Curves

The Levels control provides the simplest way to perform the basic tonal adjustments you will need to make regularly, but it’s not the answer for all corrections. Curves is a tool that can do everything Levels does, but also provides a few other capabilities. Note that Elements 7, 8, and 9 included a curves control but it only had four fixed points. You can open the Curves dialog box by clicking Image > Adjustments > Curves or by pressing Cmd/Ctrl-M.

Curves in Other Applications Lightroom and Capture NX also provide curves.