RG color space
Encyclopedia
The RG or red-green color space is a color space
that uses only two colors, red
and green
. It is an additive
format, similar to the RGB color model
but without a blue channel. Thus, blue is said to be out of gamut
. This format is not in use today, and was only used on two-color Technicolor and other early color processes for films; by comparison to a full spectrum, its poor color reproduction made it undesirable. The system cannot create white naturally, and many colors are distorted.
Any color containing a blue color component can't be replicated accurately in the RG color space. There is a similar color space called RGK which also has a black channel. 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 RGB
and CMYK
are in widespread use. Until recently, its primary use was in low-cost light-emitting diode
displays, where red and green tended to be far more common than the still nascent blue LED technology, though full-color LEDs with blue have become more common in recent years.
ColorCode 3D, a stereoscopic
color scheme, uses the RG color space to simulate a broad spectrum of color in one eye; the blue portion of the spectrum transmits a black-and-white (black-and-blue) image to the other eye to give depth perception.
family was the Color Graphics Adapter
(CGA), which includes two graphic modes: 320×200 pixels with four colors (two bits per pixel
) and 640×200 pixels black-and-white (one bit per pixel). The card as a whole implemented the "digital RGBI" 16-color space, i.e. each primary color (red green and blue) could be either on or off for a given pixel, and an additional intensity bit would brighten all three primaries if it was turned on for a pixel.
The color mode uses two bits to store red and green 1-bit components for each pixel (that is, colors in the RG color space) while the blue and intensity components were fixed for the entire screen.
This gave four possibilities for each single pixel: background (any one of the 16 colors the system offered, black or blue was most used; however only one background color could be chosen for the entire screen), red, green and yellow, with two possibilities of intensity selectable for the entire screen (except the background): low (darker) and high (lighter). This was known as Fixed palette #2. The Fixed palette #1 adds the blue component to all colors except the background, giving background (usually black was chosen), magenta (red+blue), cyan (green+blue) and white (yellow+blue), with two possible intensities, too.
Color space
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...
that uses only two colors, red
Red
Red is any of a number of similar colors evoked by light consisting predominantly of the longest wavelengths of light discernible by the human eye, in the wavelength range of roughly 630–740 nm. Longer wavelengths than this are called infrared , and cannot be seen by the naked eye...
and green
Green
Green is a color, the perception of which is evoked by light having a spectrum dominated by energy with a wavelength of roughly 520–570 nanometres. In the subtractive color system, it is not a primary color, but is created out of a mixture of yellow and blue, or yellow and cyan; it is considered...
. It is an additive
Additive color
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. Combining one of these additive primary colors with another in equal amounts produces the...
format, similar to the RGB color model
RGB color model
The RGB color model is an additive color model in which red, green, and blue light is added together in various ways to reproduce a broad array of colors...
but without a blue channel. Thus, blue is said to be out of gamut
Gamut
In color reproduction, including computer graphics and photography, the gamut, or color gamut , is a certain complete subset of colors. The most common usage refers to the subset of colors which can be accurately represented in a given circumstance, such as within a given color space or by a...
. This format is not in use today, and was only used on two-color Technicolor and other early color processes for films; by comparison to a full spectrum, its poor color reproduction made it undesirable. The system cannot create white naturally, and many colors are distorted.
Any color containing a blue color component can't be replicated accurately in the RG color space. There is a similar color space called RGK which also has a black channel. Outside of a few low-cost high-volume applications, such as packaging and labelling
Packaging and labelling
Packaging is the science, art, and technology of enclosing or protecting products for distribution, storage, sale, and use. Packaging also refers to the process of design, evaluation, and production of packages. Packaging can be described as a coordinated system of preparing goods for transport,...
, RG and RGK are no longer in use because devices providing larger gamuts such as RGB
RGB color model
The RGB color model is an additive color model in which red, green, and blue light is added together in various ways to reproduce a broad array of colors...
and CMYK
CMYK color model
The CMYK color model is a subtractive color model, used in color printing, and is also used to describe the printing process itself. CMYK refers to the four inks used in some color printing: cyan, magenta, yellow, and key...
are in widespread use. Until recently, its primary use was in low-cost light-emitting diode
Light-emitting diode
A light-emitting diode is a semiconductor light source. LEDs are used as indicator lamps in many devices and are increasingly used for other lighting...
displays, where red and green tended to be far more common than the still nascent blue LED technology, though full-color LEDs with blue have become more common in recent years.
ColorCode 3D, a stereoscopic
Stereoscopy
Stereoscopy refers to a technique for creating or enhancing the illusion of depth in an image by presenting two offset images separately to the left and right eye of the viewer. Both of these 2-D offset images are then combined in the brain to give the perception of 3-D depth...
color scheme, uses the RG color space to simulate a broad spectrum of color in one eye; the blue portion of the spectrum transmits a black-and-white (black-and-blue) image to the other eye to give depth perception.
Color Graphics Adapter (CGA)
The first color capable video card for the IBM PCIBM PC
The IBM Personal Computer, commonly known as the IBM PC, is the original version and progenitor of the IBM PC compatible hardware platform. It is IBM model number 5150, and was introduced on August 12, 1981...
family was the Color Graphics Adapter
Color Graphics Adapter
The Color Graphics Adapter , originally also called the Color/Graphics Adapter or IBM Color/Graphics Monitor Adapter, introduced in 1981, was IBM's first color graphics card, and the first color computer display standard for the IBM PC....
(CGA), which includes two graphic modes: 320×200 pixels with four colors (two bits per pixel
Pixel
In digital imaging, a pixel, or pel, is a single point in a raster image, or the smallest addressable screen element in a display device; it is the smallest unit of picture that can be represented or controlled....
) and 640×200 pixels black-and-white (one bit per pixel). The card as a whole implemented the "digital RGBI" 16-color space, i.e. each primary color (red green and blue) could be either on or off for a given pixel, and an additional intensity bit would brighten all three primaries if it was turned on for a pixel.
The color mode uses two bits to store red and green 1-bit components for each pixel (that is, colors in the RG color space) while the blue and intensity components were fixed for the entire screen.
This gave four possibilities for each single pixel: background (any one of the 16 colors the system offered, black or blue was most used; however only one background color could be chosen for the entire screen), red, green and yellow, with two possibilities of intensity selectable for the entire screen (except the background): low (darker) and high (lighter). This was known as Fixed palette #2. The Fixed palette #1 adds the blue component to all colors except the background, giving background (usually black was chosen), magenta (red+blue), cyan (green+blue) and white (yellow+blue), with two possible intensities, too.