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ELECTRONICS. RADIO ENGINEERING
THE HISTORY SPECTRAL ANALYSIS IN TELEVISION
Boris P. Khromoy,
professor of the Moscow Technical University
of Communications and Informatics, Moscow, Russia, mtuci@mtuci.ru Keywords: television, TV signals, spectral analysis.
Spectral analysis of the audio signal, which began with the history of the development of this section of communication technology, further supplemented by the spectral analysis signal of the television image. Its main difference lay in the fact that the problem of image transmission were resolved on a purely scientific level, because unlike the audio signal, the television signal on a natural level alone does not exist. Although in the scientific use the term spectrum introduced the Newton in the years 1671-1672 based on the study of light phenomena, the development of standard television systems focused on the analysis of the spectrum of TV signals. It happened because Newton was analyzing color phenomena, and the first TV systems transmitted only a black and white image. The problem of studying the spectrum of TV signal in the design of systems was fundamental, as was required of a reasonable choice of system parameters to enable the transmission of TV signals over the communication lines. Widespread at that time, medium wave and short - wave bands for this purpose were not good. In conclusion, analysis of the signal spectrum b/W image, it should be noted another feature of his. It is the presence of a "DC component". The constant component needed to transmit the value of the average lighting of the object whose image is transmitted by television. If the nature of the change how the video source of illumination occurs during the day, i.e., relatively slowly, in a TV Studio or theater stage, the change in the average illumination with the aim of achieving an artistic effect, can occur repeatedly during the transfer. Naturally, the average brightness on the TV screen should change. Thus the spectrum of the signal in a TV receiver must contain the components shown in Fig. 5. The DC component is reproduced in the range from 0 to 3 Hz. The value of 3 Hz does not mean that the average brightness may change three times in one second. However, there is a fairly rapid response TV to changes in the system average illumination of the object being transferred. All the color signal processing procedure in the SECAM system were developed based on a detailed study of the color difference signals in the transmission spectra of various color tones and effect on the frequency modulated signal is superimposed on the spectrum of the luminance signal. Thus spectral analysis from a historical point of view was the basis of analog television.
ИСТОРИЯ СПЕКТРАЛЬНОГО АНАЛИЗА В ТЕЛЕВИДЕНИИ
Хромой Борис Петрович, профессор МТУСИ, Москва, Россия, mtuci@mtuci.ru
Аннотация. Спектральный анализ звукового сигнала, с которого началась история развития этого раздела техники связи, в дальнейшим пополнился спектральным анализом сигнала телевизионного изображения. Его основное отличие заключалось в том, что проблема передачи изображения решалась на чисто научном уровне, поскольку в отличие от звукового сигнала, телевизионный сигнал на природном уровне самостоятельно не существует. Хотя в научный обиход термин спектр ввёл Ньютон в 1671-1 672 годах на основе изучения световых явлений, при разработке стандартных телевизионных систем основное внимание уделялось анализу спектра ТВ сигналов. Так произошло потому, что Ньютон анализировал цветовые явления, а первые ТВ системы передавали только черно-белое изображение. Проблема изучения спектра ТВ сигнала при разработке систем была фундаментальной, так как необходим был обоснованный выбор параметров системы для обеспечения возможности передачи ТВ сигналов по линиям связи. Широко распространенные в то время средневолновый и коротковолновый диапазоны для этой цели не годились. Все процедуры обработки цветовых сигналов в системе SECAM были разработаны на основе детального изучения спектров цвето-разностных сигналов при передаче различных цветовых тонов и их вляния на частотно модулированный сигнал, накладываемый на спектр яр-костного сигнала. Таким образом спектральный анализ с исторической точки зрения послужил основой развития аналогового телевидения. Все процедуры обработки цветовых сигналов в системе SECAM были разработаны на основе детального изучения спектров цветоразностных сигналов при передаче различных цветовых тонов и их вляния на частотно модулированный сигнал, накладываемый на спектр яркостного сигнала. Таким образом спектральный анализ с исторической точки зрения послужил основой развития аналогового телевидения.
Ключевые слова: Литература
1. Самойлов В.Ф., Хромой Б.П. Телевидение. М., Связь, 1 975, 400 с.
2. Зусманович В.М. Свет и цвет в телевидении М. - Л.: Энергия, 1 964, 208 с.
3. Гуревич М.М. Цвет и его измерение М. - Л.: Изд-во Академии наук СССР,
4. Нюберг Н.Д. Теоретические основы цветовой репродукции. М.: Советская
1 950. 268 с. наука, 1948.
Для цитирования:
Хромой Б.П. История спектрального анализа в телевидении // T-Comm: Телекоммуникации и транспорт. 2017. Том 1 1. №2. С. 68-72. For citation:
Khromoy B.P. (2017). The history spectral analysis in television. T-Comm, vol. 1 1, no.2, рр. 68-72.
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The problem of studying the spectrum ofTV signal in the design of systems was fundamental, as was required of a reasonable choke of system parameters to enable the transmission of TV signals over the communication lines. Widespread at that time, medium wave and short -wave bands for this purpose were not good. The first task was to define the lower and upper bounds of the spectrum of the TV signal and their dependence on system parameters. Lower frequency limit of the spectrum can be determined when scantling the image shown in Fig.I, in the form of two horizontal stripes - one white and one black. When a still image The lower frequency limit is determined by the number of frames
per second (or the number of fields per second in interlaced).
->
Fig. 2
If we take Z = 625, the image format is p = 4/3 and the frame rate
n = 50, we get:
Fig.l
As can be seen from Figure t, the signal corresponding to the image presented in the form of pulses with a repetition period equal to the frame transfer time - Tfr[lrao. The pulse repetition frequency equal to the frame rate, so the 1st harmonic (the lowest frequency) is equal to ffraiTK = I /Titanic — n frame/s. With interlaced scanning waveform is maintained, but its period is equal to the sweep time half-frame determined by the frequency fin,mi, = 2 n= 50 Hz in accordance with the decision taken in due time in the USSR standard. It should he noted, such scanning standard, accepted at that time was equal to 60 Hz in the USA. The question is what has caused this difference. Explanation is quite simple: in the US frequency of 60 Hz mains, and in the Soviet Union 50 Hz,
At present, ibis factor is irrelevant, and the introduction of television, the circuitry was at a much lower level and on the TV screen, the receiver was observed interference occurs in the power supply unit due to insufficient filtering of variable making up the mains voltage. This interference was made stationary and therefore barely visible, if the vertical frequency of the TV sweep generator synchronized with the mains frequency. Therefore, the lower the frequency of the TV spectrum was chosen to be the frequency of the mains.
The upper limit of the spectrum of TV signal is determined by the smallest details of the image, which can still be played on the TV screen. The CRT electron beam on the screen forms a luminous spot diameter dl equal to the thickness of one line. The beam diameter should correspond = h / Z, where h - height of (he frame, Z - the number of rows. This means that with the same horizontal and vertical detail minimum dimensions of alternating black and white cells along rows and transverse rows to be equal to the diameter of the beam.
To define the upper boundary value of the spectrum of TV signal in Fig,2 shows a "chessboard" consisting of cells, vertical and horizontal sizes equal to the beam diameter of the deployer tube. The number of pairs of these cells transmitted per second and define the upper boundary frequency.
The number of pairs on one line pZ/2 (where p = 4/3 - aspect ratio). The number of pairs on the entire frame (<p7J2)Z. the Number of pairs transferred per second (pZ/2)Zn ( where n is the number of frames transmitted per second). The obtained expression determines the boundary of (he frequency spectrum ofTV signal:
fraw-(npZ2)/2. (1)
3. 2
The calculation shows the need to transmit a very broad frequency band. A signal with such a wide range of difficult to amplify, and transmit without distortion over the air. Another problem is that the number of television channels designated for television range will be small.
The solution to the problem is possible either by reducing the number of decomposition lines Z, or a decrease in the frame rate. Roth options were unacceptable. The decrease in the number of rows will reduce clarity. This would be especially noticeable when using the US standard with decomposition at 525 lines. A low frame rate will lead to a flickering image that was well known when playing a movie.
The solution to the problem of reducing the spectrum of TV signal was possible by applying the interlacing. The idea of interlacing is implemented due to selection of the frequency of the horizontal scan of this magnitude that would have been played with I/50th the number of rows equal to Z/2, i.e. 312,5. By the end of the time interval I he beam will he in the middle of the bottom row-. As the beam moves simultaneously in two directions, ibis point went down just a half line spacing, and after the reverse beam will be in the middle of the top row and on the half interval above the line of the previous field.
Thus one complete frame now consists of two fields with a productivity transfer every 1/50 s and the total number of lines 625.The total time of transmission of the whole frame equal to 1/25 s. ! low ever, since this time interval the beam illuminates the screen twice (once odd and an even lines) flashing image invisible. Reducing the frame rate two times results in accordance with the formula (I) to the lower upper boundary frequencies up to 6.5 MHz, which corresponds to the standard accepted in the USSR
Boundary, the lower and upper frequency spectrum ol'TV signal define the requirements that must be met for a communication channel when transmitting black and white images. However, alter its implementation, work began on the creation of a color television. The transfer of the color image associated with the increase in transmitted information, but expanding the range ofTV signal turned out to be an impossible task. The fact that at the time when it became possible to transmit and receive the color image operated in the world hundreds of millions of black-and-white (b/W) TV.
The first color TVs cost much more expensive than black and white. So there was a problem of "compatibility" of color and black-and-white TV. The essence of the problem lay in the fact that would on a regular TV receiver you can adopt a program of color television, but of course only b/W. If such a problem to solve, the Park b/W TVs could gradually be replaced by color as they wear and at the request of the viewers.
To solve this problem, the following conditions need to be fulfilled.
1. The width of the spectrum of the color television signal must be the same as for b/W TV.
2. You need the same method to transmit signal b/W television to ensure that it play regular TV,
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3. The signals carrying color information of images must not cause interference on the screen h/W TV,
4. In the color receiver can be adopted a common signal b/W television. This was necessary because in early years the introduction of color television most television stations transmitted signals b/W image and the consumer should not have to have two TVs.
The solution of this problem was made possible by the study of the structure of the spectrum of TV signal in the range from the lower to the upper frequencies, [f the spectrum of the speech signal is continuous, the range ofTV signal was discrete. The explanation for this property of the spectrum is fairly simple.
Indeed, it is known that the spectrum of aperiodic signal is continuous, and the spectrum of the periodic signal is discrete. If, as an example consider the case of a still picture transmission, the signal will obviously be repeated exactly with the transmit frequency spectrum frames and hence should he discrete. Discontinuity in this case is equal to the frame rate. In addition to periodic TV signal from frame to frame, a frequency of the signal from row to row. The signals of two adjacent lines differ little from one another. In addition, each line begins with the siring blanking and sync pulse at a horizontal frequency^). Therefore, the range of TV signal contains discrete components, each separated in frequency fi,r= 15625 Hz.
The structure of the spectrum on the axis of frequencies equal fi,r, shown in Fig.3.
nf,
-U
* f
nfcro + f«™, [n+l)fn
Fig.3
ti t2 и t,
ti t2 t3 t,
Fig. 4
In conclusion, analysis of the signal spectrum b/W image, it should he noted another feature of his. It is the presence ofa "DC component". The constant component needed to transmit the value of the average lighting of the objcct whose image is transmitted by television. If the nature of the change how the video source of illumination occurs during the day, i.e., relatively slowly, in a TV Studio or theater stage, the change in the average illumination with the aim of achieving an artistic effect, can occur repeatedly during the transfer.
Naturally, the average brightness on the TV screen should change. Thus the spectrum of the signal in a TV receiver must contain the components shown in Fig. 5. The DC component is reproduced in the range from 0 to 3 Hz. The value of 3 Hz does not mean that the average brightness may change three times in one second. However, there is a fairly rapid response TV to changes in the system average illumination of the object being transferred.
Постоянная составляющая
Основной спектр
As can be seen from Fig.3 primary energy is clustered around harmonics of the frequency lines fcTp. The minimum frequency shift equal frramc- It is important to note that between harmonics of the line frequency there is a gap within which the spectral components are practically absent. These intervals it was possible to use to transfer color signal. In this case, most importantly, the color signal does not cause interference on the screen b/W TV,'
As can be seen from Fig.3 primary energy is clustered around harmonics of the horizontal frequency. The minimum frequency shift equal fitsim." It is important to note that between harmonics of the line frequency there is a gap within which the spectral components are practically absent. These intervals it was possible to use to transfer color signal. In this case, most importantly, the color signal does not cause interference on the screen b/W TV,'
This phenomenon can cause a natural question: "How is this possible?". Indeed, if the audio signal transmitted by telephone, superimposed sinusoidal interference, it will hear the subscriber. Frequency interference within the frequency range of the telephone will not lead to its disappearance.
This is not the case in television. The reason for the invisibility of the interference is illustrated in Fig,4. where the images of two adjacent frames oil the TV screen. We can say that in keeping with the classic photo is the negative and the positive. Because the images are repeated from frame to frame, the perception of the human eye they are average.
The waveform is similar to the image shown in Fig.4 has a rectangular shape.
The duration of each pulse is 1/3. and 2/3 period sweep. From the above example it is clear that the interference frequency is not a multiple of the horizontal frequency of the wilt be reproduced on the TV screen, but will not be perceived by human vision. It should be noted Uiat for die transmission of color signals are used lots of high frequency spectrum of the luminance signal, resulting in flickering images with a very small structure and in contrast to the large images shown in Fig.4. averaging more efficiently.
3 Гц 50 Га
6,5МГц
Fig. 5
The need for transmission of the DC component imposes serious the difficulties in the construction of amplifying devices, TV equipment. In this case, the amplifier stages are not separated by capacitor, and drift of the DC component of each amplifying element is amplified and leads to instability of the reproduced image. In connection with these difficulties in television amplifiers provide signal processing only in the frequency range from 50 Hz to 6.5 MHz, and a constant component transfer "indirectly", that is certainly an interesting invention.
The principle of the transfer of the constant component of the indirect way is illustrated in Fig.6a,b. There are two images: two vertical white stripes on a black background (Fig. 6a) and two black stripes on a white background (Fig. 6b). For each image, a signal is equal to the length of one row. It should be noted that for each of the image signals of all lines are the same.
3)
и *
6)
Уровень белого
Уровень чёрного
Fig. 6
ELECTRONICS. RADIO ENGINEERING
Before the beginning ofeacb line is transmitted blanking pulse, which "absorbs" the electron beam of the kinescope during the return stroke the line. The level of the tops of the blanking pulse is below the level even, is shown in Fig. 6 by a dotted line. There is an expression: "the level of the blanking pulse blacker than black". The magnitude of the differences is standardized to a certain percentage of the total range of the signal. Compare two images and waveforms shows that the average value of the brightness in Fig.6b is greater than in Fig. 6a. This is evidenced by the oscilloscope. However, both waveforms are positive to acquire coordinates, This would not have been if 1 miss both signals through a coupling capacitor. Therefore the constant component is present. The transmission of the DC component is carried out using a vertical blanking, the tops of which are fixed at the same level (Fig.6 at zero).
During image playback on the screen of the lube by fixing the levels of vertical blanking with a spccial fixing scheme. The simplest locking scheme consists of a diode, capacitor and resistor. The use of such a schema would have avoided the need to pass on TV channel of the DC component of the spectrum.
Considered range ofTV signal transmission through a communication channel converted by amplitude modulation. As is known to use ampliiude modulation results in the transfer of the spectrum in a High-frequency range side and the formation of two frequency bands - the upper and lower. This means that the TV signal spectrum is expanded twice reaching 12 MHz. The standard channel bandwidth is ii MHz, and the possibility of its use for the lower sideband spectrum of the amplitude modulated signal is suppressed, but only partially.
This is determined by the inability to create a filter with the required frequency characteristics. To fully suppress the lower sideband of the carrier frequency must be separated from the lower frequency components of the short spaced only 25 Hz. Therefore, it is suppressed and partly about the carricr retained the rest of the spectrum of 1.25 MHz.
In addition to the range ofTV signal, channel must transmit the audio signal. Audio signal is transmitted to improve the noise immunity of frequency modulation method, which is located above the carrier spectrum ofTV signal, as shown in Fig. 7.
m fuff.iuùû
Fig. 7
The presence of the lower side of the spectrum width of 1.25 MHz, upon delecting a signal in the TV receiver will result in distortion of the shape of the signal spectrum, as the amplitude of some low frequency component will be doubled. To eliminate such distortions of the frequency characteristic of the amplifier high frequency of the TV is performed in accordance with Fig.7b, i.e. with a linear slope in the lower part.,
If we consider the further conversion ofTV spectrum from a historical point of view, you should go to a color TV. The basis of color television is based on the theory of color scicncc. Colorimetry is based on the three-eo m pone nt theory of color vision. This idea was first expressed by M. V. Lomonosov in f 756. Alter 150 years the theory' developed by G. Ifelmholtz. In accordance with this theory in the retina of the eye contains the elements (cones) of the types, different spectral sensitivity. The dcpendcncc of spcctral sensitivity of die eye to the wavelength of light oscillations has been studied experimentally. With the aim of complete certainty are the basic colours for metrologieal purposes, adopted the following monochromatic radiation: for R: \ = 700 nm; for G; X = 546,1 ran; for k= 435,8 nm.
The study of the spectral characteristics of human vision have allowed to formulate requirements to the spectral sensitivity of the elements of the
transmitting TV camera. For a long time the basic design of the transmitting TV camera was three transmitting tube that fed the red, green and blue light components transmitted image obtained by using filters with appropriate spectral characteristics. The resulting signals, denoted by Eii and En served as the basis of the whole color TV system. The first task that is needed to resolve this compatibility color and b/W systems. You need to have a luminance signal which would provide signal reception on conventional b/W TV. The simplest solution is that the transmission chamber is provided with not three, but four camera lubes, one of which forms a luminance signal, usually Ev,
However, the scientists involved in the development of the TV system, on the basis of spectral analysis offered another way to get a luminance signal. Since the sum of the R, G and R, taken in the appropriate proportions, allows to obtain any color, and Ey signal can be obtained by using a specific combination of signals Er. E<; and EB. Such a combination was calculated:
Ev = Q,30EH + 0,59E[; + 0,1 I E„.
(2)
Equation (2) allows to obtain the luminance signal without complicating a TV camera. In addition, it allows instead of three color signals to pass only two. The missing signal can be obtained by calculation. A natural question arises about the optima! choice of the two transmitted color signals. This issue was resolved by the spectral analysis.
If the value of the luminance signal, determines a parameter of the image such as brightness, the color signal determines the saturation, respectively, parts of the red, green and blue colors. Pcrceivcd color saturation save set not only on the magnitude of the signal but also on the size of the parts painted in this color. The size of the image detail can be measured in millimeters, and megahertz. For example very small parts are played by a signal in the range from 3 to 6 MHz, the small details - from 1 to 3 MHz, the middle parts is 0,5 to 1 MHz.
Studies of the properties of the eye showed that with reduction of the sizes of the observed color detaiis(det) visible, the color saturation becomes less. This phenomenon is illustrated by the graph of the approximate dependence of the apparent saturation of the conditional dimensions of parts and their colors (Fig. 8).
From Fig. 8 it follows that when the reduction of the saturation of the blue parts (black intervals), saturation and frequency fj« = 0,5 - 0,6 Ml iz becomes almost equal to zero. This means that these parts appear light gray on a black background. The red parts to keep the chroma frequency fjt1 = l ,4 - 1,6 MHz. Green small parts retain the visible color almost to the upper border ofthe TV spectrum. The phenomenon loss of colour is associated is associated with (lie spectral sensitivity characteristics of the eyes. The greatest sensitivity occurs in the green, lower the red and the smallest in blue.
(HacbiiucHHOcn.)
^.Mru
Fig. 8
From Fig.8 it can be concluded that it is appropriate for transmission over the communication channel to use signals ER and En. Because the human eye has a low resolution of image details red and blue light, these signals can be transmitted in a reduced bandwidth. So the spectrum of the signal ER can be transmitted in the band of 1.5 MHz, and the signal Eg in the bandwidth of 0.5 MHz. ft should be noted that the characteristics apply only to (he human eye, as for transmitting TV camera, she plays all three signals in the full frequency band. Therefore, to reduce the width spectra transmitted signals it is neccssary to apply R| filters.
After the formation of the color signal in the reduced tend width they need to be combined with the signal EY so that they were not visible on
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(he screen b/W TV. You can use the amplitude modulation carrier frequency which would be the arithmetic average of the two adjacent harmonics of the line scanning frequency. In this case, the carrier frequency side of a spcctral line will appear in the empty gaps of the spectrum of the luminance signal, as shown in Fig.3. In accordance with Fig.4 on the screen of the cathode ray tube will be compensated color signal, which is applied to the b/W television is a hindrance. I Iowever, such compensation cannot be complete, because the change of image noise on the screen occurs from frame to frame, i.e. with a frequency of 25/2 = 12,5 Hz, and the frequency of the visual averaging is equal to 50 Hz.
Therefore, if you do not take special measures on the screen B / W receiver will be noticeable interference in the form of a fine-mesh. But these measures are necessary for color television, as much of the screen when you transfer a color image contains black / white details, and many details have poor color saturation and relatively large size.
The solution to this problem was carried out the transition from color signals EK, i.e. wc difference that can be obtained based on the following equation:
Er.v = Er - Ey = 0,70 Er - 0,59 E0 - 0,11 ER; Eu_y = EB — Ey = 0,89 E„ - 0.59 EQ - 0,30 En .
(3)
(4)
Obtaining color-difference signals is carried out using the so-called matrix consisting of a set of ordinary resistors. An important property of color-difference signals is equal to zero when transferring b/W image details. In this case, ER=E(1 = Ev and this property follows from equations (3) and (4). When transferring the colored components of the signals is not zero, but at low saturation, they are small and little noticeable disturbance.
Thus the use Er_y and En_y signals with reduced spectral components allows to weaken their visibility on the screen. I Iowever, they are allowed to solve the problem of compatibility of color and b/W TV. When you apply a color TV have two options receiving signal: color or b/W. Of course to solve the problem, you can use the manual switch. Application EH_y and E^y signals give a chance to carry out this switching automatically. As is well known modulation of the beam color cathode-ray tube is made by feeding a control signal to a modulator or to the cathode. Since the three electron beams, there are three cathode and three modulator. The compatible television can provide two feed mode works three color difference signals for example, three modulators and three luminance signal to the cathode.
If the image is black / white, the color difference signals (as it follows from the 3 and 4) are equal to zero, and the luminance signal is applied to the three cathode provides B/W image. If the color image is transferred, the signals modulators interact cathodes and the brightness and color difference component in the compensated signals. Automatically generated color image.
It remains unclear the question: "Where in the color TV takes a third color difference signal E<;-v?», No transmitted signal is generated by a simple calculation from the two transmitted signals (5) with a set of resistors:
E<;-y = - 0,51 Er_y - 0,1 9EH_Y
(5)
with phases 0° and 90°. One of the modulated signal components I, Q. In the other 0.5 MHz band both signals arc transmitted in the band of 1.4 MHz signal is transmitted Q.
in signal receiver division signals I and 0 and by using synchronous detection. To implement it, except for the diode detector signal modulated auxiliary signal is supplied and if it coincides with the phase of the carrier is an allocation phase modulation signal source, for example I To isolate the second auxiliary signal Q signal must have a phase shift of 90", NTSC system to provide a good image quality, but for its successful implementation were needed transmission line with a very high specification. The main demands were phase-frequency characteristics. The situation was complicated to transmit signals over long distances if necessary. So it was conducted research, which appeared as a result of alternative systems PAL and SECAM.
In the PAL system, as well as in NTSC is used quadrature modulation. The main difference is that in the PAL color-difference signal ER_y changes its phase from line to line at 180", When processing signals in the PAL system, there is phase distortion compensation.
in the SECAM system, developed in France and used in the Russian Federation made a very complicated pre-processing the color difference signals, aimed at improving the image quality. Firstly including Linearity signal conversion proccss in the image in the kinescope (tck = 2.8). To avoid distortion signals ER, E(i, EH before being subjected to the encoding matrix of gamma correction. Instead signals F.R_y and En_y color difference signals are transmitted DK and D|j. These signals are formed from signals ER_y and EH.y follows:
Ar = kRER_Y = -!,9 Er.v Ab = k|)Eu_Y = 1,5EB_Y;
(6)
(7)
Application of kn = -1.9 and kB =1,5 having different signs associated with the use of the frequency modulation subcarrier. The study of values of color difference signals in the transmission of various colors showed the feasibility of changing the polarity of one of the signals and the introduction of coefficients. In this case, it dominated negative frequency deviation and decreases the risk of deterioration in image quality by limiting the upper sideband of the chrominance signal. To correct the color spectrum of the signal in the SECAM system are carried out low-frequency pre-emphasis color difference signals and high-frequency pre-emphasis frequency modulated signal.
DJt and D], signals are transmitted in SECAM system arc transmitted alternately: for one line is transferred to DR signal for other Dn. Vertical detail is not reduced, since the finer details transmitted luminance signal, which is transmitted to the total number of rows. To generate control signals CRT is necessary to have at the same time all the color signals. For playback, each color signal is used twice, which is achieved using the delay line tddny = 64 ms, i.e. with a delay time equal to the length of the string.
L
fa
-v
fM] I
The above methods of selecting parameters, forming television signals and their processing have been established in the United States. All accepted for operation of color TV systems are built on them. The main difference between these systems is reduced only to apply the method of sending color information in the spectrum of the luminance signal. The first such system was the system of NTSC (National Television Sistem Comute), adopted in the United States.
The system NTSC. unlike other systems that apply multiple modified color difference signals: 1 i O which are formed from the signals EK_ y and Eu.y taken in a certain proportion.
The system NTSC, unlike other systems that apply multiple modi-fled color difference signals: I i 0 which are formed from the signals EK and En.y taken in certain proportions. According to American experts, this method allows more to improve the image quality, I and Q signals are transmitted by quadrature modulation of a subcarrier having the frequency Ip = 3.58 MFlz. The principle irfquadrature modulation is to use a sinusoidal subcarrier generated in the form of two components
Fig. 9
All the color signal processing procedure in the SECAM system were developed based on a detailed study of the color difference signals in the transmission spectra of various color tones and effect on the frequency modulated signal is superimposed on the spectrum of the luminance signal. Thus spectral analysis from a historical point of view was the basis of analog television
References
l.Samoilov V.F, Khromoy B.P. Television Moscow: Svyaz, 1975,400 p.
2. Zusmanovich V.M. Light and color television. Moscow, Leningrad: Energy, 1964. 208 p.
3. Gtirevich M.M. Color and dimension Moscow, Leningrad: Publishing House of the USSR Academy of Sciences, 1950. 268 p.
4. Nyberg N.D. Tcoretical basis of the color reproduction. Moscow: Soviet science, 1948.
