Apple Motion 4 - Manual (Page 342)

Silhouette Alpha
Silhouette Alpha is the reverse of the Stencil Alpha blend mode and is useful for cutting
holes in objects underneath.
Object used for silhouette End result Object underneath
Silhouette Luma
Silhouette Luma is the reverse of Stencil Luma.
Behind
The Behind blend mode forces the object to appear behind all other objects and groups,
regardless of its position in the Layers tab and Timeline.
If multiple objects or groups are set to Behind, they appear behind all other groups that
are not set to Behind, in the order in which they appear in the Layers tab.
Alpha Add
The Alpha Add blend mode works similarly to the Add blend mode, but instead of adding
the color channels of overlapping objects, it adds their alpha channels together. Try using
this blend mode instead of Motion’s default method of alpha channel compositing for a
different treatment of overlapping areas of translucency.
Premultiplied Mix
The Premultiplied Mix blend mode is intended for compositing images that are
premultiplied, such as those generated by 3D modeling and rendering software. (A
premultiplied image’s red, green, and blue channels are multiplied by the image’s alpha
channel.) Premultiplied Mix is useful for images with translucent lighting effects such as
lens flares, volumetric lighting, fog and haze effects, and so on.
The Premultiplied Mix blend mode performs an unpremultiply composite—the foreground
image is assumed to be premultiplied. Artifacts may appear as a result of unpremultiplying
pixels whose RGB and alpha values are very small (resulting in pixels with values of 255).
In some cases, the hardware performs bilinear filtering and then the blend mode
unpremultiplies the alpha.
342 Chapter 7 Basic Compositing