RU2099903C1 - Color television signal coding and decoding method - Google Patents

Abstract

FIELD: television engineering; equipment of TV centers, high-quality SECAM-plus TV sets, and the like. SUBSTANCE: full color signal is formed on transmitting end so that it has three noncrossing spectra: low- frequency part of brightness signal spectrum, chrominance signal spectrum, and high-frequency part of brightness signal spectrum. The latter component is produced by shifting spectrum portion located in chrominance signal frequency band upward in frequency. Receiver provides for reverse conversion. This ensures extended continuous spectrum of chrominance signal. EFFECT: improved picture sharpness; reduced brightness-chrominance cross distortions. 3 cl, 6 dwg

Description

 The invention relates to television technology and can be used in telecentre equipment with an existing fleet of televisions, in high-quality SECAM televisions, in studio equipment and SECAM-plus receivers.

 In Russia, the D / K television standard is in force, which provides for a spacing of carrier images and sound of 6.5 MHz, a width of the spectrum of the video signal of about 6 MHz and relatively high clarity of the image on the screens of black and white TVs. However, the parameters of the SECAM system adopted in our country (see, for example, B.M. Pevzner. Color television systems. "Energy", 1969, p. 100-115) are not properly coordinated with the D / K standard, as a result of which its advantages are lost. The SECAM system was developed by French experts on the basis of the task of using it in Western European countries, where the B / G television standard with a separation of image and sound carriers of 5.5 MHz was adopted. Therefore, the frequencies of the color subcarriers were chosen in such a way (4.25 and 4.40625 MHz) that the color information is transmitted in the high-frequency part of the spectrum of the B / G television channel. Given the action of the notch filters in the receiver, this gives a luminance bandwidth of about 3.5 MHz, which can be considered satisfactory for the B / G standard.

 The SECAM system was mechanically, without any correction, transferred to our standard. The portion of the spectrum of the luminance signal 3.5 5.5 MHz, corresponding to the boundary of the resolving power of the mask picture tube, is suppressed in the receiver by a notch filter. As a result, a signal with a spectrum consisting of two sections: 0-3.5 MHz and 5.5-6.5 MHz is allocated at the output of the receiver brightness channel. The first section gives clarity of the television image of about 270 television lines (as in the SECAM B / G standard). The second section lies above the resolution limits of mask picture tubes of the most common dimensions (up to picture tubes with a screen diagonal of 63 cm) and has practically no effect on image quality. Thus, having a broadband television standard, we completely lose its advantages in transmitting the SECAM signal. At the same time, the existing SECAM standard has a number of drawbacks that are noticeable in the color image and are caused mainly by cross-distortion of brightness-color and color-brightness. To reduce distortion, a SECAM encoder has a notch filter that attenuates the components of the luminance signal at a frequency of 4.3 MHz by approximately 20 dB. The presence of such a filter makes the use of separation comb filters in the SECAM receiver practically meaningless.

 The objective of the present invention is to improve the SECAM system for the domestic television standard D / K, which, on the one hand, will reduce the disadvantages discussed above while maintaining compatibility with the existing fleet of color televisions, and on the other hand, when performing the receiver in accordance with the present invention will increase the clarity of color images at least to the level of the S-VHS standard. As a prototype of the alleged invention, a standard SECAM system can be adopted, discussed in detail, for example, in the book of S.V. Novakovsky. Standard color television systems. M. Communication, 1976, p. 44-161.

 Functional diagrams of the encoder and decoder of this system are described in the book Color Television Engineering. / Edited by S.V. Novakovsky. M. Communication, 1976, p. 138-154 and 355-379.

 The essence of the alleged invention is that when encoding SECAM, a high-frequency portion of the spectrum of the luminance signal is allocated, the lower boundary of which corresponds to the lower boundary of the spectrum of the chroma signal, and the upper boundary in the simplest case lies in the frequency band of the chroma signal, and it is transferred with or without compression to frequency range 5.5-6.5 MHz. When using information compaction, the entire high-frequency part of the spectrum of the luminance signal can be transferred, up to a frequency of 6.5 MHz. Next, add the received signal with a brightness signal, in which only the low-frequency part of the spectrum of 0-3.5 MHz is stored using a linear-phase low-pass filter. They form a standard color signal and add it with a modified brightness signal and the necessary pulses, which gives a full color television signal of the proposed system.

 In the modernized television according to the invention, the full color television signal is divided into three components: a luminance signal with a spectrum of 0-3.5 MHz (the exact frequency values are not included in the application and can be specified), a converted signal with a spectrum of 5.5-6.5 MHz and color signal. The latter is decoded by the standard method. The converted signal passes the spectrum transfer unit, where it is transferred to the frequency section above the frequency of 3.5 MHz and added to the low-frequency part of the signal, forming a broadband luminance signal, the frequency band of which is determined by the method of spectrum conversion.

 The result is an increase in the clarity of the color image and the luminance-chroma and chroma-luminance distortions are completely eliminated, since the spectra of these components in the transmitted signal do not intersect.

 The proposed method of encoding and decoding a color television signal is reduced to the fact that when encoding from three primary color signals, a luminance signal and color difference signals are generated that modulate the frequency of the color subcarriers in accordance with the standard of the SECAM system; the received color signal is summed with the delayed luminance signal to form a full color television signal, and when decoding, the luminance and color signals are separated by frequency filtering, the color signal is demodulated, and three primary color signals are generated from the luminance and two color-difference signals, while in the process encoding, the luminance signal is separated by the method of frequency filtering into a low-frequency component lying below the spectrum of the color signal, and high-frequency A component whose low-frequency boundary corresponds to the low-frequency boundary of the color signal spectrum, then the high-frequency component is transferred upward in frequency from the color signal spectrum, then the low-frequency and transferred high-frequency components are added, and when decoding, the low-frequency and high-frequency components of the brightness signal are extracted, the latter is transferred over frequency down to the starting place, after which the aforementioned low-frequency and high-frequency components are summarized , restoring the original brightness signal.

 The high-frequency component of the luminance signal can be transferred during encoding and decoding by multiplying it by a constant-frequency reference sinusoidal signal and subsequent filtering, and when encoding, the amplitude is modulated by a color reference signal during the transmission of at least one color burst signal, and when decoding, they are restored reference signal using "flashes" obtained by amplitude detection of a color signal in the interval of frame signals th burst.

 In FIG. 1 is a simplified functional diagram of an encoder according to the invention; figure 2 an example of performing spectrum transfer in the encoder; figure 3 explains the process of transfer and conversion of spectra in the encoder; figure 4 is a simplified diagram of a decoder according to the invention; figure 5 shows an example of the implementation of the block transfer spectra in the decoder; 6 illustrates a signal conversion process in a decoder.

 The encoding device (figure 1), made according to the invention, contains a matrix 1 (M), the inputs of which receive the signals R, G and B of the signal sensor. The first output of the matrix is connected to the output of the encoder by a circuit containing a series-connected delay device 2 (US), a low-pass filter (LPF) 3, the first 4 and second 5 adders. The position of the delay device 2 in the brightness channel is uncritical and this device can, for example, be transferred to the output of the adder 4 without changing the parameters of the device and the invention. The output of the delay device 2 is connected to the second input of the adder 4 through a series-connected band-pass filter 6 (PF) And block 7 spectrum transfer (BPS). The second and third outputs of matrix 1, on which color-difference signals are allocated, are connected to the inputs of the chroma signal forming unit 8 (BFSC), the output of which is connected to the second input of the adder 5. Block 9 is a pulse shaper necessary for the device to operate (FI). The circuit 10 connecting the spectrum transfer unit 7 and the color signal driver 8 is shown by a dashed line and can be used in one embodiment of block 7.

 In FIG. 2 shows an example of a functional block diagram of the spectrum transfer unit 7. In the simplest case, this unit contains a series-connected multiplier 11 and a band-pass filter 12. The second input of the multiplier 11 is connected to the output of the voltage-controlled generator (VCO) 13. The output of the generator 13 is connected through a frequency divider 14 (DEL), a phase detector 15 (PD) and a low-pass filter (LPF) 16 to the VCO control input 13 and, in addition, through a key 17 and circuit 10 with a color signal generation unit 8. In this example, the execution of block 7 in the composition of block 8 is introduced amplitude modulator 18.

 In FIG. 3 shows the spectra of signals in the device of figure 1. Figure 3a corresponds to the brightness signal at the output of the delay device 2. Figure 3b shows the spectrum of the signal at the output of the low-pass filter 3. Figv is the spectrum of the signal at the output of the band-pass filter 6. Figg shows the shape of the spectrum of the signal at the output of the spectrum transfer unit 7. The spectrum of the brightness signal at the output of the adder 4 is shown in Fig.3d. Finally, FIG. 3e shows the spectrum of the full color signal at the output of the adder 5.

 In FIG. 4 is a simplified functional diagram of a decoder according to the invention. The decoder contains a series-connected delay device 19, a low-pass filter 20, an adder 21 and an RGB matrix 22. The output of the delay device 19 is connected through a band-pass filter 23 and a spectrum transfer unit 24 to the second input of the adder 21. The input of the device is through a band-pass filter 25 and a color channel 26 connected to the second and third inputs of the matrix 22. Block 27 is a pulse shaper necessary for the operation of the device. Chain 28 connects the color channel 26 to the spectrum transfer unit 24.

 In FIG. 5 shows an example of the execution of the block 24 of the transfer of spectra in the decoder corresponding to the example of the execution of block 7, presented in figure 2. Block 24 contains a series-connected multiplier 29 and a bandpass filter 30. The output of the voltage-controlled generator 31 is connected to the second input of the multiplier 29. The input of the generator 31 is connected through a low-pass filter 32 to the output of the phase detector 33, the first input of which is connected to the output of the generator 31, and the second input to the output of the amplitude detector 34, the input of which is connected via the key 35 and communication 28 to the color channel.

 In FIG. 6 shows the spectral shapes at the control points of the decoder of FIG. 4. FIG. 6a corresponds to the spectrum of the signal at the input of the decoder. In figures 6b, 6c and 6d, respectively, the spectra of the signals at the outputs of blocks 20, 23 and 25 are shown. FIG. 6d corresponds to the spectrum of the signal at the output of the spectrum transfer unit 24. Finally, FIG. 6e gives the shape of the spectrum of the luminance signal at the output of the adder 21.

Полосовой фильтр 12 выделяет составляющую спектра с частотой (ω₁+ ω_o). В результате спектр сигнала, выделенного фильтром 6, смещается на выходе блока 7 без искажений вверх на f₀, как это показано на фиг.3г.Consider the operation of the device. In accordance with FIG. 1, the luminance signal that is input to the delay device 2 is allocated at the first output of matrix 1, and the color-difference signals RY and BY passing to block 8 of the SECAM color signal generation at the second and third outputs. The low-pass filter 3 extracts from the luminance signal the low-frequency spectrum shown in FIG. 3b. The band-pass filter 6 extracts from the luminance signal a portion of the spectrum starting from the cut-off frequency of the filter 3 to the frequency determined by the implementation of the spectrum transfer unit 7. In the simplest case, when the spectrum transfer is not applied, block 7 can be made in accordance with FIG. 2, and the upper frequency of filter 6 may be approximately 4.5 MHz (FIG. 3c). The signal allocated by the filter 6 is fed to the spectrum transfer unit 7. This block can be made in accordance with figure 2. In this case, the signal passes to the input of the multiplier 11. A sinusoidal signal with a frequency f ₀ from the voltage-controlled oscillator 13 is applied to the second input of the multiplier. This frequency should be greater than the color bandwidth. In this example, f ₀ > 2 MHz. It is convenient to select this frequency according to the harmonic of the horizontal frequency. If we choose, for example, the 129th harmonic, then f ₀ 129 • 15.625 2015.625 KHz. The division factor of the frequency divider 14 is equal to the selected harmonic number. Therefore, at the output of the divider 14, a horizontal frequency signal is allocated. It is compared by a phase detector 15 with horizontal pulses, and the error signal is fed through a low-pass filter 16 to the control input of the VCO 13. A PLL system is obtained that maintains a given frequency of the signal generated by the VCO 13. As a result of the action of the multiplier 11, each harmonic of the signal supplied to the block 7, is modulated by a reference signal with a frequency f ₀ . For harmonics with a frequency f ₁ we get

The band-pass filter 12 selects a spectrum component with a frequency (ω ₁ + ω _o ). As a result, the spectrum of the signal allocated by the filter 6 is shifted upstream by f ₀ at the output of block 7 without distortion, as shown in FIG.

In order to be able to perform inverse spectrum conversion in the receiver, the proposed system provides for the transmission in the full signal of information about the frequency and phase of the signal f ₀ . In the considered example, an amplitude modulator 18 is introduced at the output of the chrominance signal generation block 8, to the control input of which a signal from the VCO 13 is supplied via key 17 and circuit 10. Key 17 is opened by a pulse from block 9 during the transmission of one of the frame synchronization signals. As a result, the color subcarrier packet corresponding to this signal is amplitude-modulated by a sinusoidal signal of frequency f ₀ . This will not affect the operation of the standard receiver, since the modulation will be cut off by the amplitude limiter in the decoder.

 The frequency-shifted portion of the luminance signal is added to the adder 4 with the low-frequency part of the spectrum. The spectrum shown in Fig. 3d is obtained. The transferred portion of the spectrum lies above the boundary of the resolving power of the mask tube and will not give distortions on the receiver screen. In order to completely eliminate the possibility of such distortions, the amplitudes of the transferred components can be further attenuated, as shown in Fig. 3d. In adder 5, the SECAM color signal generated by the standard method in block 8 is input into the luminance signal. A signal is obtained, the spectrum of which is shown in FIG. 3rd. The spectra of the luminance and chrominance components in this signal do not intersect. The clock pulses are introduced into the full signal in the usual way. To simplify the presentation, these chains are not shown in the figures.

In the receiver, made in accordance with the proposed method, the signal allocated by the video detector is input to a decoder made in accordance with FIG. 4. The spectrum of this signal has the form shown in figa. The delay device 19 compensates for the delay of the luminance signal in the color channel 26. The filter 20 selects the low-frequency part of the spectrum (Fig.6b). The band-pass filter 23 selects a portion of the spectrum (FIG. 6c) formed by the encoder unit 7. Finally, the bandpass filter 25 extracts the SECAM color signal from the full signal (Fig. 6d). The color signal is demodulated in the color channel 26. The resulting color difference signals are fed to the array 22. The high-frequency components of the luminance signal are passed to the spectrum conversion unit 24. An example of this block is shown in FIG. An example corresponds to the execution of block 7 of the encoder shown in figure 2. In block 24, the signal is supplied to the multiplier 29. A sinusoidal signal whose frequency (f ₀ ) and phase correspond to the frequency and phase of the reference sinusoidal signal generated in block 13 of the encoder is supplied to the second input of the multiplier from a voltage controlled oscillator 31. The synchronism and common mode of these signals is provided by the PLL system, which includes, in addition to the generator 31, a low-pass filter 32 and a phase detector 33. As a reference signal to the second input of the phase detector 33, sinusoidal oscillation packets received as a result of amplitude detection in the color subcarrier block 34 in the interval of one of the frame color synchronization signals, in which the AM signal is generated by the encoder unit 18. The key 35, opened by the pulses from the driver 27, provides the selection of the desired portion of the signal.

Полосовой фильтр 30 выделяет компоненту sinω₁t. Тем самым высокочастотные составляющие сигнала яркости смещаются по частоте вниз на f₀ и возвращаются на свои исходные по частоте места (фиг.6д). В сумматоре 21 эта часть спектра совмещается с низкочастотной с выхода фильтра нижних частот 20. Получается сплошной спектр, показанный на фиг.6е. При этом обеспечивается сквозная полоса пропускания канала яркости 4,5 МГц, как в стандарте Super-VHS. Четкость изображения по горизонтали увеличивается с 270 твл в прототипе до 350 твл. Это соответствует предельно возможной разрешающей способности масочного кинескопа с диагональю 63 см и шагом маски 0,7 мм.As a result of the multiplication of high-frequency components of the color signal and the reference signal with a frequency f ₀ we get

The bandpass filter 30 isolates the component sinω ₁ t. Thus, the high-frequency components of the luminance signal are shifted downward in frequency by f ₀ and return to their original places in terms of frequency (Fig.6d). In the adder 21, this part of the spectrum is combined with the low-frequency output of the low-pass filter 20. A continuous spectrum is obtained, as shown in FIG. This provides a pass-through bandwidth of the 4.5 MHz luminance channel, as in the Super-VHS standard. The horizontal image sharpness increases from 270 TV lines in the prototype to 350 TV lines. This corresponds to the maximum possible resolution of a mask picture tube with a diagonal of 63 cm and a mask pitch of 0.7 mm.

 When using the proposed signal processing method as part of the SECAM-plus system, designed for larger picture tubes, it is advisable to apply the multiplexing of the transferred part of the spectrum in blocks 7 of the encoder and 24 decoders, which allows transmitting the entire spectrum of this signal, up to a frequency of 6.5 MHz.

 If the signal of the proposed system is received on a standard SECAM TV, the image quality will be higher than when receiving a standard signal. The improvement is due to the fact that in the proposed system the spectra of luminance and color signals do not intersect. This eliminates cross-distortion of luminance and color, which in the standard SECAM system cause interfering color moiré in areas of the image with a fine luminance structure. In addition, the use of a linear-phase low-pass filter 3 in the encoder eliminates distortion at the vertical boundaries of the luminance signal in the form of repetitions and vibrations.

Claims (3)

 1. A method of encoding and decoding a color television signal, in which, when encoding from three primary color signals, a luminance signal and color difference signals are generated that frequency-modulate color subcarriers in accordance with the SECAM standard, the color signal thus obtained is added to the delayed luminance signal to form the full signal, and when decoding, the luminance and chrominance signals are separated by frequency modulation, the chroma signal is demodulated, as a result of which two colors are distinguished input signal, then the luminance signal and color-difference signals are matched, which ensures restoration of the three primary color signals, characterized in that when encoding the luminance signal is divided into low-frequency and high-frequency components by the method of frequency filtering, and the upper boundary of the spectrum of the low-frequency component corresponds to the low-frequency boundary of the color signal, and the spectrum of the high-frequency component is in the frequency band lying above the lower boundary of the spectrum of the color signal, then the high-frequency component is transferred upward in frequency beyond the spectrum of the color signal, after which the aforementioned low-frequency and high-frequency components are summed up to form a luminance signal, and when decoding, the low-frequency and high-frequency components of the luminance signal are isolated by frequency filtering, then the high-frequency component of the luminance signal is converted back to downstream frequency, after which the aforementioned low-frequency and high-frequency components are summarized Restoring luminance signal.  2. The method according to claim 1, characterized in that the transfer of the high-frequency component of the luminance signal during encoding and decoding is carried out by multiplying it by a reference sinusoidal signal of constant frequency and subsequent filtering, and when encoding with a reference signal, the color signal is amplitude-modulated during transmission at at least one frame signal of color synchronization, and when decoding, the reference signal is restored using "flashes" obtained by amplitude detection of the color signal the interval in the interval of frame color signals.  3. The method according to claim 1, characterized in that when transferring the spectrum of the high-frequency component of the brightness signal, information compression is used.

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