Track or stabilize motion – Adobe After Effects CS4 User Manual
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USING AFTER EFFECTS CS4
Animation and keyframes
Last updated 12/21/2009
You can apply the tracking data to a null object layer and parent the layer that you want to animate to the null object
layer.
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Track or stabilize motion
Tracking motion and stabilizing motion are essentially the same process, only with a different target and result. Use
Track Motion to track motion and apply the results to a different layer or effect control point. Use Stabilize Motion to
track motion and apply the results to the tracked layer to compensate for that motion (for example, to remove camera
shake).
To stabilize a layer, After Effects tracks the motion of a feature in the layer that should be stationary in the frame, and
then uses the tracking data to set keyframes to perform the opposite motion. You can stabilize to remove any
combination of changes in position, rotation, and scale, while leaving desired motion unaffected. For example, if the
camera is panning, deselect Position but select Scale and Rotation as the properties to stabilize.
When you select Rotation or Scale in the Tracker panel, you set two track points in the Layer panel. A line connects
the attach points; an arrow points from the first attach point (the base) to the second. If possible, place the feature
regions on opposite sides of the same object, or at least on objects that are the same distance from the camera. The
farther apart the regions, the more accurate the calculations and the better the result.
After Effects calculates rotation by measuring the change of angle of the line between the attach points. When you
apply the tracking data to the target, After Effects creates keyframes for the Rotation property.
After Effects calculates scale by comparing the distance between attach points on each frame with the distance between
the attach points on the start frame. When you apply the tracking data to the target, After Effects creates keyframes for
the Scale property.
When you track motion using either parallel or perspective corner pinning, After Effects applies keyframes for the
Corner Pin effect to the layer to scale and skew the target layer as necessary to fit the four-sided area defined by the
feature regions. The feature regions should lie in a single plane in the real world—for example, on the side of a bus, on
the same wall, or on the floor. The attach points should also all lie in a single plane, but not necessarily the same plane
as the feature regions.
Note: For parallel corner pinning only: To change which point is inactive, Alt-click (Windows) or Option-click (Mac OS)
the feature region of the point to make inactive. (One point must remain inactive to keep the lines parallel.)
1
Select the layer to track in the Timeline panel.
2
Do one of the following:
•
Click Track Motion in the Tracker panel (or choose Animation
> Track Motion), click Edit Target, and choose the
target to apply the tracking data to.
•
Click Stabilize Motion in the Tracker panel (or choose Animation
> Stabilize Motion). The target layer is the
tracked (source) layer.
3
Select Position, Rotation, and/or Scale to specify what kinds of keyframes to generate for the target.
4
Move the current-time indicator to the frame from which to begin tracking.
5
Using the Selection tool, adjust the feature region, search region, and attach point for each track point.
6
In the Tracker panel, click either the Analyze Forward or Analyze Backward button to begin tracking.