Another way to apply a mask is directly to a filter. This workflow allows you to isolate the results of a specific area. Perhaps it’s to enhance just the sky or to add details to a specific area of an image. The use of the Gradient Mask and Radial Mask mode can be helpful to smoothly blend a filter.
To create a Filter Mask:
Select an individual filter in the Filters area.
Click the Filter Mask button (the paintbrush icon).
Choose from one of the four types of masks: Brush, Radial, Gradient, or Luminosity.
Use the techniques covered in this chapter to edit the mask.
When satisfied with the mask, click the Done button.