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AE: Clipping mask from alpha footage

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tommy strickland
AE: Clipping mask from alpha footage
on Sep 8, 2009 at 5:13:41 am

I tried searching online, but found nothing in particular. Now I'm sure this has been asked before somewhere, maybe it is because i'm not sure how to word it in the search...

Here is what I am trying to figure out. Is it possible, to create a mask out of footage alpha without rotoscoping?

For instance I shot footage on a green screen and I rendered out an Alpha of a woman dancing.

Now is there any option in AE that when applied takes the silohette of the footage and creates a mask? Which then can be applied to other layers?

I'm running a Mac Leopard with 4GB if that matters at all.

Thank You kindly.

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Adolfo Rozenfeld
Re: AE: Clipping mask from alpha footage
on Sep 8, 2009 at 5:24:56 am

There are no less than three ways, possible more.
One is using the keyed layer as an Alpha Matte for another. This method requires that the "punching layer" sits immediately above in the timline from the "punched" layer. Then (if needed) press the Modes/Switches button at the bottom of the layer panel and you'll get a column that reads "Trk Mat". In that column set the mode for the lower layer to "Alpha Matte". It will be punched by the layer above, which will be turned off.

Second method: Apply the Set Matte effect (Effect > Channels > Set Matte) you want to be punched. You have a menu to choose which layer to use as a matte. Choose the keyed/alpha layer. The "Use for Matte" menu defaults to alpha, so you're good to go. The advantage of the method is that it doesn't require any specific order in the timeline for the layers you use.

Last method: In the Modes panel, set the alpha/keyed layer to the "Stencil" blending mode. The advantage or drawback (depending on your needs) is that every layer located below that one in that timeline will only show through the alpha layer.

Adolfo Rozenfeld ยท Adobe

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tommy strickland
Re: AE: Clipping mask from alpha footage
on Sep 9, 2009 at 4:08:11 am

Thank You so much, I was so confused on how to do that. I'm going to test this out. Thank you for helping me out, Mr. Rosenfeld.

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