The RG or red–green color space is a color space that uses only two colors: red and green. The format is not in use today, and was used only on two-color Technicolor and other early color processes for films. It was used as a additive format (ex: Kinemacolor, Prizma, Technicolor I, Raycol, etc.), similar to the RGB color model but without a blue channel, or as a subtractive format (Brewster Color I, Kodachrome I, Prizma II, Technicolor II, etc.).
By comparison with a full spectrum, its poor color reproduction made it undesirable. The system cannot create white naturally, and many colors are distorted. No color containing a blue color component can be replicated accurately in the RG color space. Thus, blue is said to be out of gamut.
A similar color space, called RGK, 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 in which red and green tended to be far more common than the still nascent blue LED technology, but full-color LEDs with blue have become more common in recent years.
ColorCode 3-D, 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.
|Additive RG||Additive RG color palette|