RG color models

Template:Short description An RG color model is a dichromatic color model represented by red and green primary colors. These can only reproduce a fraction of the colors possible with a trichromatic color space, such as for human color vision.

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

It was used to display 3D images using anaglyphs since the 1850s.<ref name=":1" /> Despite its shortcomings in color reproduction, the RG model was used in early color processes for films from 1906 to 1929 (Kinemacolor, Prizma, Technicolor, Brewster Color, Kodachrome I and Raycol).<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>Template:Cite journal</ref>

Additive RG

The additive RG color model uses red and green primaries. It was used in several processes during the early innovations of color photography, including Kinemacolor,<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Prizma, Technicolor I,<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>Cinematographic Multiplex Projection, &c. U.S. Patent No. 1,391,029, filed February 20, 1917.</ref><ref>"Moving Pictures in Color", The New York Times, February 22, 1917, p. 9.</ref><ref>Template:Cite news</ref> and Raycol.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

File:Redgreen.png

Gamut of an additive RG color model

The primaries are added together in varying proportions to reproduce a linear gamut of colors, which can reproduce only a fraction of the colors possible with a trichromatic color space.

The appearance of the color gamut changes depending on the primary colors chosen. When the primaries are complementary colors (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 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.Template:Cn 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,<ref name="Silent Cinema">Template:Cite book</ref><ref name="Way">Template:Cite bookTemplate:Dead link</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Kodachrome I,<ref>Capstaff, a former portrait photographer and physics and engineering student had already worked on colour photography before he joined C.K. Mees and other former Wratten and Wainright employees in their move to Rochester in 1912–1913 after Eastman had bought that company to persuade Mees to come and work for him.</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Prizma II,<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> and Technicolor II.<ref name=":0">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>"The First Successful Color Movie", Popular Science, Feb. 1923, p. 59.</ref><ref name="auto">"Kalmus, Herbert. "Technicolor Adventures in Cinemaland", Journal of the Society of Motion Picture Engineers, December 1938"</ref>

Subtractive RGK

File:Venn diagram for subtractive RG color.svg

The subtractive RGK color model showing the primary colors, but where the mixture is obfuscated by the black channel.

A similar color model, called RGK adds a black channel, which allows for the reproduction of black and other dark shades.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> 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 are in widespread use.

Anaglyph 3D

{{#invoke:Labelled list hatnote|labelledList|Main article|Main articles|Main page|Main pages}} In 1858, in France, Template:Interlanguage link 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.<ref name=":1">Template:Cite news</ref> Subsequently he was chronicled as being responsible for the first realisation of 3D images using anaglyphs.<ref>Template:Cite news</ref>

See also

• List of monochrome and RGB color formats
• List of motion picture film formats
• List of color film systems
• rg chromaticity
• Anaglyphic color channels

External links

• Even Proportional Color Triangle
• Cinematographic Multiplex Projection, &c. U.S. Patent No. 1,391,029, filed Feb. 20, 1917.
• "Moving Pictures in Color", The New York Times, February 22, 1917, p. 9.
• The First Successful Color Movie", Popular Science, Feb. 1923, p. 59.
• filmmakeriq.com, The History and Science of Color Film: From Isaac Newton to the Coen Brothers