13. How to Take Photos 8: Histograms

A histogram is a graph that shows the tonal range of the picture (light to dark). The x axis goes from black to white. The y axis shows the range of tones (the amount of information in the image) at given value. Histograms are helpful to see if your image is overexposed or underexposed. If the exposure is way off the mark, you can usually tell just by looking at the preview image, but when it's just a bit off, it can be hard to see in the preview screen. This is when you check to histogram and see if the tonal range is balanced (in the middle).

To view a histogram, first go to Review (Playback) Mode on your camera, then press the Info or Display button, and cycle through different ways to see the image. Don’t worry about the color histogram, just the black and white one that deals with brightness.

Histograms are more trustworthy than the preview screen on the back of your camera, because sometimes in bright light it’s hard to see the preview (with the sun glaring down). Or, if your screen brightness is too high, a photo might look over-exposed when it’s actually fine. With a histogram, you see how much information is in the photo at different tones. If all the info is on the left:

it’s probably underexposed, and if all the info is on the right:

it’s overexposed. If there’s an even amount of info on both sides, it’s probably correctly exposed – but it also depends on the subject. Ideally, you don’t want all the info right on black or white, but instead “not touching the goal posts”. Don’t worry about spikes unless they’re in a corner, indicating under or over exposure. You can play with filters till you get both those down to acceptable levels.