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Using Alpha Channel from one file to grade another

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Tim Franklin
Using Alpha Channel from one file to grade another
on Oct 20, 2014 at 12:09:30 am

Hello all,

Totally new to Davinci and don't fully know the correct procedures and workflow between it and other compositing software.

In After Effects I outputted an RGBA matte layer from After Effects so the colorist can grade my full composition. (RGB)

The way I did it I would need him to use the alpha channel from the Matte Layer.

My questions is - how do you use only a specified channel from one layer to grade the main image in Davinci?

Is this an incorrect approach? I first tried to attach the matte to the alpha channel on the main comp but because there is no transparency it did not seem to work. If I had put the matte layer in the alpha channel of the main comp would you be able to grade it from there or do you need external mattes? What channels work best for mattes?

Very sorry if this is not clear.

Any help would be greatly appreciated!

Thanks,
Tim

Tim Franklin
Freelance Visual Effects Artist/ Video Editor
Media Asset Manager, CBS Sports Network
http://www.TimSFranklin.com


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Andy Winter
Re: Using Alpha Channel from one file to grade another
on Oct 20, 2014 at 7:22:02 am

did you check the alpha channel in the media-pool?
for some reason davinci ignores it on import but
you can manually allocate it (straight/premult etc)!


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Tim Franklin
Re: Using Alpha Channel from one file to grade another
on Oct 21, 2014 at 4:19:31 pm

I was able to import the shot with the matte clip attached. To do this I selected both, right clicked, and selected the matte clip option.

I got them both into the Color panel as well but it is reading the RGB channels and not the alpha. At this point I have the matte I need in only the alpha channel of the matte clip.

Is it possible to do what you are suggesting with the matte clip either in the media pool or with a node?

Thanks!
-Tim

Tim Franklin
Freelance Visual Effects Artist/ Video Editor
Media Asset Manager, CBS Sports Network
http://www.TimSFranklin.com


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Joseph Owens
Re: Using Alpha Channel from one file to grade another
on Oct 21, 2014 at 5:02:24 pm

[Tim Franklin] "how do you use only a specified channel from one layer to grade the main image in Davinci?"

This varies slightly from one version to another... since in later versions of Resolve you can split out RGBA channels discretely to pass along to other processing nodes.

In its simplest approach, if there is a discrete travelling matte movie, which can be a straight black&white QT and doesn't need to be RGBA, there is a specific import procedure that associates it as a matte, mated with a primary source clip. Essentially, you select the foreground or finished composite plate, then import the alpha movie as a matte key element. In the COLOR page, add a second node to the grade for the primary composite source clip, right click on that second node and there should be a dialog allowing you to select the associated matte movie as a qualifying element. If you need to do inside and outside corrections, then you also need to add an "outside" node. The manual goes into some detail outlining how to implement matte clips or primary source clips that have an imbedded alpha channel. If you are actually layering plates, it is possible to add an alpha output to a node tree that creates transparency between video layers on the Resolve timeline.

jPo

"I always pass on free advice -- its never of any use to me" Oscar Wilde.


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