|
The technology of television has changed since its early days using a mechanical system invented by Paul Gottlieb Nipkow in 1884. ==Elements of a television system== '' The elements of a simple broadcast television system are:made for the 1800's going to the nowadays * An image source. This is the electrical signal representing the visual image, and may be from a professional video camera in the case of live television, a video tape recorder for playback of recorded images, or telecine with a flying spot scanner for the transfer of motion pictures to video). * A sound source. This is an electrical signal from a microphone or from the audio output of a video tape recorder. * A transmitter, which generates radio signals (radio waves) and encodes them with picture and sound information. * A television antenna coupled to the output of the transmitter for broadcasting the encoded signals. * A television antenna to receive the broadcast signals. * A receiver (also called a tuner), which decodes the picture and sound information from the broadcast signals, and whose input is coupled to the antenna of the television set. * A display device, which turns the electrical signals into visual images. * An audio amplifier and loudspeaker, which turns electrical signals into sound waves (speech, music, and other sounds) to accompany the images. Practical television systems include equipment for selecting different image sources, mixing images from several sources at once, insertion of pre-recorded video signals, synchronizing signals from many sources, and direct image generation by computer for such purposes as station identification. The facility for housing such equipment, as well as providing space for stages, sets, offices, etc., is called a television studio, and may be located many miles from the transmitter. Communication from the studio to the transmitter is accomplished via a dedicated cable or radio system. Television signals were originally transmitted exclusively via land-based transmitters. The quality of reception varied greatly, dependent in large part on the location and type of receiving antenna. This led to the proliferation of large rooftop antennas to improve reception in the 1960s, replacing set-top dipole or "rabbit ears" antennas, which however remained popular. Antenna rotors, set-top controlled servo motors to which the mast of the antenna is mounted, to enable rotating the antenna such that it points to the desired transmitter, would also become popular. In most cities today, cable television providers deliver signals over coaxial or fiber-optic cables for a fee. Signals can also be delivered by radio from satellites in geosynchronous orbit and received by parabolic dish antennas, which are comparatively large for analog signals, but much smaller for digital. Like cable providers, satellite television providers also require a fee, often less than cable systems. The affordability and convenience of digital satellite reception has led to the proliferation of small dish antennas outside many houses and apartments. Digital systems may be inserted anywhere in the chain to provide better image transmission quality, reduction in transmission bandwidth, special effects, or security of transmission from reception by non-subscribers. A home today might have the choice of receiving analog or HDTV over the air, analog or digital cable with HDTV from a cable television company over coaxial cable, or even from the phone company over fiber optic lines. On the road, television can be received by pocket sized televisions, recorded on tape or digital media players, or played back on wireless phones (mobile or "cell" phones) over a high-speed or "broadband" internet connection. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Technology of television」の詳細全文を読む スポンサード リンク
|