Mask modes
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Blending modes for masks (mask modes)
control how masks within a layer interact with one another. By default,
all masks are set to Add, which combines the transparency values
of any masks that overlap on the same layer. You can apply a mode
to each mask, but you can’t animate the mode of a mask—that is, you
can’t set keyframes or expressions for a mask mode property to make
it change over time.
You choose a mask mode for a mask from
the menu next to the mask name in the Timeline panel.
The
first mask that you create interacts with the alpha channel of the
layer. If that channel doesn’t define the entire image as opaque,
then the mask interacts with the layer frame. Each additional mask
you create interacts with masks located above it in the stacking
order in the Timeline panel. The results of mask modes vary depending
on the modes set for the masks higher in the stacking order. Mask
modes only operate between masks on the same layer.
Using
mask modes, you can create complex compound masks with multiple transparent
areas. For example, you can set a mask mode that combines two masks
and sets the opaque area to the areas where the two masks intersect.
 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
- None
- The mask has no direct influence on the alpha channel of
the layer. This option is useful when you are only using the path
of the mask for an effect such as Stroke or Fill, or if you are
using the mask path as the basis for a shape path.
- Add
- The mask is added to the masks above it in the stacking order.
The influence of the mask is cumulative with the masks above it.
- Subtract
- The influence of the mask is subtracted from the masks above
it. This option is useful when you want to create the appearance
of a hole in the center of another mask.
- Intersect
- The mask is added to the masks above it in the stacking order.
In areas where the mask overlaps the masks 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.
- Lighten
- The mask is added to the masks above it in the stacking order.
Where multiple masks intersect, the highest transparency value is
used.
- Darken
- The mask is added to the masks above it in the stacking order.
Where multiple masks intersect, the lowest transparency value is
used.
- 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.
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