JPH04278782A - Impulse noise eliminating circuit - Google Patents

Abstract

PURPOSE:To eliminate the impulse noise generated in a video signal. CONSTITUTION:A video signal, a signal obtained by delaying this video signal by a delaying circuit 10, and a signal obtained by further delaying this signal by a 1H delaying circuit 11 are inputted to a noise detecting circuit 27 through BEFs 26, 25 and 24, respectively. Simultaneously, they are inputted to a 3-line comb line filter 18 as well through BPFs 12, 13 and 14, respectively. The noise detecting circuit 27 executes an arithmetic processing based on three inputted signals, and outputs a control signal for discriminating whether an impulse noise exists or not. The 3-line comb line filter 18 also executes an arithmetic processing based on three inputted signals, and outputs a chrominance signal. In such a state, when the impulse noise is detected, an SW 17 is turned off. In this case, an SW 23 selects a signal obtained by inverting the output of the 3-line comb line filter 18 as a chrominance signal. Subsequently, an SW 22 selects a signal obtained by adding this chrominance signal and an output signal of a delay circuit 15 as a luminance signal.

Description

[Detailed description of the invention]

[Object of the invention]

0002

[Industrial Application Field] The impulse noise removal circuit according to the present invention is designed to eliminate impulse noise generated due to deterioration of the carrier wave power to noise power ratio (hereinafter referred to as CNR) in a device that receives satellite broadcasting (hereinafter referred to as BS). This invention relates to an impulse noise removal circuit that removes noise.

0003

2. Description of the Related Art In image transmission in satellite broadcasting, a video signal is frequency modulated and then transmitted. In this case, the CNR of the received radio waves may deteriorate depending on weather conditions, antenna performance, etc. If the CNR deteriorates, impulse noise will occur in the video signal when the video signal is demodulated from the received radio waves. This impulse noise appears as white and black particulate noise on the monitor screen. The screen at this time was very difficult to see.

0004

As described above, if the CNR deteriorates during satellite broadcast reception, impulse noise will occur in the video signal. This impulse noise appears as white and black particulate noise on the monitor screen. The screen at this time was very difficult to see.

The impulse noise removal circuit according to the present invention aims to provide an easy-to-see screen that does not generate particulate noise even if the CNR deteriorates during satellite broadcast reception by removing the impulse noise from the video signal. do.

[Configuration of the invention]

[0007]

[Means for Solving the Problem] A first method for obtaining a first delayed signal by delaying an input composite video signal by one horizontal scanning period.
a delay means for delaying the first delay signal by one horizontal scanning period to obtain a second delay signal; the input is the composite video signal, and the color subcarrier frequency band is a passband. a second filter means which receives the first delayed signal as an input and whose passband is a color subcarrier frequency band; a third filter having a passband of a first switch means inserted between the signal generation means and the second filter means for either conducting or cutting off the output signal of the second filter means; and inputting the composite video signal. a third delay means that obtains a third delayed signal by having the same delay time as the first filter means; and a third delay means that receives the first delay signal and has the same delay time as the second filter means. a fourth delaying means for obtaining a fourth delayed signal by having a fourth delaying means; a polarity inverting means for inverting the polarity of the color signal and outputting the same; and a fourth delaying means for inverting the polarity of the color signal and outputting the same; a first addition means for obtaining a second luminance signal; a second addition means for obtaining a second luminance signal by adding the third delayed signal and the output signal of the polarity inversion means; the luminance signal and the second
a second switch means which inputs the luminance signal of the output signal and outputs one of the luminance signals; and a second switch means which inputs the color signal and the output signal of the polarity inverting means and outputs one of the luminance signals. a fourth filter means that receives the composite video signal as an input and has a color subcarrier frequency band as a stop band; and a fourth filter that receives the first delayed signal as an input and outputs a color subcarrier frequency band a fifth filter means having a stopband as a stopband; a sixth filter means having the second delayed signal as an input and having a stopband as a color subcarrier frequency band; and the fourth, fifth, and sixth filters. a first detection means for detecting impulse noise in the white direction generated in the composite video signal; and output signals of the fourth, fifth, and sixth filter means; a second detection means for detecting impulse noise in the black direction generated in the composite video signal; and an OR means that receives the output signals of the first and second detection means and obtains a logical sum of these two signals. , and the output signal of the AND means causes the first
, the impulse noise generated in the composite video signal is removed by controlling the second and third switch means.

[0008]

[Operation] First, impulse noise generated in the video signal is detected. The next period when impulse noise is detected is
A separation circuit that separates a luminance signal and a color signal from a video signal is delayed by one horizontal scanning period, and input of the video signal via the BPF is stopped. At the same time, a signal obtained by inverting the output signal of the separation circuit is used as a color signal. A signal obtained by adding this color signal and a video signal without delay is used as a luminance signal. As a result, color signals and video signals free of impulse noise can be obtained.

[0009]

[Embodiment] Before explaining the embodiment of the impulse noise removal circuit according to the present invention, we will first explain a separation circuit that uses a 3-line comb filter to separate a luminance signal and a chrominance signal from a composite video signal. Explain with reference to. FIG. 4 is a block diagram illustrating the configuration of the separation circuit.

In this figure, a video signal is input to a three-line comb filter 18 via a band pass filter (hereinafter referred to as BPF) 12. Here, the BPF 12 is a frequency band of 3.5 of the input signal, which is the frequency band of the color subcarrier.
It allows only frequency signals in a band of 8 MHz±0.5 MHz to pass through. The same applies to BPFs 13 and 14, which will be described later. The video signal is also input to the 1H delay circuit 10. This 1H delay circuit 10 is a circuit that delays an input signal by one horizontal period and outputs the delayed signal. The output signal of the 1H delay circuit 10 is passed through the BPF 13 to the 3-line comb filter 1.
8 is input. The output signal of the 1H delay circuit 10 is also input to the 1H delay circuit 11 and the delay circuit 16. This delay circuit 16 is a circuit having a delay time equivalent to that of the BPF 13. The output signal of the 1H delay circuit 11 is BPF1
4 to a three-line comb filter 18.

The three-line comb filter 18 performs arithmetic processing on the input signal and outputs a color signal. This color signal and the output signal of the delay circuit 16 are input to an adder 19 and are added together. This generates a luminance signal. By using this method, the video signal is separated into a color signal and a luminance signal.

Next, the characteristics of impulse noise removed by the present invention will be described. The first feature is that it occurs randomly. Therefore, the impulse noises generated within three consecutive horizontal scanning periods are all different in position and vertical direction. However, this does not apply if the CNR is extremely degraded.

The second characteristic is that the DC level of a video signal in which impulse noise has occurred is higher in the white direction or black direction compared to a normal video signal. The third feature is that no color signal is superimposed on impulse noise. The impulse noise removal circuit according to the present invention uses the above-mentioned characteristics to remove impulse noise.

An embodiment of the impulse noise removal circuit according to the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention. Figure 2 is Figure 1
FIG. 2 is a block diagram showing the configuration of an embodiment of a noise detection circuit 27 in FIG. FIG. 3 is a time chart illustrating the operation of the noise detection circuit 27 of FIG. 2. Note that the same components as in FIG. 4 are given the same reference numerals.

In FIG. 1, the video signal includes impulse noise generated due to deterioration of the received CNR. This video signal is input to the 3-line comb filter 18 via the BPF 12. The video signal is also input to a 1H delay circuit 10 and a delay circuit 15. This delay circuit 15
is a circuit having a delay time equivalent to that of the BPF 12. 1
The output signal of the H delay circuit 10 is transmitted through the BPF 13 and the switch (
The signal is input to a 3-line comb filter 18 via a SW 17 (hereinafter referred to as SW). On the other hand, the output signal of the 1H delay circuit 10 is also input to the 1H delay circuit 11 and the delay circuit 16. The output signal of the 1H delay circuit 11 is inputted to the 3-line comb filter 18 via the BPF 14.

The three-line comb filter 18 performs arithmetic processing on the input signal and outputs a color signal. This color signal is input to the SW 23 and also to the inverter 21. The polarity of the color signal is reversed by this inverter 21, and S
It is input to W23.

The color signal and the output signal of the delay circuit 16 are input to an adder 19 to generate a luminance signal. This luminance signal is input to SW22. Further, the output signal of the inverter 21 and the output signal of the delay circuit 16 are input to the adder 20. The output of this adder 20 is also input to SW22.

The video signal is passed through a band rejection filter (hereinafter referred to as BEF).
) is also entered in 26. This BEF26 is the frequency band of the color subcarrier of the input signal.
．． Only frequency signals in the band of 58MHz±0.5MHz are blocked. This removes the color signal component from the video signal. The same applies to BEFs 24 and 25, which will be described later. The output signal of the BEF 26 is input to the noise detection circuit 27. Also, the output signal of the 1H delay circuit 10 is BEF25
The signal is input to the noise detection circuit 27 via. The output signal of the 1H delay circuit 11 is also input to the noise detection circuit 27 via the BEF 24.

The noise detection circuit 27 performs arithmetic processing on the input signal. The timing at which impulse noise occurs is detected and a control signal is output. This control signal is input to SW17, 22, and 23 to control these SWs. SW17 is normally in an on state, but is turned off when impulse noise is detected. Normally, the 3-line comb filter 18 includes a 1H delay circuit 10.
outputs a color signal that is synchronized with the output signal of the However, S
When W17 is turned off and the output signal of BPF 13 is no longer input, a signal inverted from the normal color signal is output.

Therefore, the SW 22 normally selects the output signal of the 3-line comb filter 18 and outputs it as a color signal, but when impulse noise is detected, the inverter 2
1 is selected as the color signal. Similarly SW22
Normally, the output signal of the adder 19 is selected and outputted as a luminance signal, but when impulse noise is detected, the output signal of the adder 20 is selected as the luminance signal.

Next, an embodiment of the noise detection circuit 27 is shown in FIG.
This will be explained with reference to FIG. Figure 2 shows the noise detection circuit 2.
7. FIG. 3 is a time chart showing the waveforms of input and output signals in each block of FIG. 2.

The video signal a is sent to the 1H detection circuit 10 and BEF2.
6 is input. Here, the signal after passing through the BEF 26 is designated as signal a'. Further, the video signal after passing through the 1H detection circuit 10 is designated as a signal b, and the video signal after this signal b passes through the 1H detection circuit 11 is designated as a signal c. Therefore, the signal after passing through BEF25 is signal b', and the signal after passing through BEF24 is signal c.
′. These signals a', b', and c' are input to the noise detection circuit 27.

The noise detection circuit 27 includes a white noise detection circuit 28 that detects impulse noise in the white direction (hereinafter referred to as white noise) and a black noise detection circuit 29 that detects impulse noise in the black direction (hereinafter referred to as black noise). and an OR circuit 50. Signals a', b', and c' input to the noise detection circuit 27 are input to a white noise detection circuit 28 and a black noise detection circuit 29, respectively. Then, the output signal of the white noise detection circuit 28 and the output signal of the black noise detection circuit 29 are input to the OR circuit 50. The output of this OR circuit 50 is a control signal.

First, the white noise detection circuit 28 will be explained. Signals a' and b input to the white noise detection circuit 28
Of ' and c', the signal a' and the signal b' are input to a maximum value detection circuit (hereinafter referred to as MAX) 30. This MAX3
0 detects only the maximum value of the two input signals and outputs the signal d. Further, the signal b' and the signal c' are input to MAX31, which outputs the signal e. Furthermore, signal a' and signal c'
is input to MAX32 and outputs signal f. This signal f is amplified by an amplifier 34 and becomes a signal h. On the other hand, signal d
and e are input to a minimum value detection circuit (hereinafter referred to as MIN) 33. This MIN33 detects only the minimum value of the two input signals and outputs a signal g.

The signal h and the signal g are each connected to a clamp 35.
is input to the clamp 36. Here clamp 35, 3
6 clamps the input signal at the pedestal level and outputs it to the comparator 37. The comparator 37 compares the two input signals and becomes High only when the level of the output signal of the clamp 36 is higher than the level of the output signal of the clamp 35.
Output the level. The output signal of this comparator 37 is the output signal of the white noise detection circuit 28.

Next, the black noise detection circuit 29 will be explained. Signals a' and b' input to the black noise detection circuit 29
, c', the signal a' and the signal b' are input to the MIN 40, which outputs the signal j. Also, signal b' and signal c' are M
It is input to IN41 and outputs signal k. Furthermore, the signal a'
and signal c' are input to MIN42, which outputs signal l. On the other hand, signals j and k are input to MAX43, and signal m
Output. This signal m is amplified by an amplifier 44 and becomes a signal n.

Signal n and signal l are each clamped at 45
is input to the clamp 46. Here clamp 45, 4
6 clamps the input signal at the pedestal level and outputs it to the comparator 47. The comparator 47 compares the two input signals and becomes High only when the level of the output signal of the clamp 45 is lower than the level of the output signal of the clamp 46.
Output the level. The output signal of this comparator 47 is the output signal of the black noise detection circuit 29.

As described above, the output signal of the white noise detection circuit 28 and the output signal of the black noise detection circuit 29 are input to the OR circuit 50. The output of this OR circuit 50 is a control signal for controlling each SW.

Next, a detailed explanation will be given based on the waveform shown in FIG. In this figure, the waveform of the video signal is simplified for ease of explanation. Here, the horizontal scanning period in which white noise occurs in the video signal a is assumed to be (n-1)H. Also, let nH be the horizontal scanning period in which black noise occurs. Therefore, for signal b, white noise occurs at nH, and black noise occurs at (n+
1) Occurs at H. Similarly, signal c is white noise (n+
1) Occurs at H, and black noise occurs at (n+2)H.

Impulse noise is not affected by passing through the BEF. Therefore, signals a, b, c and BEF26,2
The signals a', b', and c' after passing through the signals 5 and 24 have almost the same waveform.

First, detection of white noise will be explained. The signal d is the detected maximum value of the signals a' and b', and (
n-1) White noise occurs in H and nH. Also signal e
The maximum values of the signals b' and c' are detected, and white noise occurs at nH and (n+1)H. Similarly, the signal f is obtained by detecting the maximum value of the signals a' and c', and is (n-1
)H and (n+1)H, white noise occurs. A signal h is obtained by amplifying this signal f.

On the other hand, the signal g is obtained by detecting the minimum value of the signals d and e, and white noise occurs in nH. This signal g
The signal i and the signal h are respectively clamped and compared by the comparator 37, and the result is the signal i.

Next, detection of black noise will be explained. Signal j is the detected minimum value of signals a' and b', and n
Black noise occurs at H and (n+1)H. Also signal k
is the detected minimum value of signals b' and c', and (n+
1) Black noise occurs at H and (n+2)H. Similarly, signal l is the detected minimum value of signals a' and c',
Black noise occurs at nH and (n+2)H.

On the other hand, the signal m is obtained by detecting the maximum value of the signals j and k, and black noise occurs at (n+1)H. Signal n is obtained by amplifying this signal m. The signal n and the signal l are each clamped and compared by a comparator 47, and the result is the signal p. As described above, the logical sum of the signal i and the signal p is the control signal q.

As described above, impulse noise is detected by the noise detection circuit 27. If impulse noise is detected, SW17 is turned off. As a result, the output signal of the BPF 13 is not input to the 3-line comb filter 18 during the period when impulse noise is occurring. At this time, the color signal output from the 3-line comb filter 18 is an inverted version of the original color signal. Therefore, the original color signal is generated by passing it through the inverter 21. Further, by adding the output signal of the inverter 21 and the output signal of the delay circuit 15, a luminance signal free of impulse noise is generated.

[0036]

As described above, impulse noise is detected by the noise detection circuit 27. If impulse noise is detected, SW17 is turned off. With this, B
The output signal of the PF 13 is not input to the 3-line comb filter 18 during the period when impulse noise is occurring. At this time, the color signal output from the 3-line comb filter 18 is an inverted version of the original color signal. Therefore, by passing the light through the inverter 21, the original color signal can be generated. In addition, the output signal of this inverter 21 and the delay circuit 1
By adding the output signals of 5, a luminance signal without impulse noise can be generated.

[Brief explanation of the drawing]

[Fig. 1] Block diagram showing the configuration of the present invention

[Figure 2] Block diagram showing the configuration of the noise detection circuit in Figure 1

[Figure 3] Time chart explaining changes in waveform in Figure 2

[Figure 4] Block diagram showing the conventional configuration

[Explanation of symbols]

10, 11...1H delay circuit 12, 13, 14...BPF 15, 16...Delay circuit 17, 22, 23...SW 18...3 line comb filter 19, 20...adder 21...Inverter 24, 25, 26...BEF 27...Noise detection circuit

Claims (1)

[Claims] 1. A first delay means for delaying an input composite video signal by one horizontal scanning period to obtain a first delayed signal;
a second delay means that receives the composite video signal as an input and whose passband is the chrominance subcarrier frequency band; a second filter means whose passband is the frequency band;
a third filter means which receives the second delayed signal as an input and whose passband is the color subcarrier frequency band;
color signal generation means that receives the signals output from the third filter means and generates color signals from these signals; and a color signal generation means that is inserted between this color signal generation means and the second filter means, a first switch means for either conducting or cutting off the output signal of the second filter means;
a third delay means that receives the composite video signal as an input and obtains a third delayed signal by having the same delay time as the first filter means; The fourth filter means has the same delay time as the filter means.
a fourth delay means for obtaining a delayed signal; a polarity inversion means for inverting the polarity of the color signal and outputting the same; and adding the fourth delay signal and the color signal to obtain a first luminance signal. 1st
a second addition means for adding the third delayed signal and the output signal of the polarity reversing means to obtain a second luminance signal; a second switch means that receives a signal as an input and outputs one of the luminance signals; and a second switch means that receives the color signal and the output signal of the polarity reversal means as an input and outputs one of the color signals. a third switch means for inputting the composite video signal and having a color subcarrier frequency band as a stop band;
a fifth filter means that receives the first delayed signal as an input and has a color subcarrier frequency band as a stopband; and a fifth filter that receives the second delayed signal as an input and has a color subcarrier frequency band as a stopband. a sixth filter means, said fourth and fifth filter means;
, a first detection means that receives the output signal of the sixth filter means as an input and detects impulse noise in the white direction generated in the composite video signal; and output signals of the fourth, fifth, and sixth filter means. as an input, a second detection means for detecting impulse noise in the black direction generated in the composite video signal, and output signals of the first and second detection means as input,
and a logical sum means for obtaining a logical sum of these two signals,
The first, second and third
An impulse noise removal circuit characterized in that it controls a switching means.