In photography, a halo-like blurring effect of highlights or other bright areas of a photographic image. Halation is caused by light rays, after passing through the light-sensitive emulsion and the base material, reflecting from the bottom of the base material and passing back up through the emulsion, essentially re-exposing the film. Halation is eliminated on modern films by the use of antihalation dye, which absorbs the light rays before they can be reflected back up through the emulsion.
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