User Guide

401
ADOBE AFTER EFFECTS 5.0
User Guide
Tracking position using affine corner pinning
When you track position using affine corner pinning, you simultaneously track three
points in a motion footage layer with three points in a second layer. The position of a
fourth, inactive point is determined by the three active points. As the three points move,
the layer is distorted to simulate skewing, scaling, and rotation, but not perspective.
Parallel lines remain parallel, and relative distances are preserved. For example, suppose
that you have footage shot by a handheld camera that zoomed in or out during shooting
but remained perpendicular to the background; you want to replace the background.
Using affine corner pinning, the Tracker/Stabilizer calculates the relative movement
between the feature regions and track points to create the correct scaling of the
background.
Place the track points anywhere in the motion footage layer; they do not need to be in the
center or in the corner of the feature regions. The Tracker/Stabilizer applies the Corner Pin
effect to the second layer, generating keyframes for the layer and Corner Pin effect
keyframes for each corner.
When you choose affine corner pinning, the default positions of the track points form a rectangle in the center
of the motion footage layer (left). Moving the upper left tracking region moves the lower right (inactive) track-
ing region in tandem (center). You can place the track points anywhere in the motion footage layer (right).
To define tracking regions for affine corner pinning:
1 Specify the tracking region that will be inactive by Alt-clicking (Windows) or Option-
clicking (Mac OS) the region.
2 Place and resize the three active feature and search regions over the areas you want to
track.
UG.book Page 401 Wednesday, February 21, 2001 12:05 PM