Adobe AFTER EFFECTS 5.5 Help Manual page 384

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rate of 10 per second, then mask shape keyframes are added at frame numbers 1, 3, 6, 9,
12, 15, 18, 21, 24, 27, and 29.
Keyframe Fields If this box is checked, the specified keyframe rate is doubled. A
keyframe is added at each field if this box is checked and if Keyframe Rate is set to the
composition frame rate.
Use Linear Vertex Paths If this box is checked, vertices in the first keyframe move along a
straight path to their corresponding vertices in the second keyframe. Leave this
unchecked if you want some vertices to interpolate along curved paths as, for example,
when the desired interpolation involves rotating parts.
Note: If this box is unchecked, Smart Mask Interpolation attempts to choose a natural
path along which to move the changing mask shape in the interpolated keyframes. (There
is no such ambiguity if this box is checked, since each vertex must move along a straight
line to its corresponding vertex in the second input keyframe.) If the first vertices of the
input keyframes are in the same position, then the first vertex in the interpolated mask
shapes will remain fixed in this position. You can then move the changing mask shape
along a desired path by other means, for example, by setting position keyframes.
Optional controls are also available for Smart Mask Interpolation. Access these by clicking
the arrows on the left corner of the palette tab or by choosing Show Options from the
Smart Mask Interpolation palette menu. Set those values based on the following guide-
lines:
Bending Resistance Specifies how susceptible the interpolated mask shape is to
bending as opposed to stretching. Click the arrow on the text box and drag the slider to
adjust the value. A Bending Resistance of 0 specifies that, as the mask shape animates, it
tends to bend much more than it stretches; a value of 100 means that the mask shape
tends to stretch much more than it bends.
Quality Specifies how strictly Smart Mask Interpolation matches vertices from one
keyframe to another. A value of 0 means that a particular vertex in the first keyframe may
match only the same-numbered vertex in the second keyframe. For example, the 10th
vertex in the first keyframe must match the 10th vertex in the second keyframe. A value of
100 means that a vertex in the first keyframe can potentially match any vertex in the
second keyframe. Larger quality values usually yield better interpolations; however, the
larger the quality value, the longer the processing time.
Add Mask Shape Vertices If this box is checked, Smart Mask Interpolation adds vertices
to facilitate quality interpolations. In general, Smart Mask Interpolation works best when
the mask shapes have dense sets of vertices. Also, a vertex on the first mask shape cannot
match the middle of a curve or straight-line segment on the second mask shape, so
adding vertices before matching is sometimes necessary to produce the desired result.
Smart Mask Interpolation does not modify the input, or original, keyframes. Only the new
mask shape keyframes computed by Smart Mask Interpolation have additional vertices.
Selecting the Add Mask Shape Vertices box activates the corresponding text box and
menu. The number in the text box specifies how finely to subdivide the input mask
shapes, according to one of the following parameters you choose from the menu:
Pixels Between Vertices
shape after subdivision.
Specifies the number of vertices you want on the interpolated mask shapes.
Total Vertices
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Specifies the distance, in pixels, between vertices on the larger perimeter mask
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(5.5) Working with Masks and Transparency
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