What is Halation?
Halation refers to the spreading of light around bright areas in an image, typically a photograph. The term is also sometimes used in the context of movies and television. As a result of halation, the overall image has a blurred, ethereal quality. The phenomenon can very irksome to photographers when it is not desired, although some deliberately attempt to achieve it for a particular look. A number of things can be used to create accidental or intentional halation. When halation is accidental and undesired, it usually happens when the photograph is taken. As the light-sensitive emulsion on photographic film is exposed, the light passes through the emulsion and then bounces back, creating a blurred halo around areas of particular brightness. Many film companies combat this by including an antihalation later in their film, to prevent this light scatter. When the film is processed, this layer is washed out so that the film will develop normally. Some amateur photographers notice problems
