User guide

Layers, Masks, and Blending 27
Using masks
Masking can also be applied to adjustment and effect filters, where you can
isolate regions (e.g., an image background) to which you want a filter to be
applied. (See Using filter layers on p. 58). Similarly, you can use studio-based
filter masking on adjustments by using PhotoFix (see p. 46).
Creating the mask
Before you can use a mask, you have to create it on a particular layer. The mask
can start out as transparent (revealing the whole layer), opaque (hiding the
whole layer), or—if you create it from a selection (opposite)—a bit of both (with
only the selected region hidden or revealed). The mask shows as a mask
thumbnail.
The choice depends on how you want to work with the layer's contents. By
darkening portions of a clear mask, you can selectively fade layer pixels. By
lightening an opaque mask, you selectively reveal layer pixels.