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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.

Keying Out a Background with the Keylight Effect

There are many ways to pull a key in After Effects. In addition to using the Color Difference keyer, another good alternative is to use the Keylight effect. Keylight is a plug-in effect, licensed from The Foundry, that comes with After Effects CS3 Professional. It's a powerful keyer with numerous controls, and it's also one of the few effects that can pull a clean key in just one click.

If you'd like to try the Keylight effect, restart this article's exercises, completing the following steps instead of the ones in the sections "Applying the Color Difference Key Effect," "Choking the Matte," and "Removing Spill."

  1. With the Talent_DV layer selected in the Timeline panel, choose Effect > Keying> Keylight (1.2). Figure 16 shows the options.

    As with the Color Difference Key, the first step is to select the key color.

  2. In the Effect Controls panel, select the Screen Colour eyedropper. (The spelling of Colour reveals the products UK origins.)
  3. In the Composition panel, click a green area of the background near the actor's shoulder (see Figure 17).

    The results are instantaneous, and for many keying projects one click will produce the desired result. Still, you need to check for possible errors or holes. The effect's View pop-up menu will help you find and correct errors.

  4. In the Effect Controls panel, choose Status from the View pop-up menu (see Figure 18).

    The result is an exaggerated view of the matte that's generated by the key color selection. Opaque areas appear white, transparent regions appear black, and semi-transparent pixels are gray. Obviously, large areas of the image are not keyed correctly.

  5. In the Effect Controls panel, expand the Screen Matte property. Increase the Clip Black amount to 20.0, and decrease the Clip White amount to 90.0 (see Figure 19).

    This change tightens up the matte. There are still gray pixels in and around the subject, but that's okay because they blend with the background.

  6. Choose Final Result from the View menu. The key is good, but there are artifacts around the edge.
  7. Choose Colour Correction Edges from the View menu to see the edge of the matte.
  8. In the Effect Controls panel, increase the Screen Pre-blur amount to 5.0, and increase the Clip Rollback amount to 0.5.
  9. Choose Final Result from the View menu (see Figure 20).

    As is often the case in After Effects, you can achieve the same result by using different methods.

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