DX encoding

DX coding is the name of a system for coding of 135 and APS photographic film catridges so that the camera can automatically determine the film speed, number of exposures and exposure tolerance (latitude).

For the 135 format, it consists of 12 fields on the cartridge surface that are either conductive or non-conductive (painted). Corresponding contacts in the camera sense the information. For sensing of film speed, 6 contacts are sufficient.