Autodesk 62205-051408-9001 User Guide - Page 716

26 Tracking Point 2 is tracked and stabilized after point 1. Each of the 2 points is stabilized individually. 11.Play the clip. The unwanted motion is eliminated. 12.Click the Off button in the Tracker panel when stabilizing is complete. Advanced Tracking Techniques The tracker box sometimes loses its reference feature during the analysis. This is because in some clips, it may be difficult to have reference features that move predictably, remain visible, and do not change their appearance during the clip. By understanding how the Tracker analyzes the information in your clip, you can predict the Tracker's behavior and obtain the results that you want. You can also observe the Tracker data in the Timeline to troubleshoot a difficult track. Finally, there are a number of simple strategies you can use when the Tracker "loses" its reference feature. How the Tracker Works The Tracker first tracks motion of the reference feature(s), then applies or inverts that motion, depending on if you are tracking or stabilizing. Once you have set up your Trackers, the analysis can begin. This is how the Tracker analyzes and "remembers" the motion of the reference feature: • The Tracker stores the position of the reference box on frame 1. • The Tracker advances to the next frame and positions the tracker box in the same place as in the previous frame. • It searches the tracker box for an area that matches the contents of the reference box. The Tracker uses luma cues (white versus black) and shape cues to determine what is a match. • Once it finds a match, the Tracker uses the location of the match to move the center of the tracker box over the center of the match. This change in position is stored as an X and Y shift value. • On the next frame, and on all future frames, the Tracker gets a little "smarter" about where it positions the tracker box. It extrapolates the likely position of the reference feature based on the amount and direction of the motion that occurred between the last two frames. The Tracker makes an "educated guess" of where the feature may be, based on past matches. Note: This means the Tracker works best when the motion of the reference feature is regular and does not suddenly or erratically change direction or speed. • Once the Tracker has analyzed the motion of the reference feature, and stored it as Shift values for each frame, it copies the motion of the reference feature to the element that you are tracking, so that the two appear locked together. In all tracking except for stabilizing, the Tracker applies the shift values without modification. With stabilizing, the Stabilizer operator inverts the shift values, resulting in a negation (and therefore elimination) of the motion. For more information, see Stabilizing. 700