Solarization renders part of a photographic image negative and part positive. With traditional (chemical) photographic processing this is achieved by exposing a print or negative to a flash of light while still in the developing solution. Results are not completely repeatable because of variations in chemistry, porosity of substrate, intensity and duration of the light bursts. (More Below)
In the digital darkroom solarization is created by splitting tonal curves. Normally histograms are more or less bell-shaped. Solarized images can be rendered by dividing the bell in two. Over-exposed areas are darkened, while details in shadow areas may be revealed in even greater detail than possible with other dodging or brightening techniques. Color reversals and garish effects often occur.
The method was first employed artistically by surrealist photographers Man Ray and Lee Miller in 1929. Other noted photographers later adopted the technique. Two worthy of mention are Ansel Adams and Minor White.