Color Vision

Light has several independent properties, including its energy and its wavelength or frequency of vibration. Color vision takes advantage of both of these properties, allowing us to detect objects and navigate in the external world. Wavelength and energy contrasts vary independently in a visual image and therefore require different neural circuits for their analysis. The secret of color vision is to understand how the brain distinguishes wavelength from energy contrasts. The addition of wavelength contrasts to energy contrasts greatly increases the potential cues to the visual universe. In addition, energy contrasts depend on both the surface properties of an object and its position relative to its illuminant, sunlight for our past evolutionary history. Positional variations can lead to highlights and shading that can obscure the identity or existence of objects. The wavelength reflectance of an object is relatively independent of such effects and therefore a more reliable identifier. For this reason, wavelength contrast and derivative, color vision, have been important to survival. In man it has added an aesthetic dimension that far exceeds the value for survival in modern society.

Figure 1 shows a colorful Renaissance painting, which has been decomposed into its wavelength (chromatic) and achromatic (black-and-white) contrasts. When these two operations are combined in our brain, the picture is seen in color. Energy contrast leads to the perception of achromatic forms of different brightness (white, gray, or black). Wavelength contrast leads to the perception of forms that have a new dimension (color). Energy contrast provides finer detail than wavelength contrast, but the latter adds a new dimension to vision. The combination of both forms of contrast is what we normally experience as color vision.

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