Apple Motion 3 - Manual (Page 1103)

Chapter 12 Using Shapes and Masks 1103
In this example, the best place to start when rotoscoping the dolphin is the frame in
which all the fins are showing.
When rotoscoping a moving subject, it’s a good idea to play through the clip and
examine its direction and speed to get a sense of how the mask needs to be animated.
In particular, you may find it helpful to place markers indicating frames where the
subject or camera stops, changes direction, or changes speed, since these are likely
candidates for your first pass of keyframed mask changes.
By noting these changes, you can attempt to reduce the amount of keyframing by
making your first keyframed mask shape adjustments at these major changes in speed
and direction. Because animated masks are automatically interpolated to change from
one keyframed shape to another, you can let Motion do some of your work for you.
Note: If at any time the mask is deselected, you need to select the mask you’re working
on in the Layers tab so that its control points become visible in the Canvas. Make sure
that the Show Masks checkbox is selected in the Layers tab so that masks are visible.
5 Continue moving the playhead and making changes as needed, since the interpolated
shape of the mask isn’t going to be perfect.
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!