User Guide

CHAPTER 7
254
Working with Masks and Transparency
To animate a mask property:
1 In the Timeline or Composition window, select the mask that you want to animate.
2 Move the current-time marker to the time where you want to begin the animation.
3 Expand the Mask properties and locate the property that you want to change.
4 Set a value for the mask property. For information on setting a mask value, see the
corresponding section for the value you want to set. For example, for information on
setting Mask Opacity, see “Adjusting the opacity of a mask” on page 250.
5 Set an initial keyframe. For information on setting keyframes, see “Setting keyframes”
on page 163.
6 Move the current-time marker to the time where you want to add the second keyframe.
7 Change the value for the mask property.
Repeat steps 7 and 8 as many times as you want to add more keyframes.
Note: By default, when you add a control point to a mask, the new point appears on the mask
throughout the mask’s duration but reshapes the mask only at the time it was added. When
you delete a control point from a mask at a specific point in time, the point is deleted from the
mask throughout the mask’s duration. Prevent After Effects from adding and deleting control
points throughout the mask’s duration by choosing Edit > Preferences > General and
deselecting Preserve Constant Vertex Count When Editing Masks.
To designate another control point as the first vertex:
1 Create an animated mask shape, as described in the previous procedure.
2 In the Timeline window, move the current time marker to the point where you want to
designate a new first vertex.
3 Select the control point you want to designate as the first vertex. (See “Selecting masks
and control points” on page 244 for information on selecting a control point.)
4 Choose Layer > Mask > Set First Vertex.
Note: The control point designated as the first vertex appears slightly larger than the other
control points in the Composition window.
UG.book Page 254 Wednesday, February 21, 2001 12:05 PM