KR101441381B1 - Driving device of liquid crystal display device and driving method thereof - Google Patents

Abstract

The present invention relates to a driving apparatus for a liquid crystal display device and a driving method thereof, which can improve image quality and reduce power consumption while preventing display defects of an image.

To this end, the present invention provides a liquid crystal display comprising: a liquid crystal panel formed with a plurality of pixel regions; A data driver for driving a plurality of data lines; A timing controller for aligning video data from outside in accordance with driving of the liquid crystal panel and controlling the data driver and the gate driver; A maximum gray-level value is detected from the image data sorted by the timing controller, and a dimming control signal is converted so that the duty ratio is reduced according to the detected maximum gray-scale value, and the offset value and the maximum gray- An image conversion unit for converting the gray level values of the image data and supplying the gray level values to the data driver; And a backlight unit for emitting light to the liquid crystal panel in response to the converted dimming control signal.

A pulse width modulation signal, a duty ratio, a scanning backlight unit

Description

[0001] The present invention relates to a driving apparatus for a liquid crystal display device and a method of driving the same,

The present invention relates to a liquid crystal display (LCD), and more particularly, to a driving apparatus and a driving method of a liquid crystal display, which can improve image quality and reduce power consumption while preventing defective display of an image.

2. Description of the Related Art Recently, flat panel display devices that have emerged include a liquid crystal display, a field emission display, a plasma display panel, and a light emitting display.

Of the flat panel display devices, the liquid crystal display devices are excellent in resolution, color display, and image quality, and are actively applied to notebook computers, desktop monitors, and mobile terminals.

Such a liquid crystal display device displays an image by adjusting the light transmittance of the liquid crystal using an electric field. To this end, the liquid crystal display device includes a liquid crystal panel having a plurality of liquid crystal cells for displaying an image, a driving circuit for driving the liquid crystal panel, and a backlight unit for irradiating light to the liquid crystal panel.

The liquid crystal panel displays a desired image by adjusting the transmittance of the light emitted from the backlight unit according to the image signal. In recent years, in order to reduce motion blurring felt by an observer due to the retention characteristics of a liquid crystal when a moving image is displayed through a liquid crystal display device, in order to reduce motion blurring, ) Driving technology. Specifically, the backlight unit sequentially drives the plurality of lamps provided in the backlight unit along the scanning direction of the display line in accordance with the lamp driving control signal supplied from the driving circuit.

However, in the conventional liquid crystal display device to which the scanning driving technique is applied, since the time for generating light is reduced, the luminance of the displayed image is lowered. That is, when the backlight unit always generates light of constant brightness regardless of the video signal, the power consumption is increased and the motion blurring phenomenon occurs. When the light is sequentially generated by using the above-described scanning driving technique The luminance of the image is lowered.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a driving apparatus for a liquid crystal display device and a driving method thereof, which can improve image quality, There is a purpose.

According to an aspect of the present invention, there is provided an apparatus for driving a liquid crystal display, including: a liquid crystal panel including a plurality of pixel regions; A data driver for driving a plurality of data lines; A timing controller for aligning video data from outside in accordance with driving of the liquid crystal panel and controlling the data driver and the gate driver; A maximum gray-level value is detected from the image data sorted by the timing controller, and a dimming control signal is converted so that the duty ratio is reduced according to the detected maximum gray-scale value, and the offset value and the maximum gray- An image conversion unit for converting the gray level values of the image data and supplying the gray level values to the data driver; And a backlight unit for emitting light to the liquid crystal panel in response to the converted dimming control signal.

Wherein the image converting unit comprises: a histogram analyzing unit for calculating a histogram by detecting a gray-level value of each of the aligned image data on a frame-by-frame basis and for detecting the maximum gray-level value from the calculated histogram; A delay unit for delaying and outputting the aligned image data during a predetermined period of time, a duty ratio of the dimming control signal being varied according to the detected maximum gradation value, and supplying the varied duty ratio to the inverter control unit, And a gray-scale modulation unit for converting gray-scale values of the image data delayed from the delay unit according to the gray-scale modulation values and supplying the converted image data to the data driver.

Wherein the dimming control unit stores the relative brightness information in relation to the gradation level in a preset gamma value graph state and narrows the gamma value graph so that the maximum point of the gamma value graph becomes the maximum gradation value point, The duty ratio is set so as to correspond to the degree of conversion of the relative brightness according to the reduction point of the value point, thereby outputting the dimming control signal with a reduced duty ratio.

The dimming control section supplies the offset value to the gradation modulation section as the gradation modulation value or supplies the difference value between the maximum gradation value and the offset value to the gradation modulation section as the gradation modulation value.

Wherein the gradation modulation unit converts the gradation values of the delayed image data to be equal to the gradation modulation value when the offset value is input as the gradation modulation value, and when the difference between the maximum gradation value and the offset value is less than the gradation modulation value The gradation modulation value is added to the gradation value of each of the delayed image data by a ratio of the maximum gradation value, and the gradation modulation value is supplied to the data driver.

Wherein the backlight unit comprises: a backlight including a plurality of light sources for generating light on the liquid crystal panel; an inverter control unit for outputting pulse width modulation signals in response to the converted dimming control signal; And an inverter for generating AC driving signals for sequentially driving the respective light sources and sequentially supplying the AC driving signals to each of the plurality of light sources.

According to another aspect of the present invention, there is provided a method of driving a liquid crystal display (LCD) device, comprising: aligning video data from outside in accordance with driving of a liquid crystal panel; Detecting a maximum gray level value from the aligned image data and converting a dimming control signal such that a duty ratio is reduced according to the detected maximum gray level value; Converting the gradation values of the aligned image data according to an offset value from the outside and the maximum gradation value and outputting the converted image data; And irradiating light to the liquid crystal panel in response to the converted dimming control signal.

Wherein the step of converting the dimming control signal comprises the steps of: detecting a gray-scale value of each of the aligned image data on a frame-by-frame basis; calculating a histogram and detecting the maximum gray-scale value from the calculated histogram; Delaying the aligned image data during a predetermined period of time, and converting the duty ratio of the dimming control signal according to the detected maximum gray level value.

Wherein the step of converting the duty ratio of the dimming control signal comprises the steps of: storing relative luminance information with respect to a gradation level in a preset gamma value graph state in at least one memory; calculating the gamma value graph so that a maximum point of the gamma value graph becomes the maximum gradation value point; And outputting the dimming control signal having a reduced duty ratio by setting a duty ratio corresponding to a degree of conversion of the relative brightness according to a reduction point of the maximum gray scale value point.

The outputting of the converted image data may include generating a gradation modulation value according to the detected maximum gradation value and the offset value, converting the gradation value of each of the delayed image data according to the gradation modulation value, And outputting the data.

The gray level modulation value generating step may include outputting the gray level value by setting the offset value as the gray level modulation value or outputting the difference value between the maximum gray level value and the offset value as the gray level modulation value.

Wherein the converted image data output step converts the gradation values of the delayed image data to be equal to the gradation modulation value when the offset value is set as the gradation modulation value and outputs the converted gradation value as a difference between the maximum gradation value and the offset value Value is set as the gradation modulation value, the gradation modulation value is converted so that the gradation modulation value is added to the gradation value of the delayed image data by the ratio of the maximum gradation value.

As described above, the driving apparatus for a liquid crystal display according to the present invention and the driving method thereof have the following effects.

That is, the liquid crystal display according to the present invention generates the dimming control signal by decreasing the duty ratio according to the maximum gray level value of each frame of the image data. The driving power of the backlight is reduced by sequentially driving each lamp of the backlight by using the dimming control signal whose duty ratio is decreased, and the motion blurring phenomenon of the displayed image can be reduced.

Further, the liquid crystal display of the present invention changes the gradation of the image data so as to increase in accordance with the offset value from the outside and the detected maximum gradation value. Accordingly, it is possible to improve the image quality of the displayed image by compensating the brightness of the display image which may be degraded due to the decrease of the on-time of the lamps.

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

1 is a block diagram showing a driving apparatus of a liquid crystal display according to an embodiment of the present invention.

1 includes a liquid crystal panel 2 formed with a plurality of pixel regions, a data driver 4 for driving a plurality of data lines DL1 to DLm, a plurality of gate lines GL1 to GLn, A timing controller 8 for aligning the image data RGB from the outside in accordance with the driving of the liquid crystal panel 2 and controlling the data driver 4 and the gate driver 6, A maximum gradation value is detected from the image data (LR, LG, LB) arranged from the controller 8 and the dimming control signal ADim is changed so that the duty ratio is varied according to the detected maximum gradation value, An image conversion unit 10 for converting the grayscale values of the aligned image data LR, LG and LB according to an offset value (Offset) input from the outside and the maximum grayscale value and supplying the converted grayscale value to the data driver 4, , And a response to the converted dimming control signal (ADim) And a backlight unit 18 for irradiating the liquid crystal panel 2 with light.

The liquid crystal panel 2 includes a thin film transistor (TFT) formed in each pixel region defined by a plurality of gate lines GL1 to GLn and a plurality of data lines DL1 to DLm, and a liquid crystal capacitor (Clc). The liquid crystal capacitor Clc is composed of a pixel electrode connected to the TFT, and a common electrode facing the pixel electrode and the liquid crystal. The TFT supplies a video signal from each of the data lines DL1 to DLm to the pixel electrode in response to a scan pulse from each of the gate lines GL1 to GLn. The liquid crystal capacitor Clc charges the difference voltage between the video signal supplied to the pixel electrode and the common voltage supplied to the common electrode, and adjusts the light transmittance by varying the arrangement of the liquid crystal molecules according to the difference voltage. The storage capacitor Cst is connected in parallel to the liquid crystal capacitor Clc so that the voltage charged in the liquid crystal capacitor Clc is maintained until the next data signal is supplied. The storage capacitor Cst is formed by overlapping the pixel electrode with the previous gate line and the insulating film interposed therebetween. Alternatively, the storage capacitor Cst may be formed by overlapping the pixel electrode with the storage line and the insulating film interposed therebetween.

The data driver 4 converts the image data (AR, AG, AB) converted from the image converting section 10 into analog image data, that is, a video signal in accordance with the data control signal DCS from the timing controller 8 A video signal for one horizontal line is supplied to each of the data lines DL1 to DLm for every one horizontal period in which a scan pulse is supplied to each of the gate lines GL1 to GLn. That is, the data driver 4 selects a gamma voltage having a predetermined level according to the gray level of the video signal and supplies the selected gamma voltage to the data lines DL1 to DLm.

The gate driver 6 sequentially generates a scan pulse, that is, a gate-on voltage in response to the gate control signal GCS from the timing controller 8, and sequentially supplies the generated scan pulse to each of the gate lines GL1 to GLn.

The timing controller 8 arranges image data RGB input from the outside to be suitable for driving the liquid crystal panel 2 and supplies the aligned data LR, LG and LB to the image converting unit 10. [ The timing controller 8 uses at least one of a synchronizing signal supplied from the outside, that is, a dot clock DCLK, a data enable signal DE, and horizontal and vertical synchronizing signals Hsync and Vsync, (GCS, DCS) for controlling each of the data lines (4, 6). Here, the gate control signal GCS includes a gate start pulse, a gate shift clock, and a gate output enable, and the data control signal DCS includes a source start pulse (Source Start Pulse), a Source Shift Clock, a Source Output Enable, and a Polarity signal.

The image converting unit 10 detects the tone values of the image data (LR, LG, LB) aligned from the timing controller 8 on a frame-by-frame basis and calculates a histogram. Then, the dimming control signal is converted so as to vary the duty ratio according to the maximum gradation value of the frame-specific image data (RGB) detected by the histogram, and supplied to the inverter control unit 14. Then, the tone values of the image data (LR, LG, LB) aligned according to the maximum tone value detected from the above and the offset value (Offset) input from the outside are converted to be increased. In other words, the image converting unit 10 may convert the gray level values of the aligned image data LR, LG, and LB to increase in the same manner according to an offset value inputted thereto. Also, the image converting unit 10 may convert the gradation values of the aligned image data LR, LG, and LB to increase by the difference value between the offset value and the maximum gradation value. The image converting unit 10 will be described later in detail with reference to the accompanying drawings. In the present invention, only the case where the image conversion unit 10 is configured outside the timing controller 8 is described for the convenience of explanation, but the image conversion unit 10 can be incorporated in the timing controller 8. [

The backlight unit 18 includes a backlight 12 having a plurality of light sources for generating light in the liquid crystal panel 2 and an optical unit for improving the efficiency of light incident from the respective light sources, An inverter control unit 14 for outputting PWM (Pulse Width Modulation) signals in response to the dimming control signal ADim and an AC drive signal ADS for sequentially driving the light sources in response to the PWM signal, And an inverter (16) for supplying the generated light to each of the plurality of light sources.

As the light source of the backlight 12, cylindrical lamps such as CCFL (Cold Cathode Fluorescent Lamp) and EEFL (External Electrode Fluorescent Lamp) are mainly used. The lamps are driven by the AC drive signal ADS from the inverter 16 to generate light. For example, in the case of the scanning backlight unit 18, light is generated in such a manner that a plurality of silencer lamps are sequentially turned on / off. In addition, the optical unit diffuses and condenses the incident light from the light source to improve the light efficiency.

The inverter control unit 14 generates a PWM signal corresponding to the dimming control signal ADim from which the duty ratio is converted from the image converting unit 10 and supplies the PWM signal to the inverter 16. [ Here, since a plurality of inverters 16 may be provided according to the number of lamps, the PWM signal may be sequentially or simultaneously supplied to each of the plurality of inverters 16. The PWM signal is a signal whose on / off cycle of the lamp is varied in accordance with the duty ratio of the converted dimming control signal ADim. In other words, the PWM signal may be a signal whose on / off period of the ramp, for example, the high / low period of which is variable according to the duty ratio of the dimming control signal ADim.

The inverter 16 generates an AC drive signal ADS for driving the lamp. At this time, the AC drive signal ADS is supplied or cut off according to the PWM signal from the inverter controller 14, (Burst Mode).

2 is a block diagram illustrating an image conversion unit according to an embodiment of the present invention shown in FIG.

The image conversion unit 10 shown in FIG. 2 detects a gray-scale value of each of the aligned image data LR, LG and LB on a frame-by-frame basis from the timing controller 8 and calculates a histogram. A histogram analyzing unit 24 for detecting a maximum tone value Max in a frame unit, a delay unit 24 for delaying and outputting the aligned image data LR, LG, and LB during a period of detecting a maximum tone value Max in units of frames, 22), the duty ratio of the dimming control signal is varied according to the detected maximum gradation value Max to be supplied to the inverter control unit 14, and the detected maximum gradation value Max is input from the outside A dimming control section 26 for generating a gradation modulation value AMax by converting in accordance with an offset value Offset and a video data DR, DG and DB delayed from the delay section 22 in accordance with the gradation modulation value AMax And converts the converted image data (AR, AG, AB) into data And a gradation modulating unit 28 is supplied to the driver (4).

3, the histogram analyzing unit 24 detects the gray level values of the image data (LR, LG, LB) aligned from the timing controller 8 on a frame-by-frame basis. Then, the histogram is calculated by using the tone value detected on a frame-by-frame basis, and the maximum tone value Max is detected from the calculated histogram and output to the dimming control section 26.

The delay unit 22 delays the image data LR, LG, and LB aligned from the timing controller 8 so as to be synchronized with a period for detecting the maximum gradation value Max in units of frames. Then, the delayed data DR, DG, and DB are output to the gray-scale modulation unit 28. [

The dimming control unit 26 varies the duty ratio of the dimming control signal according to the maximum tone value Max detected by the histogram analyzing unit 24 and outputs a variable dimming control signal ADim. To this end, the dimming control unit 26 includes at least one memory, and stores relative luminance information with respect to the gray level (gray) as shown in FIG. 4 for each of the preset gamma values Gamma. Here, the relative brightness represents a luminance value that can be expressed for each gradation level according to a preset gamma value Gamma. The predetermined gamma value Gamma may be set in advance according to the application in which the liquid crystal display device is used. In the case where the liquid crystal display device is used as a monitor of a computer, the gamma value Gamma is set to 2.2. Hereinafter, only the case where the gamma value Gamma is set to 2.2 will be described for convenience of explanation.

5A and 5B are graphs showing a duty ratio conversion method of the dimming control signal according to the detected maximum gray level value.

5A, when the maximum tone value Max detected from the histogram analyzer 24 is 220 level in a state where the gamma value Gamma is preset to 2.2, the relative luminance for the 220 level is about 0.77 (nit )to be. Here, the uppermost point of the graph indicating the maximum relative brightness value 1.0 (nit) and the maximum gradation level 255 level in the state where the gamma value Gamma is set to 2.2 is set to "M" point for convenience. Then, a point indicating the relative luminance value 0.77 (nit) corresponding to the detected maximum gradation value Max level 220 is set to the "P" point for convenience.

5 (b), the dimming control unit 26 moves the "P" point of the 0.77 (nit) of the tone value 220 level to the gamma value Gamma 2.2 graph I.e., the uppermost point. Therefore, the maximum value point of the reduced gamma value (Gamma) 2.2 graph is the "P" point before conversion, ie, "M '" point. At this time, the "P" point before the conversion, which represents the relative luminance value 0.77 (nit) corresponding to the maximum gradation value (Max) level 220, is obtained by the reduction conversion of the gamma value (Gamma) Quot; P "points. Through the conversion process, the dimming control unit 26 sets the duty ratio of the dimming control signal to 60% so as to correspond to the converted relative brightness value 0.6 (nit) when the maximum gray-level value Max is detected as 220 level . Then, the converted dimming control signal ADim is outputted so that the duty ratio of the dimming control signal is reduced to 60%. As described above, the dimming control unit 26 reduces the gamma value graph so that the maximum point "M" point of the gamma value graph becomes the "P" point which is the maximum gradation value Max point, and the previous maximum gradation value Max " Quot ;, the duty ratio is set to correspond to the degree of conversion of the relative brightness according to the conversion point of the " P "point, that is, the point P ", and the dimming control signal ADim having the reduced duty ratio is output.

6A and 6B are other graphs showing a duty ratio conversion method of the dimming control signal according to the maximum gradation value.

6A, when the maximum gradation value Max detected from the histogram analyzer 24 is 165 levels in a state where the gamma value Gamma is preset to 2.2, the relative brightness for the 165 level is about 0.40 (nit )to be. Here, the uppermost point of the graph indicating the maximum relative brightness value 1.0 (nit) and the maximum gradation level 255 level in the state where the gamma value Gamma is set to 2.2 is set to "M" point for convenience. Then, a point indicating the relative luminance value 0.40 (nit) corresponding to the detected maximum gradation value Max level 165 is set to the "P" point for convenience.

6 (b), the dimming control unit 26 moves the "P" point of 0.40 (nit) of the tone value 165 level to the gamma value Gamma 2.2 graph I.e., the uppermost point. Therefore, the reduced value of the gamma value (Gamma) 2.2. The maximum value point of the graph is the "P" point before conversion, ie, "M '" point. At this time, the "P" point before the conversion, which represents the relative luminance value 0.40 (nit) corresponding to the maximum gradation value Max level 165, is 0.23 (nit) due to the reduction conversion of the gamma value Gamma 2.2 graph Quot; P "points. Through the conversion process, the dimming control unit 26 sets the duty ratio of the dimming control signal to 23% so as to correspond to the converted relative luminance value 0.23 (nit) when the maximum gray-level value Max is detected at 165 levels . Then, the dimming control signal ADim having the duty ratio of the dimming control signal reduced to 23% is output. As described above, the dimming control unit 26 reduces the gamma value graph so that the maximum point "M" point of the gamma value graph becomes the "P" point which is the maximum gradation value Max point, and the previous maximum gradation value Max " Quot ;, the duty ratio is set to correspond to the degree of conversion of the relative brightness according to the conversion point of the " P "point, that is, the point P ", and the dimming control signal ADim is converted so that the duty ratio is reduced.

The dimming control unit 26 also converts the detected maximum gradation value Max according to an offset value (Offset) input from the outside to generate a gradation modulation value AMax. Then, the gradation modulation unit 28 outputs the gradation modulation value AMax. Here, the offset value (Offset) input from the outside may be any one of 0 to 255 gradation levels. Accordingly, if the offset value (Offset) is input as 255, which is the maximum gradation level, the dimming control unit 26 sets the detected maximum gradation value Max to the maximum gradation level 255 level as shown in FIGS. 5B and 6B And the gradation value of the 255 level can be supplied to the gradation modulation section 28 as the gradation modulation value AMax. In this case, the offset value (Offset) can be supplied to the gradation modulation section 28 as the gradation modulation value AMax. On the other hand, the dimming control section 26 may supply the difference value between the maximum gradation value and the offset value (Offset) to the gradation modulation section 28 as the gradation modulation value AMax. In other words, if the offset value Offset is inputted as 255 which is the maximum gradation level and the maximum gradation value Max is inputted as 220, the 35 level which is the difference value is inputted to the gradation modulation section 28 with the gradation modulation value AMax .

The gradation modulation unit 28 converts the gradation value of the image data DR, DG, DB delayed from the delay unit 22 according to the gradation modulation value AMax input from the dimming control unit 26, (AR, AG, AB) to the data driver 4. At this time, the gradation modulation unit 28 may convert the gradation values of the delayed image data DR, DG, DB to be equal to the gradation modulation value AMax, or may convert the gradation values of the delayed image data DR, DG, It may be converted so that the gradation modulation value AMax is added to the gradation value. More specifically, when the offset value Offset is input as the gradation modulation value AMax, the gradation modulation section 28 outputs the gradation values of the delayed image data DR, DG, and DB to the gradation modulation values AMax, To be equalized. When the difference between the maximum gradation value and the offset value is input as the gradation modulation value AMax, the gradation modulation section 28 outputs the image data DR and DG delayed by the ratio of the maximum gradation value Max, , And DB, so that the gradation modulation values AMax are added to the respective gradation values. Of course, even if the gradation modulation value AMax is added to the gradation value of each of the delayed image data DR, DG, DB, the maximum gradation level is set to the 255 level.

As described above, the liquid crystal display according to the present invention detects the maximum tone value Max of each input image data RGB and decreases the duty ratio according to the detected maximum tone value Max, The control signal ADim is converted. The power consumption of the backlight 12 is reduced by sequentially driving the respective lamps of the backlight 12 according to the dimming control signal ADim whose duty ratio is decreased, and the motion blurring phenomenon of the displayed image is reduced . Further, the liquid crystal display of the present invention converts the gradation of the image data (RGB) to increase in accordance with the offset value (Offset) from the outside and the detected maximum gradation value AMax. Accordingly, it is possible to improve the image quality of the displayed image by compensating the brightness of the display image which may be degraded due to the decrease of the on-time of the lamps.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents. Will be clear to those who have knowledge of.

1 is a configuration diagram showing a driving apparatus of a liquid crystal display according to an embodiment of the present invention;

FIG. 2 is a block diagram illustrating an image conversion unit according to an embodiment of the present invention shown in FIG. 1. FIG.

Fig. 3 is a histogram of one frame calculated from the histogram analyzing unit of Fig. 2; Fig.

FIG. 4 is a graph showing relative brightness information relative to a gradation level stored in the dimming control unit of FIG. 2 according to a gamma value; FIG.

5A and 5B are graphs showing a duty ratio conversion method of the dimming control signal according to the detected maximum gray level value.

6A and 6B are other graphs showing a duty ratio conversion method of the dimming control signal according to the maximum gradation value.

BRIEF DESCRIPTION OF THE DRAWINGS FIG.

2: liquid crystal panel 4: data driver

6: Gate driver 8: Timing controller

10: Video converter 12: Backlight

14: inverter control unit 16: inverter

18: Backlight unit 22:

24: histogram analyzing unit 26: dimming control unit

28:

Claims (12)

A liquid crystal panel formed with a plurality of pixel regions; A data driver for driving a plurality of data lines; A timing controller for aligning video data from outside in accordance with driving of the liquid crystal panel and controlling the data driver and the gate driver; A maximum gray-level value is detected from the image data sorted by the timing controller, and a dimming control signal is converted so that the duty ratio is reduced according to the detected maximum gray-scale value, and the offset value and the maximum gray- An image conversion unit for converting the gray level values of the image data and supplying the gray level values to the data driver; And And a backlight unit for emitting light to the liquid crystal panel in response to the converted dimming control signal, The image converter A histogram analyzing unit for detecting a gray level value of each of the aligned image data on a frame basis to calculate a histogram and detecting the maximum gray level value from the calculated histogram, A delay unit for delaying and outputting the aligned image data during a period in which the maximum gray scale value is detected every frame, A dimming control unit for varying the duty ratio of the dimming control signal according to the detected maximum gray level value and supplying the duty ratio to the inverter control unit and generating the gray level modulation value according to the detected maximum gray level value and the offset value, And a gray-scale modulation unit for converting the gray-scale values of the image data delayed from the delay unit according to the gray-scale modulation values and supplying the converted image data to the data driver, The dimming control unit Storing relative luminance information relative to the gradation level in at least one memory in a preset gamma value graph state, The gamma value graph is scaled down so that the maximum point of the gamma value graph becomes the maximum gradation value point, Wherein the duty ratio is set so as to correspond to the degree of conversion of the relative brightness according to the reduction point of the maximum gradation value point to output the dimming control signal with a reduced duty ratio. delete delete The method according to claim 1, The dimming control unit And supplies the offset value to the gradation modulation section as the gradation modulation value or supplies the difference value between the maximum gradation value and the offset value to the gradation modulation section as the gradation modulation value. Device. 5. The method of claim 4, The gray- When the offset value is input as the gradation modulation value, the gradation value of the delayed image data is converted to be equal to the gradation modulation value, When the difference between the maximum gradation value and the offset value is input as the gradation modulation value, the gradation modulation value is added to the gradation value of each of the delayed image data by the ratio of the maximum gradation value, and supplied to the data driver And a driving circuit for driving the liquid crystal display device. 6. The method of claim 5, The backlight unit A backlight including a plurality of light sources for generating light in the liquid crystal panel, An inverter control unit for outputting pulse width modulation signals in response to the converted dimming control signal, And an inverter for generating AC driving signals for sequentially driving the light sources in response to the pulse width modulation signal and sequentially supplying the AC driving signals to the plurality of light sources, . Aligning video data from outside in accordance with driving of a liquid crystal panel; Detecting a maximum gray level value from the aligned image data and converting a dimming control signal such that a duty ratio is reduced according to the detected maximum gray level value; Converting the gradation values of the aligned image data according to an offset value from the outside and the maximum gradation value and outputting the converted image data; And And irradiating light to the liquid crystal panel in response to the converted dimming control signal, The step of converting the gradation value of each of the aligned image data The step of setting the offset value as a gradation modulation value or setting a difference value between the maximum gradation value and the offset value as the gradation modulation value and converting the gradation value of each of the aligned image data according to the gradation modulation value Including, The step of converting the dimming control signal Detecting a tone value of each of the aligned image data on a frame-by-frame basis, calculating a histogram, and detecting the maximum tone value from the calculated histogram, Delaying the aligned image data during a period of detecting the maximum tone value in units of frames, and And converting the duty ratio of the dimming control signal according to the detected maximum gradation value, The duty ratio conversion step of the dimming control signal Storing relative luminance information with respect to a gradation level in at least one memory in a preset gamma value graph state, Narrowing down the gamma value graph such that the maximum point of the gamma value graph is the maximum gradation value point; and And outputting the dimming control signal with a reduced duty ratio by setting a duty ratio to correspond to a degree of conversion of the relative brightness according to the reduction point of the maximum gradation value point. delete delete 8. The method of claim 7, The converted image data output step Generating the gradation modulation value according to the detected maximum gradation value and the offset value, And converting the gradation value of each of the delayed image data according to the gradation modulation value to output the converted image data. 11. The method of claim 10, The gray level modulation value generation step And outputting the offset value as the gradation modulation value or outputting the difference value between the maximum gradation value and the offset value as the gradation modulation value. 12. The method of claim 11, The converted image data output step When the offset value is set and input as the gradation modulation value, the gradation values of the delayed image data are converted to be equal to the gradation modulation value, Wherein when the difference between the maximum gradation value and the offset value is set as the gradation modulation value and the gradation modulation value is inputted, the gradation modulation value is added to the gradation value of each of the delayed image data by the ratio of the maximum gradation value. A method of driving a liquid crystal display device.

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