Apple Motion 2 - Manual (Page 858)

858 Chapter 12 Using Shapes and Masks
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 an object’s previously existing alpha channel. Additionally, blend modes affect
how masks interact with one another. Ultimately, every mask applied to an object
combines according to the specified blend modes to create that object’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 tab, particularly with the Replace and Intersect modes. For example, a
mask set to the Intersect mode masks out all other regions of an object 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.
Masks That Add and Subtract
New masks always default to the Add blend mode, allowing you to add to an existing
alpha channel without cropping what’s already there. Once you’ve drawn the first
mask, you may need to use additional masks set to Add or Subtract to refine it.
Masks set to Add create white areas in the alpha channel, making those parts of the
object opaque. This can be useful when masking several unconnected subjects in a
single image.
Mask Blend Mode pop-up menu
Result of first mask Additional masks added to the first
01112.book Page 858 Sunday, March 13, 2005 10:36 PM