In photography, reversal film or slide film is a type of photographic film that produces a positive image on a transparent base. Instead of negatives and prints, reversal film is processed to produce transparencies or diapositives (abbreviated as "diafilm" or "dia" in some languages like German or Hungarian). Reversal film is produced in various sizes, from 35 mm to roll film to 8×10 inch sheet film. A slide is a specially mounted individual transparency intended for projection onto a screen using a slide projector. This allows the photograph to be viewed by a large audience at once. The most common form is the 35 mm slide, with the image framed in a 2×2 inch cardboard or plastic mount. Some specialized labs produce photographic slides from digital camera images in formats such as JPEG, from computer-generated presentation graphics, and from a wide variety of physical source material such as fingerprints, microscopic sections, paper documents, astronomical images, etc. Reversal film is sometimes used as motion picture film, mostly in the 16 mm, Super 8 and 8 mm "cine" formats, to yield a positive image on the camera original. This avoids the expense of using negative film, which requires additional film and processing to create a positive film print for projection. History Additive method The earliest practical and commercially successful color photography reversal process was the Lumière Autochrome, introduced in 1907. This was an additive method, using a panchromatic emulsion coated on a thin glass plate previously coated with a layer of dyed potato starch grains. Autochrome plates were discontinued in the 1930s, after the introduction of Lumière Filmcolor in sheet film and Lumicolor in roll film sizes. Also using the additive principle and reversal processing were the Agfa color screen plates and films and Dufaycolor film, all of which were discontinued by 1961. Subtractive methods Leopold Godowsky, Jr. and Leopold Mannes, working with the Eastman Kodak Company, developed Kodachrome, the first commercially successful color film to use the subtractive method. Kodachrome was introduced in 1935 as 16mm motion picture film, and in 1936 as 35mm film for still cameras. The Kodachrome films contained no color dye couplers; these were added during processing. In late 1936, Agfacolor Neu was launched, Agfa having overcome earlier difficulties with color sensitivity problems. This film had the dye couplers incorporated into the emulsion, making processing simpler than for Kodachrome. Early color negative film had many shortcomings, including