How was bromine used in photographic film?

Bromine is essential to the photographic process primarily through its use in the compound silver bromide.

In traditional black-and-white film, the light-sensitive surface consists of an emulsion of minute silver bromide crystals suspended in gelatin. This material is highly sensitive to light; when exposed in a camera, the silver bromide undergoes a chemical change that creates a [latent image]. During this process, light releases electrons from the silver bromide crystal, which migrate to sensitivity specks, eventually allowing developing agents to reduce the exposed crystals into metallic silver.21

Beyond standard film, bromine is used in:
* Bromide paper: A sensitized paper coated with a silver bromide emulsion used for creating photographic enlargements or contact prints.3
* Bromoil process: A technique for making oil-pigmented prints that involves bleaching the silver image from a bromide print and applying pigment to the remaining areas.4

The development of these light-sensitive silver bromide materials was a primary driver for the initial industrial importance of bromine.1