Anti-halation backing

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An anti-halation backing is a layer found in modern photographic films. It is placed between the light-sensitive emulsion and the tough film base, or sometimes on the back of the film base. The light that passes through the emulsion and the base is absorbed by the opaque anti-halation layer. This keeps that light from reflecting off of the pressure plate or anything else behind the film and re-exposing the emulsion, reducing contrast. The anti-halation layer is rendered transparent during processing of the film.