Boxes of film for colour slides, c 1960.

UNITED KINGDOM - JULY 18: Boxes of Agfacolor and Kodachrome II film for colour transparencies. The first colour slide film was Kodachrome, introduced by Kodak in 1936. Slides are positives, images which have the same tonal values and colours as the original scene. Transparencies are viewed by transmitting light through them in a projector onto a screen, or on top of a lightbox, whereas with print film the negatives taken by the camera need to be made into positive prints. Today a variety of different slide films are available, for colour and also black and white photography. Improvements in technology relating to the fineness of the grain in the emulsion enable images of outstanding sharpness and detail rendition to be taken using modern transparency films. (Photo by SSPL/Getty Images)