Applying Filters to Image Masks
Like shape masks, you can add filters to image masks to further manipulate the
transparency effect. You may be able to improve the mask that’s created by using color
correction filters such as Brightness, Contrast, and Gamma to manipulate the contrast of
the mask, pulling out or reducing detail to create the transparency effect you need.
Filtering image masks works identically to filtering shape masks. For more information,
Applying Filters to Masks
Using Shapes, Masks, and Paint Strokes