Correcting A Drifting Feature Region (Pro Only); To Correct Drifting By Moving The Feature Region (Pro Only); To Correct Drifting By Modifying Tracking Settings (Pro Only) - Adobe AFTER EFFECTS 7.0 Manual

Correcting a drifting feature region (Pro only)

As an image moves in a shot, the lighting, surrounding objects, and angle of the object can all change, making the
once distinct feature no longer identifiable at the subpixel level. It takes time to develop an eye for choosing a
trackable feature. Even with careful planning and practice, you will often find that the feature region drifts away from
the desired feature. Re-adjusting the feature and search regions, changing the tracking options, and trying again is a
standard part of digital tracking. When drifting occurs, you may need to perform any combination of the following
adjustments:
•
Resize the feature and search regions and track again.
•
Track the shot in sections, redefining the feature region in places where the feature changes and the region drifts.
•
Track a different area with movement that closely matches that of the feature. If you are applying an effect or
adding something to a specific point, you usually want to track close to the original feature. For example, you may
want to add a glow effect to the end of a sword, but the lighting in the shot creates so much glare on the tip of the
sword that tracking it is impossible. Tracking the opposite end of the sword would generate a much different
motion path than tracking the tip. (This is where planning ahead before you shoot can really pay off.)
•
Add a high-contrast object to the scene either attached to the object or in an area that matches the movement of
the feature before you shoot.
•
Adjust the tracking options to change the comparison method or precision of the frame-to-frame tracking.

To correct drifting by moving the feature region (Pro only)

Drag the current-time indicator to the last well-tracked frame.
1
Do one of the following actions:
2
•
To correct a single frame, drag the feature and search regions to new locations. Alt-drag (Windows) or Option-
drag (Mac OS) the feature region to move it without moving the attach point. Monitor the feature region position
in the Timeline panel. After Effects automatically updates the previous tracking data to this new feature
region/attach point position.
•
To correct several contiguous frames, drag the feature and search regions to new locations, resize if necessary, and
click Analyze. Watch the tracking to make sure that it is accurate. If the tracking is not accurate, then click the
button again to stop tracking, adjust the feature region, and begin again.
3 To preview tracking, press the spacebar.
When you are satisfied with the track, click Apply to copy keyframes to the selected layer or effect.
4

To correct drifting by modifying tracking settings (Pro only)

1 Drag the current-time indicator to the last well-tracked frame.
In the Tracker Controls panel, click Options.
2
In the Motion Tracker Options dialog box, select Enable Feature Adaptiveness if colors change in the feature
3
region or its shape evolves, and then click Options. After Effects displays the Tracker Plug-in Options dialog box.
Change the following settings as needed:
4
•
If the feature has high contrast, select Luminance.
•
If the feature has a high concentration of color, select Saturation.
•
If the footage is noisy or grainy, select Process Before Match, and click Blur. Type a value of 2 to 3 pixels.
•
If the edges of the feature are fuzzy, select Process Before Match, and click Enhance.
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