Your camera’s histogram is the perfect tool for when you can’t figure out how to fix your exposure. All point and shoot and DSLR cameras come with a histogram feature, and learning how to read and interpret the information this feature provides to explain the highs and low of the shot’s exposure can help you avoid filling your camera memory cards with shot after poorly exposed shot.

What is a histogram?

A histogram is a diagram your camera produces to describe a photo’s brightness levels. They use columns to show you how many pixels there are of each brightness level. They don’t show you where the brightest or darkest spots are, but rather tell you how much brightness and darkness there is in your photo overall. Histograms are useful because the LCD on your camera is not as accurate as you might think, especially when you just glance at it under natural daylight. A histogram gives you more detailed, accurate exposure information that you can evaluate to improve your photo.

How do you read a camera histogram?

DSLR cameras all have the same histogram output. You read them from left to right. The left third of the histogram measures the darkest tones, the shadows. The middle area describes the midtones. The right portion reflects the highlights. Reading it by the axes, the horizontal axis indicates the brightness of the pixels and the vertical axis the number of pixels or amount of that brightness in the shot.

For example, imagine a histogram that has a consistently downward-sloping line, starting with white high on the left, and decreasing across the graph. This would tell you the shot has lots of shadows (tall columns meaning more pixels at a low level of brightness), a middling amount of midtones, and few highlights.

There is no ideal histogram. Every shot requires a different balance of lights and darks. For example, a photo of an onion should have more highlights because the subject is white and thus bright. But the best photos typically have few shadows, few highlights, and lots of midtones. So their histograms look something like a plateau, sloping up from the left, leveling off or peaking up and down slightly in the middle, and dropping to the right.

What do you do with the information on a histogram?

You’ve taken a photo of some beautiful subject– hopefully stationary to give you some time to think and compose a new shot – but the exposure needs improving. The first thing to look for is “clipped” highlights and shadows. “Clipping” refers to when an area of the photo’s exposure is completely black or white, meaning the camera captures no detail or information there. On the histogram, when the graph pushes all the way to the left or right edge of the chart, that tells you the shot has clipping.

Also determine how much contrast is in your shot. A wider graph indicates more contrast – more lights and more darks – while a narrower graph tells you there is less contrast and more simple midtones.

Use this information to determine if your photo needs more or less light, and if it should be more direct to increase contrast or more diffuse, to soften contrast, and ultimately improve your photo. Make exposure setting decisions and even change where you stand to shoot the photo to make these changes. Take another shot, and compare histograms.

All DSLR cameras have a histogram function. This seemingly daunting graph is actually a relatively simple and intuitive tool that proves you with a great deal of information about photos so you can improve your exposure for better shots.