A system of recording digital data on photographic film using superimposed grating patterns

The most common method for storing data in a binary form on photographic films has been to record each bit in terms of the presence or absence of a density in an area on the film. While in theory high-resolution materials have the inherent capacity for recording a tremendous number of bits within a given area, to a very great extent this has not been realizable because of technological difficulties. First of all, as the areas corresponding to the bits on the film are made smaller, they become more and more difficult to locate mechanically. And second, any film is bound to pick up a certain amount of dirt, and such particles can easily obscure individual bits and cause real havoc if high accuracy is required.