[GreenKeys] news wire photos

[Jones, Douglas W]

On Jun 16, 2011, at 1:41 PM, Rokumon Cat wrote:

> Hi,
>  
> I was wondering, how did "they" send photos over the news wires in the forties and fifties?

With a telefax machine, of course.

Fax machines are old technology.  Alexander Bain and Giovanni Caselli developed
this technology in the mid 19th century.  That's before the telephone.  The
first commercial fax service was introduced using Caselli's Pantelegraph.  The
first "pantelegram" was sent from Lyons to Paris in 1862.

The Pantelegraph used synchronized pendulums at the transmitter and receiver.
So, you have sync pulses on the line at the end of every scan line to keep them
in sync.  The scanner required that the original be done in conductive ink,
but it could scan drawings or handwritten text equally well.  The sync pulses
also advanced the paper.  At the receiving end, an electromagnet raised and
lowered the pen that recorded the result.

The communications line used was a regular telegraph line, so there was no
transmission of gray scale images.  Just black and white.

Now, move forward a century, to the Teletype-brand wire-service telefax machine
that I recall seeing in the Museum of Science and Industry in Chicago back in
the early 1960s.  The paper paper transport was essentially the same as used on
a teletype, except that the line-feed was one scan line instead of one text line.
It used a regular cloth ribbon too, but instead of a print hammer, it had a
spiral bar (one half twist in the width of the page) so that there was only one
point on the bar that was over the rather sharp metal edge of the platten at any
instant.  The bar spun at a constant rate (synched to the synch pulses in the
signal) and whenever it was supposed to record a black spot, the spiral bar,
ribbon, paper and platten were pressed together.  We're talking about 96 pixels
per inch resolution, so at baud rates under 300 baud typical of that era, we're
talking about a fairly slow fax machine.

The scanners used to transmit the image typically required that the original
be mounted on a rotating drum.  This would spin as a lead screw advanced the
photosensor across the face of the drum, with a cam on the drum producing the
sync pulses.  The fax standards used in that era are still around.  We call them
the Group 1 (6 minute per page) and Group 2 (3 minute per page) standards.

		Doug Jones
		jones at cs.uiowa.edu