[MPlayer-users] Screenshot color wrong

[Alexander Strasser]

On 2020-09-05 18:51 +0200, Polyphem wrote:
> The whole red section (~20px wide) at the right hand should be 255, see here
> the right screenshot:

Are you sure it really is like that?

It might look better and maybe it's even the purpose of that video,
but what matters is what's inside the compressed bitstream.

Looking at the output of the decoder shows me the following values:

pos		pixel
x	y	Y	Cb	Cr	comment

					approaching blue from right
882	66	16	128	128	still black
881	66	16	142	127	slightly blue
880	66	16	142	127
879	66	32	254	117     bright blue
878	66	32	254	117
877	66	32	240	118     blue value falls a bit

					approaching green from right
882	160	16	128	128     still black
881	160	16	117	115	slightly green
879	160	173	32	14	bright green
877	160	173	43	27	green value falls a bit


So I think the compressed bitstream doesn't perfectly represent,
what was originally intended. The conversion of your graphics
driver when using d3d seems to look more pleasing, but that is
not necessarily more correct. The conversion to RGB can vary.

At least at the moment I feel rather confident it isn't a bug
regarding the color/luma range and not a bug of vf screenshot
or libswscale.

Maybe the list can be of further help, if we know how you got
or created that test video and what you want to achieve.


Best regards,
  Alexander