Wendy Crumpler and Barry Haynes, well-known for their Photoshop Artistry book, offer some tips at Graphics.com for limiting the application of a curves adjustment using a layer mask. The idea is the same in all three of their examples. Apply a curves adjustment with an adjustment layer to adjust brightness, contrast or color. If you want that adjustment to affect just part of the image, mask off the unaffected portions by adding black to the layer mask that is part of any adjustment layer. This can be done by filling the mask on the adjustment layer with black and then painting with white over those areas where you want to apply the adjustment. Along the way, you get a look at how to warm up color by adjusting individual channels in the Curves dialog box. This is worth a read.
