Fax (short for facsimile ), sometimes called telecopying or telefax (last short for telefacsimile ), is a telephone transmission of scanned printed material (text or image), usually to a telephone number connected to a printer or other output device. The original document is scanned with a fax (or telecopier ) machine, which processes the content (text or image) as a single fixed graphic image, turns it into a bitmap, and then sends it through the phone system in audio frequency tone form. The receiving fax machine interprets the tone and reconstructs the image, printing a paper copy. The initial system uses the direct conversion of darkness of images to audio tones on a continuous or analog basis. Since the 1980s, most machines have modulated the transmitted audio frequencies using digital representations of compressed pages to transmit all-white or all-black areas quickly.
Video Fax
History
Transmission wire
Scottish inventor Alexander Bain worked on mechanical mechanical faxing devices and in 1846 was able to reproduce graphical signs in laboratory experiments. He received the British patent 9745 on May 27, 1843 for "Electric Printing Telegraph." Frederick Bakewell made some improvements to the Bain design and showed the telefax machine. Pantelegraph was created by the Italian physicist, Giovanni Caselli. He introduced the first commercial telefax service between Paris and Lyon in 1865, about 11 years before the invention of the phone.
In 1880, the British inventor Shelford Bidwell built the scotel phototelegraph which was the first telefax machine to scan two-dimensional original documents, requiring no representation or manual depictions. Around 1900, the German physicist Arthur Korn invented Bildtelegraph, spreading widely in continental Europe primarily, because the widely known transmission of photographs of people sought from Paris to London in 1908, was used until more radiofax distribution large.. Its main competitor is BÃÆ' Â © linographe by ÃÆ' â € ° Douard Belin first, then since the 1930s Hellschreiber , discovered in 1929 by German inventor Rudolf Hell, a pioneer in mechanical image. scanning and transmission.
The discovery of 1888 telautograph by Elisha Gray marks a further development in fax technology, enabling users to send signatures on long distances, thereby enabling the verification of remote identification or ownership.
On May 19, 1924, scientists from AT & amp; T Corporation "by a new process of transmitting images by electricity" sent 15 photographs by telephone from Cleveland to New York City, such photographs were suitable for newspaper reproduction. Previously, photographs have been sent over the radio using this process.
Western Union's "Deskfax" fax machine, announced in 1948, is a compact machine that fits comfortably on desktops, using special printer spark paper.
Wireless transmission
As the Radio Corporation of America (RCA) designer, in 1924, Richard H. Ranger invented the wireless photoradiogram, or anthoccan facsimile radio, the predecessor of the current "fax" machine. Photo of President Calvin Coolidge sent from New York to London on 29 November 1924 became the first photograph reproduced by a transoceanic radio facsimile. Commercial use of Ranger products began two years later. Also in 1924, Herbert E. Ives of AT & T transmitted and reconstructed the first color facsimile, a natural color photograph of silent film star, Rudolph Valentino, in period costumes, using red, green and blue splits.
Beginning in the late 1930s, the Finch Facsimile system was used to transmit "radio newspapers" to private homes via commercial AM radio stations and regular radio receivers equipped with Finch printers, which use thermal paper. Feeling new and potentially golden opportunities, competitors soon enter the field, but expensive luxury printers and papers, AM radio transmissions are very slow and vulnerable to static, and newspapers are too small. After more than ten years of repeated efforts by Finch and others to build such a service as a viable, public business, it seems quite satisfied with the cheaper and much more expensive daily newspapers it delivers, and with conventional spoken radio bulletins to provide News " hot ", still shows only a passing curiosity about a new medium.
In the late 1940s, the radiofax receiver was miniature enough to be mounted under the dashboard of Western Union's "Telecar" telegram delivery vehicle.
In the 1960s, the United States Army sent the first photograph via satellite facsimile to Puerto Rico from the Transaction Test Site using the Courier satellite.
Fax radio is still in use today to send weather charts and information to ships at sea.
Transmission phone
In 1964, Xerox Corporation introduced (and patented) what many considered the first commercial versions of modern fax machines, under the name (LDX) or Long Distance Xerography. This model was replaced two years later with a unit that will completely set the standard for the fax machine for years to come. Until now facsimile machines are very expensive and difficult to operate. In 1966, Xerox released Magnafax Telecopiers, a smaller 46-pound facsimile machine. This unit is much easier to operate and can be connected to any standard phone line. This machine is capable of transmitting letter-sized documents in about six minutes. The first sub-minute digital fax machine was developed by Dacom, built on digital data compression technology originally developed at Lockheed for satellite communications.
In the late 1970s, many companies around the world (mainly Japanese companies) entered the fax market. Shortly after a new wave of more compact, faster and more efficient fax machines will hit the market. Xerox continued to refine the fax machine for years after their first ground breaking machine. In the coming years, it will 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 Xerox fax technology include their active Ethernet Fax Service on their 8000 workstations in the early 1980s.
Before the introduction of the ubiquitous fax machine, one of the first was Exxon Qwip in the mid-1970s, a facsimile machine working with optical scanning of documents or rotating images on drums. The reflected light, various intensities corresponding to the light and dark areas of the document, are focused on the photocell so that the current in the circuit varies with the amount of light. This current is used to control the tone generator (modulator), the current that determines the tone frequency generated. The audio tone is then transmitted using an acoustic coupler (speaker, in this case) attached to a public phone microphone. At the receiving end, the handset speaker is mounted on the acoustic coupler (microphone), and the demodulator changes the varying tone into a variable current that controls the mechanical movement of the pen or pencil to reproduce the image on a blank sheet of paper on the identical drum spinning at the same level.
Computer facsimile interface
In 1985, Hank Magnuski, founder of GammaLink, produced the first computer fax board, called GammaFax. Such boards can provide voice calls via the Analog Expansion Bus.
Maps Fax
Fax in the 21st century
Although businesses typically maintain some kind of fax capability, technology has faced increasing competition from Internet-based alternatives. In some countries, since electronic signatures on contracts have not been recognized by law, while fax contracts with signature copies are, fax machines enjoy ongoing support in business. In Japan, faxes are still used extensively for cultural and graphemic reasons and are available to be shipped to domestic and international recipients from more than 81% of all national department stores. The convenience store fax machine typically prints somewhat smaller content from faxes sent on an electronic confirmation sheet, in A4 paper size.
In many enterprise environments, stand-alone fax machines have been replaced by fax servers and other computer systems capable of receiving and storing incoming faxes electronically, and then routing them on the user on paper or via email (which can be secured). Such systems have the advantage of reducing costs by eliminating unnecessary molds and reducing the number of incoming analog telephone lines required by the office.
Fax machines that once were everywhere also began to disappear from small offices and home office environments. Remotely operated server-server services are widely available from VoIP providers and emails that allow users to send and receive faxes using their existing e-mail account without the need for special hardware or fax lines. The personal computer also has long handled incoming and outgoing faxes using an analog or ISDN modem, so there is no need to use a stand-alone fax machine. This solution is usually suitable for users who very rarely need to use the fax service. In July 2017, the UK National Health Service is said to be the world's largest buyer of fax machines because the digital revolution has passed it.
Ability
There are several indicators of fax capability: group, class, data transmission rate, and conformance with ITU-T recommendations (formerly CCITT). Since the 1968 Carterphone decision, most fax machines have been designed to connect to standard PSTN lines and phone numbers.
Group
Analog
Faxes 1 and 2 groups are sent in the same way as analog television frames, with each scanned line transmitted as a continuous analog signal. Horizontal resolution depends on the quality of the scanner, transmission line, and printer. The analog fax machine is out of date and no longer produced. Recommendations ITU-T T.2 and T.3 were withdrawn as obsolete in July 1996.
- Group 1 fax according to ITU-T Recommendation T.2. Group 1 fax takes six minutes to transmit a single page, with a vertical resolution of 96 scan lines per inch. Group 1 fax machine is outdated and no longer produced.
- Group 2 fax according to ITU-T Recommendation T.3 and T.30. Group 2 fax takes three minutes to transmit a single page, with a vertical resolution of 96 scan lines per inch. The Group 2 fax machine is almost obsolete, and is no longer produced. Group 2 fax machines can interoperate with Group 3 fax machines.
Digital
A major breakthrough in the development of a modern facsimile system is the result of digital technology, in which the analog signals from the scanner are digitized and then compressed, resulting in the ability to transmit high-level data on standard telephone lines. The first digital fax machine was the first Dacom Rapidfax sold in the late 1960s, incorporating the digital data compression technology developed by Lockheed for the transmission of images from satellites.
Faxes 3 and 4 are digital formats, and take advantage of digital compression methods to reduce transmission time.
- Fax Group 3 complies with ITU-T Recommendation T.30 and T.4. Group 3 fax takes between six and fifteen seconds to send a single page (not including the initial time for the fax machine to shake hands and synchronize). Horizontal and vertical resolutions are allowed by the T.4 standard to vary among a set of fixed resolutions:
- Horizontal: 100 lines of scanning per inch
- Vertical: 100 scan lines per inch ("Basic")
- Horizontal: 200 or 204 lines of scanning per inch
- Vertical: 100 or 98 lines of scanning per inch ("Standard")
- Vertical: 200 or 196 line scan per inch ("Smooth")
- Vertical: 400 or 391 (note no 392) scan line by inch ("Superfine")
- Horizontal: 300 lines of scanning per inch
- Vertical: 300 scan lines per inch
- Horizontal: 400 or 408 line scan per inch
- Vertical: 400 or 391 scan lines per inch ("Ultrafine")
- Horizontal: 100 lines of scanning per inch
- Group 4 fax according to ITU-T Recommendation T.563, T.503, T.521, T.6, T.62, T.70, T.411 to T.417. They are designed to operate more than 64 kbit/s digital ISDN circuits. The permitted resolution, their superset in T.4 recommendation, is set out in recommendation T.6.
Fax Over IP (FoIP) can send and receive pre-digital documents near realtime speeds using ITU-T T.38 recommendations to send digital images over an IP network using JPEG compression. T.38 is designed to work with VoIP services and is often supported by analog phone adapters used by old fax machines that need to be connected through VoIP services. The scanned document is limited to the amount of time it takes the user to load the document in the scanner and for the device to process the digital file. Resolutions may vary from 150 DPI to 9600 DPI or more. This fax type is not associated with an e-mail to a fax service that still uses a one-way fax modem.
Class
Computer modems are often designated by a particular fax class, which indicates how much processing is derived from the computer's CPU to the fax modem.
- The Class 1 fax device performs fax data transfers in which T.4/T.6 data compression and T.30 session management are performed by software on the controller computer. This is described in ITU-T T.31 recommendations.
- The Class 2 fax device performs its own T.30 session management, but T.4/T.6 data compression is performed by software on the controller computer. The relevant ITU-T recommendation is T.32.
- Class 2.0 differs from Class 2.
- Class 2.1 is a Class 2.0 upgrade. The Class 2.1 fax device is referred to as "super G3"; they seem to be a bit faster than Class 1/2/2.0.
- The Class 3 fax machine is responsible for most fax sessions, given fewer phone numbers and text to send (including ASCII text rendering as a raster image). This device is not common.
Data transmission rate
Several different phone modulation techniques are used by the fax machine. They are negotiated during the modem-fax handshake, and the fax device will use the highest data rate supported by both fax devices, usually at least 14.4 kbit/s for Group 3 faxes.
Note that the "Super Group 3" fax uses V.34bis modulation which allows data rates up to 33.6 kbit/s.
Compression
As well as specifying the resolution (and the allowed physical size of the image sent by fax), the ITU-T T.4 recommends two compression methods to reduce the amount of data that needs to be transmitted between the fax machine to transfer the image. The two methods defined in T.4 are:
- Modified Huffman (MH), and
- Modified READ (MR) ( Relative Element Address Designate ), optional
Additional methods are specified in T.6:
- Modified Modified READ (MMR)
Then, other compression techniques were added as an option for ITU-T T.30 recommendations, such as more efficient JBIG (T.82, T.85) for two-tier content, and JPEG (T.81), T.43, MRC ( T.44), and T.45 for grayscale, palette, and color content. The fax machine can negotiate at the beginning of the T.30 session to use the best techniques applied on both sides.
Modified Huffman
Modified Huffman (MH), specified in T.4 as a one-dimensional coding scheme, is a codebook-based run-length coding scheme optimized to efficiently compress spaces. Since most faxes are made up of free space, this minimizes the sending time of most faxes. Each scanned line is compressed independently of its predecessor and successor.
READ REGISTER
Modified READ (MR), defined as an optional two-dimensional coding scheme in T.4, encodes the first scan line using MH. The next line is compared to the first, the difference is determined, and then the difference is encoded and transmitted. This is effective because most of the lines are slightly different from their predecessors. This does not continue into the end of the fax transmission, but only for a number of lines until a process is reset and a new 'first row' encoded with MH is generated. This limited number of lines is to prevent errors from spreading across all faxes, because the standard does not provide error correction. MR is an optional facility, and some fax machines do not use MR to minimize the amount of computation required by the machine. The number of restricted rows is two for the 'Standard' resolution fax, and four for the 'Fine' resolution fax.
Modified Modified READ
Recommendation ITU-T T.6 adds a further compression type of Modified Modified READ (MMR), which only allows for a large number of lines to be encoded by MR rather than in T.4. This is because T.6 makes the assumption that the transmission passes the circuit with a number of low-line errors such as digital ISDN. In this case, there is no maximum number of rows for the encoded difference.
JBIG
In 1999, the ITU-T T.30 recommendation added JBIG (ITU-T T.82) as another lossless bi-level compression algorithm, or rather the "fax profile" section of JBIG (ITU-T T.85). The JBIG compressed page generates a transmission of 20% to 50% faster than MMR compressed pages, and transmits up to 30 times faster if the page includes halftone images.
JBIG performs adaptive compression, the encoder and decoder collects statistical information about the images sent from the pixels transmitted so far, to predict the probability for each subsequent pixel to be black or white. For each new pixel, JBIG looks at the nearby ten pixels that were previously transmitted. It is estimated, how often in the past the next pixel is black or white in the same environment, and estimates from the probability distribution of the next pixel. It's inserted into the arithmetic coder, which only adds a small fraction of the order to the output if the pixels are more likely to be encountered.
The ITU-T T.85 "fax profile" restricts some of the optional features of the full JBIG standard, so the codec does not have to store data about more than three lines of last pixels of images in memory at any time. This allows streaming "endless" images, where the height of the image may not be known until the last line is transmitted.
ITU-T T.30 allows the fax machine to negotiate one of the two options of the T.85 "fax profile":
- In "base mode", the JBIG encoder must divide the image into a 128-line horizontal line (parameter L0 = 128), and restart the arithmetic encoder for each strip.
- In "option mode", there is no such limit.
Matsushita Whiteline Skip
The proprietary compression scheme used on the Panasonic fax machine is Matsushita Whiteline Skip (MWS). These can be overlaid on other compression schemes, but only operate when two Panasonic machines communicate with each other. This system detects empty areas scanned between lines of text, and then condenses several blank scanning lines into the data space of one character. (JBIG implements the same technique called "regular prediction", if the TPBON header flag is set to 1.)
Typical characteristics
The Group 3 fax machine transfers one or more printed or handwritten pages per minute in black and white (bitonal) resolution of 204ÃÆ'â € "98 (normal) or 204ÃÆ'â €" 196 (smooth) dots per square inch. Transfer rate 14.4 kbit/s or higher for modem and some fax machine, but fax machine support speed starts with 2400 bit/s and usually operates at 9600 bit/s. The transferred image format is called ITU-T (formerly CCITT) group 3 or 4 fax. Group 3 fax has .g3 and MIME image/g3fax .
The most basic fax mode only transfers black and white. The original page is scanned in a resolution of 1728 pixels/line and 1145 rows/page (for A4). The resulting raw data is compressed using modified Huffman codes optimized for written text, achieving an average compression factor of about 20. Usually the page requires 10 s for transmission instead of about 3 minutes for the same compressed raw data 1728ÃÆ'â € "1145 bits at speed 9600 bit/s. The compression method uses Huffman's code book to run the length of black and white running in a single scanned line, and it can also use the fact that two adjacent scanlines are usually quite similar, saving bandwidth by encoding just the difference.
The fax class indicates how the fax program interacts with the 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 Class 2 or Class 2.0. What is preferred for use depends on factors such as hardware, software, modem firmware, and expected usage.
Printing process
Fax machines from the 1970s to the 1990s often used direct thermal printers with thermal paper rolls as their printing technology, but since the mid-1990s there was a transition to ordinary paper faxes: thermal transfer printers, inkjet printers and laser printers.
One of the advantages of inkjet printing is that inkjet printers can be colored; therefore, many 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 color faxing; unfortunately, it's not widely supported, so many color fax machines can only send color faxes to machines from the same manufacturer.
Stroke speed
The stroke velocity in the facsimile system is the rate at which the line remains perpendicular to the direction of scanning crossed in one direction by the scanning or recording. Stroke speed is usually expressed as the number of strokes per minute. When the fax system scans in both directions, the stroke speed is twice that number. In most conventional 20th-century mechanical systems, the speed of stroke is equal to the speed of the drum.
Fax paper
As a precaution, thermal fax paper is usually not accepted in the archive or as documentary evidence in some court of law except photocopied. This is because the image-forming layer can be removed and brittle, and tends to be detached from the medium after long storage.
Internet Fax
One popular alternative is to subscribe to an Internet fax service, which allows users to send and receive faxes from their personal computers using an existing email account. No software, fax server, or fax machine is required. Faxes are accepted as attached TIFF or PDF files, or in proprietary formats that require the use of provider software. Faxes can be sent or retrieved from anywhere whenever a user can gain Internet access. Some services offer secure faxes to comply with the strict HIPAA and Gramm-Leach-Bliley Act requirements to safeguard personal and medical information and financial information safely. Utilizing a fax service provider does not require paper, dedicated fax lines, or consumable resources.
Another alternative to physical fax machines is to use computer software that allows people to send and receive faxes using their own computers, utilizing integrated fax and messaging servers. A virtual fax (email) can be printed and then signed and scanned back to the computer before emailing. Also the sender can attach a digital signature to a document file.
With the popularity of mobile phones soaring, virtual fax machines can now be downloaded as apps for Android and iOS. This app utilizes 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 standard image sizes, two forms of image data compression (encoding), image data format, and references, T.30 and various modem standards.
- Q.6 establishes a compression scheme that reduces the time required to transmit images by about 50 percent.
- Q.30 specifies the procedures used by both the sending and receiving terminals to manage fax calls, determine image size, encoding, and transfer rates, page demarcation, and call termination. T.30 also references various modem standards.
- V.21, V.27ter, V.29, V.17, V.34: The ITU modem standard used in facsimile. The first three were ratified before 1980, and set out in the original T.4 and T.30 standards. V.34 was issued for fax in 1994.
- Q.37 ITU standards for sending fax-image files via e-mail to the intended fax recipient.
- G.711 passes - this is where T.30 fax calls are made in VoIP calls encoded as audio. It is sensitive to network packet loss, jitter and clock synchronization. When using high voice compression encoding techniques such as, but not limited to, G.729, some fax tonal signals may not be transported correctly across the packet network.
- RFC 3362/t38 MIME-type image
See also
References
Further reading
- Coopersmith, Jonathan, Faxed: Rise and Fall of Fax Machine (Johns Hopkins University Press, 2015) 308 pp.
External links
- Group 3 Facsimile an '97 essay with technical details about compression and error codes, and call and release establishment.
- ITU T.30 Recommendations
Source of the article : Wikipedia
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