1952 was quickly adopted by Hollywood, making the use of three-strip Technicolor cameras and bipack cameras (used in two-color systems such as Cinecolor) obsolete in color cinematography. This "monopack" structure is made up of three separate emulsion layers, one sensitive to red light, one to green and one to blue. Safety film Although Eastman Kodak had first introduced acetate-based film, it was far too brittle and prone to shrinkage, so the dangerously flammable nitrate-based cellulose films were generally used for motion picture camera and print films. In 1949 Kodak began replacing all nitrocellulose (nitrate-based) films with the safer, more robust cellulose triacetate-based "Safety" films. In 1950 the Academy of Motion Picture Arts and Sciences awarded Kodak with a Scientific and Technical Academy Award (Oscar) for the safer triacetate stock. By 1952, all camera and projector films were triacetate-based. Most if not all film prints today are made from synthetic polyester safety base (which started replacing Triacetate film for prints in the early 1990s). The downside of polyester film is that it is extremely strong, and, in case of a fault, will stretch and not break–potentially causing damage to the projector and ruining a fairly large stretch of film: 2–3 ft or approximately 2 seconds. Also, polyester film will melt if exposed to the projector lamp for too long. Original camera negative is still made on a triacetate base, and some intermediate films (certainly including internegatives or "dupe" negatives, but not necessarily including interpositives or "master" positives) are also made on a triacetate base as such films must be spliced during the "negative assembly" process, and the extant negative assembly process is solvent-based. Polyester films are not compatible with solvent-based assembly processes. Other types Besides black & white and color negative films, there are black & white and color reversal films, which when developed create a positive ("natural") image that is projectable. There are also films sensitive to non-visible wavelengths of light, such as infrared. Common formats See list of film formats for a comprehensive table of known formats Academy format In the conventional motion picture format, frames are four perforations tall, with an aspect ratio of 1.375:1, . This is a derivation of the aspect ratio and frame size designated by Thomas Edison () at the dawn of motion pictures, which was an aspect ratio of 1.33:1. The first sound features were released in 1926–27, and while Warner Bros. was