Adobe 65008009 - After Effects CS4 Using Manual page 458

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Last updated 12/21/2009 USING AFTER EFFECTS CS4
Effects and animation presets
Set Matte effect
The Set Matte effect replaces the alpha channel (matte) of a layer with a channel from another layer above it for the
creation of traveling matte results. The Set Matte effect is intended only to provide compatibility with projects created
in earlier versions of After Effects that use the Set Matte effect.
This effect works with 8-bpc and 16-bpc color.
Original (upper-left), matte layer (lower-left), and result (lower-right)
Sometimes, it's easier and faster to create traveling mattes by using a track matte instead of using the Set Matte effect.
However, using the Set Matte effect provides some advantages over defining a layer as a track matte layer. The layer
used as the matte with the Set Matte effect can be anywhere in the layer stacking order, unlike a track matte layer, which
must be directly above the matted layer in the layer stacking order. Also, one layer can be used as the matte for multiple
layers with the Set Matte effect. (See "Track mattes and traveling mattes" on page 380.)
The layer to use as the replacement matte.
Take Matte From Layer
The channel to use for the matte.
Use For Matte
Inverts the transparency values of the matte.
Invert Matte
Scales the selected layer to match the size of the current layer. If Stretch Matte To Fit is deselected,
Stretch Matte To Fit
the layer designated as the matte is centered in the first layer.
Composites the new matte with the current layer, rather than replacing it. The
Composite Matte With Original
resulting matte allows the image to show through only where the current matte and the new matte both have some
opacity.
Premultiplies the new matte layer with the current layer.
Premultiply Matte Layer
Shift Channels effect
The Shift Channels effect replaces red, green, blue, and alpha channels in the image with values from other channels.
This effect works with 8-bpc, 16-bpc, and 32-bpc color.
The channel to use as a source.
Take Channel From
Todd Kopriva provides a post on the Adobe website that describes the use of the Remove Color Matting and Shift
Channels effects to remove black backgrounds from images.