Is there a technique to create a mask for a masked layer? Let's say I do a levels adjustment and mask it such that it's only affecting the centre portion of the image. The mask would be essentially a large soft white circle in the middle of the image, within a black surrounding. Then let say I want the adjustment to only work in the top half of the revealed mask. How can I go about that? I figure there must be a simple way to do this, but I can't seem to find it. I want to do it this way as opposed to modifying the original mask, in case I want to adjust the second masking further.