Apple Motion 4 - Manual (Page 1185)

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)
• Matte Choker: This filter, found in the Matte subcategory of the Filters library, increases
or decreases the semi-transparent area of a layer’s alpha channel by performing a
gamma correction (similar to the Gamma color correction filter) to all regions of the
alpha channel falling between solid black and solid white. This allows you to widen or
narrow the semi-transparent areas within a layer, while leaving all 100 percent solid
and transparent areas unaffected. Once you’ve added a Matte Choker to a layer, the
following parameters become available in the Filters tab of the Inspector:
• Edge Thin: A slider that allows you to modify the edges of the matte. Higher positive
Edge Thin values eat into the alpha channel, eliminating fringing around the edges
of translucent areas. Negative values fill in translucent values, filling in holes and
widening the matte into areas of fringing.
1185 Chapter 17 Using Shapes, Masks, and Paint Strokes