Talk:Rec. 2020

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Coverage of 1932 Standards[edit]

I removed a line stating rec2020 coverage of CIE 1932 color space as well as adobe and rec709. These figures referred to a SID paper, which in turn refrenced Cambridge University Press, Cambridge, 1932. So if the figures are to be used they should cite the original article. I could not access a copy of the original article and based on my calculations the numbers given were incorrect. — Preceding unsigned comment added by 146.115.5.122 (talk) 14:01, 11 December 2015 (UTC)[reply]

The Cambridge paper from 1932 was about the CIE 1931 color space. As for the calculations they are referenced and are from an NHK paper that was presented at a SMPTE conference. --GrandDrake (talk) 06:15, 13 December 2015 (UTC)[reply]

Rec. 2020 color space[edit]

The color space is the primary colors and the white point. There are several transfer functions that can be used with the Rec. 2020 color space. --GrandDrake (talk) 03:59, 5 April 2016 (UTC)[reply]

The color space could be defined by the chromaticity coordinates of the primaries, the white point, and the electro-optical conversion function, but that does not in any way elevate the 1931 XYZ chromaticity diagram (which is 2 dimensional) to a color space (which has three dimensions). The diagram at the top of the page as of this date is not of a color space, it is a chromaticity diagram. A dimension is missing for it the diagram to be of a color space; it is merely a chromaticity diagram. Lovibond (talk) 23:07, 5 April 2016 (UTC)[reply]

Color space has been defined by the primary colors and white point while the transfer function can vary and scRGB even has a dynamic range that changes depending on the bit depth. The Rec. 2020 color space can be used with the Rec. 2020 transfer function, SMPTE ST 2084, and Hybrid Log-Gamma. Also color spaces such as CIE 1931 color space, CIE 1964 color space, and Lab color space don't define a transfer function. Also there are color spaces that define a transfer function but don't define a brightness. --GrandDrake (talk) 00:02, 6 April 2016 (UTC)[reply]

None of your statement addresses the fact that the CIE 1931 chromaticity space is not a color space. The figure near the top of the article is in chromaticity space, not color space.

The CIE 1931 color space does indeed include what you refer to as a transfer function, though implicitly. It is radiometrically linear. The CIE 1964 U* V* W* color space likewise has a transfer function, based on Reilly's cube root approximation. The CIE 1976 color spaces CIELAB and CIELUV both have as their transfer function a slight modification of the cube root formula used in the 1964 U* V* W* color space. Nevertheless, none of this bears on the fact that the figure is in chromaticity space, not color space. Accordingly, your most recent edit restored a factual inaccuracy that had been corrected, and it therefore should be reverted. Lovibond (talk) 14:04, 6 April 2016 (UTC)[reply]

So what is the fixed brightness range for CIE 1931 color space, CIE 1964 color space, and Lab color space? Many color spaces don't have a fixed brightness range which is why they are shown with a 2D diagram. Also to support HDR by the end of the year Rec. 2020 will have three transfer functions. --GrandDrake (talk) 02:51, 8 April 2016 (UTC)[reply]

Irrelevant. As I pointed out earlier, this does not make the (x, y) chromaticity diagram into a color space. Do you actually believe the (x, y) chromaticity diagram is a color space? Lovibond (talk) 02:52, 9 April 2016 (UTC)[reply]

A color space is a combination of color primaries and white point which is shown as a 2D image. Also even with a defined brightness range the encoding method (RGB, YCbCr, etc...) changes the maximum brightness of the primary colors. Dolby uses the term color volume to refer to a combination of color space, transfer function, and encoding method which can be used to make a 3D image of colors at all ranges of supported brightness. --GrandDrake (talk) 03:45, 12 April 2016 (UTC)[reply]

Y' as Weighted Sum[edit]

Under "RGB and luma-chroma formats", Y' is described as a weighted average. I believe it should be described as a weighted sum. See the equation given. — Preceding unsigned comment added by 172.91.176.10 (talk) 11:41, 9 March 2020 (UTC)[reply]

No, it is a weighted average, because it can be described as then devided by 1. Who cares though. 109.252.90.66 (talk) 14:29, 3 February 2021 (UTC)[reply]

Wrong Cb / Cr formulas[edit]

The RGB and luma-chroma formats section appears to contain wrong formulas:

YCbCr are calculated as C′B = 2⋅(B′−Y′)/(1−KB) and C′R = 2⋅(R′−Y′)/(1−KR)

The YCbCr article seems to provide the correct formulas:

C′B = (1/2)⋅(B′−Y′)/(1−KB) and C′R = (1/2)⋅(R′−Y′)/(1−KR)

which could be translated to C′B = (B′−Y′)/2⋅(1−KB) and C′R = (R′−Y′)/2⋅(1−KR), also.

--91.92.16.181 (talk) 17:32, 1 December 2020 (UTC)[reply]

Fixed. 109.252.90.66 (talk) 14:26, 3 February 2021 (UTC)[reply]