Use the Histogram Equalization tool to take a histogram from a region of interest and equalize it to the rest of the image. The window level values used are based on the frequency of pixel values inside that rectangle. This tool cannot be applied to color images.
To apply histogram equalization
From the Image area top toolbar, Window Level button menu, select Histogram Equalization.
The pointer has a rectangle and graph shape attached to it. (If this type of window leveling cannot be applied because the image contains color, an icon appears beside the pointer.
)To enlarge or reduce the rectangle before you place it, move the scroll wheel on the mouse.
Place the rectangle over the area to equalize, then click.
The image brightness and contrast changes according to the values in the selected region.