Adjustment Layers

An important point to remember about color correction is that you can apply it to the whole picture, to a selected single area, or to all but a selected area. 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.

Fortunately, there's an easy way to apply a correction and then change your mind. One of the best features of Photoshop is the capability to work in layers. (You'll learn all about layers in Hour 11, "Layers.") 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 do, 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 apply 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.

There are a couple of ways to add an adjustment layer to your image. (This is Photoshop. You'll soon find that there are several ways to do almost anything you can think of.) First, and most logically, you can choose New Adjustment Layer from the Layer menu shown in Figure 6.15. They're also on a pop-up menu you reach by clicking a button at the bottom of the Layers palette (look for the button with the half-black, half-white circle).

Figure 6.15. The New Adjustment Layer submenu and the Layers palette.

Try it Yourself

Using the Adjustments Layer Submenu

To open an adjustment layer:

1.	Click the black-and-white circular icon at the bottom of the Layers palette or choose Layer New Adjustment Layer (see Figure 6.15).
2.	Select the particular kind of adjustment that you want to make from the pop-up menu. Click OK to open the appropriate adjustment dialog box.
3.	Make whatever adjustments are necessary. You can delete the layer if you're not pleased with the changes, or change the layer opacity to effectively change the strength of the corrections you have made.

Understanding Channels

Channels are another way of looking at color. Each image has one or more channels, the number depending on the color mode chosen . CMYK has four separate channels plus a composite. RGB mode has three plus the composite. Each channel holds information about a particular color element in the image. Think of individual channels as something like the plates in the printing process, with a separate plate supplying each layer of color. You can often create interesting textures or special effects by applying filters to just one channel. Figure 6.16 shows the Channels palette (twice) with RGB and CMYK channels.

Figure 6.16. You can set preferences to show channels in grayscale or in their colors.

There are also alpha channels, which have several uses. They are used to define the placement of spot colors (PANTONE, FOCOLTONE, and so on). They also contain the maps for masks you create and want to save with the image to which you have applied them.

Summary

In this hour , you looked at working with color. Variations make simple, "by eye" adjustments, letting you choose from differently enhanced thumbnails. Levels and curves apply adjustments more scientifically. You now know how to make the sky a perfect blue and the grass a greener green. Now you know that adjusting levels lets you set limits for dark, middle, and light tones in an image. You have learned about color balance and how to apply changes to hue and saturation. You have seen how to change the brightness and contrast of an image.

Color adjustment is one of Photoshop's most-used features, and one that you'll rely on whenever you need to touch up a photo or a scanned image. Practice with it as much as you can, using your own favorite images.