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Outer Glow: Picks the color of the outer part of the glow. Use the disclosure triangle to
display Red, Green, and Blue sliders for more precise color selection.
Crop: Sets whether or not the object is cropped at its original boundaries.
Mix: Sets what percentage of the original image is blended with the filtered image.
HUD Controls
The HUD contains the following controls: Intensity, Size, Rotation, Inner Glow, and Outer
Glow.
Keying Filters
Keying filters are used to isolate a subject that is surrounded by an area of fairly uniform
color or brightness by generating an alpha channel based on the shape of that area.
Keying is most commonly performed on subjects that were shot against a blue- or
green-colored background, but keys can also be based on brightness values.
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 green screen. As part of the broadcast, the green screen 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.
Blue Green Screen
The Blue Green Screen filter is intended for subjects that were shot in front of a blue
screen or green screen. 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.
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.
Edge Thin: Sets the amount of thinning done at the edges of the matte. A positive value
erodes the matte edge.
Invert Matte: Sets whether or not the matte is inverted.
1021Chapter 16 Using Filters