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Choking the Matte

Because the Color Difference Key only removes color from the clip, the edge of the actor still has an unwanted fringe. To refine the edge of your matte, you need to choke (tighten) it.

  1. Select the Talent_DV layer in the Timeline panel and choose Effect > Matte > Matte Choker. This effect gives you more control over the edge of the matte than the Simple Choker effect does. The main difference between the two is that the Simple Choker only allows you to tighten up the matte, while the Matte Choker also allows you to smooth (feather) the edges.

    In the Effect Controls panel, the top three Matte Choker controls—Geometric Softness 1, Choke 1, and Gray Level Softness 1—let you spread the matte as far as possible without changing its shape. The next three controls can be used to choke the matte.

    In this exercise, most of the default settings work well. Consider yourself fortunate if this is the case on all your future keying projects. The only setting that needs adjusting is the Geometric Softness 2 setting, which you'll use to create a slight blur along the edge of the matte.

  2. Increase the Geometric Softness 2 amount to 4.00.
  3. Check the matte by clicking the Show Channel button at the bottom of the Composition panel and choosing Alpha from the pop-up menu (see Figure 13). The matte looks great!
  4. Switch back to the RGB view to get ready to remove some green spill.
  5. Hide the Matte Choker properties to keep the Effect Controls panel tidy.
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