JPH04152778A - Agc circuit for magnetic recording and reproducing device - Google Patents

Abstract

PURPOSE:To make a basic performance as an edit device and a general recording and reproducing device compatible with high picture quality at camera video recording by implementing keyed AGC at line input and peak AGC at camera input. CONSTITUTION:A luminance signal of a video signal from an external video equipment such as other magnetic recording and reproducing device connecting to the outside of the title magnetic recording and reproducing device is inputted to a line input terminal 1 and a luminance signal of a video signal from a camera connected to the outside of this magnetic recording and reproducing device is inputted to a camera input terminal 2. The video signal inputted from the line input terminal 1 is subject to processing of keyed AGC (SYNC AGC detecting a SYNC level and to make it constant when a white peak does not exceed a prescribed level and peak AGC detecting a video image level and to make it constant when the white peak exceeds the prescribed level) and the result is fed to a selection circuit 6. On the other hand, the luminance signal inputted from the camera input terminal 2 is subject to processing of peak AGC by a peak AGC circuit 4 and the result is fed to the selection circuit 6. The selection circuit 6 selects either the luminance signal from the line input terminal 1 or the luminance signal from the camera input terminal 2 and gives the signal to a luminance signal recording processing circuit 7.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an AGC circuit for obtaining high image quality from both camera input and line input in a magnetic recording/reproducing device.

[Conventional technology]

The AGC circuit of a conventional magnetic recording/reproducing device is disclosed in Japanese Patent Application Laid-open No. 1986-
As described in Publication No. 63287, when the white peak of the video is within a predetermined value, the sync level is kept constant by the sync AGC, and when the white peak exceeds the predetermined value, the entire amplitude is kept within the predetermined value. It became the so-called Keed AGC, which is called Beak AGC.

On the other hand, when a dark subject is photographed by a camera, it is often not possible to obtain a sufficient image level due to the limitations of the camera's performance. When recording such a signal, beak A
It is more effective to improve the S/N of recorded and reproduced images by applying GC and amplifying the video level as much as possible within the effective range.
preferable. Even among conventional devices, there were portable cameras dedicated to camera photography that adopted the peak AGC method.

However, when dubbing video signals from external video equipment such as other magnetic recording and reproducing devices, applying peak AGC will change the video level before and after dubbing, so it is practically impossible to use peak AGC type equipment. It could not be used as an editing machine or a general recording/playback machine.

This type of AGC circuit was introduced in October 1982.
``Introduction to Home VTR'', published by Tsuki Corona Publishing, written by Tsukiyama et al.
An explanation is given on page 152 of , giving examples of peak AGC and keyed AGC.

[Problem to be solved by the invention]

As described above, conventional devices have not taken into account the need to achieve both image quality when used as an editing machine and general recording/playback device, and image quality when used for camera photography.

An object of the present invention is to provide an AGC circuit for a magnetic recording and reproducing device that achieves high image quality even when taken with a camera while ensuring basic performance as an editing machine and a general recording and reproducing device. The aim is also to achieve high image quality even when the video captured by the camera is further dubbed. Furthermore, it is an object of the present invention to realize a device that achieves the above object on a small circuit scale.

[Means to solve the problem]

In order to achieve the above object, peak AGC means for controlling the amplitude of the luminance signal input from the camera and keyed AGC means for controlling the amplitude of the luminance signal input from the line are provided.

Furthermore, in order to achieve high image quality even when a video signal captured by a camera is further dubbed, a sync replacement means is provided to replace the sync level after peak AGC with a constant value.

Furthermore, in order to reduce the circuit scale, most of the circuits are shared by the peak AGC means and the keyed AGC means.

[Effect]

The peak AGC means is the S of recording and playback images when taking pictures with a camera.
/N, and the keyed AGC means keeps the video level constant during editing and general recording/playback. Therefore, it is possible to achieve high image quality in camera photography while ensuring basic performance as an editing and general recording/playback device.

In addition, since the sync replacement means replaces the sync amplified by the peak AGC with a constant value, the video level will not be reduced even if the video taken by the camera is passed through the keyed AGC when dubbing the video taken by the camera. Even when the recorded video is further dubbed, high image quality can be achieved.

Furthermore, by sharing most of the circuits between the peak AGC means and the keyed AGC means, the purpose can be achieved with a small circuit scale.

〔Example〕

FIG. 1 is a block diagram of a luminance recording system according to an embodiment of the present invention. 1 is line input terminal, 2 is camera input terminal, 3
4 is a keyed AGC circuit, 4 is a peak AGC circuit, 5 is an input changeover switch, 6 is a switching circuit, and 7 is a luminance signal recording processing circuit.

Line input terminal 1 receives the brightness signal of a video signal from an externally connected video device such as another magnetic recording/reproducing device, and camera input terminal 2 receives the brightness signal of a video signal from an externally connected camera. A signal is input. Line input terminal 1
The luminance signal input from
If it exceeds 1, it is processed by peak AGC (peak AGC) which detects the video level and suppresses it to a constant value, and is sent to the selection circuit 6.

On the other hand, the luminance signal input from the camera input terminal 2 undergoes peak AGC processing by the peak AGC circuit 4 and is sent to the selection circuit 6. The selection circuit 6 selects the luminance signal from the line input terminal 1 or the luminance signal from the camera input terminal 2 according to the state of the input changeover switch 5, and sends it to the luminance signal recording processing circuit 7. The luminance signal recording processing circuit 7 performs signal processing necessary for recording such as FM modulation, and the signal is recorded on a magnetic tape (not shown).

According to this embodiment, keyed AGC is performed when other video equipment is connected to the outside for editing or general recording/playback, so the video level does not change due to recording/playback. In addition, when taking pictures with a camera connected, even if a sufficient video level cannot be obtained due to a dark subject, the video level is amplified by peak AGC and recording is performed, so the S/N of the recorded and playback image is It has the effect of improving. Therefore, according to this embodiment, it is possible to improve the image quality when taking pictures with a camera while ensuring the basic performance when used as an editing machine or a general recording/reproducing machine.

FIG. 2 is a block diagram of a luminance recording/reproducing system according to another embodiment of the present invention. 8 is a luminance signal reproduction processing circuit, 9 is a selection circuit, and IO is an output terminal. The rest is the same as the embodiment described in FIG. In the recording mode, the selection circuit 9 selects the signal from the line input terminal 1 and sends it to the keyed AGC circuit 3, and the overall operation is the same as the embodiment described in FIG.

In the reproduction mode, the signal reproduced from the magnetic tape is restored to the original luminance signal by the luminance signal reproduction processing circuit 8. The reproduced luminance signal is selected by the selection circuit 9, subjected to keyed AGC processing by the keyed AGC circuit 3, and outputted from the output terminal 10.

According to this embodiment, even a recorded video whose video level has been amplified by beak AGC is input as a playback brightness signal through the selection circuit 9 to the keyed AGC circuit 3 and subjected to keyed AGC during playback, so that the original video can be restored. You can return to the level and play. That is, even in the case of camera photography, it is possible to obtain a reproduced image in which the image level does not change. Furthermore, since recording on the tape is performed with the video level amplified, there is an effect of improving the S/N as in the embodiment described in FIG. 1.

The embodiment described in Fig. 2 has the effect of improving the S/N when taking pictures with a camera using beak AGC, but when dubbing the recorded and played video, it is necessary to use the keyed AGC on the recorder side.
Since the amplified video level returns to the original level due to C, the effect of improving the S/N cannot be obtained. In order to obtain the effect of improving the S/N during dubbing, the method shown in FIG. 3 may be used.

In Fig. 3, 11 is the sink waveform shaping circuit, and the others are the 1st waveform shaping circuit.
This is the same as the embodiment described in the figures. Beak AGC circuit 4
The sync level of the amplified video and sync level luminance signal is limited to a predetermined value by the sync waveform shaping circuit. This allows the recorded and played video to be transferred to the keyed AG.
Even if the signal is passed through C, the amplified video level is maintained as it is. Therefore, even when dubbing the video taken by the camera, there is an effect of improving the S/N, and high image quality can be obtained.

An example in which a keyed AGC and a beak AGC share a circuit to reduce the circuit scale will be described with reference to FIG. 4.

In Fig. 94, 12 is a gain control amplifier, 13 is a pedestal clamp circuit, 14 is a key pulse addition circuit, 15 is a peak value detection circuit, 16 is a selection circuit, and the others are the same as the embodiment explained in Fig. 1. .

The selection circuits 6 and 16 select the A side when the input selection switch 5 selects the line input, and select the B side when the input selection switch 5 selects the camera input. The selection circuit 6 selects the input from the line input terminal 1 and the input from the camera input terminal 2, and sends them to the gain control amplifier 12. Gain control amplifier 12
Keyed AGC and beak AGC processing is performed.

When the selection circuit 16 selects the A side, it becomes keyed AGC, and when it selects the B side, it becomes beak AGC.

First, the operation of keyed AGC will be explained. The output of the gain control amplifier 12 is clamped by a pedestal clamp circuit 13 so that the pedestal has a constant potential, and then a key pulse having a predetermined height from the pedestal is added to the back porch of the sink by a key pulse adding circuit 14. . The peak value detection circuit 15 detects the maximum amplitude value of the signal to which the key pulse has been added, and sends a control signal to the gain control amplifier so that this value becomes a predetermined value. As a result, when the video level does not exceed the key pulse level, the level of (key pulse addition circuit) is constant, that is, the sync level becomes constant (sync AGC), and when the video level exceeds the key pulse level, (video + sync ) becomes the beak AGC where the level becomes a predetermined value, so key A
GC will be realized.

On the other hand, when the selection circuit 16 selects the B side, no key pulse is added, resulting in simple beak AGC.

In other words, according to this embodiment, both keyed AGC and beak AGC can be realized with a small circuit scale, and the image quality of camera shooting can be improved while ensuring the basic performance when used as an editing machine/recording/playback machine. are added by the adder circuit 21 and supplied to the gain control amplifier 12, but at this time, the control signal from the peak value detection circuit 19 is determined by the function of the rectifier circuit 20. That is, only a control signal (in the direction of lowering the gain of the gain control amplifier 12) is supplied. Therefore, if the maximum amplitude does not exceed a predetermined value, sink AGC is performed, and if it exceeds, peak AGC is performed. On the other hand, when the selection circuit 22 selects the B side, peak AGC is always applied.

Therefore, according to this embodiment, like the embodiment described in FIG. 4, it is possible to achieve both basic performance as an editing machine/recording/playback machine and high image quality when taking pictures with a small circuit scale. can.

〔Effect of the invention〕

According to the present invention, keyed AGC can be performed during line input, and peak AGC can be performed during camera input, so that basic performance as an editing machine and general recording/playback machine and high image quality during camera recording can be achieved.

I can do it.

Another embodiment in which the keyed AGC and the peak AGC share a circuit will be described with reference to FIG. In Figure 5, 1
7 is a sync chip clamp circuit, 18 is a sync level detection circuit, 19 is a peak value detection circuit, 20 is a rectifier circuit, 2
1 is an adder circuit, 22 is a selection circuit, and the others are the same as the embodiment explained in FIG.

When the selection circuit 22 selects the A side, the keyed AGC becomes peak AGC when the B side is selected. First, the operation of keyed AGC will be explained. The output of the gain control amplifier 12 is clamped by the sync tip clamp circuit 17 so that the sync tip is at a constant potential, and then output to the sync level detection circuit 1.
8 and the peak value detection circuit 19. The sync level detection circuit 18 detects the sync level and generates a control signal to control the gain control amplifier so that the sync level becomes a predetermined value.

The peak value detection circuit 19 detects the maximum amplitude value and generates a control signal for controlling the gain control amplifier so that the maximum amplitude value becomes a predetermined value. The control signal from the sink level detection circuit 18 and the control from the peak value detection circuit 19
By replacing the subsequent sync level with a predetermined value, high image quality can be obtained even when the camera-recorded video is further dubbed.

Furthermore, by sharing the circuit between the keyed AGC and the peak AGC, the above effects can be obtained with a small circuit scale.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a luminance recording system according to an embodiment of the present invention.
FIG. 2 is a block diagram of a luminance recording/reproducing system according to another embodiment of the present invention, and FIGS. 3, 4, and 5 are block diagrams of luminance recording systems according to still further embodiments of the present invention. be. 1...Line input terminal 2...Camera input terminal 3
... Keyed AGC circuit 4 ... Peak AGC circuit closed diagram

Claims (1)

[Claims] 1. A magnetic recording and reproducing device comprising a camera input terminal into which a video signal from a camera that images a subject is input, and a line input terminal into which a video signal from an external video device is input. The AGC circuit includes a peak AGC means that detects the signal amplitude of the luminance signal from the camera input terminal and controls it to a constant level, and a peak AGC means that detects the sync level of the luminance signal from the line input terminal and controls it. A magnetic recording and reproducing apparatus characterized in that it is equipped with keyed AGC means for controlling the signal amplitude to be constant, but detecting the signal amplitude and controlling it to be constant when the signal amplitude exceeds a predetermined value.
GC circuit. 2. In the AGC circuit of the magnetic recording and reproducing apparatus according to claim 1, regarding the reproduction brightness signal in the reproduction mode,
This is input into the keyed AGC means in place of the luminance signal from the line input terminal, and the keyed AGC means is made to function as a sync AGC means for detecting the sync level of the reproduced luminance signal and controlling it to a constant level. AGC circuit of a magnetic recording/reproducing device. 3. In the AGC circuit of the magnetic recording/reproducing apparatus according to claim 1, the sync level of the luminance signal after being controlled by the peak AGC means for controlling the luminance signal from the camera input terminal to be constant is set to a certain level. An AGC circuit for a magnetic recording/reproducing device, characterized in that it is equipped with a sink replacement means for replacing a constant value with a constant value. 4. A of the magnetic recording and reproducing device according to claim 1, 2 or 3.
In the GC circuit, the keyed AGC means applies a key pulse having a predetermined height from the pedestal level to a gain control amplifier that amplifies and outputs an input luminance signal, and to a back porch portion of a sink for the output signal of the control amplifier. A key pulse generation/adding means for generating and adding the key pulse, and a signal after the key pulse is added.
Peak value detection means detects the maximum amplitude (peak value) of the entire signal including the key pulse and sends a control signal to the gain control amplifier to control the gain so that the maximum amplitude (peak value) is constant. , the peak AGC means includes a gain control amplifier that amplifies and outputs an input luminance signal, detects a maximum amplitude (peak value) of an output signal of the control amplifier, and controls the gain control amplifier so that the maximum amplitude (peak value) is constant. peak value detection means for transmitting a signal and controlling its gain; and the keyed AGC means and the peak AGC means share other elements except for the key pulse generation and addition means. AGC circuit of the device. 5. A of the magnetic recording and reproducing device according to claim 1, 2 or 3.
In the GC circuit, the keyed AGC means includes a gain control amplifier that amplifies and outputs an input luminance signal, the control amplifier, and a control signal that detects the sink level of the output signal of the control amplifier and attempts to keep it constant. sync level detection means for generating a control signal; peak value detection means for detecting a maximum amplitude (peak value) in the output signal of the control amplifier and generating a control signal to keep it constant; and the peak value detection means When a control signal from the peak value detection means is sent to the gain control amplifier to control its gain, a control restriction that allows the control signal to pass only when there is a control signal from the peak value detection means in a direction that decreases the gain. and an addition means for adding the control signal from the sync level detection means and the control signal passed through the control limiting means and sending it to the gain control amplifier to control its gain, the peak AGC means includes a gain control amplifier that amplifies and outputs an input luminance signal, a sync level detection means that detects the sync level of the output signal of the control amplifier and generates a control signal to keep it constant, and peak value detection means for detecting the maximum amplitude (peak value) in the output signal and generating a control signal to keep it constant; and a control signal from the sync level detection means and a control signal from the peak value detection means. and an addition means for adding the control signal and sending it to the gain control amplifier to control its gain, and the keyed AGC means and the peak AGC means share other elements except for the control limiting means. AGC circuit of a magnetic recording/reproducing device.