What's a television ?
a system for converting visual images (with sound) into electrical signals, transmitting them by radio or other means, and displaying them electronically on a screen.
"the days before television"
the activity, profession, or medium of broadcasting on television.
"she has a job in television"
Who invented television ?
Philo Farnsworth, in full Philo Taylor Farnsworth II, (born August 19, 1906, Beaver, Utah, U.S.—died March 11, 1971, Salt Lake City, Utah), American inventor who developed the first all-electronic television system.
Why is it called a television?
Etymology. The word television comes from Ancient Greek τῆλε (tele) 'far', and Latin visio 'sight'. ... The abbreviation TV is from 1948. The use of the term to mean "a television set" dates from 1941.
The television was not invented by a single person, but by a number of scientists' advancements contributing to the ultimate all-electronic version of the invention. The origins of what would become today's television system can be traced back as far as the discovery of the photoconductivity of the element selenium by Willoughby Smith in 1873 followed by the work on the telectroscope and the invention of the scanning disk by Paul Nipkow in 1884. All practical television systems use the fundamental idea of scanning an image to produce a time series signal representation. That representation is then transmitted to a device to reverse the scanning process. The final device, the television (or T.V. set), relies on the human eye to integrate the result into a coherent image.
Electromechanical techniques were developed from the 1900s into the 1920s, progressing from the transmission of still photographs to live still duotone images to moving duotone or silhouette images, with each step increasing the sensitivity and speed of the scanning photoelectric cell. John Logie Baird gave the world's first public demonstration of a working television system that transmitted live moving images with tone graduation (grayscale) on January 26, 1926, at his laboratory in London, and built a complete experimental broadcast system around his technology. Baird further demonstrated the world's first color television transmission on July 3, 1928. Other prominent developers of mechanical television included Charles Francis Jenkins, who demonstrated a primitive television system in 1923, Frank Conrad who demonstrated a movie-film-to-television converter at Westinghouse in 1928, and Frank Gray and Herbert E. Ives at Bell Labs who demonstrated wired long-distance television in 1927 and two-way television in 1930.
Color television systems were invented and patented even before black-and-white television was working.
Completely electronic television systems relied on the inventions of Philo Taylor Farnsworth, Vladimir Zworykin and others to produce a system suitable for mass distribution of television programming. Farnsworth gave the world's first public demonstration of an all-electronic television system at the Franklin Institute in Philadelphia on August 25, 1934.
Regular broadcast programming occurred in the United States,[1][2] the United Kingdom,[3] Germany,[4][5] France and the Soviet Union[6][7] before World War II. The first regular television broadcasts with a modern level of definition (240 or more lines) were made in England in 1936, soon upgraded to the so-called "System A" with 405 lines.
Regular network broadcasting began in the United States in 1946, and television became common in American homes by the middle 1950s. While North American over-the-air broadcasting was originally free of direct marginal cost to the consumer (cost in excess of acquisition and upkeep of the hardware) and broadcasters were compensated primarily by receipt of advertising revenue, increasingly United States television consumers obtain their programming by subscription to cable television systems or direct-to-home satellite transmissions. In the United Kingdom, France, and most of the rest of Europe, on the other hand, operators of television equipment must pay an annual license fee, which is usually used to fund (wholly or partly) the appropriate national public service broadcasters (British Broadcasting Corporation, France Télévisions, and so forth).
The elements of a simple television system are:
An image source—this may be a camera for live pick-up of images or a flying spot scanner for transmission of films
A sound source
A transmitter, which modulates one or more television signals with both picture and sound information for transmission
A receiver (television) which recovers the picture and sound signals from the television broadcast
A display device, which turns the electrical signals into visible light
A sound device, which turns electrical signals into sound waves to go along with the picture
Practical television systems include equipment for selecting different image sources, mixing images from several sources at once, insertion of pre-recorded video signals, synchronizing signals from many sources, and direct image generation by computer for such purposes as station identification. Transmission may be over the air from land-based transmitters, over metal or optical cables, or by radio from synchronous satellites. Digital systems may be inserted anywhere in the chain to provide better image transmission quality, reduction in transmission bandwidth, special effects, or security of transmission from reception by non-subscribers.
Display technology
Thanks to advances in display technology, there are now several kinds of video displays used in modern TV sets:
CRT (Cathode Ray Tube): The most common screens are direct-view CRTs for up to 40 inches (100 centimeters) (in 4:3) and 46 inches (115 centimeters) (in 16:9) diagonally. These are the least expensive and are a refined technology that can still provide the best value for overall picture quality. As they do not have a fixed native resolution, they are capable of displaying sources with a variety of different resolutions at the best possible image quality. The frame rate or refresh rate of a typical NTSC format CRT TV is 60 Hz, and for the PAL format, is 50 Hz. A typical NTSC broadcast signal's visible portion has an equivalent resolution of about 640 by 480 pixels. It actually could be slightly higher than that, but the Vertical Blanking Interval, or VBI, allows other signals to be carried along with the broadcast.
Rear projection: Most very large screen TVs (up to over 100 inches (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. Projection television has been commercially available since the 1970s, but at that time could not match the image sharpness of the CRT; current models are vastly improved, and offer a cost-effective large-screen display.
A variation is a video projector, using similar technology, which projects onto a screen.
Flat panel (LCD or plasma): 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 one inch thick and can be hung on a wall like a picture or put over a pedestal. Some models can also be used as computer monitors.
LED technology has become one of the choices for outdoor video and stadium uses, since the advent of ultra high brightness LEDs and driver circuits. LEDs enable scalable ultra-large flat panel video displays that other existing technologies may never be able to match in performance.
Each has its pros and cons. Flat panel LCD displays can have narrow viewing angles and so may not suit a home environment. Rear projection screens do not perform well in natural daylight or well-lit rooms and thus are best suited to dark viewing areas.
Pixel resolution is the amount of individual points known as pixels on a given screen. A typical resolution of 720 by 480 means that the television display has 720 pixels across and 480 pixels on the vertical axis. The higher the resolution on a specified display the sharper the image. Contrast ratio is a measurement of the range between the brightest and darkest points on the screen. The higher the contrast ratio, the better looking picture there is in terms of richness, deepness, and shadow detail.
The brightness of a picture measures how vibrant and impacting the colors are. Measured in {\displaystyle cd/m^{2}} equivalent to the amount of candles required to power the image.
Transmission band
There are various bands on which televisions operate depending upon the country. The VHF and UHF signals in bands III to V are generally used. Lower frequencies do not have enough bandwidth available for television. Although the BBC initially used Band I VHF at 45 MHz, this frequency is no longer in use for this purpose. Band II is used for FM radio transmissions. Higher frequencies behave more like light and do not penetrate buildings or travel around obstructions well enough to be used in a conventional broadcast TV system, so they are generally only used for satellite broadcasting, which uses frequencies around 10 GHz. TV systems in most countries relay the video as an AM (amplitude-modulation) signal and the sound as a FM (frequency-modulation) signal. An exception is France, where the sound is AM.
Aspect ratios
Aspect ratio refers to the ratio of the horizontal to vertical measurements of a television's picture. 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 technical aspect ratio limitations at all). The BBC's television service used a more squarish 5:4 ratio from 1936 to April 3, 1950, when it too switched to a 4:3 ratio. This did not present significant problems, as most sets at the time used round tubes which were easily adjusted to the 4:3 ratio when the transmissions changed.
References
Abramson, Albert. The History of Television, 1942 to 2000. Jefferson, NC: McFarland & Company, 2003. ISBN 0786412208
Barnouw, Erik. Tube of Plenty: The Evolution of American Television. New York: Oxford University Press, 1990. ISBN 0195064844
Bourdieu, Pierre. On Television. New York: The New Press, 1999. ISBN 1565845129
Brooks, Tim, and Earle March. The Complete Guide to Prime Time Network and Cable TV Shows. Ballantine, 2002. ISBN 0345455428
Burns, R.W. Television: An International History of the Formative Years. IET, 1998. ISBN 0852969147
Debord, Guy. The Society of the Spectacle. Zone Books, 1995. ISBN 0942299795
Derrida, Jacques, and Bernard Stiegler. Echographies of Television. Malden, MA: Blackwell Publishers, Inc., 2002. ISBN 074562037X