History of television
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Television history)
The
History of television technology can be divided along two lines: those developments that depended upon both
mechanical and
electronic principles, and those dependent only on electronic principles. From the latter descended all modern
televisions, but these would not have been possible without the discoveries and insights garnered from the development of the
electromechanical systems.
Electromechanical television
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The origins of what would become today's television system can be traced back to the discovery of the photoconductivity of the element selenium by Willoughby Smith in 1873, the invention of a scanning disk by Paul Gottlieb Nipkow in 1884, and Philo Farnsworth's Image dissector in 1927.
The 20-year old German university student Nipkow proposed and patented the first electromechanical television system in 1884.[1] Nipkow's spinning disk design is credited with being the first television image rasterizer. Constantin Perskyi had coined the word television in a paper read to the International Electricity Congress at the International World Fair in Paris on August 25, 1900. Perskyi's paper reviewed the existing electromechanical technologies, mentioning the work of Nipkow and others. The photoconductivity of selenium and Nipkow's scanning disk were first joined for practical use in the electronic transmission of still pictures and photographs, and by the first decade of the 20th century halftone photographs, composed of equally spaced dots of varying size, were being transmitted by facsimile over telegraph and telephone lines as a newspaper service.
However, it wasn't until 1907 that developments in amplification tube technology made the design practical.[2] The first demonstration of the instantaneous transmission of still monochromatic images with continuous tonal variation (as opposed to halftone) was by Georges Rignoux and A. Fournier in Paris in 1909, using a rotating mirror-drum as the scanner, and a matrix of 64 selenium cells as the receiver.[3]
In 1911, Boris Rosing and his student Vladimir Kosma Zworykin created a television system that used a mechanical mirror-drum scanner to transmit, in Zworykin's words, "very crude images" over wires to the electronic Braun tube (cathode ray tube) in the receiver. Moving images were not possible because, in the scanner, "the sensitivity was not enough and the selenium cell was very laggy".
On March 25, 1925, Scottish inventor John Logie Baird gave a demonstration of televised silhouette images in motion at Selfridge's Department Store in London. But if television is defined as the contemporaneous transmission of moving, monochromatic images with continuous tonal variation — not still, silhouette or halftone images — Baird first achieved this privately on October 2, 1925.[4] Then he gave the world's first public demonstration of a working television system to members of the Royal Institution and a newspaper reporter on January 26, 1926 at his laboratory in London. Unlike later electronic systems with several hundred lines of resolution, Baird's vertically scanned image, using a scanning disk embedded with a double spiral of lenses, had only 30 lines, just enough to reproduce a recognizable human face.
In 1927, Baird transmitted a signal over 438 miles 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. He also demonstrated an electromechanical color, infrared (dubbed "Noctovision"), and stereoscopic television, using additional lenses, disks and filters. In parallel, Baird developed a video disk recording system dubbed "Phonovision"; a number of the Phonovision recordings, dating back to 1927, still exist.[5] In 1929, he became involved in the first experimental electromechanical television service in Germany. In November 1929, Baird and Bernard Natan of Pathe established France's first television company, Télévision-Baird-Natan. In 1931, he made the first live transmission, of the Epsom Derby. In 1932, he demonstrated ultra-short wave television. Baird's electromechanical system reached a peak of 240 lines of resolution on BBC television broadcasts in 1936, before being discontinued in favor of a 405-line all-electronic system developed by Marconi-EMI.
In the U.S., Charles Francis Jenkins was able to demonstrate on June 13, 1925, the transmission of the silhouette image of a toy windmill in motion from a naval radio station to his laboratory in Washington, using a lensed disk scanner with 48 lines per picture,[6] 16 pictures per second. AT&T's Bell Telephone Laboratories transmitted halftone images of transparencies in May 1925.
Meanwhile in Soviet Russia, Léon Theremin had been developing a mirror drum-based television, starting with 16 lines resolution in 1925, then 32 lines and eventually 64 using interlacing in 1926, and as part of his thesis on June 7, 1926 he electrically transmitted and then projected near-simultaneous moving images on a five foot square screen.[6] By 1927 he achieved an image of 100 lines, a resolution that was not surpassed until 1931 by RCA, with 120 lines.
However, Herbert E. Ives of Bell Labs gave the most dramatic demonstration of television yet on April 7, 1927, when he field tested reflected-light television systems using small-scale (2 by 2.5 inches) and large-scale (24 by 30 inches) viewing screens over a wire link from Washington to New York City, and over-the-air broadcast from Whippany, New Jersey. The subjects, who included Secretary of Commerce Herbert Hoover, were illuminated by a flying-spot scanner beam that was scanned by a 50-aperture disk at 16 pictures per minute.
Electronic television
In 1911, engineer Alan Archibald Campbell-Swinton gave a speech in London, reported in The Times, describing in great detail how distant electric vision could be achieved by using cathode ray tubes at both the transmitting and receiving ends. The speech, which expanded on a letter he wrote to the journal Nature in 1908, was the first iteration of the electronic television method that is still used today. Others had already experimented with using a cathode ray tube as a receiver, but the concept of using one as a transmitter was novel.[7] By the late 1920s, when electromechanical television was still being introduced, inventors Philo Farnsworth and Vladimir Zworykin were already working separately on versions of all-electronic transmitting tubes.
The decisive solution—television operating on the basis of continuous electron emission with accumulation and storage of released secondary electrons during the entire scan cycle—was first described by the Hungarian inventor Kálmán Tihanyi in 1926, with further refined versions in 1928.[8]
On September 7, 1927, Philo Farnsworth's Image Dissector camera tube transmitted its first image, a simple straight line, at his laboratory at 202 Green Street in San Francisco. [1] By 1928, Farnsworth had developed the system sufficiently to hold a demonstration for the press, televising a motion picture film. In 1929, the system was further improved by elimination of a motor generator, so that his television system now had no mechanical moving parts. That year, Farnsworth transmitted the first live human images by his television system, including a three and a half-inch image of his wife Pem with her eyes closed (possibly due to the bright lighting required).
Farnsworth gave the world's first public demonstration of a complete all-electronic television system on 25 August 1934 at the Franklin Institute in Philadelphia. Other inventors had previously demonstrated components of such a system, or had shown an electronic system using still images or motion picture film.[9] But Farnsworth was the first to coordinate both electronically scanned television cameras and electronically scanned television receivers, and present live, moving, monochromatic images with them. Unfortunately, his cameras needed too much light, so his work came to a stop.
Vladimir Zworykin was also experimenting with the cathode ray tube to create and show images. While at Westinghouse in 1923, he developed an electronic camera tube. But in a 1925 demonstration, the image was dim, had low contrast and poor definition, and was stationary.[10] The tube never got beyond the laboratory stage, but RCA (which had acquired the Westinghouse patent) believed the patent on Farnsworth's 1927 image dissector was written so broadly that it would exclude any other electronic formation of an image. And so RCA, armed with Zworykin's 1923 patent application, filed a patent interference suit against Farnsworth. The U.S. Patent Office examiner disagreed in a 1935 decision, finding priority of invention for Farnsworth against Zworykin.[11] In October 1939, after losing an appeal in the courts and wishing to go forward with the commercial manufacturing of television equipment, RCA agreed to pay Farnsworth US$1 million (the equivalent of $13.8 million in 2006) over a ten-year period, in addition to license payments, to use Farnsworth's patents.[12]
Zworykin designed an improved electronic camera tube at RCA in 1931, which he called the iconoscope. It became the primary type of camera tube used in American television broadcasting from 1936 until 1946, when it was replaced by the image orthicon tube.
In Britain Isaac Shoenberg used Zworykin's idea to develop Marconi-EMI's own Emitron tube, which formed the heart of the cameras they designed for the BBC. Using this, on November 2, 1936 a 405 line service was started from studios at Alexandra Palace, and transmitted from a specially-built mast atop one of the Victorian building's towers; it alternated for a short time with Baird's mechanical system in adjoining studios, but was more reliable and visibly superior. So began the world's first high-definition regular service. The mast is still in use today.
Most television researchers appreciated the value of color image transmission, with an early patent application in Russia in 1889 for a mechanically-scanned color system showing how early the importance of color was realized.
John Logie Baird demonstrated the world's first color transmission on
July 3,
1928, using scanning discs at the transmitting and receiving ends with three spirals of apertures, each spiral with filters of a different primary color; and three light sources at the receiving end, with a
commutator to alternate their illumination.
[13] Baird also made the world's first color broadcast on
February 4,
1938, sending a mechanically scanned 120-line image from Baird's
Crystal Palace studios to a projection screen at London's
Dominion Theatre.
[14]
Electronic color television
In 1938 the shadow mask color television was patented by Werner Flechsig in Germany, and was demonstrated at the International radio exhibition Berlin in 1939. The analog color televisions we use today are based on this technology. On August 16, 1944, Baird gave the first demonstration of a fully electronic color television display. His 600-line color system used triple interlacing, using six scans to build each picture.[15][16]
Television sets
In television's electromechanical era, commercially made television sets were sold from 1928 to 1934 in the United Kingdom,[59] United States, and Russia.[60] The earliest commercially made sets sold by Baird in the UK in 1928 were radios with the addition of a television device consisting of a neon tube behind a mechanically spinning disk (the Nipkow disk) with a spiral of apertures that produced a red postage-stamp size image, enlarged to twice that size by a magnifying glass. The Baird "Televisor" was also available without the radio. The Televisor sold in 1930–1933 is considered the first mass-produced set, selling about a thousand units.[61]
The first commercially made electronic television sets with cathode ray tubes were manufactured by Telefunken in Germany in 1934,[62][63] followed by other makers in France (1936),[64] Britain (1936),[65] and America (1938).[66][67] The cheapest of the pre-World War II factory-made American sets, a 1938 image-only model with a 3-inch (8 cm) screen, cost US$125, the equivalent of US$1,863 in 2007. The cheapest model with a 12-inch (30 cm) screen was $445 ($6,633).[68]
An estimated 19,000 electronic television sets were manufactured in Britain, and about 1,600 in Germany, before World War II. About 7,000–8,000 electronic sets were made in the U.S.[69] before the War Production Board halted manufacture in April 1942, production resuming in August 1945.
Television usage in the United States skyrocketed after World War II with the lifting of the manufacturing freeze, war-related technological advances, the gradual expansion of the television networks westward, the drop in set prices caused by mass production, increased leisure time, and additional disposable income. While only 0.5% of U.S. households had a television set in 1946, 55.7% had one in 1954, and 90% by 1962.[70] In Britain, there were 15,000 television households in 1947, 1.4 million in 1952, and 15.1 million by 1968.
For many years different countries used different technical standards. France initially adopted the German 441-line standard but later upgraded to 819 lines, which gave the highest picture definition of any analogue TV system, approximately double the resolution of the British 405-line system. However this is not without a cost, in that the cameras need to produce four times the pixel rate (thus quadrupling the bandwidth), from pixels one-quarter the size, reducing the sensitivity by an equal amount. In practice the 819-line cameras never achieved anything like the resolution that could theoretically be transmitted by the 819 line system, and for color, France reverted to the same 625 lines as the European CCIR system.
Eventually most of Europe switched to the 625-line PAL standard, once more following Germany's example, with France adopting SECAM. Meanwhile in North America the original NTSC 525-line standard from 1941 was retained, although analog television will be totally replaced for broadcast purposes by a 1080 line digital picture/sound system in February 2009.
See also
