Performing multiple keys on a single subject, Manipulating alpha channels using filters – Apple Motion 3 User Manual
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Chapter 12
Using Shapes and Masks
Performing Multiple Keys on a Single Subject
In some instances, it may be difficult to key an entire subject with a single keying filter
while retaining fine details. For example, uneven lighting or background color might
mean that the best settings to key a subject’s hair may not work elsewhere.
If you attempt to key the entire subject with a single keying filter, chances are that you
need to use such extreme settings that a lot of edge detail is lost. In such cases, masks
can be used to isolate different parts of a subject, so that you can apply different
keying settings to each area.
To segment a subject into separate keying zones:
1
Create a new group, and place the layer you’re keying within the new group.
2
Duplicate the layer you’re keying until you have a separate duplicate for each part of
the image you want to key separately.
3
Use one of the mask tools to mask each part of the subject in each of the duplicate
layers.
Make sure that all of the duplicate layers overlap, so that there are no gaps in the
foreground.
Note: You may need to animate the overlapping masks if the foreground subject is
moving.
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 group, 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 layers, there
are also filters you can use to manipulate or even replace a layer’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 layer. Keying filters are usually
used on layers that have no alpha channel information, and they add a new alpha
channel to the layers to which they’re applied. For more information on the use of the
keying filters, see “