Cde 5

Cde 5

Television (TV) is a telecommunication medium used for transmitting moving images in monochrome (black and white), or in colour, and in two or three dimensions and sound. The term can refer to a television set, a television program ("TV show"), or the medium of television transmission. Television is a mass medium for entertainment, education, news, politics, gossip and advertising.

Television became available in crude experimental forms in the late 1920s, but it would still be several years before the new technology was marketed to consumers. After World War II, an improved form of black-and-white TV broadcasting became popular in the United States and Britain, and television sets became commonplace in homes, businesses, and institutions. During the 1950s, television was the primary medium for influencing public opinion.^[1] In the mid-1960s, color broadcasting was introduced in the US and most other developed countries. The availability of multiple types of storage media such as Betamax, VHS tape, local disks, DVDs, flash drives, high-definition Blu-ray Discs, and digital video recorders have enabled viewers to watch prerecorded material—such as movies— at home on their own time schedule. For many reasons, the storage of television and video programming now occurs on the cloud. At the end of the first decade of the 2000s, digital televisiontransmissions greatly increased in popularity. Another development was the move from standard-definition television (SDTV) (576i, with 576 interlaced lines of resolution and 480i) to high-definition television (HDTV), which provides a resolution that is substantially higher. HDTV may be transmitted in various formats: 1080p, 1080i and 720p. Since 2010, with the invention of smart television, Internet television has increased the availability of television programs and movies via the Internet through streaming video services such as Netflix, Amazon Video, iPlayer, Hulu, Roku and Chromecast.

In 2013, 79% of the world's households owned a television set.^[2] The replacement of early bulky, high-voltage cathode ray tube (CRT) screen displays with compact, energy-efficient, flat-panel alternative technologies such as plasma displays, LCDs (both fluorescent-backlit and LED), and OLED displays was a hardware revolution that began with computer monitors in the late 1990s. Most TV sets sold in the 2000s were flat-panel, mainly LEDs. Major manufacturers announced the discontinuation of CRT, DLP, plasma, and even fluorescent-backlit LCDs by the mid-2010s.^[3][4][5] In the near future, LEDs are expected to be gradually replaced by OLEDs.^[6] Also, major manufacturers have announced that they will increasingly produce smart TVs in the mid-2010s.^[7][8][9] Smart TVs with integrated Internet and Web 2.0 functions became the dominant form of television by the late 2010s.^[10]

Television signals were initially distributed only as terrestrial television using high-powered radio-frequency transmitters to broadcast the signal to individual television receivers. Alternatively television signals are distributed by coaxial cable or optical fiber, satellite systems and, since the 2000s via the Internet. Until the early 2000s, these were transmitted as analog signals, but a transition to digital television is expected to be completed worldwide by the late 2010s. A standard television set is composed of multiple internal electronic circuits, including a tuner for receiving and decoding broadcast signals. A visual display device which lacks a tuner is correctly called a video monitor rather than a television.

Facsimile transmission systems for still photographs pioneered methods of mechanical scanning of images in the early 19th century. Alexander Bain introduced the facsimile machine between 1843 and 1846. Frederick Bakewell demonstrated a working laboratory version in 1851.^{[citation needed]} Willoughby Smith discovered the photoconductivity of the element selenium in 1873. As a 23-year-old German university student, Paul Julius Gottlieb Nipkow proposed and patented the Nipkow disk in 1884.^[13] This was a spinning disk with a spiral pattern of holes in it, so each hole scanned a line of the image. Although he never built a working model of the system, variations of Nipkow's spinning-disk "image rasterizer" became exceedingly common.^[14] Constantin Perskyi had coined the word television in a paper read to the International Electricity Congress at the International World Fair in Paris on 25 August 1900. Perskyi's paper reviewed the existing electromechanical technologies, mentioning the work of Nipkow and others.^[15] However, it was not until 1907 that developments in amplification tube technology by Lee de Forest and Arthur Korn, among others, made the design practical.^[16]

The first demonstration of the live transmission of images was by Georges Rignoux and A. Fournier in Paris in 1909. A matrix of 64 seleniumcells, individually wired to a mechanical commutator, served as an electronic retina. In the receiver, a type of Kerr cell modulated the light and a series of variously angled mirrors attached to the edge of a rotating disc scanned the modulated beam onto the display screen. A separate circuit regulated synchronization. The 8x8 pixel resolution in this proof-of-concept demonstration was just sufficient to clearly transmit individual letters of the alphabet. An updated image was transmitted "several times" each second.^[17] In 1921 Edouard Belin sent the first image via radio waves with his belinograph.

In 1911, Boris Rosing and his student Vladimir Zworykin created a system that used a mechanical mirror-drum scanner to transmit, in Zworykin's words, "very crude images" over wires to the "Braun tube" (cathode ray tube or "CRT") in the receiver. Moving images were not possible because, in the scanner: "the sensitivity was not enough and the selenium cell was very laggy".^[18]

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