Absolute Beginner's Guide to Digital Photography

CHAPTER 15 THE IMPORTANCE OF LEVELS AND CURVES 231

The steepness of the curve controls the contrast of the image. A steep curve results

an image with considerable contrast. A flat curve gives the image low contrast.

Color Corrections with Curves

The Curves dialog has a curve for the combined colors, plus individual curves for

each color.

You can adjust specific color channels. In an RGB image, for example, select the

Green channel to correct a color problem (see Figure 15.17). You can see in the curve

shown in Figure 15.17 that green is emphasized when a picture is taken through a

tempered car windshield, causing magenta shadows and greenish highlights.

FIGURE 15.17
Adjusting the
green channel
curve.

The green curve is raised in the shadows (which adds green) and lowered in the

highlights (which subtracts green).

Accessing Levels and Curves Adjustment Layers

Now that you know how to use Curves and Levels, you need to learn the best way to

access them. There are two ways to open the Levels and Curves dialog boxes.

Clicking Image, Adjustments, Curves or Image, Adjustments, Levels opens the ordi-

nary controls. Layer, New Adjustment Layer, Curves or Layer, New Adjustment

Layer, Levels opens these tools in an adjustment layer. Either method produces the

same interface and changes the image’s appearance in the same way.

Professional photographers always use adjustment layers to keep changes away

from the original image. This improves clarity in the image and enables you to turn

on/off each change you make to an image.