JPH0556573B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is capable of detecting impulsive noise caused by, for example, a pit defect in a video disc, and is used for inspecting the quality of manufactured video discs. This invention relates to a noise measuring device.

[Background technology and its problems]

For example, an FM-modulated composite color video signal is recorded on an optical video disc with or without pits. Therefore, if a defect occurs in the pit because the pit is blocked by foreign matter or the shape of the peripheral edge of the pit is turned over during molding or transfer during disk manufacturing, this defect will appear on the screen.
Degrades image quality.

FIGS. 6 and 7 show such pit defects and reproduced waveforms when the pits have defects. FIG. 6 shows a case where one pit is completely missing. In FIG. 6A, P ₁ ,
P ₃ and P ₄ are normal pits, and P ₂ is a missing pit. Corresponding to this missing part, Figure 6B
As shown in , a portion in which the level does not change for a certain period appears in the reproduced output waveform. In this way, foreign objects,
A problem caused by a defect extending over one or more pits is called a dropout.

If a dropout occurs, it will be recorded
No change in reading level occurs for a time longer than the repetition period of 7.6MHz, which is the lowest frequency of the FM signal. Therefore, similar to conventional dropout detection, it can be detected by no change in the read level and compensated for by interpolation with the delayed color video signal.

FIG. 7 shows a case where one pit is partially missing. In FIG. 7A, P ₅ , P ₇ ,
_P8 is a normal pit, and _P6 is a pit with a partial defect. In the reproduced output waveform in this case, as shown in FIG. 7B, an instantaneous frequency transition occurs which is much larger than the frequency transition caused by a recorded normal signal. Since the level of this playback output waveform continues to change, it cannot be detected using the same method as dropouts.

A large instantaneous frequency transition that occurs in the reproduced output waveform when some of these bits are missing causes a relatively high 2MHz frequency transition in the video signal obtained by FM demodulation.
It appears as impulsive noise that has frequency components above and changes at a very large level. Impulse noise appears as bright spots on the screen and significantly deteriorates the image quality. However, if the video signal being recorded is, for example, a composite color video signal that is not band-limited and has a wide frequency component up to, for example, 4 MHz, this impulsive noise will enter the band of the video signal. Therefore, it cannot be removed by a noise canceler with a simple configuration.

Therefore, it is necessary to inspect the generation of this impulsive noise during manufacturing to maintain the quality of the video disc. However, conventionally, there has been no noise measurement device that measures such impulsive noise, and this measurement has only been possible through a subjective method of evaluating while monitoring the playback screen.

[Purpose of the invention]

Therefore, an object of the present invention is to provide a noise measuring device that measures impulsive noise that occurs when, for example, a portion of a pit is missing.

[Summary of the invention]

In this invention, a reproduction signal of a disk in which a recording signal consisting of an image information signal as FM modulation is recorded as a pattern of pits is supplied, a signal in a frequency band of an impulsive noise component is selected from the reproduction signal, and a signal in a frequency band of an impulsive noise component is selected from the reproduction signal. This is a noise measurement device characterized in that a measurement signal having a reference signal value or more included in a signal within a frequency band of is detected as noise.

〔Example〕

An embodiment of the invention will be described below with reference to the drawings. As mentioned above, the noise that occurs when a portion of a pit is missing is impulsive noise. This impulsive noise is, for example, a high-frequency component of 2 MHz or more. If the recorded video signal includes a band up to 4MHz, this impulsive noise is within the band of the video signal, and it is difficult to extract and measure this noise alone. Therefore, in order to extract only impulsive noise, noise is measured in a section where the signal level is constant in the video signal. The sections in which the signal level in the video signal is constant include, for example, the vertical blanking section, the sync chip portion of the horizontal blanking section, and the front porch portion.
In this embodiment, noise is measured at the sync tip in the horizontal blanking section. In this way, even if the noise is measured only in areas where the level does not fluctuate, for example, if measurements are made at one location per line, measurements will be made at 500 to 600 locations, which is sufficient for measurement on one screen.

In FIG. 1 showing an embodiment of the present invention, 1
indicates the input terminal. A composite color video signal obtained by FM demodulating the reproduced output waveform of the video disc is supplied from an input terminal 1 to an AGC (automatic gain adjustment) circuit 2. In the AGC circuit 2, the sync chip of the video signal supplied from the input terminal 1 is set to a predetermined level. The output of the AGC circuit 2 is supplied to the high pass filter 3, and the horizontal synchronization separation circuit 4
is supplied to The high-pass filter 3 is, for example, a filter with a cutoff frequency of 2MHz. The output of the high pass filter 3 is supplied to the gate circuit 5.

The video signal supplied via the AGC circuit 2 includes an impulsive noise component N, as shown in FIG. 2A. High pass filter 3
The low-frequency components in this video signal are removed through the high-pass filter 3, and only the high-frequency components including the noise component N are supplied to the gate circuit 5.

The output of the horizontal sync separation circuit 4 is supplied to a monostable multivibrator 6. The monostable multivibrator 6 is triggered by the leading edge of the horizontal sync signal from the horizontal sync separation circuit 4, and the monostable multivibrator 6 outputs the pulse shown in FIG. 2C. This pulse is supplied from the monostable multivibrator 6 to the gate circuit 5.

The gate circuit 5 is a monostable multivibrator 6
It is opened and closed by the output pulse of The pulses formed by the monostable multivibrator 6 are generated at the sync tip Sy in the horizontal blanking section, as shown in FIG. 2C. Therefore, from the gate circuit 5, the sync chip in the horizontal blanking section is
The high frequency components of Sy are output. Since the level of the video signal is constant during the horizontal blanking section,
Only impulsive noise N is output from the gate circuit 5, as shown in FIG. 2D.

The output of gate circuit 5 is supplied to comparator 7. A predetermined reference voltage is supplied to the comparator 7 from a constant voltage generation circuit 8 . Comparator 7
As a result, the output of the gate circuit 5 which is higher than this reference voltage is outputted as a pulse and taken out from the output terminal 9, as shown in FIG. 2E. Impulsive noise is measured from this pulse output.

FIG. 3 shows another embodiment of the invention. 10
indicates an input terminal, and a composite color video signal is supplied from an input terminal 10 to a gate circuit 12 via a high-pass filter 11 and also to a horizontal synchronization separation circuit 13. The output of the horizontal sync separation circuit 13 is supplied to a monostable multivibrator 14. It is supplied to the output gate circuit 12 of the monostable multivibrator 14. As in the previous embodiment, the gate circuit 12 outputs the high-frequency component in the sync chip portion of the horizontal blanking section, and only the noise N is extracted from this output.

The output of gate circuit 12 is supplied to comparator 15. The output of the reference signal generation circuit 16 is supplied to the comparator 15 . In other embodiments, no AGC circuit is provided and the level of the input video signal is not kept constant. Therefore, the noise level output from the gate circuit 12 fluctuates. A video signal is supplied from the input terminal 10 to the reference signal generation circuit 16, and a reference signal corresponding to the level of this video signal is generated.
By comparing this reference signal and the output of the gate circuit 12 by the comparator 15, the noise detection level is kept constant. The output of comparator 15 is taken out from output terminal 17.

In this way, the impulsive noise detected by the pulse output is counted, for example, during a defined frame, and the disk is evaluated based on the accumulated number of pulses.

It is also possible to check the quality of the disc by displaying the number of noises on the display, as shown in FIG. 4, for example. FIG. 4 shows impulsive noise extracted as a pulse output, displayed line by line on the display 20. 21A is a display area for odd-numbered fields, and 21B is a display area for even-numbered fields.
In the display areas 21A and 21B, the number of noises is shown as a dot for each line number shown on the vertical axis, and
The cumulative values of a predetermined number of frames are displayed on the display 20 as shown by curves a and b.

For example, a video disc is one that is played back at a constant angular velocity, and as shown in FIG. If the pit is divided above, it can be seen from the display 20 where pit defects are concentrated. In other words, on the display screen shown in Fig. 4, the noise is concentrated in the center of the line, as shown by the noise curve a in odd-numbered fields, and is not generated much, as shown by the noise curve b in even-numbered fields. . In this case, on the disk 22, 23
It is estimated that pit defects are concentrated in the area 24 shown surrounded by the broken line in B.

Note that impulsive noise can be measured in the same way if the level of the video signal is constant. Therefore, a configuration may be adopted in which noise is measured at the front porch of the vertical blanking section and the horizontal blanking section.

〔Effect of the invention〕

According to the present invention, it is possible to accurately measure impulsive noise that cannot be corrected by the dropout compensation circuit of a disc playback player. Therefore, according to the present invention, it is possible to detect a pit defect when a part of the pit is missing.
It is possible to check the quality of video discs.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of one embodiment of this invention, FIG. 2 is a waveform diagram used to explain one embodiment of this invention, FIG. 3 is a block diagram of another embodiment of this invention, and FIG. 4 is a block diagram of another embodiment of this invention. A schematic diagram used to explain a method of displaying measurement results according to an embodiment of the present invention, and FIG. 6 and 7 are enlarged views showing pit defects and waveform diagrams of reproduced output. 1, 10: input terminal, 3, 11: high pass filter, 5, 12: gate circuit, 7, 15: comparator, 9, 17: output terminal.

Claims (1)

[Claims] 1. A playback signal from a disk on which a recording signal obtained by FM modulating an image information signal is recorded as a pit pattern is supplied, a signal in a frequency band of an impulsive noise component is selected from the playback signal, and a signal in a frequency band of an impulsive noise component is selected from the playback signal. 1. A noise measurement device, characterized in that a measurement signal having a reference signal value or higher contained in a signal in a frequency band is detected as noise.