JP2853298B2 - Television signal processor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Object of the Invention) [Field of Industrial Application] The present invention relates to a television signal processing device for removing noise contained in a television signal.

[Prior art] Advances in digital signal processing technology and digital LS
In the current situation of high integration of I and mass production of large-capacity memories, digital processing of television signals is frequently performed using frame or field memories in signal processing of television receivers. One of such motion-adaptive frame or field noise reduction (noise removal) systems is one of the signal processing methods for television signals using the frame or field memory.

FIG. 7 shows an example of a conventional noise reduction system. A luminance signal (Y signal) containing a noise component indicated by X1 in FIG. The input Y signal is input to the first coefficient unit 12, and the output signal from the coefficient unit 12 is supplied to the adder 14 together with the output signal from the second coefficient unit 13. Is supplied to the output terminal 15 and to the delay circuit 16 of one frame. Then, the output signal X2 from the delay circuit 16 is input to the second coefficient unit 13.

The first coefficient unit 12 calculates a coefficient given from the nonlinear circuit 17.
The gain is controlled by ko, and the gain of the second coefficient unit 13 is controlled to (1-ko) times by the signal ko from the nonlinear circuit 17. Then, the output signals from the coefficient units 12 and 13 are added by the adder 14, and the signal X1 and the signal X2 are mixed at the mixing ratio ko.

Here, the one-frame delay circuit 16 forms a signal X2 obtained by delaying the output television signal from the adder 14 by one frame. In this signal processing circuit, the input signal X1
And the signal X2 on the past frame at exactly the same position on the screen, and the coefficient units 12 and 13, and the adder 14
, And the noise component is removed by repeatedly taking a weighted average of the mixture.

However, if the screen position is simply averaged using the same past signal, when there is no correlation between the current image signal X1 and the past image signal X2, that is, the image moves. In this case, apart from noise removal, the image is mixed with an image at another time, so that side effects such as an afterimage occur. For this reason, a so-called motion adaptive system that switches a noise reduction operation according to the motion of an image has been considered.

In order to detect the motion of the image, first, the adder 17 obtains a difference value X3 between the current input signal X1 and the signal X2 one frame before. Then, the difference value is obtained by the absolute value circuit 19, and the absolute value is given to the nonlinear circuit 17.

Here, the characteristics of the nonlinear circuit 17 are set as shown in FIG.
By the absolute value of the difference between the frames output from 19,
When the value greatly exceeds βo, “1.
0 "(= ko) is output, and conversely," 0 "is output when the absolute value is smaller than αo. The output ko from the nonlinear circuit 17 controls the coefficient units 12 and 13 to add
14 controls the mixing ratio of the mixing circuit section configured.

That is, in this device, when the image is moving, the inter-frame difference value X3 is large as in the period indicated by _TA1 in FIG. 8, and conversely, in the portion where the image is stationary, As indicated by _TA2 , the difference value X3 between frames is small, and a moving image or a still image is determined using the magnitude of the difference value X3. And when it is determined to be a still image,
By reducing the value of the mixture ratio ko, the processing effect of noise reduction by inter-frame calculation is increased, and the noise component is strongly suppressed. When it is determined that the moving image is a moving image, the value of the mixture ratio ko is increased to reduce the frame calculation effect, and the current television signal input to the input terminal 11 is output as it is to prevent side effects such as generation of an afterimage. I have to.

However, if the motion of the image is directly detected from the inter-frame difference value by using the non-linear circuit 17 that is fixedly set, as shown in the period _TC in FIG. The non-linear circuit shown in FIG.
When a noise component having an amplitude exceeding the level indicated by αo of the 17 characteristics is input, this portion is determined to be a moving image. Therefore, the noise reduction processing between frames is not performed, and the noise component is output as it is. Also, a moving portion as the period indicated by T _B in FIG. 8, a smaller inter-frame difference value X3, which is the case below αo is interframe noise this portion is determined to still image The reduction process is performed. As a result, an afterimage occurs and an unnatural screen is output. In particular, when such a malfunction occurs in a relatively flat portion of the image as in the period denoted by T _B, now produce a residual image over a wide range, its side effects become prone state attached very eyes.

In order to prevent such a side effect due to such an error in motion detection, for example, it is conceivable to reduce the value of αo so that the characteristic of the nonlinear circuit 17 is determined to be a moving image even with a small inter-frame difference value. However, when this value of αo is reduced,
For relatively large noise as the period indicated by the turn T _C, easily determined that moving it even still image, thus inverse problems arise.

That is, in such a conventional noise reduction system using the motion adaptation method, since a motion detection signal for directly controlling the noise reduction operation is detected from the inter-frame difference value, a relatively large amplitude is used. The noise component is determined as a moving image, and the noise removal operation is not performed. Also, in a moving image portion, a portion having a relatively small inter-frame difference value may be determined to be a still image. Therefore, inter-frame processing is performed in this portion, and as a result, an unnecessary afterimage is generated.
If the threshold value of the non-linear circuit of the motion detection unit is reduced to increase the motion detection sensitivity in order to prevent the occurrence of such an afterimage, an erroneous determination that a noise component is determined to be a motion of an image may occur. Will occur.

[Problems to be Solved by the Invention] The present invention has been made in view of the above points, and reliably determines a still image and a moving image of a television signal regardless of the magnitude of the amplitude of a noise component. And performing noise reduction by inter-frame or inter-field processing while preventing the unnaturalness of a moving image due to a malfunction in motion detection while maintaining the noise reduction effect in inter-frame or inter-field processing. An object of the present invention is to provide a television signal processing device.

(Means for Solving the Problems) A television signal processing apparatus according to the present invention provides, for example, a first signal component that is a high-frequency component and a second signal component that is a low-frequency component from an input television signal. The second signal component is extracted separately, a moving image and a still image are determined using the second signal component, and the first signal component is subjected to inter-frame processing to perform noise removal processing. ing.

[Operation] In the television signal processing device configured as described above, in an input television signal, noise components are generally included in a high frequency side and not much in a low frequency side. . Therefore, the inter-frame processing for performing the noise removal processing is performed on the first signal component that is the high-frequency component of the input signal, and the motion of the image is the low-frequency second signal with little noise component. It depends on the component. Therefore, without losing the effect of noise reduction, reduce the afterimage disturbance in a sufficiently large area image,
High quality images can be reproduced stably.

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows the circuit configuration, and a Y signal containing noise is input to an input terminal 21 as shown by Z1 in FIG. This Y signal is supplied to a low-pass filter 22,
By passing through this filter 22, a low-frequency component Z4 (see FIG. 2) in the Y signal is extracted. Further, the input Y signal Z1 is supplied to an adder 23, which subtracts the low-pass signal Z4 from the low-pass filter 22 to extract a high-pass component in the Y signal. The high-frequency component signal obtained from the adder 23 is supplied to a first coefficient unit 24, and the low-frequency signal from the low-pass filter 22 is supplied to an adder 25.

The output signal from the adder 25 is to be supplied to an output terminal 26, and this signal is further supplied to a one-frame delay circuit 27. In FIG. 2 from the delay circuit 27,
The output signal indicated by Z2 is supplied to a low-pass filter 28 to extract a signal of a low-frequency component and to an adder 29, which subtracts the signal from the low-pass filter 28. That is, a signal of a high-frequency component of the signal one frame before is extracted from the adder 29, and the signal of the high-frequency component is supplied to the second coefficient unit 30. Also low pass filter
The low-frequency component of the signal one frame before from 28 is supplied to the adder 31. This adder 31 is supplied with a signal component Z1 for reducing the current frame from the low-pass filter 22,
The signal component in the low band of the signal Z2 one frame before is subtracted from the signal Z4, and the adder 31 outputs the signal Z3 of the difference value.

The first and second coefficient units 24 and 30 include a motion detection circuit.
Controlled by a control signal k1 from 32, a signal output from the adder 23 in each of the coefficient units 24 and 30, and a high-frequency component of the signal Z2 which is a past signal in frame units, The gains are limited to k1 and (1-k1), respectively. Thereafter, output signals from the coefficient units 24 and 30 are added in an adder 33, and the added signal is added in an adder 25 as a high-frequency signal component of the output signal. That is, the first and second coefficient units 24, 3
The adder 33 forms a mixing circuit that can be controlled by the coefficient k1.

In this case, since the low-frequency components in the input television signal are not included in the output signals from the coefficient units 24 and 30, the low-frequency component is added to the output signal from the low-pass filter 22 by the adder 25. Supplement the ingredients.

That is, in the signal processing apparatus configured as described above, the noise reduction (noise elimination) processing between frames is limited to a high-frequency component signal containing a relatively large amount of noise components, and is performed on a low-frequency signal with a small amount of noise components. The processing between frames is not performed on the signal of the band component.

Output signals from the low-pass filters 22 and 28, that is, the low-frequency components of the current signal Z1 and the signal Z2 one frame before the current signal Z1 are supplied to the adder 31, and the difference value is obtained. The inter-frame difference value signal is supplied to the absolute value circuit 34, where the absolute value is obtained. Then, the absolute value is supplied to the motion detection circuit 32, and the state of the motion of the image is determined according to the input absolute value.

FIG. 3A shows a specific configuration example of the motion detection circuit 32. The output signal Z5 from the absolute value circuit 34 is shown in FIG.
Is input to a terminal 41, and is first applied to a nonlinear circuit.
The characteristic of the nonlinear circuit 42 is set as shown in FIG. 3B. When the output signal Z5 from the absolute value circuit 34 is equal to or smaller than the threshold value α1, the output is “0”. When Z5 is equal to or larger than the threshold value β1, “1.0” is output. And
The output signal Z6 from the non-linear circuit 42 is
The shift register 43 has, for example, (C)
It is configured as shown in the figure. That is, it is configured by connecting n stages of D-type flip-flops 431 to 43n in cascade.
The output is shifted in stages and output in parallel. The output signal from the shift register 43 is a maximum value circuit.
44, and the maximum value of the output data from each of the n stages is output from the terminal 45.

FIG. 4 shows the state of signals in the motion detection circuit 32.

That is, in the conventional type described with reference to FIG. 7, the motion detection is performed based on the signal components of all the bands, whereas in the apparatus shown in this embodiment, the adder is used.
The signal whose frame difference is calculated by 31
Motion detection is performed only on the low-frequency component signals extracted in steps 22 and 28. Therefore, the inter-frame difference signal Z3
Rises at the edge portion as indicated by the period T _D shown in Figure 2, the fall has become dull. As a result, this part is not detected as a moving image and may be missing. Therefore, the shift register 43 and the maximum value circuit 44 constituting the motion detection circuit 32 detect the maximum value of the motion signal of the surrounding pixels, thereby spatially widening the moving image portion to prevent omission.

According to the motion detection signal k1 detected in this way, the mixing circuit constituted by the coefficient units 24 and 30 and the adder 33 sets the coefficient k1 to a value close to "1.0" when the pixel is moving, The noise reduction effect by frame operation has been reduced. Conversely, when the frame difference value Z3 is small, it is determined that the image is a still image and the frame correlation is high, and the noise reduction effect by the frame calculation process is increased.

As described above, in this embodiment, the signal source for detecting the motion is limited to the signal of the low frequency component having a relatively small noise component. Thus noise components included in the inter-frame difference value signal Z3 to be output from the adder 31 is small, as shown in a period from T _C shown in FIG. 2, also relatively large noise component of amplitude, this It is possible to prevent erroneous determination as a moving image. Further, by reducing the influence of noise, the threshold values α1 and β1 of the nonlinear circuit 42 can be set to smaller values. By spatially expanding, T _B shown in Fig. 2
It is possible to reliably detect a moving portion having a relatively small inter-frame difference level as a moving image as in the period of FIG.

In addition, by limiting the signal component to be subjected to the frame operation to a high-frequency portion generally having a lot of noise components, the low-frequency component is not lost even if the detection of a moving image is lost without losing the noise reduction effect. Since no calculation is performed, the afterimage disturbance can be reduced over a wide range.

FIG. 5 shows another embodiment, and the same components as those in the embodiment of FIG. 1 are denoted by the same reference numerals and the description thereof will be omitted.

In this embodiment, in the mixing circuit composed of the first and second coefficient units 24 and 30 and the adder 33, the signal component to be subjected to the inter-frame noise reduction processing has a high-frequency component in the television signal. The signal source for obtaining the inter-frame difference value in the adder 31 to detect the motion is a low-pass filter 22.
And 28 are limited to the low-frequency component output.

A signal obtained by subtracting the output signals from the low-pass filters 22 and 28 from the current signal of the television signal input from the input terminal 21 and each of the past signals in frame units output from the one-frame delay circuit 27, That is, the high frequency signal components S0 and S1 of the current signal and the past signal are taken into the motion detection circuit 50.

FIG. 6A shows a specific configuration example of the motion detection circuit 50. The high-frequency signal components S0 and S1 of the current signal and the past signal are respectively converted into absolute value circuits 51 and 51. Take in to 52. The outputs from the absolute value circuits 51 and 52 are supplied to a maximum value circuit 53, and the maximum value of the absolute values is selected and supplied to a comparator 54. The comparator 54 compares it with a threshold ref input from a terminal 55, and outputs an output signal from the comparator 54 to a selector 56 as a selection signal. The selector 56 selects one of the threshold values (α2, β2) and (α3, β3) of the nonlinear circuit 57.

FIG. 6B shows the characteristics of the nonlinear circuit 57.

Here, the selector 56 controls the threshold value (α2, β2) to be selected when the output signal of the maximum value circuit 53 exceeds the threshold value ref of the comparator 54. The output signal of the circuit 53 is the threshold ref of the comparator 54
If it is below, the thresholds (α3, β3) are selected.

That is, in this embodiment, an edge component having a relatively high level is detected from the larger one of the high level of the current signal and the past signal of the frame unit, and when this edge component is detected, the non-linear circuit 57 operates. The threshold values α and β are made smaller than usual so that a moving image can be detected even with a smaller difference between frames. Therefore, the lack of detection of a moving image in a steep edge portion having a large level difference is reduced.

That is, according to this embodiment, it is possible to obtain a signal processing circuit which can improve the afterimage disturbance in a moving image and can realize noise removal with a sufficient noise reduction effect.

[Effects of the Invention] As described above, according to the television signal processing apparatus of the present invention, in the motion adaptive noise reduction system based on inter-frame or inter-field processing, the motion detection of an image is performed in a low-frequency region having relatively few noise components. By using the component, the occurrence of malfunction due to noise can be suppressed, and the noise removal effect is effectively improved. It is also possible to increase the sensitivity of motion detection at the same time.Furthermore, by restricting signals for performing frame or inter-field arithmetic processing to high-frequency components having a relatively large number of noise components, residual image interference in a moving image is reduced. Be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram for explaining a signal processing apparatus according to one embodiment of the present invention, FIG. 2 is a signal waveform diagram for explaining this embodiment, and FIG. 3 is a diagram of a motion detection circuit used in this embodiment. FIG. 4 is a signal waveform diagram, FIG. 5 is a block diagram for explaining another embodiment of the present invention, and FIG. 6 is a diagram for explaining a motion detecting circuit used in this embodiment. FIG. 7 is a block diagram showing a conventional noise eliminator, FIG. 8 is a signal waveform diagram for explaining this conventional example, and FIG. 9 is a diagram showing nonlinear characteristics. 22, 28 ... Low-pass filter, 23, 25, 29, 31, 33 ...
Adders, 24, 30 ... coefficient units, 27 ... one-frame delay circuits, 32, 50 ... motion detection circuits, 34 ... absolute value circuits.

Claims (1)

(57) [Claims] 1. A first signal extracting means for extracting a first low frequency component and a first high frequency component from an input television signal, and a second low frequency component from a television signal n fields before. Second signal extracting means for extracting a component and a second high frequency component; and motion detection for detecting motion by taking a difference between the first low frequency component and the second low frequency component. Means for controlling and synthesizing the first high-frequency component and the second high-frequency component based on the motion detection signal from the motion detection means, thereby providing a third high-frequency band from which noise has been removed. Means for obtaining a frequency component; noise removing means for combining the third high frequency component and the first low frequency component to output a television signal from which noise has been removed; Te Processor of the television signal, characterized by comprising a means for obtaining a television signal before the n field using the vision signal.