Intro to color keying in Motion
Keying is the process of isolating a foreground subject against a background area of uniform color or brightness to generate an alpha channel (a matte) based on the shape of the color area. Keying is commonly performed on subjects photographed against a blue or green background, but keys can be based on any color (color or chroma keying) or on a specific range of brightness values (luma keying).
Color keying (also known as chroma keying) is commonly used on television to create the familiar effect of a newsreader or show host backed by animated graphics. You can do the same thing in Motion using the Masks and Keying filters.
Important: Most keys are “pulled” using more than one tool. Good compositing artists usually combine keying filters, matte adjustment filters, spill suppression operations, and garbage or holdout masks to isolate a single subject. The Green Screen Keyer filter in Motion combines many of these operations within a single set of parameters. In some instances, it may be necessary to apply different keyer settings to different areas of the subject, requiring the use of multiple keying filters and masks.
There are two types of keyer filters in Motion:
Use the Green Screen Keyer for blue screen or green screen keying, or for keying any range of color you choose.
Use the Luma Keyer to generate mattes based on a sampled range of lightness in the image.
Two other filters provide standalone access to matte finishing operations:
Use the Matte Magic filter to refine the edges of a matte.
Use the Spill Suppression filter to manually correct matte problems created when the background color creates a reflection on the foreground subject.
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