[FFmpeg-trac] #5397(avfilter:open): Incorrect curves filter work

[FFmpeg]

#5397: Incorrect curves filter work
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             Reporter:  Ilya87      |                    Owner:
                 Type:  defect      |                   Status:  open
             Priority:  normal      |                Component:  avfilter
              Version:  git-master  |               Resolution:
             Keywords:  curves      |               Blocked By:
             Blocking:              |  Reproduced by developer:  1
Analyzed by developer:  1           |
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Changes (by ubitux):

 * analyzed:  0 => 1
 * status:  new => open
 * reproduced:  0 => 1


Comment:

 A patch can be found at http://ffmpeg.org/pipermail/ffmpeg-
 devel/2016-July/196740.html

 Note that the curves in Gimp and Photoshop doesn't behave the same at all.

 After the patch is applied, in order to get a close behavior to what you
 expect, you will have to use something like {{{-vf curves=r='0.037516/0
 1/1':g='0.040103/0 1/1':b='0.059508/0 1/1'}}}. If you define points in
 {{{(0;0}}} ({{{-vf curves=r='0/0 0.037516/0 1/1':g='0/0 0.040103/0
 1/1':b='0/0 0.059508/0 1/1'}}}, the curves will be much curvy at the
 origin and you will your unexpected darker output. This doesn't happen in
 Gimp but is closer to what you observe in Photoshop. I will attach
 screenshot of Gimp and PS to show this.

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Ticket URL: <https://trac.ffmpeg.org/ticket/5397#comment:8>
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