Adobe After Effects CS3 Bedienungsanleitung PDF herunterladen (Seite 342)

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AFTER EFFECTS CS3

User Guide

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For best results, prepare the object or region that you are tracking before you begin shooting. Because After Effects

compares image data from one frame to the next to produce an accurate track, attaching high-contrast markers to

the object or region lets After Effects more easily follow the motion from frame to frame. Lightweight, brightly

colored balls (such as ping-pong balls) placed on the feature work particularly well, in part because their appearance

is the same from all angles. The number of markers that you use corresponds to the number of points you are

tracking. For example, if you’re tracking four points using the Perspective Corner Pinning option, you’ll track four

features, to correspond to the four corners of the layer to attach. The more markers you add to your subject before

shooting, the more features you’ll have for tracking—but the more items you might have to remove later from the

image with the Clone Stamp tool. You don’t need to add a marker for each feature if there is already a distinctive

object or region at the appropriate location.

2. Add the appropriate number of track points

When you choose a mode from the Track Type menu in the Tracker Controls panel, After Effects places the appro-

priate number of track points in the Layer panel for that mode. You can add more track points to track additional

features with one tracker.

3. Select features to track, and place feature regions

Before you begin tracking, view the entire duration of the shot to determine the best features to track. What is clearly

identifiable in the first frame may later blend into the background because the angle, lighting, or surrounding

elements have changed. A tracked feature may disappear off-screen or be obscured by another element at some point

in the scene. Though After Effects can extrapolate the feature’s motion, your chances for successful tracking are

highest if you step through the entire shot to select the best candidates for tracking.

A good tracked feature has these characteristics:

• Visible for the entire shot

• A contrasting color from the surrounding area in the search region

• A distinct shape within the search region

• A consistent shape and color throughout the shot

4. Set the attach point offset

The attach point is where the target layer or effect control point will be placed. The default attach point position is in

the center of the feature region. You can move the attach point to offset the target’s position relative to the tracked

feature’s position by dragging the attach point in the Layer panel before tracking.

Forexample,toanimateacloudaboveaperson’shead,positionthefeatureregionontheheadandmovetheattach

pointabovethehead.Ifyoulefttheattachpointcenteredinthefeatureregion,thecloudwouldbeattachedtothat

point and would obscure the person’s head.

Attach point centered in feature region

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