JPS6110369A - Noise reduction device of picture signal - Google Patents

Abstract

PURPOSE:To improve the reduction effect of noise included in a low frequency component of a picture signal by separating an input picture signal into a low frequency component and a high frequency component to apply noise reduction processing to them. CONSTITUTION:The input picture signal fed to a signal input terminal 1 is separated into at least the low frequency component and the high frequency component by filter circuits 10, 11, they are subjected to a delay at a memory 4 and the noise included in each signal is reduced while the frequency of the input picture signal is separated by adding the memory output signal and the input signal subjected to frequency separation by adders 31, 32 via prescribed coefficient circuits 21, 22 and 210, 220. Further, the difference between the output signal of the memory 4 and the input picture signal is detected by a difference detection circuit 8, the 1st coefficient generating circuit 211 is controlled by the output of the 1st noise detection circuit 12 and the difference detection circuit 8 and the 2nd coefficient generating circuit 221 is controlled by the output of the 2nd noise detection circuit 13 and the difference detection circuit 8.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an image signal noise reduction device for reducing noise components contained in an image signal obtained by scanning or received, such as a known television signal. .

Conventional configuration and its problems Noise contained in image signals generated by predetermined scanning, such as television signals, and the problem of noise contained in image signals generated by predetermined scanning such as television signals, and the problem of transmitting this image signal as a radio frequency signal via a predetermined modulation device and receiving it. Noise mixed into the image signal obtained by demodulation degrades the quality of the reproduced image, and various devices have been proposed to reduce or remove this noise. FIG. 1 is an example of a device suitable for such a purpose, and will be described below with reference to it, but for convenience it will be assumed that processing is performed on television signals.

The baseband image signal supplied to the signal input terminal 1 is supplied to the memory 4 via the first coefficient circuit 2 and the adder circuit 3, and this memory 40 input signal is sent to the signal output terminal 5 of the device. The memory 4 normally provides a delay equivalent to a field, or in some cases a frame, but as is known, for image signals generated by interlaced scanning, it is in principle desirable to perform a frame delay; The time is approximately 1/3o(x). , memory 4
The output signal is sent to the adder circuit 3 via the second coefficient circuit 6.
will be returned to. Since the loop formed by the memory 4, the second coefficient circuit 6, and the addition circuit 3 described above performs integration in the time direction, the correlation between the image signals, more specifically, when the correlation in the time direction is high, i.e., a still image signal, etc. It is known that it has great utility value. However, in a normal television signal, the content of the image changes from moment to moment, or there are many cases where the correlation is completely lost due to scene changes, and the effect of the above-mentioned loop causes afterimages. It is not practical to set the second coefficient circuit to a fixed value, so a variable configuration is used. These first. The second coefficient circuit is set to have a relationship of K and 1- by the coefficient generation circuit 7, and this coefficient generation circuit 7 is controlled by a difference detection circuit 8, and also has a noise detection circuit that detects noise included in the input image signal. A circuit 9 is shown controlling the difference detection circuit 8 described above. The difference detection circuit 8 detects the difference between the input image signal and the output signal of the memory 4, and in most cases, the two outputs of the coefficient generation circuit 7, ie, K, are determined depending on the level of its absolute value.

and 1-K, but as mentioned above, the coefficient generation circuit 7 increases ViK in areas where there is no correlation between the image signals or where the correlation has decreased to reduce the amount of feedback of the output signal of the memory 4 to the input side. control.

The difference detection circuit arranged to detect the degree of correlation of input image signals operates uniformly on both signal components and noise components, so even signals with perfect correlation, such as still image signals, may contain noise. When the components are large, they are treated as uncorrelated. The noise detection circuit 9 is therefore configured in a predetermined manner such that the difference detection circuit 8 responds only to signal components, e.g.
Control is performed by changing the threshold value when determining the amplitude of Y.

The conventional noise reduction device described above is effective when the noise contained in the input image signal is uniform with respect to frequency, but it may cause triangular noise in the known FM signal transmission system or undesired wireless noise. When considering the occurrence of beat disturbances due to interference between the frequency signal and the signal to be received, the so-called noise components are not uniform, so it is necessary to uniformly control the amplitude or power of the noise component detected by the coefficient generation circuit. This has the disadvantage that the noise reduction effect deteriorates.

OBJECTS OF THE INVENTION The present invention eliminates the above-mentioned drawbacks and prevents deterioration of noise reduction performance when noise reduction is performed using a memory and correlation of image signals.

Structure of the Invention The present invention frequency-separates an input image signal into at least a low-frequency component and a high-frequency component, and delays the input image signal with a memory having a predetermined delay time. By adding the output signal and the frequency-separated input signal via a predetermined coefficient circuit, the noise contained in each signal is reduced while the input image signal is frequency-separated. a difference detection circuit for detecting the difference between the input image signal and the input image signal; and a first . a second coefficient generation circuit; a second noise detection circuit, the first coefficient generation circuit is controlled by the first noise detection circuit and the difference detection circuit, and the second coefficient generation circuit is controlled by the second noise detection circuit and the difference detection circuit. It has characteristics.

DESCRIPTION OF EMBODIMENTS Embodiments of the present invention will be described in detail below with reference to the drawings. In the figure, the same reference numerals are used for parts having exactly the same functions as those of the conventional example.

The input image signal supplied to the signal input terminal 1 is transmitted through a low-frequency three-wave circuit (L, P, F) 10 and a high-frequency three-wave circuit (H, P,
F) 11 is further supplied to the difference detection circuit 8.

The output signal of the low-frequency three-wave circuit 1o is the first coefficient circuit (K,) 2
1 to the first adder circuit 31, and also to the high frequency three-wave circuit 1.
The output signals of 1 are respectively supplied to the second adder circuit 32 via the second coefficient circuit (K2) 22, and the outputs of these two adder circuits 31 and 32 are added by the third adder circuit 33. The output has a flat frequency characteristic. The output of this adder circuit 33 is supplied to the memory 4 and the signal output terminal 6. The signal delayed by the memory 4 is frequency-separated again by a second low-frequency three-wave circuit (LPF) 10o and a high-frequency three-wave circuit (HPF) 110, and then sent to a third coefficient circuit (1-to-1) 2101. Fourth coefficient circuit (1
- to 2) the above-mentioned 1. Second addition circuit 31
．． At step 32, the low frequency and high frequency components of the frequency-separated input image signal are added. The output signal of the memory 4 is also supplied to a difference detection circuit 8 that detects the correlation in the time direction of the input image signal, that is, between fields or frames. An image signal is supplied. For example, when the difference detection circuit 8 receives an input signal such as a still image signal, its output substantially includes a first coefficient generation circuit 211 and a second coefficient generation circuit 211 in the next stage.
A control signal that changes the operation of the coefficient generation circuit 221 is not generated, and therefore these coefficient generation circuits 211 and 221 send predetermined coefficients set in advance to the first coefficient circuit 21 and the second coefficient circuit 22, respectively. How the first and second coefficient generation circuits 211 and 221 set the coefficient output signal generated when the output signal of the difference detection circuit 8 is substantially zero can be selected as appropriate; The noise reduction device of the invention has advantages over known ones. For example, in a normal television signal, not only a completely still image signal but also the content of the image changes from moment to moment in many cases.For such a signal, the correlation in the time direction of the image is low for its high frequency components, but Since the low frequency components can be considered to have a higher correlation than the high frequency components, the first coefficient generation circuit 211 can have a larger output coefficient than the second coefficient generation circuit 221. Furthermore, even if we consider that the effect of the feedback loop for noise reduction including the memory 4 causes afterimages in moving images, resulting in so-called blur, the present invention assumes that the occurrence of afterimages is the same as that of conventional devices. The difference detection circuit 8 has the advantage that the reduction effect on low frequency components of noise is superior to known ones.As described above, the difference detection circuit 8 detects the presence or absence of correlation of input image signals between fields or frames, or the degree of Y. Therefore, in principle, the difference between two input signals is detected. Therefore, the detection operation is performed for both the signal component and the noise component, and this detection output is sent to the first coefficient generation circuit 211 and the first coefficient generation circuit 211. 2 coefficient generation circuit 221 is controlled to generate the first coefficient circuit (K1) 21 and the second coefficient circuit (K1).
2) The signal output coefficients to the first coefficient generating circuit 211 are changed in the direction of increasing their values.
and the second coefficient generation circuit 221 can have different initial values, so even if the signal and noise frequency components are not separated and are detected by a common difference detection circuit, low frequency noise components The reduction effect on is improved over the known one.

It is shown that the first coefficient generation circuit 211 and the second coefficient generation circuit 221 are also controlled by the first noise detection circuit 12 and the second noise detection circuit 13, respectively. The first noise detection circuit detects the noise component from the output signal of the low frequency three-wave circuit 1o that outputs the low frequency component of the input image signal, so its output is responsive to the low frequency noise component. When the first coefficient generation circuit controlled by this output is supplied with the output of the first noise detection circuit 12,
A part or all of the detected difference signal components from the difference detection circuit 8 are regarded as invalid components, and changes in the operation of the first coefficient generation circuit 211 are suppressed. Therefore, the noise component included in Y may be reduced by the output component of the first noise detection circuit 12 based on the control signal to the first coefficient generation circuit 211 of the difference detection path 8, and various modifications are possible. It is.

Next, the second noise detection circuit 13 that controls the second coefficient generation circuit 221 detects the noise component from the output of the high frequency three-wave circuit 11 that outputs the high frequency component of the input image signal. The output is a high frequency component of noise, and the high frequency component of noise contained in the detection difference signal outputted by the low frequency noise detector is suppressed or prevented from undesirably controlling the second coefficient generation circuit. do. Therefore, in the noise reduction device according to the present invention, the first and second coefficient generation circuits are configured based on the time direction of the image signal in the detected difference signal outputted by the difference detection circuit 8, that is, the actual signal difference between fields or frames. controlled only.

In the above embodiment, the memory is shown as being common to both low frequency and high frequency components, but it may be configured independently, and the low frequency 3-wave circuit and the high frequency 3-wave circuit may also be independent. It is clear that the present invention is not limited to these configurations, such as arranging one of them and subtracting the other from the input signal, and also selecting the configuration of the coefficient circuit for K as appropriate. C. Effects of the Invention The noise reduction device according to the invention has the advantage that it is superior to known devices in reducing noise contained in input wave components. In addition, the noise contained in the input image signal is detected by separating it into low frequency components and high frequency components, and the structure is configured so that the noise reduction effect is not degraded by these noise components. It has great industrial value, as it can exhibit excellent effects even when the material is not uniform.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a conventional image signal noise reduction device, and FIG. 2 is a block diagram of a noise reduction device in an embodiment of the present invention. 12.13...Noise detection circuit, 211, 221.
...Coefficient generation circuit, 1o, 1oo--4PF. 11.110...HPF, 4...Memory, 8...Difference detection circuit, 21.22,210,2
20---Coefficient circuit, 31, 32, 33... Addition circuit. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
figure

Claims (1)

[Claims] An apparatus for reducing noise in an image signal by having a predetermined delay means and calculating the input and output signals of the delay means with a calculation means, wherein the calculation means calculates the incoming input signal and the output of the delay means. first and second calculation means for frequency-separating a signal into a low frequency region and a high frequency region with at least a predetermined frequency as a boundary and performing calculations, respectively; and a first calculation means for detecting noise contained in the low frequency component of the incoming input signal. It comprises a noise detection means and a second noise detection means for detecting noise contained in high frequency components, and the output signals of these are used as control signals for at least the first and second calculation means, respectively. An image signal noise reduction device characterized by: