Apple Motion 4 - Manual (Page 1182)

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.
Converting Between Shapes and Masks
Because masks and shapes are created in similar ways but perform different tasks, there
are occasions where you may create a shape and later want to convert it into a mask, or
vice versa. Changing shapes to masks and masks to shapes is done by changing the
object’s position in the Layers tab or by using the Object menu.
Note: Masks are not applicable to 3D paint strokes, 3D particle systems or replicators, 3D
text objects or unflattened 3D groups. In order to convert a shape to a mask on such an
object, the item must be flattened.
Different options are available when converting shapes to masks, depending on the type
of object that is being masked. The following steps apply when converting a shape to a
mask on an image-based object (movie or image sequence, images, generator, and so
on).
To convert a shape to a mask on an image
1 Use any of the shape tools to create a shape (or draw a paint stroke).
Note: You can also add a preset shape from Shapes category in the Library.
2 In the Layers tab, drag the shape object onto the layer to be masked.
1182 Chapter 17 Using Shapes, Masks, and Paint Strokes