JPH05122658A - Noise canceling circuit - Google Patents

Abstract

PURPOSE:To provide a noise canceling circuit to constantly obtain the quality of the reproducing picture of a high grade even when the characteristics of used tapes are different. CONSTITUTION:The noise canceling circuit removing noise from a reproducing video signal is provided with a high pass filter 1 extracting the high frequency component of the reproducing video signal, a limiter 2 amplitude-limiting the output of the high pass filter 1, a subtracter 6 taking difference between the output of the limiter 2 and a signal bypassing the limiter 2, a comparator 9 comparing the output level of the subtracter 6 and the reference level and a microcomputer 10 judging the output of the comparator 9 to control the level of the limiter 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noise canceling circuit which is applied to a home video tape recorder (VTR) and removes noise from a reproduced video signal.

[0002]

2. Description of the Related Art A conventional noise canceling circuit extracts a high frequency component containing noise from a reproduced video signal having noise as shown in FIG. 2 by a high pass filter 1. A part larger than noise is cut in the signal of this high frequency component. There is almost no noise in this, so subtract it from the input signal. That is, high pass filter 1
The polarity of the signal limited by the limiter 2 is reversed by the polarity reversing circuit 3, and the amplitude adjusting circuit 4 adjusts the level and the magnitude of the original signal.
The output signal without noise is obtained by synthesizing with.

By the way, the above conventional noise canceling circuit has a fixed limiter level, and the noise canceling effect is always constant even if the S / N ratio of the reproduced video signal is different. Therefore, in a home VTR, the user himself / herself sees the playback screen on the monitor
You can add preshoot or overshoot to the outline,
I am turning the image quality adjustment volume that attenuates the high frequency range. Also, depending on the model, a detail switch that weakens the effect of the noise cancellation circuit was installed, and a rental switch that included line correlation noise reduction that used line correlation was installed.
Furthermore, the characteristics of the reproducing system have not been switched according to the output characteristics of the video tape used.

[0004]

However, in the above-mentioned conventional home-use VTR, the user himself / herself makes adjustments while watching the playback screen on the monitor, which is troublesome and has a low operability. Also, since the characteristics of the playback system are not switched according to the output characteristics of the tape, if the characteristics of the noise canceller circuit etc. are determined in accordance with the high output tape at the time of designing, the image quality with a low output tape will have a poor S / N ratio. There is a problem that becomes. In addition to this, in mass production, even in a set of the same model name, there is a problem that the reproduction S / N ratio varies due to variations in the output of the magnetic head. Therefore, the present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide a noise canceling circuit for always obtaining a high-quality reproduced image quality even if the characteristics of the tapes used are different. is there.

[0005]

In order to achieve the above object, in a noise cancel circuit according to the present invention,
In a noise canceling circuit that removes noise from the reproduced video signal, a high-pass filter that extracts high-frequency components of the reproduced video signal, a limiter that limits the amplitude of the output of this high-pass filter, and a signal that bypasses the limiter output and the limiter. And a comparator for comparing the output level of the subtractor with a reference level, and a control means for determining the output of the comparator and controlling the level of the limiter.

[0006]

In the present invention having the above-mentioned structure, the reproduced video signal is passed through the high pass filter to remove the noisy high frequency component. The high-frequency component is subjected to a limiter and the amplitude-limited one is subtracted, the presence or absence of an amplitude component larger than the limiter level is compared with the reference level, and this is judged by the control means and fed back to the limiter level to determine the tape to be used. Even if the characteristics are different, it is possible to always obtain high-quality reproduced image quality.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a noise canceling circuit according to the present invention. It should be noted that parts that are the same as or correspond to those of the conventional configuration will be described using the same symbols as in FIG. As shown in FIG. 1, the noise canceling circuit of the present embodiment is supplied with a reproduced video signal, a high-pass filter 1 for extracting a high frequency component of the reproduced video signal, and a limiter for supplying an output of the high-pass filter 1 to limit the amplitude. 2, a subtractor 6 for taking the difference between the output of the limiter 2 and a signal bypassing the limiter 2, an amplifier 7 for amplifying the output of the subtractor 6, and a detection circuit 8 to which the output of the amplifier 7 is supplied. A comparator 9 for comparing the output of the detection circuit 8 with a reference level, and a microcomputer (hereinafter abbreviated as a microcomputer) 10 as a control means for judging the output of the comparator 9 and controlling the level of the limiter 2. I have it. Further, the polarity reversing circuit 3, the amplitude adjusting circuit 4, and the synthesizing circuit 5 are the same as those shown in FIG.

Next, the operation of this embodiment will be described.
In the noise canceling circuit of the present embodiment, the output of the high pass filter 1 is divided into two, and the signal b whose amplitude is not limited by the limiter 2 is subtracted from the signal a whose amplitude is not limited by the subtracter 6. Accordingly, when the noise component is higher than the limiter level, the difference occurs in the output signal c of the subtractor 6. On the contrary, when the noise component is smaller than the limiter level, the signal a and the signal b are almost the same, so that the output signal c of the subtractor 6 is hardly generated. Then, the output signal c of the subtractor 6 is amplified by the amplifier 7, and then detected by the detection circuit 8 to convert the magnitude of the noise amount into the DC level. This is compared with the reference level by the comparator 9 in the next stage. This difference is read by the microcomputer 10, and if it is higher than the reference level, the limiter level is raised,
When it is lower than the reference level, feedback is given to lower the limiter level, and control is performed so as to always approach the reference level.

Here, the reference level is arbitrary,
To obtain the target image quality, the average output head and tape are used to determine the amount of noise cancellation, and if this is used as the reference level, in the case of a head or tape with a large output,
Since the noise amount is smaller than the reference level at the output of the comparator 9, a minus is output. Therefore, if the limiter level is lowered by the microcomputer 10, a difference occurs in the output signal c, and the output level c approaches the reference level. As a result, the loss of minute signals can be suppressed, and the resolution can be increased while ensuring the S / N ratio.

On the contrary, in the case of a low output head or tape,
Since the noise amount is larger than the reference level at the output of the comparator 9, a plus is output. If this is controlled by the microcomputer 10 so as to raise the limiter level, the difference in the output signal c becomes smaller and approaches the reference level. . As a result, the noise canceling effect is enhanced and the resolution is degraded, but the S / N ratio is improved.

[0011]

As described above, according to the noise canceling circuit of the present invention, the noise canceling effect can be changed according to the state of the S / N ratio of the reproduced video signal.
With a signal having a good S / N ratio, the noise canceling effect is automatically weakened to improve the resolution while ensuring the S / N ratio.
On the other hand, a signal with a poor S / N ratio enhances the noise canceling effect and improves the S / N ratio. This saves the user the trouble of turning on / off the switch and turning the image quality adjusting volume by himself, and can obtain a high-quality reproduced image.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a noise canceling circuit according to the present invention.

FIG. 2 is a block diagram showing a conventional noise canceling circuit.

[Explanation of symbols]

 1 High Pass Filter 2 Limiter 3 Polarity Inversion Circuit 4 Amplitude Adjustment Circuit 5 Synthesis Circuit 6 Subtractor 7 Amplifier 8 Detection Circuit 9 Comparator 10 Microcomputer (Control Means)

Claims (1)

[Claims] 1. A noise cancel circuit for removing noise from a reproduced video signal, a high-pass filter for extracting high-frequency components of the reproduced video signal, a limiter for limiting an amplitude of an output of the high-pass filter, and an output and a limiter of the limiter. And a comparator for comparing the output level of the subtractor with a reference level, and a control means for judging the output of the comparator and controlling the level of the limiter. Noise cancellation circuit characterized by.