How to Read the Histogram

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Web Graphics

March 18, 2008


The histogram in your graphics program and in your digital camera can be a very useful tool to help you take better photos and improve the contrast and color in the photos you've taken. The histogram describes the range of tones in your image from black (0) to white (255). (Think of the range of tones as the brightness levels of the image from back to white.)

  • The x-axis represents the tone (brightness level) from 0-255.
  • The y-axis represents the number of pixels at that tone (level).

Reading the Histogram

The histogram looks like a curve. On the curve, the dark areas of your photo are on the left side of center and the light areas are on the right side of center.

  • A photo that is too dark (underexposed) will show more pixels on the left of the curve than on the right. If there are spikes at the extreme left, it indicates that many pixels are pure black.
  • A photo that is too light (overexposed) will show more pixels on the right of the curve than on the left. If there are spikes at the extreme right, it indicates that many pixels are pure white.
  • A photo that has weak contrast will show pixels bunched up in the middle of the histogram with few pixels to the left and right. The tonal range is limited, but you can expand the range and correct this with a Levels adjustment.

Note: A pattern of spikes to the extreme left or right of the histogram is called clipping. If the shadows are clipped, many pixels are pure black and detail is lost in the dark areas of the photo. If the highlights are clipped, many pixels are pure white and detail is lost in the light areas of the photo.

Histogram Example

The following example shows a photo taken in mist that has weak contrast.

  • In the "Before" photo, the histogram shows that the bulk of the pixels are bunched up in the middle tones.
  • After a Levels adjustment is made to the photo, the "After" photo shows much more contrast and color and the histogram has spread to cover the entire tonal range.
Misty Photo Before Misty Photo After
Photo before Photo after
Histogram before Histogram after

Using the Histogram

Display the histogram in your digital camera to determine if you need to adjust your camera settings to adjust for underexposure or overexposure.

To view the histogram in Photoshop Elements, press F9 or select Histogram from the Window menu.

You also see the histogram in the Levels window and the Camera RAW window. You can adjust the histogram in these windows to correct the contrast and color in the photo.

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Photoshop Elements: Improve Contrast and Color by Adjusting Levels

Updated on May 24, 2008