photography

A daguerreotype of the Hiller family, made in about 1885. The daguerreotype produced a photographic image by using a thin sheet of silver-plated copper that had been treated to make the silver light-sensitive. An exposure took from 5 to 40 minutes, which accounts for the stern looks of many of the early sitters.

Process for reproducing permanent images on light-sensitive materials by various forms of radiant energy, including visible light, ultraviolet, infrared, X-rays, atomic radiations, and electron beams.

Photography was developed in the 19th century; among the pioneers were Louis Daguerre in France and William Henry Fox Talbot in the UK. Colour photography dates from the early 20th century.

The most familiar photographic process depends upon the fact that certain silver compounds (called halides) are sensitive to light. A photographic film is coated with these compounds and, in a camera, is exposed to light. An image, or picture, of the scene before the camera is formed on the film because the silver halides become activated (light-altered) where light falls but not where light does not fall. The image is made visible by the process of developing, made permanent by fixing, and, finally, is usually printed on paper. Motion-picture photography uses a camera that exposes a roll of film to a rapid succession of views that, when developed, are projected in equally rapid succession to provide a moving image.

Worldwide, 60 billion photographs a year are taken (1995), of which only 3% are ever reprinted.

Digital cameras are now widely available. These store the images on an electronic card, rather than on film. The images are downloaded onto a computer. With early digital cameras the picture quality was poor, but this has improved. Photographs can be taken, downloaded, viewed, and printed out in only a few minutes. Photographers can decide which photographs they want to print out, and can also digitally alter images, by using a photopaint program to enhance or remove different features. Some digital cameras can capture moving images.