DX encoding: Difference between revisions

Revision as of 17:22, 19 May 2018

Revision as of 21:18, 6 June 2019

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[[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 an [[American National Standards Institute|ANSI]] and [[I3A]] standard, originally introduced by [[Kodak]] in March 1983, for marking [[135 film|135]] and [[Advanced Photo System|APS]] photographic film and film cartridges. It consists of 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.

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==DX cartridge barcode==

Next to the film exit lip is an [[Interleaved 2 of 5]] [[barcode]] and a printed number. The 6 digits represent the I3A assigned [[DX number]] (middle 4 digits), the number of exposures (last digit) and a proprietary manufacturer's code (first digit). 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.<ref name="Kodak_4965628">Kodak US patent 4965628</ref>

==DX film edge barcode==

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The outside of film cartridges are marked with a DX Camera Auto Sensing (CAS) code readable by many cameras. Cameras can then automatically determine the [[film speed]], number of exposures and exposure tolerance.

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.

===Electrical contacts===

On 35mm film cartridges there are two rows of six rectangular areas. The two left-most areas (with the spool post on the left) are both common (ground) and are thus always bare metal. The remaining five bits in the top row represent 32 possible film speeds. But only the 24 speeds representing the 1/3 [[f-number|stops]] from ISO 25/15° to 5000/38° are used. The codes are not in strict binary order.

In the second row, the first three bits represent eight possible film lengths, although in practice only 12, 20, 24 and 36 exposures are encoded. The remaining two bits of the second row give four ranges of exposure tolerance, or latitude.

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<ref name="Fuji_Patent_4024557">{{cite web |publisher=[[Fuji (company)|Fuji]] |url=http://www.google.com/patents?id=YQg9AAAAEBAJ&printsec=frontcover&dq=4,024,557 |id=Patent 4024557 |title=US-Patent 4024557: Film magazine having film speed indicating means |access-date=2011-07-21}}</ref>

<ref name="AP_1977_Fuji">{{cite journal |journal=[[Amateur Photographer]] |title=Fuji's Latest Auto-System |date=1977-02-16 |page=61 |url=http://www.zenitcamera.com/qa/images/fuji-cassette-ap-1977-02.jpg |access-date=2011-07-21 |dead-url=no |archive-url=https://web.archive.org/web/20180122141109/http://www.zenitcamera.com/qa/images/fuji-cassette-ap-1977-02.jpg |archive-date=2018-01-22}} [http://www.zenitcamera.com/qa/images/fuji-cassette-ap-1977-02.tif<!-- https://web.archive.org/web/20180122141126/http://www.zenitcamera.com/qa/images/fuji-cassette-ap-1977-02.tif -->]</ref>

<ref name="Paul_2005_DX-CAS">{{cite web |title=Ausführliche Informationen zum DX/CAS-Code |language=German |trans-title=Comprehensive information regarding DX/CAS code |author-first=Matthias R. |author-last=Paul |date=2005-10-22 |work=Minolta-Forum |url=http://www.mi-fo.de/forum/index.php?showtopic=10279&view=findpost&p=120737 |access-date=2011-07-21}}</ref>

<ref name="Paul_2008_Fuji-Barcode">{{cite web |title=Informationen zu Barcodes auf Rollfilmen |language=German |trans-title=Information on barcodes on rollfilms |author-first=Matthias R. |author-last=Paul |date=2008-08-24 |work=Minolta-Forum |url=http://www.mi-fo.de/forum/index.php?showtopic=21332 |access-date=2011-07-21 |archive-url=https://web.archive.org/web/20160804010215/http://www.mi-fo.de/forum/index.php?showtopic=21332 |archive-date=2016-08-04}}</ref>

<ref name="Kodak_4965628">Kodak US patent 4965628</ref>

<ref name="Fujifilm_5845869">{{cite web |url=http://www.google.com/patents?id=WQsEAAAAEBAJ&dq=5845869 |title=US-Patent #6026250 "Camera, bar code reader for camera and method of detecting bar code reading |id=US6026250A |date=2000-02-15 |orig-year=1996-12-12, 1997-12-09 |author-first1=Shigenori |author-last1=Goto |author-first2=Hisashi |author-last2=Hamada |author-first3=Shiro |author-last3=Hashimoto |author-first4=Nobuhiro |author-last4=Aoki |author-first5=Tokuji |author-last5=Sato |publisher=[[Fuji Photo Film Co., Ltd.]], [[Fuji Photo Optical Co., Ltd.]] |access-date=2018-01-22 |archive-url=https://web.archive.org/web/20180122190129/https://www.google.com/patents/US6026250?hl=de&dq=5845869 |archive-date=2018-01-22}}</ref>