Apple Motion 5.1.1 - Manual (Page 893)

Chapter 20 Shapes, masks, and paint strokes 893
Other times, you may find that it’s more convenient to mask a complex object using multiple
masks. This is frequently the case when rotoscoping an object and animating the masks. In
this example, the dog’s head is masked with four masks set to Add—one for the head, one for
each ear, and a separate mask for the mouth. This makes it easier to make adjustments later on,
especially when animating a mask to do rotoscoping.
Original object Four overlapping masks Result
Whatever the reason, you can easily combine multiple masks for any object by adjusting each
mask’s Mask Blend Mode parameter in the Inspector to create any combination.
Each mask’s blend mode determines whether the mask adds to, subtracts from, or replaces a
layer’s previously existing alpha channel. Additionally, blend modes affect how masks interact
with one another. Ultimately, every mask applied to a layer combines according to the specified
blend modes to create that layer’s final alpha channel. Mask Blend Modes can be changed at
any time.
Blend mode operations are also determined by the order in which each mask appears in
the Layers list, particularly with the Replace and Intersect modes. For example, a mask set to
the Intersect mode masks out all other regions of a layer that do not overlap it. A mask set
to Intersect affects all masks nested underneath it. Masks added above it are unaffected by
this behavior. Similarly, a mask set to Replace mode effectively turns off any masks beneath it
(including the image object’s built-in alpha channel, if one exists).
For more information on mask blend modes, see Mask controls in the Inspector on page 899.
Feather masks
One of the easiest ways to adjust a mask is to feather its edges. Feathering a mask by a few pixels
can make the masked object blend more seamlessly with a background. Feathering a mask by
larger amounts creates progressively softer edges for various design purposes.
You can feather mask edges outward or inward. The direction in which you feather a mask is
dictated by the subject you’re masking. When rotoscoping a subject, a combination of inward
and outward feathered masks may be necessary for the best results.
67% resize factor