**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.