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Animating Layers in After Effects CS3

  • Article is provided courtesy of Adobe Press.
  • Date: Nov 13, 2008.

Article Description

Animation is all about making changes over time to an object or image's position, opacity, scale, and other properties. In this step-by-step exercise, the Adobe Creative Team explores some of the fun possibilities for animating a Photoshop file in After Effects CS3.

Adjusting the Layers and Creating a Track Matte

To solve the problem of the sun, birds, and clouds overlapping the window frame, you must first adjust the hierarchy of the layers within the composition, and then you'll use an alpha track matte to allow the outside scenery to show through the window, but not appear to be inside the room.

Pre-Composing Layers

You'll start by pre-composing the Sun, Birds, and Clouds layers into one composition.

  1. Shift-click to select the Sun, Birds, and Clouds layers in the Timeline panel.
  2. Choose Layer > Pre-Compose.
  3. In the Pre-Compose dialog box, name the new composition Window Contents. Make sure that the "Move all attributes into the new composition" option is selected, and select Open New Composition. Then click OK.

    A new Timeline panel named Window Contents appears. It contains the Sun, Birds, and Clouds layers you selected in step 1 of this exercise (see Figure 18).

  4. Click the Sunrise Timeline panel to see the contents of the main composition. Notice that the Sun, Birds, and Clouds layers have been replaced by the Window Contents layer, which refers to the Window Contents composition (see Figure 19).

Creating the Track Matte

Next, you'll create the track matte to hide the outside scenery behind all areas of the image except the window pane. To do that, you'll duplicate the Window Lit layer and use its alpha channel.

When you want one layer to show through a hole in another layer, set up a track matte. You'll need two layers—one to act as a matte, and another to fill the hole in the matte. You can animate either the track matte layer or the fill layer. When you animate the track matte layer, you create a traveling matte. If you want to animate the track matte and fill layers using identical settings, you can pre-compose them.

You define transparency in a track matte using values from either its alpha channel or the luminance of its pixels. Using luminance is useful when you want to create a track matte using a layer without an alpha channel, or a layer imported from a program that can't create an alpha channel. In both alpha channel mattes and luminance mattes, pixels with higher values are more transparent. In most cases, use a high-contrast matte so that areas are either completely transparent or completely opaque. Intermediate shades should appear only where you want partial or gradual transparency, such as along a soft edge.

After Effects preserves the order of a layer and its track matte after you duplicate or split the layer. Within the duplicated or split layers, the track matte layer remains on top of the fill layer. For example, if your project contains layers A and B, where A is the track matte and B the fill layer, duplicating or splitting both of these layers results in the layer order ABAB.

Figure 20 shows a traveling matte. A is the track matte layer—a solid with a rectangular mask, set to Luma Matte. The mask is animated to travel across the screen. B shows the fill layer—a solid with a pattern effect. C shows the result: The pattern is seen in the track matte's shape and added to the image layer, which is below the track matte layer.

  1. In the Sunrise Timeline panel, select the Window Lit layer.
  2. Choose Edit > Duplicate.
  3. Drag the duplicate layer, Window Lit 2, up in the layer stack so that it's above the Window Contents layer (see Figure 21).
  4. Click Toggle Switches/Modes in the Timeline panel to display the TrkMat column so you can apply the track matte.
  5. Select the Window Contents layer and choose Alpha Matte "Window Lit 2" from the TrkMat pop-up menu. The alpha channel of the layer above (Window Lit 2) is used to set transparency for the Window Contents layer, so that the scenery outside the window shows through the transparent areas of the window pane (see Figure 22).
  6. Press the Home key and then press the spacebar to preview the animation. Press the spacebar again when you're done.
  7. Choose File > Save to save your project.

Adding Motion Blur

The birds will look more authentic if they include motion blur. You'll add the motion blur and then set the shutter angle and phase, which control the intensity of the blur.

  1. Switch to the Window Contents Timeline panel.
  2. Go to 4:22—the middle of the birds animation. With the Birds layer selected, choose Layer > Switches > Motion Blur to turn on the motion blur for the Birds layer.
  3. Click the Enable Motion Blur button at the top of the Timeline panel to display the motion blur for the Birds layer in the Composition panel (see Figure 23).
  4. Choose Composition > Composition Settings.
  5. In the Composition Settings dialog box, click the Advanced tab and reduce the Shutter Angle to 30 degrees. This setting imitates the effect of adjusting a shutter angle on a real camera, which controls how long the camera aperture is open, gathering light.
  6. Change the Shutter Phase setting to 0, and then click OK (see Figure 24).
6. Animating the Shadows | Next Section Previous Section

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