About histograms

A histogram illustrates how pixels in an image are distributed by graphing the number of pixels at each color intensity level. The histogram shows detail in the shadows (shown in the left part of the histogram), midtones (shown in the middle), and highlights (shown in the right part) A histogram can help you determine whether an image has enough detail to make a good correction.

The histogram also gives a quick picture of the tonal range of the image, or the image key type. A low‑key image has detail concentrated in the shadows. A high‑key image has detail concentrated in the highlights. And, an average-key image has detail concentrated in the midtones. An image with full tonal range has some pixels in all areas. Identifying the tonal range helps determine appropriate tonal corrections.

How to read a histogram

A.: Overexposed photo
B.: Properly exposed photo with full tonality
C.: Underexposed photo

The Histogram panel offers many options for viewing tonal and color information about an image. By default, the histogram displays the tonal range of the entire image. To display histogram data for a portion of the image, first select that portion.

You can view an image histogram as an overlay in the Curves dialog box by selecting the histogram option under Curve Display Options, and in the Curves Adjustment panel by choosing Curve Display Options from the panel menu, then Histogram.