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Chapter 10 Using Filters 921
A common example of color keying is the meteorologist on TV. This person is always
seen standing in front of an animated map of the weather, but in reality he or she is
standing in front of a big greenscreen. As part of the broadcast, the greenscreen is
keyed out, and replaced by the map. You can do the same thing in Motion.
Important: Keying a foreground subject is not always easy, and it takes time and
patience to learn how to use the parameters in each filter to achieve the best effect.
Even so, most keys are pulled using more than one tool to do the job. Good
compositing artists usually combine one or more masked keying filters, Matte Choker
filters, a Spill Suppressor filter, and one or more garbage and holdout masks to isolate a
single subject. For more information on techniques you can use to improve a key, see
“Performing Multiple Keys on a Single Subject” on page 1112.
Blue Green Screen
The Blue Green Screen filter is intended for subjects that were shot in front of a
bluescreen or greenscreen. This filter renders the blue or green areas of the image
transparent, allowing one or more background images to show through.
Parameters in the Inspector
Key: Selects one of three keying modes: blue, green, or blue/green difference.
Color Level: Sets the percentage of color purity being keyed. Values range from 0 to
100.
Tolerance: Sets the color tolerance for your key. Larger values allow a greater
difference between the set key color and other color values that are incorporated into
the key. Values range from 1 to 100.
Edge Thin: Sets the amount of thinning done at the edges of the matte. A positive
value erodes the matte edge. Values range from –100 to 100.
Invert Matte: Toggles whether or not the matte is inverted.
Mix: Sets what percentage of the original image is blended with the filtered image.
Values range from 0 to 100%.
HUD Controls
The HUD contains the same controls as the Inspector, with the exception of the Mix
control.