DX Code & Decoding

Introduction

DX (Digital indeX) encoding is an ANSI and I3A standard for marking 135 and APS photographic film and film cartridges. It has several parts, a latent image DX film edge barcode on the film below the sprocket holes, a code on the cartridge used by automatic cameras, and a barcode on the cartridge read by photo-finishing machines.

DX Cartridge Barcode

dxbarcode

Next to the film exit lip is an Interleaved 2 of 5 barcode and a printed number which represent the I3A assigned DX number, the number of exposures and a proprietary manufacturer’s code. The DX number identifies the manufacturer, film type, and by inference, the necessary developing process type. This is used by automatic photo-finishing machines to correctly process the exposed film.

DX Film Edge Barcode

dxedge

Below the sprockets under each frame of 135 film is the DX film edge barcode. The barcode is invisible until the film has been developed. It is optically imprinted as a latent image during manufacturing. They are used by photo finishers to identify and align each frame for printing. It consists of two parallel linear barcodes, one for a synchronizing clock, and the other encoding film data such as type, manufacturer and frame number.

DX Camera Auto Sensing

The outside of film cartridges are marked with a DX Camera Auto Sensing code readable by many cameras. Cameras can then automatically determine the film speed, number of exposures and exposure tolerance. The first 35mm camera to use the technology was the Konica TC-X, which was introduced in 1985.

The DX Camera Auto Sensing code takes the form of a grid of contact points on the side of the metal cartridge surface that are either conductive or non-conductive. Electrical contacts in the camera read the bit pattern. Most cameras read only part of the code; typically, only the film speed is read, and some cameras aimed at the consumer market only read enough bits to tell apart the most common film speeds. For example 100, 200, 400, and 800 can be detected by reading only S1 and S2 and ground.

original source

Decoding

dxcode

dxdecode

  • Positions 1 and 7 are always set to conduct (i.e., are metallic areas). They are used for alignment purposes.
  • The ISO value of the film is indicated by positons 2-6. Film speeds from ISO 25 to 5000 can be encoded.
  • The number of exposures are indicated by positions 8-10. Note that many Nikon bodies can actually get an extra exposure off most film when loaded correctly.
  • Finally, the exposure latitude is indicated by positions 11-12. Latitude is used by some automatic processors for print film, but is not relavent to slide film (note that the Kodak Gold film in the above photo shows that it has +3 to -1 stop latitude).

See the picture, above, for positions; see the tables in the right column to decode.
Remember, the silver areas are conductive, the other areas are usually black and non-conductive (a few manufacturers use a different base color on some cassettes).

DXn Simulator

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