JP3089127B2 - Video playback device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video reproducing apparatus such as a video tape reproducing apparatus, and more particularly to an automatic control of a chroma burst signal.

[0002]

2. Description of the Related Art FIG. 4 shows an example of a reproduction system of a VTR (video tape recorder).

A reproduction signal picked up from a video tape by a magnetic head 101 is amplified by a head amplifier / envelope detector 102.

A head amplifier / envelope detector 102
(Frequency Modulation) signal from the EQ (Equalizer) circuit 103, FM demodulator 104, NOISE REDUCTION
(Noise reduction circuit) 105 and image quality adjustment circuit 106
Y / C (luminance signal / chroma signal) is input to a MIX (mixing) circuit 114.

On the other hand, the chroma signal from the head amplifier / envelope detector 102 is
The signal is input to a Y / C MIX circuit 114 via a C (automatic chroma control) circuit 108, a color subcarrier frequency conversion circuit 109, a burst de-emphasis circuit 110, a comb filter circuit 112, and an amplifier circuit 113. The burst gate pulse used in the burst de-emphasis circuit 110 is extracted by the burst gate pulse generation circuit 111.

The luminance signal from the image quality adjustment circuit 106 and the chroma signal from the amplifier circuit 113 are mixed by a Y / C MIX circuit 114 and output to a monitor (not shown) as a video signal.

Head amplifier / envelope detector 102
Is input to the voltage conversion circuit 115 and converted into a control voltage. Based on the control voltage, the above-described EQ circuit 103, NOISE REDUCTION 105,
The image quality adjustment circuit 106 is controlled.

For example, when the level of the envelope signal is low, the EQ circuit 103 is controlled so as to emphasize the luminance signal component in the range of 4 to 4.5 MHz, and the NOISE REDUCTION is performed.
105 is controlled so as to reduce noise of a low-frequency luminance signal component, and the image quality adjustment circuit 106 does not emphasize the edge portion of the luminance signal so much, that is, 1 to 2 MHz.
The control is performed so that the luminance signal component in the range is not emphasized too much and the luminance signal component of 3.5 to 4 MHz is reduced.

As a result, the S / N (signal-to-noise ratio) of the luminance signal can be improved, and the image can be prevented from being "blurred" (black and white reversal phenomenon).

[0010]

However, in the above-mentioned conventional configuration, there is a problem that when a reproduced signal picked up from a video tape is weak, chroma noise is conspicuous on a monitor screen.

[0011]

In order to solve the above-mentioned problems, a video reproducing apparatus according to the present invention comprises a burst amplifier circuit for amplifying a chroma burst signal in a reproduced signal , and a frequency modulation circuit read from a recording medium. Low frequency change
An automatic control system circuit for automatically controlling the gain of the burst amplifier circuit according to the strength of the reproduced signal on which the converted chroma signal is superimposed is provided.

Further, the video reproducing apparatus according to the present invention has
To solve the problem, pick a playback signal from the recording medium.
Pickup to be raised and envelope of the above playback signal
Envelope detector to take out the envelope and the above envelope
A voltage conversion circuit for generating a control voltage according to the amplitude of
With the gain according to the control voltage, the chroma
A burst amplifier circuit for amplifying the burst signal;
Demodulation for demodulating frequency-modulated signals extracted from raw signals
A signal component is controlled according to the control voltage.
And a luminance signal processing system circuit for outputting a luminance signal.
It is characterized by that.

[0013]

According to the above arrangement, the frequency-modulated luminance signal
The level of the chroma burst signal can be automatically controlled in accordance with the strength of the reproduction signal in which the low-frequency-converted chroma signal is superimposed . Thereby, even if the reproduction signal from the recording medium is weak,
Chroma noise can be made less noticeable on the monitor screen.

For example, when the reproduction signal is weak, if the gain of the burst amplifier circuit is controlled to be larger than usual, the level of the chroma signal becomes relatively lower than the level of the chroma burst signal. Therefore, the color becomes light on the monitor screen, and the S
/ N can be improved.

Further , the above-mentioned luminance signal processing system circuit is provided.
According to the configuration, according to the amplitude of the envelope of the reproduction signal,
Automatically control the level of chroma burst signal. to this
Even if the playback signal from the recording medium is weak,
It is possible to make chroma noise less noticeable on the surface.
You.

In addition, the luminance signal is changed according to the control voltage.
Since the signal component is controlled, depending on the strength of the playback signal,
The signal component of the luminance signal can be controlled. This allows playback signals
Signal is weak, the S / N ratio of the luminance signal is improved,
Prevent "blur" (black and white reversal phenomenon)
If the image is strong, emphasize the outline to obtain a high-quality image.
it can.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS.

As shown in FIG. 1, a VTR reproducing system (video reproducing apparatus) according to the present embodiment has a video tape (recording medium).
A magnetic head for picking up the reproduced signal from the (pickups
1 ) and a head amplifier / envelope detector 2 for extracting an FM signal, a chroma signal, and an envelope signal from a reproduced signal. Here, the reproduction signal is a signal in which a low-frequency-converted chroma signal is superimposed on a frequency-modulated luminance signal.

Further, the reproduction system of the VTR according to the present embodiment includes a luminance signal processing system, a chroma signal processing system, and an automatic control system.

Luminance signal processing system(Luminance signal processing circuit)
Is an EQ (Equalizer) circuit 3, FM demodulator(demodulation
vessel)4, NOISE REDUCTION (noise reduction circuit) 5, image quality control
It comprises a rectifying circuit 6.

The chroma signal processing system includes a chroma amplifier 7, A
CC (automatic chroma control) circuit 8, frequency conversion circuit 9 for color subcarrier, burst de-emphasis circuit 1
0, a comb filter circuit 12, an amplifier circuit 13, and a burst amplifier circuit 16. The burst gate pulse used in the burst de-emphasis circuit 10 and the burst amplifier circuit 16 is taken out by the burst gate pulse generation circuit 11.

The automatic control system comprises a voltage conversion circuit (automatic control system circuit) 5 for generating a control voltage in accordance with the level of the envelope signal from the head amplifier / envelope detector 2, and the luminance signal processing system. EQ circuit 3,
NOISE REDUCTION 5, an image quality adjustment circuit 6, and a burst amplifier circuit 16 of the chroma signal processing system are controlled.

Further, the reproduction system of the VTR mixes the luminance signal from the image quality adjustment circuit 6 and the chroma signal from the burst amplifier circuit 16 and outputs the mixed signal as a video signal to a monitor (not shown). A MIX (mixture) circuit 14 for luminance signal / chroma signal) is provided.

In the above configuration, when the reproduction signal is weak, that is, when the level of the envelope signal is low,
The EQ circuit 3 is controlled so as to emphasize the luminance signal component in the range of 4 to 4.5 MHz, the NOISE REDUCTION 5 is controlled so as to reduce the noise of the low frequency luminance signal component, and the image quality adjustment circuit 6 controls the image quality of the luminance signal. The control is performed so that the edge portion and the like are not emphasized so much, that is, the luminance signal component in the 1-2 MHz range is not emphasized much, and the luminance signal component in the 3.5-4 MHz range is reduced.

As a result, the S / N (signal-to-noise ratio) of the luminance signal can be improved, and the image can be prevented from "blurring" (black-and-white inversion phenomenon).

Further, in the reproduction system of the VTR of the present embodiment,
When the reproduction signal is weak, the burst amplifier circuit 16 is controlled so as to amplify the burst signal (chroma burst signal) more.

As a result, the level of the burst signal becomes higher than usual. That is, the level of the chroma signal is relatively smaller than the level of the burst signal. Therefore, the color becomes lighter on the screen of the monitor, and the S / N of the chroma signal in visual perception can be improved.

When the reproduced signal is strong, that is, when the level of the envelope signal is large, the EQ circuit 3 and the NOISE REDU
In the CTION 5 and the image quality adjustment circuit 6, control reverse to the above-described control when the reproduction signal is weak is performed.

As a result, the S / N of the luminance signal is high, and a high-quality image with emphasized outlines can be obtained.

Further, in the reproduction system of the VTR of the present embodiment,
When the reproduction signal is strong, the burst amplifier circuit 16 is controlled so that the burst signal has a normal level.

As a result, on the screen of the monitor, compared to the case where the reproduced signal is weak, the color becomes darker, the S / N of the chroma signal in visual perception is high, and a vivid image can be obtained.

The burst amplifier circuit 16 includes, for example, a transistor Tr ₂ for amplifying a burst signal, a transistor Tr _{3 for} switching with a burst gate pulse, and a voltage conversion circuit 15 as shown in FIG.
And a voltage variable resistor R ₃ and the like to vary the gain of the transistor Tr ₂ in response to the control voltage.

The chroma signal which has been attenuated by the comb filter circuit 12 includes an amplifier circuit 13 consisting of transistors Tr ₁
After in amplified, is input to the base of the transistor Tr ₂ of the burst amplifier circuit 16.

When the reproduction signal is weak, the voltage variable resistor R ₃
Is lower. Therefore, the resistance value of the voltage variable resistor R ₃ is reduced. As a result, the bias of the transistor Tr ₂ is lowered, the transistor
The gain of Tr ₂ increases. Therefore, the level of the burst signal increases.

On the other hand, when the reproduction signal is strong, the control voltage applied to the voltage variable resistor R ₃ is high. Therefore, the resistance value of the voltage variable resistor R ₃ is increased. This allows
The bias of the transistor Tr ₂ is increased, the gain of the transistor Tr ₂ is reduced. Therefore, the level of the burst signal decreases. As in the level of the burst signal at this time is the normal level, the resistance value of the voltage variable resistor R ₃ is controlled.

The voltage conversion circuit 15 is specifically composed of, for example, four transistors as shown in FIG. By changing the base voltage of the transistor at the first stage by the variable resistor VR, the DC of the envelope signal is changed.
It is possible to adjust the (DC) level.

In the above embodiment, the burst gate pulse is generated by the burst gate pulse generating circuit 11. However, the horizontal synchronizing signal is separated, and a pulse obtained by delaying the horizontal synchronizing signal by the inductor and the capacitor is used as the burst gate pulse. Is also good.

The VTR reproduction system according to the present invention includes a head amplifier / envelope detector 2 for extracting an envelope from a reproduction signal read from a video tape, and a burst amplifier circuit 16 for amplifying a burst signal in the reproduction signal.
And a control voltage is generated according to the amplitude of the envelope,
A voltage conversion circuit 15 for automatically controlling the gain of the burst amplifier circuit 16 is provided.

Therefore, the level of the burst signal can be automatically controlled according to the amplitude of the envelope signal. This makes it possible to make the chroma noise less noticeable on the monitor screen even if the reproduced signal from the video tape is weak.

[0040]

As described above, the video reproducing apparatus according to the present invention comprises a burst amplifier circuit for amplifying a chroma burst signal in a reproduced signal , and a frequency converter read from a recording medium.
And an automatic control system circuit for automatically controlling the gain of the burst amplifier circuit according to the strength of the reproduced signal in which the low-frequency-converted chroma signal is superimposed on the adjusted luminance signal. The level of the chroma burst signal can be automatically controlled according to the strength of the signal. As a result, even if the reproduction signal from the recording medium is weak, it is possible to make the chroma noise less noticeable on the monitor screen.

The video reproducing apparatus according to the present invention has
And a pickup for picking up a reproduction signal from a recording medium.
And an envelope for extracting the envelope of the reproduction signal.
Rope detector and control according to the amplitude of the above envelope
A voltage conversion circuit for generating a voltage,
Amplifies the chroma burst signal in the playback signal
Burst amplifier circuit and the
Including a demodulator for demodulating the modulated frequency modulation signal,
Outputs a luminance signal whose signal component is controlled according to the voltage
And a luminance signal processing system circuit. It
Therefore, depending on the strength of the reproduced signal,
The level and the signal component of the luminance signal can be controlled, and the recording medium
Even if the playback signal from the
This makes it possible to make the noise less noticeable.
I do.

[Brief description of the drawings]

FIG. 1, showing an embodiment of the present invention, is a schematic block diagram of a reproduction system of a VTR.

FIG. 2 is a circuit diagram showing a specific example of the burst amplifier circuit of FIG.

FIG. 3 is a circuit diagram showing a specific example of the voltage conversion circuit of FIG.

FIG. 4 is a schematic block diagram of a reproduction system of a conventional VTR.

[Explanation of symbols]

Reference Signs List 1 magnetic head (pickup) 2 head amplifier / envelope detector 3 equalizer circuit (luminance signal processing circuit) 4 FM demodulator (demodulator) 5 noise reduction circuit (luminance signal processing circuit) 6 image quality adjustment circuit (luminance signal processing) System circuit) 15 Voltage conversion circuit (automatic control system circuit) 16 Burst amplifier circuit

Claims (2)

(57) [Claims] A burst amplifier circuit for amplifying a chroma burst signal in a reproduction signal; and a low-frequency luminance signal read from a recording medium.
An image reproducing apparatus, comprising: an automatic control system circuit for automatically controlling the gain of the burst amplifier circuit according to the strength of a reproduced signal on which a band-converted chroma signal is superimposed . 2. A pickup for picking up a reproduction signal from a recording medium; an envelope detector for extracting an envelope of the reproduction signal; a voltage conversion circuit for generating a control voltage according to the amplitude of the envelope; A burst amplifier circuit for amplifying a chroma burst signal in the reproduction signal with a gain, and a demodulator for demodulating a frequency modulation signal extracted from the reproduction signal, wherein a signal component is controlled according to the control voltage. And a luminance signal processing circuit for outputting a luminance signal.