Taking Photoshop’s Curves Beyond Highlights and Shadows | Webdesigner Depot
http://www.webdesignerdepot.com/2010/06/taking-photoshops-curves-beyond-highlights-and-shadows/

Photoshop’s Curves is a flexible control that can brighten or darken parts of a layer based on the layer’s luminosity. Editing tones in an image—not just grays and not always photos—can do more than fix highlights and shadows. Curves can be used to edit photos, masks, graphics and even hues. But using it requires a little know-how and imagination. Read on for more details about what Photoshop curves are, as well as how to use them properly for your designs.

Taking Photoshop’s Curves Beyond Highlights and Shadows | Webdesigner Depot