To Apply A Mask Mode - Adobe AFTER EFFECTS 7.0 Manual

A
C
F
Mask shapes that result when different modes are applied to the circle mask. The shapes 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

To apply a mask mode

In the Timeline panel, select the layer containing the mask to which you want to apply a mode and press M.
1
Click the menu next to the mask name and choose a mask mode.
2
After Effects treats the mask as if it does not exist. The mask has no impact on the layer or composition. This
None
option is useful when you want to use the mask's path for an effect such as Stroke or Fill, but do not want it to create
transparent areas in the layer.
Adds the selected mask area to the other masks for that layer, displaying all mask contents in the Composition
Add
panel. Where multiple masks intersect, the opacity of all intersecting masks is added together.
Subtracts the mask from all masks located above it in the Timeline panel. The contents of the subtracted
Subtract
mask area appear as a hole in the Composition panel. This option is useful when you want to create the appearance
of a hole in the center of another mask.
Adds the mask to all masks above it, but displays in the Composition panel only the area where the selected
Intersect
mask and any of the previous masks intersect. Where multiple masks intersect, the opacity of all intersecting masks
is added together.
Adds the mask to all the masks above it, displaying contents of all masked areas in the Composition panel.
Lighten
Where multiple masks intersect, the highest opacity value is used, so opacity doesn't build up.
Adds the mask to all masks above it, but displays in the Composition panel only the area where the selected
Darken
mask and any of the others intersect. Where multiple masks intersect, the highest transparency value is used, so
transparency doesn't build up.
Adds the selected mask to the masks above it, and displays in the Composition panel the mask contents
Difference
of all masked areas except those areas where the masks intersect.
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D
G
E
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User Guide