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Mask modes
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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