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In a classic fax system, you start using fax by dialing up a distant fax system using a touch pad on your fax machine, just as you would any other telephone. You slide a sheet of paper into the fax's scanner, and the page curls around a drum in front of a photodetector. Much as a television picture is broken into numerous scan lines, a fax machine scans images as a series of lines, takes them one at a time, and strings all of the lines scanned from the document into a continuous stream of information. The fax machine converts the data stream into a series of modulated tones for transmission over the telephone line. After a connection is made at the receiving end, another fax machine converts the data stream into black and white dots representing the original image, much as a television set reconstructs a TV image. A printer puts the results on paper using either thermal or laser printer technology.
Computer-based fax systems can do away with the paper. Fax software can take the all-electronic images you draw or paint with your graphics software and convert them into the standard format that's used for fax transmissions. A fax modem in your computer can then send that data to a standard fax machine, which converts the data into hard-copy form. Alternatively, your computer fax system can receive a transmission from a standard fax machine and capture the image into a graphics file. You can then convert the file into another graphic format using conversion software, edit the image with your favorite painting program, or turn its text contents into ASCII form using optical character recognition (OCR) software. You can even turn your computer into the equivalent of a standard fax machine by adding a scanner to capture images from paper. Your printer will turn fax reception into hard copy, although at a fraction of the speed of a standalone fax machine.
Computer-based fax beats standalone fax with its management capabilities. Computer fax software can broadcast fax messages to as wide a mailing list as you can accommodate on your hard disk, waiting until early morning hours when long-distance rates are cheapest to make the calls. You can easily manage the mailing list as you would any other computer database.
The concept of facsimile transmissions is not new. As early as 1842, Alexander Bain patented an electromechanical device that could translate wire-based signals into marks on paper. Newspaper wire photos, which are based on the same principles, have been used for generations.
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