Adobe After Effects CS4 - Manual (Page 276)

270 USING AFTER EFFECTS CS4
Animation and keyframes
Last updated 12/21/2009
than the surrounding image (such as a burning candle carried through a room). Select Saturation if the tracked feature
has a high concentration of color, surrounded by variations of the same color (such as a bright red scarf against a brick
wall).
Process Before Match Temporarily blurs or sharpens an image to improve tracking. Blur reduces noise in the footage.
Usually a value of 2 to 3 pixels is enough to produce better tracks in grainy or noisy footage. Enhance exaggerates or
refines the edges of an image and makes them easier to track.
Note: After Effects blurs or enhances the layer only for tracking. This blurring does not affect the motion source layer.
Track Fields Temporarily doubles the frame rate of the composition and interpolates each field to a full frame to track
motion in both fields of interlaced video.
Subpixel Positioning When selected, keyframes are generated to a precision of a fraction of a pixel. When deselected,
the tracker rounds off values to the nearest pixel for generated keyframes.
Adapt Feature On Every Frame Causes After Effects to adapt the tracked feature for each frame. The image data that
is searched for within the search region is the image data that was within the feature region in the previous frame,
rather than the image data that was in the feature region at the beginning of analysis.
If Confidence Is Below Specifies the action to perform when the Confidence property value is below the percentage
value that you specify.
Note: To determine an acceptable confidence threshold, track the motion and then examine the Confidence values for the
track point in the Timeline panel for problematic frames. Specify a confidence value that is slightly larger than the largest
confidence value for the problematic frames.
• Select Continue Tracking to ignore the Confidence value. This behavior is the default behavior.
• Select Stop Tracking to stop the motion tracking.
• Select Extrapolate Motion to estimate the position of the feature region. Attach-point keyframes aren’t created for
low-confidence frames, and attach-point keyframes for the low-confidence frames from previous tracks are
deleted.
• Select Adapt Feature to use the original tracked feature until the confidence level falls below the specified threshold.
At that point, After Effects adapts the tracked feature to be the contents of the feature region in the frame preceding
the one that has low confidence and continues tracking. This option isn’t available if Adapt Feature On Every Frame
is selected in the Motion Tracker Options dialog box; enabling feature adaptiveness causes After Effects to adapt
the feature region with every frame regardless of the confidence level.
Options Opens the Tracker Plug-in Options dialog box, which includes options for the AE Original Built-in Tracker.
This command is only available if you choose to use the older After Effects tracker plug-in.
Note: To show or hide motion paths in the Layer panel, select or deselect the Display Motion Paths option in the panel
menu of the Tracker panel. (The panel menu is the menu that you access by clicking the icon in the upper-right corner of
a panel.) You can also use commands in this menu to add a new track point, reveal the current track in the Timeline
panel, and toggle whether the feature region magnification is enabled.
Motion tracking properties in the Timeline panel
Each time you click Track Motion or Stabilize Motion in the Tracker panel (or choose Animation > Track Motion or
Animation > Stabilize Motion), a new tracker is created for the layer in the Timeline panel. Each tracker contains track
points, which are property groups that store the tracking data after tracking has been performed. Trackers are grouped
in the Motion Trackers property group for each layer in the Timeline panel.
To show a tracker in the Timeline panel, select the tracker from the Current Track menu in the Tracker panel and
press SS.