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Television is a telecommunication medium that is used for transmitting and receiving moving images and sound. Television can transmit images that are monochrome, in color, or in three dimensions. The word television comes . Television may also refer specifically to a television set, television program, or television transmission.
First commercially available in very crude form on an experimental basis in the late 1920s, then popularized in greatly improved form shortly after World 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, ...view middle of the document...
A standard television set is composed of multiple internal electronic circuits, including circuits for receiving and decoding broadcast signals. A visual display 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 and high-definition television . Television systems are also used for surveillance, industrial process control, and the guidance of weapons in places where direct observation is difficult or dangerous. 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.
In its early stages of development, television employed a combination of optical, mechanical, and electronic technologies 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.
The first images transmitted electrically were sent by early mechanical fax machines, 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 the telephonoscope 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 a pendulum-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 in Germany, 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 angular intervals 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.
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 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...