KR100557502B1 - Method for driving liquid crystal display device - Google Patents

Abstract

According to an aspect of the present invention, there is provided a method of driving a liquid crystal display, the method comprising: dividing one frame of the liquid crystal display into a first sub-frame and a second sub-frame; Extracting a luminance component of the unit pixel from the image information; Setting a first luminance component and a second luminance component by comparing a size corresponding to a luminance component of the unit pixel with a size corresponding to half of a maximum luminance component; Extracting first image information and second image information corresponding to the first luminance component and the second luminance component; Applying the first image information to the liquid crystal display in the first sub-frame and applying the second image information to the liquid crystal display in the second sub-frame.

Video, response time, impulse drive, luminance, luminance component

Description

Driving method of liquid crystal display device {METHOD FOR DRIVING LIQUID CRYSTAL DISPLAY DEVICE}

1A and 1B are exemplary views schematically illustrating deterioration of image quality in implementing a video through a liquid crystal display.

2A and 2B are exemplary views illustrating a change in luminance according to a video implementation of a general liquid crystal display and a CRT.

3 is a flowchart illustrating a method of driving a liquid crystal display according to an exemplary embodiment of the present invention.

4A and 4B are graphs showing transmittance of light of liquid crystals;

FIG. 5 is a diagram illustrating a luminance division method of the liquid crystal display driving method shown in FIG. 3; FIG.

6A and 6B are graphs showing a method of setting a first luminance component and a second luminance component of the method of driving the liquid crystal display shown in FIG.

7 is a graph showing the transmittance of a liquid crystal to grayscale.

** Explanation of symbols for main parts of drawings **

D: Image information D1, D1 ': First image information

D2, D2 ': Second image information Y, Y': Luminance component of the unit pixel

Y1, Y1 ': first luminance component Y2, Y2': second luminance component

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of driving a liquid crystal display device, and more particularly, to a method of driving a liquid crystal display device, which is suitable for preventing a decrease in luminance when the moving picture realization characteristic of the liquid crystal display device is improved.

The liquid crystal display (LCD) is an apparatus for displaying an image by using optical anisotropy of liquid crystal and can replace a cathode ray tube (CRT) with advantages of thinness, small size, low power consumption, and high quality. It has become the main product of flat panel display (FPD).

However, the liquid crystal display device has a disadvantage in that the video implementation characteristics are lower than those of the CRT, and research on this is being conducted. In particular, the liquid crystal display device applied to the television display device should be able to display a moving picture in high quality.

Hereinafter, the liquid crystal display device will be described in detail with reference to FIG. 1.

1A and 1B are exemplary views schematically illustrating deterioration of image quality in implementing a video through a liquid crystal display.

First, as shown in FIG. 1A, when the image of the white object 50 moving in the direction of the arrow is displayed on the black background displayed on the liquid crystal display panel 10, the liquid crystal display panel 10 is illustrated in FIG. 1B. As described above, a drag phenomenon in which the outline of the object 50 is blurred is generated.

The problem of the moving picture realization characteristic as described above is firstly due to the long response time (RT) of the liquid crystal with respect to the image signal.

In general, in a liquid crystal display device of a twisted nematic (TN) type or a super twisted nematic (STN) type, an electric field is applied to liquid crystal molecules, and then the arrangement of the liquid crystal molecules is changed so that a desired light transmittance is changed. The electro-optical response time required to reach is several times longer than 16.7 msec, which is a display period of a general screen (or frame). Therefore, even if a voltage for white display is applied to the liquid crystal that is performing black display as shown in FIG. 1, the electro-optical response time of the liquid crystal is required until the liquid crystal completely reaches the state of the white display, and one frame The optical response of the liquid crystal is not completed within the period. The drag phenomenon is observed due to the delay of the optical response of the liquid crystal.

Second, the display type of the LCD may be low because the LCD has a hold type that maintains light emission until image information of the next frame is applied. same.

FIG. 2A is an exemplary diagram illustrating a change in luminance according to a moving image of a general liquid crystal display, and FIG. 2B is a diagram illustrating a change in luminance according to a video sphere of a CRT.

First, as shown in FIG. 2A, a liquid crystal display is generally driven in a hold type in which charge accumulated in liquid crystal molecules by an applied electric field is maintained at a relatively high ratio until the next electric field is applied. For this reason, each pixel of the liquid crystal display maintains light emission until image information of the next frame is applied.

At this time, the graph shown by the dotted line is the waveform of the image information applied to the liquid crystal display device, and the graph shown by the solid line is the luminance waveform of the image displayed on the liquid crystal display device substantially corresponding to the image information.

The frame of the liquid crystal display is generally driven at a cycle of 1/60 sec.

On the other hand, in a CRT display device which displays an image by scanning an electron beam to emit phosphors on the CRT surface, as shown in FIG. 2B, luminance waveforms of the respective pixels appear in an impulse form.

Accordingly, the liquid crystal display device has a lower temporal frequency characteristic of the light displaying the moving image than the CRT, and consequently, the spatial frequency characteristic is low, thereby causing a drag of the moving image. Particularly, even if the response time of the liquid crystal is several msec or less, the characteristics of the moving picture are lower than those of the CRT, which is an impulse type, due to the characteristics of the LCD.

To solve this problem, one frame of a liquid crystal display is composed of two sub-frames, and an image signal is applied to the first sub-frame, and a black signal is input (120 Hz or 180 Hz) to the second sub-frame. An impulse (i.e., quasi-impulse) driving method for driving is proposed.

However, since the impulse type liquid crystal display device has a black signal applied to the second sub-frame as compared to the general liquid crystal display device, the luminance is reduced by about 1/2.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and by inputting two different signals having a large difference in luminance into two sub-frames, a liquid crystal capable of preventing a decrease in luminance when the moving picture realization characteristic of the LCD is improved. An object of the present invention is to provide a method of driving a display device.

In order to achieve the above object, the liquid crystal display device driving method of the present invention comprises dividing one frame of the liquid crystal display device into a first sub-frame and a second sub-frame, extracting the luminance component of the unit pixel from the image information Setting a first luminance component and a second luminance component by comparing the size corresponding to the luminance component of the unit pixel with the size corresponding to half of the maximum luminance component, and setting the first luminance component and the second luminance component. Extracting first image information and second image information corresponding to the second image information; applying the first image information to the liquid crystal display in the first sub-frame; and the second image information in the second sub-frame. Applying to the liquid crystal display.

The first luminance component may be set larger than the luminance component of the unit pixel, and the second luminance component may be set smaller than the luminance component of the unit pixel.

The luminance component of the unit pixel may be divided into a first luminance component and a second luminance component such that an average value of the first luminance component and the second luminance component is equal to the luminance component of the unit pixel.

When the size corresponding to the luminance component of the unit pixel is larger than the size corresponding to half of the maximum luminance component, the first luminance component is set to the size of the maximum luminance and the second luminance component is the size of the luminance component of the unit pixel. It can be set to twice the value of minus the maximum luminance.

Further, when the size corresponding to the luminance component of the unit pixel is less than or equal to the size corresponding to half of the maximum luminance component, the first luminance component is set to twice the size of the luminance component of the unit pixel, and the second luminance component is used. Can be set as a black signal.

The driving method of the liquid crystal display according to the present invention configured as described above will be described in detail as follows.

As described above, the impulse type liquid crystal display proposed to implement high quality moving images has a problem of decreasing luminance.

That is, in the impulse type liquid crystal display, the luminance is reduced by the black signal input to the second sub-frame among the two sub-frames for driving the impulse, and accordingly, in the present invention, the difference of the luminance components in the two sub-frames is different. Provided is a method of driving a liquid crystal display device in which the luminance is increased to prevent the luminance from being reduced.

3 is a flowchart illustrating a method of driving a liquid crystal display according to an exemplary embodiment of the present invention. For convenience of description, the luminance component of the unit pixel will be described in detail.

First, after dividing one frame of the liquid crystal display into a first sub-frame and a second sub-frame (S1), the luminance component Y corresponding to the corresponding unit pixel from the image information D for driving the unit pixel. ) Is extracted (S2). In this case, the luminance represents the degree to which the screen shines brightly, and the unit is expressed as nit, cd / m ² , or footLambert.

Next, the magnitudes of the luminance component (Y) and the maximum luminance component of the unit pixel are compared to determine the first luminance component and the second luminance component according to the size ratio of the luminance component (Y) and the maximum luminance component of the unit pixel. Set to a value (S3, S4, S4 ').

In the present embodiment, the first luminance component and the second luminance component are set by comparing the luminance component Y of the unit pixel with 50% of the maximum luminance component, that is, the size corresponding to half, but the original image information D The first luminance component and the second luminance component may be set according to other conditions unless the luminance of the entire liquid crystal display panel is reduced.

When the luminance component Y of the unit pixel is greater than 50% of the maximum luminance component, the luminance component Y of the unit pixel is divided into a first luminance component Y1 and a second luminance component Y2, and the second The first luminance component Y1 is set to the maximum luminance and the second luminance component Y2 is set to twice the luminance component Y2 of the unit pixel minus the maximum luminance (S4).

Further, when the luminance component Y of the unit pixel is equal to or smaller than (or less than or equal to 50%) the maximum luminance component, the luminance component Y of the unit pixel is equal to the first luminance component Y1 '. By dividing by the second luminance component Y2 ', the first luminance component Y1' is set to twice the luminance component Y of the unit pixel, and the second luminance component Y2 'is set as the black signal (S4'). ).

Next, the first image information D1, D1 ′ and the second image information D2, D2 ′ corresponding to the first luminance component Y1, Y1 ′ and the second luminance component Y2, Y2 ′ Extract (S5).

Finally, the first image information D1 and D1 'are applied to the liquid crystal display in the first sub-frame (S6), and the second image information D2 and D2' is applied to the liquid crystal display in the second sub-frame. In operation S7, a predetermined image is displayed on the unit pixel of the liquid crystal display.

As shown in this embodiment, a frame is divided into a first sub-frame and a second sub-frame, and two different signals having a large difference in luminance are input to the two sub-frames, thereby realizing a moving image of the LCD. It can be improved.

In this case, two different signals having a large luminance difference as described above may prevent a decrease in overall luminance of the liquid crystal display panel.

In addition, in the present embodiment, a method of driving a 120 Hz liquid crystal display device in which a 60 Hz frame is divided into two sub-frames is described. However, a method of driving a 180 Hz drive liquid crystal display device in three sub-frames is described. It can also be easily applied.

The image information applied to the liquid crystal display includes a gray voltage, which will be described in detail with reference to FIG. 4 as follows.

4A and 4B are graphs showing the transmittance of the liquid crystal to light, and FIG. 4A is a case where voltage is divided by a constant interval and FIG. 4B is a case where the transmittance is divided by a constant interval.

First, gradation may be referred to as dividing the amount of light felt by the human vision in stages. In the liquid crystal display device, an image is displayed by artificially adjusting the degree of light passing through the liquid crystal.

As a means of such adjustment, a voltage is used. In general, the transmittance of light of a liquid crystal is constant according to the magnitude of the voltage applied across the liquid crystal, that is, the intensity of an electric field passing through the liquid crystal, as shown in FIG. 4A. Will change with.

If you look at the transmittance curve, you can think of it as roughly two parts: when the voltage is initially applied (white) and when a very large voltage is applied (black), there is little change in the transmittance even though the voltage is changed. It can be seen that the transmittance changes almost in proportion to. Therefore, in order to display the gradation of the medium brightness, the middle linear section is mainly used.

At this time, in realizing the image, the gray scale is displayed by dividing the section in which the transmittance is changed almost linearly with respect to the applied voltage in several steps. However, when dividing the voltage at regular intervals, the transmittance cannot be a constant interval because of the nonlinear nature of the transmittance. That is, in order to display a fine image, the gradation of the middle part should be finely divided. As shown in the drawing, the distribution of transmittance is large at one side and the smaller at one side, resulting in uneven luminance distribution. When the image is displayed in this state, it is difficult to display the delicate gradation and the image becomes rough.

Therefore, in order to display a smooth image, it is necessary to maintain transmittance at regular intervals rather than voltage, as shown in FIG. 4B. Therefore, in order to achieve this, it is necessary to make the gray scale voltage narrower in the middle part and wider in the white or black display part. Thus, the difference between the liquid crystal display device and the human visual perception characteristic is matched. The task is called gamma correction.

Hereinafter, a driving method of a liquid crystal display according to an exemplary embodiment of the present invention will be described in detail with reference to the following.

FIG. 5 is a diagram illustrating a luminance division method of the liquid crystal display driving method shown in FIG. 3.

As shown in the figure, one frame of a signal input to the unit pixel is composed of two sub-frames, and the luminance component Y to be displayed is divided into luminance components of Y1 and Y2 in the two sub-frames.

That is, by inputting two different signal information having a large difference in luminance into two sub-frames, it is possible to prevent a decrease in luminance and to improve video characteristics in an intermediate gray scale region.

In this case, the first luminance component Y1 may be larger than the luminance component Y of the unit pixel, and the second luminance component Y2 may be smaller than the luminance component Y of the unit pixel.

In addition, the average value of the first luminance component Y1 and the second luminance component Y2 may be divided to be equal to the luminance component Y of the unit pixel.

6A and 6B are graphs illustrating a method of setting the first luminance component and the second luminance component of the method of driving the liquid crystal display shown in FIG. 3.

First, FIG. 6A is a graph showing luminance according to time in a 60 Hz driving liquid crystal display, and illustrates arbitrary signals input to one unit pixel for convenience of description.

In the graph, the luminance on the vertical axis represents relative luminance based on the maximum luminance, and the unit is%.

The luminance component Y or Y 'of the unit pixel can be derived from Equation 1 below in the image information D of 60 Hz driving.

(D / 255) ^α = Y, 0 <Y <1

Here, α is a constant having a value of 2 to 3, and in this embodiment, a value of 2.2 according to a 2.2-gamma condition is used. In addition, the above equation uses a 255-gray scale condition which is generally used to drive the liquid crystal display panel.

6b shows signals divided into a pair of luminance components according to the present invention, and shows a 120 Hz driving method.

The pair of first luminance components Y1 and Y1 'and the second luminance components Y2 and Y2' are configured such that the luminance difference is large, for example, Y = (Y1 + Y2) / 2 with respect to Y. It can be configured to satisfy the relationship.

In this case, the first luminance components Y1 and Y1 'and the second luminance components Y2 and Y2' may be set in different manners according to regions I and II shown in FIGS. 6A and 6B, and Shows one example.

0% Y ≤50%: Y1 = 2Y, Y2 = 0 (I region)

50% <Y'≤100%: Y1 '= 100%, Y2' = 2Y'-100% (II area)

That is, when the luminance component Y of the unit pixel has a luminance of 0 to 50% as in the region I, that is, when the luminance component of the unit pixel is equal to or smaller than (or less than) 50% of the maximum luminance component. In this case, the first luminance component Y1 is set to twice the luminance component Y of the unit pixel, and the second luminance component Y2 is set as a black signal. In addition, when the luminance component Y 'of the unit pixel has a value larger than 50% of the maximum luminance component as in the region II, the first luminance component Y1' is 100% luminance, that is, the maximum luminance. The second luminance component Y2 'is set to a value obtained by subtracting 100% from two times the luminance component Y' of the unit pixel.

The first image information D1 and D1 'and the second image information D2 and D2' corresponding to the first luminance component Y1 and Y1 'and the second luminance component Y2 and Y2' are represented by the above equation. It can be extracted from the following equation (3) using 1 inversely.

D1 / 255 = (Y1) ^{1 / 2.2} , D2 / 255 = (Y2) ^{1 / 2.2}

Here, 2.2 is used as the constant α and Y1 'and Y2' can be extracted in the same way.

At this time, in the I region of 0 to 50% luminance, the same effect as the conventional impulse driving method is obtained, so that a good video characteristic can be obtained, but in the II region of 50 to 100% luminance range, the characteristic similar to that of the hold type display is increased. The video characteristics become insufficient.

However, when the luminance range is changed to the gradation display range, it can be seen that the 50 to 100% luminance range is only 73 to 100% gradation range, so that there is no problem in the intermediate gradations represented by most videos, which will be described with reference to FIG. 7. do.

Fig. 7 is a graph showing the transmittance of the liquid crystal with respect to gray scale, showing a 255-grayscale condition.

As shown in the figure, it can be seen that as the transmittance increases, the grayscale increases exponentially rather than linearly.

In this case, gray scale corresponding to 50% transmittance is 186, which is about 73% of 255, that is, 50-100% luminance range is only 73-100% gradation range, and there is no problem in middle gradation represented by most videos. Can be.

Many details are set forth in the foregoing description but should be construed as illustrative of preferred embodiments rather than to limit the scope of the invention. Therefore, the invention should not be defined by the described embodiments, but should be defined by the claims and their equivalents.

As described above, in the driving method of the liquid crystal display according to the present invention, by inputting two different signals having a large difference in luminance into two sub-frames, the luminance reduction can be prevented and the video realization characteristic can be improved. have.

Claims (5)

Dividing one frame of the liquid crystal display into a first sub-frame and a second sub-frame; Extracting a luminance component of the unit pixel from the image information; Setting a first luminance component and a second luminance component by comparing a size corresponding to a luminance component of the unit pixel with a size corresponding to half of a maximum luminance component; Extracting first image information and second image information corresponding to the first luminance component and the second luminance component; Applying the first image information to a liquid crystal display in the first sub-frame; And And applying the second image information to the liquid crystal display in the second sub-frame. 2. The method of claim 1, wherein the first luminance component is set larger than the luminance component of the unit pixel and the second luminance component is set smaller than the luminance component of the unit pixel. 2. The method of claim 1, wherein dividing the luminance component of the unit pixel into a first luminance component and a second luminance component such that the average value of the first luminance component and the second luminance component is equal to the luminance component of the unit pixel. A method of driving a liquid crystal display device. The method of claim 1, wherein when the size corresponding to the luminance component of the unit pixel is larger than the size corresponding to half of the maximum luminance component, the first luminance component is set to the maximum luminance and the second luminance component is And a value obtained by subtracting the maximum luminance size from twice the luminance component size of a unit pixel. The method of claim 1, wherein when the size corresponding to the luminance component of the unit pixel is less than or equal to the size corresponding to half of the maximum luminance component, the first luminance component is set to twice the size of the luminance component of the unit pixel. And the second luminance component is set as a black signal.

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