JPH01295572A - Recording reproducing circuit for video signal - Google Patents

Abstract

PURPOSE:To reduce noise without giving adverse effect onto a video signal by devising the circuit such that the recording side and the reproducing side have characteristics opposite to each other. CONSTITUTION:A vertical noncorrelation component in a reverse phase to an input video signal is outputted from a vertical noncorrelation component detection circuit section 15, fed to an adder 13 via a limiter circuit 19 and subtracted from the said input video signal. A reproduced video signal is fed to a reproduction output terminal 22 via an adder 23, a high frequency component is extracted by a high pass filter 24 and fed to a vertical noncorrelation component detection circuit section 25. The vertical noncorrelation component on a picture is outputted from the detection circuit section 25, added to the reproduced video signal from the input terminal 21 and becomes a reproduced output video signal. The input video signal to the input terminal 11 is extracted from the output terminal 22 almost with fidelity by using nose reduction circuit sections 10, 20 of the recorder and the reproducer sides having complementary relation.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a video signal recording/reproducing circuit, and in particular, to a video signal recording/reproducing circuit that reduces noise components superimposed on a video signal during recording/reproducing. Regarding circuits.

[Conventional technology]

-When recording and reproducing video signals using a video tape recorder, video sheet recorder, etc., random noise generated by the recording amplifier and playback amplifier, modulation noise in the recording medium such as tape, etc. are mixed into the video signal. However, this causes deterioration of the SN ratio of the reproduced image. In particular, when video equipment becomes more compact and requires high-density recording such as narrower tracks, the deterioration of the S/N ratio becomes a major problem, and some kind of noise reduction measure becomes essential. .

By the way, in the past, methods using pre-emphasis and de-emphasis (including non-linear ones) have been known as general methods for improving the S/N ratio. In this case, the amount of improvement in the S/N ratio can be increased by increasing the amount of emphasis, but due to the upper limits of the transmission band of the electromagnetic conversion system and the dynamic range of the recording medium, if the amount of emphasis is too large, an inversion phenomenon occurs. Therefore, the amount of emphasis and the degree of improvement of the SN ratio are also limited accordingly.

Furthermore, as a conventional noise reduction measure, it has been proposed to provide, for example, a circuit as shown in FIG. 1 on the reproduction side. In the circuit shown in FIG. 1, a video signal reproduced by a video head or the like is supplied to a series circuit consisting of a bypass filter 2, a limiter circuit 3, and a low-pass filter 4 via an input terminal l, and a video signal from the low-pass filter 4 is Send the output to adder (subtractor in operation) 5 and return to original input terminal 1
The signal is subtracted from the reproduced video signal and sent to the output terminal 6. This is because noise components are generally high-frequency and low-level, so the bypass filter 2 extracts the high-frequency components, and the limiter circuit 3 suppresses the effective signal component and subtracts it from the original reproduced video signal. Specifically, it aims at reducing noise by reducing the gain of high-frequency minute signal components that are not affected by the limiter.

[Problem to be solved by the invention]

However, in the circuit shown in FIG. 1, since the high-frequency minute signal components included in the original video signal are also reduced, minute parts of the image cannot be completely reproduced, resulting in deterioration of image quality. Therefore, on the recording side, a reverse circuit of the circuit shown in Figure 1 above (
A circuit with an opposite transfer function) is installed to prevent changes in the characteristics of the original video signal itself.
Currently, it is not perfect, and the details of the video signal itself are lost.However, the above-mentioned correction on the recording side is performed completely, making it possible to prevent the video signal from undergoing any changes. Even in this case, if the linear operating range of the limiter is widened (the upper limit level is raised) in order to further improve the S/N ratio, the high frequency components of the recorded signal will increase significantly, giving rise to the problem of so-called inversion phenomenon.

The present invention eliminates such conventional drawbacks, and can obtain a significant noise reduction effect while preventing adverse effects such as the above-mentioned inversion phenomenon and image quality deterioration (image details become ambiguous), and improves the S/N ratio. The purpose of the present invention is to provide a video signal recording and reproducing circuit capable of reproducing significantly improved high-quality images.

[Means to solve the problem]

As shown in FIGS. 2 and 3, the video signal recording/reproducing circuit according to the present invention outputs an input video signal from an input terminal 11 and an output obtained by delaying the input video signal by a delay element 16 to an adder 17. This subtracted output is sent to the limiter circuit 19.
The signal obtained by passing through the terminal 21 and the human video signal are substantially added and recorded by the adder 13, and the reproduced video signal from the terminal 21 and the reproduced video signal are added by the delay element 26. The delayed output is subtracted by an adder 27, and this subtracted output is passed through a limiter circuit 29 to obtain a characteristic opposite to the recording side characteristic for the obtained signal and the reproduced video signal. Therefore, the above-mentioned problem is solved by substantially performing subtraction in the adder 23 to reduce the noise mixed in during recording and reproduction.

[For production]

Since the recording side and playback side have opposite characteristics,
Noise can be reduced without adversely affecting the video signal,
Furthermore, since it is provided through a limiter circuit, it is possible to prevent an inversion phenomenon.

〔Example〕

Preferred embodiments of the present invention will be described below with reference to the drawings.

2 and 3 are block circuit diagrams schematically showing the entire video signal recording/reproducing circuit as an embodiment of the present invention, FIG. 2 shows the video signal recording system, and FIG. 3 shows the video signal recording system. This shows the same regeneration system.

In these FIGS. 2 and 3, the circuit section 1O120, which is the main part of the present invention, is for reducing noise components superimposed with the above-mentioned recording/reproducing operation, and is a circuit section 1O120 that is complementary to each other. Alternatively, the circuit configuration is such that the - side exhibits a transfer characteristic opposite to the other side. That is, these noise reduction circuit units 1O120 have a relationship similar to that of an encoder and a decoder in a normal noise reduction system. The other circuit sections may be configured in the same manner as in the prior art, and in the recording system, the output from the noise reduction circuit section 10 is, for example,
In the reproduction system, the reproduction signal from the reproduction head 36 is sent to the noise reduction circuit section 20 via the reproduction amplifier 37, the demodulation circuit 38, and the de-emphasis circuit 39. is being sent to. Here, the re-emphasis circuit 31 and the de-emphasis circuit 39 may be provided as necessary, and may be provided within the circuit section 10.20, respectively. The modulation circuit 32 and the demodulation circuit 3 perform, for example, FM modulation and demodulation, respectively.The recording head 34 magnetically records electric signals on a magnetic recording medium such as a magnetic tape or magnetic sheet, and the reproduction head 36 performs, for example, FM modulation and demodulation, respectively. This magnetically recorded information is converted into an electrical signal and retrieved.

In the recording system shown in FIG. 2, a video signal from, for example, a video camera or a television tuner is supplied to the input terminal 11 of the noise reduction circuit section IO. This video signal is a monochrome image video signal, and in the case of a color video signal, only a luminance signal (Y signal) is supplied. The high frequency component of the input video signal supplied to the input terminal 11 of the recording side noise reduction circuit section 1O is extracted by the bypass filter 14 and sent to the vertical non-correlation component detection circuit section 15. In this detection circuit section 15, the high frequency component of the video signal taken out from the bypass filter 14 is delayed by IH (one horizontal period) delay element 16 and sent to an adder (subtractor) 17, By subtracting the high-frequency component of the input video signal from the 18-delayed signal, vertically uncorrelated components on the image are detected. In this case, the input video signal is
Since it is subtracted from the delayed signal, the obtained vertically uncorrelated component has a negative phase relationship with respect to the input video signal. In order to obtain an uncorrelated component having an in-phase relationship with the input video signal, the adder (subtracter) 17 may be configured to subtract the IH delay signal from the input video signal.

As described above, the vertical uncorrelated component detection circuit section 15 in FIG.
outputs a vertical non-correlation component having a negative phase relationship with respect to the input video signal, and this vertical non-correlation component output signal is sent as a subtraction signal to the adder 13 via the limiter circuit 19. Subtracted from the video signal. That is, since the vertical non-correlation component of the opposite phase is subtracted, the vertical non-correlation component (of the same phase) is substantially added to the input video signal. The output signal from the adder 13 is sent to, for example, a pre-emphasis circuit 31 via the output terminal 12 of the recording-side noise reduction circuit section IO. Incidentally, if a non-correlated component having an in-phase relationship with the input video signal is obtained from the vertical non-correlated component detection circuit section 15, the adder 13 may add it to the input video signal.

Next, in the reproduction system shown in FIG. 3, the input terminal 21 of the reproduction-side noise reduction circuit section 20 is supplied with a reproduced video signal from, for example, the aforementioned de-emphasis circuit 39.

This reproduced video signal is sent to an adder (substantially a subtracter) 23
is sent to the playback output terminal 22 via the adder 2.
The high-frequency component of the output video signal from 3 is extracted by a bypass filter 24 and sent to a vertical non-correlation component detection circuit 25.
is being sent to. The detection circuit section 25 delays the high-frequency component by IH using an IH delay element 26 and sends it to an adder (subtractor) 27, and extracts the high-frequency component from the output video signal of the adder 23 by a bypass filter 28. By sending the component as a subtraction signal to the adder 27, the high frequency component from the bypass filter 28 is sent to the IH delay element 26.
is subtracted from the IH delay signal. This allows °ζ,
The detection circuit unit 25 outputs a vertical non-correlation component on the image, and this vertical non-correlation component has a reverse phase with respect to the reproduced video signal supplied to the input terminal 21. This vertical uncorrelated component is passed through the limiter circuit 29 to the adder 2.
3, and is added to the reproduced video signal from the input terminal 21 to form a reproduced output video signal. In this case, since a vertical uncorrelated component of opposite phase is added to the reproduced video signal, the vertical uncorrelated component (of the same phase) is substantially subtracted from the reproduced video signal.

Note that by subtracting the delayed output signal of the IH delay element 26 from the output signal of the bypass filter 28 in the adder 27, an in-phase vertical uncorrelated component can be obtained with respect to the reproduced video signal, and this in-phase For vertical uncorrelated components, an adder (subtracter) is applied via a limiter circuit 29.
23 and subtracted from the reproduced video signal obtained through the input terminal 21.

Here, each bypass filter 14, 18, 24, 28 is designed with consideration given to the fact that since the power of the low frequency component of the noise is small, noise reduction processing on this low frequency side is unnecessary. It has a cutoff frequency of several hundred kHz. IH delay element 16.26
For example, a glass delay line or CCD
(charge coupled device) may be used.

The limiter circuit 19.29 has a constant gain α within the linear operation range, and the bypass filter 14.18 of the recording side circuit section 10 may be made into one by commonizing it.
The bypass filters 24 and 28 of the circuit section 20 on the reproduction side can be made common to one. In addition, the common bypass filter described above may be inserted and connected to the output side of the adder (subtractor) 17 in the circuit section 10 on the recording side, or the common bypass filter may be inserted into the output side of the adder (subtractor) 17 in the circuit section 20 on the playback side. It may be inserted and connected to the output side of the device) 27.

In such a circuit configuration, first, the operating characteristics of the recording-side noise reduction circuit section 10 shown in FIG. 2 will be explained with reference to FIG. 4.

FIG. 4A shows that the circuit portion lO is in the pass frequency band of each bypass filter 14, 18 and within the range not limited by the limiter circuit 19, that is, in the high frequency range (several hundred kHz or more) and within the linear operating range of the limiter. This shows the frequency characteristics shown in the figure, and shows the so-called comb filter characteristics. The second characteristic is that the gain of frequency components that are integer multiples of the horizontal scanning frequency r, that is, components that have correlation in the vertical direction of the image, is greater than the gain of frequency components that are an integer multiple of f, that is, the vertical direction of the image. This is to increase the gain for the uncorrelated part of (emphasize the uncorrelated component). Here, B in Fig. 4 shows the spectrum of the video signal, and since the vertical correlation of general images is high, the frequency (vertical correlation component) near the horizontal scanning frequency f, (n is an integer) ) is large, and between these frequencies,
That is, near the frequency between nf and (n+1)fw (
(vertical correlation component) has become smaller. and,
Since the recording-side noise reduction circuit unit 10 amplifies the low-power portion of the video signal by a factor of 1+2α, the amplitude of the signal does not increase so much, and even if the video signal had a large vertically uncorrelated component. In this case, since the amplitude is limited by the limiter, the amplitude does not become very large as a result. The fact that the amplitude of the signal does not increase is advantageous in preventing inversion phenomena.

Next, the operation of the reproduction side noise reduction circuit section 20 shown in FIG. 3 will be explained.

This circuit section 20 is a so-called comb filter having an IH delay element 26 in its feedback loop, and its frequency characteristics in the high frequency range (above several hundred kHz) and within the linear operating range of the limiter are as shown in FIG. expressed.

This allows vertically correlated components to pass and attenuates vertically uncorrelated components to a maximum of 1/(1+2α). Since the spectrum of the noise component superimposed on the video signal is considered to be approximately flat, the noise component passes through the circuit section 20 and becomes a spectrum having the same shape as that shown in FIG. Here, the noise is reduced by the amount indicated by diagonal lines. for example,
When the gain α within the linear operating range of the limiter circuit 29 is 2, the noise component is attenuated by about 7 dB, and the S/N ratio is improved by about 7 dB.

From the perspective of two-dimensional spatial frequency, this comb-shaped filter characteristic becomes a low-pass filter characteristic in the vertical direction of the image, and if only this reproduction side noise reduction circuit section 20 is used, the reproduced image will be blurred in the vertical direction. For storage purposes, a circuit section 10 as shown in FIG. 2 is provided in the recording system. The circuit 10 and the circuit 20 have mutually opposite transfer characteristics,
The enhancement shown in the shaded area in FIG. 4A corresponds to the attenuation shown in the shaded area in FIG. After passing through the circuit 10, the video signal is restored to its original state by passing through the circuit 20.

The input video signal of the input terminal 11 can be taken out from the output terminal 22 with high fidelity by such noise reduction circuit sections 10 and 20 on the recording side and the reproduction side that are complementary to each other (configuring circuits that are opposite to each other). I can do it.

By the way, when the vertical uncorrelated component of the video signal is large, the troughs (nf, and (r) of the video spectrum in FIG. 4B)
The power between ul) and fn increases, and if the characteristics shown in FIG. Therefore, a limiter circuit 19 is provided to prevent this. However, as mentioned above, since the spectrum of the negative video signal is as shown in FIG. 4B, the portion of the image that is limited by the limiter circuit 19 is relatively small. Furthermore, since the rising edges of the video signal are not affected by the limiter, it is possible to improve the SN ratio.

It should be noted that the present invention is not limited to the above-mentioned embodiments. For example, in the above-mentioned embodiments, the circuit section 10 on the recording side
The circuit section 20 on the playback side is in a feedforward mode, and the circuit section 20 on the playback side is in a feedback mode, but it is not necessarily necessary to have such a configuration. It suffices if they have suppressing characteristics and have a relationship of opposite characteristics to each other.

〔Effect of the invention〕

According to the video signal recording and reproducing circuit according to the present invention, since the recording side circuit and the reproducing side circuit have opposite characteristics to each other,
without any negative effect on the original video signal.
It is possible to obtain a reproduced image of high quality and high fidelity without causing the blurring of details of the reproduced image as in the past. Further, since the limiter circuit is provided, the SN ratio can be significantly improved while effectively preventing the reversal phenomenon. Furthermore, it is possible to improve the poor signal-to-noise ratio at edge portions, which is a drawback of nonlinear emphasis.

[Brief explanation of the drawing]

Fig. 1 is a block circuit diagram for explaining conventional noise reduction measures, Figs. 2 and 3 show a video signal recording and reproducing circuit as an embodiment of the present invention, and Fig. 2 shows a recording system. A schematic block circuit diagram, Fig. 3 is a schematic block circuit diagram of the reproduction system, Fig. 4 is a frequency characteristic diagram for explaining the operation of the circuit in Fig. 2, and Fig. 5 is a circuit in Fig. 3. FIG. 3 is a frequency characteristic diagram for explaining the operation of the FIG. 10... Recording side noise reduction circuit section 20...
...Reproduction side noise reduction circuit section 11.21...Input terminal 12.22...Output terminal

Claims (1)

[Claims] An input video signal and an output obtained by delaying the input video signal are subtracted, and this subtracted output is passed through a limiter circuit, so that the signal obtained by substantially adding the input video signal and the input video signal is recorded. At the same time, what are the characteristics of the recording side with respect to the signal obtained by subtracting the reproduced video signal and the delayed output of the reproduced video signal and passing this subtracted output through a limiter circuit and the reproduced video signal? A video signal recording and reproducing circuit that essentially performs subtraction to obtain almost opposite characteristics.