Apple Motion 2 - Manual (Page 869)

Chapter 12 Using Shapes and Masks 869
• Replace: This setting uses the current mask to completely replace the object’s
original alpha channel, as well as any other masks that are applied to the same
object that appear underneath the current mask in the Layers list. You can add
additional masks above, set to whatever blending mode you like.
• Intersect: Masks that are set to Intersect do not replace an object’s original alpha
channel. Instead, they mask out all regions of the object that do not overlap the
mask itself. This includes other masks applied to the same object that appear nested
underneath the intersecting mask in the Layers tab.
Invert Mask: When this checkbox is turned on, the mask is inverted—its solid and
transparent areas are swapped. This is useful if you need to switch the solid and
transparent areas of a mask you’ve already created.
Stencil: With this parameter turned on, the object’s geometric transforms are
respected by the mask. If you’re creating a mask with transformed Scale, Position,
Rotation, or other parameters, turn on this checkbox to use the modified object.
Stretch: With this parameter turned on, the mask is stretched to fit the boundaries of
the image, and remains centered on the object’s center point.
Note: Stencil and Stretch are mutually exclusive.
Applying Filters to Image Masks
Like shape masks, you can add filters to image masks to further manipulate the
transparency effect. In particular, you may be able to improve the mask that’s created
by using color correction filters such as Brightness, Contrast, and Gamma to manipulate
the contrast of the mask, pulling out or reducing detail to create the transparency
effect you need.
Filtering image masks works identically to filtering shape masks. For more information,
see “
Applying Filters to Masks ” on page 861.
Applying Behaviors to Image Masks
You can also apply behaviors to image masks to create animated transparency effects.
For more information, see “
Applying Behaviors to Masks ” on page 862.
Using Masks to Aid Keying Effects
Keying is rarely a one-step process. Although adding a keying filter is the first step,
there is usually additional work that needs to be done to create a good key that retains
detail around the edge of your subject. The mask tools and alpha channel filters
presented in this section can be used to turn a decent key into a great one.
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