Tip #4 is: Turn on your histogram display.
So what is a Histogram? It’s a graph of the values (light and dark) of the pixels in an image. You turn on the histogram in your camera either through a menu choice or, more likely, a button on the back of the camera identified as something like Display or Info. Press the button repeatedly and different information will be displayed superimposed on or next to your image. You should always turn on the histogram when you are shooting. You can turn it off if you’re just reviewing your images, but keep it on when shooting. It’s your way of evaluating your exposures. Cameras with digital viewfinders can even display the histogram in the viewfinder, which is very convenient.
So why do you need to evaluate the exposure of the images you take? Isn’t the camera handling that automatically. Well yes, it is. And that’s the problem. The camera doesn’t know what you’re photographing. It makes generalizations and assumptions about what you want. These can be way off from what you need. What happens when the exposure is wrong? Your image will be too light or too dark and you can lose information in the scene. You can correct the exposure in your editing software, but this will cause problems in your images. It’s better to get a good exposure to begin with.
The left side of a histogram graph represents the dark pixels in your image and the right side represents the light ones; in between are all the shades of light and dark. For example, if you’ve photographed a snowy landscape, you will likely see a sharp spike near the right side that represents all the light pixels in the snow and sky. You will see smaller bumps toward the left of the histogram that represents the trees and other dark elements of the pictures. If you shoot a cityscape with little or no sky, you will see a big hump in the middle of your histogram that represents all the medium values in your picture. If the buildings are bright or reflect the sky, there will be humps or spikes toward the right.
Unless you have an electronic viewfinder, you will need to take a picture and look at the back of your camera during the brief display of the image after you shoot. That’s where you will see the histogram. It only takes a moment to evaluate it. If you miss the brief display, push the playback button the back of your camera to see the image again.
So how do you evaluate the information in the histogram? What you want to see is a spread of light and dark across the histogram with no pixels pushed up against either the left of right side of the histogram. If there’s a big pile of pixels right up against either side, you are getting a lot of pure black or pure white pixels. This means you are getting no information about those parts of the image. It’s called clipping, as the information is clipped off.
If your histogram shows clipping on the left or dark side of the image, your image is underexposed. If there is clipping on the right, your image is overexposed. You will need to make changes to your exposure. If you want to take the best possible exposure, you want to see a histogram that is pushed to the right but not clipped off at the right. I won’t go into why this is here, but it is very helpful when you are editing your image. It’s worth doing if you want the best possible results.
I said above that you will need to adjust your exposure if the histogram is clipped off either at the right or left side. Even if you’re adjusting the aperture or shutter speed manually, the camera is adjusting the other one automatically to get what it thinks is the correct exposure. So how do you do that when the camera is making the exposure automatically? Well guess what—that’s what our tip is for tomorrow. It’s called exposure compensation and once you learn to do that you’ll have complete mastery of taking a properly exposed photograph.