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Important: Keying to isolate a foreground subject is not always easy; it takes time and
patience to learn how to use the parameters in each filter to achieve the best effect. Most
keys are “pulled” using more than one tool. Good compositing artists usually combine
masked keyer filters, matte adjustment filters, spill suppression operations, and garbage
or holdout masks to isolate a single subject. The Keyer filter in Motion combines many
of these operations within a single set of parameters. Two other Motion keying
filters—Matte Magic and Spill Suppression—provide standalone access to these finishing
operations. For more information on techniques you can use to improve a key, see
Applying Multiple Keys to a Single Subject.
Keying is accomplished using one of two keyer filters in Motion. The Keyer filter is a
general purpose color-keying filter that’s capable of blue screen or green screen keying,
or keying any range of color you choose. The Luma Keyer generates mattes based on a
sampled range of lightness in the image. Both keyer filters, as well as the Matte Magic
and Spill Suppression filters, are located in the Keying category of filters in the Motion
Library. (For basic information about Motion filters, see Using Filters.)
Using the Keyer Filter
The Keyer filter is intended for subjects shot in front of a blue screen or green screen.
However, this filter can also be used to pull chroma keys from any range of color within
a shot. The keyed portions of the image are rendered transparent, allowing background
images to show through.
You apply a Keyer filter like any other filter in Motion—via the Library or the Add Filter
pop-up menu in the toolbar. For more information about applying filters, see Applying
and Removing Filters.
Important: When combining masks with a keying filter, make sure the masks you use to
crop the keyed image are applied to the same image layer as the keying filter itself. Also,
apply masks after you apply a keying filter.
Automatic Versus Manual Keying
At its default settings, the Keyer filter attempts to work as automatically as possible. When
you apply the Keyer filter to an object, Motion analyzes the visible frame in the Canvas
to detect a dominant color such as a green or blue background. The dominant color
becomes the initial sample that generates the tolerance, or core transparency, of the
underlying key; this key is rendered as transparent in your composite.
However, you can override the automatic initial color sampling to key any color. You do
this by setting the Strength parameter to 0, then using the Sample Color tool to draw a
selection box over the region containing the color you want to key.
638 Chapter 13 Keying