Instruction Manual

Chapter 20 Shapes, masks, and paint strokes 898
When rotoscoping a moving subject, it’s a good idea to play the clip and examine its direction
and speed to get a sense of how the mask must be animated. You may nd it helpful to place
markers indicating frames where the subject or camera stops, changes direction, or changes
speed, because these are likely candidates for your rst pass of keyframed mask changes. By
noting these changes, you can attempt to reduce the amount of keyframing by making your
rst keyframed mask shape adjustments at these major changes in speed and direction. Because
animated masks are interpolated to change from one keyframed shape to another, you can let
Motion do some of your work for you. (For more information, see Rotoscoping tips on page 898.)
Note: If the mask is deselected, you must select it in the Layers list so its control points become
visible in the Canvas. Make sure that the Show/Hide Masks button is selected in the Layers list so
masks are visible.
5 Continue moving the playhead and making changes.
One imprecise rule of thumb is to move to the frame that’s halfway between any two keyframed
mask shapes and make new adjustments. Continue keyframing shape changes at the halfway
point between every two keyframes until the mask accurately follows the motion of the subject.
For irregularly shaped objects or objects with complex motion, don’t be surprised if you need to
add a large number of keyframes. Nobody ever said that rotoscoping was fast!
Every time you move the playhead to a new frame and make a change to the mask’s shape, a
keyframe is created in that shape’s Shape Animation channel. If you move the playhead directly
on top of a previously existing keyframe, you change the mask’s shape at that point without
creating a keyframe.
Note: You can also transform masks as you would any other layer. If you move, rotate, scale, or
change the anchor point for a mask while animation recording is enabled, you add keyframes to
additional channels in the Keyframe Editor.
You can also create, delete, and edit the timing of a mask’s Shape Animation keyframes in the
Keyframe Editor. For simplicity, each change you make to a mask is recorded as a single keyframe,
no matter how many control points you edited. The Shape Animation parameter only allows
keyframes set to Constant—you cannot use any other form of keyframe interpolation.
The process used to animate both masks and shapes is identical. To see an example of shape
animation, see Keyframe the Shape Animation parameter on page 884. For more information on
keyframing in general, see Keyframing overview on page 439.
6 When you’ve nished animating the mask, disable Record (press A).
Rotoscoping tips
A good way to start rotoscoping an image is to nd the frame with the most detail showing in
the subject you’re masking, and use that as your starting frame. For example, if you’re masking
someone walking, choose a frame where that person’s arms and legs are extended in mid-stride.
Doing so lets you specify how many control points to start with. Using as few control points to
achieve the necessary level of detail in your mask makes it much easier to animate.
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