One of the most common problems I see with digital images is that they are too dark, and occasionally too bright. I’ve no doubt they look fine to the person editing them, but when I see them on my computer, the brightness level is often either too low or too high.

But how do you tell if your images are too dark or too bright?

This is a real problem in the Internet age, where your photographs are most commonly viewed on electronic screens rather than as actual prints.

In the old days, you could spend as much time as you wanted in the darkroom, fine tuning a print to show exactly the shadows, mid tones and highlights as you wished them to look. Then you only had to consider the light that would shine on the print when displayed.

But now your photographs are viewed on phones, tablets, and desktop monitors – you have no control over the brightness settings on these devices. If a given viewer has her phone brightness turned way up, guess what? Your photo will look brighter there than it will on a tablet with the brightness turned down.

And what about your own monitor – the one you use to make fine adjustments to your images as you process them? Is it bright or dark? What about the room you work in? The darker it is the brighter your images will look on screen. This problem just gets more and more complicated.

So what do you do to have the best chance of attractively displaying your images across a wide variety of media?

You use the Histogram:

What is a histogram, I hear you ask? When applied to digital photography, it’s a graph that shows how many pixels of the various brightness levels are contained in a given image:

This example shows the Levels control in Photoshop. I’ve created a graduation from dark on the left to bright on the right, and the histogram represents the pixels of varying brightness values. The darker pixels are on the left of the graph, the brighter pixels are on the right.

If the image is all white, all of the pixels are stacked against the right side of the histogram:

Conversely, if the image is all black, the pixels are stacked against the left side:

In an actual photo you can use a histogram to make sure the image isn’t too dark or too light.

See how on the next page: