ABSTRACT
Vision has been defined as the process of discovering from images what is present in the world and where it is. This requires the brain to use a two-dimensional shifting pattern of light intensity values on the two retinae to form a representation of the form of an object, its color, movement, and position in three-dimensional space. Perceptual constancy is a key property of vision. Visual perception can be invariant over wide differences in the properties of the retinal image. Color vision permits boundaries to be seen between regions that have equal brightness, provided that the spectrum of wavelengths they reflect is different. Human color vision is trichromatic because the eye has three populations of receptors that can function in daylight, each sensitive to a different range of wavelengths. The three types of cones have their maximum absorption corresponding approximately to violet, green and yellow light.
