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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 (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.
A modern "fax machine" usually consists of an image scanner, a modem, and an inkjet, thermal, or laser printer 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.
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 printers or MFPs. Fax capabilities are also offered as options for many high-volume workgroup printers and photocopiers.
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 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 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.
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 and HIPAA, cannot be sent over the Internet unencrypted.
In many corporate environments, standalone fax machines have been replaced by "fax servers" and other computerized systems capable of receiving and storing incoming faxes electronically, and then routing them to users on paper or via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.
There are several different indicators of fax capabilities: Group, class, data transmission rate, and conformance with ITU-T (formerly CCITT) recommendations.
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.
Group 3 and 4 faxes are digital formats, and take advantage of digital compression methods to greatly reduce transmission times.
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.
Several different telephone line modulation techniques are used by fax machines. They are negotiated during the fax-modem 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.
Note that 'Super Group 3' faxes use V.34bis modulation that allows a data rate of up to 33.6 kbit/s.
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:
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.
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.
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.
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.
Group 3 fax machines transfer one or a few printed or handwritten pages per minute in black-and-white (bitonal) at a resolution of 100x200 or 200x200 dots per inch. The transfer rate is 14.4 kilobits per second (kbit/s) or higher (but fax machines support speeds beginning with 2400 bit/s). The transferred image formats are called ITU-T (formerly CCITT) fax group 3 or 4.
The most basic fax mode transfers black and white only. The original page is scanned in a resolution of 1728 pixels/line and 1145 lines/page (for A4). The resulting raw data is compressed using a modified 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.
There are different fax classes, including Class 1, Class 2 and Intel CAS.
Fax machines from the 1970s to the 1990s often used direct thermal printers as their printing technology, but since the mid-1990s there has been a transition towards thermal transfer printers, inkjet printers and laser printers.
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.
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 or .PDF files. 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 is a very popular option because it requires no paper, toner, fax line, etc. and increases efficiency and productivity in the workplace. Being service-based, there are no maintenance, upkeep or licensing issues to manage, keeping faxing as a simple, easy process.
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.
Scottish inventor Alexander Bain is often credited with the first fax patent in 1843. He used his knowledge of electric clock pendulums to produce a back-and-forth line-by-line scanning mechanism.
Frederick Bakewell made several improvements on Bain's design and demonstrated the device at the 1851 Great Exhibition in London.
In 1861, the first fax machine, Pantelegraph, was sold by Giovanni Caselli, even before the invention of workable telephones.
As a designer for the Radio Corporation of America (RCA), in 1924, Richard H. Ranger invented the wireless photoradiogram, or transoceanic 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.
An early method for facsimile transmission, the Hellschreiber, was invented in 1929 by Rudolf Hell, a pioneer in mechanical image scanning and transmission.
Prior to the introduction of the now ubiquitous fax machine, one of the first being the Xerox Qyx in the mid-1970s, facsimile machines (the word "fax" had not yet become ubiquitous) 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 tranmitted using a common 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.
In 1985, Dr. Hank Magnuski, founder of GammaLink, produced the first computer fax board, called GammaFax.