JPS6380687A - Cyclic type noise reducing device - Google Patents

Abstract

PURPOSE:To remove a noise component and to suppress an after image effect by extracting the noise component and a movingpicture component, and subtracting the moving-picture component from an input video signal after the moving-picture component is applied by a prescribed amplitude limitation. CONSTITUTION:An output video signal Vo from a cyclic type noise suppressor, which has a delay unit 20 provided with an AD converter 13 and a DA converter 14 before and behind a delaying digital memory 12, is subtracted from an input video signal Vi in a subtractor 16, and the noise component and the movingpicture component included in the input video signal Vi are extracted. An amplitude limitation circuit 17 performs an amplitude limitation of other than the amplitude of the noise component and so forth, and extracts the noise component and the principal part of the moving-picture component. The obtained noise component and the principal part of the moving-picture component are subtracted from the input video signal in the subtractor 18, and the final output video signal is obtained. Thus, the suppression of the after image effect accompanied by a cyclic type noise suppression is realized.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a cyclic noise reduction device that achieves a noise reduction effect without impairing the motion of an image.

[Prior Art] Magnetic recording and reproducing devices such as video tape recorders used for home use are subject to frequency dust and dirt, which increases as the frequency increases.
In order to remove the triangular noise peculiar to the demodulation method, generally
A method is used to reduce noise in the luminance signal by emphasizing high-frequency components using a pre-emphasis circuit before frequency modulating the luminance signal, and canceling the high-frequency emphasis using a de-emphasis circuit during signal reproduction. .

However, since the luminance signal that has passed through the de-emphasis circuit also contains noise, for example, a cyclic noise reduction device l shown in FIG. 3 may be connected to the reproduction output terminal lO of the magnetic recording and reproduction circuit. The illustrated cyclic noise reduction device 1 suppresses noise components by utilizing the difference in properties between a video signal with a high field or frame correlation and a noise component with little correlation between them, and reduces the output video signal Vo. (t)
It is called a cyclic type because it is delayed and cyclically added to the input video signal Vi (t). Input video signal Vi(t
) is supplied to the adder 3 via the coefficient 42 whose coefficient is 1-. Then, from the adder 3, an output video signal Vo (t) with reduced noise included in the human-powered video signal is taken out, while being supplied to the delay device 4 due to a signal delay of l field period or l frame period. are carried out in parallel. The delayed output video signal Vo (-τ) obtained by passing through the delay unit 4 with a delay time τ further has a coefficient K which is in the complement of l relationship with the coefficient 1- of the coefficient unit 2. By passing through the coefficient unit 5, it is supplied as KVo (with -) to the adder 3, where it is added to the input video signal Vi (t).

Therefore, the output video signal Vo (t) is (1-K)Vi
(t)+KVo (t-r), and between the input video signal Vi (t) and the delayed output video signal Vo(t-τ),
The sum of the signals obtained by multiplying the complementary coefficient 1- and K so that the sum value becomes 1 becomes the output video signal Vo (t).

[Interlayer points to be solved by the invention] The conventional cyclic noise reduction device 1 described above has a coefficient K of the coefficient multiplier 5.
It is known that the closer the coefficient K of the coefficient unit 5 is to 1 and the greater the number of fields or frames to be correlated, the higher the SN improvement can be obtained. Although this is an improvement, since the number of frames to be correlated increases, there is a problem in that afterimages become noticeable for fast-moving videos.

Therefore, in order to solve this kind of afterimage problem, for example, input video signal Vi (t) and delayed output video signal Vo (t-τ
), we focused on the fact that the signal level of the difference signal becomes higher as the video becomes larger, and a motion detector that operates by detecting this difference signal reduces the value of the coefficient only for videos with noticeable afterimages. A cyclic noise reduction device has been proposed that takes measures such as switching to a value. However, this type of motion detector uses a subtracter to form a difference signal, an absolute value circuit that takes the absolute value of the output of the subtracter, and a comparison that compares the output of the absolute value circuit with a preset reference value. Since it is composed of circuits and the like, it has a complicated structure and has problems such as high manufacturing costs.

[Means for Solving the Problems] This invention solves the above problems, and uses a delay device consisting of a delay digital memory in which an AD converter and a DA converter are connected in front and behind each other. By adding the video signal delayed by an integer line period or l frame period closest to the lead period to the video signal before delay at an appropriate ratio, and then subjecting it to delay by the delay device,
A cyclic noise reducer that cyclically reduces noise components that have no field correlation or frame correlation unlike signal components in a video signal, and subtracts an output video signal from an input video signal to the cyclic noise reducer. a first subtractor;
an amplitude limiting circuit that limits the amplitude of the output of the subtracter; and a second amplitude limiting circuit that subtracts the output of the amplitude limiting circuit from the input video signal.
The present invention is characterized in that it is configured by providing a subtracter.

[Operation] This invention extracts the noise component and the video component in the input video signal by subtracting the output video signal obtained by cyclic noise reduction from the input video signal, and applies a certain amplitude limit to the video component. After that, subtraction is performed again from the input video signal to remove noise components and suppress the afterimage effect.

[Example 7] Examples of the present invention will be described below with reference to FIG. 1.2. FIG. 1 is a circuit diagram showing an embodiment of a cyclic noise reduction device of the present invention.

In FIG. 1, a cyclic noise reduction device 11 is a conventional delay device 4.
Instead, by using a delay device 20 in which an AD converter 13 and a DA converter 14 are placed before and after the delay digital memo 2, the delay time, which is important in taking field correlation or frame correlation, can be accurately managed. The structure is based on the cyclic noise reducer 15 as described above. Delay digital memory 1
2 is the nearest integer line period to the field period, i.e. 262 line period or 263 line period or l
The delay time is the frame period.

Therefore, the cyclic noise reducer 15 focuses on the function as a pre-processing circuit for extracting the noise component and the moving image component contained in the input video signal Vi(t), and the function of the pre-processing circuit is The output video signal Vo (t) is the first
The input video signal Vi (
t) to extract the noise component and moving image component contained in the input video signal Vi(t).

Here, the noise component and the moving image component included in the output of the first subtractor 16 are subjected to amplitude limitation in the following amplitude limiting circuit 17, leaving only the components whose amplitude is less than the amplitude of the noise component. This amplitude limiting circuit 17 is for extracting the noise component and the main part of the moving image component contained in the input video signal Vi(t), and its amplitude limiting level is determined by the resistance value of the external variable resistor Rv. It is said that it can be changed arbitrarily depending on the situation. Amplitude limiting circuit 17
The noise component and the main part of the moving image component obtained in step 1 are subtracted from the input video signal Vi(t) by the second subtractor I8, and only then is the final output video signal obtained.

That is, when comparing the final output video signal obtained from the second subtractor 18 and the output video signal Vo (t) obtained from the cyclic noise reducer 15, the noise component that is initially targeted for reduction is , while a comparable reduction effect can be seen, the final output video signal is clearly suppressed for the video component, and this eliminates the afterimage effect associated with cyclic noise reduction, which has been a problem in the past. It can be seen that suppression is achieved.

In this way, the recursive noise reducer rttt converts the output video signal Vo (t) obtained from the recursive noise reducer 15 having a high noise reduction ability using the delay device 20 consisting of the delay digital memory 12 into a human-powered video signal. The noise component and the moving image component in the input video signal Vi(t) are extracted by subtraction from the signal Vi(t), and after applying a certain amplitude limit to the moving image component in the subsequent amplitude limiting circuit 17, the input video signal is inputted again. By subtracting from the video signal Vi(t), the configuration aims to remove noise components and suppress afterimage effects, so two subtracters 16 can be used without using a complicated circuit like a conventional motion detector. By preparing .18 and one amplitude limiting circuit 17,
It is possible to achieve the same effect as a motion detector, thereby reducing the manufacturing cost of the entire device and achieving a high-quality noise reduction effect.

Note that the amplitude limiting circuit I7 can arbitrarily vary the amplitude limiting level using the variable resistor Rv, so that the human video signal Vi(t
) By varying the amplitude restriction level according to the degree of noise components included in the noise component, unnecessary video components are removed by leaving only the noise components that can be reduced by cyclic noise reduction and the video components at the same level. This makes it possible to minimize the inconvenience that the effect of noise reduction is weakened due to afterimage suppression.

Although the configuration is slightly different from that of the cyclic noise reducer 15,
By using the cyclic noise reducer 25 with the same basic principle,
It is also possible to configure a cyclic noise reduction device 2I shown in FIG. This cyclic noise reduction device 21 uses a subtracter 22 to subtract the delayed output video signal Vo (-τ) from the input video signal Vj (t), and adds a coefficient K to the subtraction result δV (t) using a coefficient multiplier 23. The output of the coefficient unit 23 is multiplied by δV (
t) is further inputted to the input video signal Vi (t) by the subtracter 24.
By subtracting from , the output video signal Vo (t) is obtained. This cyclic noise reducer 25 uses two subtracters 22 and 24, so that the input video signal Vi(t)
Complementary coefficients 1- and K for multiplying the delayed output video signal Vo (by -) are made possible by a single coefficient multiplier 23.

In addition, in the case of this embodiment as well, the first. Second subtractor 16.
The principles of noise reduction and afterimage suppression by the amplitude limiting circuit 18 and the amplitude limiting circuit 17 are exactly the same as in the previous embodiment.

[Effects of the Invention] As explained above, the present invention subtracts an output video signal obtained from a cyclic noise reducer having a high noise reduction ability using a delay device made of a delay digital memory from an input video signal. By extracting the noise component and video component from the input video signal, applying a certain amplitude limit to the video component using the amplitude limiting circuit, and subtracting it from the human video signal again, the noise component can be removed and the afterimage can be removed. Since the structure is designed to suppress the effect, it can be equivalent to a motion detector by providing two subtractors and one amplitude limiting circuit, without using a complicated circuit like a conventional motion detector. As a result, the manufacturing cost of the entire device can be reduced, and a high-quality noise reduction effect can be achieved.

Furthermore, since the amplitude limiting circuit is configured to have an amplitude limiting level that is arbitrarily variable, the present invention can achieve cyclic noise reduction by varying the amplitude limiting level according to the degree of noise components included in the input video signal. It is possible to remove unnecessary video components by leaving only the video components at the same level as the noise components that can be reduced, and to minimize the inconvenience that the effect of the low noise range is weakened due to afterimage suppression. It has the effect of being able to be held down.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing one embodiment of the cyclic noise reduction device of the present invention, FIG. 2 is a circuit diagram showing another embodiment of the cyclic noise reduction device of the invention, and FIG. 1 is a circuit configuration diagram showing an example of a conventional cyclic noise reduction device. 11.21. ,,cyclic noise reduction device, 15°25,,
, cyclic noise reducer, 16. ,,first subtractor,17.
, , amplitude limiting circuit, 18. ,, second subtractor, 20. ,
, delay device, Rv, , variable resistance.

Claims (2)

[Claims] (1) A delay device consisting of a delay digital memory in which an AD converter and a DA converter are connected back and forth converts a video signal delayed by an integer line period closest to one field period or one frame period into the pre-delayed image. Cyclic noise that is added to a signal at an appropriate ratio and then delayed by the delay device to cyclically reduce noise components that have no field correlation or frame correlation unlike signal components in a video signal. a first subtracter that subtracts an output video signal from an input video signal to the cyclic noise reducer; an amplitude limiting circuit that limits the amplitude of the output of the first subtracter; and the amplitude limiting circuit. a second subtracter that subtracts the output of the input video signal from the input video signal. (2) The cyclic noise reduction device according to claim 1, wherein the amplitude limiting circuit has a configuration in which the amplitude limiting level is arbitrarily variable.