Using Photoshop's Auto Corrections

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Adjusting the tonality of your image can be as simple as selecting one of the Auto commands from Photoshop's ImageOAdjustments menu. With many photos, the tonality (and even the color) jump to just the right look for your image. No muss, no fuss — just a great-looking picture with a single command.

If you need to do something special with the image (for example, create an unusual effect), or if the image is in bad shape to begin with, the Auto commands might not be your best bet. But remember this: It never hurts to try an Auto command first. At worst, you use the Undo command, and you've wasted only a couple of seconds and a pair of keystrokes.

From least sophisticated to most, here are your three Auto correction choices:

i Auto Contrast: Auto Contrast makes the dark pixels darker and the light pixels lighter, and tries to avoid introducing any color shift (an overall change in the color appearance). The same adjustment is applied to all three of your image's color channels. You can use Auto Contrast with an image in which the colors already look good and you perhaps just need a bit of a boost to the contrast.

i Auto Levels: Each of your image's color channels gets its own adjustment, maximizing the tonal range in the channel. If one of the color channels has very little to contribute to the original image, a color cast (an unwanted tint, as shown in Figure 5-8) might be introduced. Auto Levels is fine for most images that look good already and don't need to have exact colors.

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Figure 5-8: The same photo, with and without an orange color cast.

i Auto Color: Rather than using a single brightest pixel and a single darkest pixel to determine what should be white and what should be black, Auto Color averages a few pixels at each end. That averaging prevents one single stray pixel from throwing off the calculation used to adjust your image. Auto Color is great for most typical images. You might need that Undo command, however, on some photos with very brightly colored objects or images that have extreme color casts.

Levels and Curves and You

Sometimes you need (or simply want) more control than offered by the Auto commands. You might have a more demanding problem or a more expansive artistic vision. You might need to make major corrections or create stupendous effects. Photoshop, not surprisingly, offers that sort of control over your image. In fact (and also not surprisingly), you have several ways at your disposal to manipulate the tonality of your images. Two of the most commonly used are Levels and Curves, both found in your ImageOAdjustments menu.

Before I introduce you to those two commands, let me quickly explain and dismiss a couple of other available options. Since the early days of Photoshop, the Brightness/Contrast command has lurked among the ImageOAdjustments commands. In fact, it was the image adjustment command way back when. Now, however, the feature is somewhat lacking in control and sophistication and is perhaps of most use when fine-tuning an alpha channel or layer mask. (Alpha channels are discussed in Chapter 8, and layer masks appear in Chapter 10.) In both alpha channels and layer masks, you use a grayscale representation to identify specific areas of your image. Brightness/Contrast is perfectly adequate for many adjustments that you might make to those channels.

Also of limited use is the Equalize adjustment. It finds the lightest pixel in the image and calls that white, and also finds the darkest pixel and calls that black. The rest of the pixels in the image are distributed between those values, creating an extended tonal range. In practice, you'll find that the adjustment results in extreme highlights and extreme shadows, with a rather garish image overall as well as a lack of details in the midtones.

Always keep in mind that you don't have to make changes to the entire image. If only part of an image needs repair, make a selection of that area before opening the particular adjustment dialog box you want to use. (Read about making selections to isolate areas of your image in Chapter 8.) Say, for example, that you take a beautiful photo of a room in your house — "beautiful" except that the view out the window is far too bright. Isolate the window with a selection, and then use one of your image adjustment commands to tone it down.

You can apply Levels, Curves, and Brightness/Contrast as adjustment layers. Adjustment layers make the same changes to your images as the commands in the ImageOAdjustments menu but are far more flexible. By double-clicking the adjustment layer in the Layers palette, you can reopen the adjustment dialog box and make changes to your settings. When you use an adjustment layer, you can also restrict the effect of the adjustment to one or more layers through layer clipping and layer sets. (See Chapter 8 for more information on working with adjustment layers.) You can even delete an adjustment layer, thus eliminating its effect on your image, by dragging it to the Trash icon at the bottom of the Layers palette.

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