JPS6172485A - Video signal recording regeneration device - Google Patents

Abstract

PURPOSE:To compensate an information included in a lost signal part when the signal level of a signal to be recorded exceeds a predetermined white clip level and a predetermined dark clip level by providing a compensating circuit 26. CONSTITUTION:The output signal of an LPF21 is fed to a first deemphasis circuit 22 and a second de-emphasis circuit 27 of a compensating circuit 26, by a subtractor 28, an output signal of the circuit 22 is subtracted by an output of the circuit 27 and fed to the 1st and 2nd limiters 29, 30. The output of a limiter 29 is fed to the 1st LPF31 to obtain a signal component substantially similar to a lost signal component exceeding a predetermined while clip level. The output of the limiter 30 is fed to a LDP32 to obtain a signal component substantially similar to a lost signal portion exceeding a predetermined dark clip level. The output signal of the circuit 22 and the respective output signals of the LPF 31, 32 are added by an adder 33 and outputted to a clip-spinning 23.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a video signal recording and reproducing device.

(Prior Art) FIG. 5 is a block diagram of a conventional luminance signal system of a video signal recording and reproducing apparatus.

As shown in the figure, on the recording side of the luminance signal system, the video signal input from input terminal 1 is filtered through a low-pass filter (LPF).
-1) 2, where the luminance signal is taken out and A
A GC circuit 3 automatically adjusts the signal level to a predetermined signal level, and a pre-emphasis circuit 4 emphasizes the high frequency range of the signal. After that, this signal is applied to the white clip circuit/dark clip circuit 5, where the tips of spikes that occur at the rising and falling parts of the signal are clipped, and then the tip of the synchronization signal is fixed to a certain voltage in the clamp circuit 6. It is clamped to FM'[ by FM modulator 7,
After the high-frequency part of the signal is extracted by the IPF-1) 8, the recording amplifier 9 adjusts the optimal recording current, and this recording current is passed through the rotary transformer 10 to the two video heads 11 and 12. The signal is supplied to the magnetic recording medium 13, and is recorded on a magnetic recording medium (eg, magnetic tape) 13 here.

On the reproduction side of the luminance signal system, reproduction signals reproduced from the magnetic recording medium 13 by two video heads 11.12 are supplied to two systems of reproduction preamplifiers 14.15 via a rotary transformer 10. After being amplified here and converted into a continuous reproduction signal by a switcher 16, it is supplied to a high-pass filter (HPF-2) 17, where the low-frequency variable Mk signal is removed from the reproduction signal and a drop signal is generated. Out compensation port M (D.

C) 18, compensation is made when dropout occurs, the limiter 19 removes the signal fluctuation, the FM demodulator 20 demodulates the FM, and the low-pass filter (LPF-2>2
1, the carrier component of the signal is removed, the de-emphasis circuit 22 attenuates the high frequency range of the signal, and the crisp-spinning 2
After noise reduction is performed in step 3 and amplified by an output amplifier 24, a reproduced signal is outputted from an output terminal 25.

Emphasis ff1 of the above-mentioned preen 7-door sys circuit 4
X is determined to be x-4 in the VH3 video tape recorder (VTR) standard.

In addition, the white clip level (hereinafter referred to as W clip level) and dark clip level (hereinafter referred to as D clip level) of the white clip circuit/dark clip circuit (hereinafter referred to as WD Tsuk9f circuit) 5 is as follows.
In a VH8 system VTR, the W clip level is 160% from the sync tip to the self-locking, and the D clip level is -40% from the sync tip to the black side (however, from the sync tip to the white level is 100%). , each determined.

Therefore, the signal from the pre-emphasis circuit 4 having a level exceeding the above-mentioned W(D) clip level is
When the signal is supplied to the clipping circuit 5, the signal portion exceeding the W(D) clip level is cut off, and the information present in the cut signal portion is also lost.

If the de-emphasis circuit 21's de-emphasis amount is X=4, it is the same as the emphasis of the de-emphasis circuit ff14, but in the WD clip circuit 5,
Since the signal portion exceeding the W(D) clip level has already been removed, the information in this portion cannot be reproduced, and therefore the output signal of the pre-emphasis circuit 4 cannot be faithfully reproduced, resulting in violets. .

When this smear occurs, for example, when a reproduced image has a black stripe and a white stripe adjacent to each other, a gray stripe will appear between the two, resulting in a defect in which the outline of the reproduced image will not be sharp. It will happen.

Therefore, the value of X of the de-emphasis circuit 22 is set to be smaller than the value of X of the de-emphasis circuit 4 (0<X<4).
This prevents smear from occurring even when the signal applied to the WD check circuit 5 has a large amplitude (white (black) level signal).

However, since the value of X of the de-emphasis circuit 22 is smaller than the value of (a signal that does not reach the white (black) level), the amount of damping is small, so the waveform cannot be faithfully reproduced, and the reproduced signal has a waveform with a slight overshoot. There is a drawback.

(Problems to be Solved by the Invention) The luminance signal system in the video recording and reproducing apparatus described above has the drawback that it cannot faithfully reproduce the signal to be recorded.

Especially when the signal level to be recorded is white (dark).
If the level exceeds the white (dark) clip level, the part of the signal that exceeds the white (dark) clip level will be cut off, so the information there will be lost, and when this signal is recorded and played back, it will not appear as a smear. This has the disadvantage that good reproduced images cannot be obtained.

(Means for Solving the Problem) The first de-emphasis circuit is connected in parallel to a first de-emphasis circuit having a de-emphasis amount that is almost the same as the pre-emphasis m of the pre-emphasis circuit, and the first 141271
a second de-emphasis circuit with a de-emphasis amount smaller than the de-emphasis amount of the 92 circuit, and a subtracter that subtracts the output signal of the first de-emphasis circuit from the output signal of the second de-emphasis circuit; The signal portion that is missing beyond the predetermined white clip level and approximately '1
a first limiter and a first low-pass filter for obtaining similar signal components from the output signal of the subtractor; and a first limiter and a first low-pass filter for obtaining similar signal components from the subtracter output signal; The second to get from the signal
a limiter and a second low pass filter, and a first 141
27. A video recording and reproducing apparatus having a compensation circuit including an adder for adding each output signal of the first and second low-pass filters to the output signal of the 27192 circuit.

(Function) As shown in Figure 1, when the signal level of the signal to be recorded exceeds a predetermined white clip level and a predetermined dark clip level, the compensation circuit detects the signal that is missing beyond these levels. Compensate for the information contained in the signal portion.

(Example) FIG. 1 is a diagram that best represents the features of the present invention.

FIG. 2 is a block diagram showing one embodiment of the compensation circuit which is a main part of the device of the present invention and its peripheral parts.

FIG. 3 is a timing chart showing input and output waveforms of each part of the compensation circuit 26.

Items with the same configuration as those described above are given the same reference numerals.
The explanation will be omitted.

The compensation circuit 26, which is the main part of the present invention, is as described below.
When the level of the signal to be recorded exceeds the W(D) clip level, this function is used to compensate for the information contained in the signal portion that was cut beyond the clip level when de-emphasizing it. belongs to.

The compensation circuit 26 is connected in parallel to the de-emphasis circuit (first de-emphasis circuit) 22 described above.

The compensation circuit 26 includes a de-emphasis circuit (second 141
27192 circuit) 27, subtracter 28, first and second limiters 29.30, first and second low-pass filters (
(LPF) 31, 32, and an adder 33.

The input terminal of the compensation circuit 26 (de-emphasis circuit 27) is connected to the output terminal of the low-pass filter (LPF-2>21) and the input terminal of the de-emphasis circuit 22.The output of the compensation circuit 26 (adder 33) The terminal is connected to the input terminal of the crisp-spinning 23. The output terminal of the de-emphasis circuit 22 is connected to the addition input terminal of the addition PJ 33 and the subtraction input terminal of the subtracter 28, respectively.

The output terminal of the de-emphasis circuit 27 is connected to the input terminal of the R reducer 28. The output terminal of the subtracter 28 is connected to the input terminals of the first J5 and the second limiter 29, 30, respectively.

The output terminals of the first and second limiters 29.30 are connected to the first
and the input terminals of the second low-pass filters 31 and 32, respectively.

The output terminals of the first and second low-pass filters 31 , 32 are respectively connected to two summing input terminals of the adder 33 .

The de-emphasis amount of the 14127192 circuit 22 connected in parallel to the compensation circuit 26 is X-4.

The de-emphasis ratio of the de-emphasis circuit 27 in the compensation circuit 26 satisfies O≦X<4 (the appropriate value of R is 2), and its value 1n can be varied as appropriate.

Next, the operation of the compensation circuit 26 having the above configuration will be explained.

The output signal of the low-pass filter 21 (waveform shown in FIG. 3(A)) is supplied to a de-emphasis circuit 22.27.

The output signal of the de-emphasis circuit 22 (the waveform shown in FIG. 2B) does not have the ideal shape a, as the rising part is shown by the broken line, but the tip is missing, as shown by the solid line. This is the waveform. Therefore, the information in this missing part is lost.

In other words, when the output signal of the de-emphasis circuit 22 is outputted from the output terminal 25 via the adder/stopper 33, crispening 23, and output amplifier 24, smear may occur.
The result is a conventional signal with the aforementioned drawback of poor S/N ratio (at this time, the adder 3
It is assumed that no other signal is applied to 3).

However, the present invention does not output only the output signal of the de-emphasis circuit 22 to the outside from the output terminal 25; It has a configuration for outputting a signal obtained by modifying the output signal to the outside from the output terminal 25.

Therefore, the present invention has 14127122 circuits 22
As described later, the signal level added to the output signal of
By appropriately varying the de-emphasis circuit 22
It is possible to compensate for the missing portion of the output signal.

The subtracter 28 receives the output signal of the 14127122 circuit 27 (
From the waveform shown in the same figure (C), de-emphasis circuit 2
2 output signal (waveform shown in FIG.
The waveform shown in (D)) is output.

FIG. 4 shows the pre-emphasis characteristics in the subtracter 28 when the de-emphasis amount X of the de-emphasis cycle 1B27 is varied (X-1, 2, 3, 4).

In other words, the de-emphasis circuit 27 and the subtracter 28 form the characteristics of a high-pass filter.

As shown in the figure, as X of the de-emphasis circuit 27 is decreased, more of the high frequency components of the output signal are passed through the subtracter 28 output, which is the same as when the pre-emphasis value is increased. become a state.

However, although more of the high-frequency signal portion of the signal supplied from the de-emphasis circuit 27 to the subtracter 28 can be extracted from the subtracter 28, noise is also extracted at the same time, so the output is noisy. To increase.

Therefore, it is necessary to select the optimum value for the de-emphasis amount of the eye emphasis circuit 27.

According to experiments, it has been found that a suitable value for X in the de-emphasis circuit 27 is 2 to 3.

The output signal from the first limiter 29 (waveform shown in (E) in the same figure) is applied to the first low-pass filter 31, ) is applied to the adder 33.

The output signal from the second limiter 30 (the waveform shown in (G) in the figure) is applied to the second low-pass filter 32, and the output signal from the second low-pass filter 32 (the waveform shown in ) is applied to the adder 33.

The first limiter 29 is for limiting the signal portion on the white side of the output signal of the subtracter 28, and when a 100% white level signal is applied from the synchronization tip to the white side, the subtracter 28 is the output signal of It has a limiter level that can cut out the noise at the tip of the upper limit of the differential waveform (portion C in FIG. 3(C)).

For example, P−P 1 of the maximum output signal level of the subtracter 28
90% of ull8! degree is the upper limiter level,
The lower limiter level is determined to have a width of about 10% of the P-P value (limiter level width A shown in FIG. 3(E)).

The second limiter 30 is for limiting the 4n part on the black side of the output signal of the subtracter 28, and is for limiting the noise (similar to The limiter level is such that it can cut the D part of the waveform in Figure (C).

For example, the upper limiter level is 50% F1 degree of the P-P value of the maximum output signal level of the subtracter 28, and the lower limiter level is determined with a width of about 10% of the P-P value ( Limiter level width B) shown in the same figure (G)
.

In short, it is sufficient to extract frequency components from the outputs of the first and second limiters 29 and 30 that can compensate for the missing information signal portion in the output signal of the de-emphasis circuit 22.

In other words, since it is the rising part of the signal with the waveform shown in the same figure (B), we need to calculate the harmonic components of the signal that should be present in this missing part so that it becomes the rising edge part a without missing the tip. It is sufficient to supplement the waveform shown in FIG.

The first low-pass filter 31 (second low-pass filter 32) removes unnecessary noise from the output signal from the first limiter 29 (second limiter 30).

The adder 33 adds the output signals from the first and second low-pass filters 31 and 32 to the output signal from the de-emphasis circuit 22, and adds the output signal (
The waveform shown in (1) of the same figure) is output.

Since the waveform shown in FIG. 3(I) is a signal without any omission in the rising portion e at the leading end, a good reproduced signal free from smear can be supplied to the subsequent crispening 23.

Furthermore, since the value of X of the de-emphasis circuit 22 on the reproduction side is almost the same as the value of The waveform can be faithfully reproduced even when the signal does not reach the black (black) level.

(Effects of the Invention) As described above, in the video recording and reproducing apparatus according to the present invention, the signal to be recorded can always be faithfully reproduced, regardless of the signal level of the signal.

In other words, even when the signal level of the signal to be recorded exceeds the white (dark) clip level, the missing signal portion can be well compensated for, so no smear will occur, and Even when the signal level of the signal to be recorded does not exceed the white (dark) clip level, the de-emphasis level of the first de-emphasis circuit on the playback side is the de-emphasis level of the pre-emphasis circuit on the recording side. Since it is almost the same as a suspension, even this small signal can be reproduced with a good S/N ratio.

[Brief explanation of the drawing]

FIG. 1 is a diagram that best represents the features of the present invention, FIG. 2 is a block diagram showing an embodiment of the compensation circuit which is the main part of the device of the present invention, and its peripheral parts, and FIG. 3 is a diagram showing the compensation circuit. 4 is a diagram showing the output characteristics of the subtracter 28, and FIG. 5 is a block diagram of a conventional luminance signal system of a video signal recording/reproducing apparatus. 22.27... De-emphasis circuit, 26... Compensation circuit, 28... Subtractor, 29.30... First and second limiter, 31.32... First J5 and second
low-pass filter, 33...adder. Patent Applicant: Japan Victor Co., Ltd. Representative: Humanity
-1”-CF)-ri111(H)-12f

Claims (1)

[Claims] When the signal level of a signal to be recorded exceeds a predetermined white clip level and a predetermined dark clip level, a circuit for compensating for information contained in a signal portion missing beyond these levels, connected in parallel to a first de-emphasis circuit having a de-emphasis amount that is substantially the same as the pre-emphasis amount of the pre-emphasis circuit, and having a de-emphasis amount that is smaller than the de-emphasis amount of the first de-emphasis circuit. a second de-emphasis circuit having a subtracter that subtracts the output signal of the first de-emphasis circuit from the output signal of the second de-emphasis circuit; a first signal component for obtaining a signal component from the output signal of the subtracter;
a limiter and a first low-pass filter, and a second limiter and a second low-pass filter for obtaining from the output signal of the subtracter a signal component substantially similar to the signal portion missing beyond the dark clip level. , and an adder for adding each output signal of the first and second low-pass filters to the output signal of the first de-emphasis circuit.