Task 2 showed how to use the Levels dialog box to set the white point and the black point of an image, thus optimizing the tonal range for the image. You can use the Curves dialog box to increase the contrast in the image, allowing you to selectively enhance image details. If the image seems flat or lacking in contrast, curves can make a dramatic improvement.
Open the Info Palette
Open the image you want to affect. Choose Window, Info to open the Info palette.
Open the Curves Dialog Box
Choose Image, Adjustments, Curves to open the Curves dialog box.
Set the Black and White Points
Follow the steps in Task 2 to set the black and white points for the image. Use the Eyedropper icons from the Curves dialog box rather than those in the Levels dialog box.
Click the lower-left portion of the diagonal line in the Curves dialog box to place a point on the curve. If necessary, slowly drag the point you placed downward to darken the shadow areas in the image.
Click the upper-right portion of the diagonal line in the Curves dialog box to place a point in the light areas. Slowly drag the point up to lighten the highlights, increasing the overall contrast, especially in the midtones. Click OK to apply the effect.
Compare the final results to the image from Step 1. Notice the improved detail and clarity.
Checking the Input and Output Values
In the Curves dialog box, watch the Input and Output values to understand exactly what changes you're making to the curve. The Input value refers to the original pixel values (for example, a midtone value of 128). Clicking at an Input value of 128 and dragging up to 160 means that all pixels originally valued at 128 are now a lighter value of 160. In addition, all pixel values around the input value are lightened so that the effect is applied smoothly. Keep the curve shape smooth, and the effect will look natural.