Gamut

The gamut of a colour space (or a display device) is the complete set of colours it can represent. Gamuts are usually visualised as triangles on the CIE 1931 chromaticity diagram — the corners are the red, green, and blue primaries of the space; the triangle’s interior is everything that can be produced by mixing them.

Gamut sizes, smallest to largest, for the spaces in active use:

• sRGB — the web default, 1996. Smallest of the modern gamuts.
• Adobe RGB — 1998. ~35% larger than sRGB, especially in the green-cyan region.
• Display P3 — Apple, 2015. ~25% larger than sRGB, more saturated reds and greens.
• Rec.2020 — ITU-R BT.2020, 2012. For 4K/8K HDR video. Substantially larger than P3.
• ProPhoto RGB — Kodak, 2002. Even larger; includes some colours outside the visible spectrum.

Colours that fall outside a target gamut are called “out of gamut.” Converting to the target either clips them to the nearest in-gamut colour (relative colorimetric) or shifts the whole image to preserve relationships (perceptual). The choice matters for print workflows; see our RGB vs CMYK comparison.