The first facsimile (fax) machine was invented almost at the same time as the telegraph, long before the telephone.  In 1843, a Scottish scientist named Alexander Bain obtained a patent for a "recording telegraph" that used special paper reacting to electric current.  However, it was the development of photodiodes and cheap computer chips which allowed the fax to become practical and gain wide use as a business tool.

The first step in the transmission of a document is to digitize it.  A normal page is divided into a grid of 2233 rows by 1728 columns.  Each row is read at once by a line of 1728 photodiodes.  To each of the grid square a number is associated: ‘1’ if the square is mostly black and "0" if it is mainly white.  The information about the row is then compressed and sent out in a series of one’s and zero’s over the phone line.  The fax machine at the other end of the line decodes the one’s and zeros, checks for consistency and finally prints the message or picture on a page.  The transmission has been successfully completed.

To save time, data compression is used.  In a text, a white square (or pel P-icture EL-ement) is generally followed by a string of other white squares (for example, a regular space between two words is about 20 pels).  So it is economical to define codes for different sequences instead of sending the value of each square.  By sending a special code for a full line of 1728 white squares instead of 1728 zero’s, the line can be transmitted 192 times faster!

Data compression makes the fax machine faster, more reliable, and cheaper to use.  With a reproduction quality getting closer and closer to the original, fax will increasingly replace everyday mail.  In a few years, you could receive your birthday cards by fax instead of by mail but not, of course, your birthday cake!

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