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From Light to Color

Before describing the major color perception phenomena, it is useful to describe in some detail what is known of the apparatus of human color vision. Light enters our body in the eyes. The human eye (a schematic cross-section is shown in Fig. 3.1) is a structure of approximate egg shape, held in place and moved by six muscles. It has a generic resemblance to a camera. Its shell, called the sclera, is made of dense white fibrous material, except where the transparent cornea is located through which light enters the eye. The eye is filled with a transparent fluid named vitreous humor. Suspended in the vitreous humor and held in place by a system of muscle tissue is an elastic lens. Its shape is controlled by unconscious muscle action so that the lens focuses an image of what is in front of the eye onto the inner back wall of the eye. When looking up from the pages of a book and gazing at the outside landscape, this system makes the necessary lens adjustments to project a continuously sharp picture of the outside world onto the inside back wall (complicated somewhat if the subject wears correcting glasses). Information from the surrounding world contained in streams of photons passes through the cornea, the lens, and the vitreous humor concentrated toward a slight indentation, the fovea, in the back wall of the retinal layer. Photons are focused on that spot. ...

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