JPS5928115B2 - Color video signal reproducing device - Google Patents

Description

[Detailed description of the invention] Color video signals are recorded on recording media such as magnetic tape.

When recording, the luminance signal is angularly modulated, for example, frequency modulated, and the carrier chrominance signal is frequency-converted to the lower frequency side and recorded.For playback, the luminance signal is demodulated, and the carrier chrominance signal is converted to its subcarrier. Regenerate the signal by converting the frequency so that it becomes the desired frequency, for example, the original frequency. I'm trying to get a number. In this case, a component with twice the frequency of the subcarrier converted to the lower frequency side by the nonlinear distortion of the tape system mixes into the reproduced luminance signal, and this component causes bright and dark dot interference on the reproduced screen. There is an inconvenience that occurs.

For this reason, the frequency of the subcarrier converted to the lower frequency side is made to have a special relationship with respect to the horizontal frequency. That is, for example, in the case of a PAL color video signal, its horizontal frequency is fH) the frequency of the subcarrier converted to the lower frequency side is fc), where n is a positive integer, 1, and the frequency is 2.
The component fc is made to be a matin offset, that is, 2fc (n-1) fH, therefore, fc (in-i) fH.

For example, n is selected to be 88. By the way, in a recording/playback device, the color video signal recorded or played back by the so-called tape conversion system contains a time error, and especially for the carrier color signal, this results in phase fluctuation, which causes color shift on the playback screen. Therefore, it is necessary to correct this.

Conventionally, a method (hereinafter referred to as the APC method) is known in which a signal for frequency conversion of a carrier color signal is formed based on a color subcarrier and thus a burst signal to correct this time axis fluctuation. . FIG. 1 shows the first example. During recording, a color video signal from an input terminal 10 is supplied to a low-pass filter 11 to extract a luminance signal, which is supplied to a frequency modulator 12, and from this. A frequency-modulated luminance signal is extracted, which is passed through high-pass filter 1.
From this, a luminance signal occupying the high frequency side as shown by Y in FIG. 2 is obtained, and this is supplied to the synthesizer 14.

On the other hand, the Gala H video signal from the input terminal 10 is supplied to the pan 1 bus filter 15, which changes the carrier frequency to f.
A carrier color signal of s is extracted and fed to a frequency converter 16.

Further, the conveyed color signal from the band pass filter 15 is supplied to the burst gate circuit 21 through the recording side contact R of the switch 3, from which a burst signal is extracted and supplied to the phase comparator 22. Further, an oscillation signal with a frequency of F8 from the reference oscillator 23 is supplied to this phase comparator 22 and compared with the burst signal, and the comparison error voltage is outputted to a variable frequency oscillator with an oscillation center frequency of Fc-(44-)FH. 24 and its oscillation frequency is controlled. The oscillation signal from the variable frequency oscillator 24 is supplied to the frequency converter 25, while the signal from the reference oscillator 23 is supplied to the frequency converter 25, whereby a signal having a frequency of Fc+Fs is obtained. Then, a signal whose frequency is Fc+Fs is supplied to the frequency converter 16 through the recording side contact R of the recording/reproduction changeover switch 4, and in this frequency converter 16, the carrier color signal from the bandpass filter 15 is converted into a signal whose subcarrier frequency is Fc, and this converted carrier color signal is supplied to the low-pass filter 17, from which the carrier color signal converted to the lower frequency side is sent to the synthesizer 14 as shown by C in FIG. The signal is supplied and combined with a frequency-modulated luminance signal occupying the high frequency side, and the combined signal is supplied to the head 1 through the recording side contact R of the recording/reproducing switch 2.

At the second time t, the reproduced signal from the head 1 passes through the reproduction side contact P of the switch 2 and is supplied to the Ipass filter 32 via the amplifier 31, from which a modulated luminance signal is obtained, which is sent to the limiter 33. Through demodulation circuit 3
4 and is demodulated, and this demodulated luminance signal is supplied to a synthesizer 35.

Further, the signal from the amplifier 31 is supplied to a low-pass filter 36 to obtain a carrier color signal in which the frequency of the subcarrier is converted to the lower frequency side, and this is supplied to a frequency converter 37. Then, the frequency from the frequency converter 25 is Fc
The +Fs signal is supplied to the frequency converter 37 through the reproduction side contact P of the switch 4, and thereby the carrier color signal from the low-pass filter 36 is frequency-converted so that the frequency of its subcarrier becomes the original frequency Fs. The returned carrier color signal is supplied to the combiner 35 and combined with the demodulated luminance signal, and the combined video signal is sent to the output terminal 38.
taken out from In this case, the carrier color signal returned from the frequency converter 37 is supplied to the burst gate circuit 21 through the reproduction side contact P of the switch 3, and the oscillation frequency of the variable frequency oscillator 24 is changed in the same manner as during recording. is controlled, time axis fluctuations in the reproduced carrier color signal are compensated for, and a carrier color signal without phase error is obtained.

However, in this APC method, since the time axis fluctuation is corrected using the burst signal as a reference, correction is not performed in the vertical planking section where there is no burst signal. So A
Considering the follow-up characteristics of the PC, there is a possibility that the correction by APC will not be completed immediately immediately after the blanking interval, and color unevenness will appear at the top of the screen. This can be corrected to some extent by adjusting the receiver, but when a tape sequentially duplicated using this APC TR is played back by an APC VTR, it can no longer be corrected by adjusting the receiver. Therefore, as a method to improve this drawback, a method (referred to as AFC method) in which a frequency conversion signal is formed based on a horizontal synchronization signal to correct time axis fluctuations.

) was considered. Figure 3 shows a V using the AFC method.
The reproduction system of the TR is one color 1, and the reproduction color video signal system is the same as in the case of the above-mentioned APC system, and the reproduction color video signal from the head 5 is connected to the amplifier 41 - high pass filter 42 - limiter 43 - demodulation circuit 44 line. through demodulation circuit 4
4, the luminance signal is demodulated, while the amplifier 41
- The carrier color signal is supplied to the frequency converter 47 through the low-pass filter 46 - frequency converter 47 line, and the carrier color signal converted to the lower frequency side is frequency-converted so that the frequency of its subcarrier becomes the original frequency. .

The frequency conversion signal in this case is formed as follows.

That is, the demodulated luminance signal from the demodulation circuit 44 is supplied to the synchronization signal separation circuit 51, from which a horizontal synchronization signal is obtained, which is supplied to the phase comparator 52, and the frequency from the variable frequency oscillator 53 is horizontally A signal with an odd number, for example, 351 times the frequency FH, is supplied to the frequency divider 54, from which a signal with the frequency FH is obtained, and this signal is supplied to the phase comparator 52, where it is The phase is compared with the horizontal synchronizing signal, and the comparison output signal is supplied to the variable frequency oscillator 53 to control its oscillation frequency.

The oscillation signal of the variable frequency oscillator 53 is then supplied to the frequency divider 55, from which a signal of frequency FA= is obtained, which is supplied to the frequency converter 56, and the reference oscillator 5? A signal having a frequency of Fs is supplied to the frequency converter 56, from which a signal having a frequency of FB-FAffs is obtained, and this is supplied to the frequency converter 47 as a signal for frequency conversion of the carrier color signal.

Then, the carrier color signal from the frequency converter 47 whose subcarrier frequency has been returned to its original frequency and the demodulated luminance signal are combined by the combiner 45, and the combined signal is taken out from the output terminal 48. .

Although the recording system is omitted for the sake of simplicity, it is almost the same as the APC type VTR shown in Fig. 1, and includes a frequency converter 5.
The signal of frequency FB from 6 is used as a signal for frequency conversion of the carrier color signal, and the carrier color signal is recorded with its subcarrier frequency converted to the lower frequency side, that is, Fc. By the way, as mentioned above, VTRs employing the APC system are already on the market, and there are cases where a tape recorded by this APC system VTR is played back by an AFC system VTR.

However, if a first slave tape is created from a tape obtained by sequential duplication with an APC VTR, for example a master tape, and a second slave tape obtained by duplication from this first slave tape is produced by an AFC VTR. When playing back, the time error is not completely removed, but it has the disadvantage that it remains.
To explain this below, among the time axis fluctuations, the time axis fluctuations included in the luminance signal system and therefore the horizontal synchronization signal, that is, the frequency fluctuations of the horizontal synchronization signal, are EH, and the frequency fluctuations of the subcarrier are Ec. , the EH at the time of recording when obtaining the first slave tape from the master tape is αIR,
．． Ec is βIR) EH when playing the first slave tape is αIP) EC is βIP) EH during recording when obtaining the second slave tape from the first slave tape is α
2R-Ec. β2R, EH when playing the second scrape tape, α2P, . When Ec is β2P), in the signal recorded on the second slave tape, the frequency FH2 of the horizontal synchronizing signal is converted to the lower frequency side, and the frequency Fc of the subcarrier is β, and R and βIP are the first This is because it is removed when the slave tape is played back.

When this second slave tape is played back by an AFC type VTR, the carrier color signal will be affected by the variation β during playback.
2P is added, the subcarrier frequency FcJ2 of the carrier color signal extracted from the low-pass filter 46 becomes,
Therefore, by substituting equation (2), we get:

Also, considering the frequency conversion signal from the frequency divider 55,
The frequency FA is therefore obtained by substituting equation (1).

Therefore, the frequency of the signal from the frequency converter 56 is as follows.

Therefore, the frequency FO of the signal from the frequency converter 4T is as follows.

here Because it is becomes.

In other words, the time error during recording and playback of the first slave tape remains as the playback output of this VTR, and when this is supplied to the monitor receiver, the phase of the continuous wave signal for color demodulation is determined to be normal. However, it has the disadvantage of causing color shift on the monitor screen.

In view of the above-mentioned points, the present invention is designed to prevent the above-mentioned drawbacks from occurring even when a tape copied by an APC-system 1f VTR is played back in a playback device that employs the AFC system. be. Hereinafter, an embodiment of a color video signal reproducing apparatus according to the present invention will be described with reference to the drawings. FIG. 4 shows an example of this. In this example, the carrier color signal whose frequency has been converted to the lower frequency side from the low-pass filter 46 is supplied to the burst gate circuit 61, from which a burst signal with a frequency of Fc2 is extracted. This is supplied to the frequency converter 62, and the oscillation signal with the frequency Fs from the reference oscillator 63 is supplied to this second frequency converter 62, from which a signal with the frequency FD-Fs+Fd2 is obtained, which is the frequency A converter 64 is provided.

Then, in the same manner as in the conventional example shown in FIG. 3, a signal whose frequency is FA obtained from the frequency divider 55 is supplied to the frequency converter 64, and from this, an intermittent signal whose frequency is FE=FD-FA is obtained. This is supplied to the oscillator 65, from which a continuous wave signal with an intermediate phase is obtained after the bust signals whose phases differ from each other by 9σ every horizontal interval, and this is supplied to the frequency converter 66. The signal from the frequency converter 55 is supplied to this frequency converter 66, from which a signal with a frequency of F, -FE+FA is obtained, and this is supplied to the frequency converter 47. When the second slave tape produced by an APC VTR is played back using the apparatus of the present invention configured as described above, the frequency F of the output signal of the frequency converter 62 changes.

), and the frequency FE of the output signal of the frequency converter 64 is fE-FO-FA-Fs+FO+β2R+β2
It becomes P-(44-100).

Here Fc=(44--18)FH Because it is, becomes.

Therefore, the frequency FF of the output signal of the frequency converter 66 is the frequency F of the subcarrier extracted from the frequency converter 47.

becomes, and by substituting equation (4) into this, we get becomes.

Therefore, the equation (9) is satisfied, and the time axis variation included in the carrier color signal is completely removed.

FIG. 5 shows another example of the device of the present invention, in which:
A signal whose frequency is F8 from the reference oscillator 70 is supplied to the frequency converter 71, and a signal whose frequency is F8 from the frequency divider 55 is supplied to the frequency converter 71.
is supplied to this frequency converter 71, from which a signal with a frequency of FG-Fs 10FA is obtained, which is supplied to the frequency converter 72, and the carrier chrominance signal extracted from the 1 Calo-pass filter 46 is obtained. A carrier color signal whose subcarrier frequency is FI-FG-FC is obtained from this frequency converter 72.

Then, this carrier color signal is supplied to the frequency converter 73 and also to the burst gate circuit 74, from which a burst signal of frequency f1 is obtained, which is supplied to the oscillator 75, and from this, the same as above. A continuous wave signal with a frequency of FI is obtained with a constant phase of
is supplied to the frequency converter 76, from which a signal having a frequency of FJ-FI+FA is obtained, and this is supplied to the frequency converter 73. Then, from this frequency converter 73, the frequency of the subcarrier is changed to FK-FJ-FI-FA.
A carrier color signal converted to
From this, a signal with a frequency of 4 is obtained. That is, the frequency converter 77 obtains a carrier color signal in which the frequency of the subcarrier is returned to its original value and does not include the time error included in the reproduced color video signal. Therefore, even if the reproduced tape is the second slave tape mentioned above, a carrier color signal containing no time error can be obtained from the frequency converter 77, and there is no drawback as in the prior art.

} Even when a tape copied by a conventional AFC type VTR as shown in FIG. It is something that becomes something.

As described above, according to the device of the present invention, the conventional AFC
An APC type VTR that has the advantages of an APC type VTR.
Even when playing back a tape that has been duplicated, there are no problems like in the past.

In addition, the oscillation frequency of the reference oscillator in the system that forms the frequency conversion signal may differ in temperature characteristics during recording and playback, and in conventional AFC type VTRs, the frequency conversion signal is Since it is formed based only on the horizontal synchronization signal regardless of the horizontal synchronization signal, when making a duplicate tape, the difference between the oscillation frequency of the reference oscillator on the playback side and that at the time of recording is added and recorded each time it is duplicated. Therefore, it is necessary, for example, to control the reference oscillator with the subcarrier in the Gala H resolution signal to be recorded, or to correct the frequency of the reference oscillator based on the subcarrier returned to the original state during playback. Ta. However, in a VTR that has the generation device according to the present invention and uses a system for forming a frequency conversion signal for both recording and reproduction, the frequency conversion signal is a horizontal synchronization signal associated with a subcarrier. It is formed based on
Even if the oscillation frequency of the reference oscillator changes between recording and playback, the difference is compensated for by a system that forms a frequency conversion signal and a frequency converter that returns the subcarrier frequency of the carrier color signal to its original frequency. will be removed. Therefore, there is no need to provide correction means as in the prior art. Note that although the above example was explained using a PAL color video signal as an example, the NT
The present invention can be similarly applied to color video signals of the SC system.

[Brief explanation of drawings]

Figure 1 is a system diagram of an example of a conventional APC type VTR, Figure 2 is a diagram showing the frequency spectrum of a gala->central image signal recorded on the VTR, and Figure 3 is a diagram of a conventional AFC type VTR.
Fig. 4 is a system diagram of →q of the regeneration system of
FIG. 5 is another system diagram of the device of the present invention. 5 is a magnetic unit, 41 is an amplifier, 42 is a high-pass filter, 43 is a limiter, 44 is a demodulation circuit, 46 is a low-pass filter, 51 is a synchronous separation circuit, 52 is a phase comparator,
53 is a variable frequency oscillator, 54 and 55 are frequency dividers, 47
, 62, 64, 66 and 71, 72, 73, 76, 7
7 is a frequency converter, 63 and 70 are reference oscillators, 61 and 74 are burst gate circuits, and 65 and 75 are oscillators.

Claims (1)

[Claims] 1. A signal for frequency conversion of the carrier color signal is formed based on the color subcarrier of the video signal, and a recording medium on which a color video signal including the carrier color signal frequency-converted using this signal is recorded is duplicated N times, A signal for frequency conversion of the carrier color signal is formed from the copy recording medium using the horizontal synchronization signal of the video signal as a reference, and when reproduced by a device that converts the frequency of the carrier color signal using this signal and reproduces the N- A color video signal reproducing device characterized in that means for canceling a time error included in a horizontal synchronizing signal in a reproduced video signal of a once-copied recording medium is added to the color signal frequency conversion circuit.