Using Adjustment Layers
Adjustment layers are the main reason we use Photoshop Layers so much during our workflow. An adjustment layer doesn’t add a new image to a stack, but instead allows you to perform corrections on the layers beneath it. Adjustments are only performed virtually (i.e., they are not resampled into the image data) until the entire layer stack is flattened to a single layer or printed.
Many (but not all) of the tools available in the Image ▸ Adjustments menu are available as adjustment layers. Adjustments applied as layers can be fine-tuned not only using each tool’s own sliders, but also using layer opacity settings and layer masks. Layer masks are used to limit the effects of an adjustment to the non-masked image areas.
Figure 7-8. CS5 ...