[FFmpeg-trac] #3625(swscale:new): Unscaled conversion from yuv420p to gray is slow

FFmpeg trac at avcodec.org
Fri May 9 08:18:36 CEST 2014

#3625: Unscaled conversion from yuv420p to gray is slow
             Reporter:  andreasg    |                    Owner:
                 Type:  defect      |                   Status:  new
             Priority:  normal      |                Component:  swscale
              Version:  git-master  |               Resolution:
             Keywords:              |               Blocked By:
             Blocking:              |  Reproduced by developer:  0
Analyzed by developer:  0           |

Comment (by andreasg):

 Converting from yuv420p to grayscale without scaling pretty much just
 requires copying the prefix bytes:

 I haven't looked at the implementation to see if that's what it's doing.
 I also haven't checked the quality of the old output.  I would like to
 point out that converting from yuv420p to rgb is almost three times faster
 than the current conversion to grayscale.  I could write my own
 implementation from YUV to grayscale but I would prefer not to have to
 deal with all the different variants.

Ticket URL: <https://trac.ffmpeg.org/ticket/3625#comment:2>
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