A colour model in which Red, Green, and Blue light are added together in various ways to reproduce a broad array of colours. Computer monitors and TVs emit colour as RGB light. Although all colours of the visible spectrum can be produced by merging red, green and blue light, monitors are capable of displaying only a limited gamut of the visible spectrum.
Typical RGB input devices are colour TV and video cameras, image scanners, and digital cameras. Typical RGB output devices are TV sets (CRT, LCD, plasma, etc.), computer and mobile phone displays, and video projectors. Colour printers, on the other hand, are not RGB devices, but subtractive colour devices - typically CMYK colour model where secondary colours (cyan, magenta and yellow) are used to simulate the colours required, with black (K) added to help CMY reproduce rich blacks and shadows.