Change Of Scene (Six continued)
Landers Hoang
The concept of television is the work of many individuals in the late 19th and early 20th centuries. The first practical transmissions of moving images over a radio system used mechanical rotating perforated disks to scan a scene into a time-varying signal that could be reconstructed at a receiver back into an approximation of the original image. Development of television was interrupted by the Second World War. After the end of the war, all-electronic methods of scanning and displaying images became standard. Several different standards for addition of color to transmitted images were developed with different regions using technically incompatible signal standards. Television broadcasting expanded rapidly after World War II, becoming an important mass medium for advertising, propaganda, and entertainment.[1]
Television broadcasts can be distributed over the air by VHF and UHF radio signals from terrestrial transmitting stations, by microwave signals from Earth orbiting satellites, or by wired transmission to individual consumers by cable television. Many countries have moved away from the original analog radio transmission methods and now use digital television standards, providing additional operating features and conserving radio spectrum bandwidth for more profitable uses. Television programming can also be distributed over the Internet.
Television broadcasting may be funded by advertising revenue, by private or governmental organizations prepared to underwrite the cost, or in some countries, by television license fees paid by owners of receivers. Some services, especially carried by cable or satellite, are paid by subscriptions.
Television broadcasting is supported by continuing technical developments such as long-haul microwave networks, which allow distribution of programming over a wide geographic area. Video recording methods allow programming to be edited and replayed for later use. Three-dimensional television has been used commercially but has not received wide consumer acceptance owing to the limitations of display methods.
Facsimile transmission systems pioneered methods of mechanically scanning graphics in the early 19th century. The Scottish inventor Alexander Bain introduced the facsimile machine between 1843 and 1846. The English physicist Frederick Bakewell demonstrated a working laboratory version in 1851. The first practical facsimile system, working on telegraph lines, was developed and put into service by the Italian priest Giovanni Caselli from 1856 onward.[2][3][4]
Willoughby Smith, an English electrical engineer, discovered the photoconductivity of the element selenium in 1873. This led, among other technologies, towards telephotography, a way to send still images through phone lines, as early as in 1895, as well as any kind of electronic image scanning devices, both still and in motion, and ultimately to TV cameras.
As a 23-year-old German university student, Paul Julius Gottlieb Nipkow proposed and patented the Nipkow disk in 1884 in Berlin.[5] This was a spinning disk with a spiral pattern of holes in it, so each hole scanned a line of the image. Although he never built a working model of the system, variations of Nipkow's spinning-disk "image rasterizer" became exceedingly common.[5] Constantin Perskyi had coined the word television in a paper read to the International Electricity Congress at the World's Fair in Paris on August 24, 1900. Perskyi's paper reviewed the existing electromechanical technologies, mentioning the work of Nipkow and others.[6] However, it was not until 1907 that developments in amplification tube technology, by Lee de Forest and Arthur Korn among others, made the design practical.[7]
The first demonstration of transmission of images was by Augusto Bissiri: he transmitted, in 1906, a photograph image from one room to another. In 1917, after other successful attempts by several independent inventors, he transmitted an image from London to New York City. He patented his apparatus in Los Angeles in 1928.[8][9][10][11][12]
The first demonstration of instantaneous transmission of images was by Georges Rignoux and A. Fournier in Paris in 1909. A matrix of 64 selenium cells, individually wired to a mechanical commutator, served as an electronic retina. In the receiver, a type of Kerr cell modulated the light and a series of variously angled mirrors attached to the edge of a rotating disc scanned the modulated beam onto the display screen. A separate circuit regulated synchronization. The 88 pixel resolution in this proof-of-concept demonstration was just sufficient to clearly transmit individual letters of the alphabet. An updated image was transmitted "several times" each second.[13]
In 1911, Boris Rosing and his student Vladimir Zworykin created a system that used a mechanical mirror-drum scanner to transmit, in Zworykin's words, "very crude images" over wires to the "Braun tube" (cathode-ray tube or "CRT") in the receiver. Moving images were not possible because, in the scanner, "the sensitivity was not enough and the selenium cell was very laggy".[14]
In May 1914, Archibald Low gave the first demonstration of his television system at the Institute of Automobile Engineers in London. He called his system 'Televista'. The events were widely reported worldwide and were generally entitled Seeing By Wireless. The demonstrations had so impressed Harry Gordon Selfridge that he included Televista in his 1914 Scientific and Electrical Exhibition at his store.[15][16] It also interested Deputy Consul General Carl Raymond Loop who filled a US consular report from London containing considerable detail about Low's system.[17][18] Low's invention employed a matrix detector (camera) and a mosaic screen (receiver/viewer) with an electro-mechanical scanning mechanism that moved a rotating roller over the cell contacts providing a multiplex signal to the camera/viewer data link. The receiver employed a similar roller. The two rollers were synchronised. It was unlike any other TV system of the 20th Century and in some respects, Low had a digital TV system 80 years before modern digital TV. World War One began shortly after these demonstrations in London and Low became involved in sensitive military work, and so he did not apply for a patent until 1917. His "Televista" Patent No. 191,405 titled "Improved Apparatus for the Electrical Transmission of Optical Images" was finally published in 1923; delayed possibly for security reasons. The patent states that the scanning roller had a row of conductive contacts corresponding to the cells in each row of the array and arranged to sample each cell in turn as the roller rotated. The receiver's roller was similarly constructed and each revolution addressed a row of cells as the rollers traversed over their array of cells. Loops report tells us that... "The receiver is made up of a series of cells operated by the passage of polarized light through thin slats of steel, and at the receiver the object before the transmitter is reproduced as a flickering image" and "The roller is driven by a motor of 3,000 revolutions per minute, and the resulting variations of light are transmitted along an ordinary conducting wire." and the patent states "into each... space I place a selenium cell". Low covered the cells with a liquid dielectric and the roller connected with each cell in turn through this medium as it rotated and travelled over the array. The receiver used bimetallic elements that acted as shutters "transmitting more or less light according to the current passing through them..." as stated in the patent. Low said the main deficiency of the system was the selenium cells used for converting light waves into electric impulses, which responded too slowly thus spoiling the effect. Loop reported that "The system has been tested through a resistance equivalent to a distance of four miles, but in the opinion of Doctor Low there is no reason why it should not be equally effective over far greater distances. The patent states that this connection could be either wired or wireless. The cost of the apparatus is considerable because the conductive sections of the roller are made of platinum..."
Dr. Low gave a demonstration for the first time in public, with a new apparatus that he has invented, for seeing, he claims by electricity, by which it is possible for persons using a telephone to see each other at the same time
In 1927, Ronald Frank Tiltman asked Low to write the introduction to his book in which he acknowledged Low's work, referring to Low's related patents with an apology that they were of 'too technical a nature for inclusion'.[19] Later in his 1938 patent Low envisioned a much larger 'camera' cell density achieved by a deposition process of caesium alloy on an insulated substrate that was subsequently sectioned to divide it into cells, the essence of today's technology. Low's system failed for various reasons, mostly due to its inability to reproduce an image by reflected light and simultaneously depict gradations of light and shade. It can be added to the list of systems, like that of Boris Rosing, that predominantly reproduced shadows. With subsequent technological advances, many such ideas could be made viable decades later, but at the time they were impractical.
In 1927, Baird transmitted a signal over 438 miles (705 km) of telephone line between London and Glasgow. In 1928, Baird's company (Baird Television Development Company/Cinema Television) broadcast the first transatlantic television signal, between London and New York, and the first shore-to-ship transmission. In 1929, he became involved in the first experimental mechanical television service in Germany. In November of the same year, Baird and Bernard Natan of Path established France's first television company, Tlvision-Baird-Natan. In 1931, he made the first outdoor remote broadcast, of the Derby.[21] In 1932, he demonstrated ultra-short wave television. Baird Television Limited's mechanical systems reached a peak of 240 lines of resolution at the company's Crystal Palace studios, and later on BBC television broadcasts in 1936, though for action shots (as opposed to a seated presenter) the mechanical system did not scan the televised scene directly. Instead, a 17.5mm film was shot, rapidly developed, and then scanned while the film was still wet.
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