Cameras these days come with a veritable plethora of tools to help you expose your images properly, everything from built-in exposure meters to zebras and false color displays. However, there's one tool that is often overlooked, despite the fact that it's available on nearly every digital camera today. The histogram. It's an extremely simple tool, but when used properly, it can help you make sure that you never blow out your highlights again.
In this short excerpt from John Greengo's CreativeLive course, The Photography Starter Kit, he talks about what the histogram is, how it works, and how you can use it to nail your exposures.
In short, the histogram is a chart, with the horizontal axis displaying all of the greyscale values in your image (with pure black on the left, and pure white on the right), and the vertical axis displaying the density of pixels for each of those greyscale values. Overexposure and underexposure can be judged simply by seeing whether or not the mass of pixels on the histogram touches either side of the display. In Greengo's example below, you can see an example of a properly exposed image, an overexposed image, and an underexposed image, all with the corresponding histograms.
The consensus with histograms is that the majority of your pixels should be in the middle of the scale, much like the first example above. However, depending on how you intend to expose your image from a stylistic perspective, your histogram might look a bit differently. Here are a few examples from RED's fantastic exposing with histograms post (which is definitely worth a read). First is an example of a bright "high key" image that is properly exposed, and the second example is a darker, moodier image that is also properly exposed. Both have the corresponding histograms.
There are a few drawbacks to using the histogram to judge exposure, however. Since it only gives you an overview of exposure by showing you the density of pixels, it can't give you any specific information about which parts of your image are either under or overexposed. Tools like zebras, false color displays, and waveform monitors can give you very specific greyscale information about individual parts of your image, which in many cases, might be more useful.
With that said, for shooters who are on the run and need a quick visual overview of their exposure, the histogram is an absolutely fantastic tool that can prevent you from under or overexposing.
What are some of your favorite exposure tools? Do you regularly use histograms when you shoot? Let us know down in the comments!