If every picture tells a story, then the histogram kind of serves as the synopsis to that story. The histogram is that funky-looking graph thingy that you see when you press the info or disp button on your camera (or when you press up on the navigation pad, in the case of Nikon users) when reviewing your pictures. The histogram is a graph that visually shows you the exposure of any given image and can be used to verify that you got a well exposed shot. This can come in quite handy when you are out shooting in bright sunlight (which isn’t the best idea, remember) because the screen on the back of your camera becomes harder to see, making it extremely difficult to tell if you got a proper exposure. Enter the Histogram (Oooooohhhhh. Sounds like a Bruce Lee movie filmed in The Matrix). Because the histogram is easier to see on the back of your camera, you can use it to get a gauge of how well (or poorly) exposed an image is. Here is the lowdown on histograms…
The histogram is a visual representation of the tonal range of your image, from absolute black (left) to absolute white (right) with shades of gray in between. The vertical peaks that you see in the histogram represent how many pixels have that specific gray value. How high these peaks get is really of no concern, as long as you don’t push the high peaks of the histogram flush up to the right, or to the left. Many people will say that you shouldn’t have any portion of the graph pushed up against either side, but oftentimes this is impossible. Reflections, for instance, will often push a small portion of the histogram up against the right, which is only natural, as they are usually pure white. The same goes for the dark side (Luuuuke…), if there is a bright light source (again, if you are shooting in the middle of the day) it will often cause shadows to go completely black. The question you have to ask yourself is, “Is that an integral part of the picture?” In other words, are people even going to notice that part of the background, underneath those bushes, has gone completely black? Likely not. That being said, if you are taking a picture of a bride on her wedding day, and even a portion of the histogram is pushed up against the right side, you probably want to verify that it isn’t her dress that has “blown out” (a term often used to describe overexposure).
Now, just like every rule, there are exceptions. Let’s use the scenario of a full moon with dark sky around it as an example. When looking at the histogram for something like that, you would want to see a good portion pushed up against the left hand side of the histogram, because the sky around the moon would, and should, be pure black.
Using your histogram, as well as the other information that can be brought up with it on your camera, can be a great learning tool, so learn to use it to its full potential.