Intersecting Masks
In many instances, you may find you want to cut out parts of an object, while leaving the
rest of the object alone. Using a mask set to Intersect is a good way to do this.
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Chapter 20
Using Shapes, Masks, and Paint Strokes
For example, if you import a TIFF file with an alpha channel and you want to cut out part
of it without losing alpha information, you must use the Intersect blend mode. This is
also true for layers with keying filters applied.
Original alpha channel
from key.
Intersecting mask crops
unwanted opaque areas.