Instruction Manual

Chapter 22 Motion tracking 1008
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Look Ahead Frames: Use this slider and value slider to specify the number of “future” frames
to be analyzed by the tracker. In other words, you can direct the tracker to look in a specic
location for its reference point. This is useful for footage that contains fast-moving objects,
because the reference point can quickly get away from the tracker. For more information on
using Look Ahead Frames, see Advanced strategies to improve tracking results on page 984.
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Track list: Use this list to see the trackers in the behavior. To disable a tracker, deselect its
checkbox. A tracker that is turned o is not analyzed with the track. When another track is
referenced, the track list is replaced with a Tracker pop-up menu. Click the disclosure triangle
next to the track name to reveal these additional parameters:
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Position: Displays the X and Y positions of the tracker. The X position is the value slider on
the left; the Y position is the value slider on the right. Click the disclosure triangle to display
labeled position value sliders.
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Track Size: Use this slider to adjust (in pixels) the pattern search size for the tracker. As you
adjust the track size, the Tracker Preview is updated to show the new track size (there is
no visual change in the Canvas tracker). (To adjust the Track Size without exposing its
parameters, Option-drag left in the Tracker Preview area to reduce the track size; Option-
drag right to increase the track size.)
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Search Size: Use this slider or value slider to increase or reduce the tracker’s search area size.
In Motion, you do not specify the size of a search area when setting up your trackers in the
Canvas. To change the default search size, use the slider or value slider. If Search Size is set to
200 percent, the tracker’s search area is twice the default search area size.
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Fail Tolerance: Use this parameter to dene the amount of tolerance for error, or condence
value, of the track. In other words, this parameter denes at what score the tracker determines
it is able to match a reference feature. When above the score, the tracker accepts the match.
When below the score, the tracker rejects the match. When the match is rejected, the Fail
Behavior kicks in.
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Fail Behavior: Use this pop-up menu to specify what happens if the track condence value falls
below the Fail Tolerance amount. The following options are available:
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Smart Retry: The tracker attempts to nd the reference pattern in a larger search area. If
the pattern cannot be found, the tracker switches to the Predict option. Smart Retry is the
default fail behavior.
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Stop: The analysis stops when the tracker loses the reference pattern. You can also click the
Stop button in the tracking progress dialog or press Esc to stop an analysis.
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Predict: The tracker predicts a new search area without creating keyframes until it nds
a match for the reference pattern. This is excellent for tracked objects that pass behind
foreground objects.
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Predict and Key: If a failure is detected, the tracker predicts the location of the keyframe
based on a vector of the last two keyframes, and continues tracking in the new area.
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Don’t Predict: The tracker remains in its position and searches for subsequent matches as the
clip’s frames progress. While searching for a match, the tracker does not create keyframes.
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Use Existing Keyframes: The tracker uses manually added keyframes as a guide during
analysis. After you add keyframes, return to the start frame and start the tracking analysis.
If the tracker cannot locate the track pattern, the manually created tracking keyframes are
referenced to guide the tracker.
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