Television (TV) is a widely used telecommunication Telecommunication is the transmission of messages, over significant distances, for the purpose of communication. In earlier times, telecommunications involved the use of visual signals, such as smoke, semaphore telegraphs, signal flags, and optical heliographs, or audio messages via coded drumbeats, lung-blown horns, or sent by loud whistles, for medium Mass media denotes a section of the media specifically designed to reach a large audience. The term was coined in the 1920s with the advent of nationwide radio networks, mass-circulation newspapers and magazines. However, some forms of mass media such as books and manuscripts had already been in use for centuries for transmitting and receiving moving images An image is an artifact, for example a two-dimensional picture, that has a similar appearance to some subject—usually a physical object or a person, either monochromatic Monochrome describes paintings, drawings, design, or photographs in one color or shades of one color. A monochromatic object or image has colors in shades of limited colors or hues. Monochrome images in neutral colors are called grayscale or black-and-white. "Monochromatic light" refers to light of a narrow frequency ("black and white") or color Color or colour is the visual perceptual property corresponding in humans to the categories called red, green, blue and others. Color derives from the spectrum of light (distribution of light energy versus wavelength) interacting in the eye with the spectral sensitivities of the light receptors. Color categories and physical specifications of, usually accompanied by sound Sound is a travelling wave that is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing and of a level sufficiently strong to be heard, or the sensation stimulated in organs of hearing by such vibrations. "Television" may also refer specifically to a television set A television set is a device used to view television broadcasts, television programming A television program or television show is a segment of content broadcast on television. It may be a one-off broadcast or part of a periodically recurring television series or television transmission In telecommunications, transmission is the process of sending, propagating and receiving an analogue or digital information signal over a physical point-to-point or point-to-multipoint transmission medium, either wired, optical fiber or wireless. Transmission technologies and schemes typically refer to physical layer protocol duties such as. The word is derived from mixed Latin Latin or sometimes Roman is an Italic language originally spoken in Latium and Ancient Rome. Although often considered a dead language, in view of the fact that it has no native speakers, a small number of scholars can fluently speak it and it continues to be taught in schools and universities and has been, and currently is, used in the process of and Greek Greek , an independent branch of the Indo-European family of languages, is the language of the Greeks. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. In its ancient form, it is the language of classical ancient Greek literature and the New Testament of roots, meaning "far sight": Greek tele (τῆλε), far, and Latin visio, sight (from video, vis- to see, or to view in the first person).
Commercially available since the late 1930s The history of television is both complex and far-reaching, involving the work of many inventors and engineers in several countries over many decades. Initially, work proceeded along two different but overlapping lines of development: those designs employing both mechanical and electronic principles, and those employing only electronic principles, the television set has become common in homes, businesses and institutions, particularly as a source of entertainment Entertainment consists of any activity which provides a diversion or permits people to amuse themselves in their leisure time. Entertainment is generally passive, such as watching opera or a movie. Active forms of amusement, such as recreations or sports, are more often considered to be recreation. Activities such as personal reading or practicing and news. Since the 1970s the availability of video cassettes Videotape is a means of recording images and sound on to magnetic tape as opposed to movie film or random access digital media. Videotapes are also used for storing scientific or medical data, such as the data produced by an electrocardiogram. In most cases, a helical scan video head rotates against the moving tape to record the data in two, laserdiscs The LaserDisc is a home video disc format, and was the first commercial optical disc storage medium. Initially marketed as Discovision in 1978, the technology was licensed and sold as Reflective Optical Videodisc, Laser Videodisc, Laservision, Disco-Vision, DiscoVision, and MCA DiscoVision until Pioneer Electronics purchased the majority stake in, DVDs DVD-Video is a consumer video format used to store digital video on DVD discs, and is currently the dominant consumer video format in North America, Europe, and Australia. Discs using the DVD-Video specification require a DVD drive and a MPEG-2 decoder . Commercial DVD movies are encoded using a combination of MPEG-2 compressed video and audio of and now Blu-ray Discs Blu-ray Disc is an optical disc storage medium designed to supersede the standard DVD format. Its main uses are for storing high-definition video, PlayStation 3 video games, and other data, with up to 25 GB per single-layered, and 50 GB per dual-layered disc. Although these numbers represent the standard storage for Blu-ray Disc drives, the, have resulted in the television set frequently being used for viewing recorded as well as broadcast material.
Although other forms such as closed-circuit television It differs from broadcast television in that the signal is not openly transmitted, though it may employ point to point wireless links. CCTV is often used for surveillance in areas that may need monitoring such as banks, casinos, airports, military installations, and convenience stores. It is also an important tool of distance education (CCTV) are in use, the most common usage of the medium is for broadcast television Terrestrial television is a mode of television broadcasting which does not involve satellite transmission or underground cables — typically using radio waves through transmitting and receiving antennas or aerials. The term is more common in Europe, while in the United States it is referred to as broadcast television or sometimes over-the-air, which was modeled on the existing radio broadcasting Radio broadcasting is an audio broadcasting service, broadcast through the air as radio waves (a form of electromagnetic radiation) from a transmitter to a receiving antenna. Stations can be linked in radio networks to broadcast common programming, either in syndication or simulcast or both. Audio broadcasting also can be done via cable FM, local systems developed in the 1920s, and uses high-powered radio-frequency Radio frequency is a rate of oscillation in the range of about 30 kHz to 300 GHz, which corresponds to the frequency of electrical signals normally used to produce and detect radio waves. RF usually refers to electrical rather than mechanical oscillations, although mechanical RF systems do exist (see mechanical filter and RF MEMS) transmitters to broadcast Broadcasting is the distribution of audio and video content to a dispersed audience via radio, television, or other, often digital transmission media. Receiving parties may include the general public or a relatively large subset of thereof the television signal to individual TV receivers.
Broadcast TV is typically disseminated via radio Radio is the transmission of signals by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space. Information is carried by systematically changing some property of the radiated waves, such as transmissions on designated channels in the 54–890 megahertz The hertz is the SI unit of frequency defined as the number of cycles per second of a periodic phenomenon. One of its most common uses is the description of sine wave, particularly those used in radio and audio applications frequency band A band is a small section of the spectrum of radio communication frequencies, in which channels are usually used or set aside for the same purpose.[1] Signals are now often transmitted with stereo Stereophonic sound, commonly called stereo, is the reproduction of sound using two or more independent audio channels through a symmetrical configuration of loudspeakers in such a way as to create the impression of sound heard from various directions, as in natural hearing. It is often contrasted with monophonic, or "mono" sound, where and/or surround sound Surround sound technology used in cinema and home theater systems, video game consoles, personal computers and other platforms. Commercial surround sound media include videocassettes, Video DVDs, and HDTV broadcasts encoded as Dolby Pro Logic, Dolby Digital, or DTS. Other commercial formats include the competing DVD-Audio and Super Audio CD (SACD) in many countries. Until the 2000s broadcast TV programs were generally recorded and transmitted as an analog Analog recording (Greek, ana is "according to" and logos "relationship") is a technique used to store signals of audio or video information for later playback signal, but in recent years public and commercial broadcasters have been progressively introducing digital television Digital television is the transmission of audio and video by discrete (digital) signals, in contrast to the analog signals used by analog TV broadcasting technology.
A standard television set A television set is a device used to view television broadcasts comprises multiple internal electronic circuits An electronic circuit is composed of individual electronic components, such as resistors, transistors, capacitors, inductors and diodes, connected by conductive wires or traces through which electrical current can flow. The combination of components and wires allows various simple and complex operations to be performed: signals can be amplified,, including those for receiving A tuner is a circuit module or free-standing equipment which detects electrical signals and converts them to a form suitable for further processing and decoding broadcast signals. A visual display device which lacks a tuner is properly called a monitor A video monitor also called a broadcast monitor, broadcast reference monitor or just reference monitor, is a device similar to a television, used to monitor the output of a video-generating device, such as a media playout server, IRD, video camera, VCR, or DVD player. It may or may not have audio monitoring capability. Unlike a television, a video, rather than a television. A television system may use different technical standards such as digital television Digital television is the transmission of audio and video by discrete (digital) signals, in contrast to the analog signals used by analog TV (DTV) and high-definition television High-definition television refers to video having resolution substantially higher than traditional television systems (standard-definition TV, or SDTV, or SD). HD has one or two million pixels per frame, roughly five times that of SD. Early HDTV broadcasting used analog techniques, but today HDTV is digitally broadcast using video compression (HDTV). Television systems are also used for surveillance, industrial process control, and guiding of weapons, in places where direct observation is difficult or dangerous.
Amateur television (ham TV or ATV) is also used for experimentation, pleasure and public service events by amateur radio operators. Ham TV stations were on the air in many cities before commercial TV stations came on the air.[2]
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History
Main article: History of television The history of television is both complex and far-reaching, involving the work of many inventors and engineers in several countries over many decades. Initially, work proceeded along two different but overlapping lines of development: those designs employing both mechanical and electronic principles, and those employing only electronic principlesIn its early stages of development, television employed a combination of optical Optics is the branch of physics which studies the behavior and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behavior of visible, ultraviolet, and infrared light. Because light is an electromagnetic wave, other forms of electromagnetic radiation, mechanical and electronic Electronics is the branch of science and technology which makes use of the controlled motion of electrons through different media and vacuum. The ability to control electron flow is usually applied to information handling or device control. Electronics is distinct from electrical science and technology, which deals with the generation, technologies to capture, transmit and display a visual image. By the late 1920s, however, those employing only optical and electronic technologies were being explored. All modern television systems rely on the latter, although the knowledge gained from the work on electromechanical systems was crucial in the development of fully electronic television.
American family watching TV, 1958The first images transmitted electrically were sent by early mechanical fax A fax is a document sent over a telephone line. Fax machines have existed, in various forms, since the 19th century (see "History" below), though modern fax machines became feasible only in the mid-1970s as the sophistication of technology increased and cost of the three underlying technologies dropped. Digital fax machines first became machines, including the pantelegraph The pantelegraph was an early form of facsimile machine transmitting over normal telegraph lines developed by Giovanni Caselli, used commercially in the 1860s, that was the first such device to enter practical service, It could transmit handwriting, signatures, or drawings within an area of up to 150 x 100mm, developed in the late nineteenth century. The concept of electrically powered transmission of television images in motion was first sketched in 1878 as the telephonoscope A telephonoscope was an early concept of videophone and television, conceptualized in the late 1870's through the 1890's. It was mentioned in various early science fiction works such as Le Vingtième siècle. La vie électrique and other works written by Albert Robida. It was also sketched in various cartoons by George du Maurier as a fictional, shortly after the invention of the telephone The telephone , often colloquially referred to as a phone, is a telecommunications device that transmits and receives sound, most commonly the human voice. Telephones are a point-to-point communication system whose most basic function is to allow two people separated by large distances to talk to one another. It is one of the most common household. At the time, it was imagined by early science fiction authors, that someday that light Light is electromagnetic radiation of a wavelength that is visible to the human eye . In physics, the term light sometimes refers to electromagnetic radiation of any wavelength, whether visible or not could be transmitted over wires, as sounds were.
The idea of using scanning In computing, a scanner is a device that optically scans images, printed text, handwriting, or an object, and converts it to a digital image. Common examples found in offices are variations of the desktop scanner where the document is placed on a glass window for scanning. Hand-held scanners, where the device is moved by hand, have evolved from to transmit images was put to actual practical use in 1881 in the pantelegraph, through the use of a pendulum When a pendulum is displaced from its resting equilibrium position, it is subject to a restoring force due to gravity that will accelerate it back toward the equilibrium position. When released, the restoring force combined with the pendulum's mass causes it to oscillate about the equilibrium position, swinging back and forth. The time for one-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 television. This is the concept of "rasterization Rasterization or Rasterisation is the task of taking an image described in a vector graphics format and converting it into a raster image (pixels or dots) for output on a video display or printer, or for storage in a bitmap file format", the process of converting a visual image into a stream of electrical pulses.
In 1884 Paul Gottlieb Nipkow Paul Julius Gottlieb Nipkow B was a German technician and inventor, a 23-year old university student in Germany, patented the first electromechanical television system which employed a scanning disk A Nipkow disk , also known as scanning disk, is a mechanical, geometrically operating image scanning device, invented by Paul Gottlieb Nipkow. This scanning disk was a fundamental component in mechanical television through the 1920s, a spinning disk with a series of holes spiraling toward the center, for rasterization. The holes were spaced at equal angular In geometry, an angle is the figure formed by two rays sharing a common endpoint, called the vertex of the angle. The magnitude of the angle is the "amount of rotation" that separates the two rays, and can be measured by considering the length of circular arc swept out when one ray is rotated about the vertex to coincide with the other intervals such that in a single rotation the disk would allow light to pass through each hole and onto a light-sensitive selenium Selenium is a chemical element with the atomic number 34, represented by the chemical symbol Se, an atomic mass of 78.96. It is a nonmetal, chemically related to sulfur and tellurium, and rarely occurs in its elemental state in nature sensor which produced the electrical pulses. As an image was focused on the rotating disk, each hole captured a horizontal "slice" of the whole image.
Nipkow's design would not be practical until advances in amplifier tube technology became available. The device was only useful for transmitting still "halftone" images—represented by equally spaced dots of varying size—over telegraph or telephone lines.[citation needed] Later designs would use 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 Rosing became 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.[3]
Typical modern plasma-screen television set.Scottish inventor John Logie Baird demonstrated the transmission of moving silhouette images in London in 1925, 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 of lenses.[4] This demonstration by Baird is generally agreed to be the world's first true demonstration of television, albeit a mechanical form of television no longer in use. Remarkably, in 1927 Baird also invented the world's first video recording system, "Phonovision": by modulating the output signal of his TV camera down to the audio range, he was able to capture the signal on a 10-inch wax audio disc using conventional audio recording technology. A handful of Baird's 'Phonovision' recordings survive and these were finally decoded and rendered into viewable images in the 1990s using modern digital signal-processing technology.[5]
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.[6][7][8][9]
By 1927, Russian inventor Léon Theremin developed a mirror drum-based television system which used interlacing to achieve an image resolution of 100 lines.[citation needed]
Also in 1927, Herbert E. Ives of Bell Labs transmitted moving images from a 50-aperture disk producing 16 frames per minute over a cable from Washington, DC to New York City, and via radio from Whippany, New Jersey.[citation needed] Ives used viewing screens as large as 24 by 30 inches (60 by 75 centimeters). His subjects included Secretary of Commerce Herbert Hoover.[citation needed]
In 1927, Philo Farnsworth made the world's first working television system with electronic scanning of both the pickup and display devices,[10] which he first demonstrated to the press on 1 September 1928.[10][11]
The first practical use of television was in Germany. Regular television broadcasts began in Germany in 1929 and in 1936 the Olympic Games in Berlin were broadcast to television stations in Berlin and Leipzig where the public could view the games live.[12]
In 1936, Kálmán Tihanyi described the principle of plasma television, the first flat panel system.[13][14]
Mexican inventor Guillermo González Camarena also played an important role in early television. His experiments with television (known as telectroescopía at first) began in 1931 and led to a patent for the "trichromatic field sequential system" color television in 1940,[15] as well as the remote control.[citation needed]
Geographical usage
Television introduction by country 1930 to 1939 1940 to 1949 1950 to 1959 1960 to 1969 1970 to 1979 1980 to 1989 1990 to 1999 No data Main article: Geographical usage of televisionContent
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