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The CIE 1931 color spaces are the first defined quantitative links between physical pure colors (i.e. wavelengths) in the electromagnetic visible spectrum, and physiological perceived colors in human color vision. The mathematical relationships that define these color spaces are essential tools for color management. They allow one to translate different physical responses to visible radiation in color inks, illuminated displays, and recording devices such as digital cameras into a universal human color vision response. CIE 1931 RGB color space and CIE 1931 XYZ color space were created by the International Commission on Illumination (CIE) in 1931. The CIE XYZ color space was derived from a series of experiments done in the late 1920s by William David Wright and John Guild. Their experimental results were combined into the specification of the CIE RGB color space, from which the CIE XYZ color space was derived. ==Tristimulus values== The human eye with normal vision has three kinds of cone cells, which sense light, with spectral sensitivity peaks in short (''S'', 420–440 nm), middle (''M'', 530–540 nm), and long (''L'', 560–580 nm) wavelengths. These cone cells underlie human color perception under medium- and high-brightness conditions (in very dim light, color vision diminishes, and the low-brightness, monochromatic "night-vision" receptors, called rod cells, take over). Thus, three parameters, corresponding to levels of stimulus of the three types of cone cells, can in principle describe any color sensation. Weighting a total light power spectrum by the individual spectral sensitivities of the three types of cone cells gives three effective stimulus values; these three values make up a tristimulus specification of the objective color of the light spectrum. The three parameters, noted S, M, and L, can be indicated using a 3-dimension space, called LMS color space, which is one of many color spaces which have been devised to help quantify human color vision. A color space maps a range of physically produced colors (from mixed light, pigments, etc.) to an objective description of color sensations registered in the eye, typically in terms of tristimulus values, but not usually in the LMS space defined by the cone spectral sensitivities. The tristimulus values associated with a color space can be conceptualized as amounts of three primary colors in a tri-chromatic additive color model. In some color spaces, including LMS and XYZ spaces, the primary colors used are not real colors, in the sense that they cannot be generated with any light spectrum. The CIE XYZ color space encompasses all color sensations that an average person can experience. That is why CIE XYZ (Tristimulus values) is a device invariant color representation.〔() Tristimulus Value of Color : Device Independent Color Representation〕 It serves as a standard reference against which many other color spaces are defined. A set of color-matching functions, like the spectral sensitivity curves of the LMS space but not restricted to be nonnegative sensitivities, associates physically produced light spectra with specific tristimulus values. Consider two light sources made up of different mixtures of various wavelengths. Such light sources may appear to be the same color; this effect is called metamerism. Such light sources have the same apparent color to an observer when they produce the same tristimulus values, no matter what the spectral power distributions of the sources are. All wavelengths stimulate at least two types of cone cell, because the spectral sensitivity curves of the three types of cone cells overlap (more easily seen when spectral sensitivity curves are plotted in log scale). Certain tristimulus values are thus physically impossible (for instance LMS tristimulus values that are non-zero for one component, and zeros for the others). And LMS tristimulus values for pure spectral colors would, in any normal trichromatic additive color space (e.g. RGB color spaces), imply negative values for at least one of the three primaries, since the chromaticity would be outside the color triangle defined by the primary colors. To avoid these negative RGB values, and to have one component that describes the perceived brightness, "imaginary" primary colors and corresponding color-matching functions have been formulated. The resulting tristimulus values are defined by the CIE 1931 color space, in which they are denoted ''X'', ''Y'', and ''Z''.〔. See pgs. 39–46 for the basis in human eye physiology of three-component color models, and 54–57 for chromaticity coordinates.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「CIE 1931 color space」の詳細全文を読む スポンサード リンク
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