Adobe AFTER EFFECTS CS3 PROFESSIONAL User Manual page 269

About track mattes and traveling mattes
When you want one layer to show through a hole in another layer, set up a track matte. You'll need two layers—one
to act as a matte, and another to fill the hole in the matte. You can animate either the track matte layer or the fill layer.
When you animate the track matte layer, you create a traveling matte. If you want to animate the track matte and fill
layers using identical settings, consider precomposing them.
Define transparency in a track matte using values from either its alpha channel or the luminance of its pixels. Using
luminance is useful when you want to create a track matte using a layer without an alpha channel or a layer imported
from a program that can't create an alpha channel. In both alpha channel mattes and luminance mattes, pixels with
higher values are more transparent. In most cases, you use a high-contrast matte so that areas are either completely
transparent or completely opaque. Intermediate shades should appear only where you want partial or gradual trans-
parency, such as along a soft edge.
After Effects preserves the order of a layer and its track matte after you duplicate or split the layer. Within the dupli-
cated or split layers, the track matte layer remains on top of the fill layer. For example, if your composition contains
layers A and B, where A is the track matte and B the fill layer, duplicating or splitting both of these layers results in
the layer order ABAB.
A track matte only applies to the layer directly beneath it. To apply a track matte to multiple layers, first precompose
the multiple layers, and then apply the track matte to the precomposition layer.
A
Traveling matte
A. Track matte layer: a solid with a rectangular mask, set to Luma Matte. The mask is animated to travel across the screen. B. Fill layer: a
solid with a pattern effect. C. Result: the pattern is seen in the track matte's shape and added to the image layer, which is below the track matte
layer.
See also
"About alpha channels and mattes" on page 252
"Split a layer" on page 149
Convert a layer into a track matte
Drag the layer that will be the track matte directly above the layer that will be the fill layer.
1
B
C
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