Adobe 65008009 - After Effects CS4 Using Manual page 278

Last updated 12/21/2009
• To move only the feature and search regions together, drag the edge of the feature region, or Alt-drag (Windows)
or Option-drag (Mac OS) with the Selection tool inside the feature or search region. You can also hold Alt
(Windows) or Option (Mac OS) while pressing the Up, Down, Left, or Right Arrow key. Hold Alt+Shift (Windows)
or Option+Shift (Mac OS) while pressing an arrow key to move by an increment 10 times as large.
• To move only the search region, drag the edge of the search region.
Offset the search region center from the feature region center in the direction in which the tracked feature is traveling.
• To move only the attach point, drag the attach point.
• To resize the feature or search region, drag a corner handle.
• To make all of the sides of the region match the length of the longest side, and to resize the region relative to the
original center point of the region, Shift-drag a corner handle.
• To make all of the sides of the region match the length of the longest side, and to resize the region relative to a
particular corner handle, Ctrl+Shift-drag (Windows) or Command+Shift-drag (Mac OS) the opposite corner
handle.
To restrict the movement of the track point to the x (horizontal) or y (vertical) axis during tracking, resize the height
or width of the search region to match the height or width of the feature region.
Apply tracking data to a new target
After you've tracked a motion source layer, you can apply the tracking data stored on that layer to any number of other
target layers and effect control points. For example, you can apply the track to the position of a light bulb and to the
effect control point of the Lens Flare effect.
In the Tracker panel, choose the tracked layer from the Motion Source menu.
1
Choose the track that contains the tracking data you want from the Current Track menu.
2
Click Edit Target, and choose the target.
3
In the Tracker panel, click the Apply button.
4
Correct a motion track
As an image moves in a shot, the lighting, surrounding objects, and angle of the object can all change, making the once
distinct feature no longer identifiable at the subpixel level. Also, if the search region is too small, the tracked feature
may leave its bounds from one frame to the next.
Learning to choose a trackable feature takes time. Even with careful planning and practice, the feature region can drift
away from the desired feature. Re-adjusting the feature and search regions, changing the tracking settings, and trying
again is a standard part of automatic tracking. It's not necessary to get a single good track in one try. You may need to
track the shot in sections, redefining the feature region in places where the feature changes and the region drifts. You
may even need to choose a different feature to track, one with movement that closely matches that of the feature to
track, and use the attach point offset to place the target.
After you've tracked motion, each track point has a motion path in the Layer panel that shows the position of the center
of the feature region. You can fine-tune the keyframes of the motion path in the Layer panel as you would any other
motion path. Modifying the motion path is most useful when you want to manually change the motion tracking data
before applying it to a target. In some cases, it may be easier to manually modify the motion path created by the motion
tracker than to get a perfect track.
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USING AFTER EFFECTS CS4
Animation and keyframes