[FFmpeg-user] ffmpeg makes some sources darker

[Jim Worrall]

> 
> 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!