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| AbroadPlanet Forums -> Brat-3: ACTR Students Community | Post new topic |
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13-Dec-2000 11:47 PM |
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komsaid1 |
Hi,
I have another big problem. For intro to Video I need to write 4 one-page summaries about TV innovations (like if there is a new camera which is somehow better than others), and that is due tomorrow, I don't know where to find this info. Please help me if anyone knows where I can get it, I would really aprciate your help. Roxi [Brat 3: University of Pennsylvania I] |
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14-Dec-2000 04:52 AM |
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dornabella |
television an electronic system for transmitting still or moving images and sound to receivers that project a view of the images on a picture tube or screen and re-create the sound. The technology of television has been made possible by a quirk in human vision: images are retained by the retina for a brief time after they strike it. Making use of this phenomenon, bits of a picture are displayed on a television screen fast enough that a viewer sees them assembled as complete pictures. By rapidly changing the pictures on the screen (a rate of between 25 and 30 pictures per second is sufficient), an illusion of motion is created. A television's audiovisual signal begins with the conversion of an image and accompanying sound into an electronic code by a television camera. The resulting electronic signals are usually recorded on tape, and for transmission, or broadcasting, they are impressed on high-frequency radio waves that act as carriers. After transmission by a broadcasting antenna, the carrier waves are picked up by a receiving antenna, which carries them to the television receiver. Inside the receiver the video and audio signals are separated and amplified; they then pass into the picture tube, which re-creates a picture of the original image from the video signals by means of a narrow beam of electrons that bombard the back of a screen coated with a fluorescent compound in a scanning motion. The electrons cause the coating of the screen to light up with the desired brightness in each area of the picture. The electron beam scans across the screen in horizontal lines (525 lines per picture in the United States and 625 in Europe). Each picture is scanned twice, with alternate lines illuminated on each scan. This technique tricks the eye into ignoring the flicker effect caused by displaying successive images too slowly, because it doubles the number of images displayed. Experimentation to create a workable television system began in the late 19th century. In 1884 Paul Nipkow, a German scientist, patented his ideas for a complete television system, the key to which was a rotating disc with holes in a spiral pattern. This provided an effective mechanical means of image scanning that was used until electronic scanning was technically possible. Developments in the period from 1900 to 1920 produced early versions of the picture tube, methods of amplifying an electronic signal, and the theoretical formulation of the electronic-scanning principle; these later became the basis of modern television. In 1926 in England, John L. Baird first demonstrated a true television system by electrically transmitting moving pictures. In 1932 the Radio Corporation of America demonstrated all-electronic television using a camera tube called the iconoscope (patented by Vladimir Zworykin in 1923) and a cathode-ray tube in the receiver. By the early 1950s a colour-television system had been developed based on the idea of separating the black-and-white and colour signals. The black-and-white signal gives a high level of detail and can be received by all television sets. The colour signal is projected into the clear areas of the black-and-white signal, in much the same way that one fills colour into the outline of a child's colouring book. This system also has the advantage of being compatible with black-and-white sets, which can still get a good picture from the same combined signal. Since the 1950s the improvements in colour-television technology have resulted in larger picture tubes with clearer images. Cable television systems for distributing signals over coaxial cables give improved reception and additional viewing channels. In addition, a device for projecting television onto a large screen became available in the late 1970s. Machines that can record television signals for later playback or play recorded material from videotape cassettes (especially videocassette recorders, or VCRs) or videodiscs have also become common. By the late 20th century, efforts were under way to develop high-definition television, or HDTV; this term denotes any system yielding significantly greater picture resolution than that of the ordinary 525-line screen. Initial efforts centred on increasing the density of picture lines to more than 1,000, but these were overtaken in the 1990s by the adaptation of digital technology to television transmission and reception. Conventional television transmits signals in analog form--i.e., as a series of waves that can reproduce the original images and sounds captured by cameras and microphones; these waves are then decoded and amplified within the television set. Digital HDTV systems, by contrast, transmit pictures and sounds in the form of digital data--i.e., in the 0's and 1's of the binary computer code. This numerical data is broadcast using the same high radio frequencies that carry analog waves, and computer processors within the digital television set then decode the data. Digital HDTV can provide sharper, clearer pictures and sound with very little interference or other imperfections. Perhaps more importantly, digital television sets would potentially be able to send, store, and manipulate images as well as receive them, thereby merging the functions of the television set with those of a small computer. [Brat 3: University of Pennsylvania I] |
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14-Dec-2000 08:21 PM |
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X_Ray |
Dorinka, don't forget to cite sources, or it could be concidered as plagiarism!;)
Sincerely, Nurbek. [Brat 3: University of Pennsylvania I] |
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14-Dec-2000 09:06 PM |
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komsaid1 |
Dorina, thank you very much for your efforts, and for finding out that info and posting, it shows that you are a good friend and that you are really concerned in my problem. But the information that you posted is introduction to Video and we studied it (info about HDTVs) on our first three lessons of Intro to Video. But anyway thak you very much. I got three of my summaries done, thanks to Nurbek and Erlen. One more left. Hope I'll find some more info. Ever Yours, Roxi P.S. ya nashla site pro technology, nazyvaetsya: Roxy  )))))))))))))))))[Brat 3: University of Pennsylvania I] |
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