Have Photoshop Select The Shadows And Highlights
This is a trick we use for prepress and for photo retouching because it instantly lets you select all the shadow areas (or highlight areas if you wish) for a particular image, and it’s so easy because Photoshop does all the work. To have Photoshop select just the shadow areas in your image, go under the Select menu and choose Color Range. When the dialog appears, in the Select pop-up menu, choose Shadows (or Highlights), and click OK. The shadow areas are instantly selected. This is ideal for situations where your scanner has plugged up the detail in the shadow areas (pretty common in most sub-$1,000 desktop scanners). Once the shadows are selected, you can “open them up” by going to the Levels dialog (under the Image menu, under Adjustments) and moving the midtones Input Levels slider to the left to bring back some of the shadow detail lost in the scan.