Photographic film is a strip or sheet of transparent 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 ultraviolet light, X-rays, gamma rays, and high-energy particles. Unmodified silver halide crystals are sensitive only to the blue part of the visible spectrum, producing unnatural-looking renditions of some colored subjects. This problem was resolved with the discovery that certain dyes, called sensitizing dyes, when adsorbed onto the silver halide crystals made them respond to other colors as well. First orthochromatic (sensitive to blue and green) and finally panchromatic (sensitive to all visible colors) films were developed. Panchromatic film renders all colors in shades of gray approximately matching their subjective brightness. By similar techniques, special-purpose films can be made sensitive to the infrared (IR) region of the spectrum.In black-and-white photographic film, there is usually one layer of silver halide crystals. When the exposed silver halide grains are developed, the silver halide crystals 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, incorporating different combinations of sensitizing dyes. Typically the blue-sensitive layer is on top, followed by a yellow filter layer to stop any remaining blue light from affecting the layers below. Next comes a green-and-blue sensitive layer, and a red-and-blue sensitive layer, which record the green and red images respectively. During development, the exposed silver halide crystals 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 halide crystals in the bleach step. It is removed from the film during the process of fixing the image on the film with a solution of ammonium thiosulfate or sodium thiosulfate (hypo or fixer). 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. Photographic film and film stock tend to be similar in composition and speed, but often not in other parameters such as frame size and length. Silver halide photographic paper is also similar to photographic film.

George Eastman (July 12, 1854 – March 14, 1932) was an American entrepreneur who founded the Eastman Kodak Company and helped to bring the photographic use of roll film into the mainstream.

He was a major philanthropist, establishing the Eastman School of Music, Rochester Philharmonic Orchestra, and schools of dentistry and medicine at the University of Rochester and in London Eastman Dental Hospital; contributing to the Rochester Institute of Technology (RIT) and the construction of several buildings at the second campus of Massachusetts Institute of Technology (MIT) on the Charles River. In addition, he made major donations to Tuskegee University and Hampton University, historically black universities in the South. With interests in improving health, he provided funds for clinics in London and other European cities to serve low-income residents.

In his final two years, Eastman was in intense pain caused by a disorder affecting his spine. On March 14, 1932, Eastman shot himself in the heart, leaving a note which read, "To my friends: my work is done. Why wait?"The George Eastman Museum has been designated a National Historic Landmark. Eastman is the only person represented by two stars both in the Film category in the Hollywood Walk of Fame, one in North side of the 6800 block of Hollywood Boulevard and the other one in West side of the 1700 block of Vine Street, recognizing the same achievement, that he developed, bromide paper, which became a standard of the film industry.