JPS5820507B2 - Color television program - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high-quality color television signal transmission system that prevents occurrence of cross color or hue change due to nonlinear distortion in a signal transmission system.

Typical conventional color television signal transmission systems include NTSC, PAL, and SECAM, all of which constitute a frequency multiplexed signal in which a luminance signal and a color information signal share a frequency domain. (1) The NTSC system, which multiplexes color information signals with frequency utilization efficiency in the vertical spatial frequency domain of luminance signals, is susceptible to nonlinear distortion in the signal transmission system; P that reduces the influence of nonlinear strain
The AL method and SECAM method have poor frequency utilization efficiency in the vertical spatial frequency domain of the luminance signal, and (3) in both methods, interference between the luminance signal and color information signal causes cross-color or dot-like patterns in the reproduced image. There are disadvantages such as 2.
A carrier color signal formed by orthogonal two-phase balanced modulation of a color subcarrier using two color information signals is converted into a frequency multiplexed signal that shares the frequency domain with a luminance signal using one horizontal scanning frequency offset method, and the main carrier is modulated and transmitted. (4) Nonlinear phase distortion of the carrier color signal in the signal transmission system appears as a hue shift in the reproduced image, degrading the image quality, and (5) Deterioration of the band characteristics of the signal transmission system causes color distortion. There are also drawbacks to the transmission of the color information signal itself, such as crosstalk occurring between the information signals, and especially high interference distortion of the high frequency components of the color information signal.

It is an object of the present invention to provide high-quality color television signal transmission that eliminates the various drawbacks mentioned above, does not cause interference such as cross color in reproduced images, and is not affected by fluctuations in the frequency band characteristics of the signal transmission system. The goal is to provide a method.

Another object of the present invention is to frequency-multiplex a luminance signal and a carrier color signal with efficient frequency utilization in the vertical spatial frequency domain, and further to correct and eliminate the influence of non-linear distortion in a signal transmission system. The purpose of the present invention is to provide a television signal transmission system.

That is, the color television signal transmission system of the present invention is as follows:
When transmitting a color television signal composed of a luminance signal and two color information signals, at least one of the frequency bands of the two color information signals is narrower than the upper limit of the frequency range of the luminance signal. When the frequency is set to an integral multiple of the horizontal scanning frequency, the polarity of the color information signal having the wider frequency bandwidth is alternated between the scanning lines. When the frequency is set to an odd multiple of the interrogation wave number i, the polarity of the color information signal is alternately inverted in the scanning line, and the two colors are By performing quadrature two-phase balanced modulation with the information signal to form a carrier color signal, the component of the color information signal having the narrower frequency bandwidth of the carrier color signal is extended to the arrangement of the components of the luminance signal. The color information signals are arranged at a distance from each other on the top, and high-frequency components and low-frequency components of the color information signal having a wider frequency bandwidth are inserted in the middle of the arrangement of each of the components. This is a characteristic feature.

The present invention will be described in detail below with reference to the drawings.

First, FIG. 1 shows a circuit system for forming and processing color television signals according to the conventional NTSC system.

In Fig. 1, R, G, and B signals from a color camera are supplied to color signal input terminals 1 and 2°3, respectively, and these signals are added to a signal converter (matrix circuit) 6 to convert them into a luminance signal Y. Convert these color signals into two color signals of
MHz.

After adjusting the occupied bands in addition to the low-pass filters γ, 89 of 1, 5 MHz and 0.5 MHz, the two color signals I and Q are half-odd times the horizontal scanning frequency fh, that is, (2n+1)−! -! l! -frequency fs, for example 4
A color subcarrier of 55×fh 2 T-3, 58MH2 is applied from the input terminal 4 to the modulator 10 and subjected to quadrature two-phase balanced modulation, and the carrier color signal of the modulated output is converted to the luminance signal Y, and its high frequency region is They are shared and frequency multiplexed to form an NTSC color television signal.

The signal spectrum distribution of the NTSC color television signal formed as described above is as shown in FIG. They are arranged alternately in the middle of the spectrum.

However, in such a carrier color signal, if there is non-linear distortion in the signal transmission system, it will appear as hue distortion, that is, color shift, in the reproduced image.

FIG. 3a shows one vector of the carrier color signal subjected to quadrature two-phase balance modulation on the y-coordinate axis.

In Fig. 3a, α indicates the phase of the carrier color signal sideband with respect to the color subcarrier at any time, and the upper sideband U and lower sideband both form an angle of α with respect to the y-axis, and The resultant vector R coincides with the y-axis.

The vector of the external force of the carrier color signal has a similar relationship with respect to the y-axis.

Now, the phase delay characteristics of the signal transmission system are uniform for both upper and lower band waves, but if the amplitude characteristics for the upper side band wave U are worse than the amplitude characteristics for the lower side band wave, then
As shown in FIG. 3, the vectors U and L are different in magnitude, and as a result, the resultant vector R does not coincide with the y-axis, producing a component E in the X-axis direction.

In addition, if there is non-linear distortion in the phase delay characteristics of the signal transmission system, and the phase angles of the upper and lower band waves U and L at a certain time differ from β and α, respectively, as shown in Figure 3C, Also, the resultant vector R does not coincide with the y-axis and produces a component E in the X-axis force direction.

Therefore, if there is non-linear distortion in the amplitude and phase characteristics of the signal transmission system, the color signal in the X-axis direction will generate a color signal component in the X-axis direction, and similarly crosstalk will occur between the color signals.

The PAL color television signal is a signal transmission method that avoids hue distortion due to non-linear distortion in the signal transmission system as described above, and the polarity of one of the two color signals is alternated for each scanning line. By reversing it to
As shown in the spectral distribution diagram shown in Figure 2, the luminance signal Y
There are two carrier color signal spectra between the luminance signal spectra in the high frequency region of , and the distance between them is fh/2.
The color television signal is configured such that it is arranged with an interval of fh/4 between it and the luminance signal spectrum, but the frequency band occupied by the carrier color signal in the vertical spatial frequency domain of the luminance signal Y is This is twice as large as in the case of the NTSC system shown in FIG. 2a, and interference such as cross color in the reproduced image due to interference between the luminance signal Y and the carrier color signal increases accordingly.

In other words, in both the systems shown in Figure 2a and b, since the luminance signal and the carrier color signal share the frequency domain, dots appear in the reproduced image as mutual interference due to nonlinear distortion in the signal transmission system. This causes brightness interference and cross-color interference, which significantly impairs the stability of television images.

Future high-definition color television signal transmission systems must eliminate the instability of reproduced images caused by non-linear distortion in the signal transmission path as described above, and also improve the efficiency of use of the transmission frequency band. It has to be good.

FIG. 4 shows an example of the configuration of a signal forming circuit according to the color television signal transmission system of the present invention, which is intended to transmit such high-quality signals.

In FIG. 4, R from color signal input terminals 1, 2, and 3,
The G and B color imaging output signals are added to a signal converter (matrix circuit) 6, and a luminance signal Y and a relatively wide band color signal Cw are added to the signal converter (matrix circuit) 6.
and a relatively narrow band color signal CN.

These wideband and narrowband color signals Cw and CN may be, for example, the 1 times the NTSC color television signal and the Q signal. As described in , the isotemporal rate (
UC8) Select a color signal with a wide chromaticity spatial frequency band for visual perception on the chromaticity diagram and a color signal in a direction orthogonal to the color signal on the chromaticity diagram, and calculate the phase error with respect to the carrier color signal in the reproduced image. It is also possible to make the effect not different depending on the color.

The cutoff frequency fB is used for each of the above-mentioned converted output signals.

Low-pass filter γ with fOW+”ON, 8°9
In addition, as shown in FIGS. 5a, b, and c, a luminance signal Y,
A wideband color signal Cw and a narrowband color signal CN are formed.

Here, if fOW>fON, the respective sizes can be selected to various values according to the visual characteristics as described above, and in FIGS. 5b to 5e, fOW is selected to be considerably larger than fON, An example is shown in which one of the color signals has a considerably wide band.

In the circuit example shown in FIG. 4 in which two color signals are set as described above, the frequency fS of the color subcarrier applied to the input terminal 4 is selected to be an integral multiple of the horizontal scanning frequency fh, and f8=1□
Furthermore, the upper limit fB of the frequency band of the luminance signal Y and the upper limit fON of the frequency band of the narrowband color signal cN are selected as fs-=fB+fON' (1),
This color subcarrier is directly applied to the modulator 15, where it is balanced-modulated by the narrowband color signal CN, and the color subcarrier whose phase is delayed by 100 degrees, that is, 90 degrees, is applied to the modulator 14 through the delay circuit 13, and the switching is performed. Switch 12 performs balanced modulation using a broadband color signal Cw whose polarity is alternately inverted for each horizontal scanning line, and the modulated outputs of these modulators 14 and 15 are added by adder M1, and the frequency is shown in Fig. 5d. A multi-modulated carrier color signal of quadrature two-phase modulation similar to a PAL system signal is formed that exhibits band characteristics.

This carrier color signal is added to the adder M2 and added to the luminance signal Y and the synchronization signal from the input terminal 5, and the cutoff frequency f'B of the summed output is selected as the upper limit of the narrow upper sideband in the carrier color signal. In addition to the low-pass filter 11, the frequency band is adjusted to obtain a composite color television signal having frequency band characteristics as shown in FIG. 5e.

FIG. 6 shows a spectral distribution representing in more detail the frequency band characteristics of the composite color television signal shown in FIG. 5e.

As can be seen from FIG. 6, the spectrum distribution of the luminance signal Y shown by the solid line is followed by the spectrum of the narrowband color signal CN shown by the broken line with the same fh interval, and these series of Y
The spectrum of the broadband color signal shown by the dotted line is arranged in an fh/2 interleaved manner between the spectrum of the signal and the CN signal.

For further details on the spectral distribution in FIG.
The space between (2) and (2) is the luminance signal region, (2) is the color subcarrier frequency, and between O and 0 is the total frequency band of the composite color television.

However, between ■ and ■, the luminance signal Y and the carrier color signal share the frequency domain, but this is why the color signal component spectrum is mixed in the high-frequency spectral distribution of the luminance signal. The color signal components distributed between .

Furthermore, between ■ and 0, which do not share any frequency domain with the luminance signal Y, the two color signal components are separated from each other and coexist with different occupied spectral frequencies, and the two color signal components are vertical to the carrier color signal. The occupied band of the spectral distribution in the spatial frequency domain is twice that of the conventional system, and this frequency domain is effectively used to efficiently transmit color information signals.

Therefore, in the color television signal of the present invention having the above-mentioned spectral distribution, even if there is nonlinear distortion in the signal transmission system, the occupied spectra are different from each other, so reproduction is caused by interference between color signals. Since no change in the hue of the image occurs and interference between the luminance signal and the color signal is reduced, stable transmission of color image information signals can be achieved.

Furthermore, in the above example, since the color subcarrier frequency f is selected to be an integral multiple of the horizontal scanning frequency fh, synchronization of the reproduced color subcarrier for synchronous detection of the carrier color signal on the receiving side can be easily and reliably performed. There are also benefits that can be taken.

In the above example, as shown in FIGS. 5d and 5e, the high frequency component of the wideband color signal Cw is set to share the frequency domain with the high frequency component of the luminance signal Y to a considerable extent. , for example, as shown in FIG. 5f, by choosing the color subcarrier frequency a little higher and not making the frequency band of the wideband chrominance signal Cw too wide, the frequency domain can be shared by the wideband chrominance signal Cw and the luminance signal Y. On the receiving side, the luminance signal Y and carrier chrominance signal are filtered by a one-dimensional filter, and the wideband chrominance signal CW and narrowband chrominance signal CN are filtered by a comb-shaped filter. This makes it easier to transmit stable color image signals without interference between these signals or crosstalk due to deterioration of characteristics of the signal transmission path.

Further, in the same manner as in FIG. 5f, when the luminance signal Y and the carrier color signal hardly share the frequency domain, the frequency f of the color subcarrier.

FIG. 7 shows the spectral distribution of the color television signal when fh is selected to be an arbitrary frequency regardless of the horizontal scanning frequency fh.

In the spectral distribution shown in Fig. 7, the spectra of both the wideband and narrowband color signals do not exist at positions where the luminance signal spectrum is continuously extended at the same intervals, and furthermore, the two color signal spectra are mutually exclusive. In between is fh
Since the interval of /2 is maintained, Y, Cw.

The respective spectral distributions of the CN signals do not overlap at all, and the color subcarrier frequency f, as described above, is f5〉
Since there is a relationship of fB+fcN, it is extremely easy for these signals to form multiplexed signals and to separate them using filters, and furthermore, mutual interference is further reduced.

Next, FIG. 8 shows another example of the configuration of a color television signal forming circuit according to the method of the present invention.

In the configuration of FIG. 8, R, G as in the previous example.

The camera output signals of each color B are supplied to the signal converter (matrix circuit) 6, and the converted outputs are set to the cutoff frequency fB.
, t”awl fON low-pass filter r, 8.9
In addition, a luminance signal Y, a wideband color signal Cw, and a narrowband color signal cN are respectively formed.

In this example, the frequency f8 of the color subcarrier supplied to the input terminal 4 is equal to the horizontal scanning frequency fh multiplied by an earth factor (2n+1)-7, as in the conventional NTSC system.
? The color subcarrier is applied as it is to the modulator 15, and balanced modulated by the narrowband color signal CN whose polarity is alternately inverted for each horizontal scanning line by the changeover switch 12. -, the color subcarrier whose phase is delayed by 90 degrees is added to the modulator 14 and balanced modulated by the wideband color signal Cw, and the modulated outputs of these modulators '14 and 15 are added to the adder M0. to form a quadrature two-phase modulated carrier color signal,
The following processing is performed in exactly the same manner as in the configuration shown in FIG. 4 to obtain a composite color television signal having a frequency band distribution exactly the same as that in FIG. 5e.

The frequency band characteristics of the carrier chrominance signal on each side above are as shown in Figure 5 e and f, where the upper limit of the total frequency band of the composite color television signal is the upper limit of the narrow upper sideband of the carrier chrominance signal. Since the occupied frequency band is selected to prevent the occupied frequency band from becoming wide, the sideband for the high frequency component of the wideband color signal is only the lower side, so when reproduced on the receiving side, the high frequency band of the wideband color signal Cw is The level of the low frequency components is reduced by half compared to the low frequency components.

In still another configuration example of the color television signal forming circuit according to the present invention shown in FIG. 9a, the signal converter 6
Among the converted output color signals, the narrowband color signal cN is extracted through the low-pass filter 9 with the cutoff frequency fON as in the previous example, but the wideband color signal Cw is extracted from the lowpass filter 9 with the cutoff frequency fON. It is branched and supplied to a pass filter 8 and a low pass filter 19 with a cutoff frequency fON, and the broadband filter 8 is supplied with filters 8 and 19.
A signal is supplied through a delay circuit 20 with a delay amount corresponding to the difference in delay of the passing signal between , the output signal of the wideband filter 8 is added to the subtracter M3, and the combined output is sent to the amplifier 1r.
In addition, the signal level is amplified twice to form a broadband color signal in which the voltage gain of the high frequency component is twice that of the low frequency component, as shown in FIG.

In this way, in the configuration example shown in FIG. 4, the broadband color signal whose high frequency component level has been doubled in advance is used after being added to the phase inversion circuit 18, and the narrowband color signal CN is As shown in FIG. C, the same frequency band characteristics as the conventional one are used, and these color signals are multiplexed with the luminance signal.

A color television signal having frequency band characteristics as shown in FIG. 9(d) corresponding to the above is formed.

If a color television signal with such frequency band characteristics is demodulated on the receiving side, the frequency band characteristics of the reproduced wideband color signal Cw will be completely flat because the level difference in the high frequency components at both the transmitting and receiving ends is canceled out.

FIG. 10 shows a configuration example of a signal separation circuit on the receiving side for a color television signal according to the method of the present invention.

In the configuration shown in FIG. 10, the received demodulated output signal is applied to a low-pass filter 21 having a cutoff frequency fB and a delay characteristic τB to separate the luminance signal Y, and a delay circuit 20 is applied to the above-mentioned Y signal and A subtracter M4 removes the luminance signal Y from the demodulated output signal with time to extract the carrier color signal component.

This reproduced carrier color signal is a delayed output added to a horizontal scanning period (IH) delay circuit 22 and a variable delay circuit 23 whose delay amount τC is adjusted within the range of τC = ±2 T. At the same time, the delays between the signals are jointly supplied to the adder M1 and the subtracter M, and narrowband and wideband carrier color signal components CN and Cw are obtained as respective addition/subtraction outputs.

Note that, as shown in FIG. 1, the delay amount τC of the variable delay circuit 23 is within the above-mentioned range when the frequency f5 of the color subcarrier is arbitrarily set, and the delay amount τC of the color signal whose polarity is reversed for each scanning line is determined as shown in FIG. Adjustment is made to match the delay timing, but as shown in Figures 5 and 6, if the color subcarrier frequency f5 is selected to be an integral multiple or a multiple of the horizontal scanning frequency fh, πc-C. do.

As is clear from the above, according to the color television signal of the present invention, a stable color image signal can be transmitted regardless of the characteristic deterioration of the signal transmission system, but the frequency band characteristics of the signal transmission system When the band is limited to (f5+fOw) or less, crosstalk between color signals does not occur, but the frequency band characteristics of both wide and narrow band color signals deteriorate, for example, as described in connection with FIG. 9.

In order to eliminate the deterioration of the frequency band characteristics of the reproduced color signal in the color image signal of the present invention, for example, as shown in FIG. 11, during the vertical erasing period of the television signal, the frequency f1. f2. f3゜..., fn-1, f
A reference signal in which the color subcarrier f8 is balanced and modulated in the same manner as the carrier color signal using a sine wave of n is continuously inserted and multiplexed at the same position for at least two or more scanning lines, and is transmitted together with the carrier color signal.

The phase of the color subcarrier in this case may be the phase of the color subcarrier modulated by the narrowband color signal CN, or may be the phase of the color subcarrier modulated by the wideband color signal Cw.

On the receiving side, for example, with a circuit configuration as shown in FIG. 12, the demodulated output level of the DC portion of the waveform of FIG. 11 and the reproduction level of each reference frequency component are compared for the output signal of the demodulator 24, Each frequency f1. f2. f3
．． . . . An automatic gain control (AGC) signal regarding the reference signal components of fn-0 and fn is formed in the generator 26, and each AGC signal is supplied to a channel equalizer for each of the above-mentioned frequencies to calculate the amplification gain thereof. Adjustments are made to correct deviations in the reproduction level of each reference signal, and a carrier color signal with peaceful frequency band characteristics is reproduced.

By doing so, it is possible to reproduce a stable color image signal that is not affected by phase distortion or deterioration of frequency band characteristics in the signal transmission system.

As is clear from the above explanation, in the color television signal transmission system of the present invention, ([) at least the color signal component with large energy is prevented from sharing the frequency/domain with the luminance signal component, and the luminance signal and the color signal are (ii) The two color signal components are kept at an interval of fh/2 so that their frequency spectra do not overlap, and the color subcarriers are multiplexed. As described in (11) above, the frequency spectrum of the carrier color signal in the range where the frequency domain is not shared is increased to twice that of the conventional method, and the frequency band is efficiently used for transmission. The frequency domain is shared with the luminance signal component only in the frequency domain where the energy of the color signal is low and only one color information is transmitted; (v) In the shared domain described in (IV) above, The spectral components and carrier color signal components are multiplexed and transmitted while maintaining the spectral distribution relationship of fh/2 offset,
Furthermore, (V) By inserting reference signals of multiple frequencies into the vertical erasure period etc. and transmitting them simultaneously, on the receiving side,
Since the reproduction gain of the channel equalizer is adjusted according to the reproduction level of these reference signals to correct the frequency band characteristics of the reproduced carrier color signal, the transmission method of the present invention has the following remarkable effects. is obtained.

(1) Dot interference and cross color interference due to mutual interference between the luminance signal and the color information signal do not occur, and these interferences do not cause a crawling phenomenon in the reproduced color image and cause a sense of instability.

(2) Crosstalk between color signals does not occur even due to asymmetric distortion of the upper and lower band waves of the carrier color signal in the signal transmission path, and therefore no hue change occurs in the reproduced color image.

(3) Even if the frequency of the color subcarrier is selected to be an integral multiple of the horizontal scanning frequency or an arbitrary frequency, there is no problem with the operation or function of color image transmission, and the degree of freedom in frequency selection is increased.

(4) Since the low frequency component of the color signal has a wide occupied band of spectral distribution within the transmission frequency band, the carrier color signal is not affected by non-linear distortion of the signal transmission path.
Stable color image signal transmission can be performed, and high-quality color images can be reproduced.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing the configuration of a conventional NTSC color television signal forming circuit, and FIGS. 2a and 2b are spectral diagrams showing the spectral distributions of NTSC and PAL color television signals, respectively. Third
Figures a and c are vector diagrams showing interference between carrier color signals due to transmission distortion, Figure 4 is a block diagram showing an example of the configuration of a color television signal forming circuit according to the method of the present invention, and Figure 5 is a = f is a frequency band characteristic diagram showing the distribution of frequency bands of each component signal in the color television signal according to the method of the present invention, and FIG. 6 is a frequency band characteristic diagram formed by the circuit configuration shown in FIG. FIG. 7 is a spectral diagram showing another example of the spectral distribution of the color television signal formed by the circuit configuration shown in FIG. 4, and FIG. A block diagram showing another example of the configuration of the color television signal forming circuit according to the method of the present invention, FIGS.
A frequency band characteristic diagram showing the frequency band distribution of a color television signal formed by the circuit configuration. FIG. 10 shows an example of the configuration of a circuit that receives a color television signal formed by the method of the present invention and separates each component signal. FIG. 11 is a signal waveform diagram showing an example of a reference signal added to a color television signal for reception and demodulation of a color television signal according to the method of the present invention, and FIG. FIG. 2 is a block diagram showing an example of the configuration of a circuit that demodulates a color television signal according to the present invention. 1.2.3... Color signal input terminal, 4...
・Color subcarrier input terminal, 5... Synchronization signal input terminal, 6... Signal converter (matrix circuit), γ
, 8, 9° 11... Filter, 10, 14,
15... Modulator, 12... Changeover switch, 13... Delay circuit, 16... Attenuator, 1γ... Amplifier, 18 ...Polarity inversion circuit, 19...Filter, 20.22...
...Delay circuit, 21...Filter, 23
......variable delay circuit, 24...demodulator,
25...Channel equalizer, 26...
...AGC signal generator, M, Ml. M2... Adder, M3. M,, M5...
・Subtractor.

Claims (1)

[Claims] 1. When transmitting a color television signal composed of a luminance signal and two color information signals, at least the upper limit of the frequency range of the luminance signal is within the frequency bandwidth of the two color information signals. Color subcarriers with frequencies that maintain a wider frequency spacing than the narrower frequency bandwidth,
When the frequency is set to an integer multiple of the horizontal scanning frequency, the polarity of the color information signal having the wider frequency bandwidth is alternately inverted for each scanning line, and the frequency is set to an odd multiple of l of the horizontal scanning circular wave number. Sometimes, the polarity of the color information signal having the narrower frequency bandwidth is alternately inverted in the scanning lines, and then the polarity of the color information signal is alternately inverted in the scanning lines. By performing balanced modulation to form a carrier color signal, among the carrier color signals,
Components of the color information signal having a narrower frequency bandwidth are arranged spaced apart from each other on an extension of the arrangement of the components of the luminance signal, and high frequency components of the color information signal having a wider frequency bandwidth. A color television signal transmission system characterized in that a low frequency component and a low frequency component are inserted and arranged in the middle of the arrangement of each of the components.