JP2008020611A - Liquid crystal display device and method for reducing afterimage in same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve such a problem of a liquid crystal display device that an afterimage remains in displaying moving images. <P>SOLUTION: A backlight control method includes the steps of: dividing the screen of a liquid crystal display device into a plurality of regions; detecting the time when image information is written in a divided region; reducing the luminance of the backlight in the divided region when the time of writing the image information is detected; judging the time when displaying the image information written in the divided region is established; and raising the luminance of the backlight in the divided region when displaying the image information is established. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to a method for reducing an afterimage in a liquid crystal display device and a liquid crystal display device. More specifically, the present invention relates to a method for reducing a residual image of a moving image by backlight control and a liquid crystal display device.

  Among image display devices, liquid crystal display devices have recently been increased in size and definition. Accordingly, it has come to be used not only for devices that display still images such as personal computers and digital still cameras, but also for devices that display moving images such as TV (television). A liquid crystal display device has a narrower depth and a smaller occupied area than a TV equipped with a CRT (CRT), and therefore has a high penetration rate in ordinary households.

  However, in the liquid crystal display device, the display of the still image is very beautiful, but the afterimage remains in the display of the moving image as compared with the CRT, and the display quality of the display of the moving image is not high. This is because the response speed of the liquid crystal is very slow, such as several milliseconds for several tens of microseconds of a CRT or PDP (Plasma Display Panel), and the transition state of image display is visible.

As a countermeasure,
1. The response speed is improved by improving the liquid crystal element.
2. Response speed is improved by improving the driving method of the liquid crystal.
Etc. are performed. The first method improves the liquid crystal element itself to increase the response speed, and the second method improves the liquid crystal driving method to increase the response speed. For example, an overdrive method is known in which the rising voltage of the drive waveform is made higher than the normal drive level. However, these measures have limitations. The response speed of the liquid crystal element is still several milliseconds, and an afterimage remains in displaying a moving image.

  As described above, the liquid crystal display device has a problem that an afterimage remains in displaying a moving image. An object of the present invention is to provide a method for reducing an afterimage in a liquid crystal display device and a liquid crystal display device that can reduce an afterimage by controlling an LED backlight.

  In order to achieve the above object, a backlight control method according to the present invention is a method for reducing afterimages by backlight control in a liquid crystal display device having a backlight using LEDs, and a plurality of screens of the liquid crystal display device are vertically arranged. A step of detecting the time when the image information is written in the divided region, a step of reducing the luminance of the backlight of the divided region when the time when the image information is written is detected, The step of determining the time when the display of the image information written in is confirmed and the step of increasing the luminance of the backlight of the divided area when the display of the image information is confirmed.

  In addition, it is preferable that the step of lowering the luminance of the backlight in the divided region is a step of turning off the backlight, and the step of raising the luminance of the backlight in the divided region is a step of turning on the backlight.

  In the step of increasing the luminance of the backlight, it is also preferable to pass a current larger than the current value that can be steadily flowed.

  In order to achieve the above object, the backlight according to the present invention is controlled by any one of the above methods.

  In order to achieve the above object, the backlight of the liquid crystal display device according to the present invention is controlled by any one of the above methods.

  According to the present invention, an afterimage, which is one of the weak points of a liquid crystal display device, can be improved without changing the time, cost, production line, or material, such as improving the characteristics of the liquid crystal element. That is, it is possible to reduce the afterimage of the liquid crystal display device by using only the content of the present invention, which is a method for controlling the LED backlight, without using a liquid crystal element with a special high-speed response.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS.

  FIG. 1 is a diagram showing division of a liquid crystal display screen according to the present invention. In this example, the liquid crystal display screen of horizontal: 1960 dots and vertical: 1080 dots is divided into n. That is, the first region corresponds to vertical: 1 to 1080 / n dots, the second region corresponds to vertical: (1080 / n) +1 to 2 × 1080 / n dots, and the nth region corresponds to vertical: ( This corresponds to (n−1) × 1080 / n) +1 to n × 1080 / n dots.

  FIG. 2 is a functional configuration diagram of a system for controlling the LED backlight of the present invention. The operation of the embodiment of the present invention will be described based on this figure.

  The reference value holding means 2 is means for holding information such as the number of screen divisions, screen update time, and luminance information. The number of screen divisions is the number by which the liquid crystal display screen is divided in the vertical direction, and is passed to the timing control means 1. The screen update time is the time from when the liquid crystal screen starts to update the display until the display is fixed, and is passed to the fixed time determination means 4. The luminance information is information for determining the brightness of the backlight, and is passed to the luminance control means 5. These values may be values that can be appropriately adjusted by the user, or may be fixed values. For example, the luminance information may be changed by a switch for adjusting the luminance.

  The timing control means 1 is means for detecting the timing at which an image is written on the divided screen. First, the reference value holding means 2 passes the screen division number to the timing control means 1. With this value, the liquid crystal display screen is divided as shown in FIG. A horizontal synchronization signal and a vertical synchronization signal, which are control signals for liquid crystal screen display, are input to the timing control means 1. The horizontal synchronization signal is a signal for measuring the timing in the horizontal direction when a screen is drawn by a CRT or a liquid crystal display device. When this signal is received, the CRT or the liquid crystal display device returns the display position to the left end. The vertical synchronization signal is a signal for measuring the timing in the vertical direction when a screen is drawn by a CRT or a liquid crystal display device. When this signal is received, the CRT or liquid crystal display device returns the display position to the upper left corner.

  The timing control means 1 has a counter inside, and the counter is incremented every time a horizontal synchronizing signal is inputted, and is reset every time a vertical synchronizing signal is inputted. With this counter, the timing control means 1 can determine the area displayed by the liquid crystal display device.

  The correspondence between the counter and the divided areas is determined as follows. When the vertical length of the liquid crystal display screen is m dots and the division number of the screen is n, when the counter is 1 to m / n, the liquid crystal display device displays the first area, and the counter is (m / n) When +1 to 2 m / n, the liquid crystal display device displays the second region, and when the counter is (2 m / n) +1 to 3 m / n, the liquid crystal display device displays the third region. , ((N−1) × m / n) +1 to n × m / n, the liquid crystal display device displays the nth region. From this, it can be seen that when the counter reaches m / n, 2 m / n,..., N × m / n, the writing of the image information to each divided area is completed.

  After the image information has been written to the end of the nth area, a vertical synchronization signal is input and the counter is reset. After that, the control signal for the next screen is sent.

  As described above, the timing control unit 1 outputs the counter xn / m to the area determination unit 3 when the counter reaches m / n, 2 m / n,..., N × m / n, and is divided. That the writing of the image information to the selected area is completed.

  The area determination means 3 instructs the luminance control means 5 corresponding to the value received from the timing control means 1 to reduce the luminance of the backlight in this area, and informs the fixed time determination means 4 of the number of this area. Means.

  For example, when the vertical length of the liquid crystal screen is m dots, the number of screen divisions is n, and the timing control means 1 passes “1” to the area determination means 3, the area determination means 3 is the first area luminance control means. When 5-1 is instructed to lower the brightness, “1” is notified to the fixed time determination means 4 and “n” is passed to the area determination means, the area determination means 3 sends the nth area brightness control means 5-n. An instruction to decrease the brightness is given, and “n” is notified to the fixed time determination means 4.

  The determination time determination unit 4 is a unit that instructs the luminance control unit 5 to increase the luminance of the backlight in this region when it is determined that the image of the divided region is fixed. The fixed time determination unit 4 determines whether or not the image of the divided area has been fixed based on the screen update time passed from the reference value holding unit 2. After the screen update time has elapsed after the area number is instructed by the area determination means 3, the brightness control means 5 is instructed to increase the brightness.

  For example, when “1” is notified from the region determination unit 3, the fixed time determination unit 4 instructs the first region luminance control unit 5-1 to increase the luminance after the screen update time has elapsed, and the region determination unit 3. Is notified of “2”, the fixed time determination means 4 instructs the second area brightness control means 5-2 to increase the brightness after the screen update time has elapsed, and the area determination means 3 knows “n”. If it is determined, the fixed time determination unit 4 instructs the n-th region luminance control unit 5-n to increase the luminance after the screen update time has elapsed.

  The area luminance control means 5 is a means for increasing or decreasing the luminance of the backlight according to instructions from the area determination means 3 and the fixed time determination means 4. There are as many area luminance control means 5 as the number of divisions. In the present invention, an LED is used as a backlight. Due to the high-speed response characteristics of LEDs and the linearity (linearity) of the current-brightness characteristics of LEDs, backlights using LEDs can be switched on and off instantly and changed in brightness when instructed. This is because the amount of light corresponding to the change in the amount of current can be emitted. The area luminance control means 5 adjusts the luminance of the backlight based on the luminance information passed from the reference value holding means 2.

  FIG. 3 is a diagram showing details of the area luminance control means 5. Luminance information is passed from the reference value holding means 2 to the interface unit 11. The interface unit 11 passes the received information to the control unit 12. Backlights using LEDs emit light by combining red LEDs, green LEDs, and blue LEDs. The adjustment of the luminance of the backlight may be performed by collectively adjusting the luminance of each color LED. In this case, the control unit 12 passes the brightness information to the brightness control unit 13, and the brightness control unit 13 passes the same brightness information to the individual brightness control unit 14, thereby adjusting the brightness of the backlight in a lump. Conversely, the backlight brightness may be adjusted for each LED brightness of each color. In this case, the control unit 12 passes the luminance information corresponding to each color to the individual luminance control unit 14 so that the luminance of the backlight is individually adjusted for each color.

  In the present embodiment, an example of a backlight that individually has a red LED, a green LED, and a blue LED and is individually controlled is shown. However, the LEDs used for the backlight may be not only red LEDs, green LEDs and blue LEDs, but also multicolor LEDs or white LEDs. The backlight brightness may be controlled by controlling red LEDs, green LEDs, or blue LEDs all at once, or by controlling multicolor LEDs and white LEDs all at once. Further, the white LEDs may be individually controlled together with the multicolor LEDs.

  FIG. 4 is an example of a circuit diagram for changing the luminance of the LED according to the value output from the region luminance control means 5. In this circuit, the luminance of the backlight is received as digital information. This is converted into an analog signal by a digital-analog converter (DA converter) 21 and a constant current corresponding to this is output. That is, when information for increasing the brightness is input, a high current is output, and the brightness of the LED 22 increases. On the other hand, when information for decreasing the brightness is input, a low current is output, and the brightness of the LED 22 decreases.

  For example, the following values are used as the screen division number and the screen update time, which are the reference values of the present invention. As for the number of screen divisions, the effect of reducing the afterimage is best exhibited when the image is divided into eight. The screen update time depends on the response speed of the liquid crystal and the update time of the liquid crystal screen, but is between 10 and 20 milliseconds in this embodiment.

  As described above, in this embodiment, the screen is divided into a plurality of areas as shown in FIG. 1 according to the number of screen divisions of the reference value holding means 2. Next, the timing control unit 1 detects the time when the image information is written in the divided area. Next, the area determination unit 3 receives information about the divided area in which the image information is written from the timing control unit 1, and the area determination unit 3 instructs the luminance control unit 5 corresponding to the divided area to lower the luminance of the backlight. The brightness control means 5 lowers the brightness of the backlight. Next, the fixed time determination unit 4 receives information about the divided area in which the image information is written from the timing control unit 1, and the fixed time determination unit 4 sets the divided area in the divided area after the screen update time of the reference value holding unit 2 has elapsed. The corresponding brightness control means 5 is instructed to increase the brightness of the backlight, and the brightness control means 5 increases the brightness of the backlight. In the present embodiment, when the screen update time has elapsed, it is determined that the display of the image information has been confirmed.

  In another embodiment of the present invention, the luminance control means 5 turns off the LED when an instruction to lower the luminance is given, and turns on the LED when an instruction to raise the luminance is given. In this embodiment, there is an advantage that the circuit of the luminance control means 5 is simplified because only the lighting and extinguishing are performed and there is no need to adjust the current flowing through the LED.

  In this embodiment of the present invention, the means for turning off the LED is to turn off the LED (that is, not to pass a current completely) and to keep a current that causes a negligible leakage current flowing through the LED. When driving a circuit in which a number of LEDs are connected in series, the voltage value increases. Therefore, in the former case, since this high voltage is applied to the LED drive circuit when the LED is turned off, an element having a high breakdown voltage is required for the drive circuit. On the other hand, in the latter case, a minute current always flows through the LED, and a forward voltage drop of the LED can be expected. Therefore, it is not necessary to use a high breakdown voltage element in the LED drive circuit.

  In another embodiment of the present invention, the LED is energized with a current that is greater than the current value that is steadily applied. In the present invention, the luminance of the LED is repeatedly increased or decreased or turned on and off. For this reason, the average luminance of the LED is lower than the luminance obtained from normal LED light emission. In this embodiment, the average luminance is prevented from decreasing by flowing a larger current than usual.

  In the present invention, the number of screen divisions need not match the number of luminance control means 5. If they do not match, the area determination unit 3 selects an appropriate luminance control unit 5. For example, when the number of screen divisions is 8 and the number of luminance control means 5 is 4, when the divided area number “1” is passed to the area determination means 3 and then “2” is passed, An instruction to lower the luminance is given to the one-region luminance control means 5-1, and “1” is notified to the fixed time determination means 4. When the divided area number “3” is passed, and then “4” is passed, an instruction to lower the brightness is given to the second area brightness control means 5-2, and “2” is notified to the fixed time determination means 4. The same control is performed in the following. The fixed time determination means instructs the brightness control means 5 to increase the brightness after the screen update time has elapsed since the area number was specified.

  On the contrary, when the number of screen divisions is 4 and the number of luminance control means 5 is 8, and when the division area number “1” is passed to the area determination means 3, the first area luminance control means 5- The first and second area luminance control means 5-2 is instructed to lower the luminance, and “1” and “2” are notified to the fixed time determination means 4. When the division area number “2” is passed, the third area luminance control means 5-3 and the second area luminance control means 5-4 are instructed to decrease the luminance, and “3” and “4” are determined. Inform the time determination means 4. The same control is performed in the following. The fixed time determination means instructs the brightness control means 5 to increase the brightness after the screen update time has elapsed since the area number was specified.

  In the embodiments of the present invention, the case of non-interlace has been described as the liquid crystal display device, but the present invention can also be applied to the case of interlace. In the case of interlace, the area determination means 3 is notified that the writing of image information has been completed with a counter value that is half that in the case of non-interlace.

  For example, when the liquid crystal display screen has m dots vertically and the number of screen divisions is n, when the counter becomes m / 2n, 2m / 2n,..., N × m / 2n, the region determination A counter × 2n / m is output to the means 3 to notify that the writing of the image information to the divided area is completed.

  In the embodiment of the present invention, the case where the liquid crystal screen is divided into the same size has been described. However, the liquid crystal screen is not necessarily divided into the same size. For example, an embodiment in which the upper and lower divisions are widened and the middle division is narrowed may be applied.

  All the embodiments described above are illustrative of the present invention and are not intended to be limiting, and the present invention can be implemented in other various modifications and changes. Therefore, the scope of the present invention is defined only by the claims and their equivalents.

It is a figure which shows the division | segmentation of the liquid crystal display screen concerning this invention. It is a functional block diagram of the system which controls the LED backlight of this invention. It is a figure which shows the detail of an area | region brightness | luminance control means. It is an example of the circuit diagram which changes the brightness | luminance of LED.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Timing control means 2 Reference value holding means 3 Area determination means 4 Determination time determination means 5-1 to 5-n Luminance control means 11 Interface section 12 Control section 13 Luminance control sections 14-1, 14-2, 14-3 Individual Brightness controller 21 Digital-analog converter 22 LED

Claims (5)

An afterimage reduction method by backlight control in a liquid crystal display device having a backlight using LEDs,
Dividing the screen of the liquid crystal display device into a plurality of regions in the vertical direction;
Detecting when the image information is written in the divided area;
Reducing the brightness of the backlight of the divided area when detecting the time when the image information was written;
Determining when the display of the image information written in the divided area is confirmed;
When the display of the image information is confirmed, increasing the luminance of the backlight of the divided area;
An afterimage reduction method comprising: The step of lowering the luminance of the backlight of the divided area is a step of turning off the backlight.
The afterimage reduction method according to claim 1, wherein the step of increasing the luminance of the backlight of the divided region is a step of turning on the backlight.   The afterimage reduction method according to claim 1, wherein in the step of increasing the luminance of the backlight, a current larger than a current value that can be steadily passed is passed.   The backlight controlled by the method of any one of Claim 1 to 3.   The liquid crystal display device which has a backlight controlled by the method of any one of Claim 1 to 3.

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