5.5

1126Motion User Guide
During the analysis, the tracker advances to each subsequent frame, sampling many
positions in the search region around the center point of the tracker. Some of those
positions fit the designated reference pattern more closely than others; the tracker finds
the position where the search region most closely matches the reference pattern (with
subpixel accuracy). For every frame analyzed, the tracker assigns a correlation value by
measuring how close the best match is.
In addition to searching for the reference pattern’s position, the tracker identifies how the
pattern transforms (scales, rotates, or shears) from one frame to the next. Imagine you’re
tracking a logo on the shirt sleeve of a person walking past the camera. If the person turns
slightly as he passes the camera, the reference pattern rotates. The tracker looks for the
reference pattern and any shifts in that pattern’s scale or rotation.
As it analyzes motion in your project, Motion records the data, which you can then apply to
any other object in your project.
The more trackers you use, the more spatial information you’ll record: One-point tracking
records position data; two-point tracking and four-point tracking record position, rotation,
and scale data (by comparing the relative change between the points); multiple-point
tracking can record all the control points (vertices) on a shape.
Tracking in Motion is planar; in other words, tracking does not occur in Z space (depth). For
example, when you analyze two features in a clip—and that clip is moving in 3D space—you
record the changes in position, scale, or rotation over time in the clip, but not its actual 3D
transformation.
Note: The Stabilize behavior (in the Motion Tracking category of behaviors) uses an
advanced technology that analyzes the motion of the entire frame of a clip, without the use
of trackers.
Motion tracking behavior types
There are six tracking behaviors in Motion:
Analyze Motion
Generates and stores tracking information from a video clip, but does not apply that
tracking data to other objects. However, other tracking behaviors can apply Analyze Motion
tracking results to objects. The Analyze Motion behavior lets you add multiple trackers to a
clip, to track multiple reference patterns at the same time. See Analyze motion in a clip.
Match Move
Matches a foreground element to a background element so they appear locked together.
Using Match Move, you can analyze one or more reference points in a video clip, then apply
that tracking data to nearly any other object in your project, or you can apply tracking data
supplied by another tracking behavior (such as Analyze Motion or Stabilize). You can also
apply animation data created by keyframes or other behaviors (without having to analyze
the motion of the animated source object). See Intro to match moving in Motion.