Main article: History of television
In its early stages of development, television employed a combination of optical, mechanical and electronic 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 relied on the latter, although the knowledge gained from the work onelectromechanical 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 fax machines, including the pantelegraph, 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, shortly after the invention of the telephone. At the time, it was imagined by early science fiction authors, that someday that light could be transmitted over copper wires, as sounds were. The idea 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 television. 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 television system which employed ascanning 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 whole image. Nipkow's design would not be practical until advances in amplifier tube technology became available. 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.
Vladimir Zworykindemonstrates electronic television (1929).
Using a Nipkow disk, Scottish inventor John Logie Baird succeeded in demonstrating 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 Photographic lenses. 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. 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. On 25 December 1926, Kenjiro Takayanagi demonstrated a television system with a 40-line resolution that employed a CRT display at Hamamatsu...
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