Adobe AFTER EFFECTS CS3 PROFESSIONAL User Manual page 267

A
C
E
G
Compound masks that result when different modes are applied to the circle mask. The masks in this illustration have different Mask Opacity
values.
A. Original masks B. None C. Add D. Subtract E. Intersect F. Lighten G. Darken H. Difference
The mask has no direct influence on the alpha channel of the layer. This option is useful when you are only
None
using the mask's path for an effect such as Stroke or Fill, or if you are using the mask path as the basis for a shape path.
The mask is added to the masks above it in the stacking order. The influence of the mask is cumulative with the
Add
masks above it.
The influence of the mask is subtracted from the masks above it. This option is useful when you want to
Subtract
create the appearance of a hole in the center of another mask.
The mask is added to the masks above it in the stacking order. In areas where the mask overlaps the masks
Intersect
above it, the influence of the mask is cumulative with the masks above it. In areas where the mask does not overlap
with the masks above it, the result is complete opacity.
The mask is added to the masks above it in the stacking order. Where multiple masks intersect, the highest
Lighten
transparency value is used.
The mask is added to the masks above it in the stacking order. Where multiple masks intersect, the lowest
Darken
transparency value is used.
B
D
F
H
AFTER EFFECTS CS3 261
User Guide