JP2766070B2 - Noise removal device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a television receiver, and more particularly to a television receiver having a descrambling device for receiving and reproducing a scrambled broadcast. And a signal processing circuit for achieving the above.

[Conventional technology]

In paid television broadcasts performed by satellite broadcasting or CATV, television signals are scrambled and broadcasted, and signals are restored by a descrambling circuit added to the receiver to prevent eavesdropping by anyone other than the subscriber. .

As the scramble method, for example, “TV technology Vo
l.37, 1989/6 p.56 to p.57 '', a line permutation method that changes the order of signals within a scanning line, a line rotation method that changes the order of scanning lines at random, etc. Many schemes have been proposed.

However, there is no television receiver configured to perform descrambling processing when receiving a scrambled broadcast and perform signal processing so as to improve image quality deterioration peculiar to the scramble-descramble system.

[Problems to be solved by the invention]

When receiving a scrambled broadcast, the reproduced image is degraded from the original image quality by the descrambling device. For example, in a line permutation method in which the order of signals is changed at a certain point in a scanning line as a boundary, or in a line rotation method in which transmission is performed by disturbing the order of scanning lines, the signal order at the time of transmission is input when the image is reproduced by the receiver. For this reason, for example, a DC offset occurs between signal boundaries or between lines due to sag in a video signal. This DC offset is a slight difference in amplitude, but appears as noise on the screen in the case of an overall flat image. In particular, in a system for performing descrambling digitally, an A / D converter is used to convert an analog scrambled signal into a digital signal, and the ability of a clamp circuit provided at a preceding stage of the A / D converter is improved. It greatly affects image quality.

An object of the present invention is to solve the image quality degradation that occurs when such a scrambled signal is restored by performing descrambling processing, and even during scrambled broadcasting, a high-quality image can be obtained without distinction from ordinary broadcasting. It is an object of the present invention to provide a signal processing circuit.

[Means for solving the problem]

Means for achieving the above object include a frame memory for delaying a signal by a frame, a subtractor for detecting signal correlation, a high-pass filter for filtering a difference signal from the subtractor, and the presence or absence of descrambling processing. Characteristic switching means for switching at least the pass characteristic of the high-pass filter during non-descrambling processing and descrambling processing according to the control signal detected, or the value of a coefficient multiplier for multiplying the output signal of the high-pass filter or the characteristic switching means. A noise reduction circuit with a position, comprising a mixer for adding or subtracting a signal processed by these circuits and an incoming signal, comprising a coefficient value switching means capable of switching by the control signal. This is realized by providing

Further, it is achieved by the following configuration depending on the relationship between the noise reduction circuit with position, the descrambling device, and the television receiver.

1) When the television receiver and the descrambling device are independent.

In this case, as a first plan, as shown in FIG. 4, a noise reduction circuit with a position is provided in the television receiver. The control signal from the descrambling device is guided to the television receiver, and thereby the characteristic of the noise reduction circuit of the television receiver is switched.

As a second plan, as shown in FIG. 5, a frame correlation type noise reduction circuit is provided in a descrambling device, a signal after descrambling is guided to the noise reduction circuit, and a signal after noise removal processing is transmitted to a television. This is realized by supplying the data to a John receiver.

2) When the descramble device and the television receiver are integrated.

In this case, as shown in FIG. 6, in a television receiver for receiving a scrambled broadcast, a descrambling circuit and a noise reduction circuit with a position capable of switching the noise removal characteristic of the above configuration are provided in a signal processing circuit. The characteristic is switched by a control signal from a built-in descramble circuit.

[Action]

In the above means, the descrambled signal decoded by the descrambling device is guided to a noise reduction circuit, and a noise component having no correlation is extracted for each frame by taking a difference from the signal delayed by a frame to obtain a current component. Remove noise from the signal.

At this time, if the receiver is receiving a normal video signal, performing a noise reduction process on the low-frequency component causes a problem such as an afterimage in the moving image portion. For this reason, for example, the pass characteristic of the high-pass filter is switched using a control signal that has determined whether or not scrambling has occurred in the descrambling circuit. For example, in the case of a video signal that does not require descrambling, the high-pass filter extracts only high-frequency noise components and switches so that noise reduction is effective only in high-frequency components, thereby reducing adverse effects such as afterimages.
Further, the coefficient of the coefficient unit in the noise reduction circuit is switched by the control signal to realize an optimum noise removal characteristic.

Further, when the receiver is receiving a scramble signal, the specific noise such as a DC offset due to the descrambling process becomes more prominent than the afterimage, so the control signal obtained from the descrambling circuit, The characteristics of the noise reduction circuit are set so as to be effective from low frequency components. Further, the noise removal performance is improved by increasing the coefficient of the coefficient unit as compared with a normal case.

As described above, the characteristics of the noise reduction circuit are adaptively switched between the descrambling process and the non-descrambling process, and an optimum image is obtained.

〔Example〕

Hereinafter, an embodiment of the present invention will be described with reference to FIG.

FIG. 1 is a configuration example of a noise reduction circuit for realizing the present invention in a television receiver compatible with descrambling processing.

In FIG. 1, reference numeral 1 denotes an input terminal to which a television signal is input, 2 denotes an input terminal of a signal for detecting the presence or absence of descrambling processing, 3 denotes a frame memory for delaying the television signal by a frame, and 4 denotes a delay between the current signal and the current signal. A subtractor 10 for obtaining a signal difference signal, which is surrounded by a broken line, is an example of a high-pass filter whose pass characteristics can be switched. For example, a high-pass filter 5 for extracting a high-frequency component and the descramble processing detection signal are used. It comprises a changeover switch 6 for switching the input / output signal of the high-pass filter. 7
Is a coefficient unit whose coefficient value can be changed by the scramble presence / absence detection signal, 8 is a mixer for adding or subtracting the current signal and the output signal of the coefficient unit 7, and 9 is a processing terminal of a signal subjected to noise reduction processing. It is.

 The operation of this embodiment is as follows.

After passing through a descrambling circuit, a television signal subjected to predetermined signal processing is guided to an input terminal 1 and supplied to a subtractor 4 and a mixer 8. The output signal of the frame memory 3 is supplied to the subtractor 4, and the input signal is subtracted from the frame delay signal output from the frame memory 3 to obtain a frame difference signal. This frame difference signal is a signal containing a noise component having no correlation between frames in the video signal. Next, the difference signal is guided to a high-pass filter 10 having a high-pass filter 5 and a changeover switch 6 and capable of switching a pass band. The high-pass filter 5 extracts a high-frequency component of the difference signal, thereby guiding a signal in which only high-frequency noise is extracted to a terminal a of the switch 6. The changeover switch 6 normally selects the terminal a side based on the descrambling processing presence / absence detection signal guided to the input terminal 2, and when a video signal after the descrambling processing is guided, for example, a difference signal that is not band-limited is guided. Select the terminal b side. The signal selected by the changeover switch 6 is multiplied by a certain non-linear coefficient in a coefficient unit 7 and then mixed with a current signal by a mixer 8 to obtain a signal from which noise components have been removed. At this time, the nonlinear coefficient of the coefficient unit 7 is switched by the descrambling processing presence / absence detection signal. The signal mixed by the mixer 8 is output from the output terminal 9 to the next signal processing circuit as a noise reduction output, is delayed by one frame in the frame memory 3, and is guided to the subtractor 4.

By the above operation, first, when the television receiver is receiving a signal that does not require descrambling processing,
In other words, during normal broadcast reception, attention is paid to the characteristics of the noise components, and only high-frequency noise is extracted, so when removing low-frequency noise, side effects such as tailing that generally occur in the moving image portion are reduced. You. Conversely, in the case of the video signal after the descrambling process, the changeover switch 6 is switched to the terminal “b” to use the frame difference signal from the low band to the high band, so that the low frequency noise due to the DC offset generated at the time of the descrambling is obtained. Is removed.

In addition, the non-linear coefficient value of the coefficient unit 7 is switched by a descrambling processing presence / absence detection signal, and a different coefficient is used depending on whether or not the descrambling processing is performed, thereby optimizing the noise removal characteristic. For example, at the time of the descrambling process, the noise removal effect is increased by increasing the nonlinear coefficient value, and the noise removal is also effective for the difference signal of a larger level. On the other hand, in normal times, switching is performed such that the nonlinear coefficient value is reduced in order to make the image quality degradation due to side effects unnoticeable, and settings are made such that noise removal is effective only for small-amplitude difference signals.

FIG. 3 shows an example of a nonlinear coefficient characteristic of the coefficient unit 7.
The horizontal axis is the input level of the coefficient unit, and the vertical axis is the output level after the calculation. For example, when A> B, the characteristic is such that the slope A when the descrambling is performed, and when the descrambling is not performed. Has a characteristic such that it has a slope B, and where the input level is large, the coefficient 0 is used in both cases to prevent blurring of the moving image due to the noise removal effect.
The noise removal effect can be optimized by setting the nonlinear coefficient characteristic as follows.

In the embodiment of the present invention shown in FIG. 1 as described above, as an example of the high-pass filter 10 capable of switching the pass characteristic, the input / output of the high-pass filter 5 which is the simplest and has a remarkable characteristic switch is switched by the switch 6. However, according to the present invention, as a configuration of a filter capable of switching pass characteristics,
The present invention is not limited to only this configuration, and includes all configurations having different pass characteristics. Further, the present invention is not limited to the configuration order of the filter 10 and the coefficient unit 7 that can switch the pass characteristic, and the configuration order may be reversed.

Next, another embodiment of the present invention will be described with reference to FIG.

FIG. 2 shows an example in which a non-recursive configuration is used as a noise reduction circuit for realizing the present invention in a television receiver compatible with descrambling processing.

In FIG. 2, symbols 1 to 10 are the same as those in FIG.

First, a signal input to the input terminal 1 is guided to the frame memory 3, the subtracter 4 and the mixer 8. The difference between the frame delayed signal delayed by the frame memory 3 and the incoming signal is taken out by the subtractor 4, and the difference signal is subjected to the same processing as in the embodiment of FIG. To obtain a signal after noise removal from the processing terminal 9.

As described above, in the present embodiment, the first
The same effect as that of the embodiment shown in the drawing can be obtained.

Next, regarding a configuration that can be considered depending on the relationship between the noise reduction circuit as in the embodiment of FIG. 1 or FIG. 2 and the descrambling device and the television receiver,
Several embodiments will be described.

FIG. 4 shows an embodiment in which a descrambling device and a television receiver are independent and a noise reduction circuit with a position is provided in the television receiver.

4, reference numeral 11 denotes a descrambling device, reference numeral 12 denotes a television receiver, reference numeral 13 denotes a noise reduction circuit with a position as shown in the embodiment of FIG. 1 or FIG. 2, and reference numeral 14 denotes a television receiver. Other signal processing circuits in the machine.

The operation of the present embodiment is as follows. First, a scrambled television signal is guided from a tuner or the like to a descrambling device 11, and a signal after the descrambling process is provided in a noise reduction circuit 13 with a position provided in a television receiver 12. The normal unscrambled television signal is supplied directly to the television receiver 12 and supplied to the noise reduction circuit 13 with position, which is used in the embodiment shown in FIGS. 1 and 2. As described above, the noise removal characteristic is switched by the control signal obtained from the descrambling device 11, the optimal noise removal processing is performed, and the signal is guided to the television signal processing circuit 14 at the subsequent stage.

FIG. 5 shows an embodiment in which the descrambling device and the television receiver are independent as in FIG. 4, and a noise reduction circuit is provided in the descrambling device.

In FIG. 5, reference numeral 11 denotes a descrambling device, 12 denotes a television receiver, 15 denotes a descrambling processing circuit in the descrambling device, and 16 denotes a frame correlation type noise reduction circuit.

Here, as the noise removal characteristics of the frame correlation type noise reduction circuit 16, the pass filter characteristics and the coefficient characteristics of the coefficient unit are set in the same manner as in the noise removal of the descrambled signal as described in the embodiment of FIG. By setting these characteristics, the signal descrambled by the descrambling circuit 15 is subjected to noise removal, and the signal is guided to the television receiver 12 as the output of the descrambling device 11.

In this case, for example, when the television receiver 12 also has a frame correlation type noise reduction circuit, and when a signal from the descrambling device is guided, the frame correlation type noise reduction circuit in the television receiver is used. It is desirable to stop the operation.

FIG. 6 shows an embodiment in which the descrambling device and the television receiver are integrated.

In FIG. 6, symbols 12 to 15 correspond to FIGS.
It is similar to the figure.

In the present embodiment, a descrambling circuit 15 and a noise reduction circuit 13 with a position are provided in the television receiver 12, and when a normal television signal is guided to the television receiver, the descrambling circuit is not interposed. If the signal is a scrambled television signal, the signal after the descrambling process is performed by the descrambling circuit 15 is led to the noise reduction circuit with position 13 and detected by the descrambling circuit. The noise elimination characteristic is switched by the control signal to adaptively remove the noise.

〔The invention's effect〕

According to the present invention, it is possible to improve image quality degradation caused by descrambling a scrambled video signal by optimizing the elimination characteristics of a noise reduction circuit. It is possible to obtain a high-quality video signal without distinguishing the video signal.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing another embodiment of the present invention, and FIG. 3 is a diagram showing an example of coefficient characteristics of the coefficient unit 7 in FIGS. 1 and 2. FIG. 4 is a diagram showing an embodiment in which the descrambling device and the television receiver are independent, and FIG. 5 is another drawing in which the descrambling device and the television receiver are also independent. FIG. 6 is a diagram showing an embodiment, and FIG. 6 is a diagram showing an embodiment in which a television receiver and a descrambling device are integrated. DESCRIPTION OF SYMBOLS 1 ... Input terminal of television signal, 2 ... Input terminal of detection signal of presence / absence of descrambling process, 3 ... Frame memory, 4 ... Subtractor, 5 ... High-pass filter, 6 ... Switching Switch 7, a coefficient unit capable of switching coefficient values, 8 a mixer, 9 an output terminal of a noise removal signal,
10: a pass filter whose pass characteristics can be switched, 11: a descrambling device, 12: a television receiver, 13:
Noise reduction circuit with position, 14 ... television signal processing circuit, 15 ... descrambling processing circuit,
16… Frame correlation type noise reduction circuit.

Continuation of the front page (56) References JP-A-1-233825 (JP, A) JP-A-1-120176 (JP, A) JP-A-1-220581 (JP, A) JP-A-2-186879 (JP) JP-A-62-125780 (JP, A) JP-A-62-290270 (JP, A) (58) Fields studied (Int. Cl. ⁶ , DB name) H04N 5/14-5/217

Claims (4)

(57) [Claims] 1. A noise elimination device using a frame correlation in a television receiver capable of receiving a scrambled broadcast, wherein the noise elimination device has a frequency characteristic in noise elimination performance and converts a scrambled video signal. A method of switching the frequency characteristic of the noise removal performance between a case where the noise reduction device is guided after the descrambling process and a case where an ordinary video signal that does not require the descrambling device is guided to the noise removal device. Characteristic noise removal device. 2. The means for switching the frequency characteristic of the noise elimination performance in the noise elimination device is set so that when the video signal after the descrambling process is introduced as an input, the noise elimination operates from a low frequency component. 2. The noise eliminator according to claim 1, wherein when an ordinary video signal that does not require descrambling is introduced, the noise elimination is set to operate for higher frequency components. 3. A noise elimination device using a frame correlation in a television receiver capable of receiving a scrambled broadcast, wherein the noise elimination device detects at least a frame correlation of a video signal, and the frame correlation detection device. And a means for mixing an output signal from the multiplying means and an input signal of the frame correlation detecting means, wherein the multiplying means comprises a plurality of nonlinear signals. Means for switching the plurality of non-linear coefficient values between a case where the input signal guided to the noise elimination device is a video signal after descrambling and a case where the descrambling process is not required. A noise removing device comprising: 4. The apparatus according to claim 1, wherein the means for switching the noise removal performance or the means for switching the plurality of non-linear coefficient values is controlled by a signal for determining whether or not there is a descrambling operation from the means for performing the descrambling process. The noise removing device according to claim 1, 2, or 3.