JPH02231890A - Noise reduction circuit - Google Patents

Abstract

PURPOSE:To form a color noise reduction circuit, for which there is no color blurring, by providing a feedback coefficient control circuit, detecting the contour component of a color carrier, reducing the feedback coefficient of a cyclic filter or making the feedback coefficient be zero when there is the contour component and reproducing the correct contour of the color carrier. CONSTITUTION:Since a signal, for which the contour and noise are reduced, can be obtained when the signal is passed through the cyclic filter, the contour can be detected by subtracting the output signal of an adder 3 from an input signal. This subtraction is executed by a subtracter 4 and the output of the subtracter is inputted to a coefficient control circuit 8. In the coefficient control circuit 8, there is a clip circuit to clip the input signal by a prescribed value and the component of the noise included in a contour component is removed. Then, the input signal is outputted as a control signal. The control signal executes so control that the a coefficient K of a variable coefficient device 10 can be reduced and a coefficient (1-K) of a variable coefficient device 9 can be enlarged. Thus, when the coefficient is controlled adaptively with the contour, the omission or tailing of the contour component is decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a color carrier wave processing circuit for a television receiver or the like, and particularly to a circuit for reducing noise present in a color carrier wave.

[Conventional technology]

Conventionally, in television receivers, a noise reduction circuit has been proposed that reduces only the noise component by utilizing the line correlation of color carrier signals after YC separation of a video signal. This type of color noise reduction circuit is described in "R Color Noise Reduction Circuit Described in Japanese Unexamined Patent Publication No. Sho 62-200995. Figure 2 shows the circuit. In the figure, 1 is a delay element that delays the input signal by one horizontal scanning period (IH), 2 is a clip circuit that passes only large signal levels, 3 and 5 are adders, 4 is a subtracter, and 6 is an input signal multiplied by K. 7 is a coefficient multiplier that multiplies the input signal by (1-K) by a coefficient (1-K) smaller than 1, 100 is an input terminal for inputting a color carrier wave, and 101 is an output terminal of a noise reduction circuit. It is.

Next, circuit operation will be explained using FIG. 7.

A color carrier wave for one vertical scanning period as shown in FIG. 7A is input from the input terminal 100. This color carrier wave is multiplied by (1-K) by a coefficient multiplier 7 and input to an adder 3. On the other hand, the output signal of the adder 3 passes through the delay element 1 and is delayed by one horizontal scanning period (IH), is multiplied by K by the coefficient multiplier 6, and inputted to the adder 3.

If the coefficient at this time is increased and the feedback is increased (for example, K = about 0.7), the output waveform of adder 3 becomes the seventh
It will look like Figure B. Here, coefficient units 6, 7, delay element 1,
The circuit consisting of the adder 3 is a recursive filter that uses line correlation to combine the current input signal and the previous output signal delayed by one horizontal scanning period at a predetermined ratio.・ ・4 The sound becomes a waveform that decreases. Here, a dropout occurs at the rising edge of the signal during one vertical scanning period, and a trailing trailing edge occurs.

The output signal of adder 3 is input to subtracter 4, and input terminal 1
00 is subtracted from the input color carrier. Subtractor 4
The output signal is as shown in FIG. 7C, and noise and color carrier contour components are extracted. The output signal of the subtracter 4 is input to the clip circuit 2. Here, the clipping circuit 2 outputs signals above the reference level and clips signals below the reference level without outputting them, so only signals with large amplitude levels are output. The output of the clip circuit 2 at this time is shown in Figure 7D.
Shown below. By setting the clip level to a predetermined value, a contour signal with only noise removed can be obtained here. The output of the clipping circuit 2 is input to the adder 5, where it is added to the output of the adder 3, which is the output of the cyclic filter, and output from the output terminal 101. The output waveform at this time is shown in FIG. 7E.

As can be seen from the waveform diagram, the decrease in the contour component of the color carrier signal is small, but dropouts and trailing occur after the contour.

[Problem to be solved by the invention]

In a recursive filter, the larger the value of the feedback coefficient, the more the influence of the signal component extends over several H. Therefore, if you want to reproduce the contour part, it is necessary to add the contour components over several H after the contour.

However, in the conventional example, the signal components after the contour are removed by the clipping circuit 2 and are not added to the output of the recursive filter, resulting in problems such as dropouts and trailing.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and reproduce the correct outline of a color carrier wave, thereby providing a color noise reduction circuit free from color fringing.

[Means to solve the problem]

The above object is achieved by detecting the contour component of the color carrier wave and, when the contour component is present, reducing the feedback coefficient of the recursive filter or making it zero.

[Effect]

The contour can be detected by subtracting the output signal of the recursive filter and the input signal, and the contour components are reproduced by changing the coefficients of the recursive filter according to the level of this signal, so there is no color blurring.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. 1st
In the figure, 8 is a coefficient control circuit, 9 is a variable coefficient unit whose coefficient (1-K) changes according to the control signal, and 10 is a variable coefficient unit whose feedback coefficient K changes according to the control signal. The same parts are given the same reference numerals.

Hereinafter, the operation of the circuit shown in FIG. 1 will be explained using FIG. 8.

A color carrier wave as shown in FIG. 8A is input from the input terminal 100. This signal is multiplied by (1-K) by a variable coefficient multiplier 9 and input to an adder 3. On the other hand, the output of adder 3 is output from delay element 1
The signal is delayed by one horizontal scanning period, multiplied by a coefficient K by the variable coefficient multiplier 10, and input to the adder 3. If the coefficient K at this time is a large value, for example K=0.7, then the output of the adder 3 will be as shown in FIG. 8B. (K indicates a feedback coefficient and has a value smaller than 1.0.) A dropout occurs, and a trailing edge occurs at the falling edge.

When the coefficient K is a small value, for example, K = 0.1 or less, the feedback rate becomes small, so the ratio of addition of the input signal of the adder 3 and the IH delayed feedback signal becomes larger for the input signal, and as shown in FIG. A signal with slightly reduced noise as shown in C is obtained, and the deterioration of the contour is also reduced.

Therefore, normally, the coefficient is increased to enhance the noise reduction effect, and the coefficient is decreased at the contour to prevent deterioration of the contour.

Here, we will discuss contour detection. When the signal is passed through a recursive filter, a signal from which the contour and noise have been removed is obtained as shown in FIG. 8B, so the contour can be detected by subtracting the output signal of the adder 3 from the input signal.

This subtraction is performed in subtracter 4. The output of the subtracter 4 is input to a coefficient control circuit 8. The coefficient control circuit 8 includes a clipping circuit that clips the input signal at a predetermined value to remove noise components included in the contour components. The contour signal from which the noise component has been removed is output from the coefficient control circuit 8 as a control signal. The control signal controls the coefficient (1-K) of the variable coefficient multiplier 9 to be large. FIG. 8D shows a waveform when the coefficients are controlled to adapt to the contour as described above. As shown in the figure, missing contour components and trailing are reduced.

As described above, the present invention exhibits a large noise reduction effect in flat areas, and in contour areas, it suppresses loss of color carrier waves and trailing due to the recursive filter compared to the conventional example, and reproduces colors without color blurring. be.

Next, a second embodiment of the present invention will be described using FIG. 3. In the figure, 11 is a subtracter, 12 is a variable coefficient unit,
13 is an adder, and the same parts as in FIGS. 1 and 2 are given the same reference numerals.

The circuit operation will be explained. The color carrier wave signal inputted from the input terminal 100 is inputted to the subtracter 11 and subtracted from the pre-IH signal outputted from the delay element 1. The output of the subtractor 11 becomes noise and contour components. The output of the subtracter 11 is input to a variable coefficient multiplier 12, multiplied by a coefficient (IK), the signal amplitude is reduced, and the signal is input to an adder 13. Here, the noise and the variable coefficient signal, which is the contour component, are added. Contour detection and control are the same as in the first embodiment, so a description thereof will be omitted. The second embodiment also suppresses the decrease in contour by controlling the coefficient (1-K) of the variable coefficient unit 12. The difference from the first embodiment is that the number of variable coefficient units is reduced by one and the number of subtracters is increased by one. The effect of this is 2 when there are two variable coefficient units.
It is difficult to obtain the relative accuracy of the two variable coefficient units, but the second
The embodiment has one variable coefficient unit, so there is no need to take into account the relative accuracy of the variable coefficient unit. Therefore, the second embodiment has the effect of simplifying the circuit design and suppressing an increase in the circuit scale.

Next, FIG. 4 shows a third embodiment of the present invention. In the figure, numeral 14 indicates a variable coefficient multiplier. The same parts as in FIG. 1.2.3 are given the same reference numerals. The operation of this circuit is similar to that of the second embodiment described above, but in the subtracter 11 where the addition/subtraction signals of the cyclic filter are different, IH
The input signal is subtracted from the delayed signal. Here, the output of the subtracter 11 is in opposite phase to the input signal. The output of the subtracter 11 is multiplied by K in the variable coefficient unit 14. The output of the variable coefficient unit 14 is added to the input signal input from the input terminal 100 in the adder 13 and output from the output terminal 101. In reality, the output of the variable coefficient unit 14 is in the opposite phase to the input signal, so a bow calculation is performed. Further, the coefficient K of the variable coefficient unit 14 is normally a large value, and is controlled to be small during a contour period in which a contour component exists. In this method, since the circuit is configured to subtract noise components from the input signal, it is possible to obtain an output signal with no phase shift from the input signal. Furthermore, the second
Similar to the embodiment described above, this embodiment has the effect of facilitating circuit design and suppressing an increase in circuit scale.

Further, FIG. 5 shows a fourth embodiment of the present invention.

In the figure: 15 is an amplitude detection circuit that detects the amplitude of the luminance signal, 102 is a luminance signal input terminal,
The same parts as in Figure 3.4 are given the same reference numerals. The circuit operation of this circuit system is almost the same as that of other embodiments of the present invention, except that the recursive filter is controlled according to the luminance signal.The signal level of the luminance signal is detected by the amplitude detection circuit 15. The control signal of the coefficient control circuit 8 is varied according to this signal level. As a result, the coefficient K of the recursive filter is varied, and the noise reduction effect changes.

Here, the reason why the coefficients of the recursive filter are varied according to the level of the luminance signal will be explained. Originally, a comb filter that uses line correlation is accompanied by a deterioration in vertical resolution, and the resolution deterioration becomes particularly noticeable when the feedback rate of a recursive filter is increased, but the human eye's sensitivity to color is greater than that of luminance. resolution is low, and resolution deterioration is less of a problem than brightness.

However, as the brightness level of the signal increases, the resolving power of the human eye increases and resolution deterioration becomes noticeable.

Therefore, when the level of the luminance signal is high, the coefficient of the recursive filter is made small to weaken the noise reduction effect.

When the level of the luminance signal is low, the resolving power of the human eye is low, so the coefficient of the recursive filter is increased to enhance the noise reduction effect. This suppresses resolution deterioration at high brightness and provides sufficient noise reduction effect at low brightness.As described in the first to fourth embodiments of the present invention, the output of the color noise reduction circuit is connected to the output terminal 101. However, it may be output from the output of the delay element 1.

A first specific example of the variable coefficient multiplier used in the embodiment of the present invention will be explained using FIG. 6. FIG. 6(A) is a block diagram showing the circuit configuration of a variable coefficient multiplier, with 121, 12
2 is a coefficient unit, 123 is a switch, 131 is an input terminal, 1
32 is an output terminal, and 133 is a control signal input terminal. The circuit operation of this method is as follows. In this system, there are two coefficient multipliers 121 and 122 that indicate the feedback rate, and the coefficient K1 of the coefficient multiplier 121 is set to a large value, for example 0.7, and the coefficient K2 of the coefficient multiplier 122 is set to a small value, for example 0.1. The circuit operation when this variable coefficient multiplier is used in a noise reduction circuit will be explained. Normally, the switch 123 is connected to the coefficient unit 121 to form a recursive filter with a large feedback rate, and exhibits a large noise reduction effect.During the contour period, the switch 123 is switched by the control signal input to the control signal input terminal 133, and the coefficient is switched. 122, the feedback rate is reduced and deterioration of the contour is eliminated. The embodiment can be easily implemented using such a simple switch circuit.

Note that the coefficient K2 of the coefficient unit 122 is set to 0.1, but if this value is set to zero, the input signal is output as is at the contour portion, so that the contour does not decrease.

A specific circuit diagram of this variable coefficient multiplier is shown in FIG. 6(B).

In the same figure, 30, 31, 32, 33, 34,
35, 36, ' 37 are transistors, 40.
41, 42, 44. 45 is resistance, 71, 73,
200 is a voltage source, 72 is a current source, and 2 is a ground, and the same parts as in FIG. 6(A) are given the same reference numerals. The circuit operation of this circuit will be explained. The input terminal 131 receives the input signal. The coefficient multipliers 121 and 122 serve as amplifiers. The gain of the coefficient multiplier 121 is determined by the resistance ratio of the resistor 40 and the resistor 41, and is 0.7, which is the same as the coefficient K1. The gain of the coefficient multiplier 122 is determined by the resistance ratio of the resistor 45 and the resistor 44, and is 0.1, which is the same as the coefficient K2. The output signal of the coefficient multiplier 121 is output from the collector of the transistor 30. The output signal of the coefficient multiplier 122 is output from the collector of the transistor 37.

The outputs of the coefficient multipliers 121 and 122 are input to the bases of transistors 31 and 34 of the switch 123. Normally, the voltage of voltage source 71 is lower than the voltage of voltage source 73, transistor 35 is non-conductive, and transistor 36 is conductive. Therefore, the current flowing to current source 72 is supplied from transistor 36. For this reason, the transistor 33.
34 is also conductive, and the signal input from the base of the transistor 34 passes through the transistor 33 and is output to the output terminal 13.
Output from 2. On the other hand, the control signal is input from the control signal input terminal 134. When the control signal has a large amplitude, the base of transistor 35 becomes higher than the base of transistor 36, so transistor 35 becomes conductive and transistor 36 becomes non-conductive. This causes transistor 31. 32 becomes conductive, and the signal input from the base of transistor 31 passes through transistor 32 to output terminal 1.
32. In this way, a variable coefficient multiplier can be realized with a simple circuit configuration.

As described above, by using a variable coefficient multiplier that switches the switch, a noise reduction circuit like the embodiment of the present invention can be realized, and by reliably switching the switch in the contour area, a color signal without deterioration of the contour can be obtained. There is.

A second specific example of the variable coefficient multiplier will be explained using FIG. 9.

In the same figure, 51, 52, 53, 54, 55,
56, 57, 58, 59. 60 is a transistor, 78. 77 is a DC voltage source, 74, 75. 76 is a current source, 80, 81, 82, 83, 84.85
is a resistor, 110 is a control signal input terminal, 111 is a signal input terminal, 112 is a signal output terminal, 200 is a voltage source, 201
indicates ground. This method uses a variable gain amplifier as a variable coefficient unit. The gain of this variable gain amplifier can be linearly controlled by the control signal. The circuit operation of this circuit will be explained. An input signal is input from the input terminal 111. A control signal is input from the control input terminal 110 in FIG. The output signal of the variable gain amplifier is output from the signal output terminal 112. Normally, the control signal input from the control signal input terminal 110 is kept at a constant voltage. At this time, the gain of the variable gain amplifier is kept constant by the voltage of the DC voltage source 78 and the voltage level of the control signal. A control signal is sent during a contour period when there is a contour. 15.・16・ The voltage becomes high, and the gain of the variable gain amplifier is controlled according to the level. By using such a simple variable gain circuit, coefficient control can be performed, and a color noise reduction circuit such as the embodiment of the present invention can be realized. Since the control is continuous in this method, there is an effect that problems such as a large reduction in contours or an increase in noise due to undetected contours or erroneous detection due to noise do not occur.

FIG. 10 shows a third specific example of the variable coefficient unit. It is also possible to consider a method in which the gain of the variable gain circuit is made to have nonlinear characteristics as shown in FIG. 10(A). As shown in the figure, when the contour level is low, the gain is large, and when the contour level is high, the gain changes nonlinearly. By using a nonlinear characteristic, it is thought that there is an effect that false detection of contours due to noise is eliminated compared to a linear characteristic. A specific example of such a variable gain circuit is shown in FIG. 10(B).

In the same figure, 61. 62 is a transistor;
The same parts as those in the figures are given the same reference numerals.

Transistors 1 to 61 and 62 have their bases and collectors connected and function as diodes, and the diode characteristics of these two transistors result in nonlinear gain characteristics as shown in FIG. 10(A). Note that 61 and 62 may be diodes.

As described above, by using the third specific example of the variable coefficient multiplier, a color noise reduction circuit like the embodiment of the present invention can be configured, and by nonlinearly controlling the feedback rate at the contour level, false detection of contours due to noise can be achieved. This has the effect of reproducing color signals without deterioration of contours.

Although the operation of the noise reduction circuit for color carrier waves has been described above, this noise reduction circuit can also be used for baseband color difference signals and luminance signals.

Note that this noise reduction circuit can be applied not only to television receivers, but also to signal processing circuits such as VTRs (video tape recorders) and video disc players to achieve similar noise reduction effects.

〔Effect of the invention〕

According to the present invention, a recursive filter exhibits a large noise reduction effect by increasing the feedback rate of the recursive filter in flat areas, and reduces the feedback rate of the input color carrier in contour areas by decreasing the feedback rate of the recursive filter. To suppress the occurrence of loss of contour components and trailing, and reproduce color signals without color bleeding.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention, FIG. 2 is a circuit diagram showing a conventional example of a noise reduction circuit, and FIG. 3 is a circuit diagram showing a second embodiment of the present invention. Fig. 4 is a circuit diagram showing a third embodiment of the present invention, Fig. 5 is a circuit diagram showing a fourth embodiment of the invention, and Fig. 6 is a specific example of a variable coefficient multiplier used in the embodiment of the present invention. 7 is a waveform diagram explaining the operation of the conventional example shown in FIG. 2, FIG. 8 is a waveform diagram explaining the operation of the first embodiment shown in FIG. Figure, 1st
Figure 0 is a circuit diagram showing other specific examples of variable coefficient multipliers, respectively.
It is. 1...Delay element, 3,13-Adder, 4,1
1... Subtractor, 6, 7, 9, 10, 12, 14, 121, 1
22... Coefficient unit, 100, 111, 131... Input terminal, 101, 112, 132... Output terminal, 31, 3
2, 33, 34, 35, 36, 37, 51, 52, 53
, 54, 55, 56, 57, 58, 59, 60, 61.
62...transistor, 40, 41, 42, 43, 4
4,45,80,81,82,83,84.85...Resistance, 71,73.77,78,200...Voltage source, 7
2, 74, 75.76...Current source, 201...Ground, 102...Brightness signal input terminal, 110,133...Control input terminal.

Claims (1)

[Claims] 1. A noise reduction circuit that inputs a color carrier wave, reduces its noise, and outputs the signal, which includes a recursive filter circuit that mixes an input signal and an output signal according to a function of a feedback coefficient, and outputs the mixed signal. , a subtracter for extracting a difference between an output signal obtained by passing the color carrier wave as an input signal through the recursive filter circuit and the input signal, and a contour signal of the color carrier wave is extracted from the output signal of the subtracter. a coefficient control circuit for controlling a feedback coefficient of the recursive filter circuit using the waveform shaping signal after shaping the waveform by using the waveform shaping signal. 2. In the noise reduction circuit according to claim 1, the cyclic filter circuit includes a first coefficient multiplier that multiplies the input signal by (1-K), and a delay element that delays the output signal by one horizontal scan feedback. a second coefficient multiplier that multiplies the output signal of the delay element by K; and an adder that adds the output of the first coefficient multiplier and the output of the second coefficient multiplier and uses the result as the output signal. A noise reduction circuit characterized by: 3. In the noise reduction circuit according to claim 1, the cyclic filter circuit includes a delay element that delays the output signal by one horizontal scanning feedback, and a subtraction circuit that performs subtraction between the input signal and the output of the delay element. And the output of the subtraction circuit is (1-K)
a coefficient multiplier; an adder that adds the output of the coefficient multiplier and the output of the delay element and uses the result as the output signal;
A noise reduction circuit comprising: 4. In the noise reduction circuit according to claim 1, the recursive filter circuit includes a delay element that delays the output signal by one horizontal scanning feedback, and a subtraction circuit that performs subtraction between the input signal and the output of the delay element. A noise characterized by comprising a circuit, a coefficient multiplier that multiplies the output of the subtraction circuit by K, and an adder that adds the output of the coefficient multiplier and the input signal and uses the result as the output signal. reduction circuit. 5. The noise reduction circuit according to any one of claims 1 to 4, further comprising an amplitude detection circuit for detecting the amplitude of the luminance signal inputted along with the color carrier, and the noise reduction circuit according to the amplitude detection level. A noise reduction circuit characterized by controlling a feedback coefficient K in the recursive filter circuit.