# Color spaces with RGB primaries

(Redirected from RGB color space)
RGB-Cube

Some forms of color space use color primaries defined via the additive RGB color model.[1] A particular color space that employs RGB primaries for part of its specification is defined by the three chromaticities of the red, green, and blue additive primaries, and can produce any chromaticity that is the 2D triangle defined by those primary colors (ie. excluding transfer function, white point, etc.).[2] The primary colors are specified in terms of their CIE 1931 color space chromaticity coordinates (x,y), linking them to human-visible color.

RGB is an abbreviation for red–green–blue.

## Intuition

Comparison of some RGB and CMYK colour gamuts on a CIE 1931 xy chromaticity diagram

An RGB color can be understood by thinking of it as all possible colors that can be made from three colored lights for red, green, and blue. Imagine, for example, shining three lights together onto a white wall in a dark room: one red light, one green light, and one blue light, each with dimmers. If only the red light is on, the wall will be red. If only the green light is on, the wall will look green. If the red and green lights are on together, the wall will look yellow. Dim the red light and the wall will become more of a yellow-green. Dim the green light instead, and the wall will become more orange. Bringing up the blue light a bit will cause the orange to become less saturated and more whitish. In all, each setting of the three dimmers will produce a different result, either in color or in brightness or both. The set of all possible results is the gamut defined by those particular color lamps. Swap the red lamp for one of a different brand that is slightly more orange, and there will be a slightly different gamut, since the set of all colors that can be produced with the three lights will be changed.

## Applications

A computer LCD display can be thought of as a grid of millions of little red, green, and blue lamps, each with their own dimmers. The gamut of the display will depend on the three colors used for the red, green, and blue lights, their pattern of organisation, and their luminance when on.

Some color spaces defined for this purpose with RGB primaries are sRGB and Adobe RGB (which has a significantly larger gamut). Adobe has recently developed another color space called Adobe Wide Gamut RGB, which is even larger, in detriment to gamut density.

As of 2007, sRGB is by far the most commonly used color space for computer displays. HDTVs use a similar space, commonly called Rec. 709, sharing the sRGB primaries. The sRGB space is considered adequate for most consumer applications. Having all devices use the same color space is convenient in that an image does not need to be converted from one color space to another before being displayed. However, sRGB's limited gamut leaves out many highly saturated colors that can be produced by printers or in film, and thus is not ideal for some high quality applications.

## Specifications with RGB primaries

Some color spaces with RGB primaries
Color space Standard Year Gamut White point Primaries Transfer function parameters
Red Green Blue α β γ δ βδ
a + 1 K₀/φ φ K₀
ISO RGB Limited floating floating
Extended ISO RGB Unlimited (signed)
scRGB IEC 61966-2-2 2003 D65 0.64 0.33 0.30 0.60 0.15 0.06
sRGB IEC 61966-2-1 1990, 1996 CRT 1.055 0.0031308 12/5 12.92 0.04045
HDTV ITU-R BT.709 1999 1.099 0.004 20/9 4.5 0.018
Adobe RGB 98 1998 0.21 0.71 1 0 563/256 1 0
PAL / SECAM EBU 3213-E, ITU-R BT.470/601 (B/G) 1970 0.29 0.60 1 0 14/5 1 0
Apple RGB 0.625 0.34 0.28 0.595 0.155 0.07
NTSC SMPTE RP 145 (C), 170M, 240M 1987 0.63 0.31 1.1115 0.0057 20/9 4 0.0228
NTSC-J 1987 D93
NTSC (FCC) ITU-R BT.470/601 (M) 1953 C 0.67 0.33 0.21 0.71 0.14 0.08 1 0 11/5 1 0
eciRGB ISO 22028-4 1999 (v1), 2007, 2012 Wide D50 1.16 0.008856 3 9.033 0.08
DCI-P3 SMPTE RP 431-2 2011 Theater 0.68 0.32 0.265 0.69 0.15 0.06 1.055 0.0031308 12/5 12.92 0.04045
Display P3 SMPTE EG 432-1 2010 D65
UHDTV ITU-R BT.2020, BT.2100 2012, 2016 0.708 0.292 0.170 0.797 0.131 0.046 1.0993 0.018054 4.5 0.081243
Adobe Wide Gamut RGB D50 0.735 0.265 0.115 0.826 0.157 0.018
RIMM ISO 22028-3 2006, 2012 0.7347 0.2653 0.1596 0.8404 0.0366 0.0001 1.099 0.0018 20/9 5.5 0.099
ROMM RGB, ProPhoto RGB ISO 22028-2 2006, 2013 1 0.001953 9/5 16 0.031248
CIE RGB 1931 E 0.2738 0.7174 0.1666 0.0089
CIE XYZ 1931 Unlimited 1 0 0 1 0 0 1 0 1 1 0