Absolute Beginner's Guide to Digital Photography

Black-point eyedropper

White-point eyedropper

Histogram

Midtone slider Input highlight slider

Preview Button

Pure black 0

Input shadow slider

Paper white 255

Middle gray 128

212 ABSOLUTE BEGINNER’S GUIDE TODIGITAL PHOTOGRAPHY

If a histogram from well-exposed film is clipped, you might be able to correct it by

rescanning—consult the scanner’s manual. Most scanning software has controls that

let you change the exposure of the scan.

When a histogram is clipped because of bad camera exposure, reshoot the picture.

Reshoot the image using fill light to reduce the scene’s contrast. If an image is

clipped at only one end, reshoot the picture with either more or less exposure.

Setting Brightness and Contrast with the Black Point and the

White Point

A histogram graph shows the brightness values of pixels in an image. The height of

each bar represents the total number of pixels of a given brightness in the whole

image (see Figure 14.9). The spread shows the frequency of each of the 255 tones

available for the picture. Pure black is 0; middle gray is 128, and paper white is 255.

The three images in Figures 14.10–14.12 have different histograms. The histograms

tell you whether the image has high contrast, no contrast, or a broad representation

of all brightness levels. In time, you will be able to determine what an image looks

like just by examining its histogram.

FIGURE 14.9

Controls in the

Levels dialog

box.