Use
photography: The process of forminga permanent record of an image on specially treated film or paper. Innormal black-and-white photographya camera is used to expose a film orplate to a focused image of the scenefor a specified time. The film or plateis coated with an emulsion containingsilver salts and the exposure tolight causes the silver salts to breakdown into silver atoms; where thelight is bright dark areas of silver areformed on the film after development(by a mild reducing agent) andfixing. The negative so formed isprinted, either by a contact processor by projection. In either case lightpassing through the negative filmfalls on a sheet of paper also coatedwith emulsion. Where the negative isdark, less light passes through andthe resulting positive is light in thisarea, corresponding with a light areain the original scene. As photographicemulsions are sensitive to ultravioletand X-rays, they are widelyused in studies involving these formsof electromagnetic radiation. See alsocolour photography.