halation

n.

1. A blurring or spreading of light around bright areas on a photographic image.
2. A glow around a bright object on a television screen.

[HAL(O) + -ATION.]

1. see blooming.

2. Blurred effect in a photographic image that results from light spreading beyond its normal boundaries. This effect can be achieved with special lighting techniques or through the developing process, although it sometimes results, unwanted, from a technical error.

The appearance of haloes around light sources recorded by the photographic image. Light strikes the emulsion; is diffused by the turbidity of the emulsion; is transmitted down to the back of the emulsion support; and is reflected back up again. It can be minimized by the use of light-absorbing anti-halation layers either on the back of the emulsion support or between the emulsion and the support. Historically, anti-halation backings were sometimes removed mechanically, by rubbing with the fingertips, but modern anti-halation layers are normally dyes that are washed out during processing. Black-and-white 35 mm films do not have an anti-halation backing: instead, the base is dyed grey.

— Roger W. Hicks

(hā-lā'shən)
n.

1. Blurring of the visual image due to glare from strong illumination.
2. A blurring or spreading of light around bright areas on a photographic image.

a spreading of light beyond its proper boundaries