Adobe After Effects - Manual (Page 614)

Matte effects
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Geometric Softness
Choke
Matte Choker effect
Simple Choker effect
For information on the Refine Matte effect and the Roto Brush effect, see Roto Brush effect and Refine Matte effect reference.
Third-party effects in this category included with After Effects:
mocha shape effect
See Third-party plug-ins included with After Effects.
Matte Choker effect
The Matte Choker effect repeats a sequence of choking and spreading the matte to fill undesired holes (transparent areas) in opaque regions. The
repetition is necessary because the entire matte must be choked and spread; the spreading fills the hole, but the edges of the matte must be
choked back to preserve the matte shape.
The process of choking and spreading occurs in two stages, each with its own set of identical controls. Typically, stage two does the opposite of
stage one. After a specified number of back-and-forth adjustments (which Matte Choker handles automatically), the hole is filled.
This effect works with 8-bpc and 16-bpc color.
Original (upper-left) shows areas of unwanted transparency after using Color Key (lower-left) that are removed with Matte Choker (lower-right).
You can use the Matte Choker effect to only blur the alpha channel. To use this effect as an alpha-channel blur, set Gray Level Softness to
100%.
Close a hole in a matte
1. Select the layer, and choose Effect > Matte > Matte Choker.
2. Set stage-one controls (the first three properties) to spread the matte as far as possible without altering its shape, as follows:
Specifies (in pixels) the largest spread or choke.
Sets the amount of choke. Negative values spread the matte; positive values choke it.
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