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.
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