Histogram Tool 
The
Histogram Tool generates a bar graph of a frequency distribution for the selected area.
Select the histogram tool and drag 'n' drop it onto the image viewer.
The histogram will appear. The histogram output will be updated as you drag one
of the eight smaller boxes located on the rectangle. You
can change the shape and size of the area being profiled, as well
as rotate it by grabbing the small box in the middle and turning.

Right-click
on the histogram box area to bring up the IPHistogramEntity edit box, as
seen below. Selecting
the Entity tab allows you to adjust the colors, thickness, handle size and
visibility of the histogram marker. You can also select a
Coordinate System. Make the necessary adjustments, click
Apply and then Close. The values will be updated according to
your selections.

Selecting the Rectangle
tab allows you to enter specific
values for the histogram rectangle used, including center X, Y, width,
height, angle and aspect of width/height. After entering your
values, click Apply and then Close. The histogram will be recalculated
according to the selections.
