KR102279279B1 - Liquid crystal display and driving method of thereof - Google Patents

Abstract

A liquid crystal display device according to the present invention includes a liquid crystal display panel, a backlight unit including a plurality of light sources for supplying light to at least one side of a light guide plate unit, and dividing a surface light source irradiated to the liquid crystal display panel into a plurality of blocks; a dimming value determiner that analyzes an image in units of the size of the blocks and determines a dimming value for each block for individually controlling the luminance of the light sources within a first dimming range; and a dimming value adjusting unit for adjusting the dimming values of the first blocks corresponding to the black region to a minimum value outside the first dimming range when the same as the image.

Description

Liquid crystal display device and its driving method {LIQUID CRYSTAL DISPLAY AND DRIVING METHOD OF THEREOF}

The present invention relates to a liquid crystal display capable of local dimming and a driving method thereof.

The liquid crystal display device has a tendency to gradually expand its application range due to the characteristics of light weight, thin shape, and low power consumption driving. This liquid crystal display device is used in portable computers such as notebook PCs, office automation devices, audio/video devices, indoor and outdoor advertisement display devices, and the like. The transmissive liquid crystal display, which occupies most of the liquid crystal display, displays an image by controlling the electric field applied to the liquid crystal layer and modulating the light incident from the backlight unit. The backlight unit is roughly divided into a direct type and an edge type.

The image quality of the liquid crystal display is influenced by the contrast characteristic. There is a limit to improving this contrast characteristic only by modulating the light transmittance of the liquid crystal layer by controlling the data voltage applied to the liquid crystal layer. In order to improve contrast characteristics, various methods for controlling backlight dimming of adjusting the brightness of a backlight unit according to an image have been tried. The backlight dimming control method may reduce power consumption by adaptively adjusting the brightness of the backlight unit according to an input image. The backlight dimming method includes a global dimming method for adjusting the luminance of the entire display surface and a local dimming method for locally adjusting the luminance of the display surface. The global dimming method may improve the dynamic contrast measured between the previous frame and the next frame. The local dimming method can improve static contrast, which is difficult to improve with the global dimming method, by locally controlling the luminance of the display surface within one frame period.

The direct backlight unit has a structure in which a plurality of optical sheets and a diffusion plate are stacked under the liquid crystal display panel, and a plurality of light sources are disposed under the diffusion plate. In the direct backlight unit, a plurality of light sources are disposed under the diffusion plate and local dimming can be implemented by individually controlling the light sources, but it is difficult to reduce the thickness, which makes it difficult to design a slimming liquid crystal display device. The reason why it is difficult to reduce the thickness of the direct type backlight unit is because of a gap that must be secured between the diffusion plate and the light sources. The diffuser plate of the direct backlight unit is used for the purpose of uniformizing the luminance of the display surface by diffusing the light incident from the lamp. In order for the diffuser plate of the direct backlight unit to sufficiently diffuse light, a sufficient distance between the light sources and the diffuser plate must be secured. Due to the thinning trend of liquid crystal display devices, the distance between the diffusion plate and the light sources is narrowing, but the light from the light source is not sufficiently diffused, so the brightness uniformity of the display image may be reduced due to the bright line phenomenon of the light source in the display image. there is.

The edge type backlight unit has a structure in which a light source is disposed to face a side surface of the light guide plate, and a plurality of optical sheets are disposed between the liquid crystal display panel and the light guide plate. The edge-type backlight unit may be implemented to have a thinner thickness than the direct-type backlight unit due to a structural difference. However, the edge type backlight unit converts the light irradiated from the light source to one side of the light guide plate to a linear light source or a point light source through the light guide plate, and thus local dimming is difficult to implement. Even if the local dimming method is applied, in an edge-type backlight unit that uses the property of light traveling in a straight line within the light guide plate, contrast occurs to other unwanted portions, thereby distorting the image implemented on the display panel during actual screen display.

In a liquid crystal display having an edge-type backlight unit, in order to prevent image distortion as described above, a separate image processing process using a data compensation algorithm is generally further performed. However, since the data compensation algorithm involves a temporal delay, it may cause a halo effect or flickering due to light spreading. In order to apply the data compensation algorithm, a separate logic must be additionally designed, which increases the manufacturing cost.

In order to omit the image processing process, a method of increasing the dimming value for each block as a whole may be considered, but in this case, there is a problem in that the contrast ratio of a region to be displayed in black, such as a letterbox of an image, is greatly reduced.

Accordingly, it is an object of the present invention to provide a liquid crystal display device capable of increasing the contrast ratio in a black region without applying a data compensation algorithm when a specific image including a black region of a predetermined size or more is input, and a driving method thereof. .

In order to achieve the above object, a liquid crystal display device according to an embodiment of the present invention includes a plurality of surface light sources irradiated to the liquid crystal display panel, including a liquid crystal display panel and a plurality of light sources supplying light to at least one side of the light guide plate part. a backlight unit dividing the block into blocks; a dimming value determiner configured to analyze an input image in units of the block size to determine a dimming value for each block for individually controlling the luminance of the light sources within a first dimming range; and a dimming value adjusting unit that adjusts dimming values of first blocks corresponding to the black region to a minimum value outside the first dimming range when the input image is the same as a specific image including a black region of a predetermined size or more.

The dimming value adjusting unit may downwardly adjust dimming values of second blocks adjacent to the first blocks within the first dimming range.

The specific image including the black area having a predetermined size or larger is a 21:9 image including a letter box or a 4:3 image including a letter box.

The dimming value adjusting unit compares the input image with the specific image stored in advance in a memory and determines whether the two are the same.

The first dimming range indicates 50% on-duty to 100% on-duty, and the minimum value indicates any one of 0% to 1.5% on-duty.

In addition, according to an embodiment of the present invention, there is provided a backlight unit comprising a liquid crystal display panel and a plurality of light sources for supplying light to at least one side of the light guide plate part and dividing the surface light source irradiated to the liquid crystal display panel into a plurality of blocks. The method of driving a liquid crystal display having a method comprising: analyzing an input image in units of the size of the blocks to determine a dimming value for each block for individually controlling the luminance of the light sources within a first dimming range; and adjusting dimming values of first blocks corresponding to the black region to a minimum value outside the first dimming range when the same as a specific image including a black region larger than the size.

According to the present invention, after determining a dimming value for each block within a first dimming range capable of skipping a data compensation algorithm based on image analysis, when the input image is the same as a specific image including a black region of a predetermined size or larger, the black region lowering the dimming values of the first blocks corresponding to , from the first determined value to the minimum value outside the first dimming range, and lowering the dimming values of the second blocks adjacent to the first blocks than the first determined value within the first dimming range lower it further

Through this, according to the present invention, when a special image such as a cinema image including a letter box is input, the contrast ratio in the letter box portion can be effectively increased without applying a data compensation algorithm.

1 is a block diagram showing a liquid crystal display according to an embodiment of the present invention.
FIG. 2 is a circuit diagram equivalently showing a part of a pixel array of the liquid crystal display panel shown in FIG. 1;
3A and 3B are exemplary views showing that the luminance of a surface light source is divided into blocks.
4 is a block diagram showing a detailed configuration of a dimming control unit according to the present invention.
5 is a flowchart illustrating an operation of adjusting a dimming value in a dimming controller;
6 is a diagram showing an example of block division and driving thereof;

Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to FIGS. 1 to 6 .

1 is a block diagram showing a liquid crystal display according to an embodiment of the present invention. FIG. 2 is a circuit diagram equivalently showing a part of a pixel array of the liquid crystal display panel shown in FIG. 1 . 3A and 3B are exemplary views showing that the luminance of the surface light source is divided into blocks.

1 to 3B, the liquid crystal display according to an embodiment of the present invention includes a liquid crystal display panel 10, a data driver 12 for driving data lines 14 of the liquid crystal display panel 10, The gate driver 13 for driving the gate lines 15 of the liquid crystal display panel 10, the timing controller 11 for controlling the data driver 12 and the gate driver 13, and the liquid crystal display panel 10 A backlight unit irradiating light, a light source driver 22 for driving the light sources 24 of the backlight unit, and a dimming controller 16 that analyzes an input image and controls the light source driver 22 according to the analysis result. be prepared

In the liquid crystal display panel 10, a liquid crystal layer is formed between two glass substrates. A plurality of data lines 14a to 14d and a plurality of gate lines 15a to 15d cross each other on the lower glass substrate of the liquid crystal display panel 10 as shown in FIG. 2 . The liquid crystal cells Clc are arranged in a matrix in the liquid crystal display panel 10 by the intersecting structure of the data lines 14a to 14d and the gate lines 15a to 15d. In addition, a thin film transistor TFT, a pixel electrode 1 of a liquid crystal cell Clc connected to the TFT, and a storage capacitor Cst are formed on the lower glass substrate of the liquid crystal display panel 10 .

A black matrix, a color filter, and a common electrode 2 are formed on the upper glass substrate of the liquid crystal display panel 10 as shown in FIG. 2 . The common electrode 2 is formed on the upper glass substrate in a vertical electric field driving method such as TN (Twisted Nematic) mode and VA (Vertical Alignment) mode, IPS (In Plane Switching) mode and FFS (Fringe Field Switching) mode and It is formed on the lower glass substrate together with the pixel electrode 1 in the same horizontal electric field driving method. 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 the inner surface in contact with the liquid crystal.

The data driver 12 stores data line by line in response to a clock signal from a shift register for sampling a clock signal, a register for temporarily storing digital video data (RGB), and the stored data for one line. a latch for simultaneously outputting , a digital/analog converter for selecting positive/negative gamma voltages under reference to a gamma reference voltage corresponding to the digital data values from the latches, converted by positive/negative gamma voltages It is composed of a plurality of data drive integrated circuits each including a multiplexer for selecting the data line 14 to which analog data is supplied, and an output buffer connected between the multiplexer and the data line 14 . The data driver 12 latches digital video data RGB under the control of the timing controller 11, and converts the latched digital video data RGB into positive/negative gamma compensation voltages using positive/negative gamma compensation voltages. The polarity analog data voltage is converted and then supplied to the data lines 14 .

The gate driver 13 is composed of a plurality of gate drive integrated circuits each including a shift register, a level shifter for converting an output signal of the shift register to a swing width suitable for driving the TFT of the liquid crystal cell, and an output buffer. The gate driver 13 sequentially outputs gate pulses (or scan pulses) having a pulse width of approximately one horizontal period under the control of the timing controller 11 and supplies them to the gate lines 15 .

The timing controller 11 rearranges digital video data RGB input from a system board on which an external video source is mounted to the resolution of the liquid crystal display panel 10 and supplies it to the data driver 12 . In addition, the timing controller 11 includes timing control signals DDC for controlling the operation timings of the data driver 12 and the gate driver 13 based on the timing signals Vsync, Hsync, DE, and DCLK from the system board. , GDC) occurs. The timing controller 11 inserts an interpolation frame between the frames of the input image signal input with a frame frequency of 60 Hz and multiplies the data timing control signal DDC and the gate timing control signal GDC to 60×N (N is The operation of the data driver 12 and the gate driver 13 may be controlled with a frame frequency of Hz (a positive integer of 2 or more).

The backlight unit includes a light guide plate 20 and a plurality of light sources 24 irradiating light to the side surfaces of the light guide plate 20 . In addition, the backlight unit includes a plurality of optical sheets stacked between the light guide plate unit 20 and the liquid crystal display panel 10 . In order to implement local dimming, the luminance of the surface light source incident on the liquid crystal display panel 10 may be divided into sizes of the light source blocks BL1 to BLk as shown in FIGS. 3A and 3B . The structure of the light guide plate 20 and the arrangement of the light sources 24 for the block-by-block division driving may be implemented in various forms. For example, when the light sources 24 are disposed on left and right sides of the light guide plate 20 as shown in FIG. 3A , the light guide 20 may be divided in the vertical direction. As shown in FIG. 3B , when the light sources 24 are disposed on upper and lower sides of the light guide plate 20 , the light guide plate 20 may be divided in left and right directions.

The edge type backlight unit capable of local dimming is described in Korean Patent Application No. 10-2009-0028154 (2009.04.01) and Korean Patent Application No. 10-2009-0028162 (2009.04.01) previously filed by the present application, which is capable of local dimming. ), Korean Patent Application No. 10-2009-0028160 (2009.04.01), Korean Patent Application No. 10-2009-0028156 (2009.04.01), Korean Patent Application No. 10-2009-0028158 (2009.04.01), Republic of Korea It has been disclosed in Patent Application No. 10-2009-0073372 (2009.08.10) and Korean Patent Application No. 10-2009-0082899 (2009.09.03).

The dimming controller 16 maps the input image to the virtual blocks BL1 to BLk shown in FIGS. 3A and 3B and analyzes the luminance of the input image in units of block sizes using various image analysis techniques. The dimming controller 16 pre-determines the dimming values of the light sources 24 for local dimming according to the image analysis result. Then, when the input image is the same as a predetermined special pattern, that is, a specific image including a black region of a predetermined size or more, the dimming controller 16 partially lowers the predetermined dimming value for each block and outputs it as a local dimming signal LDIM. do.

The light source driver 22 differently adjusts the intensity of the current individually supplied to the light sources 24 under the control of the dimming controller 16 . The light source driving unit 22 supplies current of the light sources 24 that are in charge of blocks corresponding to the bright portions of the display image displayed on the liquid crystal display panel 10 according to the local dimming signal LDIM from the dimming control unit 16 . On the other hand, the supply current of the light sources 24 responsible for blocks corresponding to the dark part of the display image displayed on the liquid crystal display panel 10 is adjusted to be relatively low.

4 is a block diagram showing a detailed configuration of the dimming control unit 16 according to the present invention. 5 is a flowchart illustrating an operation of adjusting a dimming value in the dimming control unit 16 . And, FIG. 6 shows an example of block division and its driving.

4 to 6 , the dimming control unit 16 includes a dimming value determining unit 161 , a dimming value adjusting unit 162 , a memory 163 , and a dimming value output unit 164 .

The dimming value determiner 161 maps the input image RGB to the light source blocks LBL1 to LBL8 and RBL1 to RBL8 with reference to the timing signals SYNC input from the system, and uses various known imaging techniques. to analyze the input image (RGB) in units of the size of the light source blocks (LBL1 to LBL8, RBL1 to RBL8), and to the representative value for each block including at least one of the mode, maximum, and average values for each block of the input image (RGB). Based on the dimming values D1 to D16 for each block for individually controlling the luminance of the light sources 24, within the first dimming range (S10). If the representative value for each block is high, the dimming value determiner 161 increases the on-duty of the dimming value of the corresponding light source block within the first dimming range, and if the representative value for each block is low, the on-duty of the dimming value of the corresponding light source block is increased. It can be lowered within the first dimming range.

Here, the first dimming range is set to an appropriate range in which a separate image processing process using a data compensation algorithm can be omitted, that is, 50% on-duty to 100% on-duty. If the first dimming range is set to be lower than the on-duty of 50%, a separate image processing process using a data compensation algorithm is required to compensate for insufficient luminance as in the prior art. Since the present invention determines the dimming values D1 to D16 for each block within the first dimming range as described above, it is possible to prevent the same problems as in the prior art, that is, the Halo effect or flickering, and separate It is effective to reduce the manufacturing cost because the compensation logic of

The dimming value adjusting unit 162 compares the input image RGB with a specific image previously stored in the memory 163 and determines whether the two are the same. A specific image includes a black area of a predetermined size or more, such as a letter box (S20). Accordingly, the specific image may be a 21:9 image including a letter box or a 4:3 image including a letter box.

When the input image RGB is the same as the pre-stored specific image, the dimming value adjusting unit 162 may adjust the dimming values D1, D8, and D8 of the first blocks LBL1, LBL8, RBL1, and RBL8 corresponding to the black region (letter box). D9 and D16) are adjusted to the minimum value outside the first dimming range (S30). Here, the minimum value indicates any one of on-duty 0% to 1.5%. The dimming value adjusting unit 162 of the present invention sets the dimming values D1, D8, D9, and D16 of the first blocks LBL1, LBL8, RBL1, and RBL8 corresponding to the black region (letter box) outside the first dimming range. By adjusting to the minimum value, when the dimming value for each block is increased as a whole in order to omit the image processing process, a problem in which the contrast ratio of a black region such as a letterbox is lowered is solved.

The dimming value adjusting unit 162 adjusts the dimming values D2, D7, D10, and D15 of the second blocks LBL2, LBL7, RBL2, and RBL7 adjacent to the first blocks LBL1, LBL8, RBL1, and RBL8 to the first Adjust downward within the dimming range (S40). Even if the local dimming method is applied, in an edge-type backlight unit using a property of light traveling in a straight line within the light guide plate, interference of light or the like has an undesirable effect between neighboring blocks. Accordingly, if the dimming values D2, D7, D10, and D15 of the second blocks LBL2, LBL7, RBL2, and RBL7 adjacent to the black area are adjusted downward within the first dimming range, it is difficult to increase the contrast ratio of the black area. much easier

In this way, when the input image RGB is the same as the pre-stored specific image, the dimming value adjusting unit 162 lowers the dimming values of the first and second blocks to a value determined within the first dimming range and includes the adjusted dimming value. A dimming value for each block is supplied to the dimming value output unit 164 . In addition, when the input image RGB is different from the pre-stored specific image, the dimming value adjusting unit 162 supplies the dimming value for each block determined within the first dimming range to the dimming value output unit 164 .

The dimming value output unit 164 outputs the dimming value for each block input from the dimming value adjusting unit 162 as a local dimming signal LDIM to the light source driver 22 ( S50 ).

As described above, according to the present invention, the dimming value for each block is first determined within the first dimming range in which the data compensation algorithm can be skipped based on image analysis, and then the input image is compared with a specific image including a black region of a predetermined size or larger. In the same case, the dimming values of the first blocks corresponding to the black region are lowered from the firstly determined values to the minimum values outside the first dimming range, and the dimming values of the second blocks adjacent to the first blocks are reduced within the first dimming range. lower than the first determined value.

Through this, according to the present invention, when a special image such as a cinema image including a letter box is input, the contrast ratio in the letter box portion can be effectively increased without applying a data compensation algorithm.

Those skilled in the art from the above description will be able to see that various changes and modifications can be made without departing from the technical spirit of the present invention. Accordingly, 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.

10: liquid crystal display panel 11: timing control unit
12: data driver 13: gate driver
16: dimming control unit 22: light source driving unit
24: light sources 161: dimming value determining unit
162: dimming value adjustment unit 164: dimming value output unit

Claims (10)

liquid crystal display panel;
a backlight unit including a plurality of light sources for supplying light to at least one side of the light guide plate and dividing the surface light source irradiated to the liquid crystal display panel into a plurality of blocks;
a dimming value determiner configured to analyze an input image in units of the block sizes to determine a dimming value for each block for individually controlling the luminance of the light sources within a first dimming range; and
a dimming value adjusting unit that adjusts dimming values of first blocks corresponding to the black region to a minimum value outside the first dimming range when the input image is the same as a specific image including a black region of a predetermined size or more;
The first dimming range indicates on-duty 50% ~ on-duty 100%,
The minimum value indicates any one of on-duty 0% to 1.5%,
An image processing process for image data to be written on the liquid crystal display panel is omitted. The method of claim 1,
The dimming value adjustment unit,
and lowering dimming values of second blocks adjacent to the first blocks within the first dimming range. The method of claim 1,
The specific image including the black area of a predetermined size or larger is a 21:9 image including a letter box or a 4:3 image including a letter box. The method of claim 1,
The dimming value adjustment unit,
and comparing the input image with the specific image stored in advance in a memory to determine whether they are the same. delete A method of driving a liquid crystal display device having a liquid crystal display panel and a backlight unit for dividing a surface light source irradiated to the liquid crystal display panel into a plurality of blocks, including a plurality of light sources for supplying light to at least one side of the light guide plate part ,
determining, within a first dimming range, a dimming value for each block for individually controlling the luminance of the light sources by analyzing the input image in units of the size of the blocks; and
adjusting dimming values of first blocks corresponding to the black region to a minimum value outside the first dimming range when the input image is the same as a specific image including a black region of a predetermined size or more;
The first dimming range indicates on-duty 50% ~ on-duty 100%,
The minimum value indicates any one of on-duty 0% to 1.5%,
The method of driving a liquid crystal display device, characterized in that the image processing process for the image data to be written on the liquid crystal display panel is omitted. 7. The method of claim 6,
The method of claim 1, further comprising: downwardly adjusting dimming values of second blocks adjacent to the first blocks within the first dimming range. 7. The method of claim 6,
The method of driving a liquid crystal display, characterized in that the specific image including a black area of a predetermined size or larger is a 21:9 image including a letter box or a 4:3 image including a letter box. 7. The method of claim 6,
and comparing the input image with the specific image stored in advance in a memory to determine whether both are the same. delete

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