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Television (TV) is a widely used telecommunication medium for sending (broadcasting) and receiving moving images, either monochromatic ("black and white") or color, usually accompanied by sound. "Television" may also refer specifically to a television set, television programming or television transmission. The word is derived from mixed Latin and Greek roots, meaning "far sight" Greek tele (t??e), far, and Latin visio, sight (from video, vis- to see, or to view in the first person). A standard television set comprises multiple internal electronic circuits, including those for tuning and decoding broadcast signals. A display device which lacks these internal circuits is therefore properly called a monitor, rather than a television. A television set may be designed to handle other than traditional broadcast or recorded signals and formats, such as closed-circuit television (CCTV), digital television (DTV) and high-definition television (HDTV). In its early stages of development, television included only those devices employing 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 rely on the latter, however the knowledge gained from the work on mechanical-dependent systems was crucial in the development of fully electronic television. In 1884 Paul Gottlieb Nipkow, a 20-year old university student in Germany, patented the first electromechanical television system which employed a scanning disk, a spinning disk with a series of holes spiraling toward the center, for "rasterization", the process of converting a visual image into a stream of electrical pulses. 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.
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