High and Low Key
Most images contain a full range of tones, from the very bright to the very dark. Sometimes, however, dramatic effects can be achieved in scenes that are predominantly white or black. Bright or dark. Inherently or achieved through choice of lights.
These effects rely heavily on lighting for their success—but the subject matter is equally important. So called high-key lighting is used to produce images that have a dominant bright tones. But in order to do this, the scene needs to be constructed so that much of the frame is filled with white, or light-toned subjects. A typical shot of a fair model in a white dress, posed against a bright background. Snow scenes also lend themselves to the high-key approach. In order to keep the picture from looking too flat, and to provide a focal points, it is helpful to have small areas of dark tone; in a portrait, these are usually provided by the eyes. Lighting should be soft—so that the scene is evenly lit without dark shadows. Slight overexposure may also be used to create the over-bright look, although in the interests of avoiding burned-out highlights, it may be better to do this using a Curves adjustment in postproduction.
Low-key shots are just the opposite, set up using mostly blacks and dark tones. A small area is usually lit with highly directional light, such as a spotlight, or overhead window. Exposure verges on the side of underexposure to ensure the theatrical look.