Adobe After Effects CS4 - Manual (Page 336)

330 USING AFTER EFFECTS CS4
Drawing, painting, and paths
Last updated 12/21/2009
3 Set options in the Mask Interpolation panel, and then click Apply.
Note: To interrupt the interpolation process, press Esc. The Info panel indicates that the process has been interrupted and
reports the number of keyframes created.
Keyframe Rate Specifies the number of keyframes that Smart Mask Interpolation creates per second between the
selected keyframes. For example, a value of 10 creates a new keyframe every 1/10 of a second. Choose Auto to set the
keyframe rate equal to the composition frame rate, which appears in parentheses. Create more keyframes for smoother
animation; create fewer keyframes to reduce render time.
Note: Regardless of the keyframe rate you choose, Smart Mask Interpolation always adds keyframes at the frame just after
the first mask path keyframe and at the frame just before the second mask path keyframe. For example, if you interpolate
between keyframes at 0 seconds and 1 second in a 30-fps composition with a keyframe rate of 10 keyframes per second,
mask path keyframes are added at frame numbers 1, 3, 6, 9, 12, 15, 18, 21, 24, 27, and 29.
Keyframe Fields Doubles the keyframe rate. When this option is selected, and Keyframe Rate is set to the composition
frame rate, a keyframe is added at each video field. Select this option for animated masking for interlaced video. If this
option is not selected, the mask may slip off the object that you are attempting to key out. For more information about
fields in interlaced video, see “
Interlaced video, noninterlaced video, and progressive scanning ” on page 92.
Use Linear Vertex Paths Specifies that vertices in the first keyframe move along a straight path to their corresponding
vertices in the second keyframe. Leave this option unselected if you want some vertices to interpolate along curved
paths; for example, when the desired interpolation involves rotating parts. If this option is not selected, Smart Mask
Interpolation creates a natural path for the mask.
Bending Resistance Specifies how susceptible the interpolated mask path is to bending instead of stretching. A value
of 0 specifies that, as the mask path animates, it bends more than it stretches; a value of 100 specifies that the mask path
stretches more than it bends.
Quality Specifies how strictly Smart Mask Interpolation matches vertices from one keyframe to another. A value of 0
specifies that a particular vertex in the first keyframe matches only the same-numbered vertex in the second keyframe.
For example, the tenth vertex in the first keyframe must match the tenth 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. Higher values
usually yield better interpolations; however, the higher the value, the longer the processing time.
Add Mask Shape Vertices Specifies that Smart Mask Interpolation adds vertices to facilitate quality interpolations. In
general, Smart Mask Interpolation works best when the mask paths have dense sets of vertices. Also, a vertex on the
first mask path cannot match the middle of a curve or straight-line segment on the second mask path, so sometimes
you must add vertices before matching to produce the desired result. Smart Mask Interpolation does not modify the
original keyframes. Only the new mask path keyframes computed by Smart Mask Interpolation have additional
vertices.
The value you set specifies how finely the input mask paths are subdivided. Pixels Between Vertices specifies the
distance, in pixels, between vertices on the larger perimeter mask path after subdivision. Total Vertices specifies the
number of vertices on the interpolated mask paths. Percentage Of Outline specifies that a vertex is added at each
indicated percent of the mask path outline length. For example, a value of 5 means that a vertex is added at each
successive segment of the outline that represents 5% of the total perimeter. To use only the vertices that were on the
path at the first frame, do not select this option.
Note: Smart Mask Interpolation may add vertices at existing vertex locations even if Add Mask Shape Vertices is not
selected. If two vertices on one mask path match a single vertex on the other, the single vertex is duplicated at the same
location so that the segment between the two vertices shrinks to that location.
Matching Method Specifies the algorithm that Smart Mask Interpolation uses to match vertices on one mask path to
vertices on the other. Auto applies the matching algorithm for curves if either of the two selected keyframes has a