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Analog Television

Analog television

Analog television encodes television picture information as an analog signal, that is, by varying the voltages and/or frequencies of the signal. All systems preceding digital television can be considered analog. Common analog television systems:
- NTSC
- PAL
- SÉCAM
- Slow-scan television
- Narrow-bandwidth television

External links

- [http://www.ee.washington.edu/conselec/CE/kuhn/ntsc/95x4.htm Conventional Analog Television - An Introduction] Category:Video and movie technology

Television

: Television is a telecommunication system for broadcasting and receiving moving pictures and sound over a distance. The term has come to refer to all the aspects of television programming and transmission as well. programming ]]

History

The development of television technology can be partitioned along two lines: those developments that depended upon both mechanical and electronic principles, and those which are purely electronic. From the latter descended all modern televisions, but these would not have been possible without discoveries and insights from the mechanical systems. The word television is a hybrid word, created from both Greek and Latin. Tele- is Greek for "far", while -vision is from the Latin visio, meaning "vision" or "sight". It is often abbreviated as TV or the telly.

Electromechanical television

The German student Paul Gottlieb Nipkow proposed and patented the first electromechanical television system in 1885. Nipkow's spinning disk design is credited with being the first television image rasterizer. However, it wasn't until 1907 that developments in amplification tube technology made the design practical. Meanwhile, 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. Perskeyi's paper reviewed the existing electromechanical technologies, mentioning the work of Nipkow and others. 1900 In 1911, Boris Rosing and his student Vladimir Kosma Zworykin achieved 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." Zworykin later went to work for RCA to build a purely electronic television, the design of which was eventually found to violate patents by Philo Taylor Farnsworth. On March 25, 1925, Scottish inventor John Logie Baird gave a demonstration of televised silhouette images at Selfridge's Department Store in London. But if television is defined as the transmission of live, moving, half-tone (grayscale) images, and not silhouette or still images, Baird achieved this privately on October 2, 1925, and 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 disc embedded with a double spiral of lenses, had only 30 lines, just enough to reproduce a recognizable human face. 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 colour, infrared (dubbed "Noctovision"), and stereoscopic television, using additional lenses, disks and filters. In parallel he developed a video disk recording system dubbed "Phonovision"; a number of the Phonovision[http://www.tvdawn.com/tvimage.htm] recordings, dating back to 1927, still exist. In 1929 he became involved in the first experimental electromechanical television service in Germany. 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. 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 disc scanner with 48 lines per picture, 16 pictures per second. AT&T's Bell Telephone Laboratories transmitted half-tone images of transparencies in May 1925. But Bell Labs gave the most dramatic demonstration of television yet on April 7, 1927, when it 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, which included Secretary of Commerce Herbert Hoover, were illuminated by a flying spot beam and scanned by a 50-aperture disc at 16 pictures per second.

Electronic television

Herbert Hoover Although the discoveries of Nipkow, Rosing, Baird and others were extraordinary, little of their technology is used in modern television. By 1934, all electromechanical television systems were outmoded, although electromechanical broadcasts continued on some stations until 1939. A.A. Campbell-Swinton wrote a letter to Nature on the 18 June 1908 describing his concept of electronic television using the cathode ray tube, which had been invented in 1897 by the German physicist and Nobel prize winner Karl Ferdinand Braun. He proposed using an electron beam in both the camera and the receiver, which could be steered electronically to produce moving pictures. He lectured on the subject in 1911 and displayed circuit diagrams, but no one, including Swinton, knew how to realize the design. Although his system was never built, the cathode ray tube did come to be used to display images in almost all television sets and computer monitors until the invention of the LCD panel. A fully electronic system was first achieved by Philo Taylor Farnsworth on September 7, 1927, although the low-resolution, light-insensitive camera tube limited the image to a plate of glass painted black, with a straight line etched across it, rotated in front of a bright carbon arc lamp. Seven years later, on August 25, 1934, at the Franklin Institute in Philadelphia, Farnsworth gave the world's first public demonstration of a working, all-electronic television system, with 220 lines per picture, 30 pictures per second. Over a three week period, vaudeville acts, athletic and sports demonstrations, politicians, and hundreds of ordinary citizens were captured on Farnsworth's cameras in the open air and simultaneously shown on his receiving sets. Farnsworth, a Mormon farm boy from Rigby, Idaho, first envisioned his system at age 14. He discussed the idea with his high school chemistry teacher, who could think of no reason why it would not work (Farnsworth would later credit this teacher, Justin Tolman, as providing key insights into his invention). He continued to pursue the idea at Brigham Young Academy (now Brigham Young University). At age 21, he demonstrated a working system at his own laboratory in San Francisco. His breakthrough freed television from reliance on spinning discs and other mechanical parts. All modern picture tube televisions descend directly from his design. Vladimir Kosma Zworykin is also sometimes cited as the father of electronic television because of his invention of the iconoscope in 1923 and his invention of the kinescope in 1929. His design was one of the first to demonstrate a television system with all the features of modern picture tubes. His previous work with Rosing on electromechanical television gave him key insights into how to produce such a system, but his (and RCA's) claim to being its original inventor was largely invalidated by three facts: a) Zworykin's 1923 patent presented an incomplete design, incapable of working in its given form (it was not until 1933 that Zworykin achieved a working implementation), b) the 1923 patent application was not granted until 1938, and not until it had been seriously revised, and c) courts eventually found that RCA was in violation of the television design patented by Philo Taylor Farnsworth, whose lab Zworykin had visited while working on his designs for RCA. The controversy over whether it was first Farnsworth or Zworykin who invented modern television is still hotly debated today. Some of this debate stems from the fact that while Farnsworth appears to have gotten there first as an inventor, RCA brought television sets to market before Farnsworth, and it was RCA employees who first wrote the history of television. Even though Farnsworth eventually won the legal battle over this issue, he was never able to fully capitalize financially on his invention.

Color television

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. Color television in the United States had a protracted history due to conflicting technical systems vying for approval by the Federal Communications Commission for commercial use. Mechanically scanned color television was demonstrated by Bell Laboratories in June 1929 using three complete systems of photoelectric cells, amplifiers, glow-tubes, and color filters, with a series of mirrors to superimpose the red, green, and blue images into one full color image. In the electronically scanned era, the first color television demonstration was on February 5, 1940, when RCA privately showed to members of the FCC at the RCA plant in Camden, New Jersey, a television receiver producing images in color by a field sequential color system. CBS began non-broadcast color experiments using film as early as August 28, 1940, and live cameras by November 12. The CBS "field sequential" color system was partly mechanical, with a disc made of red, blue, and green filters spinning inside the television camera at 1,200 rpm, and a similar disc spinning in synchronization in front of the cathode ray tube inside the receiver set. RCA's later "dot sequential" color system had no moving parts, using a series of dichroic mirrors to separate and direct red, green, and blue light from the subject through three separate lenses into three scanning tubes, and electronic switching that allowed the tubes to send their signals in rotation, dot by dot. These signals were sorted by a second switching device in the receiver set and sent to red, green, and blue picture tubes, and combined by a second set of dichroic mirrors into a full color image. The first field test (i.e., broadcast) of color television was by NBC (owned by RCA) on February 20, 1941. CBS began daily color field tests on June 1, 1941. These color systems were not compatible with existing black and white television sets, and as no color television sets were available to the public at this time, viewership of the color field tests was limited to RCA and CBS engineers and the invited press. The War Production Board halted the manufacture of television and radio equipment for civilian use from April 1, 1942 to October 1, 1945, limiting any opportunity to introduce color television to the general public. The post-war development of color television was dominated by three systems competing for approval by the FCC as the U.S. color broadcasting standard: CBS's field sequential system, which was incompatible with existing black and white sets without an adaptor; RCA's dot sequential system, which in 1949 became compatible with existing black and white sets; and CTI's system (also incompatible with existing black and white sets), which used three camera lenses, behind which were color filters that produced red, green, and blue images side by side on a single scanning tube, and a receiver set that used lenses in front of the picture tube (which had sectors treated with different phosphorescent compounds to glow in red, green, or blue) to project these three side by side images into one combined picture on the viewing screen. After a series of hearings beginning in September 1949, the FCC found the RCA and CTI systems fraught with technical problems, inaccurate color reproduction, and expensive equipment, and so formally approved the CBS system as the U.S. color broadcasting standard on October 11 1950. An unsuccessful lawsuit by RCA delayed the world's first network color broadcast until June 25 1951, when a musical variety special titled simply Premiere was shown over a network of five east coast CBS affiliates. Viewership was again extremely limited: the program could not be seen on black and white sets, and Variety estimated that only thirty prototype color receivers were available in the New York area. Regular color broadcasts began that same week with the daytime series The World Is Yours and Modern Homemakers. While the CBS color broadcasting schedule gradually expanded to twelve hours per week (but never into prime time), and the color network expanded to eleven affiliates as far west as Chicago, its commercial success was doomed by the lack of color receivers necessary to watch the programs, the refusal of television manufacturers to create adaptor mechanisms for their existing black and white sets, and the unwillingness of advertisers to sponsor broadcasts seen by almost no one. In desperation, CBS bought a television manufacturer, and on September 20, 1951, production began on the first and only CBS color television model. But it was too little, too late. Only 200 sets had been shipped, and only 100 sold, when CBS pulled the plug on its color television system on October 20, 1951, and bought back all the CBS color sets it could to prevent law suits by disappointed customers. Starting before CBS color even got on the air, the U.S. television industry, represented by the National Television System Committee, worked in 1950-1953 to develop a color system that was compatible with existing black and white sets and would pass FCC quality standards, with RCA developing the hardware elements. When CBS testified before Congress in March 1953 that it had no further plans for its own color system, the path was open for the NTSC to submit its petition for FCC approval in July 1953, which was granted in December. The first publicly announced experimental TV broadcast of a program using the NTSC-RCA "compatible color" system was an episode of NBC's Kukla, Fran and Ollie on August 30, 1953. NBC made the first coast-to-coast color broadcast when it covered the Tournament of Roses Parade on January 1 1954, with public demonstrations given across the United States on prototype color receivers. A few days later Admiral brought out the first commercially made color television set using the RCA standards, followed in March by RCA's own model. Television's first prime time network color series was The Marriage, a situation comedy broadcast live by NBC in the summer of 1954. NBC's anthology series Ford Theatre became the first color filmed series that October. NBC was naturally at the forefront of color programming because its parent company RCA manufactured the most successful line of color sets in the 1950s. CBS and ABC, which were not affiliated with set manufacturers, and were not eager to promote their competitor's product, dragged their feet into color, with ABC delaying its first color series (The Flintstones and The Jetsons) until 1962. The Du Mont network, although it did have a television-manufacturing parent company, was in financial decline by 1954 and was dissolved two years later. Thus the relatively small amount of network color programming, combined with the high cost of color television sets, meant that as late as 1964 only 3.1 percent of television households in the U.S. had a color set. NBC provided the catalyst for rapid color expansion by announcing that its prime time schedule for fall 1965 would be almost entirely in color (the exception being I Dream of Jeannie). All three broadcast networks were airing full color prime time schedules by the 1966–67 broadcast season. But the number of color television sets sold in the U.S. did not exceed black and white sales until 1972, which was also the first year that more than fifty percent of television households in the U.S. had a color set. In Mexico, Guillermo González Camarena (1917–1965), invented the early color television transmission system. He received patents for color television systems in 1940 (U.S. Patent 1942 (2296019), 1960 and 1962. The 1942 patent was for a mechanically scanned color filter adapter for an existing monochrome electronic transmission system. In August 31, 1946 he sent his first color transmission from his lab in the offices of The Mexican League of Radio Experiments in Lucerna St. #1, in Mexico City. The video signal was transmitted at a frequency of 115 MHz. and the audio in the 40 metre band. European color television was developed somewhat later and was hindered by a continuing division on technical standards. Having decided to adopt a higher-definition 625-line system for monochrome transmissions, with a lower frame rate but with a higher overall bandwidth, Europeans could not directly adopt the U.S. color standard, which was widely perceived as wanting anyway, because of its tint control problems. There was also less urgency, since there were fewer commercial motivations, European television broadcasters being predominantly state-owned at the time. As a consequence, although work on various color encoding systems started already in the 1950s, with the first SECAM patent being registered in 1956, many years had passed till the first broadcasts actually started in 1967. Unsatisfied with the performance of NTSC and of initial SECAM implementations, the Germans unveiled PAL (phase alternating line) in 1963, staying closer to NTSC but borrowing some ideas from SECAM. The French continued with SECAM, notably involving Russians in the development. The first regular colour broadcasts in Europe were by BBC2 beginning on July 1, 1967, using PAL. Germans did their first broadcast in September (PAL), while the French in October (SECAM). PAL was eventually adopted by West Germany, the UK, Australia, New Zealand, much of Africa, Asia and South America, and most Western European countries except France. In addition to France and Luxembourg, SECAM was adopted by Soviet Union, much of Eastern Europe, much of Africa and of the Middle East. Both systems broadcast on UHF frequencies, the VHF being used for legacy black and white, 405 lines in UK or 819 lines in France, till the beginning of the eighties. It should be noted that some British television programmes, particularly those made by or for ITC Entertainment, were made in colour before the introduction of colour television to the UK, for the purpose of sales to US networks. The first British show to be made in colour was the drama series The Adventures of Sir Lancelot (1956-57), which was initially made in black and white but later shot in colour for sale to the NBC network in the United States. In Japan, NHK introduced color television in the year 1960.

Broadcast television

NHK The first regularly scheduled television service in the United States began on July 2, 1928. The Federal Radio Commission authorized C.F. Jenkins to broadcast from experimental station W3XK in a suburb of Washington, D.C. But for at least the first eighteen months, only silhouette images from motion picture film were broadcast due to the narrow 10kHz bandwidth allotted by the FRC. General Electric's experimental station in Schenectady, New York, on the air sporadically since January 13, 1928, was able to broadcast reflected-light, 48-line images via shortwave as far as Los Angeles, and by September was making four television broadcasts weekly. CBS's New York City station W2XAB began broadcasting the first regular seven days a week television schedule in the United States on July 21, 1931, with a 60-line electromechanical system. The first broadcast included Mayor Jimmy Walker, the Boswell Sisters, Kate Smith, and George Gershwin. The service ended in February 1933. By 1935, electromechanical television broadcasting had ceased in the United States except for a handful of stations run by public universities that continued to 1939. The Federal Communications Commission saw television in the continual flux of development with no consistent technical standards, hence all such stations in the U.S. were granted only experimental and not commercial licenses, hampering television's economic development. Just as importantly, Philo Farnsworth's 1934 demonstration of an all-electronic system pointed the direction of television's future. On June 15, 1936, Don Lee Broadcasting began a month-long demonstration of all-electronic television in Los Angeles on W6XAO (later KTSL) with a 300-line image from motion picture film. RCA demonstrated in New York City a 343-line electronic television broadcast, with live and film segments, to its licensees on July 7, 1936, and made its first public demonstration to the press on November 6. By April 1939, regularly scheduled 441-line electronic television broadcasts were available in New York City and Los Angeles, and by November on General Electric's station in Schenectady. With the adoption of NTSC television engineering standards in 1941, the FCC saw television ready for commercial licensing, with the first such licenses issued to NBC and CBS owned stations in New York on July 1, 1941, followed by Philco's station in Philadelphia. Electromechanical broadcasts began in Germany in 1929, but were without sound until 1934. Network electronic service started on March 22, 1935, on 180 lines using only telecine transmission of film or an intermediate film system. Live transmissions began on January 15, 1936. The Berlin Summer Olympic Games were televised, using both direct television and intermediate film cameras, to 28 public television rooms in Berlin and Hamburg in August 1936. The Germans had a 441-line system on the air in February 1937, and during World War II brought it to France, where they broadcast off the Eiffel Tower. The first British television broadcast was made by Baird Television's electromechanical system over the BBC radio transmitter in September 1929. Baird provided a limited amount of programming five days a week by 1930. On August 22, 1932, BBC launched its own regular service using Baird's 30-line electromechanical system, continuing until September 11, 1935. On November 2, 1936 the BBC began broadcasting a dual-system service, alternating on a weekly basis between Marconi-EMI's 405-line standard and Baird's improved 240-line standard, from Alexandra Palace in London, making the BBC the world's first regular high-definition television service. The corporation decided that Marconi-EMI's electronic picture gave the superior picture, and the Baird system was dropped in February 1937. The outbreak of the Second World War caused the BBC service to be suspended on September 1, 1939, resuming from Alexandra Palace on June 7, 1946. The Soviet Union began offering 30-line electromechanical test broadcasts in Moscow on October 31, 1931, and a commercially manufactured television set in 1932. The first experimental transmissions of electronic television took place in Moscow on March 9, 1937, using equipment manufactured and installed by RCA. Regular broadcasting began on December 31, 1938. The first regular television transmissions in Canada began in 1952 when the CBC put two stations on the air, one in Montreal, Quebec on September 6, and another in Toronto, Ontario two days later. two days later The first live transcontinental television broadcast took place in San Francisco, California from the Japanese Peace Treaty Conference on September 4, 1951. In 1958, the CBC completed the longest television network in the world, from Sydney, Nova Scotia to Victoria, British Columbia. Reportedly, the first continuous live broadcast of a breaking news story in the world was conducted by the CBC during the Springhill Mining Disaster which began on October 23 of that year. Programming is broadcast on television stations (sometimes called channels). At first, terrestrial broadcasting was the only way television could be distributed. Because bandwidth was limited, government regulation was normal. In the U.S., the Federal Communications Commission allowed stations to broadcast advertisements, but insisted on public service programming commitments as a requirement for a license. By contrast, the United Kingdom chose a different route, imposing a television licence fee on owners of television reception equipment, to fund the BBC, which had public service as part of its Royal Charter. Development of cable and satellite means of distribution in the 1970s pushed businessmen to target channels towards a certain audience, and enabled the rise of subscription-based television channels, such as HBO and Sky. Practically every country in the world now has developed at least one television channel. Television has grown up all over the world, enabling every country to share aspects of their culture and society with others. By the late 1980s, 98% of all homes in the U.S. had at least one TV set. On average, Americans watch four hours of television per day. An estimated two-thirds of Americans got most of their news about the world from TV, and nearly half got all of their news from TV. These figures are now estimated to be significantly higher.

Technology

Broadcasting

There are many means of distributing television broadcasts, including both analogue and digital versions of:
- Terrestrial television
- Stratovision (From aircraft flying in a loop)
- Satellite television
- Cable television
- MMDS (Wireless cable)

Receiving

Television sets

In television's electromechanical era, commercially made television sets were sold from 1928 to 1934 in the United Kingdom, United States, and Russia. The earliest commercially made sets sold by Baird in the U.K. and the U.S. 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 "televisor" was also available without the radio. The Baird televisor sold in 1930-1933 is considered the first mass-produced set, selling about a thousand units. The first commercially made electronic television sets with cathode ray tubes were manufactured by Telefunken in Germany in 1934, followed by other makers in Britain (1936) and America (1938). The cheapest of the pre-War World II factory-made American sets, a 1938 image-only model with a 3-inch (8 cm) screen, cost US$125, the equivalent of US$1,732 in 2005. The cheapest model with a 12-inch (30 cm) screen was $445 ($6,256). 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. before the War Production Board halted manufacture in April 1942, which resumed in October 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. 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 four times the resolution of the British 405-line system. Eventually the whole of Europe switched to the 625-line PAL standard, once more following Germany's example. Meanwhile in North America the original NTSC 525-line standard from 1941 was retained. NTSC Television in its original form involves sending images and sound over radio waves in the VHF and UHF bands, which are received by a television set. Over-the-air broadcast television requires an antenna (aerial). This can be an outdoor Yagi antenna. In strong signal areas the antenna can be indoors, attached to or near the receiver, such as an adjustable dipole antenna called "rabbit ears" for the VHF band and a small loop antenna for the UHF band.

Specifications

Modern displays

Starting in the 1990s, modern television sets diverged into three different trends:
- standalone TV sets;
- integrated systems with DVD players and/or VHS VCR capabilities built into the TV set itself (mostly for small size TVs with up to 21" screen, the main idea is to have a complete portable system);
- component systems with separate big-screen video monitor, tuner, audio system which the owner connects the pieces together as a high-end home theater system. This approach appeals to videophiles who prefer components that can be upgraded separately. There are many kinds of video monitors used in modern TV sets. The most common are direct view CRTs for up to 40in (100cm) (in 4:3) and 46in (115cm) (in 16:9) diagonally; most big screen TVs (up to over 100 inch (254 cm)) use projection technology. Three types of projection systems are used in projection TVs: CRT-based, LCD-based, and DLP(reflective micromirror chip)-based. Modern advances have brought flat panels to TV that use active matrix LCD or plasma display technology. Flat panel LCDs and plasma displays are as little as 4in (10cm) thick and can be hung on a wall like a picture or put over a pedestal. They are multifunctional, because they are used like computer monitors too (VGA and DVI or HDMI connections). Some TVs integrate a pair of ports to connect computer cases and peripherals to it or to connect the set to an A/V home network (HAVI) (USB port for cord connection and BlueTooth/WiFi for wireless). Today, some LCD and Plasma sets have SD Card slots, so users can view pictures from a digital camera. On the new Panasonic LCDs and Plasmas (Viera), users have the capability to record onto SD card and then play it back on a hand-held PC or digital camera (anything that allows MPEG4). With SD cards now available with 1G of memory (soon 2GB, and Panasonic is also working on one that contains over 30GB of memory), a user can record over 1,000 minutes at low quality, and around 80 minutes on the highest quality. The playback of the recording is not brilliant, but these are the first generation. They will get better with time.

Signal connections

The number of ways to connect a video device to a television has increased over the years: WiFi
- HDMI - a compact 19 to 29 pin connector that carries digital video and digital audio signals. Essentially an enhanced version of DVI that includes digital audio. This is the most advanced form of connection currently available. DVI
- DVI - a 17 to 29 pin connector that carries digital video signals, designed to carry HDTV but also used in current DVD players and latest digital displays. Copy protection is available using HDCP. HDCP
- Component video - three separate RCA jacks (colored red, green and blue) carry three video signals, one brightness (luminance) and two colors (chromas), and is usually referred to as "Y, B-Y, R-Y", "Y Cr Cb" (interlaced) or "Y Pr Pb" (progressive), or YUV. Audio is not carried on this cable. This connection provides for picture quality superior to S-Video and is typically used in home theater for DVDs, satellite and analogue HDTV; less common in Europe but is starting to become more widely available. Europe
- SCART - a large 21 pin connector that may carry: one video signal composite video; or two video signals S-Video; or for picture quality similar to component video, three signals of separate red, green and blue or RGB; or for best picture quality, four video signals of separate red, green, blue and sync or RGBS; plus right and left line-level audio channels; along with a number of control signals including an aspect-ratio flag (e.g. widescreen). This system has been standard in Europe since mid-1980s for all consumer electronics, which meant that RGBS was available on even the earliest PAL DVD players and satellite receivers. Japan uses a 21 pin RGB connector which is visually similar to SCART but with different pin configurations. Japan
- S-Video - small round connector with two separate video signals, one carrying brightness (luminance), the other carrying color (chroma). Also referred to as Y/C video. Provides most of the benefit of component video, with slightly less color fidelity. Use started in the 1980s for S-VHS, Hi-8, and early NTSC DVD players to relay high quality video before component was available. Audio is not carried on this cable. Hi-8
- Composite video - The most common form of connecting external devices, putting all the video information into one signal. Most televisions provide this option with a yellow RCA jack. Audio is not carried on this cable, though two separate cables with similar red and white RCA jacks for right and left line-level audio are commonly bonded to composite video cables.
- Coaxial RF - All audio channels and picture components are transmitted through one coaxial cable and modulated on a radio frequency. Most TVs manufactured during the past 15–20 years accept coaxial connection, and the video is typically "tuned" on channel 3 or 4. This is the type of cable usually used for cable television. Most modern DVD players and other video devices no longer modulate RF output, so very old TV sets made before composite video jacks became commonplace will need a modulator.

Aspect ratios

Mechanically scanned television as first demonstrated by John Logie Baird in 1926 used a 7:3 vertical aspect ratio, oriented for the head and shoulders of a single person in close-up. Most of the early electronic TV systems from the mid-1930s onward shared the same aspect ratio of 4:3 which was chosen to match the Academy Ratio used in cinema films at the time. This ratio was also square enough to be conveniently viewed on round cathode-ray tubes (CRTs), which were all that could be produced given the manufacturing technology of the time. (Today's CRT technology allows the manufacture of much wider tubes, and the flat screen technologies which are becoming steadily more popular have no aspect ratio limitations at all.) The BBC's television service used a more squarish [http://tcc.members.beeb.net/tchistory.html 5:4] ratio from 1936 to circa 1949, when it too switched to a 4:3 ratio. In the 1950s, movie studios moved towards widescreen aspect ratios such as Cinerama in an effort to distance their product from television. Although this was initially just a gimmick widescreen is still the format of choice today and square aspect ratio movies are rare. Some people argued that widescreen is actually a disadvantage when showing objects that are tall instead of panoramic, others would say that natural vision is more panoramic than tall, and therefore widescreen is easier on the eye. The switch to digital television systems has been used as an opportunity to change the standard television picture format from the old ratio of 4:3 (approximately 1.33:1) to an aspect ratio of 16:9 (approximately 1.78:1). This enables TV to get closer to the aspect ratio of modern widescreen movies, which range from 1.78:1 through 1.85:1 to 2.35:1. There are two methods for transporting widescreen content, the better of which uses what is called anamorphic widescreen format. This format is very similar to the technique used to fit a widescreen movie frame inside a 1.33:1 35mm film frame. The image is squashed horizontally when recorded, then expanded again when played back. The anamorphic widescreen 16:9 format was first introduced via European PAL-Plus television broadcasts and then later on "widescreen" DVDs; the ATSC HDTV system uses straight widescreen format, no image squashing or expanding is used. Recently "widescreen" has spread from television to computing where both desktop and laptop computers are commonly equipped with widescreen displays, and it remains to be seen whether Work or movie enjoyment will take over. There are some complaints about distortions of movie picture ratio due to some DVD playback software not taking account of aspect ratios; but this will subside as the DVD playback software matures. Furthermore, computer and laptop widescreen displays are in the 16:10 aspect ratio both physically in size and in pixel counts, and not in 16:9 of consumer televisions, leading to further complexity. This was a result of widescreen computer display engineers' uninformed assumption that people viewing 16:9 content on their computer would prefer that an area of the screen be reserved for playback controls or subtitles, as opposed to viewing content full-screen.

Aspect ratio incompatibility

The television industry changing aspect ratios is not without teething difficulties, and can present a considerable problem. Displaying a widescreen aspect (rectangular) image on a conventional aspect (square) display can be shown:
- in "letterbox" format, with black horizontal bars at the top and bottom
- with part of the image being cropped, usually the extreme left and right of the image being cut off (or in "pan and scan", parts selected by an operator)
- with the image horizontally compressed A conventional aspect (square) image on a widescreen aspect (rectangular) display can be shown:
- in "pillarbox" format, with black vertical bars to the left and right
- with upper and lower portions of the image cut off
- with the image horizontally distorted A common compromise is to shoot or create material at an aspect ratio of 14:9, and to lose some image at each side for 4:3 presentation, and some image at top and bottom for 16:9 presentation. Horizontal expansion has advantages in situations in which several people are watching the same set, as it compensates for watching at an oblique angle.

Sound

Television add-ons

Today there are many add-ons for the television set. A few add-ons include Video Game Consoles, VCRs, Cable Boxes, Satellite Boxes, DVD players, or Digital Video Recorders, the television add-on market is ever growing.

New developments

- Broadcast flag
- CableCARD™
- Digital Light Processing (DLP)
- Digital Rights Management (DRM)
- Digital television (DTV)
- Digital Video Recorders
- Direct Broadcast Satellite TV (DBS)
- DVD
- Flicker-free (100Hz)
- High Definition TV (HDTV)
- High-Definition Multimedia Interface (HDMI)
- IPTV
- Internet television
- LCD and Plasma display Flat Screen TV
- Pay Per View
- Picture-in-picture (PiP)
- Video on-demand (VOD)
- Ultra High Definition Video (UHDV)
- Web TV

Geographical usage

Content

Advertising

Since their inception in the USA in 1941, TV commercials have become one of the most effective, most pervasive, and most popular methods of selling products of many sorts, especially consumer goods. U.S. advertising rates are determined primarily by Nielsen ratings. The exception to this is the publicly-funded British Broadcasting Corporation.

Programming

Getting TV programming shown to the public can happen in many different ways. After production the next step is to market and deliver the product to whatever markets are open to using it. This typically happens on two levels: #Original Run or First Run - a producer creates a program of one or multiple episodes and shows it on a station or network which has either paid for the production itself or to which a license has been granted by the producers to do the same. #Syndication - this is the terminology rather broadly used to describe secondary programming usages (beyond original run). It includes secondary runs in the country of first issue, but also international usage which may or may not be managed by the originating producer. In many cases other companies, TV stations or individuals are engaged to do the syndication work, in other words to sell the product into the markets they are allowed to sell into by contract from the copyright holders, in most cases the producers. In most countries, the first wave occurs primarily on FTA television, while the second wave happens on subscription TV and in other countries. In the U.S. however, the first wave occurs on the FTA networks and subscription services, and the second wave travels via all means of distribution. First run programming is increasing on subscription services outside the U.S., but few domestically produced programs are syndicated on domestic FTA elsewhere. This practice is increasing however, generally on digital only FTA channels, or with subscriber-only first run material appearing on FTA. Unlike the U.S., repeat FTA screenings of a FTA network program almost only occur only on that network. Also, affiliates rarely buy or produce non-network programming that isn't intensely local.

Social aspects

Alleged dangers

Paralleling television's growing primacy in family life and society, an increasingly vocal chorus of legislators, scientists and parents are raising objections to the uncritical acceptance of the medium. For example, the Swedish government imposed a total ban on advertising to children under twelve in 1991 (see advertising). In the U.S., the [http://www.mediafamily.org/facts/facts_tveffect.shtml National Institute on Media and the Family] (not a government agency) points out that U.S. children watch an average of 25 hours of television per week and features studies showing it interferes with the educational and maturational process. A February 23 2002 article in [http://www.sciam.com/print_version.cfm?articleID=0005339B-A694-1CC5-B4A8809EC588EEDF Scientific American] suggested that compulsive television watching was no different from any other addiction, a finding backed up by reports of withdrawal symptoms among families forced by

Analog signal

An analog or analogue signal is any variable signal continuous in both time and amplitude. It differs from a digital signal in that small fluctuations in the signal are meaningful. Analog is usually thought of in an electrical context, however mechanical, pneumatic, hydraulic, and other systems may also use analog signals. The word "analog" implies an analogy between cause and effect, voltage in and voltage out, current in and current out, sound in and frequency out. An analog signal uses some property of the medium to convey the signal's information. For example, an aneroid barometer uses rotary position as the signal to convey pressure information. Electrically, the property most commonly used is voltage followed closely by frequency, current, and charge. Any information may be conveyed by an analog signal, often such a signal is a measured response to changes in physical phenomena, such as sound, light, temperature, position, or pressure, and is achieved using a transducer. For example, in an analog sound recording, the variation in pressure of a sound striking a microphone creates a corresponding variation in the current passing through it. An increase in the volume of the sound causes the fluctuation of the current to increase while keeping the same rhythm. The primary disadvantage of analog signalling is that any system has noise—that is, random variations—in it. As the signal is copied and re-copied, or transmitted over long distances, these random variations become dominant. Electrically these losses are lessened by shielding, good connections, and several cable types such as coax and twisted pair. The effects of noise make signal loss and distortion impossible to recover, since amplifying the signal to recover attenuated parts of the signal amplifies the noise as well. Another method of conveying an analog signal is to use modulation. In this, some base signal (e.g., a sinusoidal carrier wave) has one of its properties altered: amplitude modulation involves altering the amplitude of a sinusoidal voltage waveform by the source information, frequency modulation changes the frequency. Other techniques, such as changing the phase of the base signal also work. Analog circuits do not involve quantisation of information into digital format. The concept being measured over the circuit, whether sound, light, pressure, temperature, or an exceeded limit, remains from end to end. Clocks with hands are called analog; those that display digits are called digital. However, many analog clocks are actually digital since the hands do not move in a smooth continuous motion, but in small steps every second or half a second, or every minute with a loud CLUNK. See digital for a discussion of digital vs. analog. Sources: Some of an earlier version of this article was originally taken from Federal Standard 1037C in support of MIL-STD-188.

Frequency

: Frequency is the measurement of the number of times that a repeated event occurs per unit time. It is also defined as the rate of change of phase of a sinusoidal waveform.

Measurement

To calculate the frequency of an event, the number of occurrences of the event within a fixed time interval are counted, and then divided by the length of the time interval. In SI units, the result is measured in hertz (Hz), named after the German physicist Heinrich Rudolf Hertz. 1 Hz means that an event repeats once per second, 2 Hz is twice per second, and so on. This unit was originally called a cycle per second (cps), which is still used sometimes. Other units that are used to measure frequency include revolutions per minute (rpm) and radians per second (rad/s). Heart rate and musical tempo are measured in beats per minute (BPM). An alternative method to calculate frequency is to measure the time between two consecutive occurrences of the event (the period) and then compute the frequency as the reciprocal of this time: :

f = \frac

where T is the period. A more accurate measurement takes many cycles into account and averages the period between each.

Frequency of waves

Measuring the frequency of sound, electromagnetic waves (such as radio or light), electrical signals, or other waves, the frequency in hertz is the number of cycles of the repetitive waveform per second. If the wave is a sound, frequency is what mainly characterizes its pitch. Frequency has an inverse relationship to the concept of wavelength. The frequency f is equal to the speed v of the wave divided by the wavelength λ (lambda) of the wave: :

f = \frac

In the special case of electromagnetic waves moving through a vacuum, then v = c, where c is the speed of light in a vacuum, and this expression becomes: :

f = \frac

NOTE: When waves travel from one medium to another, their frequency remains exactly the same - only their wavelength and/or speed changes.

Invariance

Apart from its being modified by Doppler effect, frequency is an invariant quantity in the universe. That is, it cannot be changed by any physical process unlike velocity of propagation or wavelength.

Examples

- The frequency of the standard pitch A above middle C is usually defined as 440 Hz, that is, 440 cycles per second () and known as concert pitch, to which an orchestra tunes.
- A baby can hear tones with oscillations up to approximately 20,000 Hz, but these frequencies become more difficult to hear as people age.
- In Europe, the frequency of the alternating current in mains is 50 Hz (close to the tone G).
- In North America, the frequency of the alternating current is 60 Hz (close to the tone B flat — that is, a minor third above the European frequency). The frequency of the 'hum' in an audio recording can show where the recording was made — in Europe or in America.

External links

- [http://www.sengpielaudio.com/calculator-wavelength.htm Conversion: frequency to wavelength and back]
- [http://www.sengpielaudio.com/calculator-period.htm Conversion: period, cycle duration, periodic time to frequency] Category:Physical quantity Category:Sound Category:Wave mechanics ko:진동수 ja:周波数 th:ความถี่

Signal (information theory)

In information theory, a signal is the sequence of states of a communications channel that encodes a message, at the transmitter end of the channel. For example, the sequence of characters "Mary had a little lamb" is an example of a message. When it is transmitted by sound, the signal is a time-sequence of air pressures. By the definition of signal, the signal-generating process is a stochastic process, that is, one in which the events of the various states possess probabilities. Conversely, useage of signal in reference to a process that generates a transmitted sequence of states in a communications channel implies that this process is stochastic. When it is not stochastic, misunderstandings can be created. Oldberg. (2005) reports that misunderstandings of this type plague the field of Defect Detection Testing.

Works cited

Oldberg, T., 2005, "An Ethical Problem in the Statistics of Defect Detection Test Reliability," ndt.net, http://www.ndt.net/article/v10n05/oldberg/oldberg.htm .

NTSC

NTSC is the analog television system in use in Korea, Japan, United States, Canada and certain other places, mostly in the Americas (see map). It is named for the National Television System(s) Committee, the industry-wide standardization body that created it.

History

The National Television System Committee was established in 1940 by the Federal Communications Commission (FCC) to resolve the conflicts which had arisen between companies over the introduction of a nationwide analog television system in the U.S. The committee in March 1941 issued a technical standard for black and white television. This built upon a 1936 recommendation made by the Radio Manufacturers Association (RMA) that used 441 lines. With the advancement of the vestigial sideband technique for broadcasting that increased available bandwidth, there was an opportunity to increase the image resolution. The NTSC compromised between RCA's desire to keep a 441-line standard (their NBC TV network was already using it) and Philco's desire to increase it to between 600 and 800, settling on a 525-line transmission. Other technical standards in the final recommendation were an frame rate (image rate) rate of 30 frames per second consisting of 2 interlaced fields per frame (2:1 interlacing) at 262 1/2 lines per field or 60 fields per second along with an aspect ratio of 4 by 3, and frequency modulation for the sound signal. In January 1950 the Committee was reconstituted, this time to decide about color television. In March 1953 it unanimously approved what is now called simply the NTSC color television standard, later defined as RS-170a. The updated standard retained full backwards compatibility with older black and white television sets. Color information was added to the black and white image by adding a color subcarrier of 3.58 Mhz to the video signal. Due to certain technical considerations, the addition of the color subcarier also required a slight reduction of the frame rate from 30 frames per second to 29.97 frames per second. The FCC had briefly approved a different color television system starting in 1950. It was developed by CBS and was incompatible with black and white broadcasts. That system used a rotating color wheel, reduced the number of scanlines from 525 to 405, and increased the field rate from 60 to 144 (but had an effective frame rate of 24 frames per second). Delay tactics by rival RCA kept the system off the air until mid-1951, and regular broadcasts only lasted a few months before manufacture of CBS-compatible systems was banned by the National Production Authority (NPA). Most of the existing devices were soon destroyed and only two receivers are known to exist today. The CBS system was rescinded by the FCC in 1953 and was replaced later that year by the NTSC color standard, which had been developed with the cooperation of several companies including RCA and Philco. A variant of the CBS system was later used by NASA to broadcast pictures of astronauts from space. A third "line sequential" system from Color Television Inc. (CTI) was also considered. The CBS and final NTSC systems were called "field sequential" and "dot sequential" systems, respectively. The first commercially available color NTSC television camera was the RCA TK-40A, introduced in March 1954. It was replaced later that year by an improved version, the TK-41, which became the standard camera used through much of the 1960s. The NTSC standard has since been adopted by many other countries, for example most of the Americas and Japan.

Technical details

Refresh rate

The NTSC format—or more correctly the M format; see broadcast television systems—consists of 29.97 interlaced frames of video per second. Each frame consists of 480 lines out of a total of 525 (the rest are used for sync, vertical retrace, and other data such as captioning). The NTSC system interlaces its scanlines, drawing odd-numbered scanlines in odd-numbered fields and even-numbered scanlines in even-numbered fields, yielding a nearly flicker-free image at its approximately 59.94 hertz (nominally 60 Hz/1.001) refresh frequency. This compares favorably to the 50 Hz refresh rate of the 625-line PAL and SECAM video formats used in Europe, where 50 Hz alternating current is the standard; flicker is more likely to be noticed when using these standards. Interlacing the picture does complicate editing video, but this is true of all interlaced video formats, including PAL and SECAM. The NTSC refresh frequency was originally exactly 60 Hz in the black and white system, chosen because it matched the nominal 60 Hz frequency of alternating current power used in the United States. It was preferable to match the screen refresh rate to the power source to avoid wave interference that would produce rolling bars on the screen. Synchronization of the refresh rate to the power cycle also helped kinescope cameras record early live television broadcasts, as it was very simple to synchronize a film camera to capture one frame of video on each film cell by using the alternating current frequency as a shutter trigger. In the color system the refresh frequency was shifted slightly downward to 59.94 Hz to eliminate stationary dot patterns in the color carrier, as explained below in "Color encoding." The mismatch in frame rate between NTSC and the other two video formats, PAL and SECAM, is the most difficult part of video format conversion. Because the NTSC frame rate is higher, it is necessary for video conversion equipment converting to NTSC to interpolate the contents of adjacent frames in order to produce new intermediate frames; this introduces artifacts, and a trained eye can quickly spot video that has been converted between formats. (See also stutter frame.)

Color encoding

For backward compatibility with black and white television, NTSC uses a luminance-chrominance encoding system invented in 1938 by Georges Valensi. Luminance (derived mathematically from the composite color signal) takes the place of the original monochrome signal. Chrominance carries color information. This allows black and white receivers to display NTSC signals simply by ignoring the chrominance. In NTSC, chrominance is encoded using two 3.579545 MHz signals that are 90 degrees out of phase, known as I (intermodulation) and Q (quadrature). The phase relationship of the I and Q signals with the 3.579545 MHz subcarrier corresponds to the instantaneous color hue captured by a TV camera; its amplitude corresponds to the color saturation (purity) of the original signal. For a TV or a display to recover color information from the varying phase and amplitude signals just described, a constant phase reference 3.579545 MHz signal is needed. A short sample of this reference signal is included in the NTSC signal as color burst, located on the back porch of each horizontal line, the time between the end of the horizontal synchronization pulse and the of the blanking pulse on each line. The color burst consists of a minimum of eight cycles of the unmodulated (fixed phase and amplitude) color subcarrier. By comparing the reference signal derived from color burst to the color signal's amplitude and phase, color hue and saturation information are recovered. When NTSC is broadcast, a radio frequency carrier is amplitude modulated by the NTSC signal just described, while an audio signal is transmitted by frequency modulating a carrier 4.5 MHz higher. If the signal is affected by non-linear distortion, the 3.58 MHz color carrier may beat with the sound carrier to produce a dot pattern on the screen. The original 60 Hz field rate was adjusted down by the factor of 1000/1001, to 59.94 fields per second, so that the resulting pattern would be less noticeable. Another important factor in choosing the new field rate was to make sure that interference between the luminance and chrominance signals would be shifted exactly 180 degrees for each scanline. There are two reasons why this is important. First, the chrominance signal was interpreted as luminance by TV sets that were in use at the time of the introduction of color TV and which didn't have notch filters to filter out the chrominance information, causing dots to appear on strongly contrasting edges (which is high-frequency video information). The field rate choice causes the dots to appear to move, which makes them harder for the human eye to follow. The effect is still noticeable on close examination, however, and is referred to as dot crawl. A second benefit to the chosen field rate was realized much later: The phase difference of the interference pattern on successive lines makes it very easy to design a simple comb filter to separate chrominance and luminance information to a greater degree.

Transmission modulation scheme

An NTSC television channel as transmitted occupies a total bandwidth of 6 MHz. A guard band, which does not carry any signals, occupies the lowest 250 kHz of the channel to avoid interference between the video signal of one channel and the audio signals of the next channel down. The actual video signal, which is amplitude-modulated, is transmitted between 500 kHz and 5.45 MHz above the lower bound of the channel. The video carrier is 1.25 MHz above the lower bound of the channel. Like any modulated signal, the video carrier generates two sidebands, one above the carrier and one below. The sidebands are each 4.2 MHz wide. The entire upper sideband is transmitted, but only 750 kHz of the lower sideband, known as a vestigial sideband, is transmitted. The color subcarrier, as noted above, is 3.579545 MHz above the video carrier, and is quadrature-amplitude-modulated with supressed carrier. The highest 250 kHz of each channel contains the audio signal, which is frequency-modulated, making it compatible with the audio signals broadcast by FM radio stations in the 88-108 MHz band. The main audio carrier is 4.5 MHz above the video carrier. Sometimes a channel may contain an MTS signal, which is simply more than one audio signal. This is normally the case when stereo audio and/or second audio program signals are used.

Quality problems

Video professionals and television engineers do not hold NTSC video in high regard, joking that the abbreviation stands for "Never The Same Color," or "Never Twice the Same Color." Cabling problems tend to degrade an NTSC picture (by changing the phase of the color signal), so the picture often loses its color balance by the time the viewer receives it. This necessitates the inclusion of a tint control on NTSC sets, which is not necessary on PAL or SECAM systems. Some complain that the 525 line resolution of NTSC results in a lower quality image than the hardware is capable of. Additionally, the large mismatch between NTSC's 30 frames per second and cinema's 24 frames per second cannot be overcome by a simple small speedup during telecine of cinematic movies for display on NTSC equipment; unlike PAL a more complex process called "3:2 pulldown" is needed, which duplicates parts of frames. This induces noticeable judder during slow pans of the camera. See telecine for more details. There is no question the NTSC system reflects the limitations and technology of a bygone era; indeed, its compatibility has been the key to its longevity and ubiquity over seven decades. The coming of digital television and high-definition television may spell its doom. There is, however, no way to predict just how many more years its characteristic notched trace may continue to flicker across television station waveform monitors and its basic but effective scheme continue to beam into living rooms over much of the globe.

Variants of NTSC

Unlike PAL, with its many and varied underlying broadcast television systems in use throughout the world, NTSC color encoding is invariably used with broadcast system M, giving NTSC-M. Britain once contemplated introducing a 405-line NTSC-A system on top of its old black-and-white television system, but the proposal was eventually scrapped in favor of the incompatible PAL-I. Only Japan's variant "NTSC-J" is very slightly different: in Japan, black level and blanking level of the signal are identical, as they are in PAL, while in American NTSC, black level is slightly higher than blanking level. Since the difference is quite small, a slight turn of the brightness knob is all that is required to enjoy the "other" variant of NTSC on any set as it is supposed to be; most watchers might not even notice the difference in the first place. The Brazilian PAL-M system uses the same broadcast bandwidth, frame rate, and number of lines as NTSC, but using PAL encoding. It is therefore NTSC-compatible in sources such as video cassettes and DVDs, but its color picture cannot be received on a standard NTSC television set.

History of the NTSC signal

- NTSC I is the original monochromatic 525/60 signal that first became standard in the U.S. in 1941 and later in Canada.
- NTSC II is the color system with some but not all aspects of the signal rigorously defined. NTSC II has a minor change in its temporal structure, becoming a 525/59.94 system. From this point 525/60 [RGB] becomes a separate production standard that interoperates with NTSC via a 1000/1001 drop frame solution.
- NTSC III came about due to digital television routing during the 1980s; all aspects of NTSC III are rigidly mathematically defined.

The current state of NTSC III

The North American analog transmission chain is strictly NTSC III now. Many NTSC II devices feed into existing transmission chains, with NTSC III compatibility being achieved by signal processing in the digital domain. Typical terrestrial TV transmitters or cable company distribution units send out NTSC III signals, especially if the originating signal comes from a TVRO or ATSC source. All free-to-air analog satcom transmissions are NTSC III. Video scrambling systems such as VideoCipher cannot acheve full NTSC III compability due to end-to-end analog processing issues. There are no known compatibility problems between NTSC II and NTSC III. Older NTSC II sets should handle NTSC III signals without any problems, even with respect to minor frequency variances the color sync subcarrier that exist in NTSC II.

Vertical Interval Reference

The standard NTSC video image contains some lines (lines 1-21 of each field) which are not visible; all are beyond the edge of the viewable image, but only lines 1-9 are used for the vertical-sync and equalizing pulses. The remaining lines were deliberately blanked in the original NTSC specification to provide time for the electron beam in CRT-based screens to return to the top of the display. VIR (or Vertical Interval Reference), widely adopted in the 1980's, attempts to correct some of the color problems with NTSC video by adding studio-inserted reference data for luminance and chrominance levels on line 19. [http://sipi.usc.edu/~weber/ee459/datasheets/LM1881.pdf] Suitably-equipped television sets could then employ this data in order to adjust the display to a closer match of the original studio image. A less-used successor to VIR also added ghost (multipath interference) removal capabilities. The remaining vertical blanking interval lines are typically used for datacasting or ancillary data such as video editing timestamps (vertical interval timecodes or SMPTE timecodes on lines 12-14 [http://www.philrees.co.uk/articles/timecode.htm] [http://www.poynton.com/notes/video/Timecode/]), test data on lines 17-18, a network source code on line 20 and closed captioning and V-chip data on line 21. Early teletext applications also used vertical blanking interval lines 14-18 and 20, but teletext over NTSC was never widely adopted by viewers [http://www.experimentaltvcenter.org/history/tools/ttext.php3?id=16].

Countries and territories that use NTSC

teletext

North America

- Canada
- Mexico
- United States

Central America and the Caribbean

- Antigua and Barbuda
- Aruba
- Bahamas
- Barbados
- Belize
- Bermuda
- British Virgin Islands
- Cayman Islands
- Costa Rica
- Cuba
- Dominica
- Dominican Republic
- El Salvador
- Guatemala
- Grenada
- Honduras
- Jamaica
- Leeward Islands
- Montserrat
- Netherlands Antilles
- Nicaragua
- Panama
- Puerto Rico
- St. Kitts and Nevis
- St. Lucia
- St. Vincent and the Grenadines
- Trinidad and Tobago
- U.S. Virgin Islands

South America

- Bolivia
- Chile
- Colombia
- Ecuador
- Guyana
- Peru
- Suriname
- Venezuela
- Brazil (PAL-M system, based on NTSC-M standard but using PAL color encoding)

Asia

- Cambodia (Historic; all of Cambodia now uses SECAM)
- Japan
- Myanmar
- Philippines
- South Korea
- Taiwan
- North Korea (Propaganda station aimed at South Korea; domestic broadcasts use PAL)
- South Vietnam (Historic; all of Vietnam now uses PAL)

The Pacific

- American Samoa
- Australia (Historic; all of Australia now uses PAL)
- Fiji
- Guam
- Marshall Islands
- Micronesia
- Midway Atoll
- Northern Mariana Islands
- Palau
- Samoa

Indian Ocean

- Diego Garcia

Middle East

- South Yemen (Historic; all of Yemen now uses PAL)
See also

- Broadcast television systems
- RCA
- PAL
References

- A standard defining the NTSC system was published by the International Telecommunication Union in 1998 under the title "Recommendation ITU-R BT.470-6, Conventional Television Systems." It isn't publicly available on the Internet, but it can be purchased from the ITU.
- Ed Reitan (1997). [http://www.novia.net/~ereitan/Color_Sys_CBS.html CBS Field Sequential Color System.]
External links

- [http://www.paradiso-design.net/videostandards_en.html Representation of the NTSC refresh rate on a television and on a DVD]
- [http://google.com/groups?selm=CHJ9wG.7CH@fc.hp.com A thorough explanation of the reasons why the field rate was changed to 59.94 Hz when color was introduced to the NTSC standard, including all the magic numbers and mathematics] Category:Video and movie technology Category:Standards ja:NTSC

SÉCAM

SÉCAM (Séquentiel couleur avec mémoire, French for "sequential colour with memory") is an analog colour television system first used in France. SÉCAM was invented by a team led by Henri de France and working at Thomson. It is, historically, the first European colour television standard.

Technical details

Just as the other colour standards adopted for broadcast usage over the world, SÉCAM is a compatible standard, which means that monochrome television receivers predating its introduction are still able to show the programs, although only in black and white. Because of this compatibility requirement, colour standards add a second signal to the basic monochrome signal, and this signal carries the colour information, called chrominance or C in short, while the black and white information is called the luminance (Y in short). Old TV receivers only see the luminance, while colour receivers process both signals. Another aspect of the compatibility being not using more bandwidth than the monochrome signal alone, the colour signal has to be somehow inserted into the monochrome signal, without disturbing it. This insertion is possible because the spectrum of the monochrome TV signal is not continuous, hence empty space exists, which can be recycled. This lack of continuity results from the discrete nature of the signal, which is divided into frames and lines. Analogue colour systems differ by the way in which empty space is used. In all cases, the colour signal is inserted at the end of the spectrum of the monochrome signal. In order to be able to separate the colour signal from the monochrome one in the receiver, a fixed frequency subcarrier has to be used, this subcarrier being modulated by the colour signal. The colour space is three dimensional by the nature of the human vision, so after subtracting the luminance, which is carried by the base signal, the colour subcarrier still has to carry a two dimensional signal. Typically the red (R) and the blue (B) information are carried because their signal difference with luminance (R-Y and B-Y) is stronger than that of green (G-Y). SÉCAM differs from the other colour systems by the way the R-Y and B-Y signals are carried. First, SÉCAM uses frequency modulation to encode chrominance information on the subcarrier. Second, instead of transmitting the red and blue information together, it only sends one of them at a time, and uses the information about the other colour from the preceding line. It uses a delay line, an analog memory device, for the purpose of storing one line of colour information. This justifies the "Sequential, With Memory" name. Because SÉCAM transmits only one colour at a time, it is free of the colour artifacts present in NTSC and PAL and resulting from the combined transmission of both signals. This means that the vertical colour resolution is halved relative to NTSC. It is however not halved compared to PAL. Although PAL does not eliminate half of vertical colour information during encoding, it combines colour information from adjacent lines at the decoding stage, in order to compensate for colour subcarrier phase errors occurring during the transmission of the Amplitude-Modulated colour subcarrier. This is normally done using a delay line borrowed from SÉCAM (the result is called PAL DL or PAL Delay-Line, sometimes interpreted as DeLuxe), but can be accomplished "visually" in cheap TV sets (PAL standard). Because the FM modulation of SÉCAM's colour subcarrier is insensitive to phase (or amplitude) errors, phase errors do not cause loss of colour saturation in SÉCAM, although they do in PAL. In NTSC such errors cause colour shifts. The colour difference signals in SÉCAM are actually calculated in the YDbDr colour space, which is a scaled version of the YUV colour space. This encoding is better suitable to the transmission of only one signal at a time. FM modulation of the colour information allows SÉCAM to be free of the dot crawl problem commonly encountered with the other analog standards and first widely noticed with the Laserdiscs. Dot crawl can be removed from PAL and NTSC-encoded signals using a comb filter. Such filters are usually only included in high-end displays. Dot crawl patterns (animated checkerboard) are easily visible along vertical lines in DVD menus displayed even by expensive (eg. plasma) displays if these displays are connected to a signal source (DVD player) using a composite PAL or NTSC connection rather than for example RGB. The idea of reducing the vertical colour resolution comes from Henri de France, who observed that colour information is approximately identical for two successive lines. Because the colour information was designed to be a cheap, backwards-compatible addition to the monochrome signal, the colour signal has a lower bandwidth than the luminance signal, and hence lower horizontal resolution. Fortunately, the human visual system is similar in design: it perceives changes in luminance at a higher resolution than changes in chrominance, so this asymmetry has minimal visual impact. It was therefore also logical to reduce the vertical colour resolution. DVD and other digital television formats have continued to exploit this visual artefact, subsampling colour both horizontally and vertically. Hence, paradoxically, VHS NTSC videos can have a greater vertical colour resolution than DVD. A similar paradox applies to the vertical resolution in television in general: reducing the bandwidth of the video signal will preserve the vertical resolution, even if the image loses sharpness and is smudged in the horizontal direction. Hence, video could be sharper vertically than horizontally. However, because of the interlacing, vertical resolution is effectively not as great as the number of scan lines. Additionally, transmitting an image with too much vertical detail will cause annoying flicker on television screens, as small details will only appear on a single line, and hence be refreshed at half the frequency. Computer-generated text and inserts have to be carefully low-pass filtered to prevent this.

History

Work on SÉCAM began in 1956. The technology was ready by the end of the fifties, but this was too soon for a wide introduction. Notably, SÉCAM did not work with the 819-line television standard then used by the then sole French TV network. France had to start the conversion by switching over to a 625-line television standard, which happened at the beginning of the sixties with the introduction of a second network. SÉCAM was inaugurated in France on October 1st, 1967, on la seconde chaîne (the second channel), now called France 2. A group of four men, all dressed in suits, presumably presenters and network officials, were shown standing in a studio. The image was originally black and white and suddenly switched to colour; one of the people said something along the lines of "now you can see us as we really are". The first colour television sets cost 5000 Francs. Colour TV was not very popular initially; only about 1500 people watched the inaugural program in colour. A year later, only 200,000 sets had been sold of an expected million. This pattern was similar to the earlier slow build-up of colour television popularity in the USA. SÉCAM was later adopted by former French and Belgian colonies, Eastern European countries, the former Soviet Union and Middle Eastern countries. However, with the fall of communism, and following a period when multi-standard TV sets became a commodity, many Eastern European countries decided to switch to PAL.

Why SÉCAM in France?

Some have argued that the primary motivation for the development of SÉCAM in France was to protect French television equipment manufacturers. However, incompatibility had started with the earlier decision to uniquely adopt positive video modulation for French broadcast signals. Also, SÉCAM development predates PAL; and because of frame rate differences (50 versus 60 Hz) and the requirement for compatibility with monochrome TV receivers, it was not possible for Europeans to adopt NTSC. SÉCAM and PAL addressed the chroma phase problem, whereas NTSC required the tint control on U.S. sets. Nonetheless, SÉCAM was partly developed for reasons of national pride. Henri de France's personal charisma and ambition may have been a contributing factor. PAL was developed by Telefunken, a German company, and in the post-war De Gaulle era there would have been much political resistance to dropping a French-developed system and adopting a German-developed one instead. Unlike some other manufacturers, the company where SÉCAM was invented, Thomson, still sells TV sets worldwide under different brands; this may be due in part to the legacy of SÉCAM. Thomson bought the company which developed PAL, Telefunken, and today even co-owns the RCA brand —RCA being the creator of NTSC. Thomson also co-authored the current American high-definition TV standard ATSC.

Why SÉCAM elsewhere?

The adoption of SÉCAM in Eastern Europe has been attributed to Cold War political machinations: Western TV was popular in the East, authorities were well aware of this, and adopted SECAM rather than the PAL encoding used in West Germany. However, East Germans responded by illegally buying PAL decoders for their SECAM sets. Eventually, the government in East Berlin stopped paying attention to so-called "Republikflucht via Fernsehen", or "defection via television". However, PAL and SÉCAM are just standards for the colour subcarrier, used in conjunction with older standards for the base monochrome signals. The names for these monochrome standards are letters, such as M, B/G, D/K, and L. See CCIR, OIRT and FCC (the standardization bodies). These signals are much more important to compatibility than the colour subcarriers. They differ by AM or FM modulation, signal polarisation, relative frequencies within the channel, bandwidth, etc. For example, a PAL D/K TV set will be able to receive a SÉCAM D/K signal (although in black and white), while it will not be able to receive a PAL B/G signal at all. So even before SÉCAM came to Eastern European countries, most viewers could not have received Western programs —and colour TV sets were not exactly widespread in the Communist bloc anyway, so the monochrome-only reception did not pose a significant problem. Another, speculative political theory is that PAL was originally German, while SÉCAM came from a country which had better political relations with Eastern Europe after the war.

SÉCAM varieties

There are three varieties of SÉCAM: # French SÉCAM (SÉCAM-L), used in France and its former colonies # SÉCAM-B/G, used in the Middle East # SÉCAM D/K, used in the Commonwealth of Independent States and Eastern Europe (this is simply SÉCAM used with the D and K monochrome TV transmission standards). Reference is sometimes made to MESÉCAM as an alternative form of broadcast SÉCAM used in the Middle East. This is incorrect, MESÉCAM is meaningful only in terms of video recording. When a colour signal is recorded onto VHS video tape, the luminance signal is recorded in its original form (albeit with some reduction of bandwidth) but the chrominance signal of about 4.4MHz is too high in frequency to be recorded directly. Instead it is first downconverted to the lower frequency of 630kHz, and the complex nature of the PAL subcarrier means that the downconversion must be done via a superhet mixer to ensure that information is not lost. The SÉCAM subcarrier, being a simple FM signal, does not need such complex processing. The VHS specification requires that it be simply divided by 4 on recording to give a subcarrier of approximately 1.1MHz, and multiplied by 4 again on playback. A true dual-standard PAL and SÉCAM video recorder therefore requires two colour processing circuits, adding to complexity and expense. Since some countries in the Middle East use PAL and others use SÉCAM, the region has adopted a shortcut, and uses the PAL mixer-downconvertor approach for both PAL and SÉCAM. This works well and simplifies VCR design. The resultant signal on tape is not, of course, compatible with a true standard SÉCAM recording, and so is referred to as MESÉCAM. This is the only time the term MESÉCAM is meaningful. It is interesting to note that it is often possible to record SÉCAM video on an unmodified PAL VCR, thus creating MESÉCAM tapes which can be played back in colour through another PAL VCR into a SÉCAM TV. Basic PAL VCRs work better for this, more sophisticated ones detect the SÉCAM signal as "not-PAL" and refuse to record it in colour. Around 1983-1984 a new colour identification standard has been introduced in order to make more space available inside the signal for adding teletext information (originally according to the Antiope standard). Identification bursts have been made per-line (like in PAL) rather than per-picture. Very old SÉCAM TV sets might not be able to display colour for today's broadcasts.

Problems with the standard

Unlike PAL or NTSC, analog SÉCAM television cannot easily be edited in its native analog form. Because it uses frequency modulation, SÉCAM is not linear with respect to the input image (this is also what protects it against signal distortion), so electrically mixing two (synchronized) SÉCAM signals does not yield a valid SÉCAM signal, unlike with analog PAL or NTSC. For this reason, to mix two SÉCAM signals, they must be demodulated, the demodulated signals mixed, and be remodulated again. Hence, post-production is often done in PAL, or in component formats, with the result encoded or transcoded into SÉCAM at the point of transmission. Reducing the costs of running television stations is one reason for some countries' recent switchovers to PAL. TVs currently sold in SÉCAM countries support both SÉCAM and PAL, and more recently baseband NTSC as well (though not usually broadcast NTSC, that is, they cannot accept a broadcast signal from an antenna). Although the older analog camcorders (VHS, VHS-C) were produced in SÉCAM versions, none of the