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Term: Color

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Term: Color


Color is one of the most difficult areas in digital imaging to specify, digitally encode, and reproduce, and for the verification that specifications have been met. The primary reason it is so challenging is that color is a perceptual phenomenon and cannot be described in an absolute and objective manner as can many other image qualities.

The manifestation of colors begins through light striking color photo receptors in the eye, each tuned to a different spectral band in the range of approximately 380 to 750 nanometers, although sensitivity is very low at either extreme. Different spectral power distributions can excite the cones in a manner that produce a similar perception of color, causing objects to look the same under one light source but dissimilar under another light source. The phenomenon is referred to as metamerism.

There are both perceptual and environmental aspects which complicate the process. First, individuals differ in the manner their cones respond to spectral frequencies, with different signals being sent to the brain from one individual to another. In extreme cases, individuals are unable to perceive one area of the visual spectrum, or not able to perceive color at all. But the greatest challenge lies in how the brain perceives the stimulus from the cones. This perception can be influenced by surrounding colors and light intensities, context, emotion and object meaning. For example, fire truck red and eggshell white aren't only used as color descriptors, but influence color perception.

To work around the difficulties involved in the variability of perception, the CIE developed models based on average color perception under controlled conditions. These models are used in management of color processes that do not make use of spectral data, which can be objectively measured and is independent of perception. Instruments such as colorimeters generally make use of color perception models, although they are unable to replicate a true perception of color, since as stated above, color is a unique and individual perceptual experience. Devices with the prefix “spectro” generally use spectral data which can be objectively described.

See also:
Color model; Gamut; Spectral power distribution; Metamerism