Apple Motion 3 - Manual (Page 307)

Chapter 3 Basic Compositing 307
The order of two objects affected by the Exclusion blend mode does not matter.
Blend Modes That Manipulate Alpha Channels
The Stencil and Silhouette blend modes let you use a single object’s alpha channel or
luma values to isolate regions of background objects and groups.
Note: Similar effects can be accomplished using shape and image masks. In addition,
masks may provide you with a greater degree of control, depending on your needs. For
more information, see “
Using Shapes and Masks ” on page 997.
Stencil modes crop out all nonoverlapping parts of objects underneath the object used
as the stencil. Silhouette modes do the opposite, punching holes in overlapping
objects underneath in the shape of the object used as the silhouette.
Stencil Alpha
The Stencil Alpha blend mode uses the alpha channel of the affected object to crop
out all nonoverlapping parts of objects and groups underneath it in the Layers list.
Stencil Luma
The Stencil Luma blend mode does the same thing as the Stencil Alpha blend mode,
but uses the affected object’s luma value to define transparency. Stencil Luma is useful
if the object you want to use for cropping has no alpha channel of its own.
Object used for stencil End result Object underneath