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Masks That Add and Subtract
New masks default to the Add blend mode, allowing you to add to an existing alpha
channel. After you draw the first mask, you might need to use additional masks set to
Add or Subtract to refine it.
Masks set to Add create white areas in the alpha channel, making those parts of the object
opaque. This can be useful when masking several unconnected subjects in a single image.
Result of first mask Additional masks added to the first
Note: To display the rest of a masked layer so you can trace it to create a second mask,
turn off the first mask in the Layers list or Timeline. The outline of the first mask remains
visible, even though it’s no longer affecting the layer’s transparency.
Predictably, masks set to Subtract have the opposite effect, creating black areas in the
layer’s alpha channel and making those parts of the object transparent. This is useful for
cutting holes in an object.
Additional masks subtracted from the firstResult of first mask
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.
1203Chapter 20 Using Shapes, Masks, and Paint Strokes