JPH0447781A - Video signal recording and reproducing device - Google Patents

Abstract

PURPOSE:To reduce noise sufficiently around a white level and to minimize fog of a picture even in a moving picture by varying an amplitude limit of an amplitude limit element in a noise reduction means corresponding to a level of a reproduced video signal inputted to the noise reduction means. CONSTITUTION:An output data of a subtractor 15 and an input signal to an NR circuit 100 are used as input addresses to a ROM 110 and a slice level of an output signal outputted from the subtractor 15 is changed depending on the input signal. That is, a threshold level of a still picture area is set larger to process a signal with bad S/N after FM demodulation around a white level so as to emphasize the noise reduction effect and a threshold level of a still picture area is set smaller to process a signal with excellent S/N around a white level so as to suppress as much as possible a fog of the picture in a moving picture portion. Thus, undesired deterioration of picture quality is not incurred and sufficient noise reduction effect is realized in each signal level.

Description

Detailed Description of the Invention [Industrial Application Field] This invention relates to a video tape recorder (hereinafter referred to as VTR), a video disc player, etc., which records and plays back video No. 48 by FM modulation. The present invention relates to a signal recording/reproducing device, and particularly to a noise reduction means for reducing noise contained in a reproduced video signal.

[Prior Art] Figure 6 shows a VT which is an example of a conventional video signal recording and reproducing device.
It is a block diagram showing the configuration of the reproduction system of R, in which (1) is a magnetic tape, (2a) and (2b) are rotary heads, (3) is a head amplifier, and (4) is an FM demodulator. circuit,
(5) A converts analog data to digital data
/D converter.

(6) is a synchronization separation circuit that separates the synchronization signal from the playback video signal, and (7) is playback signal processing that performs time axis correction of the playback video signal based on the synchronization signal output from the synchronization separation circuit (6). circuit, (8) is a time-axis noise reduction circuit (referred to as NR circuit) that removes noise from the FTR raw video signal, and (9) is a D/D circuit that converts digital data into analog data. A converter, (1o) is the output terminal.

FIG. 7 is a block diagram showing the JJ structure of the NR circuit (8), in which (11) is an input terminal, (12) is an output terminal, and (13) is a frame memory. , (14) is a ROM, and (15) is a first subtracter, which subtracts the output data of the 1-th frame memory (13) by 9 from the input data. (16) is a second subtracter that subtracts the output data of the ROM (14) from the input data. The digital N in the time axis direction is determined by each component in 1- below.
An R circuit is configured.

Although the time axis power-oriented NR circuit as described in 1- is generally excellent in noise removal effect, it causes blur in the image in the moving image part. In order to prevent blurring of the image in the moving image part as much as possible, the NR circuit shown in FIG.
, the field number is i, the first subtractor (15)
, that is, a portion where the absolute value of Xi −Yi−2 is larger than a predetermined value is determined to be a moving image, and a portion where it is smaller is determined to be a still image.

Also, ROM (14) has input X1-Yi-2 (7)
It has a functional form, and if the absolute value of Xl-Yi-2 is larger than a predetermined value, that is, O is output in the video part
A range where the absolute value of Xl-Yi-2 is smaller than a predetermined value
tK ・(Xi −Yi−2) (However, K is O≦
If it changes between K<1 and the absolute value of It is determined by the amount of reduction, O≦α (1), and the larger the absolute value of Xl-Yi-2 is than the threshold value, the more →0
) is output.

FIG. 8 shows the shape of input and output data of the ROM (14).

The above NR circuit (8) is described in Part 1 of the expanded edition of ``Digital Signal Processing of Images'' by Kei Fukinuki, published by Nikkan Kogyo Shimbun.
Since it is publicly known from pages 15 to 118, detailed explanation will be omitted.

Next, the operation of the configuration shown in FIG. 6 will be explained.

The playback signal output from the magnetic tape (1) via the rotary heads (2a) and (2b) is amplified by the head amplifier (3), then FM demodulated by the FM demodulation circuit (4) and converted into a playback video signal. Become. This reproduced video signal is then sent to the A/D
After being converted into digital data by the converter (5), it is input to the playback signal processing circuit (7), where the time axis correction of the playback video signal is performed based on the synchronization signal output from the synchronization separation circuit (6). etc. are carried out.

The signal is input to the NR circuit (8), where the noise component superimposed on the reproduced video signal is reduced in the manner described above. The output of this NR circuit (8) is converted into analog data by a D/A conversion circuit and output.

Generally, when performing FM modulation on a video signal, the frequency of the carrier is selected so that the frequency on the white level side is higher. Furthermore, due to the characteristics of the electromagnetic conversion system, such as thickness loss and space loss, the reproduced FM is
The higher the frequency, the harder it is to produce output.

Now, if the noise generated in FM modulation/demodulation, electromagnetic conversion system, etc. is white noise, as is clear from Figure 9,
The S/N ratio (signal-to-noise ratio) of the reproduced FM signal is worse as the FM carrier is higher. Even in actual measurements, the S/N ratio of the white level signal is 1 to 1 for the reproduced signal after FM demodulation than the S/N ratio of the black level signal where the carrier is set low.
It has become worse by about 2 dB.

Here, when trying to sufficiently improve the S/N ratio near the white level with the NR circuit (8) shown in FIG. The threshold value must be increased compared to the optimal value for black level. For example, if the difference in S/N ratio between the white level and the black level is about 2 dB, the threshold value must be increased by 1.25 times. This threshold value is large for signals near the gray level and black level, and although noise at all levels is sufficiently reduced, blurring is noticeable in moving images and is very unsightly. In particular, visual blur is noticeable near the gray level.

[Problems to be Solved by the Invention] Since the conventional video signal recording and reproducing device is configured as described above, when trying to obtain a sufficient noise reduction effect near the white level, the image becomes blurred in the moving image section. There was a problem in that the image was very unsightly.

This invention was made in order to solve the problems mentioned in 1-1 above, and it is possible to sufficiently reduce noise near the white level and to minimize image blurring even in the video section. The purpose of the present invention is to provide a video signal recording and reproducing device that can perform the following functions.

[Means for Solving the Problems] The video signal recording and reproducing device according to the present invention has the following features:
The present invention is characterized in that the amplitude limiting value of the amplitude limiting element in the noise reduction means is configured to be changed.

[Function] According to the present invention, since the triplet (amplitude limit in the noise reduction means) has an amplitude limit value suitable for the signal level of the reproduced video signal, noise reduction near the white level can be reduced by 1 minute. At the same time, blurring of images in the video portion can be minimized.

[Embodiments of the Invention] Hereinafter, embodiments of the present invention will be described based on the drawings.

FIG. 1 shows 1 of V −1′ R according to an embodiment of the present invention.
It is a block diagram showing the configuration of a four-cow system, and in the same figure,
(1) to (7), (ql, (+ol) are the same as those in the conventional example shown in FIG. 6, so the same arrows are attached to the corresponding parts and detailed explanation thereof will be omitted.

In Figure 1, +100+ is an NR circuit that reduces noise, including the NR
The specific configuration of the circuit (IflO) is as shown in FIG.

In Figure 2, (111 to (13), (15), (1
6) is the same as the conventional example shown in FIG. 7, so the corresponding parts are given the same reference numerals and detailed explanation thereof will be omitted.

In FIG. 2, (1101) is a ROM that changes the function form inside -C1 in response to the level of the reproduced video signal input to the NR circuit (100).

Next, the operation of the configuration shown in FIG. 1 will be explained.

The reproduction signal reproduced by the magnetic tape (1) via the rotating heads (2a) and (2b) is sent to the head amplifier (3).
After being amplified by , the signal is FM demodulated by an FM demodulation circuit (4) to become a reproduced video signal. This reproduced video signal is then converted into digital data by an A/D converter (5), and then input to a reproduced signal processing circuit (7), where it is converted into a synchronization signal output from a synchronization separation circuit (8). Based on this, time axis correction of the reproduced video signal is performed.

The signal is then input to the NR circuit (Hoo), where it undergoes noise reduction, and then converted to analog data by the D/A conversion circuit (9) and output.

The operation of the NR circuit (100) will be explained with reference to FIGS. 2 and 3. Note that, as in the conventional example, the FM allocation during FM modulation is set so that the frequency is higher on the white level side.

In FIG. 2, the reproduced video signal input to the input terminal (11) is passed through the subtracter (15) to the frame memory (1
3) The difference is taken from the data output from ROM (1
10) Input to. Figure 3 (a) shows the above ROM
(110) shows the shape of the input and output data,
The shape of the ROM (110) is Xl-Yi, similar to the conventional example.
If the absolute value of -2 is larger than a predetermined value, it is regarded as a moving image, and ROM (lto) outputs O, and in the range where the absolute value is S smaller than the predetermined value, K @(Xi -Yi-
2) (However, K varies between 0≦K<1, and Xl
If the absolute value of -Yi-2 is in the still image area, then K = α (α is a constant O≦α×1 determined by the noise low level, as in the conventional example), and the absolute value of X i -Y i-2 The larger the value, the larger the coefficient that becomes +O) is output, but depending on the input signal level, there is a threshold of Xl-Yi-2 that is determined to be a still image area, that is, a section of the still image area. The configuration is such that it changes.

In other words, as shown in Fig. 3(a), the white level signal with a poor S/N ratio after FM demodulation is set to a large threshold value in the still image area, and the black level signal with a good S/N ratio is processed. In this example, the threshold value for the still image area is set to a small value.

The configuration as described in item 1 reduces the noise contained in the reproduced video signal, so even at a white level with a poor S/N ratio, noise reduction can be performed sufficiently effectively, and the S/N ratio is relatively low. For signals below a good gray level, blur in moving images can be kept to a minimum.

FIGS. 3(b) and 3(c) show other examples of the input and output data shapes of the ROM (110), and these R
Even with the OM shape, noise can be sufficiently reduced at each signal level, and blurring of moving images can be minimized.

In the above embodiment, the NR circuit was constructed using a frame memory (13), but any memory capable of storing at least one field period, such as a field memory, can produce the same effect as the above embodiment. .

Further, in the above embodiment, the functional form is realized using the ROM (110), but the same effect as in the above embodiment can be obtained even if it is constructed using a general-purpose IC or the like.

FIG. 4 is a block diagram showing the configuration of a vertical NR circuit according to the present invention. In the same figure, (11) is an input terminal, (12) is an output terminal, and (120) is an input video signal for one horizontal scan. IH delay circuit that extends the period, (121) is a subtracter that subtracts the output of IH delay circuit (+20) from the input video signal, and (122) is a limiter that changes the amplitude limit value according to the signal level of the input video signal. , (123) is a subtracter that subtracts the output of the limiter (122) from the input video signal.

Above IH delay circuit (120), subtractor (12+)
, limiter (122), and subtracter (123) constitute a vertical NR circuit, and the operating principle of this vertical NR circuit is rNHK, home video technology.
Since it is well known, such as from pages 102 to 104, edited by Japan Broadcasting Corporation, written by Katsuya Yokoyama, detailed explanation will be omitted.

FIGS. 4(b) and 4(C) show the shape of the input and output data of the limiter (122), and as in the above embodiment, the shape of the limiter (122) is The amplitude limiting level is set high near the black level, and the amplitude limiting level is set small near the black level where the S/N ratio is relatively good.

1, the vertical NR circuit of the present invention can sufficiently reduce noise even near the white level where the S/N ratio is poor, as well as the gray level and black level, as in the above embodiment. Deterioration in image quality can be kept to a minimum near this level.

Although the shape of the limiter (122) in this embodiment is shown in FIGS. 4(b) and 4(C), it is not limited thereto.

FIG. 5 is a block diagram showing the configuration of a horizontal NR circuit according to the present invention. In the figure, (11) is an input terminal, (12) is an output terminal, and (130) is a high-frequency component of an input signal. A high-pass filter (hereinafter referred to as HPF) for extraction, (131) is a limiter that changes the amplitude limit value according to the signal level of the input video signal, and (132) is a limiter that changes the output of the limiter (131) from the input video signal. It is a subtractor that performs subtraction.

HP F (130), limiter (131)
), a horizontal NR circuit is constructed by a subtracter (132), and the operating principle of this NR circuit is well known in "rNHK, Home Video Technology" edited by Japan Broadcasting Corporation, written by Katsuya Yokoyama, pages 102-104. , detailed explanation will be omitted.

FIGS. 5(b) and (C) show the shape of input and output data of the limiter (131), and as in the above embodiment, the shape of the limiter (131) is set near its own level where the S/N ratio is poor. Increase the amplitude limit level.

The amplitude limit level is set small near the black level where the S/N ratio is relatively good.

As described above, according to the horizontal NR circuit of the present invention, as in the above-described embodiment, noise can be sufficiently reduced even near the own level where the S/N ratio is poor, and deterioration in image quality can be minimized. can be suppressed.

In this embodiment, the shape of the limiter (131) is shown in FIGS. 5(b) and 5(C), but the shape is not limited to this.

In the above embodiment, a reproduced video signal was described, but a color difference signal recorded and reproduced by FM modulation, a combo shift signal, etc.
□Similar effects can be achieved with double signal time division multiplexed signals, etc.

Further, in the above embodiment, a VTR is shown as an embodiment of the video signal recording/reproducing apparatus, but the same effect can be achieved with a video disc player or the like.

[Effects of the Invention] As described in 1-1 above, according to the present invention, since the amplitude limit value is changed according to the signal level of the reproduced video signal input to the noise reduction circuit, unnecessary image quality is reduced. This has the effect that a superior noise reduction effect can be achieved at each signal level without causing deterioration of the signal.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a video signal recording and reproducing apparatus according to an embodiment of the present invention, FIG. 2 is a block diagram showing the configuration of an NR circuit in the time axis direction according to an embodiment of the present invention, and FIG. 4 is a block diagram showing the configuration of a vertical NR circuit in another embodiment of the present invention, and FIG. 5 is a block diagram showing the configuration of a vertical NR circuit in another embodiment of the present invention. 6 is a block diagram showing the configuration of a conventional video signal recording/reproducing device. FIG. 7 is a block diagram showing the configuration of a conventional NR circuit in the time axis direction. Figure 8 is a diagram showing ROM data used in a conventional NR circuit in the time axis direction.
The figure is a diagram for explaining a conventional video signal recording and reproducing device. (13)...Frame memory, (15), (18)...
...Subtractor, (110)...ROM, (120)...
- IH delay circuit, (121). (123), (+32)...subtractor, (122)
, (+31)...Limiter, (130) ・HP F
. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] (1) A noise reduction means is provided for reducing noise contained in the reproduced video signal when the video signal recorded with FM modulation is reproduced, and the noise reduction means is composed of a delay element, an amplitude limiting element, and an arithmetic element. A video signal recording and reproducing apparatus characterized in that the amplitude limiting element is configured such that its amplitude limiting value changes in accordance with the signal level of the reproduced video signal input to the noise reduction means. playback device.