Instruction Manual

Chapter 20 Shapes, masks, and paint strokes 902
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Roundness: A slider that controls the roundness of the corners of a mask. This facilitates the
creation of rounded rectangle masks, as well as generally smoothing the edges of any mask.
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Preserve Scale: A checkbox that controls whether the Roundness setting is absolute or relative
to the overall mask size. When the checkbox is selected, the roundness will remain at the same
approximate percentage of curvature as the object is scaled. When the checkbox is disabled,
the curvature will vary as the overall mask changes size.
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Feather: A slider that feathers (softens) the edges of a mask. Positive feathering values soften
the edge of the mask from its edge outward. Negative feathering values soften the edge of
a mask inward from the edge. Feathering the edge of a mask can soften a harsh rotoscoping
job, making the masked object blend more easily with the background.
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Fallo: A slider that controls how “steep” the feathering is. Higher values result in feathering
that’s pushed in farther inward, so the edge of the feathering eect is more transparent. Lower
values result in the “core” of the feathering eect being pushed farther outward, so the edge of
the feathering eect is less transparent.
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Mask Color: A pop-up menu that controls the color of the mask as displayed in the Canvas
when it is selected. This setting has no eect on the nal output. Setting masks to dierent
colors may aid you in identifying which mask is which.
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Control Points: A list, visible when you click the disclosure triangle, displaying the position
parameters for the mask control points. Use the value sliders to adjust the position of a control
point. The left value slider represents X and the right value slider represents Y.
Image masks
Image masks overview
Another way to create transparency in a layer is by using image masks. An image mask creates
transparency in a layer by deriving an alpha channel from another image layer, such as a shape,
text, movie, or still image.
Text layer
Image layers Layers masked by text layer
Note: You can use masks and image masks together.
The power of image masks is that they do not have to be drawn or animated. Instead, you can
use virtually any image or movie clip to create transparency in another layer. By default, movie
clips create animated image masks, but you can also set an image mask to use only a single
frame. Image masks can also be used to assign masks created in other applications. For example,
you can import an animated mask that was created in another application and exported as a
QuickTime movie into your Motion project, then use it as an image mask.
When you use a layer as an image mask, you can choose which of the layer’s color channels to
apply to create transparency via the Source Channel pop-up menu in the Image Mask Inspector.
The choices include:
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Red
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Green
67% resize factor