Color Standards

Color Diagram

To understand what we are talking about, we need some visual representation. Especially for colors. This diagram is the whole scale of colors human eye can see.

spectral_locus — The wavelengths of every monochromatic color (380 to 700 nanometter) on the periphery is called the Spectral Locus.

Here is the 1976’s CIE color diagram (u’v’) which is more accurate than the 1931’s (xy) in terms of representation of visible shade : 2 shades are significantly different and will always have the same gap on the CIE color diagram of 1976.

Pointer’s Gamut

Fully aware of the difficulty of replicating the whole diagram, Pointer started in 1980 by reducing what can really be glimpsed on Earth.

RGB Gamuts

As the screen’s tiles, the camera’s sensors work with 3 primary colors : red, green and blue.

The white triangle is the maximal Gamut RGB. It won’t cover Pointer’s Gamut, nor the whole color diagram.

Unfortunately, technically we couldn’t record and replicate the colors of maximal Gamut RGB. This made its use unadapted. To be able to concretely work, some Gamut were standardized. Here are some examples.(click to enlarge) .

Notes :

The primaries, red, green and blue are not the same is these 3 Gamuts. Be careful because one video file won’t be displaying the same colors depending of the Gamut it is opened/read with. This is a FUNDAMENTAL question.
All the color shades of Rec. 709 Gamut can be found in P3 DCI Gamut and not the other way around. The importance of the working Gamut in the softwares, so it wont restrain the ones for; the rushes. (ACES is the same but at its extreme)

Recouvrement des Gamuts — Gamuts recovery. Clic ➧ Big

You need to understand that the bigger the Gamuts are, the bigger the number of color shades are too .

Illustration schématique des avantages d'un grand Gamut — Schematic diagram of the benefit of a big Gamut

the White Point

There is a fourth significant item on the color diagram: the white dot. Either the color white or any neutral object (in real life). The range of possibilities defines a curve based on the temperature of the surrounding lighting.

Planckian-locus — This curve is also called the Plankian Locus

D65 is the White Dop is usualy used, it corresponds to a 6504K° temperature

the Gamma

Once again, for technogolical and perceptual means, the light won’t be recorded/reproduced in a direct and simple way. Indeed, to obtain that the values recorded in the file to be as close as the perceived light (for example a grey recorded at 50% to appear as a grey at 50% for the eye).

The Gammas are represented by a curve giving the converstion to do before the recording/diffusion.

But some graduation curves are not perfect Gammas. A small portion is linear (a straight line) then a classic Gamma curve.

For practical reasons a perfect Gamma comes close.

Gamma 2.2 : sRGB Simplifié — Gamma 2.2 : sRGB’s simplified Gamma

Gamma 2.4 : Rec 709 et Rec2020 — Gamma 2.35- 2.4 : Rec. 709 & Rec. 2020’s simplified Gamma

Notes :

The bigger the Gamma is, the more the curve is crushed
So be careful, one video file wont display the same light depending on the Gamma it is opened/read with. This is a FUNDAMENTAL question.
Cameras have extrapolated this concept with « Log curves”. We are then talking about “gradation”.
HDR introduced new Gammas fitted to this technology of diffusion.