The BCC Matte Cleanup filter is used to help correct imperfect mattes as
well as generate interesting matte effects.
Often a key can create an imperfect matte in which traces of the background
color remain around the edge of the foreground subject. BCC Matte Clean up
allows the user to fine tune aspects of the composite blending, as well as
choke the opaque regions to remove any unwanted fringes.