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Masking footage with keyed alpha channel

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Tim Swiss
Masking footage with keyed alpha channel
on Dec 20, 2011 at 5:43:35 pm

Hey guys,
I'm bringing animated files from Photoshop into After Effects and comping them into footage.

The animations are white line drawings exported with a premultiplied alpha channel-black. I then used the Shift Channels filter to mask the black. This method is detailed here:

Once I've done this layer masks can't be applied to the animation layer. If I disable the Shift Channels filter the layer mask works fine.

Is there another method for keying out the alpha that will allow me to also use layer masks?

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John Cuevas
Re: Masking footage with keyed alpha channel
on Dec 20, 2011 at 6:33:06 pm

Apply your effects first. Now choose your layer and under "Layer" choose precompose "shift+cntl+c"(PC), now you can apply your mask.

Another method would be to create a layer(solid) over your effected layer, add a mask to that layer and change your effected layers Track Matte to alpha.

Johnny Cuevas, Editor

"I have not failed 700 times. I have succeeded in proving that those 700 ways will not work. When I have eliminated the ways that will not work, I will find the way that will work."
---THOMAS EDISON on inventing the light bulb.

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Darby Edelen
Re: Masking footage with keyed alpha channel
on Dec 21, 2011 at 11:25:09 am

The "Set Matte" effect should work for you.

Darby Edelen

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