Masking by the Numbers

© 2004, Glenn E. Mitchell II, Ph.D.The Light’s Right Studio
Have you ever wanted to make an adjustment to an image but limit the effect to just the highlights or the shadows in an image? Photoshop pros know they can press the Option-Command-~ sequence (Alt-Ctrl-~ for Windows users) and Photoshop will grab the highlights in an image and make them into a selection. Invert that selection, and the shadows are selected.
Photoshop uses a very broad definition of highlights: one that reaches well down into the middle tones. For a quick and dirty selection of the brighter portions of an image, Option-Command-~ is helpful. But, what if you need more precise control?

Figure 1.The Coliseum in Rome on a dreary day in March.
Ever take a photograph on a rainy, dreary day? Something like Figure 1 is typical. You end up with lots of contrast but not much information in the middle tones. The result is a flat, boring image.
One solution in this case is to use a tripod and bracket the sho...