Since the 1980s, most machines modulate the transmitted audio frequencies using a digital representation of the page which is compressed to quickly transmit areas which are all-white or all-black.
Scottish inventor Alexander Bain worked on chemical mechanical fax type devices and in 1846 was able to reproduce graphic signs in laboratory experiments.
The 1888 invention of the telautograph by Elisha Grey marked a further development in fax technology, allowing users to send signatures over long distances, thus allowing the verification of identification or ownership over long distances.
Fax (short for facsimile), sometimes called telecopying or telefax (the latter short for telefacsimile), is the telephonic transmission of scanned printed material (both text and images), normally to a telephone number connected to a printer or other output device.
The original document is scanned with a fax machine (or a telecopier), which processes the contents (text or images) as a single fixed graphic image, converting it into a bitmap, and then transmitting it through the telephone system in the form of audio-frequency tones.
He received British patent 9745 on May 27, 1843 for his "Electric Printing Telegraph." Frederick Bakewell made several improvements on Bain's design and demonstrated a telefax machine.
The Pantelegraph was invented by the Italian physicist Giovanni Caselli.
Around 1900, German physicist Arthur Korn invented the Bildtelegraph, widespread in continental Europe especially, since a widely noticed transmission of a wanted-person photograph from Paris to London in 1908, used until the wider distribution of the radiofax.
Its main competitors were the Bélinographe by Édouard Belin first, then since the 1930s the Hellschreiber, invented in 1929 by German inventor Rudolf Hell, a pioneer in mechanical image scanning and transmission.He introduced the first commercial telefax service between Paris and Lyon in 1865, some 11 years before the invention of the telephone.In 1880, English inventor Shelford Bidwell constructed the scanning phototelegraph that was the first telefax machine to scan any two-dimensional original, not requiring manual plotting or drawing.Previously, photographs had been sent over the radio using this process.The receiving fax machine interprets the tones and reconstructs the image, printing a paper copy.Early systems used direct conversions of image darkness to audio tone in a continuous or analog manner.