JPS599487Y2 - Video signal processing circuit - Google Patents

Description

[Detailed description of the invention] The present invention relates to a video signal processing circuit used in a recording/reproducing device such as a VTR, and in particular, when recording and reproducing a color television signal into which a VIR signal is inserted, This is to prevent the circuit from malfunctioning.

In a transmission system based on the conventional NTSC color television system, a color television signal with a VIR signal inserted may be transmitted from a broadcasting station.

As shown in FIG. 1, the VIR signal 1 is a flesh-colored carrier color signal inserted in the 19th horizontal scanning period H19 of each vertical blanking period, and has a subcarrier frequency of 3.58 MHz. , its phase, amplitude, and DC level (gray level) E1 all correspond to standard skin color.

In the figure, 2) is a horizontal synchronizing signal, and 3 is a burst signal.

A receiver that receives a color television signal into which such a VIR signal is inserted is provided with an automatic skin tone adjustment circuit.

In this automatic skin tone adjustment circuit, when the carrier color signal in the received signal has phase distortion and amplitude distortion, the VIR signal also has similar phase distortion and amplitude distortion. The shift and amplitude change are detected, and the phase distortion and amplitude distortion of the carrier color signal are corrected accordingly.

Then, when a color television signal into which a VIR signal is inserted is recorded on a VTR and the reproduced signal is applied to a receiver equipped with the above-mentioned automatic skin tone adjustment circuit, the automatic skin tone adjustment circuit is operated by the VIR signal in the reproduced signal. However, the following inconveniences may occur.

One such case is when a comb filter having a 1H delay circuit is provided in the color signal system of the recording or reproducing system of a VTR.

Comb-shaped filters are provided in the color signal system of the recording system, such as a Y-shaped comb-shaped filter for separating a luminance signal from a color video signal, and a C-shaped comb-shaped filter for separating a carrier color signal.
Some are equipped with a comb-shaped filter.

In this case, the original carrier color signal is S. If this is delayed by lH and is designated as S1, then the carrier color signal output from the C-shaped comb filter is obtained.

Therefore, when a VIR signal is applied to this C-shaped comb filter, its output signal has the amplitude of the original VIR signal.

Therefore, if the automatic skin color adjustment circuit is controlled by this signal, correct skin color adjustment will not be possible.

Next, as a system in which a comb-shaped filter is provided in the color signal system of the reproduction system, there is a system based on a high-density recording and reproduction method previously proposed by the present applicant.

In a VTR using this method, two
The rotating magnetic heads A and H are used to perform recording and reproduction alternately for each field.

When recording, the luminance signal is FM modulated using a high frequency filter, and the carrier color signal is frequency-converted to the lower frequency side.

At this time, the carrier color signal SA recorded by head A is converted to frequency fA, the carrier color signal SB recorded by head B is converted to frequency fB, and fA and f8 are frequency interleaved with each other. choose a relationship.

During reproduction, the carrier color signal SA reproduced by head A is further converted to fs+fA (fs: subcarrier frequency...
...3.58 MHz), and the carrier color signal SB reproduced by the head B is further frequency-converted to fs+fB.

At the same time, the reproduced luminance signal is FM demodulated.

And these two frequency-converted signals SA, SB
By adding this to a C-shaped comb filter, a carrier color signal with crosstalk removed can be obtained from this filter.

Furthermore, since the luminance signal has a high frequency, crosstalk can be removed by so-called azimuth loss.

According to this method, crosstalk can be removed even when guard bands are not provided between video tracks, so high-density recording can be achieved.

Even in this method, if the frequency-converted VIR signal is applied to the C-type comb filter, its output will be the original VIR signal.
The signal will be different from the IR signal, and therefore it will not be possible to perform correct skin color adjustment.

Next, a similar problem may occur when there is no comb filter.

That is, in the reproduction system of the VTR, the frequency or phase of the frequency conversion signal is controlled based on the reproduced horizontal synchronization signal and the reproduced burst signal in order to correct the time error of the reproduced carrier color signal. An AFC circuit or an APC circuit is provided.

During a period when these AFC circuits or APC circuits are not responding sufficiently, the phase of the VIR signal in the reproduced signal may not correspond to the phase of the carrier color signal, and in such cases, the above-mentioned comb shape A similar problem arises when there is a filter.

In order to solve the above problem, VI
It is conceivable that the 19th horizontal period in which the R signal is present is extracted.

However, if you do this, the burst signals during that period will also be extracted all at once, so the rise of circuits operated by burst signals, such as the ACC circuit and color killer circuit of the receiver, will be delayed and the beginning of the effective scanning period on the screen will be delayed. Color disturbance will occur in this area.

The present invention is intended to solve the above-mentioned problem, and is designed to adjust the clip level of the recording or playback clip circuit to the VI
By switching during a horizontal scanning period in which the R signal is present, the output during this period is substantially not obtained.

Embodiments of the present invention will be described below with reference to the drawings.

The automatic skin tone adjustment circuit described above is generally forced to operate by the DC level of the VIR signal, i.e., the first
The DC level of VIR signal 1 shown in the figure is at a predetermined level E1.
When this is detected, automatic skin tone adjustment is performed.

On the other hand, the brightness signal system in the recording system and reproduction system of a VTR is provided with a clip circuit to prevent overmodulation due to an excessive level of the input signal.

That is, during recording, the luminance signal is FM modulated, but at this time, for example, when recording a signal from a television camera, a signal with a very high video level may be added.

When such a high-level signal is subjected to FM modulation, it becomes overmodulated, and this portion causes so-called buzz noise.

Also, during playback, the FM-demodulated luminance signal and the frequency-converted carrier color signal are transmitted at the free channel frequency of the receiver.
After being M-modulated, it is applied to the receiver.

Even during this FM modulation, overmodulation occurs if the level of the reproduced signal is extremely high.

The above-mentioned clipping circuit is provided to prevent such overmodulation, and by clipping the luminance signal at a predetermined level before FM modulating the luminance signal during recording or reproduction, the excessive level signal is transferred to the FM modulation circuit. This is to prevent it from being added to.

This embodiment utilizes the clipping circuit described above, detects the horizontal period in which the VIR signal is inserted, and clips the VIR signal by changing the clippinder level of the clipping circuit during that period, thereby operating the automatic skin tone adjustment circuit. I tried not to do that.

FIG. 2 shows an embodiment in which a playback clip circuit is used.

In FIG. 2, signals recorded on a magnetic tape are alternately reproduced field by field by rotary heads A and B.

This switching between the heads A and B is performed by switching the switch circuit 5 using a pulse of 60 l obtained for each field from a pulse generator 4 provided in the head drum of the VTR.

The reproduced signal passes through an amplifier 6, has its amplitude limited by a limiter 7, is further applied to a dropout compensation circuit 8 to compensate for dropouts, and is then demodulated into a luminance signal by a demodulation circuit.

Note that a carrier color signal is separated from the dropout-compensated signal, and this carrier color signal is frequency-converted in the subsequent chroma system as described above.

The demodulated luminance signal undergoes frequency characteristic correction in an emphasis circuit 10, and is further applied to a clamp circuit 11 after having its petal level clamped.

This clip circuit 12 has its clipping levels set by the switch circuit 13 to VA, VB (VA <
VB).

On the other hand, the pulse from pulse generator 4 has a time constant of 18
H is forced to trigger the mono multi 14, and the fall of the output Q1 of this mono multi 14 triggers the mono multi 1
5 is threatened to be triggered.

The output Q2 of the monomulti 15 causes the switch circuit 13 to be switched.

In the above structure, the switch circuit 13 is normally closed to the contact b side, and the clip pin level is VB.

In this state, if a pulse as shown in FIG. 3B is obtained from the pulse generator 4 for each field, the monomulti 1
4 is triggered: An output Q1 as shown in FIG. 3C is obtained from this monomulti 14.

When the monomulti 15 is triggered by the fall of this output Q1, an output Q2 as shown in FIG. can be switched to

As a result, the clip level of the 19th horizontal scanning period H'l9 of the reproduced video signal shown in FIG. 3A changes from ■8 to V.
It will be lowered to 100%.

Therefore, the DC level E1 of the VIR signal 1 inserted into this H19 is clipped at level 4.

Next, when the output Q2 becomes low level again, the switch circuit 13
is switched to the contact b side again, and the clip level becomes v8 again.

As a result, the excessive level of the video signal 16 during the effective scanning period is clipped at this level VB.

As a result of the above, the output terminal 17 of the clip circuit 12 has VI
The R signal is clipped at level 4 and the video signal 1
An output signal is obtained in which the excessive level of 6 is clipped at level 8.

This output signal is subjected to FM modulation together with the carrier color signal after noise is removed by a noise canceler circuit in the subsequent stage, but since the video signal is clipped, no excessive modulation occurs, and the VIR signal is not clipped. Therefore, the automatic skin tone adjustment circuit of the receiver will not malfunction.

Also, since the burst signal 3 of H19 remains, the VTR
It is also possible to prevent malfunctions of the AFC circuit and APC circuit of the camera, and the ACC circuit and color killer circuit of the receiver.

The above is a case where a clip circuit is used in the reproduction system, but a clip circuit in the recording system may also be used.

The present invention switches the clipping level of a circuit that clips a predetermined level or higher of a video signal to be recorded or reproduced between the predetermined level and another level, and also controls the vertical blanking period of the video signal. A circuit for detecting a predetermined horizontal scanning period is provided, and by switching the clip level to the other level based on the detection signal of this detection circuit, the clipping circuit detects the white level in the predetermined horizontal scanning period. On the other hand, the present invention relates to a video signal processing circuit characterized in that a video signal having a level higher than the above-mentioned other level is substantially not obtained.

Therefore, according to the present invention, for example, a color television signal into which a VIR signal is inserted is recorded on a VTR or the like, and the reproduced signal is supplied to a receiver equipped with an automatic skin tone adjustment circuit operated by the VIR signal. In some cases, traditionally VTR
By effectively utilizing the clip circuit provided in the VTR, it is possible to prevent the automatic skin tone adjustment circuit, other circuits of the receiver, and circuits inside the VTR from malfunctioning.

[Brief explanation of drawings]

FIG. 1 is a waveform diagram for explaining the VIR signal, FIG. 2 is a circuit diagram showing an embodiment of the present invention, and FIG. 3 is a time chart of FIG. 2. Also, in the symbols used in the drawings, 1...V
IR signal, 12... Clip circuit, 13...
...Switch circuit, 14...Mono multi, 1
5...Tune mono multi, A, B... rotating magnetic head.

Claims (1)

[Scope of utility model registration request] The clipping level of a circuit that clips a predetermined level or higher of a video signal to be recorded or reproduced is switched between the predetermined level and another level, and a predetermined horizontal scan is performed during the vertical blanking period of the video signal. A circuit for detecting the period is provided, and the clip level is changed to the other level based on the detection signal of the detection circuit, so that the clip level is changed from the clip circuit to the other level in the predetermined horizontal scanning period. 1. A video signal processing circuit characterized in that a video signal having a level higher than or equal to the level of the video signal is substantially not obtained.