Animate a mask path with Smart Mask Interpolation



Smart Mask Interpolation provides a high level of control for creating mask path keyframes and smooth, realistic animation. After you select the mask path keyframes to interpolate, Smart Mask Interpolation creates intermediate keyframes based on settings you provide. The Info panel displays the progress of the interpolation and the number of keyframes created.

  1. Choose Window > Mask Interpolation.
  2. Select at least two adjacent mask path keyframes.
  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.

    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 curved segment; otherwise, it applies the polylines algorithm. Curve applies the algorithm for mask paths that have curved segments. Polyline applies the algorithm for mask paths that have only straight segments.
    Note: The mask path keyframes added by Smart Mask Interpolation are polylines when Polyline Matching Method is selected, regardless of whether the input mask paths contained curved segments.

    Use 1:1 Vertex Matches
    Specifies that Smart Mask Interpolation creates a vertex on one mask path that matches the same-numbered vertex on the other mask path. On each of the input mask paths, Smart Mask Interpolation matches the first vertices, the second vertices, the third vertices, and so forth. If the two paths have unequal numbers of vertices, this action may produce undesirable results.

    First Vertices Match
    Specifies that Smart Mask Interpolation matches the first vertices in the two mask path keyframes. If not selected, Smart Mask Interpolation searches for the best first-vertex match between the two input mask paths.
    Note: To ensure good results, make sure that the first vertices of the input mask paths match, and then select First Vertices Match.

Additional resources about animating masks with Smart Mask Interpolation

Chris and Trish Meyer provide some tips on animating masks, including using Smart Mask Interpolation, on the ProVideo Coalition website.