JPH06284354A - Picture signal level adjusting device - Google Patents

Abstract

PURPOSE:To provide a picture signal level adjusting device capable of adjusting the level of picture signals by a simple hardware and preventing the degradation of the quality of display pictures due to the difference of the loss of transmission lines. CONSTITUTION:In a picture transmitter for which a picture transmission part 1 and a picture reception part 2 are connected with the transmission line 3, the transmission level of composite video signals by the picture transmission part 1 is set at the level sufficiently higher than the level required for compensating the loss of the transmission line 3 and the picture reception part 2 is provided with an attenuator 24 for attenuating the received composite video signals and a control part 25 for optimally adjusting the level of the composite video signals by detecting the propriety of synchronizing separation in a synchronizing separator part 21 and setting an attenuation level by the attenuator 24 at an appropriate value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image signal level adjusting device, and is used in an image transmitting device to prevent deterioration of image quality due to loss of a transmission line or the like.

[0002]

2. Description of the Related Art FIG. 2 is a block diagram showing a hardware configuration of a conventional general image transmission apparatus. Image transmitter 1
The image pickup means 11 is composed of an image pickup device such as a CCD, for example, and converts light incident through the lens into an electric signal. The encoder unit 12 synthesizes the luminance signal from the image pickup unit 11 and the synchronization signal to generate a composite video signal. The amplification unit 13 amplifies the composite video signal from the encoder unit 12 to a level sufficient to send it to the transmission line 3, and performs impedance matching with the transmission line 3. The sync separator 21 separates the sync signal from the composite video signal,
The luminance signal processing unit 22 generates a signal required by the display unit 23 from the luminance signal separated from the composite video signal. Display unit 23
Is a CRT, for example, which converts an electric signal into an optical signal using the signals generated by the sync separation unit 21 and the luminance signal processing unit 22 and displays an image.

Conventionally, the amplification section 13 of the image transmission section 1 amplifies and transmits a signal larger than an appropriate level in anticipation of the loss in the transmission line 3. However, if the loss of the transmission line 3 is not constant, it is difficult to set an appropriate transmission level and the quality of the display image deteriorates. Therefore, the video AGC circuit (Auto Ga) as shown in FIG.
In Control) is provided in the image receiving unit 2 and automatic gain adjustment is performed to suppress fluctuations in level. In the figure, Q1 and Q2 are transistors and D
1, D2 is a diode, R1, R2, R3 are resistors, C1
Is a capacitor, Vcc is a power supply voltage, and when the composite video signal Vx is input, an AGC voltage Va proportional to the strength of the composite video signal Vx is output. This AGC voltage V
By adjusting the gain on the basis of a, the image signal level is optimized.

[0004]

In the above-mentioned image transmission device, when an inexpensive transmission line such as a parallel two-wire cable is used as the transmission line, the loss of the transmission line itself is almost constant and the loss during the operation is continuous. There is little level fluctuation. However, the loss of the transmission line itself is quite large, and therefore the level difference due to the length of the transmission line cannot be ignored. Conventionally, the signal transmission level of the image transmission unit must be set assuming that the loss due to the transmission line becomes the minimum value of the loss of the transmission line used for the image transmission device. The larger the value, the lower the quality of the displayed image. Further, the level adjustment by the video AGC circuit as shown in FIG. 3 is effective but complicated, and there is a problem that it is wasteful because it is a circuit focused on suppressing level fluctuation during operation. .

The present invention has been made in view of the above points, and an object of the present invention is to adjust the level of an image signal with simple hardware to display a display image due to a difference in transmission line loss. An object of the present invention is to provide an image signal level adjusting device capable of preventing deterioration of quality.

[0006]

In order to solve the above-mentioned problems, the image signal level adjusting apparatus of the present invention, as shown in FIG. 1, is an image pickup means 11 for picking up an image.
An encoder unit 12 for converting an electric signal output from the image pickup unit into a composite video signal; an image transmission unit 1 including an amplifier unit 13 for amplifying a signal from the encoder unit; and a synchronization signal separated from the composite video signal. A sync separator 21;
An image receiving unit 2 including a luminance signal processing unit 22 for separating a luminance signal from the composite video signal and an image display unit 23 for displaying an image using the signals generated by the synchronization separating unit and the luminance signal processing unit, and an image. In the image transmission device including the transmission unit 1 and the transmission line 3 connecting the image reception unit 2, the transmission level of the composite video signal by the image transmission unit 1 is sufficiently higher than the level required to compensate the loss of the transmission line 3. The image receiving unit 2 is set to a large level, and the attenuator 24 that attenuates the received composite video signal and the presence / absence of synchronization separation in the synchronization separation unit 21 are detected and the attenuation amount by the attenuator 24 is set to an appropriate value. A control unit 25 is provided for optimally adjusting the level of the composite video signal.

[0007]

According to the present invention, the level of the composite video signal sent from the image transmitting section 1 to the image receiving section 2 is set to a level sufficiently higher than the level required to compensate the loss of the transmission line 3. Therefore, even if the transmission path 3 is long, the image receiving unit 2 can obtain a sufficiently large received signal. Attenuator 24 attenuates this received signal,
Since the control unit 25 controls so that the attenuation amount is set to an appropriate value that enables the sync separation in the sync separation unit 21, the level of the image signal can be adjusted with simple hardware.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic configuration diagram of an embodiment of the present invention. A synchronization separating unit 21 of the image transmitting unit 1 and the image receiving unit 2,
The brightness signal processing unit 22 and the display unit 23 are the same as in the conventional example. In the amplification section 13 of the image transmission section 1, the signal level is sufficiently higher than the signal level required by the image reception section 2, and the quality of the display screen displayed on the display section 23 does not deteriorate even if the loss due to the transmission path 3 is added. The composite video signal is amplified to a high level and sent to the image receiving unit 2. In the image receiving unit 2, the composite video signal is input to the attenuator 24 that attenuates the composite signal from the image transmitting unit 1. The attenuator 24 is composed of, for example, a resistance voltage dividing circuit having a multistage structure as shown in FIG. 4, and the attenuation amount can be set in multiple stages by a control signal from the control unit 25. In the figure, Ri and Ro are resistors for voltage division, SWi is a switch element, and various resistance values are prepared as the resistor Ri for voltage division, and any one of the switch elements SWi is turned on by a control signal.
As a result, the input signal is divided by the resistors Ri and Ro to obtain an attenuated output signal.

The output signal attenuated by the attenuator 24 is input to the sync separation section 21 and the luminance signal processing section 22. The sync separation unit 21 has, for example, a configuration as shown in FIG. 5, and after DC reproduction of the composite video signal Vx by the capacitor C2 and the diode D3, the voltage level thereof is divided by the resistors R4 and R5 by the comparator OP. The sync signal Vs is separated by comparing the sync signal Vs with the generated reference voltage. Resistance R
Reference numeral 6 is a pull-up resistor of the open collector output of the comparator OP. The synchronization signal Vs changes in a binary manner between High level and Low level.

The attenuation amount of the attenuator 24 is set by the control unit 25 so that the attenuation amount becomes maximum at the start of the circuit operation. When the signal is attenuated by the attenuator 24, the sync separator 21 cannot separate the sync signal. The control unit 25 monitors the synchronization signal output from the synchronization separation unit 21, and if it determines that the synchronization signal is not output, it sets the attenuator 24 so that the attenuation amount decreases. Hereinafter, if the same process is repeated and the synchronization signal is output, the optimum setting value of the attenuator 24 is read from the preset conversion table from the setting value of the attenuator 24 at that time, and the control unit 25 attenuates the attenuator 24. Set the amount.

Here, as shown in FIG. 6, the control unit 25 is composed of a general CPU 25A and is capable of retriggerable one-shot multi-vibrator 25B depending on the presence or absence of a sync signal.
Is detected through the control of the attenuator 24. The retriggerable one-shot multi-vibrator 25B is triggered by a sync signal and outputs a one-shot pulse longer than the interval of the sync signal, thereby converting the presence or absence of the sync signal into a signal that can be easily detected by the CPU 25A. For example, when there is a synchronization signal, High
When there is no synchronization signal, it is converted into a low level binary signal. The loss of the transmission line 3 is generally determined at the time of construction and does not change thereafter except for a slight change over time. Therefore, the following processing may be performed only when the power of the device is turned on. When the power is turned on, a control signal is output from the CPU 25A to the attenuator 24, and the attenuator 24 is set to have the maximum attenuation amount. At this time, since the composite video signal does not reach a level sufficient for performing the sync separation, the sync separator 21 does not output the sync signal. The CPU 25A detects that the sync signal is not output from the sync separator 21 through the retriggerable one-shot multivibrator 25B. Next, a control signal for adjusting the attenuator 24 by one step to the direction in which the attenuation amount decreases is detected and the presence or absence of the synchronization signal is detected. Hereinafter, the adjustment of the attenuator 24 is repeated until the synchronization signal is detected. When the sync signal reaches a signal level at which it can be separated, the sync separator 21 outputs the sync signal. CP
The U25A reads the optimum setting value of the attenuator 24 from the setting value of the attenuator 24 when the sync signal is detected, sets the attenuator 24, and ends the processing.

FIG. 7 is a flowchart showing the processing procedure of the control unit 25. First, in # 1, the attenuator 24
Set the value of to the maximum attenuation. In # 2, it is determined whether or not the sync signal is output. When the synchronizing signal is not output, the process proceeds to # 3, the attenuator value is set to the one in which the attenuation amount is reduced by one step, and the process returns to # 2. #
When it is determined that the synchronization signal is output in 2,
The process proceeds to step # 4, the optimum attenuator setting value is read from the current attenuator setting value, the attenuator value is set to the read optimum setting value in step # 5, and the process ends.

[0013]

According to the image signal level adjusting apparatus of the present invention, the image signal level reduction due to the loss of the transmission line is complemented by the simple structure as described above, and the image receiving is performed regardless of the loss of the transmission line. Therefore, it is possible to obtain an optimum signal level in the display section and prevent deterioration of the quality of the display image on the display section.

[Brief description of drawings]

FIG. 1 is a block diagram corresponding to a claim showing a basic configuration of the present invention.

FIG. 2 is a block diagram of a conventional general image transmission device.

FIG. 3 is a circuit diagram showing a configuration example of a video AGC circuit used in a conventional example.

FIG. 4 is a circuit diagram showing a configuration example of an attenuator used in the present invention.

FIG. 5 is a circuit diagram showing a configuration example of a sync separation unit used in the present invention.

FIG. 6 is a block diagram showing an embodiment of the present invention.

FIG. 7 is a flowchart showing a processing procedure of a control unit used in the present invention.

[Description of Reference Signs] 1 image transmitter 2 image receiver 3 transmission path 11 imaging means 12 encoder unit 13 amplification unit 21 sync separation unit 22 luminance signal processing unit 23 display unit 24 attenuator 25 control unit

Claims (1)

[Claims] 1. An image transmission unit including an image pickup unit for picking up an image, an encoder unit for converting an electric signal output from the image pickup unit into a composite image signal, and an amplification unit for amplifying a signal from the encoder unit. , An image is displayed using a sync separation unit that separates the sync signal from the composite video signal, a brightness signal processing unit that separates and processes the brightness signal from the composite video signal, and the signals generated by the sync separation unit and the brightness signal processing unit. In an image transmission apparatus including an image reception unit including an image display unit and a transmission line connecting the image transmission unit and the image reception unit, the transmission level of the composite video signal by the image transmission unit compensates for the loss in the transmission line. Is set to a level sufficiently higher than that required for the image reception unit, the image receiving unit detects whether the attenuator attenuates the received composite video signal and whether or not synchronization separation is possible in the synchronization separation unit. An image signal level adjusting apparatus having a control unit for optimally adjusting the level of the composite video signal by setting the attenuation amount by the attenuator to an appropriate value.