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

FFmpeg trac at avcodec.org
Thu Dec 13 00:10:14 CET 2012

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

Comment (by ubitux):

 Replying to [comment:4 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?

 If it solves the issue, using the alpha channel as a weight factor for the
 color sounds like a good idea to me (assuming that's what you meant).

Ticket URL: <https://ffmpeg.org/trac/ffmpeg/ticket/2005#comment:8>
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