Following on from a previous post, I've created three sets of macros for selecting a part of an image based on five Blend Ranges 'luminosity' curves (nominally called Blacks, Shadows, Mid-tones, Highlights and Whites).   You can download the zip file here (the forum doesn't seem to like zip files, so I put it on my website).   A few points of note (more in the included .pdf file): The 'Preview' set just cuts out the selection so you can see exactly what is being selected. It also lets you inspect the Blend Ranges curves. The 'Select' set turns this into a selection in the image. The 'Blend' set does the same for adjustments and filters. Curve overlaps are deliberately symmetrical so together they should sum to 100%. All sets include all contiguous combinations, such as 'Blacks+Shadows'.