Color vision

The Color vision allows boundaries to be seen among areas which have equavalent brightness, provided the spectrum of wavelengths they reflect is distinct. The spectrum of light reflected from an object based on the wavelength composition of the illuminating light and the reflectance of the surface, but the color vision is not merely a matter of measuring all the wavelengths in the reflected light.

The Color vision needs a minimum of two types of receptor which respond over various wavelength ranges. This is a dichromatic color vision and is the situation for all mammals except the old world monkeys, apes, & humans. With two receptors the visual system can assign two brightness values for each pixel of the visual field. By comparing these values, the colors may be perceived. For illustration, when a pixel reflects more short-wavelength light it will look brighter to a short-wavelength receptor than a long-wavelength receptor, and will be seen as blue. When a pixel reflects more long-wavelength light it will be seen as red. In the situation that a pixel reflects equivalent amounts of short- and long-wavelength light it will look monochrome, either white or shades of gray depending on the intensity of the light.

The Human color vision is trichromatic as the eye has three populations of receptors (cones) which can function in daylight, each sensitive to various ranges of wavelengths. The three kinds of cones have maximum absorptions equivalent approximately to the violet, green, and yellow light. The wavelength of the light does not affect the character of the response of the cone. The given cone simply has a higher probability of absorbing a photon that is close to its peak wavelength. This means that the visual system has no way of detecting the absolute wavelength composition of any light. The trichromatic visual system abstract three brightness values for an object and the comparisons of these values determine its color.

The Color vision has numerous remarkable properties. It displays color constancy. An object can be viewed under a diversity of light sources with various spectral compositions, for illustration, neon lighting, sunlight, or tungsten light, and look to be the similar color even though the wavelengths of light it reflects in each situation will be quite different. While some colors in similar pixel of visual space perceptually mix to generate other color categories (example, blue and green mix to provide cyan) complementary colors (example, red and green) do not perceptually mix; reddish-green colors are never seen. This is perceptual cancellation. The Simultaneous color contrast is the perceptual facilitation of balancing colors which occurs across the boundaries. For illustration a gray disc within a red background appears little green whereas a gray disc in a green background looks little red. Each of these features can be accounted for in terms of the visual system physiology.