<Tr> <Td> </Td> <Td> This article needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (February 2011) (Learn how and when to remove this template message) </Td> </Tr> <P> Film stock is an analog medium that is used for recording motion pictures or animation . It is a strip or sheet of transparent plastic film base coated on one side with a gelatin emulsion containing microscopically small light - sensitive silver halide crystals . The sizes and other characteristics of the crystals determine the sensitivity, contrast and resolution of the film . The emulsion will gradually darken if left exposed to light, but the process is too slow and incomplete to be of any practical use . Instead, a very short exposure to the image formed by a camera lens is used to produce only a very slight chemical change, proportional to the amount of light absorbed by each crystal . This creates an invisible latent image in the emulsion, which can be chemically developed into a visible photograph . In addition to visible light, all films are sensitive to X-rays and high - energy particles . Most are at least slightly sensitive to invisible ultraviolet (UV) light . Some special - purpose films are sensitive into the infrared (IR) region of the spectrum . </P> <P> In black - and - white photographic film there is usually one layer of silver salts . When the exposed grains are developed, the silver salts are converted to metallic silver, which blocks light and appears as the black part of the film negative . Color film has at least three sensitive layers . Dyes, which adsorb to the surface of the silver salts, make the crystals sensitive to different colors . Typically the blue - sensitive layer is on top, followed by the green and red layers . During development, the exposed silver salts are converted to metallic silver, just as with black - and - white film . But in a color film, the by - products of the development reaction simultaneously combine with chemicals known as color couplers that are included either in the film itself or in the developer solution to form colored dyes . Because the by - products are created in direct proportion to the amount of exposure and development, the dye clouds formed are also in proportion to the exposure and development . Following development, the silver is converted back to silver salts in the bleach step . It is removed from the film in the fix step . Fixing leaves behind only the formed color dyes, which combine to make up the colored visible image . Later color films, like Kodacolor II, have as many as 12 emulsion layers, with upwards of 20 different chemicals in each layer . </P> <P> Early motion picture experiments in the 1880s were performed using a fragile paper roll film, with which it was difficult to view a single, continuously moving image without a complex apparatus . The first transparent and flexible film base material was celluloid, which was discovered and refined for photographic use by John Carbutt, Hannibal Goodwin, and George Eastman . Eastman Kodak made celluloid film commercially available in 1889; Thomas Henry Blair, in 1891, was its first competitor . The stock had a frosted base to facilitate easier viewing by transmitted light . Emulsions were orthochromatic . By November 1891 William Dickson, at Edison's laboratory, was using Blair's stock for Kinetoscope experiments . Blair's company supplied film to Edison for five years . Between 1892 and 1893, Eastman experienced problems with production . Because of patent lawsuits in 1893, Blair left his American company and established another in Britain . Eastman supplied Edison with film . </P>

Who made the change from individual photo plates to a reel of plastic film stock