JP2515778B2 - Video signal noise suppression method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a noise suppression method for a video signal, and more particularly to a noise suppression method for a video signal recorded and reproduced on a recording medium such as a recording disk or a magnetic tape.

BACKGROUND ART A video signal is a signal indicating information of each part of a video at a frame cycle, and autocorrelation between frames is very strong. On the other hand, since the noise component contained in the video signal generally has almost no autocorrelation, when the video signal is temporally averaged for each frame period, the energy of the signal component hardly changes and only the energy of the noise component is changed. Is reduced.
However, there is a motion in a real image, and if the averaging is simply performed, the moving image portion becomes blurred in time.

Based on such knowledge, when a video signal is recorded on a recording medium and played back, the video signal and a delayed video signal obtained by delaying this video signal by M (M is a natural number) times one frame on the playback side. A noise suppression method has already been devised, in which the noises are mixed by mixing and with a mixing ratio according to the difference (movement) in the instantaneous level between these two signals. In this conventional noise suppression system, noise is reduced by increasing the ratio of the delayed video signal and decreasing the ratio of the non-delayed video signal (hereinafter referred to as the current video signal) in the static part,
In the moving image part, the ratio of the delayed video signal is made small and the ratio of the current video signal is made large to reduce the blur.

In such a conventional noise suppression method, if noise is present even in a still image, a level difference occurs between the video signal and the delayed video signal. Therefore, the entire area of the still image is completely detected by the motion detection performed by the difference in the instantaneous level. However, the ratio of the delayed video signal is not sufficiently large, and the noise level cannot be sufficiently reduced. Therefore, it is conceivable that the reproduction side detects whether or not the image based on the video signal obtained from the recording medium is a still image, and in the case of a still image, makes the ratio of the delayed video signal sufficiently large. If so, the circuit scale on the reproducing side becomes large, which is not preferable.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a noise suppression method for a video signal capable of sufficiently suppressing noise in a still image without increasing the circuit scale on the reproducing side.

A method for suppressing noise of a video signal according to the present invention, a still image code indicating whether or not a still image is multiplexed with a video signal is recorded on a recording medium, and a mixing ratio corresponding to the still image code obtained from the recording medium is used. Video signal obtained from the recording medium and this video signal 1
The feature is that noise is suppressed by mixing with a signal obtained by delaying the frame by M times (M is a natural number).

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

In FIG. 1, a video signal output from a VTR (video tape recorder) or the like is supplied to an A / D (analog / digital) converter 2, a sync separation circuit 3 and a multiplexing circuit 4 via an input terminal 1. The A / D converter 2 is supplied with the clock pulse a having a predetermined frequency output from the pulse generation circuit 5. In the A / D converter 2, the video signal is sampled by the clock pulse a, and the obtained sample values are sequentially converted into digital data. The output data of the A / D converter 2 is supplied to the 1-frame delay circuit 6 and the motion detection circuit 7. The 1-frame delay circuit 6 includes a frame memory 8 having a storage capacity capable of storing 1-frame data.
And a memory for performing address control of the frame memory 8 so that one frame of data is sequentially written to the frame memory 8 by the clock pulse A, and then the written data is sequentially read in the written order. It is configured with the controller 9. This 1-frame delay circuit 6
Thus, the output data of the A / D converter 2 is delayed by one frame period.

Further, the motion detection circuit 7 is configured to output data corresponding to the absolute value of the difference between the output data of the A / D converter 2 and the output data of the 1-frame delay circuit 6 as data indicating the motion. The output data of the motion detection circuit 7 is supplied to the still image code generation circuit 10. A vertical sync signal separated from the video signal by the sync separation circuit 3 is supplied to the still picture code generation circuit 10. The still image code generation circuit 10 determines that the output data of the motion detection circuit 7 is a still image when the output data is equal to or less than a predetermined value for, for example, one feed period, that is, a period from when the vertical synchronization signal is once extinguished to when it is generated again. A 1-bit still image code that is in the state shown, for example, "1", and that is not a still image when the output data of the motion detection circuit 7 exceeds a predetermined value within one field period, for example, is "0" It is configured to output over the next one field period. This still image code is supplied to the multiplexing circuit 4. The multiplexing circuit 4 is configured to superimpose the still picture code at a predetermined position within the vertical blanking period of the video signal by the horizontal and vertical sync signals h and v separated from the video signal by the sync separation circuit 3. .

The video signal in which the still picture code is multiplexed by the multiplexing circuit 4 is supplied to the frequency modulator 11 and, for example, an FM of 8.1 MHz
A carrier wave is modulated to generate an FM signal. The FM signal is supplied to the optical modulator 12 and the transmittance of the optical modulator 12 is controlled. As a result, the laser light generated by the laser light source 13 is intensity-modulated by the optical modulator 12, expanded by the collimator lens 14, and then converged by the converging lens 15 to the master disc 16
A photoresist or the like which is focused on the recording surface to form a light spot having a diameter of about 1 μm and constitutes the recording surface is exposed.

On the other hand, the master disk 16 is rotating at a speed corresponding to the relative position of the light spot in the radial direction of the master disk 16 by the motor 17 and the servo loop (not shown), and at the same time, the master disk 16 is rotated once in the radial direction. Transferred at a rate of about 2 μm. Further, the converging lens 15 is controlled by a servo loop so that the laser light is always converged on the recording surface of the master disk 16. Since these are not particularly necessary for the description, they are omitted in this figure.

A reproducing apparatus for reproducing information from a master disc on which information is recorded in this way or a duplicate disc produced by transferring it to a plastic with a mold produced therefrom will be described with reference to FIG.

Disk 21 rotated by spindle motor 20
The recorded information of 1 is read by the optical pickup 22.
The pickup 22 contains a laser diode, an objective lens, a focus actuator, a tracking actuator, a photo detector, and the like.

The laser light emitted from the laser diode in the pickup 22 is converged on the recording surface of the disk 21 by the objective lens to form a light spot. The reflected light from this light spot is incident on the photodetector in the pickup 22 to read the information. Further, the position of the optical spot in the disc radial direction is controlled by the tracking actuator in the pickup 22 and the servo loop (not shown) so that the optical spot formed on the recording surface of the disc 21 is located on the recording track. It Furthermore, the objective lens in the pickup 22 is a disc driven by a focus actuator and a servo loop.
It is controlled so that the laser light is focused on the 21 recording surfaces. These are not shown in the figure because they are not necessary for the description.

The RF (high frequency) signal output from the pickup 22 is
The video signal is supplied to the FM demodulation circuit 23 and demodulated. This video signal is supplied to the A / D converter 24, the sync separation circuit 25, and the still image code reading circuit 26. The still image code reading circuit 26 generates a timing signal generated at a timing corresponding to the position where the still image code is superimposed by the horizontal and vertical synchronizing signals h and v separated from the video signal by the sync separating circuit 25, for example. The still image code is read and held by this timing signal. The still image code obtained by the still image code reading circuit 26 is a noise reduction circuit.
Supplied to 27.

On the other hand, in the A / D converter 24, the pulse generation circuit 2
The video signal is sampled by the clock pulse b having a predetermined frequency output from the circuit 8, and the obtained sample values are sequentially converted into digital data. The output data of this A / D converter 24 is the noise reduction circuit 27
Is supplied to. In the noise reduction circuit 27, A /
The output data of the D converter 24 is supplied to the subtraction circuit 29 and the subtraction circuit 30. The output data of the subtraction circuit 29 is supplied to the 1-frame delay circuit 31 and simultaneously to the output terminal 32.

The 1-frame delay circuit 31 is composed of a frame memory 32 and a memory controller 33 similarly to the 1-frame delay circuit 6 in the apparatus shown in FIG. The output data of the subtraction circuit 29 is delayed by one frame period by the one-frame delay circuit 31 and then supplied to the subtraction circuit 30 to be D /
Difference data ε obtained by subtracting the output data of the 1-frame delay circuit 31 from the output data of the A converter 24 is calculated. The output data of the subtraction circuit 30 is supplied to ROMs (read-only memories) 34 and 35 as address data.
At each address of the ROM 34, difference data ε corresponding to the address value and data f ₁ (ε) having a relationship as shown in FIG. 3 are stored in advance. Further, at each address of the ROM 35, the data f ₂ (ε) having a larger absolute value than the data f ₁ (ε) has a relationship with the difference data ε corresponding to the address value as shown in FIG. It is stored.

The data read from the ROMs 34 and 35 are supplied to the two input terminals of the changeover switch 36, respectively.
A still image code is supplied to the changeover switch 36 as a control input. The change-over switch 36 selectively outputs the data read from the ROM 34 when the still image code is “0”, and selectively outputs the data read from the ROM 35 when the still image code is “1”. Is configured. The output data of the change-over switch 36 is supplied to the subtraction circuit 29 and the A /
It is subtracted from the output data of the D converter 24.

The noise reduction circuit 27 in the above configuration has a cyclic filter configuration, and the difference data ε output from the subtraction circuit 30 is output data of the A / D converter 24, that is, data corresponding to the instantaneous level of the current video signal. And the data obtained by delaying the output data of the noise reduction circuit 27 by one frame period. This difference data ε
Data f ₁ (ε) and f ₂ (ε) corresponding to
Is output from each of. These data f ₁ (ε) and f
It can be said that ₂ (ε) is data obtained by multiplying the difference data ε by a coefficient according to the difference data ε. One of the data f ₁ (ε) and f ₂ (ε) is output from the changeover switch 36 by the still image code and the subtraction circuit
Since it is subtracted from the output data of the A / D converter 24 in 29, the subtraction circuit 29 outputs the data in which the video signal and the delayed video signal are mixed by the still image code in a mixing ratio suitable for the video signal content. Noise reduction circuit 27
Will be output.

Here, the absolute value of the data f ₂ (ε) is the data f ₁ (ε)
Is greater than the absolute value of and the still image code is "1"
, That is, in the case of a still image, this data f ₂ (ε) is A / D
Since it is subtracted from the output data of the converter 24, the ratio of the delayed video signal in the output data of the subtraction circuit 29 becomes large,
Noise will be sufficiently suppressed. When the still image code is “0”, that is, when the image is not a still image, the data f
₁ (ε) is subtracted from the output data of the A / D converter 24 to increase the ratio of the video signal and prevent blurring.

Although the still picture code is a 1-bit code in the above embodiment, the still picture code may be a multi-bit code, and by doing so, high-precision switching control is possible.

The case of recording and reproducing an NTSC video signal has been described above, but MUSE (Multiple sub-Nyquist Sampli
The present invention can also be applied to the case of recording and reproducing a high-definition television signal whose band is compressed by the ng encoding method. In this case, the motion detection unit in the MUSE decoder can also be controlled by the still image code to prevent interference (glitter) caused by erroneously detecting the still unit as the moving image unit.

EFFECTS OF THE INVENTION As described in detail above, in the method for suppressing noise of a video signal according to the present invention, a still image code indicating whether or not a still image is multiplexed with a video signal is recorded on a recording medium, and a still image obtained from the recording medium is obtained. Noise is suppressed by mixing a video signal obtained from the recording medium with a mixing ratio according to the image code and a signal obtained by delaying this video signal by M times of one frame (M is a natural number). It is possible to detect a still image without separately providing a detection unit for detecting whether or not the image is a still image, and noise of the still image can be sufficiently suppressed without increasing the circuit size on the reproducing side. Become.

[Brief description of drawings]

FIG. 1 is a block diagram showing a recording device that multiplex-records a still image code according to the method of the present invention, and FIG. 2 is a block diagram showing a reproducing device that performs noise suppression of a reproduced video signal according to the method of the present invention. FIG. 3 is a graph showing the data stored in the ROM 34 in the apparatus of FIG. 2, and FIG.
7 is a graph showing data stored in a ROM 35 in the device shown in the figure.

Claims (1)

(57) [Claims] 1. A method for suppressing noise of a video signal recorded and reproduced on a recording medium, comprising: the video signal and a signal obtained by delaying the video signal by a period N times (N is a natural number) times one frame. The amount of motion of the image obtained from the video signal is detected by the difference in the instantaneous level of, and whether the amount of motion is a predetermined value or less for at least one field period indicates whether or not the image is a still image. 1-bit still picture code is generated, the still picture code and the video signal are multiplexed and recorded on a recording medium, and the still picture code is obtained from the recording medium together with the video signal upon reproduction. It is characterized in that a video signal and a signal obtained by delaying the video signal by M times of one frame (M is a natural number) are mixed at a mixing ratio according to the still image code to suppress noise. Image The method of noise suppression.