The histogram is only available in the Studio Max edition. It is a representation of the relative frequencies of the colors in the image. There are three colored curves representing the frequencies of the red, green and blue channels. Because images have a maximum and minimum brightness level for each of red green and blue, you will start to lose detail and color accuracy when any of the histograms bunches up at either the left (too dark) or the right (too bright) of the histogram. The histogram is fixed at the top of the section list so you can always see it, even if you have another section open.