id summary reporter owner description type status priority component version resolution keywords cc blockedby blocking reproduced analyzed
1851 libswscale does incorrect range conversion for RGB->YUV and RGB->RGB gjdfgh "libswscale seems to do completely confused range conversions for RGB->YUV. RGB->RGB randomly ignores the source range (at least in the unscaled case), and always ignores the destination range. YUV->RGB ignores destination range as well. The only cases that appear to be working as expected are conversions with YUV->YUV.
Here's the output of a test program, that scales a solid image filled with gray=200, using various colorspace and range parameters. ""200"" is the input value, and the number after that the retrieved luma value or that of a RGB component. ""no-scale"" means it has been scaled with same source and destination width/height. The test program is attached as swscale.c to this ticket.
{{{
no-scale rgb-lim rgb-lim 200 -> 200
no-scale rgb-lim rgb-ful 200 -> 200
no-scale rgb-lim yuv-lim 200 -> 188
no-scale rgb-lim yuv-ful 200 -> 200
no-scale rgb-ful rgb-lim 200 -> 200
no-scale rgb-ful rgb-ful 200 -> 200
no-scale rgb-ful yuv-lim 200 -> 177
no-scale rgb-ful yuv-ful 200 -> 188
no-scale yuv-lim rgb-lim 200 -> 214
no-scale yuv-lim rgb-ful 200 -> 214
no-scale yuv-lim yuv-lim 200 -> 200
no-scale yuv-lim yuv-ful 200 -> 214
no-scale yuv-ful rgb-lim 200 -> 200
no-scale yuv-ful rgb-ful 200 -> 200
no-scale yuv-ful yuv-lim 200 -> 188
no-scale yuv-ful yuv-ful 200 -> 200
scale rgb-lim rgb-lim 200 -> 200
scale rgb-lim rgb-ful 200 -> 200
scale rgb-lim yuv-lim 200 -> 188
scale rgb-lim yuv-ful 200 -> 200
scale rgb-ful rgb-lim 200 -> 188
scale rgb-ful rgb-ful 200 -> 188
scale rgb-ful yuv-lim 200 -> 177
scale rgb-ful yuv-ful 200 -> 188
scale yuv-lim rgb-lim 200 -> 214
scale yuv-lim rgb-ful 200 -> 214
scale yuv-lim yuv-lim 200 -> 200
scale yuv-lim yuv-ful 200 -> 214
scale yuv-ful rgb-lim 200 -> 200
scale yuv-ful rgb-ful 200 -> 200
scale yuv-ful yuv-lim 200 -> 188
scale yuv-ful yuv-ful 200 -> 200
}}}
YUV->RGB ignores destination ranges, and always assumes full destination range.
RGB->YUV looks completely messed up. Maybe someone flipped a bit somewhere?
Scaled RGB->RGB ignores the destination range, and always seems to assume limitted range (so that rgb-lim->* does no conversion). Unscaled RGB->RGB ignores ranges completely, at least when the same pixel format is used.
If there's some logic behind this, I don't get it, and it's not documented.
If libswscale simply doesn't support limitted RGB range (which would lower its usefulness), at least the RGB->RGB case must be fixed." defect closed important swscale git-master invalid 0 0