JPH0419757B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a color signal recording and reproducing apparatus that records and reproduces an FM-modulated luminance signal and a carrier color signal that has been frequency-converted to a low frequency range. The present invention relates to a playback device.

FIG. 1 shows an example of a conventional color video signal processing circuit in a magnetic recording/reproducing device.

First, referring to FIG. 1, the operation of the signal processing circuit of the recording system from the input terminal 1 to the recording head 13 will be explained. The recording color video signal supplied to input terminal 1 is passed through LPF (low pass filter) 2.
and a BPF (band pass filter) 6. LPF2 and BPF6 are for separating the above color video signal, luminance signal and color signal,
A luminance signal is led to the output of the LPF2, and a chrominance signal is led to the output of the BPF6. The luminance signal separated by the LPF 2 passes through an AGC circuit (automatic gain control circuit) 3 for level adjustment, and is FM modulated by an FM modulator 4.

The band of the FM signal after modulation is approximately 1.2MHz to 1.5MHz.
It passes through the above HPF (high pass filter) 5 and is guided to the mixer 11. On the other hand, the color signal separated by the BPF 6 passes through an ACC circuit (automatic color level control circuit) 7 for level adjustment and is led to a burst emphasis circuit 8, where the burst signal portion of the color signal is emphasized by approximately 6 dB. be done. (Hereinafter referred to as burst emphasis.) This burst emphasized color signal is led to the frequency converter 9, and is approximately 0.2M
Low frequency conversion is performed to approximately Hz to 1.2MHz. This low frequency converted color signal passes through an LPF 10 with a band of about 1.2 MHz and is guided to a mixer 11. The FM signal and the low frequency conversion color signal introduced to the mixer 11 as described above pass through the recording amplifier 12 and are recorded on the video tape 14 from the recording head 13.

Next, the operation of the reproduction system signal processing circuit from the reproduction head 15 to the output terminal 28 will be explained.
The signal played back from the videotape 14 by the playback head 15 passes through a preamplifier 16 and is output to HPF1.
7 and LPF21. HPF17 and
LPF21 separates the reproduced signal into an FM signal and a low-frequency conversion color signal, and the output of HPF17 includes an FM signal.
A low frequency conversion color signal is respectively guided to the output of the LPF 21. The FM signal separated by the HPF 17 passes through a limiter circuit 18 and is demodulated into a luminance signal by an FM demodulator 19. This demodulated luminance signal is LPF
20 and is led to a mixer 27. on the other hand,
The low frequency conversion color signal separated by LPF21 is
The signal passes through the ACC circuit 22, is guided to the frequency converter 23, and is converted into a color signal in the original subcarrier band of about 358MHz±500KHz. This color signal passes through a BPF 24 and a comb filter 2 for suppressing crosstalk components of the color signal from adjacent video tracks.
5. This color signal with suppressed crosstalk components is led to the burst day emphasis circuit 26, where the burst signal portion is suppressed by about 6 dB, which is hereinafter referred to as burst day emphasis. mixer 2
Guided by 7. The luminance signal and color signal guided to the mixer 27 as described above are guided to the output terminal 28 as a reproduced color video signal.

In the conventional color signal processing circuit described above, the S/N of the reproduced burst signal is improved by burst emphasis during recording, and although not shown, the phase error of the reproduced APC circuit (automatic phase control circuit) is reduced. The residual phase jitter in the reproduced color signal component is improved.

Although it has the above characteristics, the conventional example shown in FIG. 1 has the following problems in burst emphasis and de-emphasis.

First, the quality of the reproduced image is degraded due to spurious components of the delay line used in the reproduction comb filter 25. As the comb filter 25, a 1H delay line (H represents one horizontal period) is used in the NTSC system, and a 2H delay line is used in the PAL system. The spurious component of is superimposed on the output signal of the comb filter 25. Therefore, guiding the burst-emphasized color signal to the comb filter 25 as shown in FIG. 1 increases the level of spurious components of the burst signal, deteriorating the reproduced image quality.

The second problem is phase distortion of the burst signal due to burst emphasis and de-emphasis. In other words, only the burst signal component of the color signal is
By emphasizing and suppressing by about 6 dB, the relative phase between the burst signal and the chroma signal changes, causing a hue change in the reproduced image quality.

Third, there is increased crosstalk of burst signal components from adjacent video tracks. FIG. 2 shows an example of a recorded video track pattern when the number of H deviations from adjacent video tracks is αH=1H. In particular, as shown in Figure 2, when 2αH≠(n+1) (where n is an integer), the positions of horizontal synchronization signals with adjacent video tracks are not adjacent to each other, the so-called H alignment is shifted, and bursts from adjacent video tracks Since the crosstalk component of the signal is superimposed on the chroma signal, it appears on the playback screen and significantly deteriorates the image quality.

FIG. 3 shows an example of a magnetic recording/reproducing apparatus that can solve the first and second problems mentioned above. The circuit configuration of FIG. 3 is almost the same as that of FIG. 1, and the difference is that in the conventional example of FIG. 1, the burst emphasis circuit 8 during recording is connected to the input side of the frequency converter 9, While the emphasis circuits 26 are provided on the output sides of the frequency converters 23, in this example, on the contrary, the burst emphasis circuits 8 are provided on the output sides of the frequency converters 9. A phasing circuit 26 is provided on the input side of the frequency converter 23.

First, the second problem, which is the suppression of hue changes in reproduced image quality due to relative phase changes between the burst signal and the chroma signal, will be explained.

Generally, in a circuit that switches the gain of a small signal, such as the burst emphasis circuit 8 or the de-emphasis circuit 26, the delay difference between the circuits at each gain becomes the phase difference. Therefore, the lower the frequency of a small signal is, the more the phase difference can be suppressed. That is, as shown in Fig. 1, burst emphasis and de-emphasis are conventionally performed using a color signal in a subcarrier band of approximately 3.58 MHz ± 500 KHz, whereas in the example shown in Fig. 3,
As mentioned above, when recording, the frequency converter 9
Burst emphasis is performed using a color signal that has been low frequency converted from 0.2MHz to 1.2MHz, and frequency converter 2 is used during playback.
Since the burst de-emphasis is performed using the low frequency converted color signal on the input side of No. 6, changes in the burst signal and relative phase due to the burst emphasis and de-emphasis are suppressed, and hue changes in reproduced image quality can be reduced.

Next, it will be explained that the first problem, that is, image quality deterioration due to spurious components of the delay line used in the reproduction comb filter 25 is suppressed is suppressed.

Generally, an ultrasonic delay line is used in the reproduction comb filter 25, and in order to secure the band of this ultrasonic delay line, a low frequency conversion color signal cannot be used as an input signal. Therefore, the regeneration comb filter 25 is provided on the output side of the frequency converter 23, and uses the color signal of the subcarrier band as an input signal.

Therefore, by performing burst de-emphasis on a low frequency converted color signal as in the example shown in FIG. A converted and burst de-emphasized color signal is derived. Therefore, the level of spurious components of the burst signal generated by the comb filter 25 is reduced. For example, when the burst emphasis amount and de-emphasis amount are approximately 6 dB, the spurious component of this burst signal is approximately
Reduced by 6dB. Further, image quality deterioration due to spurious components of the burst signal becomes noticeable when the chroma signal level is small, but by using the arrangement example shown in FIG. 3, image quality deterioration can be significantly suppressed.

Furthermore, in this example, it is possible to reduce the switching damage that occurs when switching the gain between the burst signal and the chroma signal during burst de-emphasis, which occurs in the conventional example shown in FIG. That is, since the frequency converter 23 and the BPF 24 are provided on the output side of the burst de-emphasis circuit 26, the above-mentioned switching flaw, which is an impulse or DC offset, has a wide band and passes through the frequency converter 23 to the BPF 24. By being guided by
The energy component of this switching wound is greatly reduced. This also reduces the phase distortion of the burst signal that was caused by switching scratches.
Suppresses hue changes in playback image quality.

FIG. 4 shows the recording and reproduction system ACC circuits 7, 22 and frequency converters 9, 23 in the example of FIG.
This is a color signal processing circuit showing an example of a multipurpose color signal processing circuit.

In FIG. 4, 29 is an input terminal for a color signal separated from a recorded color video signal, 30 is an input terminal 31 for a low-pass converted color signal separated from a reproduced signal,
Reference numeral 34 designates a switch circuit 32 as an ACC circuit, 34 as a frequency converter, 35 as an output terminal for recording low frequency conversion color signals, and 36 as an output terminal for reproduction color signals. be.

In this example, during recording, switch circuits 31, 3
3 are connected as shown in the figure, and during reproduction they are connected in the opposite direction to that shown in the figure. The circuit operation is similar to that shown in FIG. Although not shown, as the ACC detection signal for controlling the ACC circuit 32, a burst signal before the frequency converter 33 is suitable during recording, and a burst signal after the comb filter 25 during reproduction is suitable. That is, since both of the ACC detection signals are in the subcarrier band and are not subjected to burst emphasis, the level of the reproduced color signal from the output terminal 36 is kept constant, and the input level of the frequency converter 34 is approximately the same for recording and reproduction. It can be kept constant and the dynamic cleanser can be selected optimally.

In addition, in the case of the example shown in Figure 4 as described above, ACC
The circuit 32 and the frequency converter 34 can be used for both recording and reproduction, reducing the number of constituent circuits and optimizing the dynamic range of the circuit, making the circuit suitable for IC implementation.

FIG. 5 shows another example in which, unlike FIG. 4, burst emphasis during recording is performed using a subcarrier band color signal, and burst de-emphasis during reproduction is performed using a low frequency converted color signal. This is a signal processing circuit.

In FIG. 5, numeral 37 is a circuit for both burst emphasis and de-emphasis, and the rest is the same as in FIG. 4. Since the circuit operation can be easily inferred in the same manner as in FIG. 4, the explanation will be omitted. In this example, since burst emphasis is performed using the color signal in the subcarrier band, the phase distortion of the burst signal during burst emphasis increases compared to the example shown in FIG. 4. However, since switching flaws during burst emphasis are reduced by the frequency converter 34 and LPF 10 in the subsequent stage, variations in the phase distortion of the burst signal during burst emphasis are suppressed compared to the conventional example shown in Figure 1. be done.

The feature of the example shown in FIG. 5 is that the ACC circuit 32, frequency converter 34, burst emphasis and de-emphasis circuit 37 can be used for both recording and reproduction;
In addition to being able to significantly reduce the number of configuration circuits, by using the burst signal at the front stage of the burst emphasis and de-emphasis circuits during recording as the ACC detection signal, and by using the burst signal at the stage after the comb filter 25 during playback, it is possible to achieve the same result as in Fig. 4. The dynamic range has been optimized, making the circuit more suitable for IC implementation.

As mentioned above, by performing burst de-emphasis during playback using the low frequency conversion carrier color signal,
It is possible to suppress image quality deterioration due to spurious components in the reproduction comb filter, burst emphasis, and hue change in reproduced image quality due to de-emphasis.

However, in any of the above examples, the third
The problem (adjacent crosstalk) has not yet been solved.

SUMMARY OF THE INVENTION An object of the present invention is to provide a color signal reproducing device that can suppress image quality deterioration due to crosstalk of burst signals from adjacent video tracks.

In order to achieve the above object, the present invention includes a signal reproducing means for reading color signals recorded on a magnetic tape, an ACC circuit for controlling the level of the amplitude of the color signal from the signal reproducing means, and a level-controlled color signal. A frequency converter that converts the frequency to a predetermined frequency, a comb filter that suppresses adjacent crosstalk components from the level-controlled and frequency-converted color signal, and a dynamo that nonlinearly suppresses the color signal with the crosstalk component suppressed. a burst de-emphasis circuit that is provided in a path from the output of the signal reproducing means to the input of the comb filter and de-emphasizes a burst signal in the color signal; and a color signal reproducing device. is provided.

The present invention will be explained below with reference to FIGS. 6 to 13.

In FIG. 6, 38 is a chroma dynamic enhancement circuit that nonlinearly enhances a low level chroma signal depending on the level, and 39 is a chroma dynamic enhancement circuit that suppresses a low level chroma signal nonlinearly depending on the level. They are de-emphasis circuits and are selected for their mutually complementary characteristics. Other details are the same as in FIG. 3.

Hereinafter, it will be explained that crosstalk interference of burst signals from the adjacent video tracks is reduced and image quality deterioration is suppressed.

As is known, the crosstalk components of the color signals from adjacent video tracks are filtered through the reproduction comb filter 2.
5 is suppressed. This recycled comb filter 2
When using an ultrasonic delay line in 5, the average within the band
D/U ratio of 15 dB or more (where D is the required signal,
U indicates an unnecessary signal) is obtained. Furthermore, even if the playback level of the color signal from the adjacent video track to the main video track due to mistracking of the playback head is about -6 dB, the crosstalk component of the burst signal will be a small amplitude component of -20 dB or less of the main signal. Therefore, the chroma dynamic de-emphasis circuit 39 provided after the reproduction comb filter suppresses the crosstalk component of the burst signal, which is a small amplitude component.
Crosstalk interference is reduced. For example, if the suppression degree is selected to be approximately 6 dB when the input level of the dynamic de-emphasis circuit 39 is -20 dB, the burst emphasis will suppress the crosstalk component of the burst signal when the burst emphasis amount is approximately 6 dB. The result can be the same as without it. That is, in this embodiment, it is possible to ensure image quality equivalent to the image quality deterioration caused by burst interference from adjacent video tracks when burst emphasis is not performed.

As described above, in order to suppress the crosstalk of burst signals from adjacent video tracks, the chroma dynamic de-emphasis circuit 39 must be provided after the reproduction comb filter 25. Therefore, since the chroma dynamic de-emphasis circuit 39 is provided after the burst de-emphasis and uses the color signal of the subcarrier band as an input signal, the chroma dynamic de-emphasis circuit 39 de-emphasizes the chroma dynamic de-emphasis circuit 38. circuit 3
9, the circuit 38 has a frequency converter 9 and a burst emphasis circuit 8.
It must be placed before the

Further, in this embodiment, the chroma dynamic enhancement circuit 38 and the de-emphasis circuit 39 stop the chroma dynamic enhancement and de-emphasis only during the burst period,
Fluctuations in burst signals in each circuit can be suppressed, and dynamic range can be optimized. Conversely, by subjecting the burst signal to dynamic enhancement and de-emphasis in the same manner as the chroma signal, the S/N ratio of the burst signal can be slightly improved.

The embodiment shown in Fig. 6 not only improves the image quality described above, but also improves the S/N of the reproduced chroma signal, and lowers the recorded FM signal and other frequency components (e.g., pilot signal) during reproduction. Color moiré, cross color interference, etc. caused by leakage to color signals can be reduced.

FIG. 7 shows a color signal showing another embodiment of the present invention in which the ACC circuits 7, 22 and the frequency converters 9, 23 of the recording and reproducing system are used in common as shown in FIG. 4 in the example of FIG. 6. It is a playback device.

The circuit operation of this embodiment is almost the same as that shown in FIG. 6, and can be easily inferred from FIGS. 4 and 6, so a description thereof will be omitted. However, in FIG. 7, it is also possible to use the chroma dynamic enhancement circuit 38 and the burst de-emphasis circuit.

Furthermore, in the embodiment shown in FIG. 6, the burst emphasis circuit 8 may be provided after the dynamic emphasis circuit. In this case, the ACC circuit and frequency converter can also be used for both recording and playback.
Since it can be easily inferred from the figure and FIG. 6, illustration thereof will be omitted.

Next, the specific circuit configurations of the chroma dynamic enhancement circuit 38 and the de-emphasis circuit 39 used in the present invention as described above will be explained.

FIG. 8 is a block diagram showing an example of the chroma dynamic enhancement circuit 38, and FIG. 9 is a block diagram showing an example of the chroma dynamic enhancement circuit 39.

In FIGS. 8 and 9, 40 and 44 are input terminals of the respective circuits, 41 is a limiter circuit, 42 is an adder, 43 and 46 are output terminals of the respective circuits, and 45 is a subtracter. In the example of FIG. 8, the limiter circuit 41 limits the amplitude of large amplitude signals, but does not limit the amplitude of only small amplitude signals.

As a result, a dynamic characteristic is obtained in which the amount of emphasis increases when a signal has a small amplitude.

FIG. 9 is an inverse circuit of FIG. 8, and by configuring it in a negative feedback type, complementary characteristics can be obtained.

FIGS. 10 and 11 are block diagrams showing other examples of the chroma dynamic enhancement circuit 38 and the de-emphasis circuit 39, respectively.

In FIGS. 10 and 11, 47 is an inverse bell filter, and by providing this inverse bell filter 47, the chroma dynamic enhancement and de-emphasis have frequency characteristics.

FIGS. 12 and 13 are block diagrams showing still other examples of the chroma dynamic enhancement circuit 38 and the de-emphasis circuit 39, respectively.

In FIGS. 12 and 13, 48 is a trap circuit which does not have dynamic characteristics at the center of the color signal band, but has dynamic characteristics at both side bands.

As described above, in each of the above embodiments, a color signal processing circuit is provided to perform chroma dynamic emphasis and de-emphasis characteristics, and both burst emphasis and de-emphasis are performed using a low-frequency conversion carrier color signal. Therefore, burst interference caused by burst emphasis and de-emphasis can significantly improve other image quality deterioration.

As described above, in the present invention, since chroma dynamic enhancement and de-emphasis are performed, burst interference from adjacent video tracks is reduced, and good color reproduction image quality can be obtained.

[Brief explanation of drawings]

1, 3, 4, and 5 are block diagrams showing an example of a magnetic recording/reproducing device, and FIG. 2 is a tape showing an example of a recorded video track pattern when not arranged in H-line. A plan view, FIG. 6 is a block diagram showing one embodiment of the present invention, and FIG. 7 is a
In the example of FIG. 6, a block diagram showing an example in which the circuit configuration is simplified, FIG. FIG. 10 is a block diagram showing another example of the structure of the chroma dynamic enhancement circuit. FIG. 11 is a block diagram showing another example of the structure of the chroma dynamic enhancement circuit. FIG. 12 is a block diagram showing another example of the configuration of the chroma dynamic enhancement circuit. FIG. 13 is a block diagram showing another example of the configuration of the chroma dynamic enhancement circuit.
FIG. 2 is a block diagram showing an example of the configuration of the chroma dynamic de-emphasis circuit shown in FIG. 6, 24; BPF, 7, 32; ACC circuit, 8;
Burst emphasis circuit, 9, 23, 34; Frequency converter, 10, 21; LPF, 25; Regeneration comb filter, 26; Burst de-emphasis circuit, 31, 33; Switch circuit, 37; Assist and de-emphasis circuit, 3
8; Chroma dynamic enhancement circuit, 3
9; Chroma dynamic enhancement circuit.

Claims (1)

[Scope of Claims] 1. Signal reproducing means for reading color signals recorded on a magnetic tape; ACC circuit for controlling the level of the amplitude of the color signal from the signal reproducing means; A comb filter that suppresses adjacent crosstalk components from the level-controlled and frequency-converted color signal, and a dynamic decoder that non-linearly suppresses the color signal with suppressed crosstalk components. a burst de-emphasis circuit, which is provided in a path from the output of the signal reproducing means to the input of the comb filter, and de-emphasizes a burst signal in the color signal. Color signal reproducing device. 2 The above burst de-emphasis circuit is
2. The color signal reproducing device according to claim 1, wherein the color signal reproducing device is provided between an ACC circuit and a frequency converter.