Apple Motion 5.1.1 - Manual (Page 899)

Chapter 20 Shapes, masks, and paint strokes 899
It’s not always necessary to rotoscope an entire subject with a single mask. Motion lets you apply
multiple masks to a single object, so you can rotoscope different parts of a subject with separate
masks. This can make your job much easier. For example, if you’re rotoscoping someone carrying
something while walking across a room, you can use one mask for the upper part of the person’s
body, which doesn’t change shape very much, and another two masks for the legs, which change
shape considerably as the person walks.
To pan the image in the Canvas while rotoscoping, press the Space bar. You can then pan in the
Canvas without losing your mask selection or progress.
You can also use the Track Points behavior to apply tracking data to a shape or mask. For more
information on the Track Points behavior, see
Track Points on page 958.
Mask controls in the Inspector
A selected mask’s parameters appear in the Mask Inspector. These controls allow you to adjust
how the mask is drawn, how each mask operates upon an object, and how masks are combined
with one another. The Mask Inspector also lets you fine-tune mask control point positions using
value sliders.
Except for control points parameters, the parameters in the Mask HUD are identical to the
parameters in the Inspector.
Parameters in the Mask Inspector
•
Shape Type: A pop-up menu that sets the type of control points used to define the mask. For
example, if you originally created a Bezier mask, you can choose B-Spline from this menu to
change how the mask is drawn. Changing the shape type might dramatically change the
mask’s form even though its control points remain fixed at their original coordinates. There are
three options:
•
Linear: All of a mask’s control points are joined by hard angles, and the resulting mask is a
polygon. The control points of a Linear mask lie directly on its edge.
•
Bezier: Control points can be a mix of Bezier curves and hard angles, creating any sort of
mask. The control points of a Bezier mask lie directly on its edge.
•
B-Spline: Control points are all B-Spline points, with different degrees of curvature. B-Spline
control points lie outside the surface of the mask, but are connected by the B-Spline frame.
Note: You can hide the B-Spline frame by turning off Lines in the View pop-up menu above
the Canvas.
•
Mask Blend Mode: A pop-up menu that determines how a mask interacts with the alpha
channel of the layer to which it’s applied. When a layer has multiple masks, each mask can
have a different Mask Blend Mode. When this happens, each mask adds to, or subtracts from,
the layer’s alpha channel according to the selected mode. The final alpha channel is the
combined result of all masks applied. There are four choices in this pop-up menu:
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