KR101862408B1 - Method of local dimming method and liquid crystal display - Google Patents

Abstract

The present invention relates to a liquid crystal display device and a driving method thereof, the liquid crystal display device comprising: a frame rate converter for multiplying a frame frequency of an input image to divide one frame period into a first sub frame period and a second sub frame period; And selecting a logical value of BOW indicating one of a white gradation value and a black gradation value according to a result of the comparison, and comparing the input image data with the input image data based on the BOW, And generates a black gradation or white gradation data on the basis of the BOW.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a liquid crystal display (LCD)

The present invention relates to a liquid crystal display and a driving method thereof.

BACKGROUND ART [0002] Liquid crystal display devices are becoming increasingly widespread due to features such as light weight, thinness, and low power consumption driving. The transmissive liquid crystal display device displays an image by controlling an electric field applied to the liquid crystal layer to modulate light incident from the backlight unit.

In a liquid crystal display device, a motion blur phenomenon may occur in a moving picture due to the retention characteristics of a liquid crystal. (MPRT) by supplying black gradation data to the pixels during the (N + 1) th frame period after displaying the video data on the liquid crystal display device for N (N is a natural number) Reduced BDI (Black Data Insertion) technology is known. The BDI can obtain the impulsive driving effect by inserting the black gradation data between the video data to be displayed, and as a result, the motion blur can be reduced in the moving picture by reducing the moving picture response time (MPRT). BDI can reduce the video response time (MPRT), but there is a problem that luminance is lowered due to black gradation data inserted between video data.

The present invention provides a liquid crystal display (LCD) device and a driving method thereof that can improve a moving picture response time (MPRT) without lowering the brightness.

A liquid crystal display device of the present invention includes: a display panel having a pixel array including data lines, gate lines crossing the data lines, and liquid crystal cells arranged in a matrix; A backlight unit for emitting light to the display panel; A frame rate converter for multiplying a frame frequency of an input image to divide one frame period into a first sub frame period and a second sub frame period; Each of the data of the input image is compared with a predetermined center transmittance gradation, a logical value of BOW indicating one of a white gradation value and a black gradation value is selected according to the comparison result, and based on the BOW, A data modulator for modulating data and generating black gradation or white gradation data based on the BOW; And writing the data of the input image modulated based on the BOW in the first sub frame period to the pixel array of the display panel and outputting the black gradation data generated on the basis of the BOW during the second sub frame period, And a display panel driving circuit for writing gray-scale data into the pixel array of the display panel.

The center transmittance gradation is set to a data gradation value when the transmittance of the liquid crystal cell is substantially 50%.

Wherein the data modulator selects the logical value of the BOW when the data of the input image is lower than the center transmittance gradation, while when the data of the input image is the center transmittance gradation or more, 1 ". The BOW is 1 bit data.

Wherein the data modulator generates the black gradation data by adding dummy data having a bit of "0 " to the BOW when the logical value of the BOW is 0, and outputs the black gradation data when the logical value of the BOW is 1, Quot; 1 "is added to generate the black gradation data.

The data modulator modulates data of the input image based on the BOW through the following equation.

는 2~3 사이의 감마 특성 값, X는 상기 BOW를 바탕으로 변조된 입력 영상의 데이터를 각각 의미한다. Here, "# of gray scale" is the number of expressible gray scales, "CTG" is the center transmittance gradation, "gray scale "

Denotes a gamma characteristic value between 2 and 3, and X denotes data of an input image modulated based on the BOW.

The data modulator modulates data of the input image based on the BOW using a look-up table in which the gray-level values and the transmittances of the data are stored.

The data modulator calculates the compensated transmittance by multiplying the transmittance of the liquid crystal cell corresponding to the tone value of the data of the input image by 2 if BOW is "0 ", inputs the compensated transmittance to the lookup table, And modulates the data of the input image with the data output from the input unit. Wherein the data modulator calculates the compensated transmittance by multiplying the result obtained by subtracting the transmittance corresponding to the center transmittance gradation from the transmittance of the liquid crystal cell corresponding to the grayscale value of the data of the input image if BOW is "1 & And inputs the compensated transmittance to the lookup table to modulate the data of the input image with the data output from the lookup table. The transmittance corresponding to the center transmittance gradation is 50%.

The pixel array of the display panel and the light emitting surface of the backlight unit are divided into a plurality of blocks, and each of the blocks includes two or more liquid crystal cells. The backlight emission surface luminance of each of the blocks is determined according to the BOW.

The liquid crystal display further includes a local dimming control unit for controlling the brightness of the backlight emission surface for each of the blocks based on the BOW.

Wherein the local dimming control unit determines a dimming value of a block including the liquid crystal cell having the BOW of 1 as the first dimming value and sets the dimming value of the block including the liquid crystal cell having the BOW of 0 as the first dimming value, It is determined that the second dimming value is lower than the dimming value. The backlight emission surface luminance of the block controlled by the first dimming value is higher than the backlight emission surface luminance of the block controlled by the second dimming value.

The method of driving a liquid crystal display device includes: time-dividing one frame period by a frame frequency of an input image into a first sub frame period and a second sub frame period; Comparing each of the data of the input image with a preset center transmittance gradation and selecting a logical value of BOW indicating one of a white gradation value and a black gradation value according to the comparison result; Modulating data of the input image based on the BOW and generating black gradation or white gradation data based on the BOW; And writing the data of the input image modulated based on the BOW in the first sub frame period to the pixel array of the display panel and outputting the black gradation data generated on the basis of the BOW during the second sub frame period, And writing gray-scale data to the pixel array of the display panel.

In the present invention, one frame period is divided into first and second sub frame periods, black gradation data or white gradation data is assigned according to the data analysis result of the input image in the second sub frame period, and the data of the input image is modulated . As a result, the present invention can implement a BDI that can improve the video response time (MPRT) without degrading the brightness.

Furthermore, the present invention can simplify the local dimming algorithm by implementing the local dimming based on the BOW obtained as a result of the comparison of the data of the input image and the center transmittance gradation.

1 is a block diagram illustrating a data processing apparatus according to a first embodiment of the present invention.
FIG. 2 is a flowchart showing a control procedure of a data processing method according to the first embodiment of the present invention.
3 is a diagram illustrating an example in which the frame frequency of the input image is multiplied by two.
4 is a diagram showing an example of local dimming blocks.
5 is a diagram showing an example of a local dimming block linked to BOW.
6 is a block diagram showing a data processing apparatus according to a second embodiment of the present invention.
FIG. 7 is a flowchart illustrating a control procedure of a data processing method according to a second embodiment of the present invention.
8 is a view showing an example of the lookup table shown in FIG.
9 is a block diagram showing a liquid crystal display device according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Like reference numerals throughout the specification denote substantially identical components. In the following description, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.

1 is a block diagram showing a data processing apparatus 100 according to a first embodiment of the present invention. FIG. 2 is a flowchart showing a control procedure of a data processing method according to the first embodiment of the present invention. The data processing method of FIG. 2 may be implemented in the data processing apparatus 100. 3 is a diagram showing an example in which the frame frequency is doubled.

1 to 3, the data processing apparatus 100 includes a frame rate conversion unit 12, a BOW generation unit 14, a memory control unit 16, a memory 18, a data modulation unit 20, A transmission unit 22, and the like.

The frame rate converter 12 receives the digital video data RGB of the input video and the timing signals such as the data enable signal DE synchronized with the data RGB and the main clock CLK. The frame rate conversion section 12 multiplies the frame frequency of the input image by two times so that one frame period FR (N) is divided into a first sub frame period SFa (N) and a second sub frame period SFb (N) (S1 and S2 in Fig. 2) Each of the first sub frame period SFa (N) and the second sub frame period SFb (N) is a half frame period. Frame rate converter 12 transmits a subframe identification signal for distinguishing the first and second subframe periods SFa (N) and SFb (N) to the data modulator 20 and the data transmitter 22 do.

The frame frequency of the input image is 50 Hz in the PAL (Phase Alternate Line) method and 60 Hz in the NTSC (National Television Standards Committee) method. Therefore, in the PAL system, the input frequency of the frame rate conversion unit 12 is 50 Hz, and the output frame frequency multiplied by 2 is 100 Hz. In the NTSC system, the input frame frequency of the frame rate converter 112 is 60 Hz, and the output frame frequency multiplied by 2 is 120 Hz.

The BOW generator 14 compares the data of the input image with a predetermined center transmittance gradation (CTG), and selects a logical value of black or white gradation data (hereinafter referred to as " BOW ") according to the comparison result. (S3 to S5 in FIG. 2) The BOW data generation unit 14 selects '0' as BOW (BOW = 0) when the data gradation of the input image is lower than the center transmittance gradation (CTG) When the data gradation is equal to or more than the center transmittance gradation (CTG), '1' is selected as BOW (BOW = 1). Note that BOW is not selected in the input image but is generated in the BOW generator 14 by comparison with the center transmittance gradation (CTG). Since BOW is 1 or 0, 1 bit is assigned to each data of the input video and is stored in the memory 18. [

The first sub-frame data Dataa is 8-bit data of the input image, while the second sub-frame data Datab is selected as 1-bit BOW. Therefore, the size of the second sub-frame data Datab and the memory capacity are much smaller than the first sub-frame data Dataa.

Assuming that the transmittance of the liquid crystal cell (or subpixel) when the data of the highest grayscale value is written in the pixel array of the display panel is 100%, the center transmittance gradation CTG is set such that the transmittance of the liquid crystal cell is 50% And is set to a data gray scale value written in the liquid crystal cell when the transmittance is the closest to the transmittance. And 256 gradations can be expressed when the pixel data of the input image is 8-bit data. In this case, the closest gradation to the center transmittance gradation (CTG) in the 2.2 gamma characteristic curve is '187'. The center transmittance gradation (CTG) is not limited to '187' because it depends on the number of pixel data bits of the input image and the slope of the gamma characteristic curve.

The memory controller 16 stores BOW as the second subframe data Datab in the memory 18 and supplies the first subframe data Dataa to the data modulator 20. (S6 in Fig. 2) The memory controller 16 also generates a write enable signal and a read enable signal to control the data input / output of the memory 18.

The data of the input image is displayed on the liquid crystal cell only in the first sub frame period SFa (N), which is twice the frame frequency of the input image and set to the 1/2 frame period, and the second sub frame If the black gradation or the white gradation is displayed in the liquid crystal cell in the period SFb (N), the brightness of the image reproduced on the display panel is different from the brightness of the input image. In order to obtain the transmittance equal to the transmittance of the liquid crystal cell when the original data of the input image is held in the liquid crystal cell for one frame period, the grayscale of the first subframe data Dataa when BOW = 0 is smaller than the original data of the input image The gray level of the first subframe data Dataa should be modulated to a lower gray level value than the original data of the input image. To this end, the data modulator 20 modulates the data of the input image in the same manner as in Equation (1) to generate the first sub-frame data Dataa (S7 in FIG. 2)

The BOW generator 14, the memory controller 16, the memory 18, and the data transfer unit 22 may be incorporated in the data modulator 20.

The data modulator 20 supplies the first sub-frame data Data a modulated based on Equation (1) to the data transmitter 22 during the first sub-frame period SFa (N).

는 감마 특성을 의미한다.

는 2~3 사이의 값으로 설정될 수 있다. X는 제1 서브 프레임 기간(SFa(N))에 액정셀에 기입될 데이터의 계조이다.Here, "# of gray scale" is the number of gray scales that can be expressed. For example, in 8-bit data, # of gray scale is 2 ⁸ = 256 and in 6-bit data # of gray scale is 2 ⁶ = 64. The "gray scale" is the data gradation of the input image. If 8-bit data is input and the tone value of the data is 170, in Equation 1, "# of gray scale" is 256 and "gray scale"

Means the gamma characteristic.

Can be set to a value between 2 and 3. X is the gradation of data to be written to the liquid crystal cell in the first sub frame period SFa (N).

= 2.2인 감마 커브에서 액정셀(또는 서브 픽셀)의 투과율(T)이 T = 50%와 가장 가까운 계조인 CTG = 187 이다. 입력 영상 데이터의 계조가 "128"이면, 그 데이터의 계조는 CTG = 187 보다 작으므로 BOW = 0이 된다. 이 경우에, 데이터 변조부(20)는 수학식 1에 의해 입력 영상 데이터 "128"을 "175"로 상향 변조하여 제1 서브 프레임 데이터(Datab)로서 출력한다.Taking the data modulation method as an example,

= 2.2, the transmittance (T) of the liquid crystal cell (or subpixel) is CTG = 187, which is the closest gradation to T = 50%. If the gradation of the input image data is "128 ", the gradation of the data is smaller than CTG = 187, so BOW = 0. In this case, the data modulator 20 up-modulates the input video data "128 "to" 175 " according to Equation (1) and outputs it as the first sub-frame data Datab.

= 2.2인 감마 특성 커브에서 액정셀의 투과율은 21.76%이다. 1/2 프레임 기간으로 설정된 제2 서브 프레임 기간 동안 그 액정셀의 투과율은 BOW = 0 이므로 블랙 계조인 0으로 낮아진다. 따라서, 1/2 프레임 기간으로 설정된 제1 서브 프레임 기간에 그 액정셀의 투과율은 21.76%의 두배(×2)가 되어야 한다. 그 결과, 시간적으로 적분하면 21.76%가 되어야 하므로 그 액정셀의 투과율이 대략 43.3%로 되는 계조는 전술한 데이터 변조 결과와 마찬가지로,

= 2.2인 감마 특성 커브에서 "175" 이다. Describing the transmittance of the liquid crystal cell, when the gradation of the data is "128"

= 2.2, the transmittance of the liquid crystal cell in the gamma characteristic curve is 21.76%. The transmittance of the liquid crystal cell is lowered to 0, which is a black gradation, since BOW = 0 during the second sub frame period set in the 1/2 frame period. Therefore, the transmittance of the liquid crystal cell should be doubled (x2) to 21.76% in the first sub frame period set to the 1/2 frame period. As a result, since integration with time requires 21.76%, the gradation in which the transmittance of the liquid crystal cell is approximately 43.3% is the same as the data modulation result described above,

= 2.2 "in the gamma characteristic curve.

As another example, when the gradation of the input image data is "210 ", the gradation of the data is larger than CTG = 187, so that BOW = 1. In this case, the data modulator 20 down-modulates the input image data "210" to " 146 " based on Equation (1) and outputs it as the first subframe data Dataa.

The data transfer unit 22 selects the output Dataa of the data modulator 20 during the first sub frame period SFa (N) and transfers it to the data driver not shown, The data transfer unit 22 adds 8-bit data to the data driver, and outputs the 8-bit data to the data driver 22. The data driver 22 adds dummy data to BOW, which is the output Data of the memory 18, when, BOW = 0 if BOW = 0 7 bit dummy data of the addition of "0000000 _2" to output the black gradation data "00000000 _2" of 8 bit in the second sub frame period (SFb (N)), and BOW = 1, 7-bit dummy data "1111111 ₂ " is added to BOW = 1 to output 8-bit white tone data 11111111 ₂ to the second sub frame period SFb (N). The data driver modulates the digital video data RGB 'input from the data transfer unit 22 to a positive / negative gamma compensation voltage to generate a positive / negative data voltage. The data voltage output from the data driver is charged to the liquid crystal cells formed in the pixel arrays of the display panel through the data lines of the display panel. As a result, the display panel displays the data Data modulated by the data modulator during the first sub-frame period SFa (N), and outputs the data Data modulated by the data modulation section during the second sub-frame period SFb (N) (S11 in Fig. 2)

A backlight dimming control method of adjusting a brightness of a backlight according to an input image has been applied in order to improve a contrast of an image displayed on a liquid crystal display device. The backlight dimming control method may reduce the power consumption by adaptively adjusting the luminance of the backlight according to the input image.

In the backlight dimming method, there are a global dimming method (global dimming method) for adjusting the brightness of the whole display surface and a local dimming method for dividing the display screen into a plurality of blocks and locally adjusting the brightness of the display surface have.

The global dimming method can improve the dynamic contrast measured between the previous frame and the next frame. The local dimming method can improve the static contrast which is difficult to improve by the global dimming method by locally controlling the brightness of the display surface within one frame period.

The local dimming method divides the backlight emitting surface into a plurality of blocks so that the image enhances the backlight luminance of the bright block while the image lowers the backlight luminance of the relatively dark block. The local dimming method includes a step of analyzing an input image, a step of calculating a representative value for each block according to an analysis result of the input image, a step of calculating a dimming value for each block based on the representative value of each block, And a step of distributing the dimming value for each block using a temporal filter and the like. In contrast, if the data processing method of the present invention is applied to the local dimming algorithm, the local dimming algorithm can be simplified.

4 is a diagram showing an example of local dimming blocks. 5 is a diagram showing an example of a local dimming block linked to BOW.

4 and 5, the liquid crystal display of the present invention virtually divides the pixel array of the display panel and the light emitting surface of the backlight into a plurality of blocks B11 to B45 in order to realize local dimming. Each of the blocks B11 to B45 includes two or more pixels. The pixels include a red subpixel, a green subpixel, and a blue subpixel for color implementation, and each of the subpixels includes a liquid crystal cell. The light sources for illuminating the blocks B11 to B45 independently control the brightness of each of the blocks according to the local dimming value. For example, light sources controlled by a high dimming value are turned on at a high duty ratio in pulse width modulation (PWM) to increase the backlight brightness. On the other hand, light sources controlled by a low dimming value are turned on with a low duty ratio in pulse width modulation (PWM) to lower the backlight luminance. The maximum duty ratio may be 100%, and the minimum duty ratio may be 0%.

As a result of comparing the digital video data RGB of the input image with the center transmittance gradation CTG, the light emitting surface of the backlight which irradiates light to the blocks B22, B23, B32, and B34 including liquid crystals of BOW = And can be turned on at a high luminance due to the light sources that are turned on at the first dimming value during the second sub frame period SFb (N). The first dimming value may be the maximum dimming value. The blocks B22, B23, B32, and B34 including the liquid crystal cells having BOW = 1 are the blocks in which the BOW of all the subpixel data included in the block is BOW = 1 or the number of the data in which BOW = The number of blocks may be more than a predetermined ratio of all the subpixel data. Here, the predetermined ratio may be a ratio selected from 51% to 100%.

The light emitting surface of the backlight for emitting light to the blocks B11 to B15, B21, B24 to B25, B31, B34 to B35, and B41 to B45 including the liquid crystal cells having BOW = N) may be turned on at a low luminance due to the light sources controlled to the second dimming value lower than the first dimming value. The second dimming value may be the minimum dimming value. The blocks B11 to B15, B21, B24 to B25, B31, B34 to B35 and B41 to B45 including the liquid crystal cells having BOW = 0 are all the subpixel data included in the block, , The number of data having BOW = 0 may be more than a predetermined ratio of all the subpixel data included in the block. The predetermined ratio may be a ratio selected from 51% to 100%.

Such a local dimming method can be applied to the first sub frame period SFa (N) as well. On the other hand, the backlight emitting surface that emits light to all of the blocks B11 to B45 during the first sub-frame period SFa (N) may be turned on with the same brightness by the light sources that are turned on with the same dimming value.

6 is a block diagram showing a data processing apparatus according to a second embodiment of the present invention. FIG. 7 is a flowchart illustrating a control procedure of a data processing method according to a second embodiment of the present invention. The data processing method of FIG. 7 can be implemented by the data processing apparatus 100 shown in FIG. FIG. 8 is a view showing an example of a look-up table 66 shown in FIG.

6 to 8, the data processing apparatus 100 includes a frame rate conversion unit 62, a data modulation unit 64, a lookup table 66, a data transfer unit 68, and the like.

The frame rate converter 62 receives digital video data RGB of an input video and a timing signal such as a data enable signal DE synchronized with the data RGB and a main clock CLK. The frame rate converter 62 multiplies the frame frequency of the input image by two times to convert one frame period FR (N) into a first sub frame period SFa (N) and a second sub frame period SFb (N) ) (S11 and S12 in Fig. 7). Each of the first sub frame period SFa (N) and the second sub frame period SFb (N) is a half frame period. The frame rate converter 62 transmits a subframe identification signal for distinguishing the first and second subframe periods SFa (N) and SFb (N) to the data modulator 64. [

In the lookup table 66, the transmittance of the liquid crystal cell obtained for each gradation of the data is experimentally stored along with the gradation of the data through the experiment of the transmittance of the liquid crystal cell for each gradation of data. The lookup table 66 outputs the transmittance T of the data when the data is input. The lookup table 66 outputs the gray level of the data corresponding to the transmittance T when the transmittance T is inputted.

The data modulator 64 compares the data of the input image with the center transmittance gradation (CTG) and selects BOW according to the comparison result. (S12 to S14 in Fig. 7) BOW = 0 when the data gradation is lower than the center transmittance gradation CTG, while BOW = 1 when the data gradation of the input image is equal to or higher than the center transmittance gradation CTG.

The data modulator 64 can input the data of the input image to the lookup table 66 and receive the data of the transmittance outputted from the lookup table 66 to confirm the transmittance of the liquid crystal cell with respect to the data gradation of the input image. The data modulator 64 inputs the compensated transmittance calculated on the basis of the BOW and the transmittance of the input image data to the lookup table 66 and modulates the data of the input image with the data gradation received from the lookup table.

The data modulation unit 64 multiplies the transmittance T1 of the liquid crystal cell corresponding to the data gradation of the input image by 2 to calculate the compensated transmittance T as T = T1 * 2 and outputs the compensated transmittance T ) To the lookup table 66 and modulates the data of the input image with the data output from the lookup table 66. [ If BOW = 1, the data modulation unit 64 multiplies the result obtained by subtracting the transmittance (T2) corresponding to the center transmittance gradation (CTG) from the transmittance (T1) of the liquid crystal cell corresponding to the data gradation of the input image, (T) is calculated as T = (T1-T2) * 2, the compensated transmittance T is input to the lookup table 66, and the data of the input image is modulated with the data output from the lookup table 66. (S15 to S16 in Fig. 7) The transmittance T2 corresponding to the center transmittance gradation CTG may be 50% as described above.

The lookup table 66 responds to the transmittance T input from the data modulator 64 and outputs the gray level of the data corresponding to the transmittance T as the first subframe data Datab. For example, the lookup table 66 outputs the data gray value "128" as the first subframe data Datab when the transmittance T input from the data modulator 64 in Fig. 8 is 21.77.

The data modulation section 64 supplies the data modulated by the BOW and the lookup table 66 to the data transfer section 68. The data modulated by the data modulator 64 satisfies the following equation (1).

The data transfer section 68 selects the modulated data input from the data modulator section 64 during the first sub frame period SFa (N) and transfers the selected modulated data to the data driver section (not shown), while the second sub frame period SFb N), dummy data is added to the BOW input from the data modulator 64 and is transmitted to the data driver. A data transfer unit 68 is the data driver 8 bit when the data is input, BOW = 0 if BOW = each bit is "0" in the zero-7 bit dummy data "0000000 _2", the 8 bit black gray scale data by adding Quot; 00000000 ₂ "to the second sub frame period SFb (N). The data transfer unit 68 adds 8 bits of white gradation data 11111111 ₂ to 7-bit dummy data 1111111 ₂ with each bit set to 1 in BOW = 1 in the second sub frame period ( SFb (N). The data driver modulates the digital video data RGB 'input from the data transfer unit 68 to a positive / negative gamma compensation voltage to generate a positive / negative data voltage. The data voltage output from the data driver is charged to the liquid crystal cells formed in the pixel arrays of the display panel through the data lines of the display panel. As a result, the display panel displays the data modulated by the data modulator 64 during the first sub-frame period SFa (N), and displays the data modulated by the data modulation section 64 during the second sub-frame period SFb (N) .

The data processing apparatus and method according to the second embodiment of the present invention can simplify the local dimming algorithm as shown in FIGS. 4 and 5 by connecting BOW to the local dimming method in the same manner as the first embodiment described above.

9 is a block diagram showing a liquid crystal display device according to an embodiment of the present invention.

9, the liquid crystal display of the present invention includes a display panel 300, a display panel driving unit, a timing controller 110, a data processing unit 100, a backlight unit 200, a light source driving unit 210, A control unit 120, and the like.

The display panel 300 includes two glass substrates, and a liquid crystal layer is formed therebetween. In the display panel 300, the liquid crystal cells are arranged in a matrix by the intersection structure of the data lines 301 and the gate lines 302. The data lines 301, the gate lines 302, the TFTs, and the pixel electrodes (not shown) of the liquid crystal cells connected to the TFTs are connected to a thin film transistor (hereinafter, , A storage capacitor, and the like are formed. On the color filter substrate of the display panel 300, a black matrix, a color filter, and a common electrode are formed.

The liquid crystal display device of the present invention is realized by a vertical electric field driving method such as TN (Twisted Nematic) mode and VA (Vertical Alignment) mode or a horizontal electric field driving method such as IPS (In Plane Switching) mode and FFS (Fringe Field Switching) .

For local dimming, the light emitting surface of the pixel array of the display panel 300 and the opposed backlight unit 200 is virtually divided into a plurality of blocks as described above.

The timing controller 110 receives the timing signals Vsync, Hsync, DE, and CLK from an external host system and supplies the digital video data RGB to the data driver 122. The timing signals Vsync, Hsync, DE and CLK include a vertical synchronization signal Vsync, a horizontal synchronization signal Hsync, a data enable signal DE and a main clock CLK. The vertical synchronization signal Vsync and the horizontal synchronization signal Hsync may be omitted.

The timing controller 110 includes timing control signals DDC, DDC for controlling the operation timings of the data driver 122 and the gate driver 124 based on the timing signals Vsync, Hsync, DE, and CLK from the host system. GDC). The timing controller 110 supplies the digital video data RGB of the input image input from the host system to the data processing apparatus 100 and outputs the digital video data RGB 'output from the data processing apparatus 100 as data And supplies it to the driving unit 122. Also, the timing controller 110 supplies the BOW output from the data processing apparatus 100 to the local dimming control unit 120.

The host system can be any one of a TV system, a home theater system, a personal computer (PC), a set-top box for broadcast reception, a navigation system, a DVD player, a Blu-ray player, and a phone system. The host system transmits timing signals (Vsync, Hsync, DE, CLK) synchronized with the data (RGB) to the timing controller 110 together with digital video data (RGB).

The data processing apparatus 100 is implemented as the first embodiment or the second embodiment described above. The data processing apparatus 100 modulates the data of the input image using the lookup table 66 whose data and transmittance are set on the basis of Equation (1) or Equation (1), and outputs the first sub frame period SFa (N) (RGB ') to be written to the pixel array. The data processing apparatus 100 compares the data of the input image with the center transmittance gradation (CTG) to generate and output BOW, adds dummy data to the BOW, and outputs the BOW.

The display panel driver writes the digital video data RGB 'input from the timing controller 110 into the pixel array of the display panel 300 using the data driver 122 and the gate driver 124. The digital video data RGB 'includes data modulated by the above-described data modulators 20 and 64 and black gradation or white gradation data to which dummy data is added to BOW.

The data driver 122 latches the digital video data RGB 'under the control of the timing controller 110. The data driver 122 converts the digital video data RGB 'into positive / negative polarity analog data voltages using the positive / negative gamma compensation voltages and supplies them to the data lines 301. The gate driver 124 sequentially supplies a gate pulse synchronized with a data voltage output from the data driver 122 to the gate lines 302.

The backlight unit 200 is disposed under the display panel 300. The backlight unit 200 includes a plurality of light sources individually controlled on a block-by-block basis by the light source driving unit 210 to uniformly irradiate light to the display panel 300. The backlight unit 200 may be implemented as a direct type backlight unit or an edge type backlight unit. The light source of the backlight unit may be implemented as a point light source such as an LED (Light Emitting Diode).

The light source driving unit 210 adjusts the lighting time of the light sources according to the duty ratio of PWM determined according to the dimming value of each block input from the local dimming control unit 120. [ The duty ratios of the light sources are individually controlled for each block according to the dimming value for each block. The local dimming control unit 120 determines the dimming value for each block based on the BOW inputted from the timing controller 110 and controls the light source driving unit 210 as described above.

The data processing apparatus 100 and the local dimming control unit 120 may be embedded in the timing controller 110. [

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 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.

12, 62: frame rate conversion unit 14: BOW generation unit
16: memory control unit 18: memory
20, 64: data modulation unit 22, 68: data transfer unit
66: lookup table 100: data processing device
110: timing controller 120: local dimming control unit
122: Data driver 124: Gate driver
200: backlight unit 210: light source driving unit
300: Display panel

Claims (17)

A display panel having a pixel array including data lines, gate lines crossing the data lines, and liquid crystal cells arranged in a matrix form;
A backlight unit for emitting light to the display panel;
A frame rate converter for multiplying a frame frequency of an input image to divide one frame period into a first sub frame period and a second sub frame period;
Each of the data of the input image is compared with a predetermined center transmittance gradation and a logical value of BOW indicating one of a white gradation value and a black gradation value is selected in accordance with the comparison result, The data of the input image is modulated to a gray level higher than the original data and the data of the input image is modulated to a gray level lower than the raw data when the logical value of BOW indicates the white gray level value, A data modulation unit for generating black gradation or white gradation data on the basis of the data; And
The method comprising: writing data of an input image modulated based on the BOW in the first sub frame period into a pixel array of the display panel; and thereafter writing black gradation data or white gradation data generated based on the BOW during the second sub frame period And a display panel drive circuit for writing data into the pixel array of the display panel,
Wherein the center transmittance gradation is set to a data gradation value when the transmittance of the liquid crystal cell is substantially 50%. The method according to claim 1,
Wherein the data modulator comprises:
The logic value of the BOW is selected as "0" when the data of the input image is lower than the center transmittance gradation,
The logic value of the BOW is set to "1" when the data of the input image is equal to or more than the center transmittance gradation,
And the BOW is 1 bit data. 3. The method of claim 2,
Wherein the data modulator comprises:
When the logical value of the BOW is 0, dummy data in which each bit is "0 " is added to the BOW to generate the black gradation data,
And when the logical value of BOW is 1, dummy data having each bit of "1 " is added to the BOW to generate the black gradation data. The method according to claim 1,
The data modulator modulates data of the input image based on the BOW through the following equation,

Here, "# of gray scale" is the number of expressible gray scales, "CTG" is the center transmittance gradation, "gray scale "

Is a gamma characteristic value between 2 and 3, and X is data of an input image modulated based on the BOW. 3. The method of claim 2,
The data modulator
And modulates the data of the input image based on the BOW using a look-up table in which the gray-level values and the transmittances of the data are stored. 6. The method of claim 5,
Wherein the data modulator comprises:
And if the BOW is "0 ", the transmittance of the liquid crystal cell corresponding to the tone value of the data of the input image is multiplied by 2 to calculate a compensated transmittance, and the compensated transmittance is input to the lookup table, Modulates the data of the input image,
If the BOW is "1 ", a result obtained by subtracting the transmittance corresponding to the center transmittance gradation from the transmittance of the liquid crystal cell corresponding to the tone value of the data of the input image is multiplied by 2 to calculate a compensated transmittance, Up table, modulates data of the input image with data output from the look-up table,
And a transmittance corresponding to the center transmittance gradation is 50%. 3. The method of claim 2,
Wherein the pixel array of the display panel and the light emitting surface of the backlight unit are divided into a plurality of blocks,
Each of the blocks includes two or more liquid crystal cells
Wherein the backlight emission surface brightness of each of the blocks is determined according to the BOW. 8. The method of claim 7,
And a local dimming control unit for controlling the brightness of the backlight emission surface for each of the blocks based on the BOW. 9. The method of claim 8,
The local dimming control unit,
Determines the dimming value of the block including the liquid crystal cell having the BOW of "1 " as the first dimming value,
Determines a dimming value of a block including the liquid crystal cell having BOW of "0 " as a second dimming value lower than the first dimming value,
Wherein the brightness of the backlight emitting surface of the block controlled by the first dimming value is higher than the brightness of the backlight emitting surface of the block controlled by the second dimming value. A display panel having a pixel array including data lines, gate lines crossing the data lines, and liquid crystal cells arranged in a matrix form, and a backlight unit for emitting light to the display panel, , The method comprising:
Dividing one frame period into a first sub frame period and a second sub frame period by multiplying a frame frequency of an input image;
Comparing each of the data of the input image with a preset center transmittance gradation and selecting a logical value of BOW indicating one of a white gradation value and a black gradation value according to the comparison result;
Modulating the data of the input image based on the BOW, modulating the data of the input image into a gray level value higher than the original data when the logic value of the BOW indicates the black gradation value, Modulating the data of the input image to a gray level value lower than the raw data when the gray level value is indicated;
Generating black gradation or white gradation data based on the BOW; And
The method comprising: writing data of an input image modulated based on the BOW in the first sub frame period into a pixel array of the display panel; and thereafter writing black gradation data or white gradation data generated based on the BOW during the second sub frame period Writing data to the pixel array of the display panel,
Wherein the center transmittance gradation is set to a data gradation value when the transmittance of the liquid crystal cell is substantially 50%. 11. The method of claim 10,
The logic value of the BOW is selected as "0" when the data of the input image is lower than the center transmittance gradation,
The logical value of the BOW is selected as "1 " when the data of the input image is equal to or more than the center transmittance gradation,
And the BOW is 1 bit data. 12. The method of claim 11,
The step of generating black gradation or white gradation data based on the BOW may include:
Generating black gradation data by adding dummy data each bit of which is "0 " to the BOW when the logical value of BOW is 0; And
And adding the dummy data each bit of which is "1 " to the BOW when the logic value of the BOW is 1, to generate the black gradation data. 11. The method of claim 10,
Wherein modulating the data of the input image based on the BOW comprises:
The data of the input image is modulated based on the BOW through the following equation,

Here, "# of gray scale" is the number of expressible gray scales, "CTG" is the center transmittance gradation, "gray scale "

Is a gamma characteristic value between 2 and 3, and X is data of an input image modulated based on the BOW. 12. The method of claim 11,
Wherein modulating the data of the input image based on the BOW comprises:
And the data of the input image is modulated based on the BOW using a look-up table in which a gray level value and a transmittance of the data are stored. 15. The method of claim 14,
Wherein modulating the data of the input image based on the BOW comprises:
And if the BOW is "0 ", the transmittance of the liquid crystal cell corresponding to the tone value of the data of the input image is multiplied by 2 to calculate a compensated transmittance, and the compensated transmittance is input to the lookup table, Modulating the data of the input image; And
If the BOW is "1 ", a result obtained by subtracting the transmittance corresponding to the center transmittance gradation from the transmittance of the liquid crystal cell corresponding to the tone value of the data of the input image is multiplied by 2 to calculate a compensated transmittance, And modulating data of the input image with data output from the lookup table by inputting into the lookup table,
And the transmittance corresponding to the center transmittance gradation is 50%. 12. The method of claim 11,
Wherein the pixel array of the display panel and the light emitting surface of the backlight unit are divided into a plurality of blocks,
Each of the blocks includes two or more liquid crystal cells
And the backlight emission surface brightness of each of the blocks is determined according to the BOW. 17. The method of claim 16,
And controlling the brightness of the backlight emission surface for each of the blocks based on the BOW,
The step of controlling the brightness of the backlight emission surface for each block based on the BOW may include:
Determining a dimming value of a block including the liquid crystal cell having the BOW of "1 " as a first dimming value; And
And determining a dimming value of a block including the liquid crystal cell having the BOW of "0 " as a second dimming value lower than the first dimming value,
Wherein the brightness of the backlight emitting surface of the block controlled by the first dimming value is higher than the brightness of the backlight emitting surface of the block controlled by the second dimming value.

Images