Adobe AFTER EFFECTS CS3 PROFESSIONAL User Manual page 350

Apply tracking data to a new target
After you've tracked a motion source layer, you can apply that layer's stored tracking data to any number of other
target layers and effect control points. For example, you can apply the track to a light bulb's position and to the Lens
Flare effect's control point.
1 In the Tracker Controls panel, choose the tracked layer from the Motion Source menu.
Choose the track that contains the tracking data you want from the Current Track menu.
2
Click Edit Target, and choose the target.
3
4 In the Tracker Controls panel, click the Apply button.
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 motion path's keyframes in the Layer panel as you would any other
motion path. This 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.
Motion source and its motion path
A. Moving the feature and search regions B. Keyframe marker
See also
"Creating and modifying motion paths" on page 199
Correct drifting by adjusting the feature and search regions
Move the current-time indicator to the last well-tracked frame.
1
A
B
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