High-key lighting was originally developed for the film and television industry back in the days when the available technology was not capable of capturing high contrast ratios. A scene that had a large range of tones from deepest black to brightest white would have been impossible to capture with old technology. So, they came up with the high-key lighting system.
The idea is that increased lighting reduces the range of tones between black and white, or eliminates the darkest shadows altogether, making it easier to capture and display those tones that are in the image. Simply put, black and dark tones are reduced, mid-tone areas become much brighter, and bright and near-white areas are pushed to white.
Over time, though, it has become a stylistic and creative option for filmmakers and photographers alike. Many modern studios will shoot this kind of imagery for family and portrait work as it is considered quite contemporary, upbeat and light-hearted.
If you are shooting indoors, the amount of light and general lack of shadows mean that once lights are in place, your subject is not tied down to maintaining one position. They can move around and still be awash with light from all sides. High-key images are also considered very appealing. Images with a larger amount of pale or bright tones are seen as positive, fun and generally attractive. The brighter nature of the shots is also flattering.
The removal of shadows and a certain amount of reduced detail can improve a portrait. The further addition of presenting the images in black and white, where the possible confusion of colour has been removed, is also very effective.
What constitutes a high-key image appears to be a matter of some creative debate. It is held by artists in some areas, who declare that a high-key image should not contain deep shadows and have limited areas of dark tones: essentially, a low contrast image.
Some will say that a generally well exposed mid-tone subject, with a pure white background, constitutes a high-key photo. Still more will take the image to extreme levels of overexposure, with much detail being lost in the process, to leave the barest amount of detail and tonal range.
A general rule is that a high-key image when viewed as a histogram, either on your camera’s LCD display or within your favourite Raw processing application, has its average tones to the far right of the histogram. The further to the right, the brighter the image. It is often referred to as ‘shooting to the right’.
This is done as a result of either deliberate overexposure of an already bright scene at the shooting stage, or lighting the scene in order to achieve a histogram pushed to the far right. Your approach to shooting and lighting high-key may develop over time, but ‘shooting to the right’ can be a good starting reference.
High-key photography is not always something that can be done well with post-processing alone. Solid lighting elements in the original shooting setup have to be in place to ensure a well-balanced high-key image. If the image you shoot is not lit correctly, you may not be able to process your way out of the problem, so this is something to bear in mind.
You have plenty of light falling on your scene, but you need to make sure your exposures are set to get the brightest areas pushed as close to absolute white as you can, even going into overexposure to keep the greatest ratio of tones in the mid-tone and lighter areas. Shadows, although you can have them, are as minimal as possible.
Make sure that you also shoot with as low an ISO setting on your camera as possible. This gives you some processing overhead if you find you do need to do some heavy tweaking of your images after the shooting stage. Given the amount of light you are employing in your shots, fast shutter speeds should be no problem to achieve. Depth of field and aperture are creative choices, but you may be limited by the sync speeds your camera and flash can achieve.