Finding a Good Reference Feature

Your choice of reference feature directly affects the accuracy of the Tracker. As you work with the Tracker, you will develop an eye for evaluating what makes good reference features.

Play a clip several times before you choose a reference feature. Ideally, you want a reference feature that:

• Appears in every frame of the sequence being tracked.
• Cannot be confused with any other similar feature nearby in the frame; for instance, a button on a shirt would be a poor choice if there are identical buttons close by that the Tracker could accidentally lock on to.
• Moves exactly as you want your element to move.
• Has shape and luma cues that allow for good registration ("locking") of a match both vertically and horizontally.

The Tracker uses the luma (or light vs. dark) and shape information of the reference feature to locate matches in subsequent frames.

Finding perfect reference features all the time is rare. For example, finding a feature that is present in every frame is not always possible. You may have to track two different features, track a feature that disappears behind another one, or track a feature that moves out of the frame. For more information on how to work with these kinds of situations, see Advanced Tracking Techniques.

In the best possible situation, you have planned the reference features during pre-production and deliberately marked them during production. In the worst situation, the reference feature is so poorly defined that the only way to track it is manually. For more information, see Snapping to Update the Reference Box.

Note: You may want to add an effect to the clip to make the reference feature better, such as contrast adjustments or emboss, then track the altered clip. Finally, you would remove or turn off the effect before final rendering.