3-bit RGB palette

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The eight possible colors using 3-bit RGB.

The 3-bit RGB palette is a digital color palette consisting of eight colors: black, red, green, yellow, blue, magenta, cyan, and white. The eight colors are made from three primaries (red, green, and blue), each given two intensities (off or on). In binary, each primary color is represented by a bit, and the value of the bit is the color's intensity. So, for the color red, the red bit would be on, and the blue and green bits would be off. For cyan, the green and blue bits would be on, and the red bit would be off. Black is all three bits off, while white is all three bits on.

Color Order

Although the same eight colors are used in every 3-bit RGB color palette, the order in which they're presented is different on various platforms. From a binary standpoint, there are six possible orders, RGB, RBG, GRB, GBR, BRG, and BGR, however, only two were ever common: RGB in European countries and BRG in Japan.

European Standard

From what I've been able to find, this is the oldest 3-bit RGB color palette used in computers. It was first standardized by the European Computer Manufacturers Association in 1976 and was designed for transmitting information across color TV signals. The first European color teletext machines used it, and, when European companies started developing home computers, it was only natural for them to follow the existing standard.

Color
Name Black Red Green Yellow Blue Magenta Cyan White
Binary 000 001 010 011 100 101 110 111
RGB #000000 #FF0000 #00FF00 #FFFF00 #0000FF #FF00FF #00FFFF #FFFFFF

Japanese Standard

When Japan first introduced their color home computers with the NEC-8000 series in 1979, they used the order BRG. They probably were not familiar with the existing European standard since it was still only used by European broadcasters and wasn't used in a European home computer until 1981. Each subsequent NEC computer model maintained the color order for backward compatibility, and the later Sharp X1 and FM-8 home computers followed their lead.

Two European platforms did use this color scheme, but neither based it on the Japanese standard. The SECAM version of the Atari 2600 uses it due to an artifact of how its display chip produced color, and the Sinclair QL used this order to match the first half of the 16-color palette of its predecessor, the ZX Spectrum.

Color
Name Black Blue Red Magenta Green Cyan Yellow White
Binary 000 001 010 011 100 101 110 111
RGB #000000 #0000FF #FF0000 #FF00FF #00FF00 #00FFFF #FFFF00 #FFFFFF

Colour Maximite

The Colour Maximite is a hobby computer developed in 2012. Though of European design, it breaks with tradition and uses the order BGR.

Color
Name Black Blue Green Cyan Red Magenta Yellow White
Binary 000 001 010 011 100 101 110 111
RGB #000000 #0000FF #FF0000 #FF00FF #00FF00 #00FFFF #FFFF00 #FFFFFF

Platforms

The following platforms use a 3-bit RGB palette:

Platform Released Palette Notes
Atari 2600 1982-??-?? Japanese SECAM model only.
BBC Micro 1981-12-01 European Used in modes 2, 7, 8 (lo-res), 9 (lo-res), and 13.
Casio PV-1000 1983-10-?? Japanese
Colour Maximite 2012-09-?? Maximite Mode 3 and 4. Uses a custom palette.
ECMA-48 1976-03-?? European A European Computer Manufacturers Association formatting standard for text terminals.
Electron 1983-08-25 European Mode 2.
Fujitsu FM-7 1982-11-?? Japanese Including FM-7, FM New 7, and FM-77 before FM-77 AV
Fujitsu FM-8 1981-05-?? Japanese
Oric 1982-09-01 European Including the Oric 1, Atmos, Stratos, and Telestrat
NEC PC-8000 1979-05-09 Japanese
NEC PC-8800 1981-11-?? Japanese When in 640×200 resolution. Up to the MkII
NEC PC-9800 1982-10-?? Japanese Original model with 8086 CPU when in 640×200 resolution.
Sharp MZ 700 1982-??-?? Japanese
Sharp X1 1982-??-?? Japanese All models before the X1 Turbo Z
Sinclair QL 1984-01-12 Japanese When in 256×256 resolution mode. Although a European computer, it strangely adopted the Japanese standard.
Videotex 1979-??-?? European A text formatting standard. Described in the C1 control codes.
World System Teletext 1976-09-?? European A text formatting standard. Used in levels 1 and 1.5.

Dithering

When using 50% dithering, 8 colors becomes 36.

Eight colors isn't enough to produce complex art, however, good graphic artists took advantage of dithering to simulate additional colors. Dithering produces better results on higher display resolutions, and the Japanese platforms usually had higher resolutions to accommodate their more complex writing system, so their graphics tended to look better than the European platforms. The image to the right shows how, by dithering between two colors at 50% each, the palette of eight colors expands to 36 colors (although some are very similar looking).

And graphic designers didn't have to limit themselves to 50% dithering. The image below shows every combination using all 17-steps of ordered dithering using a 4x4 matrix. Keep in mind that most 8-bit computers, even the higher-resolution Japanese models, usually didn't exceed 640x200 resolution, so the dithering wouldn't blend as well as on a modern monitor.

Click to expand.

While ordered dithering can simulate plenty of additional colors, graphic artists rarely limited themselves to it. The best artists of the time used custom dithering patterns like striping, dithering three or more colors, and various other visual tricks to best manipulate the limited colors to make the viewer perceive them as more. See the screenshots below for examples of custom dithering patterns.

Media

Despite the low amount of colors, plenty of graphic media has been made using the 3-bit RGB palette which takes advantage of complex dithering patterns. Even with only eight colors, these artists were able to produce impressive results. Here are some examples:

Links

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