JPH03254288A - Noise elimination device for video tape recorder - Google Patents

Abstract

PURPOSE:To obtain an optimum noise elimination characteristic in response to a noise level by controlling a limiter level of a line correlation noise elimination means and a high frequency noise elimination means based on a difference between a reproduced video signal and a reproduced signal retarded CONSTITUTION:A limiter level control means C takes a difference between a reproduced video signal delayed by one horizontal scanning period and a reproduced video signal not retarded. A noise component is extracted from the difference signal and the limiter level of a line correlation noise elimination means A and a high frequency noise elimination means B is adjusted based on the noise component. The line correlation noise elimination means A and the high frequency noise elimination means B subtract the noise component from the reproduced video signal based on the adjusted limiter level to eliminate the noise component included in the reproduced video signal. Thus, the noise elimination effect is sufficiently enhanced independently of the quantity of the noise level on the video tape.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a video tape recorder capable of reproducing video signals recorded on a video tape, and in particular to a video tape recorder capable of reproducing a video signal recorded on a video tape, and in particular to a video tape recorder capable of reproducing a video signal recorded on a video tape. The present invention relates to a tape recorder noise removal device.

[Prior art] Video tape recorders record FM on magnetic tape.
The signal is reproduced and demodulated into a video signal by an FM demodulator. The video signal reproduced in this way contains noise due to the influence of the demodulation system such as the head and the magnetic tape, so this is removed by a noise removal device.

FIG. 3 is a block diagram showing a demodulation system of a conventional video tape recorder. Referring to the figure, an FM signal reproduced by a video head 1 is amplified by a preamplifier 2, and then an equalizer 3 corrects frequency characteristics and delay time characteristics. The FM signal corrected by the equalizer 3 is demodulated into a video signal by a demodulator 4, and further demodulated by a de-emphasis circuit 5 and a low-pass filter 6 into a video signal substantially at the time of recording. This demodulated video signal is then subjected to noise reduction in a line correlation noise removal circuit 7 and a high frequency noise removal circuit 8, and outputted as a luminance signal by an output amplifier. The line correlation noise removal circuit 7 is a noise reduction circuit that utilizes the line correlation of video signals. Furthermore, the high-frequency noise removal circuit 8 is a circuit for removing noise contained in high-frequency components. Easy noise component is IMH
This circuit focuses on the fact that it is near z.

FIG. 4 is a circuit diagram showing details of the line correlation noise removal circuit. Referring to the figure, a reproduced video signal inputted from a low-pass filter 6 is delayed by one horizontal scanning period by a one horizontal scanning period delay circuit (hereinafter referred to as an IH delay circuit) 10 and then applied to a subtraction circuit 11. . A subtraction circuit 11 takes the difference between the undelayed reproduced video signal and the reproduced video signal delayed by one horizontal period. The video signal has line correlation, and the difference between adjacent horizontal scanning signals is small, and what appears as a difference signal is a noise component with no line correlation and a part of the video signal.

Since the noise component is usually smaller than the video signal component, the limiter circuit 1 is set to an appropriate limiter level.
2, it is possible to extract only the noise component. The noise component extracted in this way is transferred to the resistor 13.
It is set to an appropriate level by a1 resistor 13b1 capacitor 13c and is applied to the subtraction circuit 14. The subtraction circuit 14 can reduce noise included in the reproduced video signal by subtracting the noise signal from the video signal.

FIG. 5 is a block diagram of the high frequency noise removal circuit 8. Referring to the figure, the signal from the line correlation noise removal circuit 7 passes through a low-pass filter 15 consisting of a resistor 15a and a capacitor 15b to remove high-frequency components, and then a subtraction circuit 16 removes high-frequency components from the original reproduced video signal. The signal from which the component has been removed is subtracted, and only the high frequency component is extracted. The amplitude of this extracted high frequency component is limited by the limiter circuit 17, and only the noise component is obtained. This noise component is adjusted to a predetermined level by a resistor 19a, a 19bs capacitor 19C, and then applied to a subtraction circuit 20. Noise is reduced by subtracting high-frequency noise components from the original reproduced video signal by the subtraction circuit 20.

[Problems to be Solved by the Invention] In the line correlation noise removal circuit 7 and the high frequency noise removal circuit 8, the limiter level of the limiter circuits 12 and 17 is set appropriately by taking advantage of the fact that the noise component is smaller than that of the video signal. The noise component is extracted by setting the reproduced video signal at a certain level and passing it through a limiter circuit 12.17 whose level is set for the reproduced video signal.

However, since it removes minute signal components below the limiter level as well as noise, 1. If an attempt is made to increase the noise removal effect by increasing the limiter level, many minute components of the reproduced video signal will be lost, and the reproduced image will not show fine parts and will lack definition. Conversely, if the limiter level is lowered too much, the screen will become noisy. Therefore, at present, the limiter level is fixed so that an optimal image can be obtained in self-edge reproduction.

However, when playing a magnetic tape that has been repeatedly played and has become highly demagnetized, such as a rental video tape, the noise removal effect becomes insufficient with a limiter level that has a large fixed noise level. There is this inconvenience. That is, while the noise level of a videotape varies depending on the amount of use, etc., the limiter level is fixed, so a sufficient noise removal effect may not be achieved.

The present invention has been made in view of the above-mentioned problems, and it is an object of the present invention to provide a noise removal device for a video tape recorder that can sufficiently exhibit a noise removal effect regardless of the magnitude of the noise level of the video tape. .

[Means for Solving the Problems] To achieve the above object, the videotape noise removal device of the present invention calculates the difference between a reproduced video signal delayed by one horizontal scanning period and a reproduced video signal not delayed, a horizontal scanning line correlation noise removal means for extracting a noise component in a horizontal scanning period by amplitude limiting the difference signal at a predetermined limiter level, and removing the noise by subtracting this noise component from a reproduced video signal that is not delayed; and a reproduced video signal. a high-frequency noise removal means for amplitude-limiting the high-frequency components of the signal at a predetermined limiter level, extracting noise contained in the high-frequency components, and subtracting the noise contained in the high-frequency components from the reproduced video signal; and limiter level control means for controlling a limiter level in the horizontal scanning line correlation noise removal means and a limiter level of the high frequency noise removal means based on the difference between the signal delayed by a period and the reproduced video signal not delayed. It is characterized by

[Operation of the Invention] The present invention having the above configuration calculates the difference between the reproduced video signal delayed by one horizontal scanning period by the limiter level control means and the reproduced video signal not delayed.

A noise component is extracted from this difference signal, and the limiter levels of the line correlation noise removing means and the high frequency noise removing means are adjusted based on this noise component.

The line correlation noise removing means and the high frequency noise removing means remove noise components included in the reproduced video signal by subtracting the noise components from the reproduced video signal based on the adjusted limiter level.

[Example] A videotape noise removal device according to the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention. Note that the reproduction head 1, preamplifier 2, equalizer 3, demodulator 4, de-emphasis 5, low-pass filter 6, and output amplifier 9 are the same as in FIG. 3, and the same symbols are used.

Referring to the figure, the FM signal reproduced by the reproduction head 1 has its frequency characteristics and delay characteristics corrected by the equalizer 3 and demodulated by the demodulator 4, as in the conventional example, and the high frequency is attenuated by the de-emphasis circuit 5. After that, the reproduced video signal is applied to a low-pass filter 6. The signal is then passed through the low-pass filter 6 to the line correlation noise removal means A and the limiter level control means C. The line correlation noise removal means A generates a signal delayed by one horizontal period and supplies it to the limiter level control means C. The limiter level control means C calculates the difference between the reproduced video signal delayed by one horizontal scanning period and the undelayed reproduced video signal from the line correlated noise removing means A, and based on this difference signal, the line correlated noise removing means A and high-frequency noise removal means B described later
Generates a control signal to control the limiter level. The line correlation noise removing means A and the high frequency noise level removing means B switch the limiter level in response to a control signal from the limiter level controlling means C. Then, the noise contained in the reproduced video signal is reduced using this switched limiter level.

FIG. 2 is a circuit diagram showing details of the line correlation noise removing means A1 and the high frequency noise removing means B. Referring to the figure, the line correlation noise removing means A is the IH delay circuit 2.
1, a subtraction circuit 22, a limiter circuit 23, a level matching circuit 24, a subtraction circuit 25, and a voltage dividing circuit 26.

The level matching circuit 24 includes resistors R4, R5, and a capacitor C1. In addition, the voltage dividing circuit 26 includes resistors R1, R2, R
Consists of 3.

The high-frequency noise removal means B includes a low-pass filter 27, a subtraction circuit 28, a limiter circuit 29, a level matching circuit 30, a voltage dividing circuit 31, and a subtraction circuit 32.

The voltage dividing circuit 31 includes resistors R7, R8, and R9, and the level matching circuit 30 includes resistors RIO1R11, R12,
It consists of capacitors C3 and C4.

The limiter level control means C includes a subtraction circuit 33, a bypass filter 34, a limiter circuit 35, an integration circuit 36, a comparator 37, a transistor 38, a transistor 39,
It has a transistor 40.

The mutual relationship between the line correlation noise removal means A5, the high frequency noise removal means B, and the limiter level control means C will be explained in more detail. The reproduced video signal from the low-pass filter 6 is delayed by one horizontal scanning period by the IH delay circuit 21 and is applied to the subtraction circuit 22 and the subtraction circuit 33.

Subtraction circuits 22 and 33 each take the difference between the reproduced video signal from the low-pass filter 6 and the reproduced video signal delayed by one horizontal scanning period from the IH delay circuit 21, and extract the video signal and noise component having no line correlation. .

The component extracted by the subtraction circuit 22 is sent to the limiter circuit 2
3 and extracted by the subtraction circuit 33, only the high-frequency component is extracted by the bypass filter 34, and then applied to the limiter circuit 35.
By limiting the amplitude, high-level video signals among high-frequency components are removed, and only noise components are provided to the integrating circuit 36. By being integrated by this integrating circuit 36, the noise level component is converted into a DC level. The limiter level of the limiter circuit 35 is set based on the noise level in consideration of the number of times the video tape is played. Incidentally, the input to the above-mentioned nox filter 34 may be taken out from the subtraction circuit 22.

Next, the comparator 37 compares the DC level signal from the integrating circuit 36 with a reference voltage set based on the noise level considering the number of reproductions in advance, and when the noise is larger than the reference voltage, the transistors 38, 39, 40 give a signal to the base of. transistor 3
8 turns on, line correlation noise removal means A
The bias voltage of the limiter circuit 23 is a potential obtained by dividing the power supply voltage Vcc by a voltage dividing circuit 26 consisting of a resistor R1 and resistors R2 and R3. Also, by turning on the three transistors, the limiter circuit 2 of the high frequency noise removal means B
The bias voltage 9 has a level divided by the resistor R7 and the resistors R8 and R9.

Furthermore, by turning on the transistor 40, the resistor R11 of the level matching circuit 30 and the capacitor C3 are connected to the resistor R1.
2. Capacitor C4 is connected in parallel. In this case, the limiter level is set to become higher when the bias is lowered. Therefore, the limiter level of the limiter circuit 23 of the line-correlated noise removing means A, the limiter levels of the two limiter circuits of the high-frequency noise removing means B, and the attenuation ratio of the level matching circuit 30 are switched to correspond to the magnitude of the noise level. It will be done.

The operation of the noise removing device for a video tape recorder having the above configuration will be explained. When the noise level contained in the reproduced video signal from the low-pass filter 6 is low, the difference between the reproduced video signal delayed by one horizontal scanning period and the reproduced video signal not delayed is small, so the bypass filter 34 and limiter circuit 35 are The noise level passed through and applied to the integrating circuit 36 is low, and the DC level signal that is the output of the integrating circuit 36 is also low. Therefore, since the DC level signal is smaller than the reference voltage of the comparator 37, no switching signal is output from the comparator 36, and the transistors 38, 39
．． 40 remains OFF.

Therefore, the limiter level of the limiter circuit 23 of the line correlation noise removing means A and the limiter level of the limiter circuit 29 of the high frequency noise removing means B are set to limiter levels that match low noise.

That is, the limiter circuit 23 connects the power supply voltage Vcc to the resistor R1.
A bias potential is set by dividing the voltage by the voltage dividing circuit 26 of R2 and R2. In addition, the limiter circuit 29
The bias potential is set by dividing the voltage by resistors R7 and R8.

Next, when a highly demagnetized video tape is used and the noise level of the reproduced video signal from the low-pass filter 6 is high, the difference between the reproduced video signal delayed by one horizontal scanning period and the reproduced video signal not delayed is The bypass filter 34 extracts only the high-frequency components of the largely uncorrelated noise components and part of the video signal output from the subtraction circuits 22 and 33, and the video signal is further removed by the limiter circuit 35 to remove the noise components. only is taken out. This noise component is integrated in the integration circuit 36 and converted into a DC level signal. This DC level signal is compared with the reference voltage in the comparator 37, and when it exceeds the reference voltage, the transistor 38 is turned on, the bias voltage of the limiter circuit 23 is divided by resistors R1, R2, and R5, and the limiter level is also be made expensive. Similarly, the transistors 38 and 39 are turned on, and the limiter level potential of the limiter circuit 29 is also raised. Further, the output level of the level matching circuit 30 is also lowered by adding the resistor R12. As described above, in response to the switched limiter level, the line correlation noise removal means A and the high frequency noise removal means B can remove noise even if it is a high level noise. In addition, the filter characteristics of the level matching circuit 30 can be switched by the capacitor C4 connected together with the resistor R12, so that an appropriate filter effect corresponding to the noise level can be obtained.

According to the above embodiment, by switching the limiter levels of the line-correlated noise removing means A1 and the high-frequency noise removing means B at the reproduced noise level, the optimum noise removing characteristic according to the noise level can be obtained. Particularly in self-edge playback, line correlation noise removal means A and high frequency noise removal means B minimize deterioration in sharpness, making it possible to obtain high quality images even on rental video tapes with large demagnetization.

In the above embodiment, the limiter levels of the line correlation noise removing means A and the high frequency noise removing means B and the matching ratio of the noise matching circuit 30 are switched in two stages depending on the noise level, but the comparator 37 is removed, Integrating circuit 36
The limiter level and attenuation ratio may be changed linearly by directly applying the output to the transistors 38, 39, and 40.

Furthermore, FETs may be used in place of the transistors 38, 39, and 40.

Furthermore, the limiter level control means C is replaced with a digital circuit from an analog circuit, and the difference signal from the attenuation circuit 22 or 33 is digitally processed, and the limiter level control means C is changed from an analog circuit to a digital circuit.
It is also possible to generate a signal for controlling the limiter level of the signal and the attenuation ratio of the level matching circuit 30.

That is, the gist of the limiter level control means C is to control the limiter levels of the line correlation noise removal means A and the high frequency noise removal means B according to the noise level.
In addition, various design changes can be made as long as the gist is not changed.

[Effects of the Invention] According to the present invention, the limiter level control means controls the line correlation noise removal means and the high frequency noise removal means based on the difference between the reproduced video signal delayed by one horizontal scanning period and the reproduced video signal that is not reproduced. By controlling the limiter level, optimum noise removal characteristics can be obtained depending on the noise level.

Therefore, unlike the conventional fixed limiter level, an effect can be obtained in that an image with sharpness can be displayed even on a video tape with a high noise level.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention, FIG. 2 is a circuit diagram showing details of the line correlation noise removal means, limiter level control means, and high frequency noise removal means shown in FIG. 1.
Figure 4 is a block diagram showing the demodulation system of a conventional video tape recorder, Figure 4 is a circuit diagram showing details of the line correlation noise removal circuit shown in Figure 3 above, and Figure 5 is the high frequency noise removal circuit shown in Figure 3 above. FIG. In the figure, A is a line correlation noise removal means, B is a high frequency noise removal means, C is a limiter level control means, 21 is an IH delay circuit, 22.25.28.32, and 33 are subtraction circuits, 23.29, and 35 is a limiter circuit, 3
4 is a bypass filter, 36 is an integrating circuit, 37 is a comparator, 26.31 is a voltage dividing circuit, 24.30 is a level matching circuit, and 38, 39, and 40 are transistors.

Claims (1)

[Claims] The difference between a reproduced video signal delayed by one horizontal scanning period and a reproduced video signal not delayed is taken, and the amplitude of this difference signal is limited at a predetermined limiter level to extract noise components in the horizontal scanning period. and horizontal scanning line correlation noise removal means for removing noise by subtracting this noise component from a reproduced video signal that is not delayed; a high-frequency noise removal means for extracting and subtracting the noise contained in the high-frequency components from the reproduced video signal; A noise removing device for a video tape recorder, comprising: a limiter level in the removing means; and a limiter level control means for controlling the limiter level of the high frequency noise removing means.