[FFmpeg-trac] #11182(swscale:closed): yuvtestsrc and yuv444p->rgba->yuv444p conversion result in huge difference

[FFmpeg]

#11182: yuvtestsrc and yuv444p->rgba->yuv444p conversion result in huge difference
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             Reporter:  Andrew-R     |                    Owner:  (none)
                 Type:  defect       |                   Status:  closed
             Priority:  normal       |                Component:  swscale
              Version:  unspecified  |               Resolution:  invalid
             Keywords:  colorspace   |               Blocked By:
  color_primaries                    |
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
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Comment (by Balling):

 yuv444-rgba-problem1.png shows the difference only in the second raw and
 third raw because those values are out-of-gamut. Indeed, green is 0x80,
 0x80, 0x0. That means it is full range, as 0x0 value is prohibited in
 limited range YCbCr. Now, let us use calculator
 https://res18h39.netlify.app/color

 This calculator does not support full range YCbCr, so we should convert it
 to limited range. 128 in full range Y becomes float value
 0.5019607843137254 that becomes *219+16 = 125.9294117647059, 126 Y limited
 range, Cb 128 becomes 0 float and that becomes 128 Cb; Cr at 0 becomes
 -0.5 float and that becomes 16 in limited range, so it is 126, 128, 16. In
 R'G'B' that is -76, 232, 128.

 There is no bug, RGB cannot preserve such a value in R, red is negative.
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Ticket URL: <https://trac.ffmpeg.org/ticket/11182#comment:46>
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