Preserving the Original with Adjustment Layers
When you apply a correction to the whole picture, it might improve some parts and make others worse, so you really need to look carefully at the end result and decide whether the good outweighs the bad. You might wish you’d applied the correction to only part of the image, or you might want to go back and try different settings. Fortunately, Photoshop provides you with an easy way to apply a correction and then change your mind as many times as you want.
As we’ve discussed, one of Photoshop’s best features is the capability to work in layers. (You’ll learn all about layers in Hour 11, “Creating Layered Images.”) For now, you can think of layers as sheets of transparency film that you place over your image and paint or paste on. If you like what you see, you can merge the layers so that the additions become part of the image. If not, you can throw them away and try again. In addition to the layers that you paint on, Photoshop lets you create several kinds of special layers, including adjustment layers. These work like normal layers, except that instead of holding paint or pasted pictures, they hold the color adjustments that you make to the image.
You can add an adjustment layer to your image in a few different ways. First, and most logically, you can choose New Adjustment Layer from the Layer menu. You can also add an adjustment layer using the pop-up menu at the bottom of the Layers panel (look for the button with the half-black, half-white circle). Finally, Photoshop CS4 brings us the Adjustments panel, which enables you to add and modify all your adjustment layers in one place (see Figure 5.18).