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Using Smart Mask Interpolation (Production Bundle only)


    Previous versions of After Effects provided limited controls for interpolating masks. Now, Smart Mask Interpolation increases your ability to control how mask shape keyframes are created and gives you greater possibility for smooth, realistic animation. You select the mask shape keyframes to interpolate between, and Smart Mask Interpolation creates intermediate keyframes based on settings you provide. The Info palette displays the progress of the interpolation and, upon completion of the interpolation, displays the number of keyframes created.

    The Smart Mask Interpolation palette, showing the basic controls (left) and the optional controls (right)
    The Smart Mask Interpolation palette, showing the basic controls (left) and the optional controls (right)

To use Smart Mask Interpolation:

  1. Select at least two adjacent keyframes between which you want the mask shape interpolated.
  2. Choose Animation > Keyframe Assistant > Smart Mask Interpolation.
  3. Set the options in the Smart Mask Interpolation palette based on the following guidelines and click Apply:
  4. Keyframe Rate

    Sets how many keyframes per second to add between the selected keyframes. For example, a value of 10 means that a new keyframe will be added every 1/10 of a second. Type the value in the box or choose a rate from the menu. Choosing Auto from the menu choices sets the keyframe rate equal to the composition frame rate. If you choose Auto, the keyframe rate appears in parentheses.

    Note: Regardless of the keyframe rate, Smart Mask Interpolation always adds keyframes at the frame just after the first mask shape keyframe and at the frame just before the second mask shape keyframe. For example, if Smart Mask Interpolation interpolates between keyframes at 0 seconds and 1 second in a 30-fps composition with a keyframe 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  the arrows button 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 guidelines:

    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

    Specifies the distance, in pixels, between vertices on the larger perimeter mask shape after subdivision.

    Total Vertices

    Specifies the number of vertices you want on the interpolated mask shapes.

    Percentage of Outline

    Specifies that a vertex is added at each indicated percent of the mask shape 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.

    Leave this box unchecked to use only the vertices that were there at the first frame.

    Note: Smart Mask Interpolation may add vertices at existing vertex locations even if Add Mask Shape Vertices is not checked. If two vertices on one mask shape match a single vertex on the other, the single vertex is duplicated at the same spot so that the segment between the two vertices shrinks to that spot.

    Matching Method

    Specifies the algorithm that Smart Mask Interpolation uses to match vertices on one mask shape to vertices on the other. Choose one of the following from the menu:

    Auto

    Specifies that if either of the two selected keyframes has a curved piece, the matching algorithm for curves is applied. If not, the algorithm for polylines is applied.

    Curve

    Specifies that the algorithm for mask shapes that have curved pieces is applied.

    Polyline

    Specifies that the algorithm for mask shapes that have only straight pieces is applied.

    Note: The mask shape keyframes added by Smart Mask Interpolation are polylines when the Polyline Matching Method is selected, whether or not the input mask shapes contained curved pieces.

    Use 1:1 Vertex Matches

    If this box is checked, then Smart Mask Interpolation forces a vertex on one mask shape to match the same-numbered vertex on the other mask shape. On each of the input mask shapes, Smart Mask Interpolation matches the first vertices, the second vertices, the third vertices, etc. If the two shapes have unequal numbers of vertices, then this action may produce undesirable results.

    First Vertices Match

    If this box is checked, Smart Mask Interpolation matches the first vertices in the two mask shape keyframes. If this box is unchecked, Smart Mask Interpolation searches for the best first-vertex match between the two input mask shapes.

    Note: To quickly get good results, make sure that the first vertices of the input mask shapes match and then run Smart Mask Interpolation with the First Vertices Match box checked.

To interrupt the interpolation process:

    Press Esc. The Info palette indicates that the process has been interrupted and reports the number of keyframes created before the interruption.