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Tutorial

Adobe After Effects 6.5

Keep motion in perspective

Picture this scenario: Your footage zooms in towards a person holding a signboard; you want to superimpose some animated artwork onto the signboard. This is easily done in Adobe® After Effects® 6.5 Professional edition with the new scale tracking feature. But what if the person turns away from the camera? The signboard turns, but the artwork doesn’t; not the effect we want! For this case, you can use Perspective Corner Pin tracking.

This tutorial shows you how to use Perspective Corner Pin tracking, provides some general tracking tips, and features many new tracking enhancements in After Effects 6.5.

Download the footage and artwork we used.

1. Add a motion tracker to your footage.

Create a new project, and drag your motion footage and a graphic file to the project window (video.mov and animation.mov in our example). To create a new composition that matches the dimensions of the motion footage, drag your motion footage (or our video.mov file) in the project window to the Create A New Composition button. Choose 100% from the Magnification Ratio menu in the lower left corner of the Composition window. Select the layer in the compo-sition window, and click Track Motion in the Tracker Controls palette; the layer opens in its own window, and a track point appears on it. Expand the layer and Motion Trackers in the Timeline window; then select Tracker 1. To rename the tracker, press Enter

(Windows) or Return (Mac OS) on your keyboard, and type a name (for example, type

s ignboard motion

), then press Enter or Return again to accept the change. Choose Perspective Corner Pin from the Track Type menu in the Tracker Controls palette.

The Perspective Corner Pin track type keeps track of the position of four different feature regions and trans-forms the shape of a targeted layer accordingly. Using this track type, you can track the position of the four corners of the signboard and conform another layer’s shape to it (animation.swf in our example).

2. Specify the areas you want to track.

Make sure that Magnify Feature When Dragging is selected in the Tracker Controls palette menu. Position your pointer within a track point while avoiding the track point’s attach point (the intersecting lines in the center of the track point) and avoiding the edges of the feature and search regions (the two boxes), so that the pointer appears black and with four arrows. Then drag the track point until the feature region is centered over a corner of the signboard. (The underlying image area is magnified as you move the feature region around the layer.) Drag each remaining track point to a different corner of the sign board.

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ADOBE AFTER EFFECTS 6.5

Keep motion in perspective

Tutorial

As you adjust the track point with the selection tool, the pointer icon changes to show which part of the track point you adjust if you drag.

3. Analyze the motion tracking.

In the Tracker Controls palette, click the Analyze Forward button to begin tracking motion; click Stop if any track point drifts away from a signboard corner. To fix the drifting track point, click Options in the Tracker Controls palette, choose Adapt Feature from the pop-up menu at the bottom of the dialog box, enter 20% in the If Confidence Is Below box, and click OK. In the Time Controls palette, click Previous Frame in the Tracker Controls palette until the first frame before the track point started to drift. Click Analyze Forward in the Tracker Controls palette to restart tracking motion. (Each time you analyze a frame, new tracker data automatically replaces any existing tracker data.)

As the signboard turns away from the camera, the image area within each feature region changes shape. This causes the tracker to drift away in search of an area that matches the initial feature region. By setting the tracker option to Adapt Feature when the tracker’s confidence

falls too low, you let the tracker reset the feature region to track the last good frame before the tracker confi-dence fell. Alternatively, you can have the tracker stop tracking, continue tracking, or extrapolate motion when the confidence falls.

4. Apply the tracking data to another layer.

Drag the file (animation.swf in our example) to which you want to apply the motion tracking, from the project window to the Timeline window, making sure it’s above the motion footage layer (video.mov layer in our example). Press Alt+Home (Windows) or Option+Home (Mac OS) to move the layer’s start point to the beginning of the composition. In the Tracker Controls palette, choose the layer with motion footage (video.mov in our example) from the Motion Source menu, click the Edit Target button, and choose the new file (animation.swf in our example), and click OK. Click Apply in the Tracker Controls palette to add the tracking data to the targeted layer. In the Timeline window, expand the layer (animation.swf in our example), its Effects group, and the Corner Pin group that contains the tracking data.

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ADOBE AFTER EFFECTS 6.5

Keep motion in perspective

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5. Preview your animation.

Bring the Composition window to the foreground, and click the RAM Preview button in the Time Controls palette.

6. Tweak the targeted layer’s motion.

If you need to adjust the animation, expand the layer, its Effects group, and the Corner Pin group in the Timeline window. Drag the current-time indicator to a frame in which the layer isn’t in the right perspective; then scrub the associated values (Upper Left, Upper Right, Lower Left, or Lower Right) in the Switches/Modes column to reshape the layer as needed.