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Chapter 55 Keying, Mattes, and Masks 811
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Step 3: Eliminate fringing with the Matte Choker filter
After keying out as much of the background as you can without touching the
foreground subject, apply the Matte Choker filter to eliminate any faintly remaining
blue or green fringing or pixels surrounding the edge of your foreground subject.
Using the Matte Choker filter to eliminate this fringing works similarly to using the
Thin/Spread slider in the Chroma Keyer. You may find that, for some clips, the Matte
Choker filter works better than using more aggressive settings in the Chroma Keyer,
giving you a better chance of preserving as much fine detail around the edges of your
foreground subject as possible. Adjust the Edge Thin slider to the right to remove faint
areas of the key color around your foreground subject and to smooth out the rough
edges of your key.
A second Matte Choker filter can also be applied to fill holes in the foreground subject that
appear as a result of aggressive settings applied to key out the background. By adjusting
the Edge Thin slider to the right, you can fill in semitranslucent areas in your foreground
subject, without changing the background areas you’ve already keyed out. For more
information about the Matte Choker filter controls, see “Matte Filters” on page 682.
Step 4: Readjust the Chroma Keyer filter’s settings
When keying, additional filters you add usually affect the overall results of previously
applied filters, so after applying the Matte Choker, you’ll probably want to readjust the
Chroma Keyer filter’s settings to take into account the effect the Matte Choker is
having. Changes you make to the Chroma Keyer filter’s settings affect what the Matte
Choker does, so go back and forth between the Chroma Keyer and Matte Choker filters
until you find a balance of settings that effectively removes the background without
eating into your foreground subject.
Step 5: Desaturate the key with spill suppressor filters
If you have some slight color spill from the background around the edge of your
foreground subject, you can use the Enhance control of the Chroma Keyer to
desaturate the color spill so that it’s not noticeable.
If you have other regions of color spill that appear within your foreground subject—
showing through a sheer dress, for instance—you may want to use the Spill Suppressor
- Blue or Spill Suppressor - Green filter to selectively desaturate just the key color so
that it’s not noticeable. The spill suppressor filters may affect the overall color of the
foreground subject, however, so you may need to use a color correction filter to
compensate for this effect.