While a high-key photo is predominantly presented in white and light tones, low-key images are mostly very dark or black. When this kind of image works, it is because the darkness that encompasses most of the photo focuses attention on the areas that are not dark, providing a sense of mystery. Low-key imagery tends to work because it is human nature to replace the mystery of darkness with imaginary scenes or objects. To make this kind of image, you should look for an overall dark scene. In addition to a pervading sense of darkness, the scene needs to be lit with intermittent light. In an effective low-key image, one area of interest can specifically be lit; for example, the eyes in a portrait on a black velvet background, or a shaft of moonlight.
Alternatively, there can be lighting more spread out across a generally dark scene. In this case, it’s often effective to look for chiaroscuro —moody lighting that shows contrasts between shadows and brightness. Post-processing techniques can help you create a low-key image after the fact. However, it is very desirable to start with a photographic subject that is appropriate for low-key treatment.
You should look for subjects that are largely dark with intermittent illumination of significant features, or specific areas lit either by direct light or using chiaroscuro. As with high-key imagery, it’s desirable to bracket exposures, because a good creative low-key exposure may register in your camera’s light meter as surprisingly underexposed. Essentially, you want to expose for the lit part of your composition—and let the rest of the image go completely black.
Be careful to avoid an average light meter reading as the way to judge the brightness of a low-key scene. Since you really don’t care how dark the black background gets in these images, it’s best to take a spot meter reading of the lit areas of your subject.
Shades of Gray
By definition, every black and white image consists of a range of grays. The majority of black and white photos work by contrasting dark against light. These darks and lights are shades of gray, of course. High-key images, consisting of a subtler shade of gray, work with the tones towards the lighter end of the scale. Low-key images primarily use the dark tones on the grayscale. Yet another effective black and white strategy is to employ midtones as the predominant compositional element.
These compositions use midtone gray values to work together in an endless compositional dance. The nearness of tonal values means that there are relatively few sharp breaks in a predominantly midtone gray composition— you won’t find many hard black forms or white areas that are highlights. When a midtone gray composition works, it is because the eye looks to the subtlety of the relationship between the tonal gradations.
So when you are considering this kind of composition, be careful to present tonal values that work well together. You should look for subjects that present intricate patterns of grays working off one another. Do not expect the drama of a dark shape against a light background, the Zen simplicity of lines in a high-key setup, or the unrelenting angst of a low-key photo. The virtue of the grayscale is a virtue of subtlety.
As opposed to high-key and low-key imagery, midtone photos should be captured so they are neither underexposed nor overexposed. To achieve this kind of “just right” Goldilocks exposure, consider using your light meter set to average the scene. If what you see in front of you tends to be a little dark, you may have to lighten things a bit with your exposure. Conversely, if things seem too bright you may have to underexpose slightly to damp things down.