Adobe After Effects CS3 - Manual (Page 346)

AFTER EFFECTS CS3
User Guide
341
Note: To determine an acceptable confidence threshold, track the motion and then examine the Confidence values for
the track point in the Timeline panel for problematic frames. Specify a confidence value that is slightly larger than the
largest confidence value for the problematic frames.
• Select Continue Tracking to ignore the Confidence value. This is the default behavior.
• Select Stop Tracking to stop the motion tracking.
• Select Extrapolate Motion to estimate the position of the feature region. Attach-point keyframes aren’t created for
low-confidence frames, and attach-point keyframes for the low-confidence frames from previous tracks are
deleted.
• Select Adapt Feature to use the original tracked feature until the confidence level falls below the specified
threshold. At that point, After Effects adapts the tracked feature to be the contents of the feature region in the
frame preceding the one that has low confidence and continues tracking. This option isn’t available if Adapt
Feature On Every Frame is selected in the Motion Tracker Options dialog box; enabling feature adaptiveness
causes After Effects to adapt the feature region with every frame regardless of the confidence level.
Options Opens the Tracker Plug-in Options dialog box, which includes options for the AE Original Built-in Tracker.
This command is only available if you choose to use the older After Effects tracker plug-in.
Motion tracking properties in the Timeline panel
Each time you click Track Motion or Stabilize Motion in the Tracker Controls panel (or choose Animation > Track
Motion or Animation > Stabilize Motion), a new tracker is created for the layer in the Timeline panel. Each tracker
contains track points, which are property groups that store the tracking data after tracking has been performed.
Trackers are grouped in the Motion Trackers property group for each layer in the Timeline panel.
To show a tracker in the Timeline panel, select the tracker from the Current Track menu in the Tracker Controls panel
and press SS.
You can rename trackers and track points and modify and animate their property values in the Timeline panel just
as you do for other layer properties and property groups. You must click Apply in the Tracker Controls panel to apply
the property changes to the target.
Feature Center Position of the center of the feature region.
Feature Size Width and height of the feature region.
Search Offset Position of the center of the search region relative to the center of the feature region.
Search Size Width and height of the search region.
Confidence Property through which After Effects reports the amount of certainty regarding the match made for
each frame. In general, this is not a property that you modify.
Attach Point Position assigned to the target layer or effect control point.
Attach Point Offset Position of the attach point relative to the center of the feature region.