JP3028663B2 - Noise reduction device for video tape recorder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video tape recorder (hereinafter, "VTR") provided with a noise reducer having an improved S / N according to the number of dubbing times.

[0002]

2. Description of the Related Art The noise reducer has the following problems.
This is an apparatus that reduces noise mixed in an image signal by using a frame memory. This device utilizes autocorrelation between frames of an image signal. That is, the image signal is a signal in which image information is repeated at a frame period, and the autocorrelation between the frames is very strong, but the noise component included in the image signal has little autocorrelation. Therefore, when the image signal is averaged temporally for each frame period, the energy of the signal component hardly changes,
Only the energy of the noise component is reduced, and the S / N is improved. However, this method is effective for a still image, but has a problem that an afterimage occurs in a moving image. Therefore, a method is known in which a moving image portion is detected and the afterimage is made inconspicuous by changing the S / N improvement amount.

The circuit shown in FIG. 2A is an example of a method for reducing the afterimage of a moving image. In the figure, an inter-frame difference signal (hereinafter, referred to as a difference signal) obtained by subtracting an input signal and a one-frame delay signal by a subtractor 1 is passed through a limiter 2, added to an input signal by an adder 3, and output. At the same time, data is written to the one-frame memory 4 As the difference signal, a noise component having no inter-frame autocorrelation and a difference of the signal component changed between frames are obtained. Of the difference signal, a noise component having no inter-frame autocorrelation is obtained in a still image portion and its amplitude is small, and a difference of the signal component changed between frames is obtained in a moving image portion and its amplitude is large. When the amplitude of the difference signal is small, time averaging of the video signal is sufficiently performed to improve the S / N, and when the amplitude of the difference signal is large, that is, when it is determined that the video signal has changed. The limiter operates so that a change in the input signal can be obtained as it is at the output.

As a criterion for judging the magnitude of the amplitude of the difference signal, as shown in FIG.
Set. Conventionally, in an analog HD-VTR, the threshold value ± T of the limiter of the noise reducer is set to a value in which the S / N is improved assuming the reproduction of the first generation tape and the afterimage is not conspicuous in the moving image. For this reason, the noise was increased by about 3 dB in the copied tape, so that the S / N ratio could not be sufficiently improved with the limiter threshold.

FIG. 1 shows an example of the configuration of an analog HD-VTR. In FIG. 1, an A / D converter converts a video signal composed of a luminance signal Y, a blue color difference signal P _B , and a red color difference signal P _R. 5, and is converted into a digital signal, which is then input to a vertical nonlinear emphasis circuit 6. S / N is improved by the vertical nonlinear emphasis circuit 6 (Y3 dB, C
6 dB), encodes a TDM (time division multiplexed) signal, and sends it to a shuffling frame memory 8 that rearranges data in the time direction. This frame memory 7
Is sent to the horizontal nonlinear emphasis circuit 8,
Here, the S / N is further improved (7 dB for each of Y and C).
The output signal of the horizontal nonlinear emphasis circuit 8 is
After being converted into an analog signal by the D / A converter 9 and emphasis by the horizontal linear emphasis circuit 10,
Analog HD which is modulated and amplified by the frequency modulator 11
-Recorded on the tape 13 by the VTR.

On the other hand, in reproducing the video signal recorded on the tape 13, first, the output signal of the analog HD-VTR is amplified and demodulated (14, 15), then de-emphasized by the horizontal linear de-emphasis circuit 16, and A / A The signal is converted into a digital signal by the D converter 17 and sent to the horizontal non-linear de-emphasis circuit 18 where the S / N is improved (7 dB for each of Y and C). The output of the horizontal non-linear de-emphasis circuit 18 is deshuffling and TDM
It is sent to the signal decoding frame memory 19 and the time sequence is restored. The S / N of the output of the frame memory 19 is improved by the vertical nonlinear emphasis circuit 120 (Y3d
B, C6 dB) and a noise reducer (hereinafter, referred to as
It is called NR. ) 21 S / N is improved by being converted into an analog signal by a D / A converter 22, the luminance signal Y, the color difference signals P _B of blue is reproduced and output as the color difference signals P _R of the red.

In the analog HD-VTR having such a configuration, the NR after vertical nonlinear emphasis processing is performed.
The threshold T of the limiter 2 (FIG. 2) when noise reduction is applied at the position 21 will be obtained. When a 38 dB S / N signal enters the NR 21 assuming the first generation of the tape, the limiter threshold necessary for improving the still image by 3 dB in the noise reducer of FIG. Assuming that there are 175 gradation levels and the noise σ is normally distributed, S / N = S _pp / σ. Therefore, in order to obtain the improvement amount of 3 dB, it is considered that it is necessary to take a noise distribution up to 3σ. At this time, the threshold T is T = 175 × 10
^-38 / ²⁰ × 3 ≒ 6.6. However, once dubbing is performed, about 3 dBS / N is deteriorated. Therefore, similar S / N improvement is not performed at the threshold value of this limiter.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a noise reducer capable of improving the S / N even when reproducing a dubbed tape.

[0009]

In a VTR system, when there is a signal indicating that a recorded tape is a copy in dubbing, the threshold value of the limiter of the noise reducer is automatically increased to increase the S / N. The amount of improvement is adjusted.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Returning again to the configuration example of the analog HD-VTR shown in FIG. 1, the present invention is to automatically limit the noise reducer when a signal indicating that the tape is a dubbed tape is sent to the VTR. S / N by increasing the threshold of
It aims to improve. At the time of reproduction, the copy signal detection circuit 23 detects the generation number of the dubbing tape as seen from the master tape, and the number of times of copying,
A ROM address selection signal is sent to the ROM according to the detected number of times of copying, and an optimum limiter threshold is read from the ROM table 24 to apply an optimum noise reduction.

FIG. 3C shows an optimum limiter threshold value read from the ROM table.
When a tape having good N is played back, the threshold value is T / S / N.
In the case of reproducing a copy tape having a poor threshold value, the threshold value is automatically increased to T ′.

[0012] Such an analog HD-VTR according to the present invention.
In the configuration described above, the number of copies is detected, for example, by recording a dubbing identification signal on a tape to be dubbed. As shown in FIG. 3, each segment of the tape pattern includes a video signal area V and an audio signal area A.
And an index area I between them. The present invention digitally records the number of copies of the generation dubbing tape counted from the master tape in a part of the index area I of the tape pattern,
At the time of reproduction, this copy number signal is detected, and the optimum value of the threshold value of the noise reducer can be automatically selected. Of course, the recording of the dubbing identification signal on the dubbing tape is not limited to the index area, but can be selected by a person skilled in the art as needed if there is an optimal area.

[0013]

As described above, according to the present invention, the number of copies by dubbing is detected, and the optimum threshold value of the limiter of the noise reducer can be automatically selected according to the number of copies. Improved S / N
A good image can be reproduced.

[Brief description of the drawings]

FIG. 1 is a block circuit diagram of the present invention.

FIG. 2 is an explanatory diagram of a noise reducer.

FIG. 3 is a diagram illustrating an example of a tape pattern.

[Explanation of symbols]

21. Noise reducer 23. Copy signal detection circuit 24. ROM table for limiter

Claims (1)

(57) [Claims] 1. A noise reducer using inter-frame correlation, a copy number detection device recorded on a dubbing tape, and a copy number signal from the copy number detection device.
Preload the threshold of the noise reducer limiter
A ROM table I, depending on the copy number signal from said copy count detection device
A noise reduction device for a video tape recorder, wherein a threshold value of a limiter of the noise reducer is selected from the ROM table .