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What Is a Histogram?
Annika Jansen
What is the histogram in photography and how do you use it?
Have you ever taken a photo that looked perfect on your camera's screen, only to find it suddenly too dark or too bright on your computer? A histogram helps you prevent this! This tool gives you insight into your photo's exposure, so you can immediately see whether details are being lost in the shadows or highlights. But how do you read a histogram, and how do you adjust your settings for the perfect exposure? In this article, we dive into the world of histograms and show you how to get the most out of this tool.
What is a histogram?
A histogram is a graph that shows the distribution of light and dark tones in your photo. The left side of the graph represents the shadows, the middle represents the midtones, and the right side represents the highlights. The shape of the histogram lets you immediately see whether your photo is well exposed or whether details are being lost due to underexposure or overexposure. By understanding and using the histogram, you gain more control over the exposure of your photos.
When you see high peaks in your histogram, this means there is more information at that tone in the image. A histogram doesn't literally represent colors, but rather the brightness of a color. For example, dark blue has a dark tone and will therefore appear further to the left. Light blue, on the other hand, will appear on the right side, because it is a light tone.
How do you read a histogram in photography?
You read a histogram from left to right, just like a book. The horizontal axis shows brightness ranging from dark tones (black) to light tones (white), with many different shades of gray in between. The vertical axis of the histogram indicates the number of pixels at each brightness level. There are no fixed values attached to this, so it represents a relative amount. The higher the peak in the graph, the more pixels of that brightness level are found in your photo.
A generally well-exposed photo has a histogram that resembles a mountain — a nice curve with its peak in the middle of the histogram. But there are always exceptions to the rule! After all, you don't always shoot in the same kind of situation. Your histogram will often differ depending on the environment you're in and the camera settings you use. You'll also read more about this below, in the section about photos with a lot of black or white. So it essentially comes down to the fact that the 'perfect' histogram doesn't exist. What is important, though, is that the peaks don't suddenly drop straight down, and that too many pixels aren't bunched up at the edges of the histogram. This would mean that details in the shadows or highlights of your photo will be lost.
How do you recognize overexposure and underexposure?
When you're unsure whether your photo is properly exposed, a histogram is very useful. At a single glance, you can immediately see whether you're shooting too dark or too light.
With an overexposed photo, you'll see little to no peak at all on the left side of the histogram. The right side of the histogram, on the other hand, will show a high peak. This tells you that your photo contains too much light/white and too little shadow/black.
An underexposed photo will essentially show the reverse of the histogram above. On the left side of the histogram, you'll now see a high peak, while the right side shows little to no peak at all. This means there's too much shadow/black and too little light/white.
Photos with a lot of black or white
There are also cases where your histogram should actually have a peak on the left or right side.
If you photograph a subject with a lot of white in it, your histogram will indicate the photo is too light, with a peak on the right side. But you actually want this photo to be light, because otherwise the white tones won't come through properly. This means your photo is still correctly exposed, despite the histogram showing a large peak on the right side.
The reverse is true for a dark photo, for example when you take a portrait with a black background. The histogram will then show a high peak on the left side, since your camera assumes the scene is very dark. But a photo with a black background is of course meant to be dark, as there will be a lot of black in the image. In this situation, the photo is well exposed if you have a peak on the left side.
Do you see that your photo is too light or too dark according to the histogram? Then you can adjust the exposure by opening up your aperture, using a longer shutter speed, or increasing your ISO. Together, these three elements form the exposure triangle and determine how light or dark your photo becomes.
Left: Here you see an underexposed histogram: the shadows dominate, and details in dark areas may be lost.
Middle: This histogram shows a well-exposed photo: no extreme shadows or overexposed areas.
Right: An overexposed histogram: the highlights are completely white, causing details in the light areas to disappear.
Practical tips
Check your histogram in bright light
On a sunny day, your camera's screen can be misleading. Use the histogram instead to check whether your photo is properly exposed, especially when details in the highlights or shadows matter.
Prevent overexposure in RAW photos
Shooting in RAW? Make sure your highlights don't 'clip' (become completely white), because you can't recover these details in post-processing. Slight underexposure is often better than overexposure.
Pay attention to the subject
Not every histogram needs to be perfectly balanced. A silhouette photo, for example, has a peak in the shadows, while a snowy landscape sits mainly in the highlights. Always analyze the histogram in the context of your photo.
Use the 'ETTR' technique
'Expose to the Right' (ETTR) is a technique where you set the exposure so the histogram shifts slightly to the right, without losing any highlights. This results in a photo with less noise and more detail to work with in post-processing.
A powerful tool in photography
The histogram is an important tool in photography that helps you better understand and control the exposure of your photos. By using it regularly, you'll not only learn how to prevent underexposure and overexposure, but also develop a sharper photographic eye. So grab your camera, experiment with different settings, and never be caught off guard by a photo that's too dark or too light again. Your perfect exposure starts with the histogram!
