JP2697515B2 - Dropout compensation circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to, for example, a color signal dropout compensation circuit of a VTR.

[0002]

2. Description of the Related Art FIGS. 3 and 4 are diagrams for explaining a conventional dropout compensating circuit, respectively. FIGS. 5 and 6 are diagrams of various parts relating to the conventional dropout compensating circuit shown in FIGS. It is a signal waveform diagram.

[0003] First, a dropout compensation circuit shown in FIG. 3 in which crosstalk is removed from a carrier chrominance signal by a three-line comb filter and then dropout compensation is performed will be described.

As shown in FIG. 1, a reproduction signal system 1 of a recording / reproduction-only or reproduction-only VTR 1 has a color signal reproduction system 1A,
It comprises a luminance signal reproduction system 1B.

The above-described color signal reproducing system 1A includes a reproducing head H
Low-pass filter 2, which separates and outputs a low-frequency conversion color signal from a reproduced video signal amplified by a reproduction amplifier (not shown) and a signal level of the low-frequency conversion color signal from the low-pass filter 2 ACC circuit (not shown), frequency conversion circuit for frequency-converting the low-frequency conversion color signal from this ACC circuit to a carrier color signal, ACC phase-shifted by 90 degrees every horizontal scanning period (1H) by a PS (phase shift) method A crosstalk removing comb filter 4 for removing crosstalk of a carrier color signal (signal a shown in FIG. 5A) from a circuit 4, a carrier color signal from a comb filter 4 generated by dropout of a video tape or the like. It has a dropout compensating circuit 5 for compensating for the loss of the signal b shown in FIG. 5B.

The above-described comb filter 4 for removing crosstalk includes 1H delay circuits 4a and 4b, an adder 4c, and a subtractor 4.
d, a so-called three-line comb filter composed of 1/2 amplifiers 4e and 4f. The carrier chrominance signal b is delayed by 1H after the crosstalk of the carrier chrominance signal a is removed.
Is output. However, due to the filter characteristics, FIG.
As shown in (A) and (B), the carrier chrominance signal b as the output signal is not completely equivalent to the carrier chrominance signal a as the input signal.

The above-mentioned dropout compensation circuit 5 is composed of a switch SW comprising fixed contacts S1, S2 and a movable contact S3.
The movable contact S3 is constituted by a 1,1H delay circuit 5a and a (phase) inverting circuit 5b. During a period in which a switching control signal (signal d shown in FIG. 5D) described later is supplied, the movable contact S3 is fixed to the fixed contact S1.
Is switched to the fixed contact S2 side, and the carrier color signal b containing much noise is not output due to the dropout, and the carrier color signal containing no noise 1H before (the signal e shown in FIG. 5E) ) Is output. Switching control signal d
Is not supplied, the movable contact S3 is switched to the fixed contact S1, so that the transport color signal b is output.

The above-mentioned luminance signal reproducing system 1B comprises a high-pass filter 6 for separating and outputting the FM luminance signal from the reproduced video signal, and a double limiter circuit for double-limiting the FM luminance signal from the high-pass filter 6 so as to remove the inversion phenomenon. 7, an FM demodulator 8 for demodulating the FM luminance signal from the double limiter circuit 7, and a de-emphasis circuit (not shown) for attenuating a high-frequency component of the luminance signal from the FM demodulator 8 by a predetermined amount.

When the signal level of the FM luminance signal supplied from the high-pass filter 6 of the luminance signal reproducing system 1B drops by a predetermined amount between the color signal reproducing system 1A and the luminance signal reproducing system 1B, it is determined that a dropout occurs. A drop-out detection circuit 9 for outputting a drop-out detection signal (signal c shown in FIG. 5C), and a 1H delay circuit 10 for outputting a switching control signal d obtained by delaying the drop-out detection signal c by 1H. It is interposed.

The carrier chrominance signal e output from the chrominance signal reproduction system 1A and the luminance signal output from the luminance signal reproduction system 1B are added by an adder (not shown) at the subsequent stage, and then the video signal is subjected to dropout compensation. It goes without saying that it is output as

Next, the dropout compensation circuit shown in FIG. 4 in which the crosstalk removal of the carrier color signal is performed by the two-line comb filter and then the dropout compensation is performed will be described. The same components as those described above are denoted by the same reference numerals, and description thereof will be omitted. The main configuration different from the circuit shown in FIG. 3 is that a 2-line comb filter is used as the crosstalk removing comb filter 4 instead of the 3-line comb filter. That is, the delay circuit 10 is eliminated.

As shown in FIG. 1, a color signal reproduction system 1A includes a reproduction amplifier (not shown), a low-pass filter 2, an ACC circuit (not shown), a frequency conversion circuit 3, a comb filter for removing crosstalk 4, and a dropout compensation. It has a circuit 5. The comb filter 4 includes a 1H delay circuit 4g, a subtractor 4h, 1/2
The carrier chrominance signal (signal f shown in FIG. 6 (B)), which is formed of a two-line comb filter composed of an amplifier 4i and from which the crosstalk of the carrier chrominance signal a is removed, is fixed to the fixed contact S1 of the dropout compensation circuit 5. Output to However, due to the filter characteristics, as shown in FIGS. 6A and 6B, the carrier chrominance signal f as the output signal is not completely equivalent to the carrier chrominance signal a as the input signal.

The drop-out compensation circuit 5 switches the movable contact S3 from the fixed contact S1 to the fixed contact S2 while the drop-out detection signal (signal c shown in FIG. 6 (C)) is supplied. The carrier chrominance signal f containing a large amount of noise due to the generation is not output, and the carrier chrominance signal (no signal g shown in FIG. 6D) containing the noise 1H before is output. During the period in which the dropout detection signal c is not supplied, the movable contact S3 is switched to the fixed contact S1, so that the carrier color signal f is output.

The luminance signal reproducing system 1B has a high-pass filter 6, a double limiter circuit 7, an FM demodulator 8, and a de-emphasis circuit (not shown). A dropout detection circuit 9 is interposed between the color signal reproduction system 1A and the luminance signal reproduction system 1B.

[0015]

In the configuration shown in FIG. 3, as described above, as shown in FIGS. 5A and 5B, the output signal is changed due to the characteristics of the three-line comb filter. Since the carrier chrominance signal b is not completely equivalent to the carrier chrominance signal a as the input signal, the dropout portion included in the carrier chrominance signal a cannot be completely compensated.

That is, a signal a (shown in FIG. 5A) in which a carrier color signal whose signal level is "1" due to occurrence of dropout during the 1H period becomes "0" during the 1H period is a three-line comb. After passing through the filter 4, the signal level does not become “0” during the 1H period, but becomes “1/1” during the 1H period.
2 ", and a distorted signal b (shown in FIG. 5B) which becomes" 3/4 "in each 1H period before and after that. When the signal b is compensated by the dropout compensating circuit 5, the signal e becomes a signal e (shown in FIG. 5E). The signal level in the 1H period is "3 /" instead of "1/2". 4 ", the signal levels in the 3H period centered on the 1H period are all" 3/4 ", and the signal levels in all other periods are" 1 ". There is a disadvantage in image quality that only the horizontal scanning lines are lighter in color. In particular, when a dropout occurs over a period of 5 to 6H or more, this disadvantage is remarkable.

Also in the configuration shown in FIG. 4 described above, the characteristics of the two-line comb filter cause
As shown in (A) and (B), the carrier chrominance signal f which is the output signal is not completely equivalent to the carrier chrominance signal a which is the input signal. Could not compensate.

That is, a signal a (shown in FIG. 6A) in which the carrier chrominance signal whose signal level is "1" due to the occurrence of dropout during the 1H period becomes "0" during the 1H period is a two-line comb. After passing through the filter 4, the signal level does not become “0” during the 1H period, but becomes “1/1” during the 1H period.
2 ", and a distorted signal f (shown in FIG. 6B) which is also" 1/2 "during the 1H period is output. When the signal f is compensated by the dropout compensation circuit 5, the signal f becomes a signal g (shown in FIG. 6D). The signal level in the 1H period is "1" instead of "1/2". This is completely compensated for, but the signal level after 1H in the 1H period changes from “1” to “１ ／”, so that the signal level here decreases, so that one horizontal period related to this period is reduced. The image quality is degraded in which only the scanning lines become lighter in color.

[0019]

In order to solve the above-mentioned problems, the present invention provides a dropout compensation circuit having the following configuration.

A dropout compensating circuit for compensating for a dropout of a carrier chrominance signal output from a comb filter constituting a chrominance signal system of a magnetic reproducing apparatus, which is obtained by detecting a dropout of a reproduced FM luminance signal. A dropout detection circuit that outputs a dropout detection signal, a delay circuit that outputs a delay signal obtained by delaying the dropout detection signal by one horizontal scanning period, and a logical sum of the dropout detection signal and the delay signal A drop-out compensating circuit comprising: a logical sum circuit that outputs a signal; and compensating for a drop-out of the carrier chrominance signal using the logical sum signal.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A dropout compensating circuit according to the present invention will be described below with reference to FIGS. 1 and 2 are circuit diagrams of first and second embodiments of a dropout compensating circuit according to the present invention, respectively. FIGS. 7 and 8 are diagrams of the dropout compensating circuit according to the present invention shown in FIGS. 1 and 2, respectively. It is a signal waveform diagram of each part of the 1st, 2nd Example circuit.

First, a first embodiment of the dropout compensation circuit according to the present invention will be described. In the present embodiment, dropout compensation is performed after crosstalk removal of the carrier chrominance signal is performed by a three-line comb filter, and the configuration is the 1H delay circuit in the circuit configuration shown in FIG. It is equivalent to an OR circuit 12 interposed between 10 and the switch SW1.

As shown in FIG. 1, a reproduction signal system 1 of a recording / reproduction VTR or a reproduction-only VTR is a color signal reproduction system 1.
A, a luminance signal reproducing system 1B.

The above-described color signal reproducing system 1A includes a reproducing head H
Low-pass filter 2, which separates and outputs a low-frequency conversion color signal from a reproduced video signal amplified by a reproduction amplifier (not shown) and a signal level of the low-frequency conversion color signal from the low-pass filter 2 An ACC circuit (not shown), a frequency conversion circuit 3 for frequency-converting the low-frequency conversion color signal from the ACC circuit into a carrier chrominance signal, and a carrier chrominance signal from the ACC circuit advanced by 90 degrees every 1H by the PS method (FIG. The cross color removing comb filter 4 for removing the cross talk of the signal a) shown in A), the carrier color signal from the comb filter 4 generated by dropout of the video tape or the like (FIG. 7)
A dropout compensation circuit 5 for compensating for the loss of the signal b) shown in FIG.

The above-described comb filter 4 for removing crosstalk includes 1H delay circuits 4a and 4b, an adder 4c, and a subtractor 4.
d, a so-called three-line comb filter composed of 1/2 amplifiers 4e and 4f. The carrier chrominance signal b is delayed by 1H after the crosstalk of the carrier chrominance signal a is removed.
Is output. However, due to the filter characteristics, FIG.
As shown in (A) and (B), the carrier chrominance signal b as the output signal is not completely equivalent to the carrier chrominance signal a as the input signal.

The above-mentioned dropout compensating circuit 5 includes a switch SW composed of fixed contacts S1, S2 and a movable contact S3.
The movable contact S3 includes a 1,1H delay circuit 5a and a (phase) inversion circuit 5b, and during a 2H period when a switching control signal (signal h shown in FIG. 7E) from the OR circuit 12 described later is supplied. Is switched from the fixed contact S1 side to the fixed contact S2 side, the signal portion of the carrier color signal b containing much noise due to the dropout is not output, and the noise in the 1H period immediately before the 1H period in which the dropout occurs is output. Carrier signal having a signal portion not including
The signal i) shown in (F) is output. During the period in which the switching control signal h is not supplied, the movable contact S3 is switched to the fixed contact S1, so that the carrier color signal b in which the signal level does not decrease is output.

The above-mentioned luminance signal reproducing system 1B is a high-pass filter 6 for separating and outputting the FM luminance signal from the reproduced video signal, and a double limiter circuit for double-limiting the FM luminance signal from the high-pass filter 6 so as to remove the inversion phenomenon. 7, an FM demodulator 8 for demodulating the FM luminance signal from the double limiter circuit 7, and a de-emphasis circuit (not shown) for attenuating a high-frequency component of the luminance signal from the FM demodulator 8 by a predetermined amount.

If the signal level of the FM luminance signal supplied from the high-pass filter 6 of the luminance signal reproducing system 1B drops by a predetermined amount between the color signal reproducing system 1A and the luminance signal reproducing system 1B, it is determined that the FM signal has dropped out. A dropout detection circuit 9 for outputting a dropout detection signal (signal c shown in FIG. 7C), and a 1H delay dropout detection signal (a signal shown in FIG. 7D) obtained by delaying the dropout detection signal c by 1H. A 1H delay circuit 10 for outputting d), a dropout detection signal c and a 1H delay dropout detection signal d are supplied, and an OR circuit 12 for outputting a logical sum signal (switching control signal h) of both detection signals c and d is provided. It is interposed.

The carrier chrominance signal e output from the chrominance signal reproduction system 1A and the luminance signal output from the luminance signal reproduction system 1B are added by an adder (not shown) at the subsequent stage, and the video signal is subjected to dropout compensation. It goes without saying that it is output as

In the configuration shown in FIG. 1 described above, the characteristics of the three-line comb filter shown in FIG.
As shown in (A) and (B), the carrier chrominance signal b which is an output signal is not completely equivalent to the carrier chrominance signal a which is an input signal, but is synchronized with the output of the dropout detection signal c during the 2H period. Since the movable contact S3 of the switch SW1 of the dropout compensation circuit 5 is switched to the fixed contact S2,
In the signal i thus obtained (shown in FIG. 7 (F)), the signal level of the dropout 1H period and the immediately following 1H period are “1”, so that the dropout portion included in the carrier chrominance signal a is Even if it cannot be completely compensated, it is possible to solve the problem that the color of only three horizontal scanning lines related to the 3H period is reduced as in the related art, and it is possible to suppress the color of only one horizontal scanning line so as to reduce the color. In particular, there is an effect on image quality that color fading is not visually noticeable even when dropout occurs for a period of 5 to 6H or more.

Next, a description will be given of a second embodiment of the dropout compensation circuit according to the present invention. In the present embodiment, dropout compensation is performed after crosstalk removal of the carrier chrominance signal is performed by a two-line comb filter, and the configuration is the dropout detection in the circuit configuration shown in FIG. 1H between circuit 9 and switch SW1
This is equivalent to the one using the delay circuit 10 and the OR circuit 12. The same components as those described above are denoted by the same reference numerals, and description thereof will be omitted.

As shown in FIG. 1, the color signal reproducing system 1A includes a low-pass filter 2, an ACC circuit (not shown), a frequency conversion circuit 3, a comb filter for removing crosstalk 4, and a dropout compensation circuit 5. The above-described comb filter 4 for removing crosstalk includes a 1H delay circuit 4g, subtractors 4h, 1
The carrier chrominance signal f (FIG. 8) is formed of a so-called two-line comb filter composed of a / 2 amplifier 4i, and from which the crosstalk of the carrier chrominance signal a (shown in FIG. 8A) has been removed.
(Shown in (B)). However, as shown in FIGS. 7A and 7B, the carrier chrominance signal f, which is the output signal, is not completely equivalent to the carrier chrominance signal a, which is the input signal, due to the filter characteristics.

The dropout compensation circuit 5 includes a switch SW1, a 1H delay circuit 5a, and a (phase) inversion circuit 5b.
The movable contact S3 is switched from the fixed contact S1 to the fixed contact S2 during a 2H period in which a switching control signal (signal h shown in FIG. 8E) from the OR circuit 12 described later is supplied. The carrier chrominance signal f containing a large amount of noise due to the occurrence of dropout is not output, but a carrier chrominance signal containing no noise 2H before (signal j shown in FIG. 8F) is output. A period during which the switching control signal h is not supplied,
Since the movable contact S3 has been switched to the fixed contact S1, the transport color signal f is output.

The above-mentioned luminance signal reproducing system 1B has a high-pass filter 6, a double limiter circuit 7, an FM demodulator 8, a de-emphasis circuit (not shown) and the like.

If the signal level of the FM luminance signal supplied from the high-pass filter 6 of the luminance signal reproducing system 1B drops by a predetermined amount between the color signal reproducing system 1A and the luminance signal reproducing system 1B, it is determined that a dropout has occurred. A dropout detection circuit 9 for outputting a dropout detection signal (signal c shown in FIG. 8C), and a 1H delay dropout detection signal (a signal shown in FIG. 8D) obtained by delaying the dropout detection signal c by 1H. A 1H delay circuit 10 for outputting d), a dropout detection signal c and a 1H delay dropout detection signal d are supplied, and an OR circuit 12 for outputting a logical sum signal (switching control signal h) of both detection signals c and d is provided. It is interposed.

Of course, the carrier color signal j output from the color signal reproduction system 1A and the luminance signal output from the luminance signal reproduction system 1B are added by an adder (not shown) at the subsequent stage, and then the video signal is subjected to dropout compensation. It goes without saying that it is output as

In the configuration shown in FIG. 2 described above, the characteristics of the two-line comb filter cause
As shown in (A) and (B), the carrier chrominance signal f as the output signal is not completely equivalent to the carrier chrominance signal a as the input signal, but is synchronized with the output of the dropout detection signal c during the 2H period. Since the movable contact S3 of the switch SW1 of the dropout compensation circuit 5 is switched to the fixed contact S2,
In the signal j thus obtained (shown in FIG. 8F), the signal level of the dropout 1H period and the signal level of the immediately following 1H period are “1”. Compensation can be completely compensated and the color fading at 1H immediately after the dropout period as in the related art can be prevented, so that high image quality with uniform color shading can be obtained.

[0038]

The dropout compensating circuit according to the present invention is a dropout compensating circuit for compensating for a dropout of a carrier chrominance signal output from a comb filter constituting a chrominance signal system. The dropout of the carrier chrominance signal is compensated for using a logical sum signal of a dropout detection signal obtained by detecting a signal dropout and a delay signal obtained by delaying the dropout detection signal by one horizontal scanning period. With this configuration, for example, a signal level reduction component due to dropout included in the carrier color signal after the crosstalk has been removed from the carrier color signal having the dropout over 5 to 6 horizontal scanning periods is minimized and is excellent. Therefore, the quality of the image quality can be greatly improved without deteriorating the image quality such as fading color.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a first embodiment of a dropout compensation circuit according to the present invention.

FIG. 2 is a circuit diagram of a second embodiment of a dropout compensation circuit according to the present invention.

FIG. 3 is a diagram for explaining a conventional dropout compensation circuit.

FIG. 4 is a diagram for explaining a conventional dropout compensation circuit.

5 is a signal waveform diagram of each part of the conventional dropout compensation circuit shown in FIG.

FIG. 6 is a signal waveform diagram of each section of the conventional dropout compensation circuit shown in FIG.

FIG. 7 is a signal waveform diagram of each part of the circuit of the first embodiment of the dropout compensation circuit according to the present invention shown in FIG. 1;

FIG. 8 is a signal waveform diagram of each part of the circuit of the second embodiment of the dropout compensation circuit according to the present invention shown in FIG. 2;

[Explanation of symbols]

 Reference Signs List 1 VTR 1a Color signal system 1b Luminance signal system 5 Dropout compensation circuit 9 Dropout detection circuit 10 Delay circuit 12 OR circuit b, f Carrier color signal c Dropout detection signal d Delay signal h OR signal

Claims (1)

(57) [Claims] 1. A dropout compensating circuit for compensating for a dropout of a carrier chrominance signal output from a comb filter constituting a color signal system of a magnetic reproducing apparatus, wherein the dropout compensation circuit detects a dropout of a reproduced FM luminance signal. A dropout detection circuit that outputs the obtained dropout detection signal; a delay circuit that outputs a delay signal obtained by delaying the dropout detection signal by one horizontal scanning period; An OR circuit for outputting an OR signal, wherein the OR signal is used to compensate for a dropout of the carrier chrominance signal.