Understanding the Histogram to Improve Exposure in Your Photos

While taking photos, have you ever asked yourself or a fellow photographer whether your image is bright enough or dark enough? How can one know if the image is correctly exposed? How not to overdo it in post-processing? The answers to all these questions hide in a little graph called the Histogram, which is a valuable tool for any photographer. If you still feel a little intimidated by it, continue reading and we will shed some light on this mysterious yet easy to use tool for photographers.

So what is a Histogram?

The Histogram is a graph that shows the distribution of tones in a photograph from deep shadows to bright highlights. The horizontal axis of a Histogram shows all the tones, starting with pure black on the far left, moving through shadows to medium grey, then continuing to highlights and finally ending with pure whites on the far right of the axis. The vertical axis represents the number of pixels in the image that is in each tone.

Where can I find it on my camera?

Reviewing the Histogram in preview mode is the most useful. After taking a photo, preview it on your camera screen in playback mode. To see a histogram, Canon users can press Display or Info button, depending on the model of camera. Nikon users can press the Up or Down button for the same effect (note that this feature may need to be activated in the Menu settings). 

How do I use a histogram for correct exposure?

The Histogram does not itself correct the exposure, but rather acts as an information tool. An ‘ideal’ Histogram usually looks like a curve that is stretched all the way from left to right, just touching the edges on both sides. That means that all the pixels in your image are of a particular tone and no loss of detail or “clipping” occurs.

An underexposed image is represented by a curve shifted to the left. An overexposed image can be seen on a curve shifted to the right. Gaps in histogram on either of the sides mean that the image lacks information in either shadows or in highlights. This can easily be corrected by adding or subtracting light from the image by using exposure compensation (+/- button).

Spikes in the Histogram on either side mean that some “clipping” of tones occurs and that there is loss of detail in either shadows or highlights of the image. Often this information is unrecoverable, so it is usually best to avoid spikes.

Remember that there is no rule without exception, and the Histogram does not always have to be stretched for best results. For example, in this photo of a feather, dark tones are absent and therefore the Histogram only shows brighter tones.

For highly contrasted images, a histogram will most likely resemble a U-shape. This is often the case when photographing sunrises or sunsets and scenes containing both bright sunlight and deep shadows. Therefore, use the Histogram as a guide, but do not forget to trust your senses!

How does the Histogram help in post-processing?

After you have downloaded an image and opened it in your favourite editing software, have a look at the Histogram. You will notice immediately whether your image needs to be brightened or darkened, whether it needs more or less contrast. Referring to the Histogram while toggling the sliders also helps not to overdo it and keep all the tonal range of the image.

So is your histogram already a “happygram”?