History Of Telivision Essay, Research Paper
The TelevisionB**** G********History***** *, 1999 The Television The invention of television has been basically the quest for a sufficient device for scanning the image (Everson 12). The first such device was the so-called Nipkow disk, patented by the German inventor Paul Gottlieb Nipkow in 1884. This was a flat, circular disk that was perforated with a series of small holes arranged in a spiral radiating from the center to the rim. As the disk was revolved in front of the eye, the outermost hole scanned a strip across the top of the image, and the succeeding holes scanned strips lower down until the entire image had been scanned. This particular method was not sufficient for the televisions needs. Scottish engineer John Logie Baird improved Nipkow’s design by incorporating a photoelectric cell into his system. Baird’s system used one Nipkow disk to scan a scene and another disk to receive the picture. The photoelectric cell converted light from the scanned scene into electrical signals that could be used to play back the image. Because of its clumsy nature, however, the Nipkow disk failed to operate well when made in large sizes and revolved at high speeds to create a useable image (Patchett 386).The first truly successful television pickup devices were the iconoscope which was invented by the Russian-born American physicist Vladimir Kosma Zworykin in 1923, and the image dissector tube, invented by the American radio engineer Philo Taylor Farnsworth soon after. With the availability of the tubes and the advances in radio transmission and electronic circuits that occurred in the years following World War I, practical television systems became a possibility (McPherson 203-204). And so thusly the Americans invented the first usable television systems. Television is the instantaneous transmission of images, such as pictures or scenes, fixed or moving, by electronic means over electrical transmission lines or by electromagnetic radiation (Osborne 1). To understand how Farnsworth made the TV image work one first must understand how an image is dissected and sent electronically. First you have to divide an image into a large number of individual small light or dark spots. In this form, the spots are so small and so numerous that the picture appears to the eye of the observer as an integrated pattern. Television pictures are also formed of a pattern of tone elements that blend to form a complete picture. Unlike the dots of a still image transmission, however, which are all present simultaneously on the paper surface, the individual dots of the television image appear on the receiving surface one after another in temporal succession; they form an image because our eyes blends them into a complete picture.
Breaking up an image into a sequence of individual dots that can later be reassembled into the proper positions to re-create the picture is accomplished by a technique known as scanning. The eye of the scanner sweeps over the entire picture in much the same way as the eye of a reader sweeps over a page of print, word by word and line by line. The scanner generates an electrical signal proportional to the brightness of the scanned spot. At the receiver, a second scanner re-creates an image of the object by creating a spot of light in exact agreement with the transmitter scanner. Modern television systems, however, utilize the motion of a beam of electrons that sweeps across the screens of camera tubes or receiving tubes. The advantage of scanning with an electron beam is that the beam can be moved with great speed and can scan an entire picture in a small fraction of a second. The Illustration to the left shows the path followed by an electron beam in scanning the entire area of a picture or image. The solid lines represent the path of the beam over the image surface and the dotted lines show the flyback thing. During the flyback which is necessary to bring the beam back to the starting point of the next line the beam current is suppressed. The illustration shows a simple scanning pattern of few lines. In actual television scanning, a large number of lines are used and the pattern is scanned in two parts.A complete individual scanning pattern such as the one shown produces a single static picture similar to a single frame of motion. As the pattern is repeated a number of times per second, changes in a moving image are recorded, and these changes blend into continuous motion for the observer. The greater the number of lines scanned from top to bottom of an image, and the greater the number of elements recorded on each line as it is scanned from left to right, the greater is the resolution, or the capacity of the image to show fine details or small objects. In the U.S., broadcasters and receiver manufacturers have agreed on a standard of 525 horizontal lines per frame and a frequency of 30 frames per sec. Clearer television pictures can be obtained by increasing the number of lines (Bartlett 70). BibliographyBartlett, Eugene R. Cable Television Technology And Operations. New York: McGraw-Hill, 1990.Everson, George. The Story of Television; the Life of Philo T. Farnsworth. New York: Arno Press, 1974.McPherson, Stephanie Sammartino. TV’s Forgotten Hero: The Story of Philo Farnsworth. Minneapolis: Carolrhoda Books, 1996.Osborne, Basil Whitworth. Colour Television Reception And Decoding Technique. London: Maclaren, 1968. Patchett, G. N. Principles of Colour Television. London: N. Price, 1962.