Adobe AFTER EFFECTS CS3 PROFESSIONAL User Manual page 341

AFTER EFFECTS CS3 335
User Guide
A B C
Layer panel with track point
A. Search region B. Feature region C. Attach point
The feature region defines the element in the layer to be tracked. The feature region should surround
Feature region
a distinct visual element, preferably one object in the real world. After Effects must be able to clearly identify the
tracked feature throughout the duration of the track, despite changes in light, background, and angle.
The search region defines the area that After Effects will search to locate the tracked feature. The
Search region
tracked feature needs to be distinct only within the search region, not within the entire frame. Confining the search
to a small search region saves search time and makes the search process easier, but runs the risk of the tracked feature
leaving the search region entirely between frames.
The attach point designates the place of attachment for the target —the layer or effect control point to
Attach point
synchronize with the moving feature in the tracked layer.
Note: When you begin tracking, After Effects sets the quality of the motion source layer to Best and the resolution to Full
in the Composition and Layer panels, which makes the tracked feature easier to find and enables subpixel processing and
positioning.
After Effects uses one track point to track position, two track points to track scale and rotation, and four points to
perform tracking using corner pinning.
See also
"Expressions" on page 543
Motion tracking workflow
The implicit first step of any workflow is to determine the result that you want to achieve before you begin. What
sort of motion will you track, and what will you apply the tracking data to?
As with many workflows in the real world, you may have to repeat some of these steps. You can track a layer as many
times as desired and apply any combination of tracking results.
1. Set up the shot
For motion tracking to go smoothly, you must have a good feature to track, preferably a distinctive object or region.