An RG color model is a dichromatic

color model In color science, a color model is an abstract mathematical model describing the way colors can be represented as tuples of numbers, typically as three or four values or color components. When this model is associated with a precise description ...

represented by red and

green Green is the color between cyan and yellow on the visible spectrum. It is evoked by light which has a dominant wavelength of roughly 495570 nm. In subtractive color systems, used in painting and color printing, it is created by a com ...

primary color Primary colors are colorants or colored lights that can be mixed in varying amounts to produce a gamut of colors. This is the essential method used to create the perception of a broad range of colors in, e.g., electronic displays, color prin ...

s. These can only reproduce a fraction of the colors possible with a

trichromatic Trichromacy or trichromatism is the possession of three independent channels for conveying color information, derived from the three different types of cone cells in the eye. Organisms with trichromacy are called trichromats. The normal expl ...

color space, such as for human

color vision Color vision, a feature of visual perception, is an ability to perceive differences between light composed of different frequencies independently of light intensity. Color perception is a part of the larger visual system and is mediated by a co ...

. The name of the model comes from the initials of the two primary colors: red and green. The model may be either

additive Additive may refer to: Mathematics * Additive function, a function in number theory * Additive map, a function that preserves the addition operation * Additive set-function see Sigma additivity * Additive category, a preadditive category with fin ...

or subtractive. It was used to display 3D images using anaglyphs since the 1850s. Despite its shortcomings in

color reproduction Color reproduction is an aspect of color science concerned with producing light spectra that evoke a desired color, either through additive (light emitting) or subtractive (surface color) models. It converts physical correlates of color percep ...

, the RG model was used in early color processes for films from 1906 to 1929 ( Kinemacolor, Prizma,

Technicolor Technicolor is a family of Color motion picture film, color motion picture processes. The first version, Process 1, was introduced in 1916, and improved versions followed over several decades. Definitive Technicolor movies using three black-and ...

, Brewster Color, Kodachrome I and Raycol).

Additive RG

The

RG color model uses red and green primaries. It was used in several processes during the early innovations of color photography, including Kinemacolor, Prizma,

I, and Raycol. Redgreen

The primaries are added together in varying proportions to reproduce a linear gamut of

color Color (or colour in English in the Commonwealth of Nations, Commonwealth English; American and British English spelling differences#-our, -or, see spelling differences) is the visual perception based on the electromagnetic spectrum. Though co ...

s, which can reproduce only a fraction of the colors possible with a

color space. The appearance of the color gamut changes depending on the primary colors chosen. When the primaries are

complementary colors Complementary colors are pairs of colors which, when combined or mixed, cancel each other out (lose chroma) by producing a grayscale color like white or black. When placed next to each other, they create the strongest contrast for those two ...

(e.g. red and cyan), then an equal mixture of the primaries will yield a neutral color (gray or white). However, since red and green are ''not'' complementary colors, an equal mixture of these primaries will yield yellow, and a neutral color cannot be reproduced by the color space. Until recently, its primary use was in low-cost

LED A light-emitting diode (LED) is a semiconductor device that emits light when current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy in the form of photons. The color of the light (corresp ...

displays in which red and green LEDs were more common and cheaper than the still nascent blue LED technology. However, this preference no longer applies to modern devices. In modern applications, the red and green primaries are equal to the primaries used in typical RGB color spaces. In this case, the RG color model can be achieved by disabling the blue light source.

Subtractive RG

The subtractive RG color model uses red and green filters for film exposure, but complementary cyan-green (for red) and orange-red (for green) for the developed prints. This allows the generation of white, although the color model cannot achieve black, regardless of the primaries chosen. It was used in several processes during the early innovations of color photography, including on Brewster Color I, Kodachrome I, Prizma II, and

II.Kalmus, Herbert. "Technicolor Adventures in Cinemaland", ''Journal of the Society of Motion Picture Engineers'', December 1938

Subtractive RGK

A similar color model, called RGK adds a black channel, which allows for the reproduction of black and other dark shades. However, it does not allow the reproduction of neutral colors (gray/white) because the primaries are not complementary. Outside of a few low-cost high-volume applications, such as packaging and labelling, RG and RGK are no longer in use because devices providing larger gamuts such as

CMYK The CMYK color model (also known as process color, or four color) is a subtractive color model, based on the CMY color model, used in color printing, and is also used to describe the printing process itself. The abbreviation ''CMYK'' refers ...

are in widespread use.

Anaglyph 3D

In 1858, in France, delivered a report to l'Académie des sciences describing how to project three-dimensional magic lantern slide shows using red and green filters to an audience wearing red and green goggles. Subsequently he was chronicled as being responsible for the first realisation of 3D images using anaglyphs.

References

External links