[FFmpeg-trac] #2005(avcodec:new): Wrong palette colors with DVD subtitles encoding

[FFmpeg]

#2005: Wrong palette colors with DVD subtitles encoding
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             Reporter:  ubitux      |                    Owner:
                 Type:  defect      |                   Status:  new
             Priority:  normal      |                Component:  avcodec
              Version:  git-master  |               Resolution:
             Keywords:  dvdsub      |               Blocked By:
             Blocking:              |  Reproduced by developer:  1
Analyzed by developer:  0           |
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Comment (by Cigaes):

 {{{
  0 0 00c5c5c5 00000000     116427
  0 1 00c5c5c5 ffffff00     110562
  0 2 00c5c5c5 ff000000     181452
  0 3 00c5c5c5 00000000     116427
 }}}
 In other words, the dvdsub encoder considers that the transparent light
 gray is slightly nearer opaque yellow than transparent black. The culprit
 is {{{color_distance()}}} in {{{dvdsubenc.c}}}. A quick fix would be to
 get it to return 0 when both alphas are 0. A possibly better fix would be
 to multiply everything by alpha, i.e. consider the colors as a cone rather
 than an hypercube. Do you have any preference?

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Ticket URL: <https://ffmpeg.org/trac/ffmpeg/ticket/2005#comment:4>
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