JPH05150730A - Multi-screen type display device - Google Patents

Abstract

PURPOSE:To make the brightness level constant by detecting variance of automatic brightness limiting device(ABL) control by performing feedback control with a control voltage so that a reference signal level matches a comparison signal level at all times. CONSTITUTION:A reference voltage inserting circuit 3 inserts a reference voltage in the flyback period of an inputted video signal or an overscanning equivalent period and extracts the reference voltage out of the rear stage of a contrast and/or brightness control circuit 11. A reference voltage signal extracted from the video signal of a specific core (image display device) is used as a reference signal and a reference voltage signal extracted from the video signal of another core, i.e. a comparison signal is compared with the reference signal to generate the control voltage. The feedback control is performed with this control voltage so that the reference signal level matches the comparison signal level. Consequently, variance in gain of the contrast and/or brightness control circuit 11 and ABL circuit 14 can be absorbed and all the cores can be constant in brightness level.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-screen display device, and more particularly, to a method for reducing variations in brightness in each core.

[0002]

2. Description of the Related Art A multi-screen display that stacks up a TV set to compose one screen has a shorter depth and relatively higher brightness than a front-projection-type or rear-projection-type large-screen display. Used in. Individual television sets (hereinafter referred to as cores) are in practical use, such as cathode ray tube direct-view type and projection type. Above all, the projection type is lighter than the direct view type,
Since the screen surface is flat, it has become popular.

Some multi-screen displays include, for example, four cores 1a to 1d as shown in FIG. FIG. 13 is a diagram showing a system configuration of the multi-screen display in FIG. 40
Is an image enlarging device, 4a to 4d and 41 are video signal input terminals, 1a to 1d are cores, 6 is an ABL comparison circuit, and 60a.
˜60d are ABL control information input terminals. A video signal is output from the image enlarging device 40 and added to the core 1a in the upper left part so that the first half of the horizontal and vertical scanning periods of the normal video signal is displayed in the full screen. Similarly, a video signal output from the image enlarging device 40 is output to the core 1b at the upper right such that the latter half of the horizontal scanning period and the first half of the vertical scanning period of the video signal are displayed in full screen. Added. Similar processing is performed on the core 1c and the core 1d.

Here, since the contents of the input video signal are basically different in each core, when the ABL (automatic brightness limiting) operates independently for each core, the contrast of each core is different. Will end up. Therefore, as shown in FIG. 13, the ABL control information of each core is input to the ABL comparison circuit 6, and the ABL of the core having the highest average brightness is input.
The control information controls the screen brightness of all cores in common. As a result, the ABL does not operate independently for each core, and the brightness of all the cores is controlled in principle to be constant.

[0005]

In the above-mentioned prior art, the core which outputs the maximum value of the control information of ABL feeds back its own control information, and therefore AB
Closed loop control by L is performed. However, the cores other than that are given the control information of other cores instead of the control information of their own, and thus become open loop control. Therefore, due to variations in control characteristics of the respective cores, that is, variations in contrast and / or gain of the brightness control circuit or ABL circuit, there is a problem that the contrasts of the respective cores do not completely match and the brightness level varies. It was For example, when gray with a constant brightness is displayed on the four cores in FIG. 12 and high-luminance characters and the like are displayed only on the core 1a to make the average brightness of the screen higher than a predetermined brightness,
The ABL of the core 1a automatically outputs the ABL control information to the contrast and / or brightness control circuit in an attempt to reduce the average brightness of its own screen. The average brightness of the other cores 1b to 1d is lowered by the ABL control information of the core 1a. However, if the contrast and / or the gain of the brightness control circuit or the ABL circuit varies, 1a to 1d
There is a problem in that the brightness levels of the cores are different from each other, and the brightness at the boundary of each core becomes discontinuous. An object of the present invention is to provide means for absorbing variations in ABL control characteristics as a system and keeping the brightness level of each core constant.

[0006]

In order to achieve the above object, according to the present invention, a reference voltage insertion for inserting a common reference voltage during a blanking period or a period corresponding to overscan of a video signal input to each core. A circuit is provided, and the reference voltage signal in the video signal is taken out from the subsequent stage of the contrast and / or brightness control circuit of each core, and feedback control is performed on each core so that the reference signal level of each core is the same.

[0007]

As a result, variations in the contrast and / or gain of the luminance control circuit or ABL circuit can be absorbed, and variations in the luminance level of each core due to the above factors can be suppressed.

[0008]

FIG. 1 shows a block diagram of a first embodiment of the present invention. Here, in order to simplify the description, a case where four cores as shown in FIG. 12 are used will be described as an example.

FIG. 1 shows cores 1a to 1d, a contrast and / or brightness control circuit 11, a CRT (cathode ray tube) drive circuit 12, a CRT 13, and an ABL (automatic brightness limiting) circuit 1.
4, a high voltage generation circuit 15, a reference voltage application terminal 16, a beam current detection resistor 17, a + B (power supply voltage) application terminal 18, and a switch 50. However, the contrast and / or brightness control circuit 11 extends the contrast of the video signal (or increases the brightness) when the control voltage is high.
However, if it is low, the operation is performed so as to suppress the contrast of the video signal (or reduce the brightness). Further, the ABL circuit 14 detects the beam current flowing from the high voltage generation circuit 15 by the beam current detection resistor 17 and generates a control voltage applied to the contrast and / or brightness control circuit 11. Reference voltage inserting circuits 3a to 3d insert the reference voltage in the overscan period of the video signal input to the contrast and / or brightness control circuit 11. Two
Is a comparison circuit, which compares the reference voltage inserted in the video signal of each core and outputs the comparison result. Reference numeral 6 denotes an ABL comparison circuit, which compares the ABL control information of each core, selects the core showing the maximum beam current value, outputs the ABL control information of the core showing the maximum beam current value, and switches 50 of each core. Control.

FIG. 2 shows an example of operating characteristics of the ABL circuit 14. The horizontal axis represents the beam current and the vertical axis represents the control voltage.

The operation of this embodiment will be described below.
It is assumed that a predetermined image is displayed on the screen of the CRT 13 of each core by the image signal input from the image signal input terminals 4a to 4d. For example, in the core 1a, the beam current Ib flows from the high voltage generation circuit 15 according to the screen brightness on the CRT 13. + Voltage applied to terminal 18
Let B be the resistance value of the beam current detection resistor 17 and R be A
A voltage + BR-Ib (= Vz) is generated at the input of the BL circuit 14. The beam current Ib increases as the display screen becomes brighter, and conversely Vz decreases. The average brightness of the screen, that is, the beam current Ib is at a predetermined level (see FIG. 2).
In the case of Ia) or less, the ABL circuit 14 sends a constant voltage (Vcc in FIG. 2) to the ABL comparison circuit 6. When the beam current Ib becomes equal to or higher than a predetermined level (Ia in FIG. 2), the ABL circuit 14 outputs Vz at that time to the ABL comparison circuit 6. That is, the ABL circuit 14 operates so as to lower the control voltage and lower the average brightness when the beam current Ib exceeds a predetermined level. The ABL circuits 14 of the other cores also perform the same operation. The ABL comparison circuit 6 selects the lowest value among the control voltages output from all the cores, that is, the ABL control information of the core showing the maximum beam current value,
Add control information (minimum control voltage) to all cores.

Here, if the switches 50 of all the cores are on the side of 50a, the average brightness is the highest and A
A core that outputs BL control information performs closed-loop control by its own ABL control information, but other cores perform open-loop control because their ABL control information is not fed back. Therefore, variations in the gain of the respective open loops, that is, variations in the contrast and / or the gain of the luminance control circuit 11 and the ABL circuit 14 cause variations in the luminance.

Therefore, the circuit for absorbing the variation in gain, which is a feature of the present invention, that is, the reference voltage inserting circuits 3a to 3 is used.
The operation of d and the comparison circuit 2 will be described.

FIG. 3 is an example of a block diagram for one system of the reference voltage inserting circuits 3a to 3d. 16 is a reference voltage (B /
W) input terminal, 31 is a buffer, 33 is a switch for switching input to the contrast and / or brightness control circuit 11, and 32 is a switching pulse (SP) input terminal for controlling the switch. The reference voltage (B / B) is commonly applied to the input terminal 16 for the reference voltage insertion circuits 3a to 3d of each core.
W) is added.

FIG. 4 is an example of an operation waveform diagram showing the principle of reference voltage insertion in the circuit of FIG. In FIG. 4, T represents an overscan period. In the multi-screen display device, the overscan period is set to, for example, 8
% Is set. The reference voltage (B / W) is, for example, a signal in which the white level (W) and the black level (B) are alternately switched every 1H of the video signal. Switching pulse (SP)
Is a control pulse having a pulse width T which is synchronized with the falling edge of the horizontal synchronizing pulse, for example. The switching pulse (SP) controls the input signal to the contrast and / or brightness control circuit 11, and causes the buffer 31 to apply the reference voltage (B / W) during the overscan period in the first half of the scanning period. During other periods, the video signal is input from the video signal input terminal 4. Therefore, 1H is applied during the overscan period of the first half of the video signal.
The white level (W) and black level (B) reference voltages are alternately inserted every time.

Next, examples of a block diagram and an operation waveform diagram of the comparison circuit 2 are shown in FIGS. 5 and 6, respectively. In this example,
For example, the average brightness of the screen of the core 1d is the highest, and the ABL comparison circuit 6 selects the ABL control information of the core 1d,
It is assumed that the ABL control information is output to each core. Here, the reference voltage signal inserted in the video signal of the core 1d having the highest average brightness is used as a reference signal, and the reference signal is compared with the reference voltage signal (comparison signal) inserted in the video signal of another core. To do. Switch 5 in each core
0 is switched by the ABL comparison circuit 6, and for the core 1d having the highest average brightness, the switch 50 is tilted to the side of 50a so that its own ABL control information is fed back, and for the other cores 1a to 1c, the switch 50 is switched.
To 50b so that the control voltage from the comparison circuit 2 is fed back. 23a to 2 in FIG.
3d is an input terminal of a video signal after contrast and / or brightness control, 51, 52a to 52d and 53a to 53d.
Is a switch, 21 is a comparator, 22a to 22d are low-pass filters, 211 is a comparison signal input terminal, 212 is a reference signal input terminal, and 24a to 24d are control voltage output terminals. The switch 51 is connected to the input terminal 23 of the video signal of the core different for each 1H by the rising edge of the pulse of the SW 51 shown in FIG. 6, and the comparator 21 for each 1H using the reference voltage signal of the video signal of each core as the comparison signal. To enter. The switches 52a to 52d select the video signal of the core 1d having the highest average brightness as a reference signal, and input the reference signal to the comparator 21. For controlling the switches 52a to 52d, for example, a control signal of the switch 50 of the cores 1a to 1d may be used. The comparator 21 compares the inserted white level (W) and black level (B) reference voltage signals and outputs a comparison signal (1
a, 1b, 1c) and the black level (B) of the reference voltage signal are higher or lower than the reference voltage signal of the reference signal (1d). The comparator 21 may be, for example, a voltage comparator. Switches 53a-5
3d is a low-pass filter corresponding to each core showing the comparison result of only the reference voltages of the white level (W) and the black level (B) inserted in the overscan period of the video signal by the pulses of SW53a to SW53d shown in FIG. 22a to 22d
To enter. For example, the comparison result is input to the low-pass filter 22a corresponding to the core 1a every 8H cycle by the SW 53a. However, the video signal of the reference signal (1d) is also input to the comparator 21 as a comparison signal, and the comparison result is sent to the low-pass filter 22d.
Since the switch 50 of the core 1a is connected to the side of 50a, the output of the low-pass filter 22d is not sent to the contrast and / or brightness control circuit 11 of the core 1d. That is, the switch 50a is set to 50a so that its own ABL control information is fed back to the contrast and / or brightness control circuit 11 of the core having the highest average brightness.
Connected to the side. Further, the switch 50 is set to 50 so that the control voltage from the comparison circuit 2 is fed back to the contrast and / or brightness control circuit 11 of the other cores.
Connect to side b. This can prevent an erroneous control amount from being sent to the contrast and / or brightness control circuit 11.

Then, the low pass filters 22a to 22d.
The control voltage extracted by is input to the contrast and / or brightness control circuit 11. As a result, the cores 1a to 1c are feedback-controlled so that the reference voltage of each of the cores 1a to 1c matches the reference voltage of the core 1d, and the variation in the gain of the ABL circuit or the like can be absorbed and the variation in the brightness level due to the variation can be suppressed.

Although the example in which the average brightness of the core 1d is the highest has been described above, the operation is the same when the average brightness of the other cores is also high, and the description thereof will be omitted.

In this embodiment, the case where the reference signal is inserted into the overscan period of the horizontal cycle has been described as an example, but the reference signal may be inserted into the vertical overscan period. In this case, it goes without saying that the control pulse and the switching pulse (SP) for the switches 51, 53a to 53d are generated in accordance with the vertical cycle.

A second embodiment of the present invention is shown in FIG. This is characterized in that the reference voltage is inserted in the blanking period instead of the overscan period. Reference voltage (B /
W) is a signal in which the white level (W) and the black level (B) alternate with each other for every 1H of the video signal. The switching pulse (SP) controls the input signal to the contrast and / or brightness control circuit 11 of FIG. The reference voltage insertion circuit 3 shown in FIG.
When P) is ON, the reference voltage (B / W) from the buffer 31
Is applied, and the video signal is input from the video signal input terminal 4 during the other period. Therefore, the white level (W) and black level (B) reference voltages are inserted every 1H in the blanking period of the video signal.

FIG. 8 is an example of an operation waveform diagram of the comparison circuit 2 of FIG. 5 when the above-mentioned reference voltage is inserted in the blanking period. In FIG. 5, the switch 51 is connected to the input terminal 23 of the video signal which is different for every 2H by the rising edge of the pulse of the SW 51 shown in FIG. 8, and the white level (W) and the black level (B) of each video signal are used as a reference. The voltage signal is input to the comparator 21 as a comparison signal. Further, the switch 52 selects the video signal of the core having the highest average brightness as the reference signal and inputs it to the comparator 21. Since the ABL control variation correction operation after the comparator 21 is the same as that described above, description thereof will be omitted. Here, the white level (W) reference voltage is still inserted in the blanking period of the video signal output from the contrast and / or brightness control circuit 11, but normally it is retraced in the CRT drive circuit 12. Since an erasing circuit is included, no diagonal white line (return line) appears on the screen. The feature of this embodiment is that by inserting the reference voltage in the blanking period, it is possible to insert and compare the reference voltage with a margin, and the overscan period is very short, and it is difficult to insert and compare the reference voltage. Effective at any time.

It should be noted that in this embodiment as well, as in the case of the first embodiment, the insertion position of the reference signal may be not only the horizontal blanking period but also the vertical blanking period. Nor.

Next, an embodiment of the comparison circuit 2 is shown in FIG.
Further, examples of operation waveform diagrams of the comparison circuit 2 are shown in FIGS. 10 shows the case where the reference voltage is inserted during the overscan period, and FIG. 11 shows the case where the reference voltage is inserted during the blanking period. In this embodiment, for example, the average brightness of the screen of the core 1d is the highest, and the ABL comparison circuit 6 selects the ABL control information of the core 1d and outputs the ABL control information to each core. Further, the reference voltage signal inserted in the video signal of the core 1d having the highest average brightness is used as a reference signal, and the reference signal is compared with the reference voltage signal (comparison signal) inserted in the video signal of another core. .. In FIG. 9, 23a to 23d are video signal input terminals, 52a to 52d and 53a to 53d are switches, and
1a to 21d are comparators, 22a to 22d are low-pass filters, 211a to 211d are input terminals for comparison signals, 21
2a to 212d are reference signal input terminals, and 24a to 24d.
Is an output terminal of the control voltage. Input terminals 23a-23d
A video signal after contrast and / or brightness control from the cores 1a to 1d with a reference voltage (B / W) inserted therein is input to and is sent to the comparators 21a to 21d corresponding to each core. The switches 52a to 52d select the video signal of the core 1d having the highest average brightness as a reference signal, and commonly input the reference signal to the comparators 21a to 21d. Each of the comparators 21a to 21d compares the inserted white level (W) and black level (B) reference voltage signals, and outputs the comparison signal (1a,
It outputs voltage information indicating whether the reference voltage signals of the white level (W) of 1b and 1c) and the black level (B) are higher or lower than the reference voltage signal of the reference signal (1d). Switches 53a to 53
When the reference voltage (B / W) is inserted in the overscan period, d is the white level (W) and the black level (W) inserted in the overscan period of the video signal by the pulse of SW53 shown in FIG. The comparison result of only the reference voltage of B) is the low-pass filter 22a-22d corresponding to each core.
To enter. When the reference voltage (B / W) is inserted in the blanking period, the switches 53a to 53d are
By the pulse of SW53 shown in FIG. 11, the comparison result of only the reference voltage of the white level (W) and the black level (B) inserted in the overscan period of the video signal is sent to the low-pass filters 22a to 22d corresponding to each core. input. The operations of the comparison circuit 2 and the core 1 after this are the same as those described above, and therefore will be omitted. The feature of the comparison circuit 2 is that by providing the comparators 21a to 21d corresponding to the respective cores, the control voltage can be fed back to all the cores every 1H, and more rapid control can be performed.

Next, a third embodiment of the present invention is shown in FIG. Since the basic configuration of this embodiment is almost the same as that of the first embodiment shown in FIG. 1, only the core 1a is shown. The present embodiment is characterized in that the ABL control information is detected not from the beam current but from the average value of the CRT drive voltage. In FIG. 14, reference numeral 12 is a CRT drive circuit, which includes a power supply voltage applying terminal 121 and resistors 122 and 12
5, 126, 128 and transistors 124, 127
And a color-difference signal input terminal 124 and a blanking circuit 129, and supplies -R, -G, -B primary color signals to the CRT 13. The resistor 141 and the capacitor 142 are AB
The average value of the CRT drive voltage input to the L circuit 14 is generated. Reference numeral 143 is a terminal for inputting the average value of the CRT drive voltage, and 144 is a terminal for outputting the control voltage.

FIG. 15 is a graph showing the operation of the ABL circuit 14. The horizontal axis represents the average value of the CRT drive voltage, and the vertical axis represents the control voltage.

The operation of this embodiment will be described below.
It is assumed that a predetermined image is displayed on the screen of the CRT 13 by the input image signal. Transistor 12
To the collector of No. 7, the video signal blanked by the blanking circuit 129, that is, the CRT drive voltage is output. The CRT drive voltage is applied to the resistor 141 and the capacitor 14.
2 is averaged, and this average value is sent to the terminal 143. A
The BL circuit 14 outputs a constant control voltage (Vcc in FIG. 15) when the average brightness of the screen, that is, the average value of the CRT drive voltage is below a predetermined level (Va in FIG. 15). When the average value of the CRT drive voltage is equal to or higher than a predetermined level, the control voltage is reduced in proportion to the input voltage as shown in FIG. As described above, the ABL circuit 14 detects the average value of the CRT drive voltage, and when the average brightness of the CRT screen, that is, the average value of the CRT drive voltage becomes equal to or higher than a predetermined level, the control voltage is decreased to reduce the contrast and / or the brightness. It operates so as to suppress the output amplitude of the control circuit 11. Contrast and / or brightness control circuit 11 or A
The correction operation of the gain variation of the BL circuit 14 is the same as that of the first embodiment, and therefore its description is omitted.

The feature of this embodiment is that the ABL control information is CR.
Even in the case of the circuit configuration that detects from the average value of the T drive voltage,
That is, a circuit that absorbs variations in gain can be applied.

FIG. 16 shows a fourth embodiment of the present invention. This embodiment shows a more practical configuration.

The minimum value circuit 16 is a beam current detection resistor 17
This is a circuit that compares the voltage detected in step 3 with the external voltage applied to the terminal 216a (this becomes the voltage detected by the beam current detection resistor 17 of another core) and selects the smaller voltage. Further, since the terminals 216a to 216d are connected to each other, the output of the minimum value circuit 16 of each core becomes the same as the voltage detected by the beam current detection resistor 17 of the core having the highest average brightness, and the ABL circuit 14 performs simultaneous output. The contrast and / or brightness control circuit is controlled.

The minimum value circuit 16 may have the configuration shown in FIG. 17, for example. The terminal 218a is an application terminal for the voltage detected by the beam current detection resistor 17, and the terminal 217a is an output terminal.

For example, if the voltage at the terminal 218a is at the terminal 216
When it is smaller than a, the transistor 223 is cut off and the voltage of the terminal 218a is output to the output terminal 217a, and at the same time, the base-emitter of the transistor 224 is connected to output the voltage of 218a to the terminal 216a.

On the contrary, when the voltage of the terminal 218a is higher than that of the terminal 216a, the transistor 224 is cut off while the transistor 223 is operated and the emitter-collector is conductive, so that the voltage of the terminal 216a is changed.
is output to a.

The use of such a minimum value circuit in the core simplifies the configuration as compared with FIG. Now, as described above, only connecting the minimum value circuit 16 results in open loop control except for the core having the highest average brightness.
The brightness level of each core varies due to the gain variation of the contrast and / or the luminance control circuit and the like. Therefore, the comparison circuit 102 controls the contrast control circuit 111 and the brightness control circuit 112.

In addition to the contrast and / or brightness control circuit 11 controlled by the ABL circuit 14, a contrast control circuit 111 and a brightness control circuit 112 are provided to control the contrast and brightness without the switch 50 of FIG. It is possible.

For example, as shown in FIG. 18, the comparison circuit 102 mainly includes a microcomputer 70 and A / D converters 71a and 7a.
2a, 71b, 72b, 71c, 72c, 71d, 72
d and D / A converters 73a, 74a, 73b, 74
b, 73c, 74c, 73d, 74d.

A / D converters 71a, 71b, 71
The video signals after contrast and / or brightness control are input to c and 71d, and the A / D converters 72a and 72d are input.
The voltages detected by the beam current detection resistor 17 are input to b, 72c, and 72d.

A / D converters 71a, 71b, 71
The conversion timings of c and 71d are, of course, reference voltage insertion positions, and the conversion timing pulse may be generated by software by using horizontal / vertical synchronization (Hsync, Vsync) as an interrupt signal of the microcomputer 70, for example. Of course, a dedicated logic circuit may be used. The insertion of the reference voltage may be the same as that in the first or second embodiment, and the description thereof will be omitted.

The microcomputer 70 includes an A / D converter 72a,
Based on the data converted by 72b, 72c and 72d, the minimum value of the voltage detected by the beam current detection resistor 17, that is, the core having the highest average brightness is selected.

On the other hand, the A / D converters 71a, 71b,
In 71c and 71d, the reference signals of the core 1a, the core 1b, the core 1c, and the core 1d after the contrast and / or brightness control are A / D converted, and the white level and black level information is taken into the microcomputer 70.

The concept of the operation of the microcomputer 70 will be described with reference to FIG.

There is information on the white level and the black level of the core 1a, core 1b, core 1c, and core 1d fetched by the microcomputer 70. Of these, the black level information is directly input to the comparators 122a, 122b, 122c. The white level is input to the comparators 121a, 121b, 121c as the amplitude level information by taking the difference from the black level. Here, assuming that the core 1d is selected as the core having the highest average luminance, the information on the black level and the amplitude level of the core d is calculated by the comparators 122a, 122b, 122c, 121a, 121.
This is the reference information for b and 121c. That is, the comparator 1
The output of 22a, 122b, 122c becomes the control information of the black level of each core, and the comparators 121a, 121b, 121
The output of c becomes the control information of the amplitude level of each core. The black level control information controls the brightness and the amplitude level information controls the contrast. Of course, what has been described so far is the software processing of the microcomputer 70. Actually, as shown in FIG. 18, for example, the black level control information (corresponding to the output of the comparator 122a) of the core 1a is D / A.
The converter 74a converts the analog voltage to control the brightness control circuit 112, and the amplitude level control information (corresponding to the output of the comparator 121a) is converted to an analog voltage by the D / A converter 73a, and the contrast control circuit 111.
To control. The same applies to the cores 1b and 1c.

By the above, feedback control is performed for all the cores, and it is possible to suppress the brightness variation due to the open loop control described above.

A major feature of this embodiment is that the comparison circuit 102
And a contrast control circuit 111 controlled by the same
The brightness control circuit 112 and the brightness control circuit 112 are completely separated from the minimum value circuit 16, the ABL circuit 14, and the contrast and / or brightness control circuit 11, and thus operate independently.

The circuit system including the minimum value circuit 16, the ABL circuit 14, and the contrast and / or brightness control circuit 11 does not operate unless it is in the operating region of the ABL circuit 14 (for example, the beam current in FIG. 2 is Ia or more). Comparison circuit 10
2. Contrast control circuit 111, brightness control circuit 112
Since the circuit system consisting of can always perform feedback control, it is possible to suppress the brightness variation of each core not only in the operating region of the ABL circuit 14 but also in the non-operating region of the ABL circuit 14, and it is possible to suppress changes over time and changes in temperature. Is an effective system against.

Here, the video signal after the contrast and / or brightness control is divided and output from the output of the CRT drive circuit 12. In this way, the C of each core is extracted.
It goes without saying that it is possible to suppress the brightness variation due to the gain variation of the RT drive circuit 12.

FIG. 20 shows the fifth embodiment of the present invention.

The circuit shown in FIG. 20 is substantially different from the circuit shown in FIG. 16 in that the voltage detected by the beam current detection resistor 17 is not taken into the comparison circuit 202, and the reference voltage is inserted in the same manner.

In FIG. 16, this is done to select the core with the highest average brightness, but in the embodiment shown in FIG. 20, the core with the highest average brightness is not selected.

That is, the reference core is fixed.

For example, assume that the core 1d is fixed as a reference core.

First, consider the case where the core 1a has the highest average luminance. At this time, the contrast of the core 1a and / or
The brightness control circuit 11 is in the state where the brightness level is lowered most by the ABL circuit 14. However, since the reference is the core 1d, feedback control is applied to the core 1a via the comparison circuit 202 to the contrast control circuit 111 and the brightness control circuit 112 so as to increase the brightness. As a result, the brightness of the screen tries to increase, but soon
The voltage detected by the beam current detection resistor 17 decreases, and the increase in brightness is suppressed via the minimum value circuit 16 and the ABL circuit 14. At the same time, the output of the minimum value circuit 16, that is, the voltage detected by the beam current detection resistor 17 is also transmitted to other cores.

As a result, the level of the core 1d is also lowered, the difference from the core 1a is reduced, and finally it stabilizes when the reference signals match.

Since the other cores are the same as those in FIG. 16, the description thereof will be omitted. Further, when the core 1d has the highest average brightness, the operation is exactly the same as that in FIG.

In this way, even if the reference core is fixed, the same operation as in FIG. 16 can be performed.

According to this embodiment, the beam current detecting resistor 1
Since the voltage detected in 7 is not taken in, for example,
The A / D converters 71a, 71b, 71c, 7 of FIG.
1d becomes unnecessary and the minimum value selection by the microcomputer becomes unnecessary, and the configuration of 202 becomes simple.

FIG. 21 shows the sixth embodiment of the present invention.

The feature of FIG. 21 is that the output of the comparison circuit 202 is an amplifier 80R, 80G, 80B, a clamp circuit 81R,
That is, it is fed back to 81G and 81B and controlled independently of RGB. This is for example contrast and / or
It can be used when the output of the brightness control circuit 311 is a primary color signal output. Of course, the comparison circuit 302 performs A / D conversion and comparison processing for the three RGB colors and amplifiers 80R and 80
Although a D / A converter for controlling the G, 80B and clamp circuits 81R, 81G, 81B is required, the control procedure is the same as that in FIG. Further, the insertion of the reference voltage may be the same as in the first embodiment or the second embodiment, so the description will be omitted.

By controlling RGB independently in this way,
It is possible to more accurately suppress variations in RGB signals among the cores, and exert an outstanding effect in adjusting and maintaining white balance in a multi-screen.

A seventh embodiment of the present invention is shown in FIG.

The major feature of FIG. 22 is that the reference voltage inserting circuit is incorporated in the core. Figure 2 otherwise
Since it is exactly the same as 0, description of the operation itself is omitted.

In this embodiment, since the reference voltage inserting circuit is different for each core, the white level and the black level should be different for each core. So, for example, core 1a, core 1
b, the core 1c, and the core 1d are simultaneously displayed with white patterns so that the color temperature of all the cores is the same. For example, after adjusting the gain of the CRT drive circuit, the contrast and / or brightness of each core is controlled. The white level voltage applied to the reference voltage inserting circuit is adjusted so that the white level of the subsequent reference voltage matches. Next, core 1a, core 1b, core 1
c, the gray pattern is displayed on the core 1d at the same time, and the CRT cutoff is adjusted so that all the cores have the same brightness, and then the contrast of each core and / or
The black level voltage applied to the reference voltage insertion circuit is adjusted so that the black level of the reference voltage after the brightness control matches.

After that, the comparator circuit 202 is caused to operate in exactly the same manner as in FIG. 20, so that the variation in the brightness of each core can be suppressed.

According to this embodiment, it is not necessary to have the reference voltage inserting circuit on the image enlarging device 40 side, and the image enlarging device 4
The configuration of 0 becomes simple.

Since the insertion position of the reference voltage and the like may be the same as those in the first or second embodiment, the description thereof will be omitted.

FIG. 23 shows the eighth embodiment of the present invention. FIG. 23 shows an example in which the present invention is applied to, for example, a 12-screen multi-screen display.

When the number of cores increases, there is a problem in production when the terminals 216a, 216b, 216c, 216d are simply connected as shown in FIG. For example, as shown in FIG. 24, when different pictures are to be displayed on four of the twelve, it is necessary to control each picture. Therefore, the matrix switch 90 is provided to collectively control the terminals 216a to 216l of each core. The matrix switch 90 may be constituted by, for example, an analog switch, a control circuit 91 may be provided, and the control circuit 91 may be controlled by the microcomputer of the comparison circuit 402. Although it has been changed, the comparison circuit may be configured by a microcomputer as in the case of FIG. 20, for example. Of course, it is necessary to increase the number of A / D converters and D / A converters by the number of cores. Since the operation itself is the same as that in FIG. 20, the description is omitted. A ninth embodiment of the present invention is shown in FIG.

The feature of FIG. 25 is that digital data transmission is carried out by the data modem 95 built-in comparison circuit 402 and the RS232C interface in the core.

The data modem 95 converts the reference signal after contrast and / or brightness control into digital data in the core and sends it to the comparison circuit 402, and decodes the control information from the comparison circuit 402 to control the contrast. The circuit 111 and the brightness control circuit 112 are controlled.

On the other hand, the comparator circuit 402 is also provided with data modems 96a, 96b, 96c and 96d as shown in FIG. 26 to perform data transmission with the data modem 95 of each core. Since the processing procedure of the microcomputer 70 may be the same as that in FIG. 20, detailed description thereof will be omitted. By thus connecting the image enlarging device and the multi-screen with the digital data transmission line, the effect of the present invention can be exhibited even if there is a noisy installation location or the ground potential fluctuates due to the image enlarging device and the multi-screen being far apart. ..

FIG. 27 shows a tenth embodiment of the present invention.

The feature of this embodiment is that the comparison circuit 502 controls the contrast control circuit 111 and the brightness control circuit 112, including the ABL function of the core.
6 to contrast and / or brightness control circuit 11, A
Since the BL circuit 14 and the minimum value circuit 16 are excluded from the configuration, there is an advantage that the configuration of the core is simplified.

The comparison circuit 502 is the comparison circuit 102 of FIG.
The same configuration as is possible, but with the minimum value circuit 16 and AB in the core
Since there is no L circuit, it is only necessary to add these functions to the microcomputer 70. That is, for example, the terminals 76a, 76
The voltage detected by the beam current detection resistor 17 of each core applied to b, 76c, and 76d is compared, and the beam current is shown in FIG.
The control voltage of FIG. 2 may be applied to the contrast control circuit 111 and / or the brightness control circuit 112 to the core having the largest current value among the cores exceeding Ia.

The other functions of the microcomputer 70 are the same as those in the fourth embodiment, and the detailed description will be omitted.

FIG. 27 shows an eleventh embodiment of the present invention.

The feature of the present embodiment is that, for example, in addition to the configuration of FIG. 22, γ conversion circuits 97a, 97b, 97c, 97d are added, and γ of the CRT 13 of the cores 1a, 1b, 1c, 1d is added.
It is to absorb variations in characteristics.

Γ conversion circuits 97a, 97b, 97c, 97
d is the A / D converter 17 as shown in FIG. 29, for example.
This can be realized by changing the input / output characteristics of the video signal converted into a digital signal in 2 by a LUT (look-up table) and converting it into an analog signal in the D / A converter 174. It goes without saying that the LUT can be composed of, for example, a ROM.

That is, the means described in FIG. 22 (seventh embodiment) suppresses the variation in the ABL control characteristics among the cores, and the γ conversion circuits 97a, 97b, 97c, 9 are provided.
In 7d, variations in the γ characteristic of the CRT 13 can be absorbed, and a single uniform multi-screen display can be obtained.

Here, the γ conversion circuits 97a and 97 are used.
b, 97c, 97d are placed outside the core, but core 1
It may be inside a, 1b, 1c, 1d or inside the image enlarging device 40. In addition, the γ conversion circuits 97a and 97
Although FIG. 22 is shown as the configuration of the other party to which b, 97c, and 97d are connected, it goes without saying that there is no problem even if the configurations of FIG. 16 and FIG.

[0079]

According to the present invention, by the feedback control by the comparison circuit, it is possible to suppress the brightness variation due to the dispersion of the ABL control characteristics of each core, and to obtain the brightness continuity at the boundary of each core, and to display the image. The quality can be improved.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a first embodiment of the present invention.

FIG. 2 is a graph showing the operation of the ABL circuit according to the first embodiment of the present invention.

FIG. 3 is a configuration diagram of a reference voltage insertion circuit used in the present invention.

FIG. 4 is a timing chart showing the operation of the reference voltage insertion circuit of the present invention.

FIG. 5 is a configuration diagram of a comparison circuit used in the present invention.

FIG. 6 is a timing chart showing the operation of the comparison circuit of the present invention.

FIG. 7 is a diagram showing a second embodiment of the present invention.

FIG. 8 is a timing chart showing another operation example of the comparison circuit of the present invention.

FIG. 9 is another configuration diagram of a comparison circuit used in the present invention.

FIG. 10 is a timing chart showing an operation example of another comparison circuit of the present invention.

FIG. 11 is a timing chart showing another operation example of another comparison circuit of the present invention.

FIG. 12 is a configuration diagram showing installation of an image display device.

FIG. 13 is a block diagram showing a conventional example.

FIG. 14 is a configuration diagram showing a third embodiment of the present invention.

FIG. 15 is a graph showing the operation of the ABL circuit according to the second embodiment of the present invention.

FIG. 16 is a diagram showing a fourth embodiment of the present invention.

17 is a circuit configuration diagram of a minimum value circuit 16 of FIG.

18 is a configuration diagram of a comparison circuit 102 in FIG.

FIG. 19 is an operation conceptual diagram of the microcomputer 70.

FIG. 20 is a diagram showing a fifth embodiment of the present invention.

FIG. 21 is a diagram showing a sixth embodiment of the present invention.

FIG. 22 is a diagram showing a seventh embodiment of the present invention.

FIG. 23 is a diagram showing an eighth embodiment of the present invention.

FIG. 24 is a diagram illustrating the operation of FIG. 23.

FIG. 25 is a diagram showing a ninth embodiment of the present invention.

FIG. 26 is a configuration diagram of the comparison circuit 402 in FIG. 25.

FIG. 27 is a diagram showing a tenth embodiment of the present invention.

FIG. 28 is a diagram showing an eleventh embodiment of the present invention.

29 is a configuration example of the γ conversion circuit 97a of FIG. 28.

[Explanation of symbols]

1a to 1d ... Core, 2 ... Comparison circuit, 3 ... Reference voltage insertion circuit, 6 ... ABL comparison circuit, 11 ... Contrast and / or brightness control circuit, 12 ... CRT drive circuit, 13 ...
CRT, 14 ... ABL circuit, 15 ... High voltage generating circuit, 21
... comparators, 22a to 22d ... low-pass filters, 40 ...
Image enlarging device, 50 ... Switch, 16 ... Minimum value circuit, 1
11 ... Contrast control circuit, 112 ... Luminance control circuit,
70 ... Microcomputer, 102, 202, 302, 402, 5
02 ... Comparison circuit, 90 ... Matrix circuit, 95, 96
a, 96b, 96c, 96d ... Data modem, 97a,
97b, 97c, 97d ... γ conversion circuit, 98 ... LUT

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Takeshi Maruyama 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Stock Company Hitachi Ltd. AV Equipment Division

Claims (16)

[Claims] 1. A multi-screen display device for displaying a single image by combining a plurality of cathode ray tube image display devices (cores), and means for detecting an average beam current for each core, and the detection. Means for selecting the largest beam current value information from the average beam current for each core, and commonly controlling the contrast and / or brightness of all cores according to the selected beam current value information, or for each core Means for detecting the average value of the CRT drive voltage, and selecting the largest average value information from the detected average value of the CRT drive voltage for each core, and according to the selected average value information of the CRT drive voltage, Multi-screen display having ABL (Automatic Brightness Limiting Device) control means composed of means for commonly controlling contrast and / or brightness A) In the device, a reference voltage inserting circuit for inserting a reference voltage during the blanking period of the video signal in the preceding stage of the contrast and / or brightness control of the core or during the period corresponding to overscan, and the contrast and / or the The reference voltage inserted in the video signal after the brightness control is taken out, and the core reference voltage showing the maximum beam current average value or the core reference voltage showing the maximum CRT drive voltage average value is selected as the reference signal, An ABL control variation correction circuit including a comparison circuit for comparing with a reference voltage of another core and a switch for switching a control signal input to the contrast and / or brightness control circuit of each core is provided. Multi-screen display device. 2. A multi-screen type display device for displaying a single image by combining a plurality of cathode ray tube type image display devices (cores), and means for detecting an average beam current for each core and the detection. Means for selecting the largest beam current value information from the average beam current for each core, and commonly controlling the contrast and / or brightness of all cores according to the selected beam current value information, or for each core Means for detecting the average value of the CRT drive voltage, and selecting the largest average value information from the detected average value of the CRT drive voltage for each core, and according to the selected average value information of the CRT drive voltage, Multi-screen display having ABL (Automatic Brightness Limiting Device) control means composed of means for commonly controlling contrast and / or brightness A) In the device, a reference voltage inserting circuit for inserting a reference voltage during the blanking period of the video signal in the preceding stage of the contrast and / or brightness control of the core or during the period corresponding to overscan, and the contrast and / or the The reference voltage inserted in the video signal after the brightness control is taken out, and the core reference voltage showing the maximum beam current average value or the core reference voltage showing the maximum CRT drive voltage average value is selected as the reference signal, AB comprising a comparison circuit for comparing with a reference voltage of another core, and a contrast and / or brightness control circuit for controlling the contrast and / or brightness of each core by the output of the comparison circuit.
A multi-screen display that is provided with a variation correction circuit for L control. 3. The contrast and / or brightness control circuit according to claim 2, wherein the contrast and / or brightness of each core is controlled by the output of the comparison circuit, the beam current value information, or the average of the CRT drive voltage. A multi-screen display characterized in that it is provided after a contrast and / or luminance circuit controlled by value information. 4. A multi-screen display device which displays a single image by combining a plurality of cathode ray tube image display devices (cores), and means for detecting an average beam current for each core, and the detection. Means for selecting the largest beam current value information from the average beam current for each core, and commonly controlling the contrast and / or brightness of all cores according to the selected beam current value information, or for each core Means for detecting the average value of the CRT drive voltage, and selecting the largest average value information from the detected average value of the CRT drive voltage for each core, and according to the selected average value information of the CRT drive voltage, Multi-screen display having ABL (Automatic Brightness Limiting Device) control means composed of means for commonly controlling contrast and / or brightness A) In the device, a reference voltage inserting circuit for inserting a reference voltage during the blanking period of the video signal in the preceding stage of the contrast and / or brightness control of the core or during the period corresponding to overscan, and the contrast and / or the The reference voltage inserted in the video signal after the brightness control is taken out, the reference voltage of any core is used as a reference signal, and a comparison circuit that compares it with the reference voltage of another core, and the contrast of each core at the output of the comparison circuit and An ABL control variation correction circuit including a contrast (or) brightness control and / or a brightness control circuit is provided, and the core contrast and the core contrast and the CRT drive voltage average value information are selected according to the selected beam current value information or CRT drive voltage average value information. (Or) ABL control means configured with a means for controlling brightness in common controls the contrast and / or brightness of each core. After control, the multi-screen system displays and controls the contrast and (or) the brightness of each core by variation correction circuit of the ABL control. 5. The contrast and / or brightness control circuit for controlling the contrast and / or brightness of each core by the output of the comparison circuit according to claim 4, wherein the contrast and / or brightness control circuit is beam current value information or an average of CRT drive voltage. A multi-screen display characterized in that it is provided after a contrast and / or luminance circuit controlled by value information. 6. A multi-screen type display device for displaying a single image by combining a plurality of cathode ray tube type image display devices (cores), and means for detecting an average beam current for each core, and the detection. Means for selecting the largest beam current value information from the average beam current for each core, and commonly controlling the contrast and / or brightness of all cores according to the selected beam current value information, or for each core Means for detecting the average value of the CRT drive voltage, and selecting the largest average value information from the detected average value of the CRT drive voltage for each core, and according to the selected average value information of the CRT drive voltage, Multi-screen display having ABL (Automatic Brightness Limiting Device) control means composed of means for commonly controlling contrast and / or brightness A) In the device, a reference voltage inserting circuit for inserting a reference voltage during the blanking period of the video signal in the preceding stage of the contrast and / or brightness control of the core or during the period corresponding to overscan, and the contrast and / or the The reference voltage inserted in the video signal after the brightness control is taken out, and the reference voltage of any core is used as a reference signal to compare with the reference voltage of another core, and the RGB primary color of each core at the output of the comparison circuit. An ABL control variation correction circuit comprising an amplitude control circuit and / or a DC level control circuit for controlling the amplitude and / or DC level of a signal is provided, and the selected beam current value information or the CRT drive voltage The contrast of each core is controlled by an ABL control unit configured to commonly control the contrast and / or the brightness of the core according to the average value information. Beauty (or) after controlling the luminance in common, multi-screen system displays and controls the contrast and (or) the brightness of each core by variation correction circuit of the ABL control. 7. The amplitude control circuit and / or the DC level control circuit for controlling the amplitude and / or DC level of the RGB primary color signals of each core by the output of the comparison circuit according to claim 6, are beam current value information. Alternatively, a multi-screen type display characterized in that it is provided at a subsequent stage of a contrast and / or luminance circuit controlled by the average value information of the CRT drive voltage. 8. A multi-screen type display device for displaying a single image by combining a plurality of cathode ray tube type image display devices (cores), and means for detecting an average beam current for each core, and the detection. Means for selecting the largest beam current value information from the average beam current for each core, and commonly controlling the contrast and / or brightness of all cores according to the selected beam current value information, or for each core Means for detecting the average value of the CRT drive voltage, and selecting the largest average value information from the detected average value of the CRT drive voltage for each core, and according to the selected average value information of the CRT drive voltage, Multi-screen display having ABL (Automatic Brightness Limiting Device) control means composed of means for commonly controlling contrast and / or brightness (A) In the device, a matrix switch for distributing the beam current value information of each core or the average value information of the CRT drive voltage for each arbitrary group unit, and the return of the video signal in the preceding stage of the contrast and / or brightness control of each core. A reference voltage inserting circuit for inserting a reference voltage during a line period or a period corresponding to overscan, and a reference voltage inserted in a video signal after the contrast and / or brightness control of each core is taken out to obtain a reference voltage of an arbitrary core. As a reference signal, a comparison circuit that compares the reference voltage of another core with the reference voltage, and a contrast that controls the contrast and / or the brightness of each core with the output of the comparison circuit and / or
A brightness control circuit and an ABL control variation correction circuit are provided, and the selected beam current value information or CR
A, which is configured to commonly control the contrast and / or the brightness of the core according to the average value information of the T drive voltage.
The BL control means controls the contrast of each core and / or
A multi-screen type display characterized in that after the brightness is controlled in common, the contrast and / or brightness of each core is controlled by the variation correction circuit of the ABL control. 9. The contrast and / or brightness control circuit for controlling the contrast and / or brightness of each core by the output of the comparison circuit according to claim 8, wherein the beam current value information or the average of the CRT drive voltage is used. A multi-screen display characterized in that it is provided after a contrast and / or luminance circuit controlled by value information. 10. A multi-screen type display device for displaying a single image by combining a plurality of cathode ray tube type image display devices (cores), and means for detecting an average beam current for each core, and the detection. Means for selecting the largest beam current value information from the average beam current for each core, and commonly controlling the contrast and / or brightness of all cores according to the selected beam current value information, or for each core Means for detecting the average value of the CRT drive voltage, and selecting the largest average value information from the detected average value of the CRT drive voltage for each core, and according to the selected average value information of the CRT drive voltage, A multi-screen type disc having an ABL (automatic brightness limiting device) control means constituted by means for commonly controlling contrast and / or brightness. In the ray device, a reference voltage inserting circuit arranged in the core for inserting the reference voltage during the blanking period of the video signal in the preceding stage of contrast and / or brightness control of each core or during the period corresponding to overscan, and the core A comparison circuit that extracts the reference voltage inserted in the video signal after contrast and / or brightness control and compares it with the reference voltage of another core using the reference voltage of any core as the reference signal, and the output of the comparison circuit. The contrast and / or brightness control circuit for controlling the contrast and / or brightness of each core, and the ABL control variation correction circuit comprising digital data transmission means for information transmission between each core and the comparison circuit are provided and selected. And means for commonly controlling the core contrast and / or brightness according to the beam current value information or the CRT drive voltage average value information. A multi-screen characterized by controlling the contrast and / or brightness of each core in common by the ABL control means, and then controlling the contrast and / or brightness of each core by the variation correction circuit of the ABL control. Scheme display. 11. The contrast and / or brightness control circuit for controlling the contrast and / or brightness of each core by the output of the comparison circuit according to claim 10, wherein the contrast and / or brightness control circuit is beam current value information or an average of CRT drive voltage. A multi-screen display characterized in that it is provided after a contrast and / or luminance circuit controlled by value information. 12. A means for displaying an image by combining a plurality of cathode ray tube image display devices (cores) and detecting an average beam current for each core or an average value of CRT drive voltage. In the multi-screen display device including means, the detected average beam current value information, CRT driving voltage average value information and other core average beam current value information, or CRT driving voltage average value information. From the larger beam current value information or the average value information of the CRT drive voltage, and the selected beam current value information or C
Means for controlling the contrast and / or brightness of the core according to the average value information of the RT drive voltage, and the reference voltage during the blanking period of the video signal in the preceding stage of the contrast and / or brightness control of each core or during the period corresponding to overscan. And a reference voltage inserting circuit for inserting the reference voltage inserted in the video signal after the contrast and / or brightness control of each core, and the reference voltage of the core showing the maximum beam current average value or the maximum A comparison circuit that selects the reference voltage of the core indicating the average value of the CRT drive voltage as a reference signal and compares it with the reference voltage of another core, and a contrast that controls the contrast and / or the brightness of each core by the output of the comparison circuit. And / or a brightness control circuit, which is provided with an ABL control variation correction circuit. 13. A multi-screen type display device which displays a single image by combining a plurality of cathode ray tube type image display devices (cores), and means for detecting an average beam current for each core, and the detection. Means for selecting the largest beam current value information from the average beam current for each core, and commonly controlling the contrast and / or brightness of all cores according to the selected beam current value information, or for each core Means for detecting the average value of the CRT drive voltage, and selecting the largest average value information from the detected average value of the CRT drive voltage for each core, and according to the selected average value information of the CRT drive voltage, A multi-screen type disc having an ABL (automatic brightness limiting device) control means constituted by means for commonly controlling contrast and / or brightness. In the ray device, a contrast voltage of each core and / or a reference voltage insertion circuit that inserts a reference voltage during a blanking period of the video signal before the brightness control or a period corresponding to overscan, and the contrast of each core and / or The reference voltage inserted in the video signal after the brightness control is taken out, the reference voltage of any core is used as a reference signal, and a comparison circuit that compares it with the reference voltage of another core, and the contrast of each core at the output of the comparison circuit and And / or a brightness and brightness control circuit for controlling the brightness, and an ABL control variation correction circuit, and C
A means for controlling the contrast and / or the brightness of the core in common by providing a γ conversion circuit for correcting the γ characteristic of the RT (cathode ray tube) according to the selected beam current value information or the average value information of the CRT drive voltage. After the contrast and / or brightness of each core are controlled in common by the ABL control means configured by, the contrast and / or brightness of each core is controlled by the variation correction circuit of the ABL control. Screen type display. 14. The contrast and / or brightness control circuit for controlling the contrast and / or brightness of each core by the output of the comparison circuit according to claim 13, wherein the contrast and / or brightness control circuit is beam current value information or an average of CRT drive voltage. A multi-screen display characterized in that it is provided after a contrast and / or luminance circuit controlled by value information. 15. A multi-screen type display device for displaying a single image by combining a plurality of cathode ray tube type image display devices (cores), and means for detecting an average beam current for each core and the detection. Means for selecting the largest beam current value information from the average beam current for each core, and commonly controlling the contrast and / or brightness of all cores according to the selected beam current value information, or for each core Means for detecting the average value of the CRT drive voltage, and selecting the largest average value information from the detected average value of the CRT drive voltage for each core, and according to the selected average value information of the CRT drive voltage, A multi-screen type disc having an ABL (automatic brightness limiting device) control means constituted by means for commonly controlling contrast and / or brightness. In the ray device, a contrast voltage of each core and / or a reference voltage insertion circuit that inserts a reference voltage during a blanking period of the video signal before the brightness control or a period corresponding to overscan, and the contrast of each core and / or The reference voltage inserted in the video signal after the brightness control is taken out, the reference voltage of any core is used as a reference signal, and a comparison circuit that compares it with the reference voltage of another core, and the contrast of each core at the output of the comparison circuit and A multi-screen type display characterized in that an ABL control variation correction circuit comprising a contrast and / or brightness control circuit for controlling (or) brightness is provided and the reference voltage inserting circuit is built in the core. 16. The contrast and / or brightness control circuit for controlling the contrast and / or brightness of each core according to the output of the comparison circuit according to claim 4, wherein the contrast and / or brightness control circuit is beam current value information or an average of CRT drive voltage. A multi-screen display characterized in that it is provided after a contrast and / or luminance circuit controlled by value information.