When to Use Levels or Curves in Photoshop ~ Les Meehan

Many Photoshop users learn to use the Levels dialog and then never progress to learning how to use the Curves. Let me give you several reasons why learning to use the Curves will make you more of an expert with Adobe Photoshop. For more : http://www.picturecorrect.com/tips/when-to-use-levels-or-curves-in-photoshop/