DX Encoding

DX (Digital indeX) Encoding refers to a measurement that appears on both 135 and advanced photo system (APS) film packages. With the DX printed on the side of a film’s cartridge, the camera can automatically read the film’s speed, the number of available exposures and the range of brightness that the film can endure.

DX encoding looks like a barcode (a series of thin and think black lines) on the side of the package where the end of the negative sticks out of the reel. Using electrical contacts, a camera electronically ascertains the details of a particular roll’s capabilities.

DX encoding can represent any one of 32 different film speeds, along with one of eight possible film lengths. However, film lengths generally revolve around the four most popular exposures: 12, 20, 24 or 36 exposures for a given roll.

The American National Standards Institute (ANSI) appointed the American Standards Association (ASA) to be responsible for setting not only the patterns of DX codes, but also a number of other photographic measurements.