Chapter 13: motion tracking, Motion tracking overview, About motion tracking – Adobe After Effects CS3 User Manual
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Chapter 13: Motion tracking
Motion tracking overview
About motion tracking
With motion tracking, you can track the movement of an object and then apply the tracking data for that movement
to another object—such as another layer or an effect control point—to create compositions in which images and
effects follow the motion. You can also stabilize motion, in which case the tracking data is used to animate the
tracked layer to compensate for movement of an object in that layer. You can link properties to tracking data using
expressions, which opens up a wide variety of uses.
After Effects tracks motion by matching image data from a selected area in a frame to image data in each succeeding
frame. You can apply the same tracking data to different layers or effects. You can also track multiple objects in the
same layer.
Motion tracking has many uses. Here are some examples:
•
Combining elements filmed separately, such as adding video to the side of a moving city bus or a star to the end
of a sweeping wand.
•
Animating a still image to match the motion of action footage, such as making a cartoon bumblebee sit on a
swaying flower.
•
Animating effects to follow a moving element, such as making a moving ball glow. Michele Yamazaki provides a
tutorial on the Toolfarm website that shows how to use motion tracking to obscure a logo in motion footage:
.
•
Linking the tracked object’s position to other properties, such as making stereo audio pan from left to right as a
car races across the screen.
•
Stabilizing footage to hold a moving object stationary in the frame to examine how a moving object changes over
time, which can be useful in scientific imaging work.
•
Stabilizing footage to remove the jostling of a handheld camera.
Depending on the encoder you use, it is possible to decrease the size of your final output file by stabilizing motion
footage. Random motion, such as from the jostling of a handheld camera, can make it difficult for many compression
algorithms to compress your video.
You set up, initiate, and apply motion tracking with the Tracker Controls panel.
As with all properties, you can modify, animate, manage, and link tracking properties in the Timeline panel.
You specify areas to track by setting track points in the Layer panel. Each track point contains a feature region, a search
region, and an attach point. A set of track points is a tracker.