The histogram (what is a histogram) of the visible image can be displayed in the top right corner of the image window or in a separate window. See Settings, Image window, Histogram for the histogram display setting.

The histogram is displayed in a separate window. It can be resized and placed anywhere on your screen and displays the histogram of the current displayed image. The display changes when the next image of a scene is displayed.

The histogram is display top left inside the image window. Below the histogram bar graph, the grayscale bar displays the distribution of the palette from black to white. The start and end values of the grayscale palette are displayed with the yellow lines inside the histogram.
Change the brightness and contrast of an image by displaying the histogram and using the the brightness and contrast tool.