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Fundaments, operation, transmitter and receiver, advantages and disadvantages
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Facsimile
- 1. ABWCABWC FACSIMILEFACSIMILE Dr. M V Raghavendra, Dept of Electronics & Communication Contents:Contents: What is Facsimile History Standards Basic concept FAX Block diagram Transmitter Receiver CCD Key aspects of FAX standards Transmission time Facsimile data Line transmission formats High Resolution scanners Advantages Disadvantages
- 2. ABWCABWC WHAT IS FACSIMILE? 2 Telecommunication Channel Dr M V Raghavendra Fax-“facsimile" (Latin word) “make copy”-is a process of converting optical images into electrical signals for transmission over communication systems (phone line, internet etc). Facsimile (FAX) makes copies of a document over a telecommunication channel anywhere in the world at the same speed as the one the originating fax scans.
- 3. ABWCABWC HISTORY OF THE FACSIMILE MACHINE • In 1843, The first fax machine was invented by Scottish mechanic and inventor Alexander Bain. • In 1850, a London inventor named F. C. Blakewell received a patent what he called a "copying telegraph". • In 1860, a fax machine called the Pantelegraph sent the first fax between Paris and Lyon. The Pantelegraph was invented Giovanni Caselli. • In 1902, Dr Arthur Korn invented an improved and practical fax, the photoelectric system. • In 1924, the telephotography machine (a type of fax machine) was used to send political convention photos long distance for newspaper publication. It was developed by the American Telephone & Telegraph Company (AT&T). • In 1926, RCA invented the Radiophoto that faxed by using radio broadcasting technology. • On March 4, 1955, the first radio fax transmission was sent across the Atlantic. • In 1964, Xerox Corporation introduced (and patented) what many consider to be the first commercialized version of the modern fax machine, under the name (LDX) or Long Distance Xerography. 3Dr M V Raghavendra
- 4. ABWCABWC FACSIMILE STANDARDS 1. Like telephones, all faxes comply to standards set by the International Telecommunications Union division for Telecommunications. 2. The Specific recommendation for Facsimile is ITU-T Rec. T.4 and ITU-T Rec. T.30. 3. The recommendation defines the characteristics of facsimile terminals which enable documents to be transmitted on: a) The general switched telephone network, b) International leased circuits c) The Integrated Services Digital Network (ISDN). 4Dr M V Raghavendra
- 5. ABWCABWC BASIC CONCEPT 5 1. At the sending end, there an optical sensor which read the paper. 2. Usually, a modern fax machine also has a paper-feed mechanism so that it is easy to send multi-page faxes. 3. The white and black spots that the optical sensor reads are encoded they can travel through a phone line. 4. At the receiving end, the information is decoded and sent to the printer which marks the paper with black (or colour) dots (or prints). SENDER RECEIVER Telephone Channel Dr M V Raghavendra
- 6. ABWCABWC FAX BLOCK DIAGRAM 6 Optical Reader A/D Converter Digital Data Compression Modulator Telephone Line Demodulator Digital data Expansion Printer Head Control Logic Operator Controls Motor Control Circuit Roller Drive Motors Printer D/A Converter Data is read from CCD row by row Data is compressed To remove white spaces/ Repetitive parts FSK Modulated Signal (Audible) Compressed data Is restored Control signals are decoded Motors drive • Horizontal motion • Line feed • Form Feed Dr M V Raghavendra
- 7. ABWCABWC FAX TRANSMITTER 7 FSK signal Data is read from CCD row by row Data is compressed To remove white spaces/ Repetitive parts Dr M V Raghavendra
- 8. ABWCABWC FAX RECEIVER Signal is Demodulated Compressed data Is restoredPrint marks are Imparted onto paper Motors drive • Horizontal motion • Line feed • Form Feed Control signals are decoded Human Operator can manually control: • Line feed (LF) • Form Feed (FF) Data received From telephone line 8Dr M V Raghavendra
- 9. ABWCABWC KEY ASPECTS OF THE FAX STANDARD Scanning Track: 1. The message should be scanned in the same direction in the transmitter and receiver. 2. Viewing the message area in a vertical plane, the picture elements should be processed as if the scanning direction were from left to right. 3. Subsequent scans are adjacent and below the previous scan. 9Dr M V Raghavendra
- 10. ABWCABWC TRANSMISSION TIME PER TOTAL CODED SCAN LINE 1. The total coded scan line is defined as the sum of data bits plus any required fill bits plus the end of line (EOL) bits. 2. The minimum transmission times of the total coded scan line should be 13 milliseconds 3. The maximum mission transmission time of any total coded scan line should be 20 miliseconds. 4. Optional error correction is utilized to transmit the total coded scan line. 10Dr M V Raghavendra
- 11. ABWCABWC FACSIMILE DATA 1. A total of 1,728 picture elements represent one horizontal scan line of 215 mm length. 2. End-of-line (EOL) is a unique code word (Format: 000000000001 (12 bits)) that can never be found within a valid line of data; therefore, resynchronization after an error burst is possible. 3. Fill: A special word added to ensure that the transmission time of Data, Fill and EOL is not less than the minimum transmission time of the total coded scan line. 4. Return To Control (RTC): The end of a document transmission is indicated by sending six consecutive EOLs. i.e. 000000000001 , . . . . . . . . . ., 000000000001 (total of 6 times) 11Dr M V Raghavendra
- 12. ABWCABWC FORMATS FOR A LINE OF DATA 12 RTC- Return To Control used to mark end of transmission Data for Line 1 Data for Line 2 Data for Line 3 6 EOL marks used To indicate end of transmission Dr M V Raghavendra
- 13. ABWCABWC HIGHER RESOLUTION SCANNERS 1. A scanner scans one horizontal row of pixels at a time, moving that scan line down the page with a carriage motor. 2. The dpi number is the optical resolution of the CCD sensor cells. 3. A 1200 dpi scanner takes 1200 samples per inch (creates 1200 pixels per inch) horizontally from the width being scanned. 13Dr M V Raghavendra
- 14. ABWCABWC HIGHER RESOLUTION SCANNERS 1. Higher Resolution (dpi) is possible through proper control of the carriage stepping motor. 2. Example: A 1200x2400 dpi scanner is geared so that each pulse of the carriage motor moves in 1/2400 inch steps vertically. 3. At 300 dpi, the carriage moves eight motor steps at a time vertically, then stops and re- samples the scan line to 1/4 size horizontally, to create the image. 14Dr M V Raghavendra
- 15. ABWCABWC Dr M V Raghavendra 15 ADVANTAGES AND DISADVANTAGES Advantages:Advantages: •Faxes have a distinct advantage over postal mail in that the delivery is nearly instantaneous. •Can be delivered at any time. •No need to give commands of printing separately on receiving the fax document. Disadvantages:Disadvantages: •Need a separate space for the machine. •Needs a telephone line. •Needs power/electricity •Requires paper for receiving and sending faxes •Aging of papers could lead to difficulties in managing records.
- 16. ABWCABWC Dr M V Raghavendra 16