Autodesk 62205-051408-9001 User Guide - Page 705

Using the Tracker ❚❘❘ positioned at the frame where the Tracker loses the reference feature. Make the necessary adjustments to the Tracker. See Advanced Tracking Techniques for ideas on how to handle various tracking situations. 10.Repeat steps 7 and 10 until you have completed the track. 11.Click the Off button in the Tracker panel to turn off the tracking process. The element selected in step 1 follows the motion of the reference feature. 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. Determining a Good Reference Frame The reference frame should be the frame where the reference feature is most representative in terms of shape, size, and rotation. It is usually the first frame, but it can be any frame that contains part of the motion you want to track since the analysis can proceed either forward or backward. Positioning the Reference and Tracker Boxes You can position the reference and tracker boxes using the mouse, the stylus, or the numerical controls in the Timeline. By default, when you move the reference box, the tracker box automatically moves with it. If you move or resize the tracker box, however, the reference box does not follow. Once you move or resize the tracker box, the size and position of each box remain independent of the other. You can re-establish the relationship using the Reset Tracker option. 689