How to Read and Use a Histogram

Aug 15, 2017

You’ve seen a histogram before—that spiky graph on your camera’s rear LCD display or on your electronic viewfinder (EVF). Traditionally reserved to higher-end digital cameras, histograms are now found even in base-level cameras. You may even have one on your phone.

So what is a histogram, and why would you want to use one? Basically it’s a tool that tells you if your image is overexposed or underexposed. It’s one of the best and easiest ways to accurately judge the exposure of your image.

Most beginning photographers take a picture and then look at the reproduced image on the camera’s LCD or EVF of their camera to judge the exposure. The problem is that both of these displays have adjustable brightness. The image may appear darker or brighter than it really is on the LCD or EVF for the same reason a computer screen looks dark in bright sunlight, and bright in a dark room.

Few novice photographer use it, but those who are truly dedicated to their craft learn how to read their histogram and put the information in it to use. This blog will provide a crash course.

Reading the Histogram Graph

The histogram is a graph. The horizontal axis shows you the tonal distribution (dark to light). The vertical axis shows you the number of pixels in a particular tone.

Generally speaking, you want a histogram graph that resembles a bell curve. If your image is too bright or too dark, you’ll lose details. Remember, at times this may be intentional.

Sometimes uneven distribution is OK. Some pictures are not evenly exposed by design, like when you’re shooting a snow scene or when you’re taking a picture of something against a white background. The same is true when you’re shooting a dark object, like a silhouette.

There’s no ‘correct’ histogram reading. The important thing is that you know what you want your image to look like. Don’t just examine the histogram on pictures that turn out great. Examine it when your pictures are overexposed or underexposed so you know what to look for while shooting.

Once you get good at reading the histogram, you’ll know instinctively when to try a different shutter speed, increase or decrease the ISO, adjust the exposure compensation, or switch to a smaller or larger aperture.

Now, having said all that, for those who have a camera with a “highlight indicator”  in the playback options, I suggest turning that on for an easy way to get correct exposure: When the highlights are overexposed, they will be blinking at you when you view the LCD/EVF screen. We refer to these as “blinkies). When you see these “blinkies” you need to lower the exposure, which means smaller aperture or higher shutter speed.

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