color television
enUSNoun | 1. | ![]() |
单词 | color television | |||
释义 | color televisionenUS
color television→ 彩色电视机zhCNColor TelevisionenUScolor television[¦kəl·ər ¦tel·ə‚vizh·ən]Color Televisiontelevision designed to transmit images in color. Color television allows the viewer to perceive images more completely by transmitting the wealth of colors in the surrounding world. The transmission of color images by television is based on the theory of three-component color vision. A variety of natural colors can be reproduced optically by means of three primary colors. In accordance with this principle, a color television camera uses three light filters—red, green, and blue—to create three monochromatic images on the light-sensitive targets of the television camera tube. The optical images are then converted into three linear video signals ER, EG, and EB, which are proportional to the red (R), green (G), and blue (B) components, respectively, of the color registered during the image-scanning process. Special methods are used to encode the color information in the television signal and transmit the signal via a communications channel. In a color television receiver the video signals are extracted (by decoding) from the television signal; when fed to the receiver’s kinescope (picture tube), they control the brightness of the luminescence from the phosphors. Thus, in the most common three-color, three-beam kinescope with a shadow mask, the video signals are fed simultaneously to the control electrodes of three electron guns. As a result the current of the electron beams varies with the amplitude of the video signals. The phosphors on the kinescope screen are usually applied in the form of a mosaic of small circles (phosphor dots) grouped in triads (Figure 1). Each dot luminesces with its particular color when an electron beam strikes it, producing red (Rr), green (Gr), or blue (Br). Because of the shielding effect of the mask, the beams only excite their own colors in the phosphor dot triads. Thus, each beam separately produces a red, green, or blue color on the screen, and together the beams produce an image having a color that depends on the ratio of the brightness of the red, green, and blue colors of the luminescence. By additive color synthesis, any color can be produced within the limits of the receiver’s primary color triangle on the chromaticity diagram (Figure 2). When necessary for correct color reproduction, a matrix color corrector is used in the transmission channel to convert the linear video signals to video signals for the receiver’s primary colors. In addition to the linear matrix correction, the linear video signals ER, EG, and EB undergo a nonlinear correction (gamma correction) to compensate for the nonlinearities of the camera tube and receiver kinescope. As a result, nonlinear video signals where γ is an index for the degree of modulation in the kinescope characteristic. The signals Signal formation and transmission. The video signals Color television systems that transmit simultaneously usually require three standard television channels or one broadband channel with a passband of 3 × 6 = 18 MHz. A three-channel color television system using simultaneous transmission is therefore incompatible with the standard black-and-white system of television. Inasmuch as compatibility is one of the principal technological and economic requirements for color broadcasting systems, various methods are used to multiplex the spectrum of the transmitted signal (see LINE MULTIPLEXING) so that the television signal of one color program may have a frequency spectrum up to 6 MHz. One such method, which is used in all the standard color television systems, is to use special encoding matrices (Figure 3,a) to replace the broadband signals The amplitude or frequency of the subcarrier frequency oscillations is modulated by the color-difference signals in the color encoder so that a chrominance signal Uc is produced. The signals Producing the color image in the receiver. In a color television receiver the total signal eT from the output of the video detector is fed to a decoder consisting of an electrical bandpass filter, detectors for the subcarrier frequency oscillations, and a decoding matrix. The bandpass filter extracts the signal Uc + Ucs from the signal eT, and the former is fed to the input of the subcarrier detectors; the color-difference signals Historical outline. In 1907–08 the Russian engineer I. A. Adamian proposed a method of simultaneous transmission for motion-picture frames, and in 1925 he proposed a system of three-color television that used sequential transmission of color fields obtained by means of the disk invented by P. Nipkow; the Scottish inventor J. Baird gave the first practical demonstration of the system in 1928. In 1929 a simultaneous color television system using mechanical scanning was demonstrated at the laboratory of the American Telephone and Telegraph Company (USA); three independent channels were used to transmit the signals. The Soviet engineer Iu. S. Volkov proposed the use of a cathode-ray tube with three screens for a color television receiver in 1929; the three color-separated images (for the primary colors R, G, and B) were combined by means of beam splitters (beam-splitting Note on Figure 3. (a) Simplified block diagram of a compatible color television system with luminance and chrominance signals transmitted within a single (multiplexed) frequency spectrum, (b) nominal spectrum format of the total television signal formed; (TS) transmitted scene, (CSO) color-separating optical system, (TCT) television camera tubes, (GC) color gamma correctors, (EC) encoder, (DC) decoder, (K) kinescope, (ER), (EG), and (EB) video signals at the camera tube outputs, semireflecting mirrors). In the period 1938–50 an electronic, sequential color television system was developed in the USA by the Columbia Broadcasting System; it was used in the USA from 1951 to 1953 as the standard system of television broadcasting. A similar system was developed in the USSR between 1948 and 1953 and was used for experimental broadcasting in Moscow from 1954 to 1956. Color television broadcasting was begun in 1953 in the USA with the NTSC system, which was adopted as the standard in the USA in 1954, in Canada in 1964, and in a number of other countries on the American continent, as well as in Japan in 1960. A new color television system was created in the USSR in 1958; it featured quadrature modulation of the color subcarrier, which made it compatible with the black-and-white television system, and was first used for experimental television broadcasting in 1959. By 1966 the Soviet-French SECAM III system had been developed, and it was put into service simultaneously in the USSR and France in October 1967 (seeSECAM). Color television broadcasting was begun in 1967 in the German Federal Republic, Great Britain, the Netherlands, and other countries in Western Europe as well as in Australia, which used the PAL system developed between 1962 and 1966 in the German Federal Republic. Standard systems. As of 1978 there are three standard systems of color television: SECAM, NTSC, and PAL. They differ primarily in the methods used to form the television signal. The SECAM system has been adopted in the USSR and most of the socialist countries, as well as in France and a number of African countries. The signal Uc is formed by alternate frequency modulation of the subcarrier oscillations with the signals The NTSC (National Television Systems Committee) system forms the Uc signal by the balanced amplitude modulation of two subcarrier oscillations having the same frequency f0 = 3.579545 MHz with the video signals The PAL (phase alternation line) system is similar to the NTSC system; the principal difference is that in PAL the oscillations of the subcarrier frequency, which are modulated by the signal Use and future development. Color television is replacing black-and-white for broadcasting, and work is in progress on systems of stereoscopic color television. Color television technology is being used more widely for nonbroadcast television in practically all fields of application. It has been used in space research to monitor the condition of astronauts and the docking of spacecraft (for example, in July 1975 during the docking of the Soviet and American spacecraft Soyuz and Apollo) and to transmit from space color images of the earth’s surface and other objects in space. Color television is also used in medicine, for example, for endoscopy and for demonstrations of surgical procedures. Applications of color television in metallurgy, physics, and chemistry are also promising. Both professional and amateur color video recording on magnetic carriers (tapes, disks, and cards) is becoming more and more common; arrangements are being made to produce large editions of color video recordings on polyvinyl chloride disks and to manufacture relatively inexpensive attachments that enable television receivers to reproduce such recordings. Soviet television is moving in the direction of a complete transition to color. To this end, arrangements are being made to produce on an ever greater scale the studio and remote equipment needed for transmitting color programs. The territory served by color broadcasting is being expanded through the use of satellites with stationary orbits in the Ekran communications system and a network of ground repeaters. A color television complex capable of transmitting 20 programs is being constructed in Moscow. Currently under development is a system for transmitting a wide range of reference data in the form of pages that are reproduced on a television screen. The most important problems in color television today include the transition to single-tube television cameras in conjunction with single receiver kinescopes. In the field of stereo color television, methods are being sought for compressing the frequency band, systems are being developed for the transmission of images from several positions, and research and development of holographic television methods is continuing. REFERENCESTelevidenie, 3rd ed. Edited by P. V. Shmakov. Moscow, 1970.Novakovskii, S. V. Tsvetnoe televidenie. Moscow, 1975. Novakovskii, S. V. Standartnye sistemy tsvenogo televideniia. Moscow, 1976. Tekhnika tsvetnogo televideniia. Edited by S. V. Novakovskii. Moscow, 1976. S. V. NOVAKOVSKII color televisionenUS
Synonyms for color television
|
|||
随便看 |
|
英语词典包含2567994条英英释义在线翻译词条,基本涵盖了全部常用单词的英英翻译及用法,是英语学习的有利工具。