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 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Standards Institute|ANSI]] PH1.14, which provided standards for 135 film magazines for still picture cameras and was superseded by [[I3A|NAPM]] IT1.14 in 1994; it is now part of [[International Organization for Standardization|ISO]] standard 1007, whose latest revision was issued in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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===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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===DX Camera Auto Sensing===

[[File:Codage DX.jpg|thumb|right|upright=1.5|DX CAS code positions; this film is rated at ISO 400/27°, has a 24-exposure length, and an exposure tolerance of ±1 stops.

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.

<ul>

<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>]]

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.

TheWith 135 film cartridges, the DX Camera Auto Sensing code takesuses thea form of a2×6 grid of rectangular contact pointsareas on the side of the metal cartridge surface; these thatareas are either conductive (bare metal) or non-conductive. Electrical contacts in the camera read the bit pattern(painted). The Mostleft-most camerasarea readof onlyboth partrows of(with the code;spool typically,post onlyon the filmleft) speedare iscommon read,(ground) and someare camerasthus aimedalways atbare themetal. consumerElectrical marketcontacts onlyin readthe enoughcamera bits to tell apartread the mostbit common film speedspattern. ForDiagramatically example,(with 100,spool 200,post 400,to andthe 800 can be detected by reading only S1 and S2 and ground.left):

====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 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.

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.

Most cameras read the film speed only (first row).

Diagramatically (with spool post to the left):

{| class="wikitable"

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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

Most cameras read the film speed only, which is in the first row. Some cameras aimed at the consumer market only read enough bits in the first row to distinguish the most common film speeds. For example, 100, 200, 400, and 800 can be distinguished by reading only S1, S2, and ground.

====Film speed====

The five bits after the ground contact in the top row can be encoded to a maximum of 32 different film speeds, but only the 24 speeds from ISO 25/15° to 5000/38°, inclusive, spaced in intervals of {{frac|3}} step, are used.

The film speed codes are in binary order if the first three bits (S1, S2, S3) are considered to be a "base" identifyingidentify a trio of film speeds and the last two bits (S4 and S5) are considered an adjustment of +0, +{{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, so 000xx designates the trio of speeds (25-32-40). Similarly, the next group of three speeds are encoded 10010 (50/18°), 10001 (64/19°), and 10011 (80/20°); it is clear from examination these all (ISO 50-64-80) 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.

====Film length====

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.

====Exposure tolerance====

The remaining two bits of the second row give four ranges of exposure tolerance, or latitude.

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

====Reading DX Camera Auto Sensing codes====

* "G" is ground.

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

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

Where "G" is ground, "T" represents the connection to ground and "F" for the lack of connection.

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

<div>

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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>