DX encoding: Difference between revisions

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{{Short description|Standard marking on film cartridges}}

{{Use dmy dates|date=June 2019|cs1-dates=y}}

[[File:Kodak DX Logo.png|thumb|DX Encoding Logo]]

[[Image:Dx135can.jpg|frame|right|135 Film Cartridge with ''DX barcode'' (top) and ''DX CAS'' code. The CAS code shows this is (top row) ISO 125 film, (bottom row) 24 exposures, +3/−1 f-stop exposure tolerance. The DX barcode reads 017563, showing [[DX number]] 109-12, 24 exposures.]]

'''DX''' ('''D'''igital inde'''X''') encoding is a standard for marking [[135 film|35 mm]] and [[Advanced Photo System|APS]] photographic film and film cartridges, originally introduced by [[Kodak]] in 1983. It includes multiple markings, which are a [[latent image]] [[barcode]] on the bottom edge of the film, below the sprocket holes, a conductive pattern on the cartridge used by automatic cameras, and a barcode on the cartridge read by photo-finishing machines.

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===DX film edge barcode===

[[Image:Dx-film-edge-barcode.jpg|thumb|left|DX film edge barcode; data track decodes to [[DX number]] 47-1 ([[Agfa-Gevaert|Agfa]] [[Agfa Perutz|Perutz Primera 200]]), frame 22A]]

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. The barcode is used by photo finishers to identify each frame for printing. It consists of two parallel linear barcodes, one for a synchronizing clock called the "clock track", and the other encoding film data such as type, manufacturer and frame number, called the "data track".<ref name=":0" /> The barcode nearest the film edge (away from the sprocket holes) contains the data track. The data track sequence repeats every half frame, beginning with six start bits, followed by seven bits of DX Number Part 1, one unassigned bit, four bits of DX Number Part 2, a seven-bit frame/half-frame number, one unassigned bit, one parity bit, and finishes with four stop bits.<ref>{{Cite journal|last1=Gschwind|first1=Rudolf|last2=Zbinden|first2=Erwin|last3=Trumpy|first3=Giorgio|last4=Delaney|first4=John|date=2017|title=Color negatives at the demise of silver halides|url=https://doi.org/10.5167/uzh-142330|journal=ICOM-CC 18th Triennial Conference Preprints, Copenhagen, 4–8 September 2017|volume=|pages=188–191|doi=10.5167/uzh-142330 |via=[[University of Zurich]]}}</ref> The seven-bit frame/half-frame number is called the "DXN" number (different than the [[DX number|"DX Number Part 1" and "DX Number Part 2"]]), and is an extension on the original DX edge code, patented by Eastman Kodak in 1990.<ref name=":0">{{cite patent|country=US|number=4965628|title=Photographic film with latent image multi-field bar code and eye-readable symbols|status=patent|pubdate=1990-10-23|gdate=1990-10-23|inventor1-last=Olliver|inventor2-last=Johnson|inventor3-last=Patton|inventor1-first=Richard|inventor2-first=Cortlandt|inventor3-first=David |assign=Eastman Kodak Company}}</ref><ref>{{cite patent|country=EP|number=0838718B1|title=Method of printing frame numbers from DX-coded photographic film not having frame number codes|status=|pubdate=|gdate=|invent1=|inventor1-first=}}</ref>

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The complete encoding scheme is illustrated in the truth table below using letters and color.

* "G" is ground.

* "T" representsmeans the contact is connected to ground.

* "F" representsmeans the contact is disconnected from ground.

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