Adobe After Effects CS3 - Manual (Page 261)

AFTER EFFECTS CS3
User Guide
256
The motion path of the spaceship (top) is copied to the background layer (bottom left) and used by the Vegas effect (bottom right).
1 In the Timeline panel, click the name of the Position property or Anchor Point property from which you want to
copy the motion path. (This selects all keyframes. To select only some of the motion path’s keyframes, Shift-click
them.)
2 Choose Edit > Copy.
3 To create a new mask, select the layer on which to create the mask, and choose Layer > Mask > New Mask.
4 In the Timeline panel, click the name of the Mask Path property for the mask to which to paste the motion path
keyframes.
5 Choose Edit > Paste.
Selecting and copying Position keyframes (left); then pasting them in the selected Mask Path property (right)
See also
“Work with motion paths” on page 197
Create a mask from a channel with Auto-trace
You can convert the alpha, red, green, blue, or luminance channel of a layer to one or more masks by using the Auto-
trace command. Auto-trace creates as many Bezier masks as necessary to outline the specified channel values in the
layer. Auto-trace creates masks with the smallest number of vertices possible while conforming to the settings that
you choose. You can modify a mask created with Auto-trace as you would any other mask, and you can link its path
to other path types, such as shape paths on a shape layer, using expressions.
When you apply Auto-trace, affected layers are automatically set to Best Quality to ensure accurate results.
To reduce the number of masks created by Auto-trace, apply a keying effect to the layer to isolate your subject before
applying Auto-trace.
1 In the Timeline panel, do one of the following:
• To create mask keyframes at a single frame, drag the current-time indicator to the desired frame.