[FFmpeg-trac] #3236(avfilter:new): lut3d video filter swaps color channels

[FFmpeg]

#3236: lut3d video filter swaps color channels
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             Reporter:  FredTester  |                    Owner:
                 Type:  defect      |                   Status:  new
             Priority:  normal      |                Component:  avfilter
              Version:  git-master  |               Resolution:
             Keywords:  lut         |               Blocked By:
             Blocking:              |  Reproduced by developer:  0
Analyzed by developer:  0           |
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Comment (by FredTester):

 Ubitux, your diff patch didn't change the problem.

 I also verified, that the .cube file loads correctly.

 The problem must be somewhere inside the interpolation functions.

 To test that, I swapped r and b inside the FILTER define of vf_lut3d.c:

 {{{
 475:    dst[x + b] = av_clip_uint##nbits(vec.r * (float)((1<<nbits) - 1));
 \
 476:    dst[x + g] = av_clip_uint##nbits(vec.g * (float)((1<<nbits) - 1));
 \
 477:    dst[x + r] = av_clip_uint##nbits(vec.b * (float)((1<<nbits) - 1));
 \
 }}}

 That seems too be nonsense, but with this change the destination frame is
 correct. This means, that the error must be within the functions called by
 FILTER.

 By the way: I attached a new .cube file, which I built on the Iridas
 specifications. The color values represent straight lines from 0 to 1, so
 that the destination frame will be identical to the source frame after the
 filter is processed.

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Ticket URL: <https://trac.ffmpeg.org/ticket/3236#comment:8>
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