Adjust > Histogram
Histogram
A histogram illustrates how pixels in an image are distributed by graphing the number of pixels at each color intensity level. The histogram shows whether the image contains enough detail in the shadows (shown in the left part of the histogram), midtones (shown in the middle), and highlights (shown in the right part) 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 a number of pixels in all areas. Identifying the tonal range helps determine appropriate tonal corrections.
A histogram illustrates how pixels in an image are distributed.
1. Do one of the following:
 Choose Adjust > Histogram
 
Click the Histogram button
2. To view information about a specific value, place the cursor at that point on the histogram. To select a range of values, click and drag in the graph. When you release the mouse, the range is deselected.
3. Use the following options:
Red
Displays a distribution graph of the red color channel.
Green
Displays a distribution graph of the green color channel.
Blue
Displays a distribution graph of the blue color channel.
Grayscale
Displays a distribution graph of the grayscale values.
Logarithmic
Use this option to display the values on a logarithmic scale.
Channel
Use this option to display detailed information about the red, green, or blue color channel.
Mean
Displays the mean value for the selected channel.
StdDev.
Displays the standard deviation for the selected channel.
Median
Displays the median value for the selected channel.
Min
Displays the minimum value for the selected channel.
Max
Displays the maximum value for the selected channel.
Level
The value or range of values (from 0 to 255) of the point over which the cursor is positioned in the graph.
Count
The number of pixels that are the selected value(s).
Percentage
The percent of image pixels that are the value(s) of the selected point or range.
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