When you select 'histogram' from the menu of your camera, you'll see the image you want to photograph, with date, time, exposure settings and other information. Next to the image is the histogram graph. It shows you the black to gray to white tones of your picture in a vertical range. The technology recognizes the tonal levels of areas within the image, according to the number of pixels for each black, gray or white tone. The high points on a histogram represent the tones with the greatest number of pixels. When there are more high points to the left of the histogram, your digital image has many dark tones. More high points to the right represents an image with many lighter tones.