In tests I did with bars a while back when prores started being supported in
Avid if I brought something in prores and exported prores all was well. Same
with DNX in and out. When ever I tried to cross the codec streams there would
be a slight shift in the gamma area as many others have notice for years. The
assumption was those codec converting exports were using the flawed QT Engine.
Since my tests a while ago I've heard others say if you transcoded the media
from prores to dnx in Avid or dnx to prores in Avid you could then export a same
as source and the levels would not get shifted. I've never tried to confirm or
deny that myself. My gut tells me anytime you don't stay with a prores import
for a prores output or the same with dnx you are likely to see the slight gamma
shift. I may be wrong but that's what I always seen when I tested this stuff.
--- In Avid-L2@yahoogroups.com, Michael Brockington <brocking@...> wrote:
>
> Hi Job:
>
> I've posted this in the forums to un-mangle my test results:
>
> http://community.avid.com/forums/p/113013/654515.aspx#654515
>
> My supposition, based on these tests, is that when you do a
> Same-as-source export with RGB levels, the Avid does not actually change
> the pixel values, but sets a flag telling the quicktime library how to
> interpret the pixel values. When the quicktime library is called to
> display the image or serve it up to another application, it checks the
> flag, and if it is RGB, adjusts the levels to crush below 16 and clip
> above 235.
>
> You can confirm this by checking the following test case. Export
> with RGB levels set. It will look crushed/clipped in the finder and
> other applications, as you might expect. Re-import that quicktime with
> CCIR levels checked. You will get back exactly what you started with,
> with no crushing or clipping.
>
> Unfortunately, as my tests show, the handling of the 601/RGB flag
> differs in certain cases between DNxHD and ProRes.
>
> Cheers,
> --Michael
>
> On 12-09-22 11:53 PM, Job ter Burg (L2B) wrote:
> >
> > , ProRes exports always behave as though they were exported
> > > as RGB, regardless of whether RGB or 601 was chosen in the export
> > dialogue.
> > >
> > > This is consistent with the results you just reported, as well as the
> > > odd results I reported earlier in this thread.
> >
> > Michael,
> >
> > That doesn't make sense to me. If the APR export would behave like it
> > was exported as RGB (which would crush 0-15 and clip 236-255), a
> > re-import into Avid would show different levels, and it does not. All
> > levels below 16 and over 235 are maintained.
> >
> > It's hard to follow your test results as they show up mangled up here.
> >
> > How and where are you determining that the APR export "behaves like RGB"?
> >
> > J
> >
> >
>
>
>
> [Non-text portions of this message have been removed]
>
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