What does a histogram tell us?

One of the most important and valuable tools that Photoshop gives us when editing, retouching or restoring images is the histogram. In fact, histograms are so valuable that they aren’t limited just to Photoshop. You’ll find histograms in lots of other image editing programs as well, like Photoshop Elements, Adobe Lightroom, the Camera Raw plug-in and more.

Learning and understanding how to read histograms is probably the single most important concept to become familiar with when working with pictures from a digital camera. A histogram can tell you whether or not your image has been properly exposed, whether the lighting is harsh or flat, and what adjustments will work best. It will not only improve your skills on the computer, but as a photographer as well.

So what exactly is a histogram? A histogram is a graph that shows the current tonal range of our image. By “tonal range”, I mean the brightness values of the image. A histogram shows us how much of the image is currently pure black (the darkest an image can be), how much of it is currently pure white (the brightest an image can be), and how much of it falls somewhere between black and white.

Ok, now let’s see some visual examples for better understanding

1. As you can see, the first image was underexposed because it has a loss of shadow detail, and important dark areas are “muddy” or indistinguishable from black. In other words, an underexposed image is too dark. Shown on the left, is the histogram for the first image, the high peaks are on the left side of the graph.

2. What you should be aiming for, is a histogram that displays the majority of the peaks within the center of the graph like the histogram shown below the second image.

3. The last image is the opposite of the first one. It has a loss of highlights detail, and important light areas are “muddy” or indistinguishable from white. This means that the last photo is overexposed and, as shown in the histogram, the high peaks are on the right side of the graph.

So, to resume all in one sentence: in most cases, when the high peaks are on the left side of the graph the image is underexposed (too dark), when the majority of peaks are in the center of the graph the image is properly exposed and when the high peaks are on the right side of the graph the image is overexposed (too bright).

Exceptions to the rule

There are times when it’s perfectly acceptable for the graph to display high peaks at either end of the histogram.

  • For instance, if there is naturally a lot of white within the scenery (snow shots), then you would see high peaks on the right side of the histogram, even when the photo is perfectly exposed.
  • On the otherhand, if there is a lot of black within the scenery or object you are photographing, then the high peaks would naturally occur on the left hand side of the graph.
  • Furthermore, if there is a good mixture of black and white within the scenery, you may find high peaks at both ends of the histogram.

Keep in mind that it’s a good habit to take a look at the histogram when you retouch a photo, but notice that there’s no such a thing as perfect histogram and if you want to go creative, don’t let the histogram limit your mind.

© 2012-2017 Andrei Ivascu