Fax

"T.30" redirects here. For other uses, seeT30 (disambiguation)andFax (disambiguation).

Fax(short forfacsimile), sometimes calledtelecopyingortelefax(short fortelefacsimile), is thetelephonictransmission of scanned printed material (both text and images), normally to a telephone number connected to a printer or other output device. The original document is scanned with afax machine(or atelecopier), which processes the contents (text or images) as a single fixed graphic image, converting it into abitmap,and then transmitting it through the telephone system in the form of audio-frequency tones. The receiving fax machine interprets the tones and reconstructs the image, printing a paper copy.Early systems used direct conversions of image darkness to audio tone in a continuous or analog manner. Since the 1980s, most machines transmit an audio-encoded digital representation of the page, usingdata compressionto transmit areas that are all-white or all-black, more quickly.

This fax machine from 1999 used relatively newinkjet printingtechnology on normal paper.

Like many fax machines, this 1990 model usedthermal printingon relatively expensivethermal paperwhich came in rolls. The roll was inserted into a compartment in the machine.

Initially a niche product, fax machines became ubiquitous in offices in the 1980s and 1990s.They have largely been rendered obsolete byInternet-based technologies such asemailand theWorld Wide Web,but are still used in some medical administration and law enforcement settings.

History

Wire transmission

See also:Wirephoto

Scottish inventorAlexander Bainworked on chemical-mechanical fax-type devices and in 1846 Bain was able to reproduce graphic signs in laboratory experiments. He received British patent 9745 on May 27, 1843, for his "Electric Printing Telegraph".Frederick Bakewellmade several improvements on Bain's design and demonstrated a telefax machine.ThePantelegraphwas invented by the Italian physicistGiovanni Caselli.He introduced the first commercial telefax service between Paris and Lyon in 1865, some 11 years before the invention of thetelephone.

In 1880, English inventorShelford Bidwellconstructed thescanning phototelegraphthat was the first telefax machine to scan any two-dimensional original, not requiring manual plotting or drawing.An account ofHenry Sutton's "telephane"was published in 1896. Around 1900, German physicistArthur Korninvented theBildtelegraph,widespread in continental Europe especially following a widely noticed transmission of a wanted-person photograph from Paris to London in 1908,used until the wider distribution of the radiofax.Its main competitors were theBélinographebyÉdouard Belinfirst, then since the 1930s theHellschreiber,invented in 1929 by German inventorRudolf Hell,a pioneer in mechanical image scanning and transmission.

Input (left) and output (right) of a telautograph transmission

The 1888 invention of thetelautographbyElisha Graymarked a further development in fax technology, allowing users to send signatures over long distances, thus allowing the verification of identification or ownership over long distances.

On May 19, 1924, scientists of the AT&T Corporation "by a new process of transmitting pictures by electricity" sent 15 photographs by telephone from Cleveland to New York City, such photos being suitable for newspaper reproduction. Previously, photographs had been sent over the radio using this process.

The Western Union "Deskfax" fax machine, announced in 1948, was a compact machine that fit comfortably on a desktop, using specialspark printerpaper.

Wireless transmission

Main article:Radiofax

Children read a wirelessly transmitted newspaper in 1938.

As a designer for theRadio Corporation of America(RCA), in 1924,Richard H. Rangerinvented the wireless photoradiogram, or transoceanicradio facsimile,the forerunner of today's "fax" machines. A photograph of PresidentCalvin Coolidgesent from New York to London on November 29, 1924, became the first photo picture reproduced by transoceanic radio facsimile. Commercial use of Ranger's product began two years later. Also in 1924,Herbert E. IvesofAT&Ttransmitted and reconstructed the first color facsimile, a natural-color photograph of silent film starRudolph Valentinoin period costume, using red, green and blue color separations.

Beginning in the late 1930s, the Finch Facsimile system was used to transmit a "radio newspaper" to private homes via commercial AM radio stations and ordinary radio receivers equipped with Finch's printer, which used thermal paper. Sensing a new and potentially golden opportunity, competitors soon entered the field, but the printer and special paper were expensive luxuries, AM radio transmission was very slow and vulnerable to static, and the newspaper was too small. After more than ten years of repeated attempts by Finch and others to establish such a service as a viable business, the public, apparently quite content with its cheaper and much more substantial home-delivered daily newspapers, and with conventional spoken radio bulletins to provide any "hot" news, still showed only a passing curiosity about the new medium.

By the late 1940s, radiofax receivers were sufficiently miniaturized to be fitted beneath the dashboard ofWestern Union's "Telecar"telegramdelivery vehicles.

In the 1960s, theUnited States Armytransmitted the first photograph via satellitefacsimiletoPuerto Ricofrom theDeal Test Siteusing theCourier satellite.

Radio fax is still in limited use today for transmitting weather charts and information to ships at sea. The closely related technology ofslow-scan televisionis still used byamateur radiooperators.

Telephone transmission

A two-page fax message sent in 2006

External images
LDX system, Scanner and Printer
Magnafax Telecopier by Xerox

In 1964, Xerox Corporation introduced (and patented) what many consider to be the first commercialized version of the modern fax machine, under the name (LDX) or Long Distance Xerography. This model was superseded two years later with a unit that would set the standard for fax machines for years to come. Up until this point facsimile machines were very expensive and hard to operate. In 1966, Xerox released the Magnafax Telecopiers, a smaller, 46 lb (21 kg) facsimile machine. This unit was far easier to operate and could be connected to any standard telephone line. This machine was capable of transmitting a letter-sized document in about six minutes. The first sub-minute, digital fax machine was developed byDacom,which built on digital data compression technology originally developed atLockheedfor satellite communication.

By the late 1970s, many companies around the world (especially Japanese firms) had entered the fax market. Very shortly after this, a new wave of more compact, faster and efficient fax machines would hit the market. Xerox continued to refine the fax machine for years after their ground-breaking first machine. In later years it would be combined with copier equipment to create the hybrid machines we have today that copy, scan and fax. Some of the lesser known capabilities of the Xerox fax technologies included their Ethernet enabled Fax Services on their 8000 workstations in the early 1980s.

Prior to the introduction of the ubiquitous fax machine, one of the first being theExxonQwipin the mid-1970s, facsimile machines worked by optical scanning of a document or drawing spinning on a drum. The reflected light, varying in intensity according to the light and dark areas of the document, was focused on aphotocellso that the current in a circuit varied with the amount of light. This current was used to control a tone generator (amodulator), the current determining the frequency of the tone produced. This audio tone was then transmitted using anacoustic coupler(a speaker, in this case) attached to the microphone of a commontelephone handset.At the receiving end, a handset's speaker was attached to an acoustic coupler (a microphone), and ademodulatorconverted the varying tone into a variable current that controlled the mechanical movement of a pen or pencil to reproduce the image on a blank sheet of paper on an identical drum rotating at the same rate.

Computer facsimile interface

In 1985,Hank Magnuski,founder ofGammaLink,produced the first computer fax board, calledGammaFax.Such boards could provide voice telephony viaAnalog Expansion Bus.

In the 21st century

Laser fax having a compact, built-inlaser printer,2001.

Although businesses usually maintain some kind of fax capability, the technology has faced increasing competition fromInternet-based alternatives. In some countries,becauseelectronic signatureson contracts are not yetrecognized by law,while faxed contracts with copies of signatures are, fax machines enjoy continuing support in business.InJapan,faxes are still used extensively as of September 2020 for cultural andgraphemicreasons.They are available for sending to both domestic and international recipients from over 81% of allconvenience storesnationwide. Convenience-store fax machines commonly print the slightly re-sized content of the sent fax in the electronic confirmation-slip, inA4 papersize.Use of fax machines for reporting cases during theCOVID-19 pandemichas been criticised in Japan for introducing data errors and delays in reporting, slowing response efforts to contain the spread of infections and hindering the transition toremote work.

In many corporate environments, freestanding fax machines have been replaced byfax serversand other computerized systems capable of receiving and storing incoming faxes electronically, and then routing them to users on paper or via anemail(which may be secured).Such systems have the advantage of reducing costs by eliminating unnecessary printouts and reducing the number of inbound analog phone lines needed by an office.

Professional laser fax machine for office use with the Super G3 standard for faster fax transmission.

The once ubiquitous fax machine has also begun to disappear from the small office and home office environments.Remotely hosted fax-server services are widely available from VoIP and e-mail providers allowing users to send and receive faxes using their existing e-mail accounts without the need for any hardware or dedicated fax lines. Personal computers have also long been able to handle incoming and outgoing faxes using analog modems orISDN,eliminating the need for a stand-alone fax machine. These solutions are often ideally suited for users who only very occasionally need to use fax services. In July 2017 the United Kingdom'sNational Health Servicewas said to be the world's largest purchaser of fax machines because the digital revolution has largely bypassed it.In June 2018 theLabour Partysaid that the NHS had at least 11,620 fax machines in operationand in December theDepartment of Health and Social Caresaid that no more fax machines could be bought from 2019 and that the existing ones must be replaced by secure email by March 31, 2020.

Leeds Teaching Hospitals NHS Trust,generally viewed as digitally advanced in the NHS, was engaged in a process of removing its fax machines in early 2019. This involved quite a lot ofe-faxsolutions because of the need to communicate with pharmacies and nursing homes which may not have access to the NHS email system and may need something in their paper records.

In 2018 two-thirds of Canadian doctors reported that they primarily used fax machines to communicate with other doctors. Faxes are still seen as safer and more secure and electronic systems are often unable to communicate with each other.

Hospitals are the leading users for fax machines in the United States where some doctors prefer fax machines over emails, often due to concerns about accidentally violatingHIPAA.

Capabilities

There are several indicators of fax capabilities: group, class, data transmission rate, and conformance withITU-T(formerlyCCITT) recommendations. Since the 1968Carterfone decision,most fax machines have been designed to connect to standardPSTNlines and telephone numbers.

Group

Analog

Group 1 and 2 faxes are sent in the same manner as a frame ofanalog television,with each scanned line transmitted as a continuous analog signal. Horizontal resolution depended upon the quality of the scanner, transmission line, and the printer. Analog fax machines are obsolete and no longer manufactured. ITU-T Recommendations T.2 and T.3 were withdrawn as obsolete in July 1996.

• Group 1 faxes conform to the ITU-T Recommendation T.2. Group 1 faxes take six minutes to transmit a single page, with a vertical resolution of 96scan linesper inch. Group 1 fax machines are obsolete and no longer manufactured.
• Group 2 faxes conform to the ITU-T Recommendations T.3 and T.30. Group 2 faxes take three minutes to transmit a single page, with a vertical resolution of 96 scan lines per inch. Group 2 fax machines are almost obsolete, and are no longer manufactured. Group 2 fax machines can interoperate with Group 3 fax machines.

Digital

The Dacom DFC-10—the first digital fax machine

The chip in a fax machine. Only about one quarter of the length is shown. The thin line in the middle consists of photosensitivepixels.The read-out circuit is at left.

A major breakthrough in the development of the modern facsimile system was the result of digital technology, where the analog signal from scanners was digitized and then compressed, resulting in the ability to transmit high rates of data across standard phone lines. The first digital fax machine was theDacomRapidfax first sold in late 1960s, which incorporated digital data compression technology developed byLockheedfor transmission of images from satellites.

Group 3 and 4 faxes are digital formats and take advantage of digital compression methods to greatly reduce transmission times.

• Group 3 faxes conform to the ITU-T Recommendations T.30 and T.4. Group 3 faxes take between 6 and 15 seconds to transmit a single page (not including the initial time for the fax machines to handshake and synchronize). The horizontal and vertical resolutions are allowed by the T.4 standard to vary among a set of fixed resolutions:
  • Horizontal: 100 scan lines per inch
    • Vertical: 100 scan lines per inch ( "Basic" )
  • Horizontal: 200 or 204 scan lines per inch
    • Vertical: 100 or 98 scan lines per inch ( "Standard" )
    • Vertical: 200 or 196 scan lines per inch ( "Fine" )
    • Vertical: 400 or 391 (note not 392) scan lines per inch ( "Superfine" )
  • Horizontal: 300 scan lines per inch
    • Vertical: 300 scan lines per inch
  • Horizontal: 400 or 408 scan lines per inch
    • Vertical: 400 or 391 scan lines per inch ( "Ultrafine" )
• Group 4 faxes conform to the ITU-T Recommendations T.563, T.503, T.521, T.6, T.62, T.70, T.411 to T.417. They are designed to operate over 64 kbit/s digitalISDNcircuits. The allowed resolutions, a superset of those in the T.4 recommendation, are specified in the T.6 recommendation.

Fax Over IP (FoIP) can transmit and receive pre-digitized documents at near-realtimespeeds usingITU-T recommendation T.38to send digitised images over anIP networkusingJPEGcompression. T.38 is designed to work withVoIPservices and often supported byanalog telephone adaptersused by legacy fax machines that need to connect through a VoIP service. Scanned documents are limited to the amount of time the user takes to load the document in a scanner and for the device to process a digital file. The resolution can vary from as little as 150 DPI to 9600 DPI or more. This type of faxing is not related to the e-mail–to–fax service that still uses fax modems at least one way.

Class

Computer modems are often designated by a particular fax class, which indicates how much processing is offloaded from the computer's CPU to the fax modem.

• Class 1 (also known as Class 1.0) fax devices do fax data transfer, while the T.4/T.6 data compression and T.30 session management are performed by software on a controlling computer. This is described in ITU-T recommendation T.31.
• What is commonly known as "Class 2" is an unofficial class of fax devices that perform T.30 session management themselves, but the T.4/T.6 data compression is performed by software on a controlling computer. Implementations of this "class" are based on draft versions of the standard that eventually significantly evolved to become Class 2.0.All implementations of "Class 2" are manufacturer-specific.
• Class 2.0 is the official ITU-T version of Class 2 and is commonly known as Class 2.0 to differentiate it from many manufacturer-specific implementations of what is commonly known as "Class 2". It uses a different but standardized command set than the various manufacturer-specific implementations of "Class 2". The relevant ITU-T recommendation is T.32.
• Class 2.1 is an improvement of Class 2.0 that implements faxing over V.34 (33.6 kbit/s), which boosts faxing speed from fax classes "2" and 2.0, which are limited to 14.4 kbit/s.The relevant ITU-T recommendation is T.32 Amendment 1.Class 2.1 fax devices are referred to as "super G3".

Data transmission rate

Several different telephone-line modulation techniques are used by fax machines. They are negotiated during the fax-modemhandshake,and the fax devices will use the highest data rate that both fax devices support, usually a minimum of 14.4 kbit/s for Group 3 fax.

ITU standard	Released date	Data rates (bit/s)	Modulation method
V.27	1988	4800, 2400	PSK
V.29	1988	9600, 7200, 4800	QAM
V.17	1991	14400,12000,9600, 7200	TCM
V.34	1994	28800	QAM
V.34bis	1998	33600	QAM
ISDN	1986	64000	digital

"Super Group 3" faxes use V.34bis modulation that allows a data rate of up to 33.6 kbit/s.

Compression

As well as specifying the resolution (and allowable physical size) of the image being faxed, the ITU-T T.4 recommendation specifies two compression methods for decreasing the amount of data that needs to be transmitted between the fax machines to transfer the image. The two methods defined in T.4 are:

• Modified Huffman(MH).
• Modified READ(MR) (Relative Element Address Designate), optional.

An additional method is specified in T.6:

• Modified Modified READ(MMR).

Later, other compression techniques were added as options to ITU-T recommendation T.30, such as the more efficientJBIG(T.82, T.85) for bi-level content, andJPEG(T.81), T.43,MRC(T.44), and T.45 for grayscale, palette, and colour content.Fax machines can negotiate at the start of the T.30 session to use the best technique implemented on both sides.

Modified Huffman

Main article:Modified Huffman coding

Modified Huffman (MH), specified in T.4 as the one-dimensional coding scheme, is a codebook-based run-length encoding scheme optimised to efficiently compress whitespace.As most faxes consist mostly of white space, this minimises the transmission time of most faxes. Each line scanned is compressed independently of its predecessor and successor.

Modified READ

Modified READ, specified as an optional two-dimensional coding scheme in T.4, encodes the first scanned line using MH.The next line is compared to the first, the differences determined, and then the differences are encoded and transmitted.This is effective, as most lines differ little from their predecessor. This is not continued to the end of the fax transmission, but only for a limited number of lines until the process is reset, and a new "first line" encoded with MH is produced. This limited number of lines is to prevent errors propagating throughout the whole fax, as the standard does not provide for error correction. This is an optional facility, and some fax machines do not use MR in order to minimise the amount of computation required by the machine. The limited number of lines is 2 for "Standard" -resolution faxes, and 4 for "Fine" -resolution faxes.

Modified Modified READ

Main article:Group 4 compression

The ITU-T T.6 recommendation adds a further compression type of Modified Modified READ (MMR), which simply allows a greater number of lines to be coded by MR than in T.4.This is because T.6 makes the assumption that the transmission is over a circuit with a low number of line errors, such as digitalISDN.In this case, the number of lines for which the differences are encoded is not limited.

JBIG

In 1999, ITU-T recommendation T.30 addedJBIG(ITU-T T.82) as anotherlosslessbi-levelcompression algorithm, or more precisely a "fax profile" subset of JBIG (ITU-T T.85). JBIG-compressed pages result in 20% to 50% faster transmission than MMR-compressed pages, and up to 30 times faster transmission if the page includeshalftoneimages.

JBIGperformsadaptive compression,that is, both the encoder and decoder collect statistical information about the transmitted image from the pixels transmitted so far, in order to predict the probability for each next pixel being either black or white. For each new pixel, JBIG looks at ten nearby, previously transmitted pixels. It counts, how often in the past the next pixel has been black or white in the same neighborhood, and estimates from that the probability distribution of the next pixel. This is fed into anarithmetic coder,which adds only a small fraction of a bit to the output sequence if the more probable pixel is then encountered.

The ITU-T T.85 "fax profile" constrains some optional features of the full JBIG standard, such that codecs do not have to keep data about more than the last three pixel rows of an image in memory at any time. This allows the streaming of "endless" images, where the height of the image may not be known until the last row is transmitted.

ITU-T T.30 allows fax machines to negotiate one of two options of the T.85 "fax profile":

• In "basic mode", the JBIG encoder must split the image into horizontal stripes of 128 lines (parameter L0 = 128) and restart the arithmetic encoder for each stripe.
• In "option mode", there is no such constraint.

Matsushita Whiteline Skip

A proprietary compression scheme employed on Panasonic fax machines is Matsushita Whiteline Skip (MWS). It can be overlaid on the other compression schemes, but is operative only when two Panasonic machines are communicating with one another. This system detects the blank scanned areas between lines of text, and then compresses several blank scan lines into the data space of a single character. (JBIG implements a similar technique called "typical prediction", if header flag TPBON is set to 1.)

Typical characteristics

Group 3 fax machines transfer one or a few printed or handwritten pages per minute in black-and-white (bitonal) at aresolutionof 204×98 (normal) or 204×196 (fine) dots per square inch. The transfer rate is 14.4 kbit/s or higher for modems and some fax machines, but fax machines support speeds beginning with 2400 bit/s and typically operate at 9600 bit/s. The transferred image formats are calledITU-T(formerly CCITT) fax group 3 or 4. Group 3 faxes have thesuffix.g3and theMIME typeimage/g3fax.

The most basic fax mode transfers in black and white only. The original page is scanned in a resolution of 1728pixels/line and 1145 lines/page (forA4). The resulting raw data iscompressedusing a modifiedHuffman codeoptimized for written text, achieving average compression factors of around 20. Typically a page needs 10 s for transmission, instead of about three minutes for the same uncompressed raw data of 1728×1145 bits at a speed of 9600 bit/s. The compression method uses a Huffman codebook for run lengths of black and white runs in a single scanned line, and it can also use the fact that two adjacent scanlines are usually quite similar, saving bandwidth by encoding only the differences.

Fax classes denote the way fax programs interact with fax hardware. Available classes include Class 1, Class 2, Class 2.0 and 2.1, and Intel CAS. Many modems support at least class 1 and often either Class 2 or Class 2.0. Which is preferable to use depends on factors such as hardware, software, modem firmware, and expected use.

Printing process

Fax machines from the 1970s to the 1990s often used directthermal printerswith rolls of thermal paper as their printing technology, but since the mid-1990s there has been a transition towards plain-paper faxes:thermal transfer printers,inkjet printersandlaser printers.

One of the advantages of inkjet printing is that inkjets can affordably print incolor;therefore, many of the inkjet-based fax machines claim to have color fax capability. There is a standard called ITU-T30e (formally ITU-T Recommendation T.30 Annex E) for faxing in color; however, it is not widely supported, so many of the color fax machines can only fax in color to machines from the same manufacturer.

Stroke speed

Stroke speed in facsimile systems is the rate at which a fixed line perpendicular to the direction ofscanningis crossed in one direction by a scanning orrecording spot.Stroke speed is usually expressed as a number of strokes per minute. When the fax system scans in both directions, the stroke speed is twice this number. In most conventional 20th century mechanical systems, the stroke speed is equivalent to drum speed.

Fax paper

Paperroll fordirect thermalfax machine

As a precaution, thermal fax paper is typically not accepted in archives or as documentary evidence in some courts of law unless photocopied. This is because the image-forming coating is eradicable and brittle, and it tends to detach from the medium after a long time in storage.

Fax tone

A CNG tone is an 1100 Hz tone transmitted by a fax machine when it calls another fax machine. Fax tones can cause complications when implementingfax over IP.

Internet fax

See also:Internet fax

One popular alternative is to subscribe to anInternet faxservice, allowing users to send and receive faxes from theirpersonal computersusing an existingemail account.No software, fax server or fax machine is needed. Faxes are received as attachedTIFForPDFfiles, or in proprietary formats that require the use of the service provider's software. Faxes can be sent or retrieved from anywhere at any time that a user can get Internet access. Some services offer secure faxing to comply with stringentHIPAAandGramm–Leach–Bliley Actrequirements to keep medical information and financial information private and secure. Utilizing a fax service provider does not require paper, a dedicated fax line, or consumable resources.

Another alternative to a physical fax machine is to make use of computersoftwarewhich allows people to send and receive faxes using their own computers, utilizingfax serversandunified messaging.A virtual (email) fax can be printed out and then signed and scanned back to computer before being emailed. Also the sender can attach a digital signature to the document file.

With the surging popularity of mobile phones, virtual fax machines can now be downloaded as applications for Android and iOS. These applications make use of the phone's internal camera to scan fax documents for upload or they can import from various cloud services.

Related standards

• T.4 is the umbrella specification for fax. It specifies the standard image sizes, two forms of image-data compression (encoding), the image-data format, and references, T.30 and the various modem standards.
• T.6 specifies a compression scheme that reduces the time required to transmit an image by roughly 50-percent.
• T.30 specifies the procedures that a sending and receiving terminal use to set up a fax call, determine the image size, encoding, and transfer speed, the demarcation between pages, and the termination of the call. T.30 also references the various modem standards.
• V.21,V.27ter,V.29,V.17,V.34:ITU modem standards used in facsimile. The first three were ratified prior to 1980, and were specified in the original T.4 and T.30 standards. V.34 was published for fax in 1994.
• T.37The ITU standard for sending a fax-image file via e-mail to the intended recipient of a fax.
• T.38The ITU standard for sending Fax over IP (FoIP).
• G.711pass through - this is where the T.30 fax call is carried in a VoIP call encoded as audio. This is sensitive to networkpacket loss,jitterand clock synchronization. When using voice high-compression encoding techniques such as, but not limited to,G.729,some fax tonal signals may not be correctly transported across the packet network.
• RFC3362image/t38 MIME-type
• SSL FaxAn emerging standard that allows a telephone based fax session to negotiate a fax transfer over the internet, but only if both sides support the standard. The standard is partially based on T.30 and is being developed by Hylafax+ developers.

See also

• 3D Fax
• Black fax
• Called subscriber identification(CSID)
• Error correction mode(ECM)
• Fax art
• Fax demodulator
• Fax modem
• Fax server
• Faxlore
• Fultograph
• Image scanner
• Internet fax
• Junk fax
• Radiofax—image transmission over HF radio
• Slow-scan television
• T.38Fax-over-IP
• Telautograph
• Telex
• Teletex
• Transmitting Subscriber Identification(TSID)
• Wirephoto

Further reading

• Coopersmith, Jonathan,Faxed: The Rise and Fall of the Fax Machine(Johns Hopkins University Press, 2015) 308 pp.
• "Transmitting Photographs by Telegraph",Scientific Americanarticle, 12 May 1877, p. 297

External links

• Group 3 Facsimile Communication—A '97 essay with technical details on compression and error codes, and call establishment and release.
• ITU T.30 Recommendation