[FFmpeg-trac] #3643(swscale:open): XYZ to RGB color space

[FFmpeg]

#3643: XYZ to RGB color space
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             Reporter:  TTeam        |                    Owner:  (none)
                 Type:  enhancement  |                   Status:  open
             Priority:  normal       |                Component:  swscale
              Version:  git-master   |               Resolution:
             Keywords:  xyz          |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
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Comment (by Balling):

 Related
 https://patchwork.ffmpeg.org/project/ffmpeg/patch/20241216112118.424999-8-ffmpeg@haasn.xyz/

 I do not understand this patch at all, Haasn. It is correct to tag it as
 SMPTE primaries, those are fake primaries (centre white), they are not
 used ''as XYZ HAS NO primaries''.

 >XYZ to RGB colorspace conversion use only sRGB matrix

 It is correct for typical HD video, that has BT.709 primaries, you must
 use BT.709 primaries XYZ matrix as specified in Nvidia docs or here:
 https://en.wikipedia.org/wiki/SRGB#Correspondence_to_CIE_XYZ_stimulus (The
 2003 amended version of the sRGB standard points out that higher accuracy
 is needed when the samples are encoded with more than 8 bits. **It
 provides the matrix**), the primaries in BT.2020 will have to be converted
 to BT.709 or different XYZ matrix will have to be used.


 If **I do not understand something** please tell me so (what does it mean
 in your patch "possibly simply by using a more fitting
 RGB intermediate like SMPTE428"), also see page 7 of https://5253154.fs1
 .hubspotusercontent-na1.net/hubfs/5253154/st2067-40-2021.pdf


 Also this is how you get YCbCr two cofficients from primaries, as such:
 https://imgur.com/a/i6742tj
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Ticket URL: <https://trac.ffmpeg.org/ticket/3643#comment:6>
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