Alpha channel mask (easy one this!)

[Thorsten Miess]

Put the layer with the alpha channel above the other layer and choose on the layer beneath the alpha-channel-layer Track Matte>Alpha Trackmatte (or inverted if you want to)(its all in the timeline)

This Method effects only a single layer.

For effecting all layers underneath your alpha-channel-layer change its blending mode to>Stencil Alpha (or one of the other 3)

And if you want a mask for a layer:

Select your aplha-channel-layer (i love this words 🙂 ) and choose layer>Auto Trac. After changing a few settings in the upcoming menu(dont worry you even dont need to change) click apply and a mask will appear on a new solid.
Now you can copy the mask to your layer that should have the transparency from the…one more time: alpha-channel-layer.

Hope this helped

[Joey Foreman]

You could also place the layer you want the alpha channel taken from under the layer you want to use it, and activate the T button in the timeline. This will take Alpha from all layers under the affected layer.

[Darby Edelen]

There’s also the Channel > Set Matte effect, or any number of the Channels effects that could be used, although these behave very differently from previously mentioned options. The alpha is taken from the source layer with no regard for the source layer’s position or transform properties and applied to the affected layer.

Darby Edelen
Lead Designer
Left Coast Digital
Santa Cruz, CA