[FFmpeg-trac] #9085(avcodec:reopened): JPEG: YCCK too green

FFmpeg trac at avcodec.org
Sun Mar 21 09:42:56 EET 2021

#9085: JPEG: YCCK too green
             Reporter:  Balling     |                    Owner:
                 Type:  defect      |                   Status:  reopened
             Priority:  normal      |                Component:  avcodec
              Version:  git-master  |               Resolution:
             Keywords:  mjpeg cmyk  |               Blocked By:
             Blocking:              |  Reproduced by developer:  0
Analyzed by developer:  0           |

Comment (by Balling):

 Replying to [comment:17 pdr0]:
 > You're right about APP14, and it is YCCK
 > ISO/IEC 10918-6:2013 (E), section 6.1:
 >   ColorTransform    = 2 [YCCK]
 > See post nine
 > https://stackoverflow.com/questions/50798014/determining-color-space-
 > Why are the photo CD PhotoYCC equations on wikipedia
 > https://en.wikipedia.org/wiki/Photo_CD#Encoding
 > different than intel's PhotoYCC Color Model equations ?

 There is also a flag in APP14 which says whether K is inverted or not!
 Afaik, inverted is used in EPostscript. ISO/IEC omits that.

 Now, that stackoverflow managed to omit the fact that there are also
 legacy YCbCr formats, that Microsoft managed to incorectly define (and
 thus deprecate) in their corporate version of IJG JPEG library.

 As to why those are different in Intel... RGB are not between 0 and 1,
 that is why. Nonlinear RGB' in PhotoYCC are from -0.43357 to 1.402278,
 while Linear RGB values are from -0.20 to 2.00.

Ticket URL: <https://trac.ffmpeg.org/ticket/9085#comment:18>
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