Hi Job:
Thanks for doing some testing. I've reproduced your results.I've done
more tests as well, and can conclude that ProRes files exported
Same-as-source from Avid do behave differently than DNxHD exports in a
couple of cases.
In a nutshell, 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.
Here's a table of my results that lead me to this conclusion.I limited
my testing to DNxHD220x and ProRes HQ, but imagine the results would
hold for other codecs in the same family.
The DNxHD results are as expected.I have highlighted the 2 cases in this
table where the ProRes results differ from the DNxHD.In both cases, it
appears the ProRes results ignore the export flag being set to 601, and
are always treated as though the Avid export flag was set to RGB.
Codec
Export from Avid
Quicktime display (finder preview, After Effects)
Re-import to Avid
Levels in Avid -- compare re-import to original
DnxHD 220x
RGB
Clipped and stretched *
601
Unchanged
601
Full range (unchanged)
601
Unchanged
RGB
Clipped and stretched
RGB
Gamma correct, clipped **
601
Full range (unchanged)
RGB
Nothing clipped, range squeezed ***
ProRes HQ
RGB
Clipped and stretched
601
Unchanged
601
*/Clipped and stretched/*
601
Unchanged
**
RGB
Clipped and stretched**
RGB
Gamma correct, clipped
601
*/Clipped and stretched/***
RGB
*/Gamma correct, clipped/*
*Clipped and stretched -- indicates values have been truncted below 16
and above 235, then stretched to the range 0-255.
** Gamma correct, clipped -- no values exist above 235 or below 16, but
everything in between is unchanged.
*** Nothing clipped, range squeezed -- the full range of values 0-255
have been scaled into the range 16-235.So no values exist above 235 or
below 16, but nothing has been truncated.
It seems likely the RGB/601 setting for Avid quicktime exports just sets
a flag in the quicktime file -- no pixel values are actually changed in
the file during output.If this were not the case, then it would take
longer to output an RGB file as 601, or vice-versa, when in practice,
quicktime output seems to take the same length of time regardless of the
RGB/601 output setting.
When 601 is set on import, it overrides any RGB flag setting in the
quicktime file, allowing access to the original pixel values.
When RGB is set on import Avid actually changes the pixel values of the
imported file, mapping 16 to 0 and 235 to 255, crushing all values below
16 and all values above 235.The pixel values are permanently truncated.
Avid may never read the RGB/601 flag from the quicktime file on import
since the user always specifies one or the other on import.
In these tests, After Effects shows the same results as desktop preview
in the finder.So it is honouring the 601/RGB flag correctly when
importing DNxHD quicktimes, and it is also treating ProRes quicktimes as
always having the RGB flag set.Unlike Avid, it has no way to override
the 601/RGB flag on import.
On 12-09-22 2:16 AM, Job ter Burg (L2B) wrote:
>
> Michael,
>
> I re-tested this, albeit in 6.0, on Mac.
>
> - Traditional Import the Belle Nuit Test Chart at 709 setting to Apple
> ProRes MXF
> - Splice into sequence
> - Export Same As Source with 709 levels
> - Re-Import (a Fast Import) that exported file at 709 setting
> - Second import matches the first one 100%, also when watched on the WFM.
>
> My guess is that you are determining the color levels some other way,
> and perhaps the application you are using for that is using Quicktime
> to feed the signal. The way that I describe above makes no use of the
> Quicktime software at all. It just rewraps from MXF to QT (Same As
> Source export), then from QT to MXF (Fast Import).
>
> Job.
>
>
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