Adobe After Effects CS3 - Manual (Page 267)

AFTER EFFECTS CS3
User Guide
262
Difference The mask is added to the masks above it in the stacking order. In areas where the mask does not overlap
the masks above it, the mask operates as it would alone on the layer. In areas where the mask overlaps the masks
above it, the influence of the mask is subtracted from the masks above it.
Adjust the edges of a mask
To finely expand or contract all edges of a mask, use the Mask Expansion property. This property’s value represents,
in pixels, how far from the original mask edge you are expanding or contracting the adjusted edge.
1 In the Timeline panel, expand the Mask properties of the layer you want to adjust.
2 Drag the underlined value for Mask Expansion.
Note: To reset a mask to its default boundaries, select the mask in the Timeline panel and choose Layer > Mask > Reset Mask.
Adjust mask feather
Feathering softens the edges of a mask by fading it from more transparent to less transparent over a user-defined
distance. Using the Mask Feather property, you make mask edges hard-edged or soft-edged (feathered). By default,
the feather width straddles the mask edge, half inside and half outside. For example, if you set the feather width to
25, the feathering extends 12.5 pixels inside the mask edge and 12.5 pixels outside it. You can also extend or contract
the mask edges using the Mask Expansion property to control where the mask feathering appears.
Setting the Mask Feather property
A. Masked layer with 5-pixel feather B. Masked layer with 40-pixel feather C. Result with 5-pixel feather D. Result with 40-pixel feather
Mask feathering takes place only within the dimensions of the layer. Therefore, a feathered mask’s path should always
be slightly smaller than the layer area and should never move to the very edge of the layer. If a mask feather extends
beyond the layer area, the feathered edge ends abruptly.
1 To display the Mask Feather property for selected layers, press F.
2 (Optional) To constrain horizontal and vertical feather amounts to change proportionally, select the Constrain
Proportions switch next to the Mask Feather property.
3 Modify the Mask Feather property as you would any other property—by dragging the underlined value or clicking
the underlined value and entering an amount in the text box.
C D
B A