects remains relatively constant under varying illumination conditions. A green apple for instance looks green at midday, when the main illumination is white sunlight, and also at sunset, when the main illumination is red. This helps with object identification. It is an example of subjective constancy.
History
Ibn al-Haytham gave an early explanation of color constancy by observing that the light reflected from an object is modified by the object's color. He explained that the quality of the light and the color of the object are mixed, and the visual system separates light and color. He writes:Again the light does not travel from the colored object to the eye unaccompanied by the color, nor does the form of the color pass from the colored object to the eye unaccompanied by the light. Neither the form of the light nor that of the color existing in the colored object can pass except as mingled together and the last sentient can only perceive them as mingled together. Nevertheless, the sentient perceives that the visible object is luminous and that the light seen in the object is other than the color and that these are two properties. Monge (1789), Young (1807), von Helmholtz (1867), Hering (1920), and von Kries (1902, 1905), as well as subsequent researchers Helson and Jeffers (1940), Judd (1940), and Land and McCann (1971), have all made significant contributions to the investigation of colour constancy.
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