Television
"TV" redirects here. For other uses, see Television (disambiguation) andTV (disambiguation).
American family watching TV, 1958
Television (TV) is a telecommunicationmedium that is used for transmitting and receiving moving images and sound. Television can transmit images that are monochrome (black-and-white), in color, or in three dimensions. The word television comes from Ancient Greek τῆλε (tèle), meaning "far", andLatin visio, meaning "sight". Televisionmay also refer specifically to atelevision set, television program, ortelevision transmission.
First commercially available in very crude form on an experimental basis in the late 1920s, then popularized in greatly improved form shortly afterWorld War II, the television set has become commonplace in homes, businesses, and institutions, particularly as a vehicle for entertainment,advertising, and news. During the 1950s, television became the primary medium for molding public opinion.[1] In the mid-1960s, color broadcasting and sales of color television sets surged in the US and began in most other developed countries.
The availability of storage media such as video cassettes (mid-1970s),laserdiscs (1978), DVDs (1997), and high-definition Blu-ray Discs (2006) enabled viewers to use the television set to watch recorded material such as movies and broadcast material. Internet television has seen the rise of television programming available via the Internetthrough services such as iPlayer, Hulu, and Netflix.
In 2009, 78% of the world's households owned at least one television set, an increase of 5% from 2003.[2] The replacement of bulky, high-voltagecathode ray tube (CRT) screen displays with compact, energy-efficient, flat-panel alternatives such as LCDs (bothfluorescent-backlit and LED-backlit),plasma displays, and OLED displays was a major hardware revolution that began penetrating the consumer computer monitor market in the late 1990s and soon spread to TV sets. In 2013, 87% of televisions sold had color LCD screens.[3]
The most common usage of television is for broadcast television, which is modeled on the radio broadcastingsystems developed in the 1920s. Broadcast television uses high-powered radio-frequency transmitters to broadcast the television signal to individual television receivers. Thebroadcast television system is typically disseminated via radio transmissions on designated channels in the 54–890MHz frequency band.[4] Signals are often transmitted with stereo orsurround sound in many countries. Until the 2000s, broadcast television programs were generally transmitted as an analog television signal, but over the course of the following decade, several countries went almost exclusively digital.[citation needed] In addition to over-the-air transmission, television signals are also distributed by cable andsatellite systems.
A standard television set is composed of multiple internal electronic circuits, including circuits for receiving and decoding broadcast signals. A visualdisplay device which lacks a tuner is properly called a video monitor rather than a television. A television system may use different technical standards such as digital television (DTV) andhigh-definition television (HDTV). Television systems are also used for surveillance, industrial process control, and the guidance of weapons in places where direct observation is difficult or dangerous.[citation needed] A 2004 study by the Children’s Hospital and Regional Medical Center in Seattle, Washington, found a link between infant exposure to television and ADHD.[5]
History
Main article: History of television
In its early stages of development, television employed a combination ofoptical, mechanical, and electronictechnologies to capture, transmit, and display moving images. Modern broadcast TV systems do not involve mechanical image scanning methods, although the knowledge gained from working on electromechanical systems was crucial in the development of fully electronic television.
Braun HF 1 television receiver, Germany, 1958
The first images transmitted electrically were sent by early mechanical faxmachines, including the pantelegraph, developed in the late 19th century. The concept of electrically powered transmission of TV images in motion was first sketched in 1878 as thetelephonoscope shortly after the invention of the telephone. At the time, it was imagined by early science fiction authors that someday light could be transmitted over copper wires as sounds were at that time.
The concept of using scanning to transmit images was put to actual practical use in 1881 in the pantelegraph through the use of apendulum-based scanning mechanism. From this period forward, scanning in one form or another has been used in nearly every image transmission technology to date, including TV. This is the concept of "rasterization", the process of converting a visual image into a stream of electrical pulses.
In 1884, Paul Gottlieb Nipkow, a 23-year-old university student inGermany,[6] patented the first electromechanical TV system which employed a scanning disk, a spinning disk with a series of holes spiraling toward the center, for rasterization. The holes were spaced at equal angularintervals such that, in a single rotation, the disk would allow light to pass through each hole and onto a light-sensitive selenium sensor which produced the electrical pulses. As an image was focused on the rotating disk, each hole captured a horizontal "slice" of the entire image.[7]
Nipkow's design was not practical until advances in amplifier tube technology became available. Later designs used a rotating mirror-drum scanner to capture the image and a cathode ray tube (CRT) as a display device, but moving images were still not possible due to the poor sensitivity of the selenium sensors. In 1907, Russian scientist Boris Rosingbecame the first inventor to use a CRT in the receiver of an experimental television system. He used mirror-drum scanning to transmit simple geometric shapes to the CRT.[8]
Vladimir Zworykindemonstrates electronic television (1929).
Using a Nipkow disk, Scottish inventorJohn Logie Baird successfully demonstrated the transmission of moving silhouette images in London in 1925[9] and of moving, monochromatic images in 1926. Baird's scanning disk produced an image of 30 lines resolution, just enough to discern a human face, from a double spiral oflenses.[10] This demonstration by Baird is generally agreed to be the world's first true demonstration of TV, albeit a mechanical form no longer in use. Remarkably, in 1927, Baird also invented the world's first video recording system, "Phonovision;" because the signal produced by his 30-line equipment was in the audio frequency range, he was able to capture it on 10-inch gramophone recordsusing conventional audio recordingtechnology. A handful of Baird's Phonovision recordings survive and were finally decoded and rendered into viewable moving images in the 1990s using modern digital signal-processing technology.[11]
In 1926, Hungarian engineer Kálmán Tihanyi designed a television system utilizing fully electronic scanning and display elements and employing the principle of "charge storage" within the scanning (or "camera") tube.[12][13][14][15]
On 25 December 1926, Kenjiro Takayanagi demonstrated a TV system with a 40-line resolution that employed a CRT display at Hamamatsu Industrial High School in Japan.[16] This was the first working example of a fully electronic television receiver. Takayanagi did not apply for a patent.[17]
By 1927, Russian inventor Léon Theremin developed a mirror-drum-based TV system which usedinterlacing to achieve an image resolution of 100 lines.[18]
In 1927, Philo Farnsworth made the world's first working television system with electronic scanning of both the pickup and display devices,[19] which he first demonstrated to the press on 1 September 1928.[19][20]
WRGB claims to be the world's oldesttelevision station, tracing its roots to an experimental station founded on 13 January 1928, broadcasting from theGeneral Electric factory in Schenectady, NY, under the call letters W2XB.[21] It was popularly known as "WGY Television" after its sister radio station. Later in 1928, General Electric started a second facility, this one in New York City, which had the call letters W2XBSand which today is known as WNBC.
The two stations were experimental in nature and had no regular programming, as receivers were operated by engineers within the company. The image of a Felix the Catdoll rotating on a turntable was broadcast for 2 hours every day for several years as new technology was being tested by the engineers. Milton Berle claimed that he was involved in a very early television experiment inChicago, Illinois, in 1929.[22]
At the Berlin Radio Show in August 1931, Manfred von Ardenne gave the world's first public demonstration of a TV system using a cathode ray tube for both transmission and reception. The world's first electronically scanned TV service began in Berlin in 1935. In August 1936, the Olympic Games in Berlin were carried by cable to TV stations in Berlin and Leipzig where the public could view the games live.[23]
In 1935, the German firm of Fernseh A.G. and the United States firm Farnsworth Television owned by Philo Farnsworth signed an agreement to exchange their television patents and technology to speed development of TV transmitters and stations in their respective countries.[24]
On 2 November 1936, the BBC began transmitting the world's first public regular high-definition service from the Victorian Alexandra Palace in north London.[25] It therefore claims to be the birthplace of TV broadcasting as we know it today.
In 1936, Kálmán Tihanyi described the principle of plasma display, the first flat panel display system.[26][27]
Mexican inventor Guillermo González Camarena also played an important role in early TV. His experiments with TV (known as telectroescopía at first) began in 1931 and led to a patent for the "trichromatic field sequential system" color television in 1940.[28]
Although TV became more familiar to the general public in the US at the 1939 World's Fair, the outbreak of World War II prevented it from being manufactured on a large scale until after the war's end. True regular commercial television network programming did not begin in the US until 1948. During that year, conductor Arturo Toscanini made his first of ten TV appearances conducting the NBC Symphony Orchestra,[29] andTexaco Star Theater, starring comedianMilton Berle, became television's first gigantic hit show.[30] Since the 1950s, television has been the main medium for molding public opinion.[1]
Amateur television (ham TV or ATV) was developed for non-commercialexperimentation, pleasure, and public service events by amateur radiooperators. Ham TV stations were on the air in many cities before commercial TV stations came on the air.[31]
In 2012, it was reported that TV revenue was growing faster than film for major media companies.[32]
Color TV
Color TV is part of the history of television, the technology of television, and practices associated with television's transmission of moving images in color video.
In its most basic form, a color broadcast can be created by broadcasting three monochrome images, one each in the three colors of red, green and blue (RGB). When displayed together or in either rapid succession or optically overlapped, these images will blend together to produce a full color image as seen by the viewer.
One of the great technical challenges of introducing color broadcast televisionwas the desire to conserve bandwidthpotentially three times that of the existing black-and-white standards and not use an excessive amount of radio spectrum. In the US, after considerable research, the National Television Systems Committee (NTSC)[33]approved an all-electronic system developed by RCA which encoded color difference information (rendering the hue and saturation of colors) separately from the brightness information (rendering the lightness and darkness of colors) and greatly reduced the resolution of the color difference information in order to conserve bandwidth. The brightness image remained compatible with existing black-and-white television sets at full resolution, while color TVs could decode both the extra information (low resolution color difference) and the brightness image and then combine the brightness image with the color difference image to produce a full-color image. The higher resolution black-and-white and lower resolution color-difference images combine in the eye to produce a seemingly high-resolution full-color image. The NTSC standard represented a major technical achievement.
Although all-electronic color was introduced in the US in 1953,[34] high prices and the scarcity of color programming greatly slowed its acceptance in the marketplace. The first national color broadcast (the 1954Tournament of Roses Parade) occurred on January 1, 1954, but during the following 10 years most network broadcasts, and nearly all local programming, continued to be in black-and-white. It was not until the mid-1960s that color sets started selling in large numbers, due in part to the color transition of 1965 in which it was announced that over half of all network prime-time programming would be broadcast in color that fall. The first all-color prime-time season came just one year later.
Early color sets were either floor-standing console models or tabletop versions nearly as bulky and heavy, so in practice they remained firmly anchored in one place. The introduction of GE's relatively compact and lightweight Porta-Color set in the spring of 1966 made watching color television a more flexible and convenient proposition. In 1972, sales of color sets finally surpassed sales of black-and-white sets. Also in 1972, the last holdout among daytime network programs converted to color, resulting in the first completely all-color network season.
Color broadcasting in Europe was not standardized on the PAL format until the 1960s, and broadcasts did not start until 1967. By this point many of the technical problems in the early sets had been worked out, and the spread of color sets in Europe was fairly rapid.
By the mid-1970s, the only stations broadcasting in black-and-white were a few high-numbered UHF stations in small markets and a handful of low-power repeater stations in even smaller markets such as vacation spots. By 1979, even the last of these had converted to color, and by the early 1980s B&W sets had been pushed into niche markets, notably low-power uses, small portable sets, or use as video monitor screens in lower-cost consumer equipment in the television production and post-productionindustry.
Color bars used in a test pattern, sometimes used when no program material is available.
No comments:
Post a Comment