High key, low key
Experiment with the classics of overall near-white and its opposite of dark with high contrast
The extremes of overall brightness and contrast are high-key and low-key images. Because they push the limits of tonal range, they tend to be more a feature of black and white than of colour. A high-key treatment depends on a large area and high value of whiteness, and on high contrast. For it to work well, there usually need to be some smaller, darker elements that are integral to the image. Raising the brightness and contrast throws emphasis on whatever darker areas remain. The boat on the lake above was shot in colour, and not as high-key as the result here, but it lent itself well to the high-key treatment. At this time of day, the mountains and sky in the reflection are bathed in blue, and so can be lightened selectively during the conversion. This was done by raising the blue strongly, also cyan and red to a lesser degree, and this whitened the image overall without affecting the boat.
Low-key also responds to thoughtful processing to maintain the depth of shadows and the contrast between them and the small lit area. This example left is reasonably conventional for low key; the setting is a dark interior, with weak side-lighting that reveals enough of the subject to make it obvious, and a background that can, and probably should, go to black.
A single rowing boat on Altausseer See in Austria. Early morning blue light allowed these to be raised to very pale in conversion
A Shan man near Inle Lake, Myanmar, standing in a darkened room lit only by a small window: a typical low-key situation