Photo Tips: How to Read a Histogram

This post was originally written for IHeartFaces and published on March 14 2016 and republished on AmandalynnJones.com in January 2017. 

If you have ever looked at that little graph on the back of your camera (or at the top of your adjustment panels in Lightroom and Photoshop) and wondered what it was?  

A histogram is a visual graph that shows you the quantity of each tone in an image. The left side of the graph represents shadows and the right represents highlights. The “ideal” exposure represented on a histogram starts with a low quantity of pixels at the shadow end, that increases smoothly to peak in the middle, and then gradually drops off again on the highlight end.

How to Read a Histogram

I find that Histograms are often overlooked, most of the photographers that I chat with never look at them, but reading your histogram is a really handy tool to use when trying to nail your exposure in camera, and most advanced cameras have a function so that you can use to see the image you’ve just taken next to the graph right away. I find it especially helpful for confirming that my meter reading gave me the correct exposure before I move on to the next shot, rather than relying on myLCD screen (which can often be misleading in differently lit environments, especially if your screen’s brightness setting auto-adjusts).

Most editing programs also have histogram graphs as well, which is extremely useful during editing because it takes the guesswork out of which areas need to be adjusted. For example, this image has good midtones and no blown highlights, but the shadows are getting clipped pretty heavily and are very blue.

Adjusting the blacks/shadows slider toward the right until the graph is more balanced is going to increase the tonal range of the photo and brighten the heavy shadows without wiping out the areas of the images that were already properly exposed. Adding contrast helped to further shift the tones toward the right. I also adjusted the white balance to balance the blue spike I noted in the original.

As a rule of thumb for someone just getting started using their histogram to gauge their camera settings, images with wider tonal ranges (which translates on a histogram to having most of the pixels spread out in a nice wide hill somewhere in the middle) tend to have more accurate exposure and less loss of detail in deep shadows or blown highlights (also known as “clipping”, when the side of the hill hits either end of the histogram).

Adjusting the histogram reading works the same as adjusting your in-camera meter. If you’re getting something like the histogram on the left that image is probably underexposed (in this case by almost 2 stops) and you want to increase your exposure. If you’re getting something like the histogram on the right that image is probably going to be overexposed (in this case by 2 stops) and your highlights are going to be blown out, so you want to decrease the exposure.

But like every other rule of photography, once you understand it you can bend or break it to create artistic images. A great example of this is low and high key, meaning that the tones you might normally want to be in that mound in the middle are intentionally skewed toward darks or lights (respectively), decreasing the tonal range and creating drama.

Finally, one important thing to know is don’t panic if your images aren’t translating into “ideal” histograms, many great images won’t; especially if the subject has true white or black tones or your scene has high or low contrast. The histogram, like every other kind of light reading tool, is just a guide to help you get to an “acceptable” mid-range exposure according to an algorithm. YOU are the artist, so what you do with it from there is up to you.