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Telechrome was the first all-electronic single-tube
color television Color television or Colour television is a television transmission technology that includes color information for the picture, so the video image can be displayed in color on the television set. It improves on the monochrome or black-and-white t ...
system. It was invented by well-known Scottish television engineer,
John Logie Baird John Logie Baird FRSE (; 13 August 188814 June 1946) was a Scottish inventor, electrical engineer, and innovator who demonstrated the world's first live working television system on 26 January 1926. He went on to invent the first publicly dem ...
, who had previously made the first public television broadcast, as well as the first color broadcast using a pre-Telechrome system. Telechrome used two
electron gun An electron gun (also called electron emitter) is an electrical component in some vacuum tubes that produces a narrow, collimated electron beam that has a precise kinetic energy. The largest use is in cathode-ray tubes (CRTs), used in nearly ...
s aimed at either side of a thin, semi-transparent
mica Micas ( ) are a group of silicate minerals whose outstanding physical characteristic is that individual mica crystals can easily be split into extremely thin elastic plates. This characteristic is described as perfect basal cleavage. Mica is ...
sheet. One of the sides was covered in
cyan Cyan () is the color between green and blue on the visible spectrum of light. It is evoked by light with a predominant wavelength between 490 and 520 nm, between the wavelengths of green and blue. In the subtractive color system, or CMYK col ...
phosphor and the other red-orange, producing a limited
color gamut In color reproduction, including computer graphics and photography, the gamut, or color gamut , is a certain ''complete subset'' of colors. The most common usage refers to the subset of colors which can be accurately represented in a given ci ...
, but well suited to displaying skin tones. With minor modifications, the system could also be used to produce 3D images. Telechrome was selected as the basis for a UK-wide television standard by a committee in 1944, but the difficult task of converting the two-color system to three-color
RGB The RGB color model is an additive color model in which the red, green and blue primary colors of light are added together in various ways to reproduce a broad array of colors. The name of the model comes from the initials of the three addi ...
was still underway when Baird died in 1946. The introduction of the
shadow mask The shadow mask is one of the two technologies used in the manufacture of cathode-ray tube (CRT) televisions and computer monitors which produce clear, focused color images. The other approach is the aperture grille, better known by its tr ...
design by
RCA The RCA Corporation was a major American electronics company, which was founded as the Radio Corporation of America in 1919. It was initially a patent trust owned by General Electric (GE), Westinghouse, AT&T Corporation and United Fruit Comp ...
produced a workable solution for color television, albeit one with considerably less image brightness. Interest in alternative systems like the Telechrome or Geer tube faded by the late 1950s. The only alternatives to see widespread use were
General Electric General Electric Company (GE) is an American multinational conglomerate founded in 1892, and incorporated in New York state and headquartered in Boston. The company operated in sectors including healthcare, aviation, power, renewable ene ...
's slot-mask, and
Sony , commonly stylized as SONY, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan. As a major technology company, it operates as one of the world's largest manufacturers of consumer and professional ...
's
Trinitron Trinitron was Sony's brand name for its line of aperture-grille-based CRTs used in television sets and computer monitors. One of the first truly innovative television systems to enter the market since the 1950s, the Trinitron was announced in ...
, both were modifications of the RCA concept. All CRT-based methods have since been almost completely replaced by LCD television, starting in the 1990s.


Background


Mechanical and hybrid color

Baird performed one of the earliest public demonstrations of color television system on 3 July 1928 using an all-mechanical system with three Nipkow disk scanners synchronized with a single disk on the receiving end and three colored lights that were turned on and off in synchronicity with the broadcaster. The same basic system was used on 4 February 1938 to create the first color broadcast transmissions from
The Crystal Palace The Crystal Palace was a cast iron and plate glass structure, originally built in Hyde Park, London, Hyde Park, London, to house the Great Exhibition of 1851. The exhibition took place from 1 May to 15 October 1851, and more than 14,000 exhibit ...
to the
Dominion Theatre The Dominion Theatre is a West End theatre and former cinema on Tottenham Court Road, close to St Giles Circus and Centre Point, in the London Borough of Camden. Planned as primarily a musical theatre, it opened in 1929, but the following year ...
in
London London is the capital and List of urban areas in the United Kingdom, largest city of England and the United Kingdom, with a population of just under 9 million. It stands on the River Thames in south-east England at the head of a estuary dow ...
. Baird was not the only one to experiment with mechanical color television, and a number of similar devices were demonstrated throughout this period, but Baird is recorded as the first to show a real over-the-air transmission in a public demonstration. In 1940 he introduced a much better solution using a system known today as hybrid color. This used a traditional black and white CRT with a rotating colored filter in front. Three frames, sent one after the other in a system known as ''sequential scan'', were displayed on the CRT while the colored wheel was spun in synchronicity. This design was physically very long, leading to deep receiver chassis, but later versions folded the optical path using mirrors to produce a somewhat more practical system. Again, Baird was not the only one to produce such a system, with CBS displaying a very similar system at almost the same time. However, Baird was not happy with the design later stated that a fully electronic device would be better.


Fully electronic systems

The basic problem facing designers of color televisions was this: sending each frame of the moving image meant sending three complete images, one each for red, green and blue. Sequential systems, like Baird's earlier efforts, sent the three images one after another. In order for motion to appear smooth, images must change at least 16 times a second. To reduce flicker, over 40 frames per second (fps) is mandatory. For this reason, very high refresh (field) rates were necessary. CBS' system refreshed at 144 fps, 48 fps for each individual color. (
Peter Carl Goldmark Peter Carl Goldmark (born Péter Károly Goldmark; December 2, 1906 – December 7, 1977) was a Hungarian-American engineer who, during his time with Columbia Records, was instrumental in developing the long-playing microgroove 33 rpm phonogr ...
's CBS team tried several field rates. Within the 6 MHz allowable channel bandwidth, the most acceptable rate was 144 fps. This rate made pictures incompatible with existing systems working at 50 or 60 Hz. A system sending all three signals at the same time at a conventional refresh rate would be greatly preferable. Transmitting such a signal could be accomplished by using three camera tubes, each with a color filter in front of them, using mirrors or prisms to aim at the same scene through a single lens. Each signal would then be separately broadcast using three conventional TV channels, and using the
luminance Luminance is a photometric measure of the luminous intensity per unit area of light travelling in a given direction. It describes the amount of light that passes through, is emitted from, or is reflected from a particular area, and falls with ...
concept, one of those could be received on a conventional black and white set. This would use a considerable amount of
bandwidth Bandwidth commonly refers to: * Bandwidth (signal processing) or ''analog bandwidth'', ''frequency bandwidth'', or ''radio bandwidth'', a measure of the width of a frequency range * Bandwidth (computing), the rate of data transfer, bit rate or thr ...
, but this was a small cost in the era of only a few television channels. The problem, however, was how to combine the three separate signals back into a single display. The system used in the cameras, with three separate tubes combined together optically, was not practical due to the cost of a receiver set with three CRTs as well as the unwieldily chassis needed to contain them. One such example was the
RCA The RCA Corporation was a major American electronics company, which was founded as the Radio Corporation of America in 1919. It was initially a patent trust owned by General Electric (GE), Westinghouse, AT&T Corporation and United Fruit Comp ...
Triniscope, which produced useful images but was extremely complex, required constant adjustment, and was the size of a contemporary refrigerator to produce a display. A number of experiments were carried out using more conventional tubes and then filtering them, but the low output of the CRTs produced very dim images that were dismissed as impractical. Baird had previously worked on a high-intensity CRT system known as the "teapot tube" that saw some use in the UK and US as a projection system in theatres. These were normally built with two such CRTs side-by-side, with one acting as a hot backup in case the primary tube failed. In 1941 Baird converted a teapot projector to produce a two-color image by placing filters in front of the two tubes and projecting them onto a smaller screen to improve the effective intensity. He first showed this in 1941, and in 1942 the BBC described the resulting color image as "entirely natural". The image, of Paddy Naismith, is the first known image of color television to be published. A projection system with two CRTs was better than three, but still not practical for a home receiver. Baird continued to consider other solutions. One used a single conventional CRT with the two images displayed in a single frame, with the top half of the image containing the image for one color and the bottom the other. Lens systems focused on the display were positioned to see only the top or bottom image, passed them through filters, and then recombined them on a screen. There were drawings showing a similar system with three frames. Like many similar efforts from other experimenters, Baird abandoned this approach.


Two-gun Telechrome

Still searching for a single-tube solution that was bright enough for direct viewing, in 1942 Baird hit upon the Telechrome concept. His solution was essentially to combine two tubes into one large spherical enclosure. In the center of the enclosure was a translucent
mica Micas ( ) are a group of silicate minerals whose outstanding physical characteristic is that individual mica crystals can easily be split into extremely thin elastic plates. This characteristic is described as perfect basal cleavage. Mica is ...
sheet forming the display, covered on one side with
cyan Cyan () is the color between green and blue on the visible spectrum of light. It is evoked by light with a predominant wavelength between 490 and 520 nm, between the wavelengths of green and blue. In the subtractive color system, or CMYK col ...
phosphor A phosphor is a substance that exhibits the phenomenon of luminescence; it emits light when exposed to some type of radiant energy. The term is used both for fluorescent or phosphorescent substances which glow on exposure to ultraviolet or v ...
, the other with an orange-red color, producing a limited but useful
color gamut In color reproduction, including computer graphics and photography, the gamut, or color gamut , is a certain ''complete subset'' of colors. The most common usage refers to the subset of colors which can be accurately represented in a given ci ...
. Two
electron gun An electron gun (also called electron emitter) is an electrical component in some vacuum tubes that produces a narrow, collimated electron beam that has a precise kinetic energy. The largest use is in cathode-ray tubes (CRTs), used in nearly ...
s arranged on either side of the screen fired at it, producing the two colors. The image was viewed from one side, seeing one of the colors directly and the other being transmitted through the screen from the other side. This was the first single-tube color television system. The earliest test models used screens only a few inches across and had the guns arranged almost at right angles to it, making for a very large tube. Later models were built inside very large Hackbridge-Hewittic (H-H) vacuum tubes, which the company originally designed for use as high-power
rectifier A rectifier is an electrical device that converts alternating current (AC), which periodically reverses direction, to direct current (DC), which flows in only one direction. The reverse operation (converting DC to AC) is performed by an inve ...
s in power supplies. Arthur Johnson, a glass blower who had previously worked for both Baird and H-H, produced the new models. These had screens ten inches across, comparable to monochrome screens of the era. The guns fired upward at about a 45 degree angle, allowing them to sit below the display in the chassis. As was the case in the teapot tube, the necks were very long. Baird also demonstrated the use of the two-gun tube as the basis for
stereoscopic Stereoscopy (also called stereoscopics, or stereo imaging) is a technique for creating or enhancing the illusion of depth in an image by means of stereopsis for binocular vision. The word ''stereoscopy'' derives . Any stereoscopic image is ...
3D television. Baird's image pickup was a flying-spot scanner. This scanner produced alternating blue-green and orange-red scanning beams. Beam separation provided the necessary parallax for anaglyph stereo pictures. Viewers wore colored glasses. The glasses steered the images: One eye saw only the orange-red image. The other eye saw only the blue-green image. This stereoscopic viewing method is identical to the process in
Anaglyph 3D Anaglyph 3D is the stereoscopic 3D effect achieved by means of encoding each eye's image using filters of different (usually chromatically opposite) colors, typically red and cyan. Anaglyph 3D images contain two differently filtered colored ...
movies.


Three-gun Telechrome

The colour gamut of the two-gun system was limited, unable to produce strong greens or blues. To produce a wider gamut, a system using the three primary colours would be needed. For two colours one can aim at either side of the screen, but for three there is no "third side" that can be used. Baird's solution used a variation on his two-colour system, using one side of the screen as-is, and patterning the other side with a series of horizontal triangular ridges. One gun, normally shown as red in most diagrams, fired onto the flat side of the screen, as in the two-colour model. The other two guns were arranged above and below the ridged side of the screen, so they fired onto one side or the other of the ridges. These were coloured green and blue. When all three guns fired, the image would be combined into a single display. The problem with this approach was that it was very difficult to focus the electron guns on the ridges without the signal bleeding over to the ridges on either side. This problem was compounded by the changing angle between the gun and the ridges as the signal progressed down the screen. Similar designs were attempted by a number of researchers, the best known was the Geer tube that used pyramid-shaped patterns with three guns arranged around the back. None of these systems could ever be made to work reliably, with focusing and alignment being continual problems. There is no documentary evidence that a successful version of the three-gun Telechrome tube was ever built, although images of Baird holding what is claimed to be a prototype are widely duplicated. The image shows a three-neck tube, but the third neck is the original Hewittic port, now used to hold the internal screen. Burns published a typical photo of the two-gun, three-neck tube. Baird also described a 3D system using the ridged tube that eliminated the need for glasses. In this case, the tube was rotated so the peaks ran vertically instead of horizontally and the red gun was removed. The guns formerly used for green and blue were now used for left and right images. The basic concept is identical to the
lenticular printing Lenticular printing is a technology in which lenticular lenses (a technology also used for 3D displays) are used to produce printed images with an illusion of depth, or the ability to change or move as they are viewed from different angles. E ...
system used in magazines and other printed materials to produce 3D images. However, there is no evidence such a system was ever trialled.


Public demonstrations

Baird gave a number of demonstrations of the two-color system throughout the war, and held a full press demonstration on 12 August 1944. These were generally reported in glowing terms, notably an October 1944 report in ''Electronics'' that described the images as bright and the 3D effect "excellent". Not all reports were so positive. One concluded that Baird had "done a real service in demonstrating the value of colour television", but suggested that the two-color system would ultimately have to be replaced with a three-color system. They went on to note: They also dismissed the 3D work, which Baird had apparently ended by this point, as a "stunt".


Telechrome and the Hankey Committee

In 1943, with the war clearly turning in the Allies favor,
Winston Churchill Sir Winston Leonard Spencer Churchill (30 November 187424 January 1965) was a British statesman, soldier, and writer who served as Prime Minister of the United Kingdom twice, from 1940 to 1945 during the Second World War, and again from ...
formed a series of committees to consider post-war redevelopment. Among these were plans to re-open the
Alexandra Palace Alexandra Palace is a Grade II listed entertainment and sports venue in London, situated between Wood Green and Muswell Hill in the London Borough of Haringey. It is built on the site of Tottenham Wood and the later Tottenham Wood Farm. Origi ...
broadcaster, and more widely, nationwide television. To consider this, in September 1943 Churchill formed the Television Committee, better known to history as the Hankey Committee. The Committee met numerous times during the next year, and asked Baird to prepare a number of papers on the topic of post-war broadcasting. Among his suggestions, he stated that the BBC's monopoly should be ended and independent broadcasters should be licensed, which was delivered along with a request to start such a service. The Committee agreed with this position. He also described the Telechrome system, and this appears to have had a great impact on the Committee. In his comments to the Hankey Television Committee, Baird suggested two-color, 1,000-line pictures. Such pictures would have required considerable radio bandwidth. The pictures would be incompatible with the pre-war, EMI / BBC, 405-line system. Before the Hankey Committee, Baird also considered the possibility of compatible color systems. In December 1944, the committee delivered its preliminary report. The report called for a system that had "on the order of 1,000 lines" of resolution. The system would optionally be capable of color and 3D displays. The system also be able to run beside the pre-war 405-line system by Marconi and EMI. Baird was called to a 29 February 1944 meeting of Cable and Wireless (C&W) to discuss the formation of a color television studio. After some discussion, C&W chairman Edward Wilshaw noted that there was an agreement in place that precluded Marconi from entering the market until 1949, which would place them at a significant disadvantage compared to other companies. He suggested that the matter be deferred, as any immediate changes would produce friction between C&W, the
General Post Office The General Post Office (GPO) was the state postal system and telecommunications carrier of the United Kingdom until 1969. Before the Acts of Union 1707, it was the postal system of the Kingdom of England, established by Charles II in 1660. ...
and the BBC. The matter was dropped, and it would not be until the
Television Act 1954 The Television Act 1954 was a British law which permitted the creation of the first commercial television network in the United Kingdom, ITV. Until the early 1950s, the only television service in Britain was operated as a monopoly by the Briti ...
that the possibility was again considered.


Telechrome ends

From 1944 Baird was suffering from increasingly poor health, and late that year he suffered an attack of fever that left him almost invalid. Nevertheless, he formed a new company, John Logie Baird Ltd., with offices and labs in a downtown London house. Baird visited the lab less and less frequently over time, and his wife noticed why in a November 1945 visit when he was seen to have to stop and pant after climbing every stair of the building's four stories. He caught a cold over Christmas 1945, and suffered a stroke in February 1946. He was ordered bedridden but refused to stay there, and continued to deteriorate until his death on 14 June. Telechrome died with Baird, but the company by this time had introduced its first truly successful product. This combined a black and white television, a radio receiver and a record-changing
record player A phonograph, in its later forms also called a gramophone (as a trademark since 1887, as a generic name in the UK since 1910) or since the 1940s called a record player, or more recently a turntable, is a device for the mechanical and analogu ...
in a single large cabinet. The company was purchased in 1948 and switched hands several times, eventually being used as a brand name by
Thorn Electrical Industries Thorn Electrical Industries Limited was a British electrical engineering company. It was listed on the London Stock Exchange, but merged with EMI Group to form Thorn EMI in 1979. It was de-merged in 1996 and became a constituent of the FTSE 100 ...
for a time.


Telechrome and Trinitron

Many years later, former Baird employee Edward Anderson was quoted as saying that they "had the equivalent of the Sony Trinitron tube on the drawing board". This has been used by a number of non-technical authors to suggest that the
Trinitron Trinitron was Sony's brand name for its line of aperture-grille-based CRTs used in television sets and computer monitors. One of the first truly innovative television systems to enter the market since the 1950s, the Trinitron was announced in ...
is in some way technically related to the Telechrome in spite of the two systems having nothing in common.


Patents

*


References


Citations


Bibliography

* * * * * * * {{cite journal , url=https://books.google.com/books?id=it8DAAAAMBAJ , journal=Popular Mechanics , date=March 1945 , title=Television in Color With a Two-Sided Screen , ref=CITEREFTwoSided1945


External links


Telechrome tube
the only remaining Telechrome, the original 4-inch model. History of television Television technology Vacuum tube displays Early color television