Grahame N's Web Pages

THE CELLULOID IMAGE


"FROM SCANNING DISC TO CATHODE RAY TUBE, LCD & BEYOND"

f rom Grahame L. Newnham B.Sc.


The discovery of a feature of the human optical system named 'persistence of vision' initially spawned various optical toys that simulated a moving image. It had been known since time immemorial that if the human eye was subjected to a series of still images in a fast enough series (perhaps at a rate of at least twelve pictures per second) then the brain would register these individual images as a moving picture.

Apart from these optical tricks - a spinning card with say a parrott on one side and a cage on the other would be seen as a parrott in the cage or a revolving cylinder containing drawings on the inside would simulate continuous movement when spun and viewed from the top or through a series of holes - the world had to wait for other technical developments for this phenomenen to be of any real practical (and commercial!) use.

In the case of movies, it was the production of a light sensitive flexible material (camera film) by George Eastman to be marketed by the Kodak company that set in trail the ability to record and later reproduce actual moving images - true moving picture recordings. Although various claims are officially recorded it was really a series of almost simultaneous discoveries / inventions by Edison (well actually his English assistant W. Dickson) in the USA, William Freise-Green and W. Paul in the UK and the Lumiere Brothers in France who all, around the 1890s showed the world, recordings on film of real moving pictures.

Although theorised soon after the turn of the century by scientists like Cambell Swinton in the UK (electronic), and Milhaly in Hungary/Germany (mechanical), the means of transmitting live moving pictures of a scene to be viewed remotely at the same instant had to wait till the early 1920s. A German, Paul Nipkow (1860 - 1940) patented an "Electrical Telescope" in January 1883; although his actual system didn't work, it was his idea of using a rotating disc with a series of offset holes to break up a scene into a series of lines that led many (once electronic amplification and photo cells had been developed) to produce remote moving images. Most of these demostrations in the early 1920s were only of silhouettes and it was Scotsman John Logie Baird who first demostrated the transmission of reflected light images rather than silhouettes. Although only 30 lines were used, the picture was tall and narrow (like the faces etc. it was intended to transmit) and Baird's system had the lines closer nearer the centre so as to improve central definition. With just 30 lines and a frame rate of 12.5 per second, it was possible to transmit the signal by radio using a standard medium wave transmitter. The scanning disc television system was born - by the late 1920s there were half hour broadcasts two or three times a week. Some scanning disc televisions were sold, others made from D-I-Y kits. They could be operated using the signal from a domestic radio receiver - however results could hardly match what one could see in the cinema or from amateur movies. Higher definition was needed, which would be difficult if not impossible to achieve by mechanical means and a higher frequency radio signal also had be be developed.

 

gln - sorry not yet complete - Aug 2009


 

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First published March 2004 ........ Last updated: 19 October 2012 ........ cel10.htm .......... İMM1X-G.L. Newnham