User Guide

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ADOBE AFTER EFFECTS 5.0
User Guide
4 Select Rectangle or Oval.
5 If you want, specify the size and location of the mask’s bounding box. For information
on coordinates, see “Info palette” on page 62.
6 Click OK.
About Mask Paths
A mask in After Effects is a drawn path consisting of path segments and control points.
Segments are the lines or curves that connect two control points. Control points define
where each segment of a path starts and ends.
In addition, the mask you create can be either an open or closed path. An open path has
different beginning and ending points; for example, a straight line is an open path. A
closed path is continuous and has no beginning or end; for example, a circle is a closed
path. Closed-path masks can create transparent areas for a layer. Open paths cannot create
transparent areas for a layer, but are useful when used as a parameter for an effect; for
example, creating a visible line or shape from the mask using the Stroke effect. For more
information, see “Applying effects to a mask” on page 256.
Creating masks from motion paths
You can copy Position, Anchor Point, or an effect’s point position keyframes and paste
those keyframes to a selected mask. This is useful to create animations that follow the edges of
a mask. When you create masks from motion paths, make sure that you copy keyframes from
a single position property only—do not copy the keyframes of any other property. For infor-
mation on motion paths, see “Setting layer position” on page 171.
To create a mask from a motion path:
1 In the Composition window, display the motion path from which you want to create
the mask.
2 In the Timeline window, select the successive keyframes along the motion path you
want to use as a mask. Click the Position property name to select all the keyframes. Shift-
click successive keyframes to select only a few keyframes.
3 Choose Edit > Copy.
UG.book Page 241 Wednesday, February 21, 2001 12:05 PM