Light meters in modern cameras do a wonderful job with exposure, but they will sometimes lead you astray. You can check the playback image on your camera’s LCD screen, but that’s not entirely accurate, either. If you’ve ever thought you’d nailed a shot, only to find out later that you’d blown out, or “clipped”, the highlights or the blacks, you will appreciate a histogram.
A histogram is a graphical representation of the tones that are present in an image and is another tool to help you set your exposure. Most of today’s cameras have a histogram feature when you review your photos and many include a histogram in Live View. Checking your histogram is one of the best and easiest ways to ensure you get the exposure you want in the field and help you avoid unpleasant surprises when you get home and start processing your photos.
Intro to Histograms
Histograms show how much of each tone, or luminance value, is in an image, from pure black to pure white and everything in between. Most cameras and virtually all post processing applications have them but, for this article, I’ll use Lightroom to illustrate histograms, simply because they’re easier than looking at the back of a camera. Often, the histogram will look like a mountain or mountain range. A whole lot of math goes into creating histograms, but we don’t need to worry about the calculations, only what the resulting histogram can tell us.
Many cameras can show four different histograms, one for the overall luminance values and three more showing the luminance values for the red, green and blue channels (see opening photo). Whether your camera has only one or all four, histograms are terrific tools for showing you if you’ve blown out any whites or blacks while you’re in the field, so you can adjust your settings and reshoot the composition.
If you’re shooting RAW, note that the histogram on the back of your camera is based on the JPG preview you see when reviewing your shots on the LCD screen. Your RAW file will have a bit more latitude that this histogram will show. A very small amount of clipping on the camera histogram is probably OK.
Why Will Understanding a Histogram Improve My Photos?
The biggest benefit to using histograms is avoiding over- or underexposing an image. You want our darkest darks and brightest whites to have a bit of detail or texture. If you blow out your whites or blacks when you take the photo, there is nothing you can do to bring them back. The histogram shows you your exposure in a graphical way and tells you how much of the scene your camera is recording and how much is being lost.
If your camera has histograms for the red, green and blue channels, they can be useful, too. There are times when a particular color will be so bright that it gets blown out! The main (RGB) histogram may look OK, because it’s a combination of the three channels, but one of those channels may still be clipped. Take a look at the histogram on the back of the camera at the top of this article. The RGB histogram shows I wasn’t clipping any brights. However, when I check the blue channel, that shows I was clipping the brightest blues. Now, imagine photographing a fiery red sunset or a deep red rose where the RGB histogram shows no clipping. Yet you look at your red channel histogram and see the brightest reds are clipped. Because you checked the histogram, you can adjust your exposure settings to bring back detail in your sunset or flower and take the photo again.
Histograms also aid your artistic process by helping you get your tones where you want them so that the tonality conveys the mood and feeling you’re going for. You might want to shoot high key, or go for more of a dark and moody look. Getting it right in the camera saves a lot of time and effort in post processing and gives you a better quality file to work with.
How to Read the Histogram
What information is the histogram giving you?
The histogram’s horizontal axis represents the luminance (brightness) values of the image. Towards the left, you have the blacks, with the left edge representing pure black, with no detail. This would be Zone 0 in Ansel Adams’ Zone System. In the middle are the mid tones, similar to middle gray or Zone 5.
On the right are the whites, with the right edge being pure white, with no detail, representing Zone 10. Highlights are found toward the right, between the mid tones and the whites. Shadows are found towards the left, between the mid tones and blacks. (In Lightroom, if you slowly move your cursor over the histogram, you’ll see the different areas light up and, just below the histogram, you’ll see which sliders affect that area of tonality. (See image above.)
The vertical axis of the histogram represents how much of each luminance value there is in your photo. The higher the peak of any part of the histogram, the more pixels of that tone are present in the image. A shot that’s mostly mid tones will peak in the center of the histogram. A shot of a polar bear on the ice will peak towards the right and a shot of a black bear in the dark woods will peak to the left. A histogram can have several peaks, if several different tones are prominent in a composition.
Each histogram will be different, based on the tones in your specific image. Most of the time, you want to capture the entire range of tones in an image, from pure white to pure black. And, most of the time, you want to avoid having your whites slam up against the right edge of the histogram, as that would mean there is a lot of featureless white in the image. Similarly, most of the time you’d want to avoid having your blacks crash up against the left side of the histogram as that would mean a lot of featureless black.
There are times when your artistic vision might require a lot of featureless white, like a shot of animals in the arctic snow or certain high-key shots, but that should be a conscious choice. Similarly, a portrait photographer might want a shot with deep shadows and a black backdrop, where the histogram will push up against the left side, but that’s a stylistic choice. And, of course, astrophotography under dark skies will push your histogram far to the left.
Sometimes, you’ll be shooting an image where there are no blacks or, conversely, no whites. In this situation, it’s OK if the histogram doesn’t stretch from one side all the way across to the other. A foggy day is unlikely to have pure blacks. A predawn exposure won’t have pure whites.
And, sometimes, no matter what adjustments you make to your camera settings, your histogram will peak on both ends, indicating you’re clipping brights and darks. That’s telling you that the scene has too wide a dynamic range for your camera to capture in one shot. You will need to bracket your shots and use exposure blending or HDR when you process your photos. Alternately, you can decide to let some of your darks clip to pure black (like for a silhouette) and preserve all of the detail in the bright sunset.
The bad news is that there is no single perfect histogram. Every scene will have a different one.
The good news is that the perfect histogram is whatever you want it to be. The perfect histogram for your image is the one that reflects your artistic vision for the shot.
The more experience you get with your camera, the less you’ll need to rely on the histogram. You’ll start to know that you’ve got the right exposure. Many professional photographers can walk up to a scene and instinctively know what settings to use to capture the perfect exposure. They may never check the histogram.
As for myself, I don’t want my reds to blow out during that glorious sunset. Nor do I want the dark foreground to become featureless black. I still check my histogram whenever I’m in a situation with tricky lighting.
Need help understanding the histogram? Ask in the comments below!
Frank Gallagher is a photographer and writer from Washington, DC. He built up his photography business after a career in nonprofits during which he developed extensive experience in visual storytelling. He enjoys sharing his love of photography with others.