Color additivity



An additive color model involves light emitted directly from a source or illuminant of some sort. The additive reproduction process usually uses red, green and blue light to produce the other colors. See also RGB color model. Combining one of these additive primary colors with another in equal amounts produces the additive secondary colors cyan, magenta, and yellow. Combining all three primary lights (colors) in equal intensities produces white. Varying the luminosity of each light (color) eventually reveals the full gamut of those three lights (colors). Computer monitors and televisions are the most common application of additive color.

Results obtained when mixing additive colors are often counterintuitive for people accustomed to the more everyday subtractive color system of pigments, dyes, inks and other substances which present color to the eye by reflection rather than emission. For example, in subtractive color systems green is a combination of yellow and blue, in additive color, red + green = yellow and no simple combination will yield green. It should be noted that additive color is a result of the way the eye detects color, and is not a property of light. There is a vast difference between yellow light, with a wavelength of approximately 580 nm, and a mixture of red and green light. However, both stimulate our eyes in a similar manner, so we do not detect that difference. (see eye (cytology), color vision.)





James Clerk Maxwell is credited as being the father of additive color. He had the photographer Thomas Sutton photograph a tartan ribbon three times, first with a red, then green, then blue color filter over the lens. The three images were developed and then projected onto a screen with three different projectors, each equipped with the corresponding red, green, or blue color filter used to take its image. When brought into register, the three images formed a full color image, thus demonstrating the principles of additive color.