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Fax (short for facsimile or telefacsimile) is a telecommunications technology used to transfer copies of documents, especially using affordable devices operating over the telephone network.
A fax machine is essentially an image scanner, computer printer, and modem, combined together into a highly specialized package. The scanner converts the content of a physical document into a digital image, the modem sends the image data over a phone line, and the printer at the other end makes a duplicate of the original document.
Obviously, a very high-quality fax machine with some additional electronics can connect to a computer, and can be used to scan documents into a computer, to print documents from the computer, and to make photocopies. Such high-end devices are called multifunction printers and cost more than fax machines.
Modern fax technology became feasible only in the mid-1970s as the sophistication and cost of the three underlying technologies improved to a reasonable level. Fax machines first became popular in Japan, where they had an clear advantage over competing technologies like telex; it is faster to write Japanese ideographs than to type them. Over time, they gradually became affordable and were very popular around the world by the mid-1980s.
However, although most businesses still maintain some kind of fax capability, the technology appears increasingly dated in the world of the Internet.
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. 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 (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 also uses 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.
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.
||Data Rates (bit/s)
||9600, 7200, 4800
||14400, 12000, 9600, 7200
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 and inkjet 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.
A modern alternative for sending a fax is sending an email with one or more image files as attachments. This allows color and is more versatile with respect to resolution.
At the receiving end, much research has occurred into how to more efficiently process incoming faxes, now that digital storage is much cheaper than it was in the 1970s, and junk faxes have become a common problem (and an enormous waste of paper).
Some high-end communications servers do not automatically print out all incoming faxes, but instead integrate them into a single in-box along with other forms of store and forward communications like email and voice mail (see unified messaging).
The following passage is from Chapter V, Section 7 of the Royal Commission on National Development in the Arts, Letters and Sciences , 1949-1951:
- "The vigorous brief of the Canadian Daily Newspapers Association was devoted entirely to a discussion of the consequences to the present newspaper business if the new device of facsimile broadcasting should become, as seems possible, an effective and popular rival to newspapers as we know them. We can claim only an imperfect knowledge of this new medium of communication. In brief, as we understand it, this process can deliver directly into the home a printed newspaper as readily and by essentially the same means as radio and television are now received. No printing machinery or delivery services are needed, and any radio station could go into the newspaper business for a small fraction of the investment required to establish a normal newspaper. The Canadian Daily Newspapers Association states that this development will attract newcomers to the newspaper field, and that the facsimile reader will be able in his home to dial any one of several newspapers just as now he tunes his receiving set to radio programmes."
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.
In 1861 the first fax machine, Pantelegraph , was sold by Giovanni Casselli .
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 todayís "Fax" machines. A photograph of President Calvin Coolidge sent from New York to London in November 1924 became the first photo picture reproduced by transoceanic radio facsimile. Commercial use of Rangerís product began two years later.
An early method for facsimile transmission, the Hellschreiber, was invented in 1929 by Rudolf Hell, a pioneer in mechanical image scanning and transmission.
In 1985 Dr Hank Magnuski, founder of GammaLink, produced the first computer fax board, called GammaFax.
Last updated: 10-29-2005 02:13:46