Screen capture of the settings on the mask dialog to select the image highlights. Before the mask is actually generated, I also blurred the selection by 10 pixels, and feathered with a -2. The idea here is to avoid generating annoying halos in the transformed image. I want to do 2 things with the mask -- (1) is to bring up the shadow levels, and then bring down the highlights. You can probably do it all with one brightness transform, but doing it in two stages allows you to mess with one thing at a time. First -- the shadows.