JPH0369276A - Noise reduction circuit - Google Patents

Abstract

PURPOSE:To always obtain the optimum noise reduction effect in spite of the state of an image by detecting a noise quantity included in a video signal, and varying noise reduction effect characteristic based on a detected result. CONSTITUTION:The detection of the noise quantity by a noise quantity detection circuit 8 is performed by amplifying an original flat part in the video signal, and detecting a noise component included in the part. And the switching timing of the value of a coefficient K at each of multipliers 2 and 6 is controlled based on the output of the detecting cross-section 8 of the noise quantity from which the noise quantity is detected. For example, the correlative quantity of the video signal is ordinarily set at 905 as reference, and such control that the value of the coefficient K is varied to binary values 0.00 and 0.75 based on whether it is less than or over 90% is performed, and when a large quantity of noise exist, the coefficient K is kept at 0.75 not being set at 0.00, thereby, the characteristic is switched so as to obtain the noise reduction effect.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention multiplies an input current video signal and a correlated video signal delayed by a certain period of time from the video signal by predetermined coefficients. However, regarding the cyclic noise reduction circuit that reduces noise by using the correlation between the video signals by adding both video signals, for example, it is applicable to all video devices that handle video signals such as video tape recorders. Used for equipment.

In addition, as a cyclic noise reduction circuit, its delay time is
By setting the time required to scan one line of the video signal, it becomes a line cyclic noise reduction circuit, and by setting the time required to scan one field of the video signal, it becomes a field cyclic noise reduction circuit, which performs one frame scanning of the video signal. By setting the time required for , it becomes a frame cyclic noise reduction circuit.

(Prior Art) FIG. 4 shows a conventional example of a field cyclic noise reduction circuit among the above-mentioned cyclic noise reduction circuits.

In the figure, an input terminal 11 through which one field of video signals is led is connected to a plus input of an adder 17 that detects the correlation amount of the video signal, and a first multiplier 12 that multiplies by a coefficient (1-K). The output of the adder 13 is output to the subsequent video signal processing system (not shown) via the output terminal 14, and is delayed by 1 minute. It is guided to a delay circuit 15 that performs the following steps. The output of this delay circuit 15 is led to the minus input of an adder 17, and also to the other input of the adder 13 via a second multiplier 16 that multiplies a coefficient.

That is, the video signal input from the input terminal 11 is given to the plus input of the adder 17, and after being multiplied by (1-K) by the first multiplier 12, it is given to one input of the adder 13. . Further, the video signal which is manually inputted earlier than this video signal and delayed by one field by the delay circuit 15 is given to the minus input of the adder 17, and after being multiplied by the second multiplier 16, the adder 13 is given to the other input of

On the other hand, the adder 17 subtracts the video signal one field before from the video signal input from the input terminal 11 to extract a signal indicating the correlation between the two video signals, and this signal is applied to each multiplier 12. It is given to 16 people.

Each multiplier 12.16 determines the value of the coefficient based on the signal indicating this correlation and based on the noise reduction effect conversion characteristics shown in FIG. Here, the value of the coefficient is 1.0
The closer the value is to 0, the greater the noise reduction effect becomes, but conversely, in moving image parts where the correlation is low, an afterimage occurs.

Therefore, in moving image parts, that is, parts with low field correlation, the afterimage is reduced by changing the value of the coefficient according to the amount of correlation.

That is, when the signal output from the adder 17 is a signal showing a correlation of 90% or more, each multiplier 12.1
The value of the coefficient set by 6 is 0.75, and when the signal output from the adder 17 is a signal showing a correlation of 90% or less, the value is set by each multiplier 12 and 1.6. The value of the coefficient is set to 0.00.

Therefore, when the signal from the adder F is a signal showing a correlation of 90% or less, since K=0.00, the video signal input from the input terminal 11 is outputted as is to the output terminal 14. become. That is, in this case, noise reduction will not be performed. Further, when the signal from the adder 17 is a signal showing a correlation of 90% or more, since K=0.75, the video signal input from the input terminal 11 is input to the first multiplier 12 at that level. is converted to 1/4 and given to the adder 13, and the video signal from the delay circuit 15 is sent to the second multiplier 1.
6, the level is converted to 3/4 and the adder 13
given to. Therefore, since the video signals have a correlation, the video signals added by the adder 13 become the video signals at the original level and are applied to the output terminal 14, and are also applied to the delay circuit 15 again. At this time, since there is no correlation between the noise components included in the video signal of each field, the level of the noise components added by the adder 13 is compressed. By performing such operations cyclically, the noise components are gradually compressed, and the noise components are removed from the video signal output from the output terminal 14.

(Problem to be Solved by the Invention) However, as described above, in the conventional noise reduction circuit, the correlation amount of the video signal and the value of the coefficient have a certain noise reduction effect conversion characteristic as shown in Fig. 2. Depending on the settings, all screens with a lot of noise components will be processed as video (K = 0.OO) and noise reduction will not be performed, or screens with very good S/N may have afterimages. A problem occurred in which the problem was noticeable.

The present invention has been made in view of the above circumstances, and its purpose is to provide a noise reduction circuit that can obtain an optimal noise reduction effect for any image and simultaneously eliminate the adverse effects caused by the noise reduction effect. Our goal is to provide the following.

(Means for Solving the Problems) In order to solve the above problems, the present invention provides an input current video signal and a certain period of time (time required for scanning one line, one field, or one frame) from the video signal. ) A cyclic type that uses the correlation of the video signals to reduce noise by multiplying each video signal with delayed correlation by a predetermined coefficient and then adding both video signals. The noise reduction circuit includes a noise amount detection means for detecting the amount of noise included in the video signal, and a noise amount detection means for detecting the amount of noise included in the video signal;
The apparatus further includes a characteristic changing means for changing the noise reduction effect conversion characteristic determined by the relationship between the correlation amount of the video signal and the coefficient based on the amount of noise detected by the detecting means.

(Function) The amount of noise contained in the video signal input from the input terminal is detected by the noise amount detection means, and based on the detection result, the amount of correlation between the video signal delayed by one field and the current video signal, and each of these For example, the correlation amount of the video signal is usually 90%.
is the standard, and the value of the coefficient is set to 0. O
0 and 0.75 (Ii!), and when the amount of noise is large, even if the correlation is 90% or less, if it is 60% or more, the coefficient K is changed. Instead of setting it to 0.00, it maintains 0.75 and changes its characteristics so that a noise reduction effect can be obtained.

(Embodiment) An embodiment of the present invention will be described below with reference to the drawings. In this embodiment, a case where the present invention is applied to a field recursive noise reduction circuit similar to the prior art described above will be described.

FIG. 1 is a block diagram showing the electrical configuration of the noise reduction circuit of the present invention.

In the figure, 1 is an input terminal, 2 is a first multiplier, 3 is an adder, 4 is an output terminal, 5 is a delay circuit, 6 is a second multiplier,
Reference numeral 7 denotes an adder, and since the configuration thereof is the same as that of the noise reduction circuit shown in the conventional example, a description thereof will be omitted here.

In the present invention, in the above configuration, a noise amount detection circuit 8 for detecting the amount of noise contained in the video signal is connected to the input terminal 1, and the output of this noise amount detection circuit 8 is guided to each multiplier 2.6. There is.

Here, the detection of the amount of noise by the noise amount detection circuit 8 is as follows.
This is done by amplifying originally flat parts of the video signal, such as horizontal synchronization parts, vertical synchronization parts, or vertical blanking parts, and extracting noise components contained therein. The switching timing of the value of the coefficient in each multiplier 2.6 is controlled based on the output of the noise amount detection circuit 8 which has detected the amount of noise in this manner.

FIGS. 2 and 3 show each multiplication I's 2 based on the amount of noise detected by the noise amount detection circuit 8.

6 shows an example of the noise reduction effect conversion characteristics that are switched in step 6.

That is, in FIG. 2, the correlation amount of the video signal is set at 90%, and the value of the coefficient is changed to two values of 0.00 and 0.75 depending on whether it is less than or more than 90%. Further, in FIG. 3, the correlation amount of the video signal is set at 60%, and the value of the coefficient is changed to two values of 0.00 and 0.75 depending on whether it is less than or more than 60%.

Next, the operation of the noise reduction circuit having the above configuration will be explained.

The video signal input from the input terminal l is given to the plus input of the adder 7, and the first multiplier 2 outputs (
1-K) and then applied to one input of adder 3. In addition, this video signal is input before the delay circuit 5.
The video signal delayed by one field is sent to the adder 7
The signal is applied to the negative input of the adder 3, and after being multiplied by the second multiplier 6, it is applied to the other input of the adder 3.

The video signal input from the input terminal 1 is also given to the noise amount detection circuit 8, and the noise amount detection circuit 8 extracts noise components included in, for example, the horizontal synchronization part of the derived video signal. A signal indicating the amount of noise is given to each multiplier 2, 6.

On the other hand, the adder 7 subtracts the video signal one field before the video signal input from the input terminal l, thereby providing a signal indicating the correlation between the two video signals to each multiplier 2 and 6. giving.

In each multiplier 2.6, first, based on the signal indicating the amount of noise given from the noise amount detection circuit 8, if the included noise components are small, the coefficients are adjusted according to the characteristics shown in FIG. Its operation is determined to switch values. Then, based on the signal indicating the correlation given from the adder 7, the value of the coefficient is determined based on the noise reduction effect conversion characteristic shown in FIG. That is, when the signal given from the adder 7 is a signal showing a correlation of 90% or less, the coefficient K is set to 0.00 and each multiplier 2
, 6, and when the signal given from the JIB calculator 7 is a signal showing a correlation of 90% or more,
Multiplication processing is performed in each multiplier 2 and 6 with coefficient K set to 0.75.

On the other hand, based on the signal indicating the amount of noise given from the noise amount detection circuit 8, if there are many noise components included, the operation is performed to switch the value of the coefficient according to the characteristics shown in FIG. is determined. Then, based on the signal indicating the correlation given from the adder 7, the value of the coefficient is determined based on the noise reduction effect conversion characteristic shown in FIG. That is, when the signal given from the adder 7 is a signal showing a correlation of 60% or less, multiplication processing is performed in each multiplier 2 and 6 with the coefficient K set to 0.00, and the signal given from the adder 7 is When the obtained signals are signals showing a correlation of 60% or more, multiplication processing is performed in each multiplier 2.6 with the coefficient K set to 0.75. As a result, when the amount of noise is large and the correlation between videos etc. is low (
However, even if the noise reduction effect is 60% or more, the multiplication processing performed in each multiplier 2 and 6 is performed with the coefficient K set to 0.75, so that the video signal with the noise reduction effect is input to each input of the adder 13. will be given to

Note that in the above embodiment, switching of the noise reduction effect is explained as a binary change (that is, the value of k is 0.00 and 0.75), but it is possible to change the noise reduction effect in multiple values or in a continuous manner. . In addition, in the above embodiment, the case where the value of the coefficient is changed has been explained, but it can also be applied to a video correction method using ξ ivy, and in this case, if the limiter value is changed depending on the amount of noise. good. Furthermore, in the above embodiment, a field cyclic noise reduction circuit has been described, but it can be applied to a line cyclic noise reduction circuit by setting the delay time of the delay circuit to the time required for scanning one line. Moreover, by setting the time required for one frame scanning, it is possible to apply it to a frame cyclic noise reduction circuit.

(Effects of the Invention) The noise reduction circuit of the present invention detects the amount of noise contained in a video signal manually inputted from an input terminal using a noise amount detection means, and based on the detection result, a video signal delayed by a fixed time and a current Since the noise reduction effect characteristics determined by the amount of correlation with the video signal and the value of the coefficient multiplied by each video signal are changed, it is possible to always obtain the optimum noise reduction effect regardless of the image condition. In addition to this, it is also possible to eliminate the harmful effects caused by this.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the electrical configuration of the noise reduction circuit of the present invention, FIGS. 2 and 3 are noise reduction effect conversion characteristic diagrams showing the relationship between the coefficient value and the correlation amount of the video signal, and FIG. FIG. 4 is a block diagram showing the electrical configuration of a conventional noise reduction circuit. ... Input terminal ... First multiplier ... Adder ... Output terminal ... Delay circuit ... Second multiplier ... Noise amount detection circuit

Claims (1)

[Claims] 1) Multiplying the current input video signal and a correlated video signal delayed by a certain period of time from the video signal by predetermined coefficients, and then adding both video signals. Accordingly, in a cyclic noise reduction circuit configured to reduce noise using the correlation of video signals, there is provided a noise amount detection means for detecting the amount of noise included in the video signal; 1. A noise reduction circuit comprising: characteristic changing means for changing a noise reduction effect conversion characteristic determined by a relationship between a correlation amount of a video signal and the coefficient, based on the determined noise amount.