Correcting a drifting feature region (PB only)
There are two main methods for realigning a feature region if it drifts off track during tracking. If most of the footage tracked accurately, you may need only to move the feature region in selected frames. If drifting occurs early in the footage, you can modify the tracking settings and then track again from the beginning. Under certain conditions, you can correct drifting by simply enlarging the search region (for example, if the search region is too small to contain erratic movement of the feature region from one frame to the next). Note that increasing the size of the search region increases the tracking time.
To correct drifting by moving the feature region: - Drag the current-time indicator to the last well-tracked frame.
- Do one of the following:
- To correct a single frame, drag the feature region or track point to new locations. Alt-drag (Windows) or Option-drag (Mac OS) the feature region to move it without moving the track point. Use the Details section of the window to monitor the feature region position. The tracker automatically updates the previous tracking data to this new feature region/track point position.
- To correct several contiguous frames, drag the feature region or track point to new locations as described above and click Analyze. Watch the tracking to make sure it is accurate. If not, press any key to stop tracking, adjust the feature region, and begin again.
- To preview tracking, press the spacebar.
- When you are satisfied with the track, click Apply to copy keyframes to the selected layer.
To correct drifting by modifying tracking settings: - Drag the current-time indicator to the last well-tracked frame.
- Click Options and change the following settings:
- If colors change in the feature region, increase the Track Adaptiveness value.
- Select Process Before Match, select Blur, and then type a value of 2 to 3 pixels. Select Enhance if the edges of the feature are fuzzy. Deselect the Blur option if you want to use Subpixel Matching.
- Choose a value from 1/2 to 1/16 for Subpixel Matching. A smaller fraction increases the accuracy of the tracker but also increases tracking time.
- If the area to be tracked has high contrast, change the Use option to Luminance. Try Saturation if the area has a high concentration of color.
- If the area is partially obscured during tracking, set a tolerance value for Extrapolate Motion if Accuracy Is Below_%. Determine the proper value by creating a trial track and then examining the accuracy displayed in the Tracker controls panel for any frames with an obscured feature region. Type a value that is slightly larger than the largest accuracy value for the problem frames.
- If you can clearly track backward from some point at the end of the motion, select Track in Reverse. When used with forward tracking, Track in Reverse can help isolate problem areas where the Tracker controls can't maintain a good track.
- Click OK in the Motion Tracker Options dialog box and, in the Tracker panel, click Analyze. Watch the tracking to make sure it is accurate. If not, press any key to stop tracking, adjust the settings, and begin again.
- To preview tracking, press the spacebar.
- When you are satisfied with the track, click Apply to copy keyframes to the selected layer.
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