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==§♥§THE CLAN HAS STRIKED AGAIN!!!!§♥§== |
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{{wiktionarypar|facsimile}} |
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[[Image:Samfax.jpg|thumb|200px|A [[Samsung]] fax machine]] |
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'''Fax''' (short for '''facsimile''', from [[Latin]] ''fac simile'', "make similar", i.e. "make a copy") is a [[telecommunications]] technology used to transfer copies ([[wikt:facsimile|facsimiles]]) of documents, especially using affordable devices operating over the [[telephone]] network. The word '''telefax''', short for '''telefacsimile''', for "make a copy at a distance", is also used as a [[synonym]]. The device is also known as a telecopier in certain industries. When sending documents to people at large distances, faxes have a distinct advantage over postal mail in that the delivery is nearly instantenous, yet its disadvantages in quality and its proprietary format have relegated it to a position beneath [[email]] as the prevailing form of electronic document transferral. |
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==Overview== |
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A "fax machine" usually consists of an [[image scanner]], a [[modem]], a [[Computer printer|printer]], and usually a [[Telephone|phone]] combined into a single package. The scanner converts the content printed on a physical document into a digital image, the modem sends the image data over a phone line to another device, and the printer at the far end produces a copy of the transmitted document. |
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Some fax machines can be connected to a computer, and the individual components -- the scanner, printer, and occasionally the modem -- can be used independently. Such devices are usually called [[multifunction printer]]s or MFPs. Fax capabilities are also offered as options for many high-volume workgroup [[Computer printer|printers]] and [[Photocopier|photocopiers]]. |
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Although devices for transmitting printed documents electrically have existed, in various forms, since the mid to late 19th century (see "History" below), modern fax machines became feasible only in the mid-[[1970s]] as the sophistication increased and cost of the three underlying technologies dropped. Digital fax machines first became popular in [[Japan]], where they had a clear advantage over competing technologies like the [[teleprinter]], since at the time (before the development of easy-to-use [[Input method editor|input method editors]]) it was faster to handwrite [[kanji]] than to type the characters. Over time, faxing gradually became affordable, and by the mid-[[1980s]], fax machines were very popular around the world. |
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Although many businesses still maintain some kind of fax capability, the technology has faced increasing competition from [[Internet]]-based systems. However, fax machines still retain some advantages, particularly in the transmission of sensitive material which, due to mandates like [[Sarbanes-Oxley Act|Sarbanes-Oxley]] and [[Health Insurance Portability and Accountability Act|HIPAA]], cannot be sent over the Internet unencrypted. In some countries, because [[digital signature]]s on contracts are not recognized by law while faxed contracts with copies of signatures are, fax machines enjoy continuing popularity in business. |
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In many corporate environments, standalone fax machines have been replaced by "[[Fax server|fax servers]]" and other computerized systems capable of receiving and storing incoming faxes electronically, and then routing them to users on paper or via secure [[email]]. 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. |
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==Capabilities== |
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There are several different indicators of fax capabilities: Group, class, data transmission rate, and conformance with [[ITU-T]] (formerly [[CCITT]]) recommendations. |
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Fax machines utilize standard [[PSTN]] lines and telephone numbers. |
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===Group=== |
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====Analog==== |
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Group 1 and 2 faxes were sent in the same manner as a frame of [[analog 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. |
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* 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 98 [[scan line]]s per inch. Group 1 fax machines are obsolete and no longer manufactured. |
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* Group 2 faxes conform to the ITU-T Recommendations T.30 and T.3. Group 2 faxes take three minutes to transmit a single page, with a vertical resolution of 100 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. |
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====Digital==== |
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Group 3 and 4 faxes are digital formats, and take advantage of digital compression methods to greatly reduce transmission times. |
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* Group 3 faxes conform to the ITU-T Recommendations T.30 and T.4. Group 3 faxes take between six and fifteen 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: |
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**Horizontal: 100 scan lines per inch |
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***Vertical: 100 scan lines per inch |
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**Horizontal: 200 or 204 scan lines per inch |
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***Vertical: 100 or 98 scan lines per inch ('Standard') |
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***Vertical: 200 or 196 scan lines per inch ('Fine') |
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***Vertical: 400 or 391 (note not 392) scan lines per inch ('Superfine') |
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**Horizontal: 300 scan lines per inch |
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***Vertical: 300 scan lines per inch |
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**Horizontal: 400 or 408 scan lines per inch |
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***Vertical: 400 or 391 scan lines per inch ('Ultrafine') |
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* Group 4 faxes conform to the ITU-T Recommendations T.563, T.503, T.521, T.6, T.62, T.70, T.72, T.411 to T.417. They are designed to operate over 64 kbit/s digital [[ISDN]] circuits. Their resolution is determined by the T.6 recommendation, which is a superset of the T.4 recommendation. |
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Fax Over IP (FOIP) can transmit and receive pre-digitized documents at near realtime speeds. 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 like the e-mail to fax service that still uses fax modems at least one way. |
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===Class=== |
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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. |
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*Class 1 fax devices do fax data transfer where 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. |
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*Class 2 fax devices perform T.30 session management themselves, but the T.4/T.6 data compression is performed by software on a controlling computer. The relevant ITU-T recommendation is T.32. |
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*Class 2.1 fax devices are referred to as "super G3"; they seem to be a little faster than the other 2 classes. |
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*Class 3 fax devices are responsible for virtually the entire fax session, given little more than a phone number and the text to send (including ASCII to image rendering). These devices are not common. |
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===Data transmission rate=== |
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Several different telephone line modulation techniques are used by fax machines. They are negotiated during the fax-[[modem]] [[handshaking|handshake]], 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. |
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:{| class="wikitable" |
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!ITU Standard |
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!Released Date |
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!Data Rates (bit/s) |
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!Modulation Method |
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|- |
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|[[V.27]] |
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|1988 |
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|4800, 2400 |
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|[[phase-shift keying|PSK]] |
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|- |
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|[[V.29]] |
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|1988 |
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|9600, 7200, 4800 |
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|[[quadrature amplitude modulation|QAM]] |
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|- |
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|[[V.17]] |
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|1991 |
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|14400, 12000, 9600, 7200 |
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|[[trellis modulation|TCM]] |
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|- |
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|[[V.34]] |
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|1994 |
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|28800 |
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|[[quadrature amplitude modulation|QAM]] |
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|- |
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|[[V.34bis]] |
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|1998 |
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|33600 |
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|[[quadrature amplitude modulation|QAM]] |
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|} |
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Note that 'Super Group 3' faxes use [[V.34bis]] modulation that allows a data rate of up to 33.6 kbit/s. |
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===Compression=== |
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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 are: |
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*[[Modified Huffman coding|Modified Huffman]] (MH), and |
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*[[Modified READ]] (MR) |
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====Modified Huffman==== |
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Modified Huffman (MH) is a codebook-based run-length encoding scheme optimised to efficiently compress whitespace. As most faxes consists mostly of white space, this minimises the transmission time of most faxes. Each line scanned is compressed independently of its predecessor and successor. |
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====Modified Read==== |
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Modified Read (MR) 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. MR 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 two for 'Standard' resolution faxes, and four for 'Fine' resolution faxes. |
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The ITU-T T.6 recommendation adds a further compression type of [[Modified Modified READ]] (MMR), which simply allows for 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 digital ISDN. In this case, there is no maximum number of lines for which the differences are encoded. |
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====Matsushita Whiteline Skip==== |
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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. |
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===Typical characteristics=== |
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Group 3 fax machines transfer one or a few printed or handwritten pages per minute in black-and-white (bitonal) at a [[Optical resolution|resolution]] of 100x200 or 200x200 dots per inch. The transfer rate is 14.4 kilo[[bit]]s per second (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 called [[ITU-T]] (formerly CCITT) fax group 3 or 4. |
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The most basic fax mode transfers black and white only. The original page is scanned in a resolution of 1728 [[pixel]]s/line and 1145 lines/page (for [[A4 paper size|A4]]). The resulting raw data is [[data compression|compressed]] using a modified [[Huffman coding|Huffman code]] optimized for written text, achieving average compression factors of around 20. Typically a page needs 10 s for transmission, instead of about 3 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. |
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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 preferrable to use depends on factors such as hardware, software, modem firmware, and expected use. |
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Fax machines from the 1970s to the 1990s often used direct [[thermal printer]]s as their printing technology, but since the mid-1990s there has been a transition towards [[thermal transfer printer]]s, [[inkjet printer]]s and laser printers. |
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One of the advantages of inkjet printing is that inkjets can affordably print in [[color]]; therefore, many of the inkjet-based fax machines claim to have color fax capability. There is a standard called [[ITU-T30e]] for faxing in color; unfortunately, it is not yet widely supported, so many of the color fax machines can only fax in color to machines from the same manufacturer. |
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==Alternatives== |
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One popular alternative is to subscribe to an [[internet fax]] service. Fax service providers allow users to send and receive faxes from their personal computers using an existing email account. No software, fax server or fax machine is needed. Faxes are received as attached [[TIF|.TIF]] or [[PDF|.PDF]] files, 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 even offer secure faxing to comply with stringent [[HIPAA]] and [[Gramm-Leach-Bliley Act]] requirements to keep medical information and financial information private and secure. Utilizing a fax service provider requires no paper, toner, fax line, etc. |
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Another alternative to a physical fax machine is to make use of computer [[software]] which allows people to send and receive faxes using their own computers. See [[Fax server]] and [[Unified messaging]]. |
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==History== |
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Scottish inventor [[Alexander Bain (inventor)|Alexander Bain]] is often credited with the first fax patent in [[1843]]. He used his knowledge of electric [[clock]] [[pendulum]]s to produce a back-and-forth line-by-line scanning mechanism. |
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[[Frederick Bakewell]] made several improvements on Bain's design and demonstrated the device at the 1851 [[Great Exhibition]] in London. |
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In [[1861]], the first fax machine, [[Pantelegraph]], was sold by [[Giovanni Caselli]], even before the invention of workable [[telephone]]s. |
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As a designer for the [[Radio Corporation of America]] (RCA), in 1924, [[Richard H. Ranger]] invented the wireless photoradiogram, or transoceanic [[radiofax|radio facsimile]], the forerunner of today’s "Fax" machines. A photograph of President [[Calvin Coolidge]] sent 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. Radio fax is still in common use today for transmitting weather charts and information. Also in 1924, [[Herbert E. Ives]] of [[AT&T]] transmitted and reconstructed the first color facsimile, using color separations. |
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An early method for facsimile transmission, the [[Hellschreiber]], was invented in [[1929]] by [[Rudolf Hell]], a pioneer in mechanical image scanning and transmission. |
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Prior to the introduction of the now ubiquitous fax machine, one of the first being the [[Exxon]] Qwip in 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 a [[photocell]] to be converted to an electrical signal varying in frequency. This audio tone was then transmitted using a common [[Handset|telephone handset]] inserted in an [[acoustic coupler]] serving as a [[modem]]. At the receiving end, the same technique (handset in acoustic coupler) converted the varying tone into 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. A pair of these expensive and bulky machines could only be afforded by companies with a serious need to communicate drawings, design sketches or signed documents between distant locations such as an office and factory. |
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In [[1985]], Dr. [[Hank Magnuski]], founder of [[GammaLink]], produced the first computer fax board, called [[GammaFax]]. |
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==See also== |
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{{Wiktionarypar2|fax|facsimile}} |
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*[[3Dfax]] |
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*[[Black fax]] |
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*[[Called Subscriber Identification]] (CSID) |
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*[[Error correction mode]] (ECM) |
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*Fax-over-IP [[T.38]] |
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*[[Fax server]] |
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*[[Faxlore]] |
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*[[Fultograph]] |
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*[[Junk fax]] |
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*[[Telautograph]] |
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*[[Transmitting Subscriber Identification]] (TSID) |
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== External links == |
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* [http://www.hffax.de/html/hauptteil_faxhistory.htm A Brief History of Facsimile], at HFFAX wireless facsimile site |
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* [http://www.technikum29.de/en/communication/fax.shtm The historical evolution of Fax], at technikum29, museum of calculator, computer and communication technology |
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* [http://www.garretwilson.com/essays/computers/group3fax.html Group 3 Facsimile Communication] a '97 essay with technical details on compression and error codes, and call establishment and release. |
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* [http://www.faxmachines.org.uk/types-of-fax-machines/ Types of Fax Machines] Different type of fax machines by Grouping, Data Transmission speed. |
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[[Category:Telecommunications equipment]] |
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[[Category:ITU-T recommendations]] |
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[[Category:Office equipment]] |
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[[Category:Computer peripherals]] |
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[[Category:Scottish inventions]] |
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[[ar:فاكس]] |
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[[br:Pelleiler]] |
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[[bg:Факс]] |
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[[cs:Fax]] |
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[[de:Fax]] |
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[[el:Τηλεομοιοτυπία]] |
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[[es:Fax]] |
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[[eo:Fakso]] |
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[[fr:Télécopieur]] |
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[[it:Telefax]] |
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[[he:פקס]] |
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[[nl:Fax]] |
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[[ja:ファクシミリ]] |
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[[ko:팩시밀리]] |
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[[no:Telefaks]] |
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[[pl:Telefaks]] |
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[[pt:Fax]] |
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[[ro:Fax]] |
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[[ru:Факс]] |
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[[sk:Fax (zariadenie)]] |
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[[sl:Telefaks]] |
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[[fi:Faksi]] |
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[[sv:Telefax]] |
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[[th:โทรสาร]] |
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[[tr:Belgegeçer]] |
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[[ur:نسخۂ کامل]] |
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[[bat-smg:Faksos]] |
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[[zh:傳真機]] |
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