Adjusting Tolerance

Reduce the tolerance value if the reference feature becomes hidden by another object for several frames and does not change direction during that time. This prevents the Tracker from setting incorrect keyframes while the reference feature is hidden.

Adjusting the tolerance value can prevent or reduce the need to track manually.

This strategy works best when the frame-to-frame motion of the reference feature (while it is hidden) has the same direction and speed as the frame-to-frame motion it had just before it became hidden.

The Tracker can extrapolate likely future locations of the reference feature while it is out of view. The position of the tracker box may then coincide with the position of the reference feature when it reappears.

For example, say a truck enters the frame from the left in your clip. After several frames it enters a tunnel, stays in the tunnel for several frames, and then exits the tunnel on the right. You use the headlight on the truck as a reference feature. You pause the analysis as the headlight enters the tunnel, lower the tolerance until the Tracker cannot find a match, and then restart the analysis. When the headlight reappears, the tracker box is positioned over it, the Tracker finds a match, sets a keyframe, and continues tracking.

Note: Tolerance is "animatable". That is, you can change the tolerance value at different points during the analysis.

To adjust tolerance:

1. Analyze the clip with the default tolerance value.
2. Pause the analysis when the Tracker loses its reference feature.
3. Press Backspace to return to the frame where the reference feature is first hidden by another object.
4. On the Tracker panel, reduce the tolerance value until the two diagonals in the tracker box disappear. The two diagonals indicate that a keyframe was set. Make sure you lower tolerance enough so that the Tracker does not make a bad match.
5. Restart the analysis.

The analysis resumes. No keyframes are set while the reference feature is hidden. The Tracker extrapolates the estimated position of the reference feature until it reappears.