JPH0442670A - Noise reduction device - Google Patents

Abstract

PURPOSE:To prevent occurrence of a limit cycle and to maximize prescribed noise reduction by adopting the constitution such that a gain of a function realized by a ROM is brought into zero when an amplitude of a difference of an input signal is very small in linear area and the gain is increased as the difference increases. CONSTITUTION:When the amplitude of function shape realized by ROM13 is very small, a gain is set not to be the unity. Thus, a digital data being a line sequential color difference signal R-Y/B-Y outputted from an NR circuit 7 is minimized for deterioration in noise reduction and timewise fog and converged into the same data as the inputted digital data. Thus, no limit cycle takes place and the noise reduction is maximized.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention is applicable to video signal recording and reproduction* for video tape recorders (hereinafter referred to as VTRs), video disc players, etc.
This relates to a noise removal device used in St.

[Prior Art] FIG. 7 shows digital noise reduction in the time axis direction using a frame memory to remove noise components superimposed on a video signal, which is applied to a playback system of a video signal recording and playback device. 1 is a block diagram showing the basic configuration of an NR circuit (hereinafter referred to as an NR circuit).

In the figure, (10 is a multiplier that multiplies the digital input signal by a constant K (0≦1). (12) is a frame memory that delays the input signal by one frame and outputs it.

(1G) is a subtracter that subtracts the output of the frame memory (12) from the input signal. (11) is also a subtracter, and subtracts the output of the multiplier (10) from the input signal.

Each of the above elements +lot, (+11. (+21.
The transfer function H(z
l is.

Hizl = (1-K)/(1-Kz), which results in a low-pass filter in the 1-time axis direction.

In such a low-pass filter in the time axis direction,
Although it has an excellent noise removal effect for static single cars, it causes blurring of images in video parts. Therefore, there is an h method in which the gain of the multiplier (14) is changed in the range of 0≦K<1 according to the movement.

8th + 5th! ;l is the conventional N
It is a block diagram showing the configuration of one circuit, and in the same figure,
(≦6) is ROM. Since the other configurations are the same as those in FIG. 7, the same reference numerals are given and the explanation thereof will be omitted.

Here, if the signal manually input to the N1 circuit is Xi, the noise-reduced output signal is Yi, and the output of one frame before that, that is, the output of the frame memory (12) is Yi-1, then as shown in FIG. The configuration is Yi = Xi −K ・(Xi
-Yi-1) However, l can be expressed as a frame number.

In order to prevent blurring over an hour in the case of a moving image, Xl-Yi-
If the value of 1 is large, it is judged as a video and K・(Xi
-Yi-1) is the necessary force to change f (X
i -Yi-1) t23< t.

The configuration of Fig. 8 is Yi = Xi −f(X1Yi−
It is the ROM of the eighth factor that sets the cono function f (Xi −Y i−1), which is 1).

Figure 9 shows the N1 circuit having the above-mentioned basic configuration.
1 is a block diagram showing a configuration when applied to noise removal of color signals in a reproduction system; in the same figure, (1) is a magnetic tape which is a recording medium;

(2a) and (2b) are rotary heads for recording and reproducing video signals, (3) is a head amplifier, and (4) is a reproducing F.
An FM demodulation circuit that demodulates the M signal, (5) an A/D converter that performs A/D conversion, and (8) the above A/D converter (5)
The line-sequential time-division color TV @ (hereinafter referred to as T
Luminance signal (Y) and color difference signal (referred to as CI signal)
The luminance signal (Y) and the line-sequential color signal (+?-Y ) /(B
-Y) is a reproduced signal imaginary circuit that outputs.

(15) is the N1 circuit, and the above line sequential color signal (Y)/
(B-Y) noise component is reduced. (8) is the line sequential color signal (R-Y)/(B-Y) to the original color difference signal (
R-Y), a vertical interpolation circuit that restores (B-Y),
(9a).

(sbj A9C) is a D/A converter that converts digital data into analog data.

Next, using FIGS. 10, 11, and 12, calculate the R
An example of a functional form realized by OM (1B) will be explained.

An example of the functional form realized by the ROM (16) shown in FIG. 10(a) is to increase the gain when the fluctuation between frames is small, and to
The setting is such that the output data of OM (1B) is kept constant, and when the fluctuation becomes larger, the input data is output as is without being subtracted.

That is, lXi - Yi-11≦10 (hereinafter).

(referred to as linear region), ≦0.9, ]1≦Xi −
Yi-1≦20 (hereinafter referred to as constant area) throat is f
(Xi -Yi-1) ≦9, -20≦X1-Yi-
When 1≦-11 (hereinafter referred to as constant region), f (X
i −Yi−l ) =−9,21≦Xi −Yi−1
When ≦30, -30≦Xi -yi-1≦-21 (hereinafter referred to as quasi-moving image area), = -0,9, l Xi -
When Yi-11≧31C (hereinafter referred to as a moving image area), f (Xi - Yi-1)≦0.

In other words, in the case of a still image with a small value of Xl-Yi-1, the amount of noise reduction for one color signal is increased, and in the case of a moving image with a large value of Xl-Yil, the value of K is brought closer to 0. The configuration is such that priority is given to not causing temporal blur.

Here, as shown in FIG. 11(a), the N1 circuit (15
) is input to the line sequential color signal (R-Yl/(B-Yl
The case of digital data of a step response in which the value changes from 72 to 92 will be described. At this time, the N1 circuit (I5
) is shown in Figure 11(a), and the specific values are shown in Figure 11(b).As is clear from these Figures, the output of the N1 circuit (15) is converged to 87. Ru.

This means that the function form set in the ROM (161) is t
When Xi - Yi-l 1≦10, then = 0.9, but since the output data is expressed as finite-length digital data, This is because, as shown in FIG. 2, the value becomes substantially equal to 1, and the system function of the N1 circuit (15) becomes unstable. Such a phenomenon is called a limit cycle, and is well known in Chapter 9, Section 3.1 of Digital Signal Processing (Part 2), translated by Gen Date, so a detailed explanation will be omitted.

Further, as shown in FIG. 12, the same applies to the digital data of the step response changing from 92 to 72.

Therefore, the digital data of the line sequential color signal (It-Yl/(B-Yl) having a value different from the actual digital data value is output from the NRu path (15), and the hue of the screen changes.

Regarding the N1 circuit in the 2-time axis direction, please refer to "Image Digital Signal Processing" (written by Takahiko Fukinuki, published by Nikkan Kogyo Shimbun).
Since it is well known, including chapter 7, pages 3 and 3, pages 115 to 117, detailed explanation will be omitted. In addition, the above TC
Since the I@ issue is also well known, including chapter 5, 2.3, pages 60 to 61 of the above-mentioned book, a detailed explanation will be omitted.

[Problems to be Solved by the Invention] Since the conventional noise removal device is configured as described above, the function form realized by the ROM has a finite register length, so in the case of minute amplitude components in the linear region, Generally, the gain of the N1 circuit becomes 1, and the output data of the N1 circuit does not converge to the original value. For example, when used in a video signal recording and reproducing device, when a step response signal is input, the hue of the color difference signal etc. There was a problem that the .

This invention was made to solve the above-mentioned problems, and avoids limit cycles.

It is an object of the present invention to provide a noise removal device that can effectively reduce noise components contained in a reproduced signal.

[Means for Solving the Problems] The noise removal device according to the present invention changes the function form realized by the ROM by bringing the gain close to 0 when the difference value input in the linear region is a minute amplitude component, and The structure is such that the gain increases as the value increases.

[Operation] According to the present invention, when the setback value input in the linear region is a minute amplitude component, the limit cycle phenomenon can be generated by bringing the gain close to 0 and increasing the gain as the difference value increases. This allows for maximum noise reduction.

[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 the N1 circuit according to an embodiment of the present invention.

(13) is the ROM of the present invention, and the other configurations are the same as the conventional example shown in FIG. 8, so the same symbols are attached.
Their explanation will be omitted.

FIG. 2 is a block diagram showing the configuration of a reproduction system of a VTR that records and reproduces TCIg numbers. In the figure, (1),
(2a), (2b), (3) to (6), (
8) Since (9a), (9b), and (9c) are the same as the conventional example shown in FIG. 9, the same reference numerals are given to the corresponding parts and detailed explanation thereof will be omitted.

In Fig. 2, the difference from the conventional example shown in Fig. 9 is that N1
There is only a circuit (7), and the specific configuration of this N1 circuit (7) is as shown in the block diagram of FIG. 1 above.

Next, the operation of the above configuration will be explained with reference to FIGS. 1 to 3.

As in the case of the conventional example, the reproduced signal processing circuit (8) outputs a luminance signal (Y) and a line sequential color signal (R-Y) /(B-Y
) digital data is output. Here, the digital data of the line sequential color signal (R-Y)/(B-Y) is N
1 circuit (7).

Line sequential color signal (R-Y
) /(B-Y) is the line sequential color signal (R-Y)/ which is delayed by one frame in the subtracter (10) as in the conventional example.
(B-Y) digital data is subtracted.

In other words, the output of the subtractor (lO), that is, ROM (
13) 17) The input is X i -Y i-1 theari,
The sono output is f (Xi -Yi-1) -t'al.

Here, the functional form realized by the ROM (13) will be explained.

Subtractor (10) < 7) When the output is Xi −Yi-1=O, f (Xi −Yi-1) = 0° In the above linear region, l≦Xi −Yi-1≦lO
When Hf (Xi −Yi−1) =XiY i−1
, when -10≦X1-Yi-1≦-1, f(Xi-Yi
-1) = Xi -Yi-1+ 1, and other areas are the same as the conventional example.

In other words, the functional form realized by the ROM (13) is based on the same principle as the conventional ROM (1B), in which the amount of color signal noise reduction is increased for still images or screens with little movement, and For large screens, the configuration is such that priority is given to preventing temporal blurring by reducing noise in color signals. Also, R
If the function form realized by OM (13) has a small amplitude in the linear region mentioned above, the gain is set so that it does not become 1, so the output data of the N1 circuit (7) will converge to the input value. Become.

Figure 4(a) shows an example of this, where the N1 circuit (7) when a step response changing from 72 to 92 is input.
Fig. 4(b) shows the specific numerical values at that time.

Further, FIGS. 5(a) and 5(b) show the output waveform and specific numerical values of the N1 circuit (7) when a step response varying from 92 to 72 is input.

In this way, the line-sequential color signal (R-Y)/(B-Y) digital data output from the N1 circuit (7) minimizes noise reduction degradation and temporal blurring.
Also, the digital data value is converged to the same value as when it was input.

This line-sequential color signal (R-Y)/(B-Y) is restored to color difference signals R-Y, B-Y in a vertical interpolation circuit (8), and then D/A converted along with the luminance signal (Y). Vessel (9a
), (9b), and (9c) are converted into analog data and output.

Therefore, on the screen, there is no phenomenon in which a hue that is changed from the video signal when the hue is recorded is output.

Note that in the above embodiment, the function form realized by the ROM as shown in FIG. , the limit cycle phenomenon does not occur, and the same effects as the above embodiments are achieved.

Furthermore, in the above embodiment, the line sequential color signal (RY) /(
Although the case where the N1 circuit is provided for the luminance signal or the TCI signal has been described, the same effects as in the above embodiments can be obtained.

Further, in the above embodiment, the N1 circuit using a frame memory has been described, but if the same effect can be obtained, any memory capable of recording over at least one field period, such as a field memory, may be used.

Furthermore, in the above embodiment, the V for recording and reproducing the TCI signal is
Although we have explained the case of a TR, if it is a VTR that incorporates an N1 circuit in the time axis direction using a frame memory,
VTRs employing other recording methods such as the 2-channel 3-segment method may be used, and other video signal recording and reproducing devices such as laser discs can also produce similar effects.

[Effects of the Invention] As described above, according to the present invention, when the difference value inputted in the linear region of the function form realized by the ROM has a minute amplitude, the gain approaches 0 and increases as the difference value increases. Since it is configured to do so, it is possible to prevent the occurrence of the limit cycle phenomenon and to perform the predetermined noise reduction to the maximum extent.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an 81 circuit according to an embodiment of the present invention, and FIG. 2 is a VTR using the 81 circuit.
FIG. 3 is a block diagram showing the configuration of the reproduction system of the present invention. FIG. 3 is a diagram showing the functional form realized by the 81 circuit ROM of the present invention. FIGS. 4 and 5 are diagrams showing the relationship between input data and output data of the 81 circuit. FIG. 6 is a diagram showing the relationship and the process from input to output; FIG. 6 is a diagram showing the functional form realized by the ROM according to another embodiment of the present invention; FIG.
The figure is a block diagram showing the principle of the 81 circuit, and Figure 8 is the conventional 81 circuit.
9 is a block diagram showing the configuration of one circuit. FIG. 9 is a block diagram of a VTR playback system incorporating a conventional 81 circuit. FIG. 10 is a diagram showing a functional form realized by a conventional 81 circuit ROM. 11 and 12 are diagrams showing the relationship between input data and output data of the conventional 81 circuit and the process from input to output.゛(7)...81 circuit, (10), (11)...subtractor, (12)...frame memory, (13)...
...ROM. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] (1) A memory capable of storing a video signal for at least one field period, a first subtraction means for subtracting the video signal and the output of the memory, and an amplitude limiting means for limiting the amplitude of the output of the first subtraction means. and a second subtraction means for subtracting the output of the amplitude limiting means from the video signal, in which the characteristics of the amplitude limiting means are inputted. When the video signal is Xi, the output of the memory is Yi-1, and the output of the amplitude limiting means is Zi, then Xi-Yi-1=0.
If , then Zi=0, if Xi-Yi-1>0, then 0<Zi≦Xi-Yi-1
-1, if Xi-Yi-1<0, Xi-Yi-1+1≦Zi
<0, A noise removal device characterized in that it is configured to satisfy the following condition.