Calculates and displays a histogram of the distribution of gray values in the active image or selection.

The x-axis represents the possible gray values and the y-axis shows the number of pixels found for each gray value. The total pixel count is also calculated and displayed, as well as the mean, modal, minimum and maximum gray value.

[insert image Histogram]

Use the List button and Save command to save the histogram data. Click on Log to display a log-scaled version of the histogram. The number to the right of Value:, which changes as you move the cursor, is the grayscale value corresponding to the x-axis cursor position and Count: is the number of pixels that have that value.

With RGB images, the histogram is calculated by converting each pixel to grayscale using the formula

gray = 0.299 * red + 0.587 * green + 0.114 * blue

or the formula

gray = (red + green + blue) / 3

depending whether “Weighted RGB Conversions” is checked or not in Edit>Options>Conversions.

With 16-bit images, the range of gray values between the Min and Max values is divided into 256 bins.

With 32-bit images, the number of bins is specified in this dialog box:

[insert image Dialog]

Check Use min/max and the x-axis range is determined by the minimum and maximum values in the image or selection, or specify X Min and X Max values to fix the x-axes range. Enter a Y Max value to fix the y-axis range or enter “Auto” to have the range determined by the largest bin count.

In ImageJ 1.35a or later, hold down the Alt key (or press alt-h) to use this dialog with 8-bit, 16-bit and RGB images.