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Reformatted table to make DX CAS scheme more apparent.
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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 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 consistsincludes of severalmultiple partsmarkings, which are a [[latent image]] DX[[barcode]] filmon edgethe barcodebottom onedge of the film, below the sprocket holes, a codeconductive pattern on the cartridge used by automatic cameras, and a barcode on the cartridge read by photo-finishing machines.
 
The DX encoding system was incorporated into [[American National Standards Institute|ANSI]] PH1.14, which provided standards for 135 film magazines for still picture cameras and was superseded by [[I3A|NAPM]] IT1.14 in 1994; it is now part of [[International Organization for Standardization|ISO]] standard 1007, whose latest revision was issued in 2000.
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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 takesuses thea form of a2×6 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 detecteddistinguished by reading only S1 and, S2, and ground.
 
====Electrical contacts====
[[File:Codage DX.jpg|thumb|right|upright=1.5|DX CAS code positions
 
<ul>
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 intervals spaced at {{frac|3}} steps, from ISO 25/15° to 5000/38°, are used.▼
<li>1: Ground</li>
<li>2–6: Film speed</li>
<li>7: Ground</li>
<li>8–10: Film length</li>
<li>11–12: Exposure latitude</li>
</ul>]]
▲On 35mm film cartridges there are two rows, ofeach with six rectangular areas. The two left-most areasarea of both rows (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 intervals spaced at {{frac|3}} steps, from ISO 25/15° to 5000/38°, are used.
 
The film speed codes are in binary order if the first three bits (S1, S2, S3) are considered to be a "base" identifying a trio of speeds and the last two bits (S4 and S5) are considered an adjustment of +{{frac|3}} or +{{frac|2|3}} stops within that trio. For example, ISO speed 25/15° is encoded as 00010, while 32/16° is 00001 and 40/17° is 00011. These share a common encoding of 000xx for the first three bits, differing only in the last two bits. Similarly, the next three speeds are encoded 10010 (50/18°), 10001 (64/19°), and 10011 (80/20°); it is clear from examination these all share the same 100xx encoding for the first three bits. By comparison to the preceding set of three speeds, the encoding for 25/15° (00010) and 50/18° (10010) have the same xxx10 encoding for the last two bits; likewise, 32/16° (00001) and 64/19° (10001) share the xxx01 encoding, which indicates +{{frac|3}} stop compared to the xxx10 encoding, and 40/17° (00011) and 80/20° (10011) share the xxx11 encoding, which indicates +{{frac|2|3}} stop compared to the xxx10 encoding.
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In this scheme:
Where "G" are the two common-ground contacts, "S" is the film speed, "L" the film length, and "T" the exposure tolerance.
* "G" are the two common-ground contacts
* "Sx" are the film speed contacts
* "Lx" are the film length contacts
* "Tx" are the exposure tolerance contacts
 
====Reading DX Camera Auto Sensing codes====
The encoding scheme is illustrated in the truth table below using letters and color.
* "G" is ground
Where "G" is ground, "T" represents the connection to ground and "F" for the lack of connection.
* "T" represents the contact is connected to ground
* "F" represents the contact is disconnected from ground
 
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<ref name="Minolta_AF-E">{{cite web |publisher=[[Konica Minolta]] |___location=Japan |url=http://ca.konicaminolta.jp/oldnew/minolta/1980/1984.html |archive-url=https://web.archive.org/web/20080323040027/http://ca.konicaminolta.jp/oldnew/minolta/1980/1984.html |title=Introduction of the Minolta AF-E / Freedom II in July 1984 |work=Minolta camera history |archive-date=2008-03-23}}</ref>
<ref name="Minolta_7000AF">{{cite web |publisher=[[Konica Minolta]] |___location=Japan |url=http://ca.konicaminolta.jp/oldnew/minolta/1980/1985.html |archive-url=https://web.archive.org/web/20080323040256/http://ca.konicaminolta.jp/oldnew/minolta/1980/1985.html |title=Introduction of the Minolta 7000 AF in February 1985 |work=Minolta camera history |archive-date=2008-03-23}}</ref>
<ref name="Fuji_Patent_4024557">{{cite webpatent |publishercountry=US |status=Patent |number=4024557A |assign=[[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-datepridate=2011-07-21}}{{deadAugust 1, 1975 link|datepubdate=JuneMay 17, 1977 2024|botinvent1=medic}}{{cbignoreKeiichi Aoyama |botinvent2=medicKeeji Kaneko |invent3=Katsuji Muramatsu |invent4=Ikuo Fuutagawa}}</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 |url-status=live |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=de |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 |url-status=dead |archive-url=https://web.archive.org/web/20160326152153/http://www.mi-fo.de/forum/index.php?showtopic=10279&st=0&p=120737&#entry120737 |archive-date=2016-03-26}} [https://archive.today/20190609120650/http://www.so-fo.de/t10279f164-Filmrueckspulung-Minolta-Dynax-1.html%23msg120737<!-- Cached thread in another forum: http://www.so-fo.de/t10279f164-Filmrueckspulung-Minolta-Dynax-1.html#msg120737 -->]</ref>
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