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Managing Color With ColorSync


Color Perception

The eye contains two types of receptors, cones and rods. The rods measure illumination and are not sensitive to color. The cones contain a chemical known as Rhodopsin, which is variously sensitive to reds and blues and has a default sensitivity to yellow. The color the eyes see in an object depends on how much red, green, and blue light is reflected to a small region in the back of the eye called the fovea, which contains a great majority of the cones present in the eye. Black is perceived when no light is reflected to the eye.

Even the conditions in which color is viewed greatly affect the perception of color. The light source and environment must be standardized for accurate viewing. When viewing colors, people in the graphic arts industry, for example, avoid fluorescent and tungsten lighting, use a particular illuminant that is similar to daylight, and proof against a neutral gray surface.

Color images frequently contain hundreds of distinctly different colors. To reproduce such images on a color peripheral device is impractical. However, a very broad range of colors can be visually matched by a mixture of three "primary" lights. This allows colors to be reproduced on a display by a mixture of red, green, and blue lights (the primary colors of the additive color space shown in Figure 1-4 ) or on a printer by a mixture of cyan, magenta, and yellow inks or pigments (the primary colors of the subtractive color space shown in Figure 1-4 ). Black is printed to increase contrast and make up for the deficiency of the inks (making black the key, or K, in CMYK).


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