Understanding how to use the Tracker tool and apply the tracking data to elements in a composition, and determining to which parameters you want to apply the tracking data are key factors for producing basic to complex effects. The more experience you gain from using the Tracker tool and applying tracker data to elements, the more you see all the effects that trackers can produce. If your composition is jittery, use the stabilizing feature within the Tracker tool or the Panner tool to remove, for example, unwanted camera jitter.
Tracking and stabilizing are often processes of trial and error. You should track or stabilize with default settings, and if the tracker box strays, fine-tune the analysis.
Much of the tracking and stabilizing work you do will be done using the Reaction supertool—see Reaction Compositing and Effects, and the 2D Transform Tool—see 2D Transform Tool.
The Tracker is a tool for following and capturing the motion of an on-screen feature, and then applying that stored motion to a second element, so that the two appear to be locked together. You can track any number of features in a length of footage:
You can apply the stored motion to various elements:
Center point of an object For example, you could track a halo over the head of a person in a clip. Assume that in the clip a woman tilts her head and advances toward the camera. You would want the halo to reflect the position, scaling, and rotational changes of the tracked features on the woman's head.
Control points of an object The shape of the object changes to reflect the motion of the reference feature its control points are locked to. For example, if you want to replace the label on an actor's clothing, each corner on the new label would track a corner on the old label. The shape of the new label would change to correspond to those movements.
Stabilizing is a powerful process that represents one of the most common uses of the Tracker.
In most tracking the Tracker applies the reference motion to the desired element so that the two are locked. In stabilizing, the Stabilize filter uses the Tracker data to invert the analyzed motion to correct unwanted camera or subject motion.You can stabilize any number of features in a composition:
With stabilizing, the shift values are inverted, for example, (3, -2) would become (-3, 2) before they are applied. This inversion results in an elimination of the motion.
The Stabilize filter uses the Tracker data to move the image so that the reference feature occupies the same position it did in the preceding frame. In other words, the reference feature stays still because the frame is being moved.
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