Histograms are the solution to a fundamental problem in photography: Our eyes don’t always tell the truth. Have you ever been in a dark room, turned on your phone, and felt it blind you like nobody’s business? The same thing can happen in photography. Several times, I’ve taken pictures at night, and they look great on my camera’s LCD — until I open them the next day on my computer and realize they’re all hopelessly underexposed. Enter the histogram. This is the best way to know exactly, mathematically, the brightness of your pixels, no matter the lighting conditions around you. So, let’s dive in.
1) What are histograms?
Histograms are graphs of your camera’s pixels. Specifically, they show brightness.
This is pretty useful. You don’t have to rely on your eyes to tell the brightness of a photo — you get to use math instead.
Here’s a sample photo paired with its histogram:
This photo is very dark. The histogram is shifted pretty far to the left.
Here’s another example:
The photograph above is a pretty “normal” brightness — and the histogram is roughly centered.
Here’s the last example:
Are things starting to make sense?
Here’s our tally so far:
- Dark photo: Leftward histogram
- Bright photo: Rightward histogram
- Medium photo: Centered histogram
Essentially, a histogram’s layout is like this:
Do you think you have the hang of it? Hopefully, it makes sense so far.
Also, you’ve probably noticed that I’m only using black-and-white photos at this point. That’s because color histograms have a bit more information, and they take some extra effort to understand (although they’re still pretty easy).
2) Why do histograms matter?
Aside from what I’ve already said — that histograms help you out in dark conditions — there are a few other reasons why they’re important.
Most importantly, a histogram is one of the best ways to figure out if you’ve lost any detail in the highlights or shadows of an image.
It’s a simple concept: When there are pixels all the way to one side of the histogram or another, black or white, you’ve lost some of the information in your photo. For example, in the image below, you can tell that I’ve lost details in the highlights, since the histogram has a tall column on the very right:
The same goes for this photo, which has regions that are totally black:
When you’re out taking pictures, and you don’t know whether you’ve lost important details, the histogram is a great place to start.
Personally, I use histograms all the time to make sure that I’m exposing properly, and especially to make sure that I’m not overexposing an image. (Overexposure is worse than underexposure, since it’s much harder to recover lost details in the highlights.)
3) How to use histograms
It’s very easy to use histograms properly.
In fact, you don’t need to look at most of the histogram.
Focus your attention only on the right-hand side of the histogram, where the bright tones appear. Ask yourself if anything is overexposed (which you’d see as a column touching the right-hand side).
For example, this histogram comes from the sand dunes photo above:
You don’t even need to look at the photo itself to know that it’s overexposed. There’s a tall column up against the right-hand side, which means that certain parts of the image are completely white. Not good.
So, the most important thing about your histogram is that it tells you when you’ve overexposed a shot. This might not always be a problem — if the sun is in your photo, the center of it should be completely white — but it’s usually something to avoid.
Your pixels have to be completely white before it’s impossible to recover highlight detail. Normal highlight regions? They’re perfectly fine and easy to recover, so long as nothing is 100% white.
The most important thing is to avoid blowing out any highlights. If you make that mistake, there’s no easy post-processing fix. That’s why I like histograms so much — they make it easy to know for sure if any highlight detail in an image is gone.
4) Understanding color histograms
The histograms I’ve shown so far are accurate, but they’re only for black and white images.
In color photography, histograms get a bit more complex. That’s because your camera sensor has red, green, and blue photosites within every pixel. So, naturally, a color histogram has red, green, and blue components.
Here’s an example photo paired with the histogram:
This leads to an interesting result: You can lose information in one color without losing information in the others.
For example, you might have a very bright photo where some of the blue channel is overexposed, but the red channel and green channel are fine, like the image below. Is that a problem?
Yes, that is a problem!
It means you’ll be able to recover some highlight information, but the colors in your highlights won’t look quite right when you do. They’ll shift in strange directions, because you’ve lost a lot of blue information.
Overexposing just one of the three color channels is nearly as bad as overexposing all of them.
Luckily, most cameras let you see all the color histograms at once, so you aren’t flying blind. You’ll want to enable this feature (otherwise, the camera might just show a monochromatic histogram by default, which isn’t very precise). For example, on my Nikon DSLR, I’m able to see this screen when reviewing an image:
5) How to enable the histogram in your camera
Hopefully, you agree that it’s a good idea to enable the color histogram in your camera.
How do you do that? It varies:
- On most Nikon cameras, go to Menu > Playback icon > Playback display options > RGB histogram. Then, when you’re reviewing a photo, press the “up” button on the direction pad multiple times to cycle through different displays.
- On most Canon cameras, go to Menu > Playback icon > Histogram display > Brightness/RBG > RGB. Then, when you’re reviewing a photo, press the “Info” button multiple times to cycle through the different displays.
- On most Sony cameras, go to Menu > Gear icon > DISP Button > Histogram. Then, when you’re reviewing a photo, press the DISP button to cycle through different displays (or the “up” button on the direction pad if your camera doesn’t have a DISP button).
Every camera is different. Even if you have a Nikon, Canon, or Sony camera, your exact model might have some differences. When in doubt, consult your user manual. Or, just search for the answer online.
6) An alternative to the histogram
Histograms aren’t the only tool for this job. There are also blinkies, which make overexposed regions of a photo blink black and white upon review.
Blinkies aren’t always as good as histograms — specifically, they don’t tell you about individual color channels — but a lot of people find them easier to understand. They also do a good job showing exactly where any overexposure occurs.
If your camera has this option, it’ll be under the same menu as the histogram setting. This is called “Highlights” for Nikon and “Highlight alert” for Canon. For Sony, they’re automatically on once you enable the histogram.
It’s a simple fact that you can’t trust your eyes to be perfectly accurate. You can’t trust the camera’s LCD, either — and with histograms, you don’t need to.
The only important thing is to know how to read them. Once you understand how to read a histogram, you’ll be at a huge advantage in photography. You won’t end up overexposing or underexposing an image by accident, since you’ll already know exactly how bright it is.
Personally, I use histograms a lot (and blinkies, too). The same is true for almost every photographer I know. They’re a great tool, and one that is worth learning how to use properly.