The fax machine (Facsimile) uses a method of encoding image data, transmitting it over telephone lines or radio broadcast, and receiving hard (text) copy, line drawings, or photographs. It provides an inexpensive, fast, and reliable method for transmitting contracts and resumes. Fax machines work by digitizing an image, dividing it into a grid of dots.
Electronically, a bit that has a value of either '0' or '1' depending if it is black or white represents each dot. In this approach, the fax machine translates a picture into a series of zeros and ones (called bit map) that can be transmitted like normal computer data. On the receiving side, a fax machine reads the incoming data, translates the zeros and ones back into dots, and reprints the picture.
The idea of fax machine has been around since 1842, when Alexander Bain invented the Telegraph.
Some scientists worked in this topic since the 1800's.
However, fax machines did not become popular until the mid 1980's.
In 1983, the adoption of a standard protocol for sending faxes at rates of 9600 bps contributed to the fax popularity.
This standard was created by CCITT and was known as Group 3. Group 3 protocol supports two classes of resolution: 203 by 98 dots per inch (dpi) and 203 by 196 dpi.
Modern fax machines contain optical scanners for digitizing images on paper as well as photocopiers and Internet fax services.
New fax machines confirm Group 3 protocol and support the Group 4 fax protocol that requires ISDN lines.