A histogram is a representation of the number of pixels in a photo at each luminance percentage. A histogram that stretches from the left side of the panel to the right side indicates a photo that takes full advantage of the tonal scale. A histogram that doesn’t use the full tonal range can result in a dull image that lacks contrast. A histogram with spikes at either end indicates a photo with shadow or highlight clipping. Clipping can result in the loss of image detail.

The left side of the histogram represents pixels with 0% luminance; the right side represents 100% luminance.

A histogram is made up of three layers of color that represent the Red, Green, and Blue color channels. Gray appears when all three channels overlap; yellow, magenta, and cyan appear when two of the RGB channels overlap (yellow equals the Red + Green channels, magenta equals the Red + Blue channels, and cyan equals the Green + Blue channels).

In the Develop module, the Histogram panel is a working tool. You can adjust the photo by adjusting the histogram itself.

To preview shadow and highlight clipping, position the mouse over a clipping triangle in the upper-left or upper-right corner of the Histogram. A mask of the clipped areas appears in the photo. Click a triangle to keep the mask on.