Apple Motion 3 - Manual (Page 1113)

Chapter 12 Using Shapes and Masks 1113
The process of improving a keying effect, or of customizing an alpha channel created
using one or more shape or image masks, may require the use of special filters.
Although you can apply any filter directly to a shape or image mask to modify that
particular mask’s effect, the filters described in this section modify a layer’s entire alpha
channel directly, including the sum total of all masks and other filters that have been
applied to that layer.
For example, if you’ve applied a keying filter, you can use the following filters to modify
the resulting alpha channel even though no mask appears for that layer in the Layers
tab or Timeline.
Channel Blur: This filter, found in the Blur category of the Filters library, lets you
selectively blur the alpha channel. You can set the amount of horizontal and vertical
blur independently.
Original (color channel) Original (alpha channel)
Channel Blur (color channel) Channel Blur (alpha channel)