Adobe After Effects - Manual (Page 479)

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Take Matte From Layer
Use For Matte
Invert Matte
Stretch Matte To Fit
Composite Matte With Original
Premultiply Matte Layer
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Set Channels effect
The Set Channels effect copies channels from control layers (source layers) to the red, green, blue, and alpha channels of the effect layer. For
example, you can take the luminance values of the pixels of a control layer and use them as the blue values for the pixels of the effect layer.
This effect works with 8-bpc and 16-bpc color.
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. In After Effects CS6 or later, this effect works in 32-bit 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.)
The layer to use as the replacement matte.
The channel to use for the matte.
Inverts the transparency values of the matte.
Scales the selected layer to match the size of the current layer. If Stretch Matte To Fit is deselected, 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 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.
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.
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