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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.
| ITU Standard | Released Date | Data Rates (bit/s) | Modulation Method |
|---|---|---|---|
| V.17 | 1991 | 14400, 12000, 9600, 7200 | TCM |
| V.29 | 1988 | 9600, 7200, 4800 | QAM |
| V.27 | 1988 | 4800, 2400 | PSKIn telecommunication, the term phase-shift keying (PSK) has the following meanings: 1. In digital transmission, angle modulation in which the phase of the carrier is discretely varied in relation either to a reference phase or to the phase of the immediat |
| V.34 | 1994 | 28800 | QAM |
A modern alternative for sending a fax is sending an email with one or more imageIn common usage, an image (from Latin imago or picture is an artefact that reproduces the likeness of some subject—usually a physical object or a person. Images may be two-dimensional (e. a photograph) or three dimensional (e. a statue). They are typicall fileA file in a computer system is a stream (sequence) of bits stored as a single unit, typically in a file system on disk or magnetic tape. While a file is usually presented as a single stream, it most often is stored as multiple fragments of data at differes as attachmentThe term attachment has multiple meanings: An email attachment Psychological attachment: see Attachment theory Attachment as a vice in Buddhism; see Buddhism.s. This allows color and is more versatile with respect to resolution.
The following passage is from Chapter V, Section 7 of the Royal Commission on National Development in the Arts, Letters and Sciences , 1949-1951:
Scottish inventor Alexander BainAlexander Bain ( June 11, 1818 September 18, 1903) was a Scottish philosopher and educationalist. He was born in Aberdeen, and went to school there, but took up the profession of a weaver, hence the punning description of him as Weevir, rex philosophorum' is often credited with the first fax patent in the 1840sEvents and Trends First signing of the Treaty of Waitangi (Te Tiriti o Waitangi) on February 6, 1840 at Waitangi New Zealand. The treaty between the British Crown and Maori made New Zealand a British colony and is considered the founding point of modern N. He used his knowledge of electric clockA clock (from the Latin cloca " bell") is an instrument for measuring time. A clock can be a physical instrument (an especially accurate one is called a chronometer). The clock in its modern form (24 hour clock) has been in use since at least the 15th cen pendulums to produce a back-and-forth line-by-line scanning mechanism.
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, produces the first computer fax board called GammaFax.