I created a star mask in Deep Sky Stacker and am trying to apply that mask (mask is a tiff file). I open both the mask and the main deep sky image in photoshop (Mac), select the image and in its layer panel and "add mask". Then view the mask ("option click") and paste the inverted mask file into the mask. This does not mask out the stars in the mask. Is there a better (or more correct) way to apply this external mask file in photoshop?
Thanks for the explanation. The "density" was set to 100%, which as I understand is part of the effect the mask has, but I went to "preferences/transparency" and set the grid size to small and the color to dark or medium, and the mask was more effective. It also made clear to me the difficulty in matching the black in the mask to the background dark sky. Thanks for your help!