What A Histogram is, Why It’s Useful, & How To Read It
Going through the motions of creating and choosing a good image is an evaluative process, and yet, for many people, a critical tool used for image evaluation on many levels is ignored. One of the advantages of a digital workflow is our easy access to the histogram at pretty much every step of the photographic process, and in fact, evaluating an image based on a camera’s reproduction (EVF, LCD) simply won’t be as dependable or consistent as the information that can be garnered from the histogram.
The trouble is, how is a histogram read, and in what ways it is actually useful?
At the most basic level a histogram will help you dial in and recognize mathematically (not through a preview image) if an exposure is correct. Granted, ‘correct exposure’ and the pursuit of it, is a bit of a fool’s errand. After all, ’correct’ is a variable based on opinion and intention than it is an unvarying control. However, if we release ourselves from the trappings of a pedant, we can probably all agree for the purpose of education, and getting on with things, that correct exposure is a relatively neutral one with as much information retained as possible, with no blown out highlights nor overdone blacks. That’s simple enough to grasp, though not always so simple to achieve.
Getting it right in camera when it comes to metering seems rather banal, and simple, especially given digital’s trial & error and chimping ways.
But while trial and error and chimping are mighty fine, they both rely largely on the camera’s primary LCD display, and that, I’m afraid, just won’t do because it’s not entirely accurate, and it’s small and difficult to see details. Various screens will also display an image differently than others, just as your images often look a little different in your EVF than they do on the rear LCD. The histogram, however, should render the same anywhere. It will always measure between complete black and complete white – measuring luminance levels along the X axis and quantity of light for a given luminance along the Y axis.
But the information isn’t useful only at the moment of capture, but in post processing, and to get a little more into it have a look at the video below by Nathaniel Dodson of Tutvid, who’s made a nice, approachable video on the utility of a histogram and explains why it’s so critical.
Note: a histogram will not take the utility away from the visual preview on your EVF or LCD for composition, framing, sharpness, et cetera.