[FFmpeg-user] ffmpeg makes some sources darker

[Andy Furniss]

Jim Worrall wrote:
>>
>> Strange, unless there is something in the pngs that causes a
>> different viewer to produce different output.
>>
>> I looked again (display from ancient imagemagic) and can't see any
>> difference - psnr/ssim agree.
>>
>> The pngs are not the same md5sum wise
>
> OK - you’re definitely getting way over my head, but you’re right, it
> is strange.  My Mac OS viewers definitely show the three pngs as
> different, although it is a bit subtle and you have to switch between
> them in place to see it.
>
> However, I opened them in Photoshop.  Here, master.png and
> yuv-709.png look the same, and slightly brighter than yuv.png.
>
> I ran the histogram in Photoshop and it shows master and yuv-709 as
> identical, and with a bit higher luminosity than yuv as you
> expected.
>
> Somehow, the Mac OS viewer is seeing something that other viewers
> don’t!
>
> However I think you’ve found the solution with the colormatrix bt709
> business.  That should fix it.  I’ll confirm and post again.
> Thanks!

Should be that, the png is a different issue/feature - I don't know
what's correct or not. I guess you saw my other post that showed the
gamma difference. Whether you see it or not is going to be down to the
viewer/ICC/OS setup. I haven't got a clue which is correct - I mean we a
re likely seeing 709 on an srgb monitor so not the same as a 709  TV -
perhaps the "corrected" version is the correct one. Not that when
playing the movie you would be using a png viewer anyway. What you get
from players may be a bit pot luck! Even with the same player there can
be differences between output types (xv,vdpau,opengl).

If you really want playback colour perfection, mpv can do correction
using ICC profiles for different displays.