# PhotoshopElements

# About histograms

You can use the histogram to analyze the image’s tonal distribution to see if you need to correct it. A histogram shows the distribution of an image’s pixel values in a bar chart. The left side of the chart shows the values of the image shadow (starting at level 0), and the right side shows the highlight (level 255). The vertical axis of the chart represents the total number of pixels within a given level.

You can view an image’s histogram in the Histogram palette. Histograms are also available in the Levels dialog box and the Camera Raw dialog box. You can update the histogram as you work so that you can see how your adjustments are affecting the tonal range. When the cached data warning icon appears, click it to refresh the histogram’s data.

Histogram palette

A.
  Channel menu

B.
  Palette menu

C.
  Uncached Refresh button

D.
  Cache Data Warning icon

E.
  Statistics

If many pixels are bunched up at either the shadow or highlight ends of the chart, it may indicate that image detail in the shadows or highlights may be clipped—blocked up as pure black or pure white. There is little you can do to recover this type of image. If you are working with a scanned image, you can try rescanning to produce a better tonal range. If your digital camera can display an image histogram, check it to see whether your exposure is correct and make exposure adjustments if necessary. See your camera’s documentation for more information.

The histogram may show that an image is not using the full tonal range available if some pixels aren’t available in the shadows and highlights. You can fix an image with limited tonal range by stretching the tonal range using either the Levels command or one of the Enhance > Auto commands.

How to read a histogram

A.
  Overexposed photo with clipped highlights

B.
  Properly exposed photo with full tonality

C.
  Underexposed photo with clipped shadows

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- About camera raw image files
- Using the histogram and RGB values in camera raw

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- This page on the Web