Apple Motion 2 - Manual (Page 873)

Chapter 12 Using Shapes and Masks 873
4 Apply the appropriate keying filter to each of the isolated parts of the subject, and
adjust each filter’s settings as necessary.
Eventually, you may find you can achieve an optimal key for each part of the subject.
Furthermore, with all duplicates nested within a single layer, you can continue to
manipulate the subject as a single object.
Manipulating Alpha Channels Using Filters
In addition to using shape and image masks to create transparency within objects,
there are also filters you can use to manipulate or even replace an object’s alpha
channel.
For example, all of the keying filters create transparency by generating an alpha
channel based on colors or luminance values in that object. Keying filters are usually
used on objects that have no alpha channel information, and they add a new alpha
channel to the objects to which they’re applied. For more information on the use of the
keying filters, see “
Keying Filters ” on page 760.
The process of improving a keying effect, or of customizing an alpha channel created
using one or more shape or image masks, may require the use of special filters.
Although you can apply any filter directly to a shape or image mask to modify that
particular mask’s effect, the filters described in this section modify an object’s entire
alpha channel directly, including the sum total of all masks and other filters that have
been applied to that object.
For example, if you’ve applied a keying filter, you can use the following filters to modify
the resulting alpha channel even though no mask appears for that object in the Layers
tab or Timeline.
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