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Keying in After Effects CS3

Article Description

Does the idea of keying conjure up images of a meteorologist on the evening news, or a shooting technique used in motion pictures? With After Effects, even the simplest, least-expensive project can take advantage of keying. The Adobe Creative Team takes us through a step-by-step example of this technique.

Adding the Foreground Subject

Next, you'll add the Talent_DV.mov footage item to the composition.

  1. Press the Home key to make sure that the current-time indicator is at the beginning of the time ruler.
  2. Drag the Talent_DV.mov item from the Project panel to the Timeline panel. The Talent_DV image appears in the foreground of the Composition panel (see Figure 4).

This is a simple greenscreen shot. If you manually preview the shot by dragging the current-time indicator across the time ruler, the actor doesn't move very much, which will aid in your keying. However, notice that the backdrop isn't lit evenly. The upper portion is much brighter than the lower portion. This situation might cause some problems.

When After Effects pulls a key, it looks at the entire frame. The larger the area that must be analyzed and the larger the variation in color, the greater the risk that you won't be able to remove all of the background color. You can reduce this risk by using a garbage mask. A garbage mask (or matte) is so named because it's used to mask out bad or unnecessary parts of an image. When you create a garbage mask for a layer, it's a good idea to keep it fairly loose. If the foreground subject is moving, you need to leave enough room in the garbage mask to accommodate the motion. If you make it too tight, you'll have to animate the mask over time—and that isn't much fun. Remember, a garbage mask is used to help solve problems—not create new ones.

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