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You can also create, delete, and edit the timing of a mask’s Shape Animation keyframes
directly 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 Animating Shapes. For more information on keyframing in general,
see Keyframes and Curves.
Rotoscoping Tips
A good way to start rotoscoping an image is to find 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 both that person’s arms and
legs are out in mid-stride. This allows you to decide how many control points you need
to start with. Using the minimum number of control points you can to achieve the
necessary level of detail in your mask makes it much easier to animate.
You should also bear in mind that it’s not always necessary to rotoscope an entire subject
with a single mask. Motion allows you to apply multiple masks to a single object, so
you can rotoscope different parts of a subject with separate masks. This can make your
job much easier. For example, if you’re rotoscoping someone carrying something while
walking across a room, you could use one mask for the upper part of the person’s body
which doesn’t change shape very much, and another two masks for the legs, which
change shape considerably as the person walks.
You can also use the Track Points behavior to apply tracking data to a shape or mask.
For more information on the Track Points behavior, see Shape Track Points Behavior.
Mask Parameters
A selected mask’s parameters appear in the Mask tab of the Inspector.
With the exception of the control points parameters, the parameters in the Mask HUD
are identical to the parameters in the Inspector.
Mask Controls in the Inspector
These controls allow you to adjust how the mask is drawn, how each mask operates upon
an object, and how masks are combined with one another. The Mask tab also allows you
to fine tune mask control point positions using value sliders.
1170 Chapter 17 Using Shapes, Masks, and Paint Strokes