JPH02186879A - Noise reduction circuit - Google Patents

Abstract

PURPOSE:To obtain a clear and natural picture by correctly deciding a noise and a moving picture by a moving picture decision circuit. CONSTITUTION:An input terminal 22 is provided in a moving picture decision circuit 9 and the output of a constant generation circuit 13 is controlled by the output signal of a noise detection circuit 21. When the moving picture decision circuit 9 constituted in such a way is used, the moving picture can be correctly distinguished from the noise even when the noise is large. When the noise is decided, the noise is conventionally reduced and when the moving picture is decided, an afterimage effect is lowered. Then, a noise reduction effect is suppressed. Thus, in the case of the moving picture, even when the absolute value of difference between an input signal and a 1-frame delay circuit is small, the clear and natural picture can be obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applied to high-definition receivers, digital television, etc., and relates to a noise reduction circuit that reduces noise in television video signals. .

[Prior Art] FIG. 10 is a block diagram showing the configuration of a conventional noise reduction circuit using frame correlation.
is an input terminal, into which a digitized television signal is input. (2) is a subtraction circuit whose one input is the digital television signal arriving at the input terminal (1) and whose other input is the output signal of the l-frame delay circuit (5), which will be described later; and (3) is the subtraction circuit described above. A nonlinear circuit whose input is the output signal of circuit (2), (4) is the nonlinear circuit (3) above.
(5) is an l-frame whose input is the output signal of the adder circuit (4); The delay circuit (6) is the output terminal of the adder circuit (4).

Next, the operation of the above configuration will be explained.

The television signal containing noise input through the input terminal (1) is input to the subtraction circuit (2), where it is subtracted from the signal from one frame before, which is delayed by the one frame delay circuit (5). The output signal is input to the nonlinear circuit (3). This nonlinear circuit (3) multiplies the input signal by a variable coefficient (K) (0≦K<1) that changes depending on the level of the human input signal, and outputs the result to the addition circuit (4). This addition circuit (
4) adds the output signal of the nonlinear circuit and the current television signal input from the input terminal (1), outputs the added signal to the one-frame delay circuit (5), and outputs the signal from the output terminal ( 6) Output.

In the noise reduction circuit as described above, the current preview signal (A) and the output signal of the 1 frame delay circuit (5) are
1), a signal of K(B-A)IA (1-K)A0KB (0≦K<1) is output to the output terminal (6).

In other words, this noise reduction circuit is suitable for the current television signal (^
) is temporally averaged using a weight (K) for each frame period. Generally, when a television signal is a still image, it is a signal that repeats at a frame period, and the autocorrelation between the frames is very strong. On the other hand, noise components included in television signals have almost no autocorrelation.

Therefore, when the television signal is temporally averaged for each frame period, the energy of the signal component hardly changes, and only the energy of the noise component becomes low, making it possible to reduce noise.

However, when the television signal is a moving image, if it is temporally averaged for each frame period, an afterimage effect may occur. Therefore, the input/output characteristics of the nonlinear circuit (3) are set as shown in FIG. 8, and the absolute value of the difference between the input signal (A) and the output signal (B) of the one-frame delay circuit (5), that is, The television signal is determined to be a still image in the portion where IA-Bl is small (IA-Bl≦P), and the variable coefficient (K) is made close to 1 to increase the noise removal effect, and the A-Bl The television signal is determined to be a moving image in the portion where the difference is large (l A−B l >P), and the variable coefficient (
By setting K) to O, the input television signal (A) is output as is.

[Problem to be solved by the invention] Conventional noise reduction circuits are configured as described above, so even if it is a moving image, if lA-Bl is small, it is determined to be noise and there is no afterimage effect. It will be done. For example, the first
As shown in Figure 1, the same figure (a) or two frames earlier, (b)
If the data is from the previous frame or the original frame (c), then if the data is passed through a conventional noise reduction circuit, the result in the same figure (
The video signal with diagonal lines inserted in a) is determined to be noise, and as a result, as shown in Figure 12 (b) and (c), an afterimage appears in the previous frame and the original frame, resulting in an extremely unsightly image. There was a problem. .

This invention was made to solve the above-mentioned problems, and even if the absolute value of the difference between the input signal and l-frame delayed signal is small, it is correctly determined to be a moving image and the afterimage effect is eliminated. The purpose of the present invention is to provide a noise reduction circuit that can reduce the noise.

[Means for Solving Problem v1] The noise reduction circuit according to the present invention has a noise reduction circuit that is configured to reduce noise when the difference between a signal obtained by delaying a noise-reduced output signal by a natural number of frames and an input television signal is small, and when the difference is small, The feature is that a video judgment circuit is provided that determines when pixels above the level appear in a concentrated manner as a moving image, and in other cases as noise, and the coefficients are varied according to the judgment result of this moving image judging circuit. shall be.

[Function] According to the present invention, when the moving image determining circuit determines that the noise is noise, the noise is reduced as before, and when it is determined that the moving image is a moving image, the afterimage effect is lowered to suppress the noise reduction effect, As a result, in the case of a moving image, a clear and natural image can be obtained even if the absolute value of the difference between the input signal and the one-frame delay circuit is small.

[Embodiment of the Invention] Hereinafter, an embodiment of the present invention will be described based on the drawings.

FIG. 1 is a block diagram showing the configuration of a noise reduction circuit according to an embodiment of the present invention. In the figure, (1) is an input terminal to which a digitized television signal is input. (2) is a subtraction circuit whose one input is the digital television signal arriving at the input terminal (1), and whose other input is the output signal of a one-frame delay circuit (5), which will be described later; and (3) is the subtraction circuit described above. (7) is a first delay circuit that receives the television signal arriving at the input terminal (1);
8) is a second delay circuit that inputs the output signal of the nonlinear circuit (3), (9) is a video judgment circuit that uses the output signal of the nonlinear circuit (3) as input, and (10) is a coefficient variable circuit. In one example, a switch circuit (4) is a switch circuit that receives the output signal of the second delay circuit (8) and is controlled by the output signal of the video judgment circuit (9).
) is used as one input, and the above switch circuit ( ]
(5) is an l-frame delay circuit that receives the output signal of the adder circuit (4) as its input; (6) is the output terminal of the adder circuit (4); be.

Next, the operation of the above configuration will be explained.

Similar to the conventional example shown in FIG. 1O, the television signal inputted through the input terminal (1) is subtracted in the subtraction circuit (2) from the previous l-frame signal delayed by the l-frame delay circuit (5). , its output signal is input to the nonlinear circuit (3). The input/output characteristics of this nonlinear circuit (3) are the same as those of the conventional example as shown in FIG. 8, and the signal (A) arriving at the input terminal (1) and the output signal (B) of the 1-frame delay circuit (5) When the absolute value of the difference IA-Bl is large (IA
-B l >P), the input signal (A) is output as is to the output terminal (6) by determining that it is a moving image and setting the coefficient (K) to O.

On the other hand, if the absolute value IA-Bl of the above difference is small (IA
-Bl≦P) can be divided into the following two cases. In other words,
When the moving image determining circuit (9) determines that the signal is a moving image, the switch circuit (10) is opened to output the input signal (A) as it is to the output terminal (6). In addition, when the video judgment circuit (9) determines that the signal is noise, the switch circuit (10) is short-circuited.
The output terminal (6) receives a signal from which noise has been removed as in the conventional example,
In other words, (1-K)A+KB (where ≠0) is output.

Here, the first and second delay circuits (7).

(8) is for compensating for the delay caused by the moving image determining circuit (9).

Next, the moving image determination circuit (9) will be explained in detail.

Generally, when taking frame differences from a television signal,
Differences caused by video movement are concentrated in several pixels, and differences caused by noise are concentrated in a single pixel. Utilizing this property, the moving image determining circuit (9) determines whether the output signal of the nonlinear circuit (3) is caused by a moving image or noise.

The 21st λ1 shows a specific configuration example of the I'll constant circuit (9) in the F-recording;
) is the output signal (K・(B-A)) of the nonlinear circuit (3)
is the input terminal for manual input, (+2) is the input terminal (1
1) Absolute value circuit whose input is the signal arriving at (13)
(14) is a constant generation circuit that generates a constant (Q); (14) is a comparison circuit that uses the output signal of the absolute value circuit (12) as one input and the output signal of the constant generation circuit (13) as the other input; (15) is a one-pixel delay circuit that receives the output signal of this comparison circuit (14), and (16) represents a one-pixel delay circuit that receives the output signal of this one-pixel delay circuit (15).

(17) is a first OR circuit which takes the output signal of the comparison circuit (14) as one input and the output signal of the 1-pixel delay circuit (15) as the other input; (+8) shows the 1-pixel delay The output signal of the circuit (15) is used as one input, and the above 1
A second OR circuit whose other input is the output signal of the pixel delay circuit (16), (19) is the first OR circuit (17)
The output signal of the above-mentioned second OR circuit (1
AND circuit whose other input is the output signal of (8), (20
) is an output terminal for outputting the output signal of this AND circuit (19) to the switch circuit (10) shown in FIG.

Next, the operation of the configuration shown in FIG. 2 will be explained.

The output signal (K・(B−A)) of the nonlinear circuit (3) is first input to the absolute value circuit (12), where the absolute value signal (K・IA−Bl) is input to the next stage comparison circuit. (14), where it is compared with the constant (Q) input from the constant generation circuit (13). Here, the constant (Q) is the maximum value of the above absolute value signal (K・l A−B l ).
K-IA-Bl), 0≦Q<MAX (K
-IA-Bl).

This comparison circuit (14) is When K.IA-Bl≧Q, outputs the logical value rlJ.

・When IA-Bl<Q, a logical value of "0" is output.

Then, this output signal is sent to the one pixel delay circuit (15) and (1
6), the OR circuits (17) and (18
) and an AND circuit (19) according to the logic shown in Table 1 below.

According to Table 1, the output signal of the AND circuit (19) is output to the control input terminal of the switch circuit (10), and the AND circuit (
When the output signal of 19) is "0", the switch circuit (10)
becomes "short circuit", and when it is "1", it becomes "open".

In other words, as shown in Figure 3, the vertical axis shows the absolute value circuit (12
) and the sample points are plotted on the horizontal axis, the output signal of the AND circuit (19) becomes rl'' for the sample marked as moving image in Fig. 3, and the output signal of the switch circuit (10 ) is left open, and the input signal (A) is output as is from the output terminal (6). Regarding the sample signal marked as noise in Fig. 3, the output signal of the AND circuit (19) becomes "0", and the switch circuit (10) is "short-circuited" and the output terminal (6) is connected to (1-K). A+KB (≠0) is output.

In the above embodiments, the input/output characteristics of the nonlinear circuit (3) are fixed as shown in FIG. ) may be configured to change the characteristics of Fourth
The figure is a block diagram showing the configuration of a noise reduction circuit according to another embodiment of the present invention. In the figure, (21) has a television signal arriving at the input terminal (1) as one input;
This is a noise detection circuit whose other input is the output signal of the subtraction circuit (2), and outputs the output signal of this noise detection circuit (21) to the nonlinear circuit (3) and the moving image determination circuit (9).

Since the other configurations are the same as those in FIG. 1, the same reference numerals are given and explanations thereof will be omitted.

In the noise reduction circuit having the above configuration, the noise detection circuit (
21), for example, averages the noise of the synchronization signal part of the television signal, and when the noise is equal to or greater than a certain predetermined constant, that is, 3
The circuit is configured to output a logical value of ``1'' when one note is loud, and output a logical value of ``0'' when the noise is below a constant, that is, when the noise is small. Also, unlike the video signal part, the synchronization signal part is the output signal of the subtraction circuit (2) or only noise, regardless of the movement of the subject, so it is difficult to know the degree of noise in the human-powered television signal. can. Receiving the output signal of this noise detection circuit (21), the nonlinear circuit (3) selects the input/output characteristics shown in Figure 8 when the noise is small, and selects the input/output characteristics shown in Figure 9 when the noise is large. This increases the noise removal effect.

Also, if the value of the constant (Q) in the video judgment circuit (9) when the noise is large is the same as the value when the noise is small, the noise will be determined as a video, so the above constant a(Q) Is there a need to make it bigger?

FIG. 5 is a block diagram showing another specific example of the configuration of the moving image determination circuit (9) configured to eliminate such misjudgments. In this diagram, the differences from FIG. An input terminal (22) is provided in the moving image determination circuit (9), and the output of the constant generation circuit (13) is controlled by the output signal of the noise detection circuit (21).

The moving image determining circuit (9) configured in this manner has the effect of being able to correctly distinguish between moving images and noise even when the noise is large as shown in FIG.

Further, in the above embodiment, when the moving image determining circuit (9) determines that the moving image is a moving image, the switch circuit (10) changes the coefficient by which the output signal of the nonlinear circuit (3) is multiplied, so that the noise reduction effect is set to "0". Alternatively, instead of the switch circuit (10), a coefficient circuit is used that multiplies the coefficient rlJ when it is determined to be noise, and multiplies it by the coefficient L (0≦L<1) when it is determined that it is a moving image. It may be configured to suppress the noise reduction effect in the case of moving images.

Furthermore, in the embodiment described above, the motion picture determination circuit (9) determines whether noise or motion pictures are present on one scanning line of the television signal, as shown in FIG.

The same effect as in the above embodiment can be obtained even if the l-line delay circuits (2:l) and (24) are used for the scanning lines above and below the pixel of interest.

[Effects of the Invention] As described above, according to the present invention, since noise and moving images are configured to be correctly determined by the moving image judgment circuit, it is possible to sufficiently reduce noise, and at the same time, in the case of moving images, it is possible to reduce the afterimage effect. This has the effect of suppressing the noise reduction effect and producing clear and natural images.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a noise reduction circuit according to an embodiment of the present invention, FIG. 2 is a block diagram showing a specific example of the configuration of a moving image determination circuit, and FIG. 3 explains the operation of FIG. 2. Correlation graph of absolute A4 output signal and sample point for
FIG. 4 is a block diagram showing a configuration of a noise reduction circuit according to another embodiment of the present invention, FIGS. 5 and 6 are block diagrams showing other configuration examples of a moving image determination circuit, and FIG. 8 and 9 are input/output characteristic diagrams of the nonlinear circuit, and FIG. 10 is a block diagram showing the configuration of a conventional noise reduction circuit. FIGS. 11 and 12 are signal diagrams for explaining the operation of the conventional example, respectively. (2)...Subtraction circuit, (3)...Nonlinear circuit, (4
)... Addition circuit, (5)... l frame delay circuit,
(9)...Movie judgment circuit, (10)...Switch circuit. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] (1) In a noise reduction circuit configured to reduce noise using frame correlation of a television signal, a frame delay circuit delays a noise-reduced signal by a natural number of frames, and an output signal of the frame delay circuit. and an input television signal; a nonlinear circuit that multiplies the output signal of the subtraction circuit by a variable coefficient that changes depending on the level of the output signal of the subtraction circuit; a moving image determining circuit that determines that the moving image is a moving image when a predetermined value or more is concentrated; a coefficient variable circuit that varies a coefficient by which the output signal of the nonlinear circuit is multiplied in accordance with an output signal of the moving image determining circuit; and this coefficient. an adder circuit that adds the output signal of the variable circuit and the input television signal, and when the moving image determining circuit determines that the input television signal is a moving image, the output coefficient of the variable coefficient circuit is made smaller than the output coefficient in other cases. A noise reduction circuit characterized in that it is configured to be variable.