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Primary colors are sets of colors that can be combined to make a useful range of colors. For human applications, three primary colors are typically used, since human color vision is usually trichromatic. For ''additive'' combination of colors, as in overlapping projected lights or in electronic visual displays, the primary colors normally used are red, green, and blue. For a ''subtractive'' combination of colors, as in mixing of pigments or dyes for printing, the colors magenta, yellow, and cyan are normally used. However, red, yellow, and blue are commonly used as primaries when painting or drawing.〔 〕 See RGB color model, CMYK color model, and RYB color model for more on these popular sets of primary colors. Any particular choice for a given set of primary colors is derived from the spectral sensitivity of each of the human cone photoreceptors; three colors that fall within each of the sensitivity ranges of each of the human cone cells are red, green , and blue.〔(The Science of Color - Steven K. Shevell, Optical Society of America - Google Books )〕 Other sets of colors can be used, though not all will well-approximate the full range of color perception. For example, an early color photographic process, autochrome, typically used orange, green, and violet primaries. However, unless negative amounts of a color are allowed the gamut will be restricted by the choice of primaries. The combination of any two primary colors creates a secondary color. The most commonly used additive color primaries are the secondary colors of the most commonly used subtractive color primaries, and vice versa. == Biological basis == Primary colors are not a fundamental property of light but are related to the physiological response of the eye to light. Fundamentally, light is a continuous spectrum of the wavelengths that can be detected by the human eye, an infinite-dimensional stimulus space. However, the human eye normally contains only three types of color receptors, called cone cells. Each color receptor responds to different ranges of the color spectrum. Humans and other species with three such types of color receptors are known as trichromats. These species respond to the light stimulus via a three-dimensional sensation, which generally can be modeled as a mixture of three primary colors.〔 Before the nature of colorimetry and visual physiology were well understood, scientists such as Thomas Young, James Clerk Maxwell, and Hermann von Helmholtz expressed various opinions about what should be the three primary colors to describe the three primary color sensations of the eye.〔 〕 Young originally proposed red, green, and violet, and Maxwell changed violet to blue; Helmholtz proposed "a slightly purplish red, a vegetation-green, slightly yellowish (wavelength about 5600 tenth-metres), and an ultramarine-blue (about 4820)".〔 〕 In modern understanding, human cone cells do not correspond precisely to a specific set of primary colors, as each cone type responds to a range of color wavelengths. Species with different numbers of receptor cell types would have color vision requiring a different number of primaries. For example, for species known as tetrachromats, with four different color receptors, one would use four primary colors. Since humans can only see to 380 nanometers (violet), but tetrachromats can see into the ultraviolet to about 300 nanometers, this fourth primary color for tetrachromats is located in the shorter-wavelength range. Many birds and marsupials are tetrachromats, and it has been suggested that some human females are tetrachromats as well,〔Backhaus, Kliegl & Werner ''Color Vision: Perspectives from Different Disciplines'' (De Gruyter, 1998, ISBN 3110161001), pp.115–116, section 5.5.〕〔Pr. Mollon (Cambridge University), Pr. Jordan (Newcastle university) "Study of women heterozygote for colour difficiency" (Vision Research, 1993)〕 having an extra variant version of the long-wave (L) cone type. The peak response of human color receptors varies, even among individuals with "normal" color vision; in non-human species this polymorphic variation is even greater, and it may well be adaptive. Most placental mammals other than primates have only two types of color receptors and are therefore dichromats; to them, there are only two primary colors. It would be incorrect to assume that the world "looks tinted" to an animal (or human) with anything other than the human standard of three color receptors. To an animal (or human) born that way, the world would look normal to it, but the animal's ability to detect and discriminate colors would be different from that of a human with normal color vision. If a human and an animal both look at a natural color, they see it as natural; however, if both look at a color reproduced via primary colors, such as on a color television screen, the human may see it as matching the natural color, while the animal does not, since the primary colors have been chosen to suit human capabilities. == Additive primaries == Media that combine emitted lights to create the sensation of a range of colors are using the additive color system. Typically, the primary colors used are red, green, and blue.〔 〕 Television and other computer and video displays are a common example of the use of additive primaries and the RGB color model. The exact colors chosen for the primaries are a technological compromise between the available phosphors (including considerations such as cost and power usage) and the need for large color triangle to allow a large gamut of colors. The ITU-R BT.709-5/sRGB primaries are typical. Additive mixing of red and green light produces shades of yellow, orange, or brown.〔"Some Experiments on Color", ''Nature'' 111, 1871, in 〕 Mixing green and blue produces shades of cyan, and mixing red and blue produces shades of purple, including magenta. Mixing nominally equal proportions of the additive primaries results in shades of grey or white; the color space that is generated is called an RGB color space. The CIE 1931 color space defines ''monochromatic'' primary colors with wavelengths of 435.8 nm (violet), 546.1 nm (green) and 700 nm (red). The corners of the color triangle are therefore on the spectral locus, and the triangle is about as big as it can be. No real display device uses such primaries, as the extreme wavelengths used for violet and red result in a very low luminous efficiency. 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「Primary color」の詳細全文を読む スポンサード リンク
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