About applying filters or behaviors to masks
You can apply filters and behaviors to masks. Masks remain editable even after the application of a filter or mask.
Filters and masks
Applying a filter to a mask is an extremely powerful way to further manipulate the alpha channel created by a mask. For example, you can apply the Crystallize filter to a mask to add stylized, jagged edges that resemble facets of crystal.
When you apply a filter to a mask, it’s useful to bear in mind that a mask is just a grayscale image. In the example above, the Crystallize filter creates patterns in the grayscale mask image, which results in a rippled translucent pattern.
You apply a filter to a mask the same way you apply a filter to any other layer in your project. For more information, see Apply and remove filters.
Behaviors and masks
When you apply a behavior to a mask, the mask is animated like any other layer. However, because the mask affects only the transparency in a layer, and not the position, rotation, or scale of the layer, the result is similar to that of a “traveling matte,” where the mask moves in the layer it’s applied to, hiding and showing different areas of the image as it moves.
You apply a behavior to a mask the same way you apply a behavior to any other layer in your project. For more information, see Apply behaviors overview.