Update for info below: Shortcut for CS5 (and probably CS4) is Contr-Alt-2
Just learned this fix for images that are too light and lack contrast. If you have Photoshop click on Control/Alt/Tilde and this will highlight the light areas. Then you can either Control-J to add the selection to a new layer and use Multiply blend mode to darken the light areas, or you can make a levels adjustment. (No doubt a Curves adjustment too!) On keyboard, the tilde (~) is found to the left of the number 1. I may have overdone this one just a bit!