KR20110066723A - Liquid crystal display and picture quality controlling method thereof - Google Patents

Abstract

PURPOSE: A liquid crystal display and a picture quality controlling method thereof are provided to improve the performance of an MPRT by outputting black data and gray data alternately. CONSTITUTION: In a liquid crystal display and a picture quality controlling method thereof, data is inputted to a corresponding analysis region. Data(RGB) is inputted to the corresponding analysis region and is modulated into a black data having a peak black gradation value. The black data is outputted during a first sub frame period. The data is modulated into up-shifted data radiate the luminance value as an original luminance value at duty of 50%. The modulated data is outputted during a second sub frame period.

Description

Liquid crystal display and image quality control method {LIQUID CRYSTAL DISPLAY AND PICTURE QUALITY CONTROLLING METHOD THEREOF}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display and a method of controlling image quality thereof, which can improve moving picture response time (hereinafter, referred to as "MPRT") performance.

An active matrix liquid crystal display device displays a moving image using a thin film transistor (“TFT”) as a switching element. This liquid crystal display device is thinner and higher resolution than cathode ray tube ("CRT"), so it is applied to display in portable information equipment, office equipment, computer, etc., and is rapidly replacing CRT. .

In the liquid crystal display, a blurring phenomenon in which a screen is not clear and blurry appears in a moving image due to the retention characteristics of the liquid crystal. As shown in FIG. 1, the CRT emits phosphor for only a very short time and displays data in a cell, and then displays an image by impulse driving without emitting light in the cell. In contrast, the liquid crystal display displays an image by a hold driving in which data is supplied to the liquid crystal cell during the scanning period and then the data stored in the liquid crystal cell is maintained for the remaining field period (or frame period) as shown in FIG. .

Since the video displayed on the CRT is displayed by impulse driving, a perceived image felt by the viewer as shown in FIG. 3 becomes clear. On the other hand, in the LCD, the contrast of the perceptual image felt by the viewer is not clearly seen and blurred due to the retention characteristics of the liquid crystal in the video. This difference in perceptual image is due to the integration effect of the image which persists temporarily in the eye following the movement. Therefore, even if the response speed of the liquid crystal display is fast, MPRT performance is degraded due to a mismatch between eye movement and a static image of each frame. In order to improve a motion blur phenomenon, a black data insertion technique is known in which video data is displayed on a screen, and then black data is supplied to the screen to impulse drive the liquid crystal display.

The black data embedding technique time-divides one frame period of a picture into a first subframe period SF1 and a second subframe period SF2 as shown in FIG. 5, and performs digital video data RGB during the first subframe period SF1. ) Is sequentially displayed on the screen, and black data BD is inserted during the second subframe period SF2 to sequentially display the screen.

However, in the black data insertion technology, the luminance decreases as much as the black data BD is inserted, and the reproduction rate of the image is greatly reduced. In addition, since a bright image is displayed during the first subframe period SF1 and a dark image is displayed during the second subframe period SF2, the bright image and the dark image are repeated periodically, resulting in severe flicker.

Accordingly, it is an object of the present invention to provide a liquid crystal display device and an image quality control method thereof capable of improving MPRT performance while minimizing luminance degradation and flicker.

In order to achieve the above object, the liquid crystal display device according to an embodiment of the present invention comprises a liquid crystal display panel on which modulation data is displayed; A timing controller dividing one frame period into a first sub frame period and a second sub frame period; A backlight for irradiating light onto the liquid crystal display panel including one or more light sources; And extracting a frame representative value by analyzing input data, adjusting the on time duty of the light sources based on the frame representative value, and taking the input data into consideration of the frame representative value and the adjusted duty. And an image quality control circuit for adjusting to.

The image quality control circuit may include an image analyzer configured to analyze the input data on a frame-by-frame basis in an analysis area having a predetermined size; A representative value deriving unit for deriving a maximum gray value in the analysis region as the frame representative value; A duty controller for adjusting the duty of the light sources to the maximum during the second sub frame period, and differently adjusting the duty of the light sources to the maximum gray value during the first sub frame period; And a data modulator for adjusting the input data to the modulated data in consideration of the maximum gray scale value and the adjusted duty.

The duty controller is configured to control the duty of the light sources to 0% so that the light sources are turned off during the first sub frame period when the maximum gray level is less than or equal to a preset intermediate gray level value, and to be turned on in full during the second sub frame period. Control the duty of the light sources to 50%; If the maximum gray value exceeds the intermediate gray value, the duty of the light sources is controlled to 50% so that the light sources are turned on in full during the second sub frame period, and the intermediate gray value and the maximum gray value during the first sub frame period. The duty of the light sources is controlled to C (C≤50)% so as to be turned on for a period corresponding to the luminance difference between them.

The duty (C%) of the light sources is controlled to increase in proportion to the luminance difference between the intermediate gray value and the maximum gray value.

The data modulator may modulate the data input to the analysis area into black data and output the black gray data for the first sub frame period when the maximum gray level value is less than or equal to the intermediate gray level value, and output the data input to the analysis area to the duty 50. Modulate the data into an upwardly adjusted data such that the luminance value equals to the original luminance value (luminance value at duty 100%) at% and output the same during the second sub frame period; When the maximum gray value exceeds the intermediate gray value, the data input to the analysis region is modulated into white data and output during the second sub frame period, and the data input to the analysis region is duty (50 + C)%. S modulates the data up-adjusted so as to have the same luminance value as the original luminance value (luminance value at 100% duty) and outputs the same during the first sub frame period.

The analysis area is set to the entire screen or is set for each block; The duty of the light sources is adjusted in units of the analysis region.

According to an exemplary embodiment of the present invention, a liquid crystal display panel on which modulation data is displayed, a timing controller for dividing one frame period into a first sub frame period and a second sub frame period, and one or more light sources may be included in the liquid crystal display panel. A method of controlling an image quality of a liquid crystal display having a backlight for irradiating light may include: analyzing the input data on a frame-by-frame basis in an analysis area having a predetermined size (A); Deriving a maximum gray value in the analysis region (B); (C) adjusting a duty of the light sources to a maximum during the second sub frame period, and differently adjusting the duty of the light sources to the maximum gray value during the first sub frame period; And adjusting (D) the input data to the modulated data in consideration of the maximum gray scale value and the adjusted duty.

The liquid crystal display and the image quality control method according to the present invention improve the MPRT performance by outputting the black data and the gray data alternately because the luminance degradation or the flicker is not remarkably seen in the low gradation image below the intermediate gradation value. In this low gradation image, the light source is controlled with a 50% duty, reducing the backlight power consumption to 1/2 or less of the conventional one.

In addition, the liquid crystal display and the image quality control method according to the present invention outputs gray data and white data alternately because the luminance degradation or flicker may be remarkably recognized in the high gradation image exceeding the intermediate gradation value. In addition, by controlling the light sources with a duty of (50 + C)%, the backlight is turned off in some periods during which gray data is displayed, thereby greatly improving MPRT performance while minimizing brightness and flicker, and reducing backlight consumption.

Hereinafter, exemplary embodiments of the present invention will be described with reference to FIGS. 6 to 11.

6 shows a liquid crystal display according to an embodiment of the present invention.

Referring to FIG. 6, a liquid crystal display according to an exemplary embodiment of the present invention includes a liquid crystal display panel 10, a timing controller 11, a data driving circuit 12, a gate driving circuit 13, and an image quality control circuit 14. , A light source driving circuit 15, and a backlight 16. The data driving circuit 12 and the gate driving circuit 13 constitute a panel driving circuit.

The liquid crystal display panel 10 includes two glass substrates and a liquid crystal layer formed therebetween. A plurality of data lines DL and a plurality of gate lines GL cross on the lower glass substrate of the liquid crystal display panel 10. The liquid crystal cells Clc are arranged in a matrix form on the liquid crystal display panel 10 due to the cross structure of the data lines DL and the gate lines GL. In the lower glass substrate of the liquid crystal display panel 10, TFTs, pixel electrodes 1 of liquid crystal cells Clc connected to TFTs, storage capacitors Cst, and the like are formed.

The black matrix, the color filter, and the common electrode 2 are formed on the upper glass substrate of the liquid crystal display panel 10. The common electrode 2 is formed on the upper glass substrate in a vertical electric field driving method such as twisted nematic (TN) mode and vertical alignment (VA) mode, and has an in plane switching (IPS) mode and a fringe field switching (FFS) mode. In the same horizontal electric field driving method, the pixel electrode 1 is formed on the lower glass substrate. A polarizing plate is attached to each of the upper glass substrate and the lower glass substrate of the liquid crystal display panel 10, and an alignment layer for setting a pretilt angle of the liquid crystal is formed on an inner surface of the liquid crystal display panel 10 in contact with the liquid crystal.

The data driver circuit 12 includes a plurality of data drive integrated circuits. The data drive integrated circuit includes a shift register for sampling a clock signal, a register for temporarily storing data, and a latch for storing data one line at a time in response to a clock signal from the shift register and simultaneously outputting one line of stored data. A digital / analog converter for selecting a positive / negative gamma voltage under reference to a gamma reference voltage and generating a positive / negative data voltage according to a digital data value from a latch. And a multiplexer for selecting a data line to which a polarity data voltage is supplied, and an output buffer connected between the multiplexer and the data line. The data driving circuit 12 latches the modulation data R'G'B 'under the control of the timing controller 11, and the latched data R'G'B' is subjected to the positive / negative gamma compensation voltage. After conversion to the positive / negative analog data voltage using the supply to the data lines (DL). The operation of the data driving circuit 12 is performed twice every frame.

The gate driving circuit 13 includes a plurality of gate drive integrated circuits. The gate drive integrated circuit includes a shift register, a level shifter for converting an output signal of the shift register into a swing width suitable for driving a TFT of a liquid crystal cell, an output buffer, and the like. The gate driving circuit 13 sequentially outputs scan pulses (or gate pulses) to the gate lines GL under the control of the timing controller 11. The operation of the gate driving circuit 13 is performed twice every frame.

The timing controller 11 controls signals for controlling the operation timing of the data driving circuit 12 and the gate driving circuit 13 based on timing signals Vsync, Hsync, DE, and DCLK from an external system board. (DDC, GDC) occurs. The timing controller 11 multiplies the data control signal DDC and the gate control signal GDC so that the data driving circuit 12 has a frame frequency of 120 × N (N is a positive integer of 2 or more) Hz, for example, a frame frequency of 240 Hz. ) And the operation of the gate driving circuit 13. The timing controller 11 time-divisions one frame period into a first sub frame period and a second sub frame period, and modulates the modulated data R'G'B 'input from the image quality control circuit 14 to a multiplied frame frequency. Synchronization is supplied to the data drive circuit 12.

The backlight 16 includes one or more light sources to irradiate the liquid crystal panel 10 with light. The backlight 16 may be implemented as one of a direct type and an edge type. The direct backlight 16 has a structure in which a plurality of optical sheets and a diffusion plate are stacked below the liquid crystal display panel 10 and a plurality of light sources are disposed below the diffusion plate. The edge type backlight 16 has a structure in which a plurality of optical sheets and a light guide plate are stacked below the liquid crystal display panel 10 and a plurality of light sources are disposed on the side of the light guide plate. The light sources can be implemented with line light sources such as Cold Cathode Fluorescent Lamps (CCFLs) and External Electrode Fluorescent Lamps (EEFLs), and can also be implemented as light emitting diodes (LEDs). It can be implemented with point light sources.

The light source driving circuit 15 drives the light sources in response to the light source control signal LCS input from the image quality control circuit 14.

The image quality control circuit 14 derives a frame representative value based on the analysis result of the input data RGB, generates a light source control signal LCS based on the frame representative value, and adjusts the on time duty of the light sources. In addition, the input data RGB is modulated in consideration of the frame representative value and the adjusted duty.

7 shows the image quality control circuit 14.

Referring to FIG. 7, the image quality control circuit 14 includes an image analyzer 141, a representative value derivator 142, a duty controller 143, and a data modulator 144.

The image analyzer 141 analyzes the input data RGB in units of frames on the analysis region (s) of a predetermined size and outputs the analysis result to the representative value deriving unit 142. In this case, the analysis area may be set to the entire screen (when implementing global dimming) or may be set for each block (when implementing local dimming).

The representative value deriving unit 142 derives the frame representative value based on the analysis result of the input data RGB. The frame representative value indicates the maximum gray scale value B in the analysis area. The representative value deriving unit 142 derives, as the maximum gray value B, the highest gray value among the gray values satisfying the specific threshold in the analysis area. The specific threshold may be determined differently in consideration of the number of pixel data having each gray value and / or the distribution density of each gray value.

The duty controller 143 compares the maximum gray value B input from the representative value deriving unit 142 with a preset intermediate gray value A. FIG. The intermediate grayscale value A refers to a grayscale value that exhibits half the luminance of the peak white grayscale value while driving the light sources at 100% of the on-time duty. For example, when the peak white gray value is 255 gray, the intermediate gray value A may be set to 160 gray.

As a result of the comparison, when the maximum gray value B is less than or equal to the intermediate gray value A, the duty controller 143 turns off the light sources corresponding to the analysis region during the first sub frame period SF1 as shown in FIG. 8. Control their duty to 0% and control their duty to 50% so as to be turned on (full) during the second sub frame period SF2. Thus, the total duty of the light sources during one frame period is adjusted to 50%. For example, when the maximum gray value B of 80 gray is input in response to the middle gray value A of 160 gray, as shown in FIG. 9, the duty controller 143 sets the duty of the light sources to the first sub frame period SF1. 0% and 50% in the second sub frame period SF2.

As a result of the comparison, when the maximum gray value B exceeds the intermediate gray value A, the duty controller 143 turns on the light sources corresponding to the corresponding analysis area in full during the second sub frame period SF2 as shown in FIG. 8. Control their duty at 50% so as to be ON, and turn them ON for a period corresponding to the luminance difference between the intermediate gray value A and the maximum gray value B during the first subframe period SF1. The duty is controlled to C (C≤50)%. Thus, the total duty of the light sources for one frame period is adjusted to (50 + C)%. In the first sub frame period SF1, the duty C% of the light sources increases as the luminance difference between the intermediate gray value A and the maximum gray value B increases. For example, when the maximum gray value B of 200 gray is input in response to the middle gray value A of 160 gray, as shown in FIG. 10A, the duty controller 143 sets the duty of the light sources to the second sub frame period SF2. 50% and 20% in the first sub frame period SF1. The 20% duty is the minimum value to achieve a luminance difference between 200 gray and 160 gray. In addition, when the maximum gray value B of 240 gray is input in correspondence with the middle gray value A of 160 gray as shown in FIG. 10B, the duty controller 143 sets the duty of the light sources to the second sub frame period SF2. 50% and 40% in the first sub frame period SF1. 40% duty is the minimum value to achieve the luminance difference between 240 gray and 160 gray.

The data modulator 144 compares the maximum gray value B input from the representative value deriving unit 142 with the middle gray value A, and considers the comparison result and the duty adjusted by the duty controller 143. To modulate the input data RGB.

As a result of the comparison, if the maximum gray value B is less than or equal to the intermediate gray value A, the data modulator 144 may select the peak RGB gray value 0 gray as the data RGB input to the corresponding analysis region as shown in FIG. 8. It modulates the data into black data and outputs it during the first sub frame period SF1, and outputs the data RGB inputted in the corresponding analysis area to the luminance value equal to the original luminance value (luminance value at 100% duty) at 50% duty. It modulates the data up-adjusted so as to output a second subframe period SF2. For example, as shown in FIG. 9, when the maximum gray value B of 80 gray is input in response to the middle gray value A of 160 gray, the data modulator 144 converts black data of 0 gray to modulated data R′G. The data adjusted during the first sub frame period SF1 and up-adjusted so as to exhibit the same luminance value as the original luminance value at a duty of 50% as the modulation data R'G'B '. Output is performed during the second sub frame period SF2.

As a result of the comparison, when the maximum gray value B exceeds the intermediate gray value A, the data modulator 144 displays the data RGB input to the corresponding analysis area as shown in FIG. 8, with the peak white gray value 255 gray. It modulates into white data having a value and outputs it during the second sub frame period SF2, and outputs the data RGB input to the corresponding analysis area from the duty (50 + C)% to the original luminance value (the luminance value at 100% duty). ) Is modulated with data adjusted upwardly so as to have the same luminance value as?) And output during the first sub frame period SF1. For example, as shown in FIG. 10A, when the maximum gray value B of 200 gray is input in response to the middle gray value A of 160 gray, the data modulator 144 converts the white data of 255 gray to the modulated data R′G. The data adjusted during the second sub frame period SF2 and adjusted upward to exhibit the same luminance value as the original luminance value at 70% duty as modulation data R'G'B '. Output is performed during the first sub frame period SF1. Also, as shown in FIG. 10B, when the maximum gray value B of 240 gray is input in response to the middle gray value A of 160 gray, the data modulator 144 converts the white data of 255 gray to the modulated data R'G. The data adjusted during the second sub frame period SF2 and adjusted upward to exhibit the same brightness value as the original brightness value at 90% duty as modulation data R'G'B '. Output is performed during the first sub frame period SF1.

As such, the image quality control circuit 14 improves the MPRT performance by alternately outputting black data and gray data because luminance degradation or flicker is not visually noticeable in a low gray level image below the intermediate gray scale value A. Furthermore, since the image quality control circuit 14 controls the light sources with a 50% duty, the backlight power consumption is reduced to 1/2 or less of the conventional one.

The image quality control circuit 14 alternately outputs gray data and white data in a high gradation image exceeding the intermediate gradation value A, so that the luminance deterioration or flicker can be visually recognized. In addition, the image quality control circuit 14 controls the light sources with a duty of (50 + C)% to turn off the backlight in some periods during which gray data is displayed, thereby greatly improving MPRT performance while minimizing brightness and flicker, Reduce power consumption

11 illustrates a method for controlling image quality of a liquid crystal display according to an exemplary embodiment of the present invention.

Referring to FIG. 11, the image quality control method analyzes input data RGB on a frame-by-frame basis for analysis area (s) of a predetermined size (S10, S20). Dimming implementation) or block-by-block setting (local dimming implementation).

The image quality control method derives the maximum gray value B in the analysis area based on the analysis result of the input data RGB. (S30) In step S30, the highest gray level value satisfying a specific threshold value in the analysis area is obtained. The gray scale value is derived as the maximum gray scale value (B). The specific threshold may be determined differently in consideration of the number of pixel data having each gray value and / or the distribution density of each gray value.

This image quality control method compares the derived maximum gradation value B with a preset intermediate gradation value A (S40). Here, the intermediate gradation value A is obtained by driving the light sources at 100% on-time duty. It means a gradation value that exhibits half the luminance of the peak white gradation value. For example, when the peak white gray value is 255 gray, the intermediate gray value A may be set to 160 gray.

If the maximum gray value B is less than or equal to the intermediate gray value A (Yes), the image quality control method is adapted to turn off the light sources corresponding to the corresponding analysis area during the first sub frame period SF1. The duty is controlled to 0%, and their duty is controlled to 50% so as to be fully turned on for the second sub frame period SF2. The image quality control method modulates the data RGB input to the corresponding analysis area into black data having a peak black gray value (0 gray), outputs the same during the first sub frame period SF1, and inputs the data to the corresponding analysis area. The data RGB is modulated into data adjusted upward to exhibit the same luminance value as the original luminance value (luminance value at 100% duty) at the duty 50%, and is output during the second sub frame period SF2. S50)

When the maximum gray value B exceeds the intermediate gray value A as a result of the comparison (No), the image quality control method indicates that the light sources corresponding to the corresponding analysis area are turned on in full during the second sub frame period SF2. Their duty is controlled to 50% as much as possible, and their duty is set to C% so as to be turned on for a period corresponding to the luminance difference between the intermediate gray value A and the maximum gray value B during the first sub frame period SF1. To control. Thus, the total duty of the light sources for one frame period is adjusted to (50 + C)%. The duty C% of the light sources within the first sub frame period SF1 is adjusted in proportion to the luminance difference between the intermediate gray value A and the maximum gray value B. FIG. The image quality control method modulates the data RGB input to the corresponding analysis area into white data having a peak white gray value (255 gray), outputs the same during the second sub frame period SF2, and inputs to the analysis area. The resultant data RGB from the duty (50 + C)% to the data adjusted upward so as to have the same luminance value as the original luminance value (the luminance value at the 100% duty), and then, during the first sub frame period SF1. Output (S60)

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the technical spirit of the present invention. Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification but should be defined by the claims.

1 is a characteristic diagram showing light emission characteristics of a cathode ray tube;

2 is a characteristic diagram showing light emission characteristics of a liquid crystal display device;

3 is a diagram illustrating a perceptual image of a cathode ray tube felt by a viewer;

4 is a diagram illustrating a perceptual image of a liquid crystal display that a viewer feels.

5 is a diagram for explaining a conventional black data insertion technique.

6 illustrates a liquid crystal display according to an exemplary embodiment of the present invention.

7 is a view showing in detail the image quality control circuit of FIG.

8 is a view for explaining that the duty control and data modulation is performed in the image quality control circuit.

9 is a view showing an example of the operation of the image quality control circuit when the maximum gradation value is less than the intermediate gradation value.

10A and 10B are diagrams showing an example of the operation of the image quality control circuit when the maximum gradation value exceeds the intermediate gradation value.

11 is a view illustrating a method of controlling image quality of a liquid crystal display according to an exemplary embodiment of the present invention.

<Description of Symbols for Main Parts of Drawings>

10 liquid crystal display panel 11 timing controller

12: data driving circuit 13: gate driving circuit

14: image quality control circuit 15: light source driving circuit

16: backlight 141: image analyzer

142: representative value deriving unit 143: duty control unit

144: data modulation unit

Claims (11)

A liquid crystal display panel on which modulation data is displayed; A timing controller dividing one frame period into a first sub frame period and a second sub frame period; A backlight for irradiating light onto the liquid crystal display panel including one or more light sources; And Analyzing input data to derive a frame representative value, adjusting the on-time duty of the light sources based on the frame representative value, and taking the input data into the modulation data in consideration of the frame representative value and the adjusted duty. And a picture quality control circuit for adjusting. The method of claim 1, The image quality control circuit, An image analyzer configured to analyze the input data on a frame-by-frame basis for an analysis area having a predetermined size; A representative value deriving unit for deriving a maximum gray value in the analysis region as the frame representative value; A duty controller configured to adjust the duty of the light sources to the maximum during the second sub frame period and to adjust the duty of the light sources to be different according to the maximum gray value during the first sub frame period; And And a data modulator for adjusting the input data to the modulated data in consideration of the maximum gray scale value and the adjusted duty. The method of claim 2, The duty adjustment unit, When the maximum gray value is less than or equal to a preset intermediate gray value, the duty of the light sources is controlled to 0% so that the light sources are turned off during the first sub frame period, and the duty of the light sources is turned on to full light during the second sub frame period. Controlled at 50%; If the maximum gray value exceeds the intermediate gray value, the duty of the light sources is controlled to 50% so that the light sources are turned on in full during the second sub frame period, and the intermediate gray value and the maximum gray value during the first sub frame period. And control the duty of the light sources to C (C≤50)% so that the light is turned on for a period corresponding to the luminance difference therebetween. The method of claim 3, wherein And the duty (C%) of the light sources is controlled to increase in proportion to the luminance difference between the intermediate gray value and the maximum gray value. The method of claim 3, wherein The data modulator, If the maximum gray value is less than or equal to the intermediate gray value, the data input to the analysis region is modulated with black data and output during the first sub frame period, and the data input to the analysis region has an original luminance of 50% duty. Modulate the data up-adjusted to exhibit the same luminance value as the luminance value (luminance value at 100% duty) and output the same during the second sub frame period; When the maximum gray value exceeds the intermediate gray value, the data input to the analysis region is modulated into white data and output during the second sub frame period, and the data input to the analysis region is duty (50 + C)%. And modulate the data to be up-regulated so as to have the same luminance value as the original luminance value (luminance value at 100% duty), and output the same during the first sub frame period. The method of claim 2, The analysis area is set to the entire screen or is set for each block; And the duty of the light sources is adjusted in units of the analysis region. A liquid crystal display panel on which modulated data is displayed, a timing controller dividing one frame period into a first sub frame period and a second sub frame period, and a backlight for irradiating light to the liquid crystal display panel including one or more light sources; In the image quality control method of the liquid crystal display device, Analyzing the input data on a frame-by-frame basis for an analysis area of a predetermined size (A); Deriving a maximum gray value in the analysis region (B); (C) adjusting a duty of the light sources to a maximum during the second sub frame period, and differently adjusting the duty of the light sources to the maximum gray value during the first sub frame period; And And adjusting the input data to the modulated data in consideration of the maximum gray scale value and the adjusted duty. The method of claim 7, wherein Step (C) is, When the maximum gray value is less than or equal to a preset intermediate gray value, the duty of the light sources is controlled to 0% so that the light sources are turned off during the first sub frame period, and the duty of the light sources is turned on to full light during the second sub frame period. Controlled at 50%; If the maximum gray value exceeds the intermediate gray value, the duty of the light sources is controlled to 50% so that the light sources are turned on in full during the second sub frame period, and the intermediate gray value and the maximum gray value during the first sub frame period. And controlling the duty of the light sources to be C (C≤50)% so as to be turned on for a period corresponding to the luminance difference therebetween. The method of claim 8, And the duty (C%) of the light sources is controlled to increase in proportion to the luminance difference between the intermediate gray value and the maximum gray value. The method of claim 7, wherein The step (D), When the maximum gray value is less than or equal to the intermediate gray value, data input to the analysis region is modulated into black data for output during the first sub frame period, and the data input to the analysis region is at an original luminance of 50% duty. Modulate the data up-adjusted to exhibit the same luminance value as the luminance value (luminance value at 100% duty) and output the same during the second sub frame period; When the maximum gray value exceeds the intermediate gray value, the data input to the analysis region is modulated into white data and output during the second sub frame period, and the data input to the analysis region is duty (50 + C)%. And modulating the data up-adjusted so as to have the same luminance value as the original luminance value (luminance value at 100% duty), and outputting the same during the first sub frame period. The method of claim 7, wherein The analysis area is set to the entire screen or is set for each block; And the duty of the light sources is adjusted in units of the analysis region.

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