Anti-halation backing
Encyclopedia
An anti-halation backing is a layer found in most photographic film
s. It is usually a coating on the back of the film base
, but sometimes it is incorporated between the light-sensitive emulsion
and the base. The light that passes through the emulsion is absorbed by the anti-halation layer. This prevents any light from being reflected back through the emulsion from the rear surface of the base, or from anything behind the film, and causing a halo
-like effect around bright points or edges in the image. The anti-halation layer is rendered transparent or washed out (as in K-14
films) during processing
of the film.
The lack of an anti-halation layer in Kodak's High Speed Infrared film (HIE) is the cause of the ethereal "glowing" effect often associated with infrared photography, rather than an artifact of IR itself.
Photographic film
Photographic film is a sheet of plastic coated with an emulsion containing light-sensitive silver halide salts with variable crystal sizes that determine the sensitivity, contrast and resolution of the film...
s. It is usually a coating on the back of the film base
Film base
A film base is a transparent substrate which acts as a support medium for the photosensitive emulsion that lies atop it. Despite the numerous layers and coatings associated with the emulsion layer, the base generally accounts for the vast majority of the thickness of any given film stock...
, but sometimes it is incorporated between the light-sensitive emulsion
Photographic emulsion
Photographic emulsion is a light-sensitive colloid, such as gelatin, coated onto a substrate. In silver-gelatin photography, the emulsion consists of silver halide crystals suspended in gelatin, and the substrate may be glass, plastic film, paper or fabric....
and the base. The light that passes through the emulsion is absorbed by the anti-halation layer. This prevents any light from being reflected back through the emulsion from the rear surface of the base, or from anything behind the film, and causing a halo
Halo
Halo may refer to:* Halo , a glow or ring of light around a head or person in art-Game franchise and spin-offs:*Halo , a video game franchise by Bungie and Microsoft Game Studios...
-like effect around bright points or edges in the image. The anti-halation layer is rendered transparent or washed out (as in K-14
K-14 process
K-14 was the developing process for Kodak's Kodachrome transparency film; the last version having been designated Process K-14M. The process differed significantly from its contemporary, the E-6 process, in both complexity and length. Kodachrome film has no integral color couplers; dyes are...
films) during processing
Photographic processing
Photographic processing is the chemical means by which photographic film and paper is treated after photographic exposure to produce a negative or positive image...
of the film.
The lack of an anti-halation layer in Kodak's High Speed Infrared film (HIE) is the cause of the ethereal "glowing" effect often associated with infrared photography, rather than an artifact of IR itself.