JPH05244565A - Adaptive noise reducer - Google Patents

Abstract

PURPOSE:To effectively reduce reproduction noise. CONSTITUTION:This reducer is provided with a difference detection means 56 detecting a difference between reproduced video signals of preceding and succeeding fields or frames, a variable limiter circuit 57 receiving a difference detection output, a subtractor 53 subtracting its limiter output from a present reproduction video signal to reduce noise, and a noise quantity detection circuit 60 detecting the absolute quantity of noise included for a specific period of the difference detection output and outputting a control signal in response to the absolute quantity and the limiter quantity is adaptively controlled in response to the noise quantity by selecting the limiter characteristic of the variable limiter circuit 57 depending on the control signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an adaptive noise reducer suitable for use in a reproducing system such as a high definition analog VTR.

[0002]

2. Description of the Related Art In a magnetic recording / reproducing apparatus such as an analog VTR for high definition, a rotary magnetic head apparatus as shown in FIG. 15 is used.

In the figure, reference numeral 100 denotes a rotating drum (or rotating disk), and recording / reproducing magnetic heads (Ha, Hb) arranged close to each other so that two-channel recording can be performed on the rotating drum 100. And (Hc,
Hd) are arranged so as to maintain respective intervals of approximately 180 °.

By rotating the rotary drum 100 at double speed, the magnetic tape 101 shown in FIG.
divided recording over a to 102d (2 segment recording)
To be done. Therefore, for example, the track 102a is recorded by the magnetic head Ha, and the track 102b is recorded by the magnetic head Hb. This is 1 field 2
It is called a segment 2-channel recording system.

Since the two-channel recording system is used, the reproduction output of two heads is used for one field, and the seam of the head is located at approximately the middle position of one screen as shown by the broken line in FIG.

[0006]

The magnetic heads Ha to Hd.
It is preferable that the recording / reproducing characteristics are the same, but it is difficult to match the recording / reproducing characteristics. If the recording / reproducing characteristics do not match, the seam of the head becomes conspicuous as shown in FIG. In particular, when reproducing the magnetic tape 101 having poor image quality such as the noise of the reproduced video signal, the seams of the heads become conspicuous and the reproduced image quality is significantly deteriorated.

As a means for improving the variation in characteristics of the magnetic head and the deterioration of the reproduced image quality which is likely to occur when a magnetic tape having a poor image quality is used, a method of interposing a noise reducer in the reproducing system has been proposed. There is.

In this case, it is desirable to apply a large amount of noise reduction when the amount of noise is large, and a small amount when it is not. However, since such adaptive noise reduction processing is not performed, the image quality is deteriorated by returning. It may happen. This is because, for example, an afterimage occurs when a large amount of noise reduction is applied to a reproduced video signal having a small amount of noise, and the afterimage deteriorates the image quality.

Therefore, the present invention solves such a conventional problem, and proposes an adaptive noise reducer capable of producing an appropriate noise reduction effect by adaptively applying noise reduction. Is.

[0010]

In order to solve the above problems, the present invention is provided with a difference detecting means for detecting a difference between reproduced video signals of one field or one frame before and after, and this difference detection output. Variable limiter circuit, a subtracter that subtracts the limiter output from the current playback video signal to reduce noise, and an absolute amount of noise included in a specific section of the difference detection output, and control according to that absolute amount And a noise amount detection circuit for outputting a signal, and the limiter amount is adaptively controlled according to the noise amount by selecting the limiter characteristic of the variable limiter circuit based on the control signal. It is characterized by that.

[0011]

The adaptive noise reducer 50 (5 shown in FIG.
In 1), the absolute value of the noise N included in the specific section of FIG. 3 is accumulated by the accumulator 62, and the type of the control signal C stored in the encoder 63 is selected according to the magnitude of the value. The control signal Ca is output when the cumulative value is small, and the control signals Cb and Cc are selected as the cumulative value increases.

The variable limiter circuit 57 is controlled by the control signal C.
Limiter characteristic, that is, the control signal Ca as shown in FIG.
Limiter characteristics La to Lc having different values are selected according to Cc.

When the amount of noise is small, the limiter characteristic La is selected by the control signal Ca, so that the amount of subtraction from the currently reproduced video signal is small. At this time, since it can be estimated that the amount of noise originally included in the currently reproduced video signal is small, the amount of subtraction may be small.

When the amount of noise is large, the limiter characteristic Lc is selected by the control signal Cc. At this time, therefore, the amount of subtraction from the currently reproduced video signal becomes large. This is because it can be estimated that the amount of noise contained in the currently reproduced video signal at this time is large. In this way, by adaptively controlling the limiter characteristic of the variable limiter circuit 57 by the noise amount,
An appropriate noise reduction effect can be obtained.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an example of an adaptive noise reducer according to the present invention will be described in detail with reference to the drawings when applied to a reproducing system of a magnetic recording / reproducing apparatus for recording / reproducing a high-definition signal.

FIG. 7 shows an example of an analog VTR recording system 10R configured to record and reproduce a high-definition signal, and FIG. 8 shows the reproducing system 10P. For convenience of description, the recording system 10R of FIG. 7 will be described.

In FIG. 7, the luminance signal Y and the pair of color difference signals PB (= BY) and PR (= RY) are band-limited by low-pass filters 1, 2 and 3, respectively, and then A / D converter. It is converted into a digital signal by 4, 5, 6. Digitized luminance signal Y and a pair of color difference signals P
B and PR are subjected to time-division compression / multiplexing processing in a time-division multiplexing circuit (TDM encoder) 7 so that the color difference signals are compressed and a pair of color difference signals are line-sequentially applied to the luminance signal Y.
Are multiplexed into.

When recording two channels of video signals,
For example, in the A channel, the color difference signal PB is compressed on the time axis to form a compressed color difference signal, and this and the luminance signal Y are line-sequentially time division multiplexed to generate a video signal. In the B channel, the color difference signal PR is time-axis compressed to form a compressed color difference signal, and this and the luminance signal Y are line-sequentially line-sequentially time-axis multiplexed to generate a video signal. Then, the shuffling circuit 8 performs shuffling processing on each channel.

The video signals SA and SB which have been subjected to the time division multiplexing process and the shuffling process are D / A converters 11 and 12.
After being converted into an analog signal in, the band is limited by the low pass filters 13 and 14. Then, after being supplied to the FM modulators 15 and 16 of the next stage and subjected to FM modulation so as to be suitable for recording, dedicated magnetic heads Ha and Hb (Hc and Hd) are used via recording amplifiers 17 and 18. 2 channels are recorded.

FIG. 8 shows a reproducing system 10P. The video signal reproduced by the magnetic heads Ha to Hd described above is supplied to the FM demodulators 30 and 31, and the video signal is FM demodulated, and also supplied to the A / D converters 34 and 35 via the low-pass filters 32 and 33. After being converted into a digital signal, the adaptive noise reducer 50, 5 according to the present invention is formed.
After noise reduction processing is performed by 1, the deshuffling circuit 36 performs deshuffling processing.

The deshuffled video signal is supplied to a time division demultiplexing circuit (TDM decoder) 40 and a luminance signal Y is supplied.
And the color signal C. The luminance signal Y and the pair of color difference signals are converted into analog signals by the corresponding D / A converters 41, 42, 43.

A concrete example of the adaptive noise reducers 50 and 51 used in the reproducing system 10P will be described with reference to FIG. Since the noise reducers 50 and 51 have the same configuration, only the noise reducer 50 will be described.

A reproduced video signal for the A channel which has been digitally converted is supplied to the terminal 52, and this is supplied to a memory 54 having a capacity of 1 field (or 1 frame) via a subtractor 53 and stored therein. The memory 54 is a 1-field delay memory necessary for performing the noise reduce process, and the reproduced video signal delayed by 1 field by the interposition of the memory 54 is an output terminal 55.
And is supplied to the subtractor 56 together with the currently reproduced video signal for noise reduction processing, and the difference between adjacent fields is detected. The subtractor 56 functions as a difference detecting means between adjacent fields.

Since the video signal has a strong vertical correlation, most of the difference between adjacent fields becomes a noise component. Therefore, the difference detection output is considered to be an output proportional to the amount of noise contained in the reproduced video signal. ..

The difference detection output is supplied to the variable limiter circuit 57 and also to the noise amount detection circuit 60. The noise amount detection circuit 60 has a limiter 61, and the limiter 6
4σ of noise N that is the difference detection output when 1 (σ is the variance value)
Are taken out. Considering that the noise N has a normal distribution (Gaussian noise distribution) as shown in FIG. 2, most noise N existing in the reproducing system can be extracted by applying a limiter so as to pass up to 4σ.

The difference detection output output from the limiter 61 is supplied to the accumulator 62 having an integral structure, and the noise component existing in a specific section of the reproduced video signal is accumulated over a predetermined period. In this example, the specific section is a section of the reference signal (ramp waveform) inserted in the vertical blanking period as shown in FIG. The predetermined period is, for example, one field period (or one frame or one horizontal period section)
Refers to.

A gate pulse GP as shown in FIG. 3B is supplied to the input terminal 62a of the accumulator 62 to accumulate the noise N only in the section of the reference signal. The gate pulse GP is also synchronized with the field signal, and the accumulated state is reset in field units.

Assuming that the noise distribution is normally distributed as shown in FIG. 2, when the noise amount is accumulated over a predetermined period, the cumulative value (= Σ) has a linear characteristic as shown in FIG. It is proportional to the amount of accumulated noise in.

The cumulative output of the noise N is supplied as an input to the encoder 63. The encoder 63 is a circuit for converting the control signal C into several stages corresponding to the cumulative value Σ as shown in FIG. 5, and in this example, the input / output relationship of FIG. 5 is tabulated. In the figure, the control signal C has a 2-bit structure because it shows an example of three stages. However, in practice, about eight stages are preferable, so the control signal C at that time has a 3-bit structure.

The control signal C is supplied as a limiter characteristic selection signal for the variable limiter circuit 57 while being held by the hold circuit 64. The limiter characteristics also have limiter characteristics that differ by the number corresponding to the type of control signal C. Since the example of FIG. 6 corresponds to the characteristic of FIG. 5, it has a limiter characteristic of three stages.

As described above, when the amount of noise N included in the predetermined period is large, that is, when the cumulative value is large, it is considered that the amount of noise included in the currently reproduced video signal is also large. Also, a limiter characteristic like the curve La in FIG. 6 is selected. Then, the limiter output level (the level of the difference detection output) output from the variable limiter circuit 57 also increases, and the subtraction amount in the subtraction process from the current reproduction video signal increases, so that the current reproduction video signal contains The contained noise can be effectively suppressed.

On the other hand, when the amount of noise N included in the predetermined period is small, the cumulative value also becomes small, but at that time, it is considered that the amount of noise included in the currently reproduced video signal is also small. Shows the limiter characteristics as well.
A limiter characteristic such as the curve Lc is selected. Then, the limiter output level output from the variable limiter circuit 57 also decreases, and the subtraction amount from the currently reproduced video signal in the subtractor 53 decreases. Therefore, even in this case, noise included in the currently reproduced video signal can be effectively suppressed.

Thus, by adaptively controlling the limiter characteristic of the variable limiter circuit 57 by the noise amount, the noise amount contained in the currently reproduced video signal can be effectively suppressed.

In FIG. 1, noise reduction processing is performed independently for the A channel and the B channel, but the limiter characteristics of the variable limiter circuits provided in each system are adaptively adjusted by the average of noise detected from both channels. Can also be controlled.

FIG. 9 shows an example thereof. In the structure of the adaptive noise reducer 51 for the B channel, the same parts as those of the adaptive noise reducer 50 for the A channel are designated by the corresponding reference numerals. The respective difference detection outputs of the subtracters 56 and 96 are supplied to the accumulators 62 and 72 via the limiters 61 and 71, respectively, and the noise N in each channel is integrated. The averaging circuit 73 obtains an average of noises within a predetermined period for each integrated output.

The output is supplied to the encoder 63, the corresponding control signal C is selected, and the corresponding variable limiter circuits 57 and 97 are simultaneously controlled by the hold output. As a result, the variable limiter circuits 57 and 97 are the same. The limiter characteristic is selected. As a result, similar noise reduction processing is performed on the A channel and the B channel.

Instead of the averaging process, the limiter characteristic may be adaptively controlled by the larger noise.

The example described above uses the memories 54, 9 used.
Although all 4 are 2-port memories, when the 3-port memory is used, time axis correction processing (TBC processing), deshuffling processing and the like can be simultaneously performed in addition to the noise reduction processing. This is because the 3-port memory can freely control the read state of 2 outputs for 1 input.

FIG. 10 shows an example in which a 3-port memory is applied to the basic configuration of FIG. In FIG. 10, 75 is this 3-port memory. The 3-port memory 75 is controlled by one type of write clock and two types of read clock.

Reference numeral 80 denotes a clock forming circuit, which generates a first write clock and a first read clock which are synchronized with the clock of the reproduced video signal input to the terminal 52 (clock having received reproduction jitter). Therefore, the reproduced video signal is supplied to the sync separation circuit 81 to separate the horizontal and vertical sync signals, and these are supplied to the PLL circuit 82 to generate a reference clock synchronized with the input horizontal and vertical sync signals.

The reference clock is supplied to each of the write and read clock generation circuits 83 and 84, the reproduced video signal is written in synchronization with the write clock, and read out in synchronization with the read clock. The read output is available at the first output port R1D. The delayed video signal output from the first output port R1D is used as a signal for noise reduction.

On the other hand, the second read clock generation circuit 85 operates by the reference clock (clock with the aligned time axis) output from the PLL circuit 86. Therefore, the second read clock obtained from the generation circuit 85 is a clock signal whose time axis is aligned. The second output port R2D by the second read clock
From, the reproduced video signal stored in the previous field is read. Since the read delayed video signal is read based on the second read clock whose time axis is aligned, it is output as a delayed video signal whose time axis is corrected.

First and second output ports R1D, R2
The output timing from D can be arbitrarily adjusted by the enable signals (not shown) for the first and second read clocks.

By using such a 3-port memory 75, the noise reduce process and the TBC process can be simultaneously performed. When the 3-port memory 75 is used, the deshuffling process can be performed by controlling the read address at the same time as the time axis correction. Figure 1
0 can also be applied to the configuration of FIG.

By the way, in the above description, the section in which the reference signal is inserted is used as the section for detecting the noise amount, but the noise N may be detected on the spatial frequency axis of the video signal. For example, as shown in FIG. 11A, it is possible to detect the noise N included in the segment synchronization signal and adaptively configure the noise reducer based on the detected noise.

FIG. 12 shows an embodiment using the spatial frequency axis and corresponds to FIG. The noise amount detection circuit 60 is shown in FIG.
However, the current reproduction video signal is used as a signal for detecting noise, and this is supplied to the high-pass filter 65 to extract only the noise component contained in the reproduction video signal. After that, the gate pulse GPS shown in FIG. 11B is supplied to the terminal 62a of the accumulator 62, and the noise N in a specific section near the segment synchronization signal is extracted and accumulated.

Since the encoder processing is performed based on the accumulated output and the limiter characteristic is selected by the control signal obtained here is the same as in the case of FIG. 1, the description thereof will be omitted.

FIG. 13 shows an embodiment corresponding to FIG.
The configuration is the same as the configuration of FIG. 12, and the high-pass filters 61, 7 are added to the reproduced video signal of each channel.
A noise averaging process is performed using the noise N extracted in 1.

FIG. 14 is applied to the noise reducer having the 3-port memory of FIG. 10, and its detailed description will be omitted.

[0050]

As described above, according to the present invention, since the noise reduction processing is adaptively performed, the noise contained in the reproduced video signal can be effectively suppressed, so that the image quality can be improved as compared with the prior art. You can

In particular, in a magnetic recording / reproducing apparatus of the type in which the image can be switched in the center of the screen, the noise reduction effect is exerted in the most prominent area of the screen even if the variation in the head characteristics itself cannot be corrected. Therefore, a remarkable improvement effect of the image quality is recognized.

[Brief description of drawings]

FIG. 1 is a system diagram showing an example of an adaptive noise reducer according to the present invention.

FIG. 2 is a diagram of noise distribution characteristics.

FIG. 3 is a waveform diagram showing a relationship between a reference signal and a gate pulse.

FIG. 4 is a diagram of a noise accumulation state.

FIG. 5 is a diagram showing input / output characteristics of an encoder.

FIG. 6 is a diagram showing input / output characteristics of a variable limiter circuit.

FIG. 7 is a system diagram of a recording system showing an example in which the magnetic recording / reproducing apparatus is applied to a high definition analog VTR according to the present invention.

FIG. 8 is a system diagram showing an example of a reproducing system when the magnetic recording / reproducing apparatus according to the present invention is applied to a high-definition analog VTR.

FIG. 9 is a system diagram showing another example of the adaptive noise reducer according to the present invention.

FIG. 10 is a system diagram showing another example of the adaptive noise reducer according to the present invention.

FIG. 11 is a diagram showing a relationship between a segment synchronization signal and a gate pulse.

FIG. 12 is a system diagram showing another example of the adaptive noise reducer according to the present invention.

FIG. 13 is a system diagram showing another example of the adaptive noise reducer according to the present invention.

FIG. 14 is a system diagram showing another example of the adaptive noise reducer according to the present invention.

FIG. 15 is a diagram of a rotary magnetic head device for HDVTR.

FIG. 16 is a diagram of a track pattern when a rotary magnetic head device is used.

FIG. 17 is a diagram showing a relationship between a screen and a head seam.

[Explanation of symbols]

 10R recording system 10P reproducing system 50,51 adaptive noise reducer 53 subtractor 54 memory 56 difference detecting means (subtractor) 57 variable limiter circuit 60 noise amount detecting circuit 62,72 accumulator 63 encoder 75 three-port memory

Claims (1)

[Claims] 1. A difference detecting means for detecting a difference between reproduced video signals of preceding and following one field or one frame, a variable limiter circuit to which the difference detection output is supplied, and the limiter output subtracted from the current reproduced video signal. And a noise amount detection circuit that detects an absolute amount of noise included in a specific section of the difference detection output and outputs a control signal according to the absolute amount. An adaptive noise reducer characterized in that the limiter amount is adaptively controlled according to the noise amount by selecting the limiter characteristic of the variable limiter circuit based on the above.