Demystifying the photography histogram

In my last blog, the one about my 10 most-used Tools in the Snapseed photograph editing app, I referred to the histogram, but said that I would save any discussion about this for another blog. Well, this is that other blog. Welcome to the world of the histogram.

In photography, a histogram is a graph that shows the distribution and magnitude of the dark and bright tones in your photo, which when read from left to right, ranges from darks to whites, or in photography-speak, shadows, midtones, and highlights. It's probably easier to grasp if you focus on the linear scale below the histogram.

 Some histograms, like the one below, can show the distribution of colours within the blue, red, green, and neutral range. But for now, concentrate on blacks and whites.

Here’s how to think about a histogram in plain language:

The left side of the histogram represents dark tones (the shadows);

The right side represents bright tones (the highlights);

The middle represents midtones (the in-between grays and colours);

The height of the graph at each point shows how many pixels in the photo have that brightness.

So, when you take a photo and look at its histogram:

If the graph is bunched to the left, your photo is probably too dark (underexposed);

If it’s bunched to the right, it’s likely too bright (overexposed);

If it’s spread nicely across the middle, it often means you have a balanced exposure with a good range of tones.

In short, a photographer’s histogram is a visual tool that helps check exposure — whether the image has the right balance of light and dark — without relying just on how it looks on the screen.

Let's now look at the histogram you'll come across when you open the Tune Tool in Snapseed.

You want to focus on the little bar chart in the bottom left corner, the icon I have marked with an arrow.

If you now click on this icon, the histogram will appear.

What does this histogram tell you about this photograph? What will happen to the histogram if you swipe to the right? What happens to the histogram if you swipe to the left?

A histogram is a useful guide for obtaining the correct exposure, or as near to correct as you can, when you're editing. I don't use them routinely, but sometimes they can act as prompt to adjust the brightness.

Thanks for taking the time to read this blog, which I hope has demystified the histogram. I know when I first became interested in photography and was on a very steep learning curve, the histogram was something I thought I'd leave until later. I am glad I eventually did get to grips with it, understanding what it represents and what it's telling me.

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© Mike Young 2025.