Tuesday, December 11, 2018

[Avid-L2] Re: Avid Timeline setting effects matte key alpha channel level?

 

I should have included MacPro mid 2010 upgraded to 12core 3.33GHz Mac OS 10.12.6 Avid MC 8_9_4.  I have definitely seen this behavior on earlier versions of Avid on multiple systems.



---In Avid-L2@yahoogroups.com, <bigfish@...> wrote :

I've seen this issue for years  but today I got more of a handle on it.  For years when I have to lay out keyable graphics to tape I've stepped into the matte key clip and grabbed the alpha channel and the fill channel to cut them into the timeline individually so the elements can be ingested to EVS playback etc.... to have the matte and fill signals ganged for playback into a switcher.

When I've done this I've always noticed that even if the matte key graphic was imported to legal video the alpha channel will still display as full range when you step into the matte key effect or when it is cut back into the timeline.  What always confused me is that when I would go to do a digital cut the output would be at legal limit.  Once the digital cut was done the level jumped back.  Today I discovered that the timeline settings quality setting is causing this.  If I am yellow, yellow/green or green the alpha channel media is full range but as soon as I toggle the timeline to 10bit green the level is legal.  WTF?  All these years I couldn't see the rhyme or reason to this behavior but now I see that the digital cut tool was forcing the output to 10 during output and once the digital cut was done the timeline reverts back to 8 bit green.

I now understand what seemed inconsistent in the past must have been this behavior.  Now the real question is why would an 8 bit timeline quality setting yield full range on the alphas but 10 bit is legal.  That doesn't make any sense to me.  I've heard over the years that Avid under the hood works in full range for the alpha no matter what scaling was done during import.  So I assume the actual video essence of the alpha is full range but somehow the 8 bit vs 10 effects only alpha channel info.  Otherwise all my video would be jumping video levels with every toggle.

Anybody at Avid that can shine some light on this behavior?

John Moore Barking Trout Productions Studio City, CA bigfish@...

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Posted by: bigfish@pacbell.net
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