X-rays, after having passed through the body, are made to strike a photographic film, much like a black-and-white camera film.

The film has a coating of halides (chlorides/bromides) of silver. The halides affected by X-rays are reduced to metallic silver after treatment with “developers”. The unaffected (“unexposed”) halides are washed out chemically and the film, rinsed with water, is dried.

The finely particulate silver actually appears dark (rather than shiny!). Thus, areas of the film exposed by X-rays are dark, unexposed areas are transparent. X-ray films are viewed as “negative” films against an illuminated background. Nowadays an X-ray image can also be stored in a digital form on a computer.

X-ray images can also be viewed with a fluorescent screen like that of a monitor. In such an image exposed areas are bright, unexposed areas dark. Needless to say, such images are temporary. This method is called fluoroscopy. It exposes the patient to much higher doses of X-radiation and is far more hazardous.