JPS5824994B2 - Color video signal defect compensation device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides compensation for defects in a reproduced video signal in a composite video signal reproduction device in which a luminance signal and a chrominance signal are synthesized within the same band in a frequency interleaving relationship. The present invention relates to a device, and particularly to a defect compensation device for a video signal in a device that uses a comb-shaped filter to separate a luminance signal and a color signal.

As is well known, in order to transmit a luminance signal and a chrominance signal in the same band, there is a method of combining the two signals in a frequency interleaving relationship.

For example, if the horizontal scanning frequency is fh and the subcarrier frequency of the color signal is fs, then if the relationship between fh and fs is chosen as shown below, the color signal is a luminance signal whose frequency is distributed at intervals of horizontal scanning frequency n. The signal is inserted between the components, and even if the two signals are combined, no interference will occur between them.

Taking advantage of this, in the NTSC color television system, the horizontal scanning frequency is set to 15734.264H.
z, and the color subcarrier is 1/2 456 times 3.5.
79545 MHz (hereinafter simply referred to as 3.58 MHz), and the luminance signal and color signal are combined and transmitted within a band of approximately 4.1 MHz.

The frequency distribution at this time is shown in FIG. 1a.

In the figure a, the shaded area is where the chrominance signal and the luminance signal share a band, and if this band is analyzed in more detail, it becomes as shown in the figure.

Here, the solid line shows the luminance signal, the broken line shows the color signal,
Does not interfere with brightness signal.

゛By the way, when recording and playing back video signals,
In order to save bandwidth, a method is known in which the horizontal scanning frequency remains unchanged and the frequency of the color subcarrier is lowered, as shown in FIG. 1C.

In this case, for example, the frequency of the color subcarrier is set to 1.534090 MHz, which is 195 times 1/2 of the horizontal scanning frequency (
(hereinafter simply referred to as 1.53 MHz).

In this case, the band of the luminance signal can be narrowed to 3 MHz and the color signal can be included within that band, so that the band can be saved when recording and reproducing.

However, since the band where both the color signal and the brightness signal exist is in the middle range of the brightness signal, if the brightness signal including the color signal is displayed as is on a TV receiver, the interference with the brightness signal by the color subcarrier will be noticeable. Dots appear on the screen, making it difficult to see.

In addition, the color signal is extracted using a band pass filter, and 1.
If the frequency is simply converted from 53 MHz to 3.58 MHz, cross color interference will occur due to the luminance signal, and the quality of the color signal will deteriorate significantly.

A comb-shaped filter is generally used to remove such interference.

This comb filter is shown in FIG.

In the figure a, 1 is -horizontal scanning time delay line (hereinafter IH
(referred to as a delay line), which delays the input signal by a time corresponding to the IH interval.

2 is an adder circuit that adds the human input signal and the IH-delayed signal at the same level.

On the other hand, 3 is a subtraction circuit that subtracts the input signal and the IH delayed signal at the same level.

The frequency characteristics of the outputs of the adder circuit 2 and the subtracter circuit 3 at this time are as shown in FIG.

Here, the Y-shaped filter has a pass band peak at a frequency that is an integral multiple of the horizontal scanning frequency fh where the luminance signal is distributed, and a peak at a frequency that is an odd multiple of 1/2 of fh where the color signal component is distributed. It has a peak in the attenuation range.

In addition, the C-shaped filter has a passband peak at a frequency that is an odd multiple of 1/2 of the horizontal scanning frequency fh, where the color signal component is distributed, and attenuates at a frequency that is an integral multiple of fh, where the luminance signal component is distributed. It has a peak in the area.

Therefore, by using a comb-shaped filter with such a configuration, with the frequency ink=living relationship,
It is possible to independently separate the luminance signal and chrominance signal that are combined within the same band.

FIG. 3 is a block diagram of a processing circuit for signals recorded and reproduced using the buried subcarrier method.

Here, the signal recording medium may be, for example, a video disk in which geometric changes are recorded on the surface of a disk, a VTR in which signals are recorded on a magnetic tape, or other methods.

Furthermore, in order to record on a recording medium, it is desirable that the video signal be FM modulated and recorded.

The signal read from the recording medium is amplified by a preamplifier 4, subjected to amplitude limitation by a limiter circuit 5, and then demodulated by an FM demodulator 6.

Reference numeral 7 denotes a band pass filter having a band of 1.53 MHz±0.5 MHz, which extracts a band in which color signals are distributed centered at a frequency of 1.53 MHz±0.5 MHz.

Here, Δf indicates the jitter component of the reproduced signal.

However, this band also includes a luminance signal component that is synthesized with the color signal in a frequency interleaving relationship.

8 is 5.113636MHz (hereafter simply 5, 1
A variable frequency oscillator centered at 1 MHz),
Approximately 1.53 MHz whose phase is locked to the burst in the input signal by a known AFC method (not shown in the figure)
The device is configured to have the same frequency fluctuation as that of the color burst of the color signal in the video signal reproduced by the variable frequency oscillator and the stable 3.58 MHz crystal oscillator.

Therefore, its frequency is 5.11 MHz±Δf. 9
is a frequency conversion circuit with 5.11 MHz±Δf and 1.53
This produces sum and difference frequencies of MHz±Δj.

1° is a band pass filter of 3.58 MHz ± 0.5 MHz, and 5.11 MHz in the signal from the frequency conversion circuit 9.
Remove the difference component between MHz±Δf and 1.53MHz±Δ.

Therefore, the frequency of the color signal output from the bandpass filter 10 is (5,11 MHz±Δf)−(1,53 MHz±Δ
f) = 3.58 MHz, which matches the frequency of the crystal oscillator, the jitter component is canceled out, and at the same time matches the frequency of the color subcarrier of the standard television signal of the NTSC system.

11 is a C-shaped filter, which is composed of an IH delay line 12 and a subtraction circuit 13, and has a frequency of 3.58 MHz±0.5.
The luminance signal component distributed in the MHz frequency band is attenuated and only the color signal component is extracted.

14 is a frequency conversion circuit, 5.11 M from oscillator 8
The sum and difference frequencies of the Hz±Δf signal and the 3.58 MHz color signal from the C-shaped filter 11 are generated.

15 is a band pass filter of 1.53 MHz±0.5 MHz, and the frequency component of the difference in the output of the frequency conversion circuit 14 is 5.11 MHz±Δf −3,58 MHz.
= 1.53 MHz±Δf color signal component is extracted.

16 is a phase shift circuit that performs an appropriate phase shift on the color signal centered at 1.53 MHz±Δf, and shifts the 1.53 MHz signal included in the buried subcarrier type signal from the delay line 17.
The phase is set to be the same as that of the color signal centered at Hz±Δf.

Reference numeral 18 denotes a subtraction circuit, which essentially constitutes a Y-shaped filter, and attenuates the color signal synthesized with the luminance signal in a frequency interleaving relationship to extract only the luminance signal.

Reference numeral 19 denotes an adder circuit which outputs the color signal centered on 3,58 MH2, which has no jitter component from the C-shaped square filter 11, and the color signal from the Y-shape filter substantially formed by the subtractor circuit 18. By adding the luminance signal, NTSC
Obtain the color video signal of the system.

By the way, it is known that when a signal is recorded and reproduced, a black and white spotty pattern noise occurs in the center of the reproduced signal.

This is caused by defects in signals from video disks, VTRs, etc., and causes include scratches on the surface of the disk, attached dust, or missing magnetic material on the magnetic tape.

Such noise significantly degrades the quality of the reproduced image, so it is necessary to compensate for the portion where the noise occurs with another signal.

FIGS. 4a and 4b show conventional means for compensating for such defects in the reproduced signal.

The same parts as in FIG. 3 are indicated by the same reference numerals.

In FIG. 4a, the buried subcarrier video signal demodulated by the first FM demodulator 6 is normally passed through a switch circuit 20 through Y-shaped and comb-shaped filters as explained in FIG. 3. and is connected to a circuit that converts the color signal into an NTSC color signal.

21 is an IH or an integral multiple thereof delay line, 22 is a limiter
123 indicates a second FM demodulator, and the first FM demodulator 6
A signal is obtained with a predetermined time delay relative to the other signal.

A circuit 24 detects defects in the reproduced signal, and outputs a signal to switch the switching circuit 20 when a defect is detected.

912f, this defect detection circuit 24 is shown in FIG.
, a configuration that detects amplitude fluctuations of the reproduced FM signal may be used.

However, any configuration may be used as long as it can detect defects in the reproduced signal.

If a defect is detected in the reproduced signal, the switching circuit 20 switches to output the signal from the second FM demodulator 23, and changes the section of the reproduced signal where the defect exists to IH or an integral multiple thereof. The defect is compensated for by replacing it with the signal of

FIG. 4 shows another conventional example of the defect compensation method.

The signal from the recording medium is transmitted through a preamplifier 4, a limiter 5,
It is demodulated by an FM demodulator 6 and connected to subsequent circuits, usually through a switching circuit 20, as in FIG. 4a.

40 is an AM modulation circuit, 41 is a delay line having a delay time approximately an integral multiple of IH, 42 is an AM detection circuit, and 43 is a carrier wave oscillation circuit, which delays the output of the switching circuit 20 by a predetermined time.

A defect detection circuit 24 detects a defect in the reproduced signal and generates a signal for switching the switching circuit 20 in the defective section.

Therefore, the defective section is replaced with a signal approximately an integral multiple of IH, and the defect is compensated for.

By the way, an ultrasonic delay line is generally used as an IH delay line, but this ultrasonic delay line has a lot of spurious signals due to internal reflection, and in particular, a lot of signals delayed by 3H are output as spurious signals, and for example, this level can be as high as -22 dB. reach

Therefore, the output of the IH delay line has a ripple in the frequency characteristic caused by this spurious, and in particular, since the 3H spurious is the main cause, the period of this ripple is 1/2 fh.

Therefore, when accurately delaying an AM modulated signal using an ultrasonic delay line, an extremely stable carrier wave oscillator is required, and a crystal oscillator is generally used.

Therefore, the configuration shown in FIG. 4A requires an expensive crystal oscillator, and is not as inexpensive as the configuration shown in FIG. 4A.

In the circuits shown in FIGS. 4a and 4b, in the section where the signals are swapped, the phase of the color signal must be continuous with the phase before the swap.

If you do not do this, the comb filter will not be configured correctly in the replaced section and the luminance signal will have a frequency of 1.53 MHz.
At the same time, the chrominance signal is emphasized by about 6 dB, and at the same time, the chrominance signal is lost.

Therefore, the delay time of the delay circuit 21 or 41 must be selected to be longer or shorter than an odd multiple of IH by a half cycle of 1.53 MHz, or it must be selected to be an even multiple of IH.

Moreover, the delay line used here needs to have a wide band that can sufficiently pass not only the divination range of the FM modulated signal or the carrier wave of the AM modulated wave, but also the sideband of the 1.53 MHz color signal. It is.

If this selection is not made, the 1.53 MHz color signal will not be transmitted correctly, and therefore the comb-shaped filter will not work properly, resulting in an unnatural section in which defects are compensated.

However, how long is a half cycle of 1.53 MHz longer than IH?If a delay line with a short delay time is used, the delay time of the luminance signal is half a cycle of 1.53 MH2 in order to match the phase of the color signal. This produces an error of about 0.32 μsec, which clearly causes discontinuity in the luminance signal on the screen, making it look unnatural.

Furthermore, if there is jitter in the reproduced signal, the phase of the color signal will fluctuate irregularly, and the comb filter will no longer work completely even if it is replaced.

On the other hand, when the defective section is replaced with a signal delayed by 2H, the phase of the color signal and the phase of the luminance signal match, but the broadband IH
Two delay lines are required, which not only makes the circuit expensive but also has a large amount of delay, so even if it is replaced, the correlation with the preceding and succeeding signals becomes weaker, resulting in unnaturalness on rapidly changing screens. be.

This is particularly noticeable in luminance signals to which the human eye is sensitive.

Furthermore, if there is jitter in the reproduced signal, the delay line is large, and the chrominance signal will experience larger phase fluctuations than when using an IH delay line, and the operation of the comb filter will therefore be affected. Become more complete.

Further, in the case of the configuration as shown in FIG. 4a, there is a drawback that defects in a section longer than the delay time of the delay circuit 21 cannot be compensated for.

According to the present invention, it is an object to provide a defect compensation device that eliminates the drawbacks of such conventional methods and can be realized with an inexpensive configuration.

FIG. 5 shows an example in which the present invention is implemented in the apparatus shown in the block diagram shown in FIG.

Here, the same blocks as in FIG. 3 are indicated with the same reference numerals.

The signal read from the recording medium is demodulated by the preamplifier 4, limiter 5, and FM demodulator 6, and then converted to 1.53MH.
A band pass filter 7 of z±0.5 MHz separates the band including the color signal and the luminance signal.

8 is a variable frequency oscillator centered at 5, 11 MHz, which has the same jitter as the burst signal in the input signal, and its output is applied to the frequency conversion circuit 9, which converts the output signal of the filter 7. Convert frequency.

3.58 MHz±0. in the output of the frequency conversion circuit 9.
The color signal and luminance signal included in the 5MHz band are 3,
58 MHz ± 0.5 MHz bandpass filter 1
After being separated by 0, it is applied to the switch circuit 25.

The switch circuit 25 is usually a bandpass filter 10.
is connected so as to lead the output thereof to a subsequent comb-shaped filter 11 consisting of an IH delay line 12 and a subtraction circuit 13.

11 constitutes a C-shaped filter, 3.58 MH
Extract the color signal of z±0.5 MHz.

This output is led to the adder circuit 19 and simultaneously applied to the frequency conversion circuit 14, which converts the frequency to 1.53 M
1.53 in the buried subcarrier signal that has been frequency-converted to a chrominance signal of Hz±0.5 MHz, passed through a band-pass filter 15, a phase shift circuit 16, and a delay line 17.
The subtraction circuit 1 matches the phase and level with the MHz color signal.
8 to form a substantially Y-shaped filter.

27 is a switching circuit, which normally switches the output of the subtraction circuit 18;
It is connected to guide the luminance signal to the adder circuit 19.

Therefore, from the adder circuit 19, the luminance signal and the 3.58 MHz
The color signals of the NTSC system are added to obtain a color video signal of the NTSC system, and the signal is sent to a color receiver to display a color video.

24 is a defect detection circuit that detects defects in the reproduced signal,
A signal is generated to switch the switching circuits 25 and 27.

Next, the operation when a defect is detected will be explained.

When the defect detection circuit 24 detects a defect in the reproduced signal, the switching circuit 25 has a movable contact that sets the output of the inverting amplifier circuit 26 that is inverting and amplifying the output of the IH delay line 12 as the output of the switching circuit 25. It will switch like this.

When the switching circuit 25 switches in this way, the output of the comb filter 11 is actually the output of the IH delay line, and the phase of the 3.58 MHz color signal is kept continuous.
The color signal of the defective section is compensated.

Further, at this time, a closed loop consisting of the IH delay line 12, the inverting amplifier 26, and the switching circuit 25 is formed, so even if the defective section extends beyond the IH, the color signal can be compensated.

On the other hand, compensation of the luminance signal is performed by the switching circuit 27, the AM modulation circuit 28, the IH delay line 28, and the AM detection circuit 30.

That is, the luminance signal from which the color signal has been removed by the subtraction circuit 18 by substantially forming a Y-shaped filter is normally applied to the addition circuit 19 through the switching circuit 27.

When a defect is detected, the movable contact of the switching circuit 27
The M modulation circuit 28, IH delay line 29, and AM detection circuit 30 switch to output the IH-delayed luminance signal, thereby compensating for the defective section.

Moreover, at this time, the switching circuit 27, the AM modulation circuit 28, the I
Since a closed loop is formed by the H delay line 29 and the AM detection circuit 30, it is possible to compensate the luminance signal even if the defective section extends beyond IH.

At this time, it is of course desirable that the IH delay line 29 used in the delay circuit be one that can accurately transmit all bands of the luminance signal, but in practice, a line with a narrower band is sufficient.

In other words, with the Y-shaped filter, 1.53 MH
In order to compensate for the defective section by delaying the luminance signal from which the 1.53MHz color signal is removed, even if it is not accurately transmitted to the band where the 1.53MHz color signal is distributed, the signal is replaced in the section where the signal is replaced. The unnaturalness is not noticeable.

Therefore, even if the delay line has a band narrower than that required by the IH delay line used in FIG. 4, there is no problem in practice.

Therefore, for example, NTSC, which is generally inexpensive and easy to obtain,
It is also possible to use an IH delay line centered at the color subcarrier frequency (approximately 3.58 MHz) of the system, and an expensive delay line with a wide band is not necessarily required.

In this case, the carrier wave oscillator is a 3.58 MHz carrier wave oscillator used to configure a 5.11 MHz variable frequency oscillator.
It is also possible to use a crystal oscillator in combination, and there is no need to provide a particularly expensive crystal oscillator for the IH delay circuit, and a very inexpensive circuit configuration including the IH delay line can be achieved.

Further, in this case, the switching circuit 25 is the bandpass filter 7.
Since the switching circuit 27 switches the signal delayed by the delay line 17, the defect detection circuit 2
The timing delay in defect detection caused by 4 is sufficiently compensated for.

Therefore, noise caused by a delay in switching when starting to compensate for a defect, which has been a problem in conventional compensation circuits, is no longer generated, and stable compensation can be achieved.

Furthermore, the luminance signal for compensation uses a signal delayed by IH, and therefore, in FIG. Does not occur.

In addition, since the delay time of the luminance signal can be set accurately to IH, the discontinuity of the luminance signal that occurs when compensation is made with a signal delayed longer or shorter by the time equivalent to a half cycle of 1.53 MH2 from IH in Figure 3. No sagging occurs.

On the other hand, the frequency conversion circuit 9 uses the chrominance signal as a compensation signal, which removes frequency fluctuations caused by sick signals. It is possible to eliminate imperfections in the movement of

On the other hand, in FIG. 5, the inverting circuit 26 is used to compensate for the C-shaped filter, but it is also possible to use an IH delay line instead, and in this case,
Eliminates cross-color interference.

As described above, according to the present invention, the delay line constituting the comb-shaped filter for separating the luminance signal and chrominance signal from the signal of the buried subcarrier system has a band that only passes the band of the chrominance signal component. delay lines are available, and
This delay line is commonly used as a delay line for the chrominance signal defect compensation device, and the delay line for the luminance signal defect compensation device also compensates for defects only in the luminance signal component after the chrominance signal is separated. All delay lines can be constructed of narrowband delay lines without requiring a wideband delay line.

[Brief explanation of drawings]

FIGS. 1A, 1B, and 1C are diagrams showing color video signals synthesized in a frequency interleaving relationship, and FIG. 2A is a block diagram of a comb-shaped filter. C is a diagram showing its frequency characteristics, FIG. 3 is a block diagram showing an example of a circuit that converts a buried subcarrier system signal into an NTSC system color video signal, and FIGS. 4a and b show defects. Block diagram showing a conventional example of a signal compensation circuit, No. 5
The figure is a block diagram showing a color video signal defect compensating device in one embodiment of the present invention. 24... Defect detection circuit, 25, 27...
...Switching circuit, 28...AM modulation circuit, 29.
...IH delay line, 26...Inverting amplifier circuit, 11...C-shaped filter, 18...
...Subtraction circuit, 19...Addition circuit.

Claims (1)

[Claims] 1 Reproducing a signal from a recording medium on which a color video signal in which a luminance signal and a color signal are synthesized in a frequency interleaving relationship, extracting a frequency band in which the color signal is included from the reproduced signal; The signal component is guided to a first contact of a first changeover switch, the movable contact of the first changeover switch is guided to a C-shaped filter including a first horizontal scanning time delay line; The separated color signal, which is the output of the C-shaped filter, is guided to a mixer, and is added to the reproduced signal in an opposite phase to the color signal in the reproduced signal, thereby adding the color signal component in the reproduced signal. The luminance signal from which the color signal component has been removed is guided to a first contact of a second changeover switch, the movable contact of the second changeover switch is connected to the mixer, and the luminance signal and the color signal component are removed. A standard color television signal is obtained by mixing the color signal with the color signal, and a part of the output of the first one horizontal scanning time delay line is inverted in phase to be connected to the second contact of the first changeover switch. and apply the luminance signal from which the color signal component has been removed to the second contact of the second changeover switch via a second one-horizontal scanning time delay line, only during the period in which the reproduced signal is missing. A color video signal defect compensation device, characterized in that the movable contacts of the first and second changeover switches are configured to switch from the first contact to the second contact, respectively.