RGB color model

The RGB colour model is an additive system that combines red, green, and blue light in varying intensities to produce a broad spectrum of colours. Widely used across electronic imaging—from digital cameras and scanners to televisions, computer monitors, and LED displays—RGB underlies most modern visual technologies. Its origins lie in nineteenth-century theories of human colour perception, and its practical development has paralleled advances in photography, television, and computing.
RGB is a device-dependent model, meaning that identical RGB values may appear differently on different displays because of variations in phosphors, dyes, illumination and ageing. Colour management systems are therefore needed to maintain consistent colour appearance across devices.

Additive Colour Principles

In the RGB system, colour is produced by superimposing three beams of red, green and blue light. Each beam represents a component of the final colour and can vary continuously from zero to full intensity. Because RGB is additive, the intensities of emitted or reflected light are combined wavelength by wavelength, and the resulting optical spectrum determines the perceived colour.

• When all three components are at zero intensity, the result is black.
• When they are at full equal intensity, the mixture forms white whose quality depends on the primaries and the system’s white point.
• Equal non-zero intensities give shades of grey, while differing intensities create coloured hues.

The hue is dominated by the component with the greatest intensity: a predominance of red yields a reddish hue, strong green produces greenish tones, and so on. When two primaries are equally strong, a secondary colour is produced: cyan (green + blue), magenta (blue + red), or yellow (red + green). These secondary colours act as complements to the primaries.
RGB stands in contrast to subtractive colour models, particularly CMY and CMYK, which apply to inks, dyes and pigments. Subtractive systems filter white light, absorbing various spectral components. Their colour mixing is fundamentally different: overlapping dyes remove wavelengths, and mixing cyan, magenta and yellow ideally produces black.

Device-Dependent Nature and Applications

RGB is most effective for technologies that emit or modulate light directly. Typical input devices include digital cameras, professional video systems and image scanners. Output devices include cathode-ray tube televisions, LCD and OLED displays, projection systems, LED screens, and mobile devices.
Printers, however, use subtractive CMYK inks and cannot reproduce colours directly in RGB. Conversion between RGB and CMYK is essential in digital printing workflows.
Because devices vary in their colour primaries and gamma characteristics, RGB values do not specify absolute colours unless they are linked to a calibrated colour space. Well-defined RGB spaces such as sRGB or Adobe RGB include precise chromaticity coordinates and white points, converting the relative RGB model into an absolute standard.

Physiological Basis and Selection of Primaries

The RGB model derives from the trichromatic nature of human colour vision. The human retina contains three types of cone cells sensitive to long (L), medium (M) and short (S) wavelengths, peaking near 570 nm, 540 nm and 440 nm respectively. Differences in stimulation of these cones are interpreted by the brain as variations in hue.
Good RGB primaries are chosen to maximise the separation of cone responses to create a wide colour triangle in chromaticity space. Colours lying outside a given triangle cannot be reproduced by any positive mixture of that system’s primaries.
When the chromaticities of primaries and the white point are specified, the RGB model becomes a defined colour space. The commonly used sRGB standard, designed for digital imaging, uses primaries aligned with the CIE Standard Illuminant D65.

Historical Development of RGB Theory

The scientific foundation of RGB rests on the Young–Helmholtz theory of trichromacy, developed through the nineteenth century by Thomas Young and Hermann von Helmholtz. Their work explained colour perception with three receptor types and inspired James Clerk Maxwell’s colour triangle, which formalised additive mixing.
Early photographic experiments using RGB filters began in the 1860s. Maxwell produced one of the first colour photographs by projecting three monochrome plates taken through red, green and blue filters. Variants of additive RGB systems, including orange-green-violet screen plates, were later used in Autochrome Lumière and other early twentieth-century colour techniques. Some pioneers, such as Sergey Prokudin-Gorsky, produced rich colour images using three filtered exposures and projection-based recombination.
Although additive capture methods persisted into the mid-twentieth century, print reproduction employed subtractive CMYK processes using complementary colour plates derived from RGB exposures.

RGB in Television Technologies

Patents for mechanically scanned colour systems date from the late nineteenth century. John Logie Baird demonstrated the first RGB colour transmission in 1928 and the first colour broadcast in 1938, using mechanically rotating colour wheels for scanning and display.
Developments in electronic colour television continued into the 1940s. The CBS field-sequential system, which used high-speed RGB colour wheels, provided early demonstrations of broadcast colour. The breakthrough for mass-market electronic displays came with shadow mask CRT technology, patented by Werner Flechsig in 1938, which used triads of red, green and blue phosphors excited by electron beams.
Subsequent decades saw the emergence of LCD, plasma, OLED and quantum-dot displays, each implementing RGB primaries through different physical mechanisms but retaining the additive colour principle.

RGB in Early Personal Computing

Personal computers of the late 1970s and early 1980s integrated RGB-based video systems to varying degrees. Some systems, such as the Apple II and VIC-20, used composite video outputs. Others, including the Commodore 64 and Atari 8-bit family, employed S-Video-derived formats with separate luminance and chrominance signals. Later IBM-based systems adopted dedicated RGB monitor standards, refining colour output fidelity for home computing and graphics applications.