KR20160083369A - Liquid crystal display and driving method of thereof - Google Patents

Abstract

A liquid crystal display according to the present invention comprises a liquid crystal display panel, a backlight unit which includes light sources of supplying light to at least one side of a light guide plate part and divides a surface light source emitted to the liquid crystal display panel into blocks, a dimming value determining part which analyzes an input image by the sizes of the blocks and determines a dimming value for each block for individually controlling the luminance of the light sources in a first dimming range, and a dimming value controlling part which controls the dimming value of the first blocks corresponding to a black region with a minimum value out of the first dimming range when the input image is identical to a specific image including the block region of a preset size or more. So, contrast range in the black region can be improved.

Description

TECHNICAL FIELD [0001] The present invention relates to a liquid crystal display (LCD)

The present invention relates to a liquid crystal display capable of local dimming 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. This liquid crystal display device is used as a portable computer such as a notebook PC, an office automation device, an audio / video device, and an indoor / outdoor advertisement display device. A transmissive liquid crystal display device that occupies most of the liquid crystal display device controls an electric field applied to the liquid crystal layer to modulate light incident from the backlight unit to display an image. The backlight unit is roughly divided into a direct type and an edge type.

The image quality of the liquid crystal display device depends on the contrast characteristics. The method of modulating the light transmittance of the liquid crystal layer by controlling the data voltage applied to the liquid crystal layer limits the improvement of the contrast characteristic. In order to improve the contrast characteristic, various backlight dimming control methods for adjusting the brightness of the backlight unit according to an image have been attempted. The backlight dimming control method may reduce the power consumption by adaptively adjusting the brightness of the backlight unit according to the input image. The backlight dimming method includes a global dimming method for adjusting the brightness of the entire display surface and a local dimming method for locally adjusting the brightness of the display surface. 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.

A direct-type backlight unit has a structure in which a plurality of optical sheets and a diffusion plate are stacked under a liquid crystal display panel and a plurality of light sources are disposed under a diffusion plate. In the direct type backlight unit, a plurality of light sources are disposed under the diffusion plate, and the light sources are individually controlled to implement the local dimming. However, it is difficult to reduce the thickness of the direct light type backlight unit, thereby making it difficult to design the slim design of the liquid crystal display device. The reason why it is difficult to reduce the thickness of the direct-type backlight unit is because of the gap that must be ensured between the diffusion plate and the light sources. The diffusion plate of the direct-type backlight unit is used for the purpose of diffusing the light incident from the lamp to make the brightness of the display surface uniform. In order for the diffusion plate of the direct-type backlight unit to sufficiently diffuse the light, a sufficient gap must be ensured between the light sources and the diffusion plate. Although the interval between the diffusion plate and the light sources is narrowed due to the trend of thinning of the liquid crystal display device, since the light from the light source is not sufficiently diffused, the luminance uniformity of the display image may be lowered due to a line- have.

The edge type backlight unit has a structure in which a light source is disposed so as to face the side face 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 can be realized to be thinner than the direct type backlight unit due to the structural difference. However, the edge type backlight unit converts light radiated from one light source to one side of the light guide plate through a light guide plate or converts a point light source into a planar light source, making it difficult to implement local dimming. Even if the local dimming method is applied, the edge type backlight unit that uses the property of straightening the light in the light guide plate causes the unintended portions to be shaded to distort the image implemented on the display panel in the actual screen display.

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

In order to omit the image processing, it is possible to increase the dimming value for each block as a whole. However, in this case, the contrast ratio of the area to be displayed in black, such as a letterbox of the image, is greatly reduced.

It is therefore an object of the present invention to provide a liquid crystal display device and a method of driving the same that can increase a 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 .

According to an aspect of the present invention, there is provided a liquid crystal display comprising a liquid crystal display panel, a plurality of light sources for supplying light to at least one side of the light guide plate, A dimming value determining unit for determining a dimming value for each block for individually controlling the brightness of the light sources within a first dimming range by analyzing an input image on a block size basis, And a dimming value adjusting unit adjusting the dimming value of the first blocks corresponding to the black area to a minimum value outside the first dimming range when the input image is the same as a specific image including a black area of a predetermined size or more.

The dimming value adjusting unit adjusts the dimming value of the second blocks adjacent to the first blocks in the first dimming range.

The specific image including the black region of the predetermined size or more is a 21: 9 image including a letter box, or a 4: 3 image including a letter box.

The dimming value adjustment unit compares the input image with the specific image stored in advance in the memory to determine whether the input image is the same or not.

The first dimming range indicates on duty from 50% to on duty 100%, and the minimum value indicates either on duty 0% to 1.5%.

According to an embodiment of the present invention, there is provided a backlight unit including a liquid crystal display panel and a plurality of light sources for supplying light to at least one side of the light guide plate, the backlight unit dividing the surface light source irradiated to the liquid crystal display panel into a plurality of blocks The method comprising the steps of: determining a dimming value for each block for individually controlling the brightness of the light sources in a first dimming range by analyzing an input image on a block size basis; Adjusting the dimming value of the first blocks corresponding to the black region to a minimum value outside the first dimming range if the specific image includes the black region larger than the predetermined size.

The present invention firstly determines a dimming value for each block based on image analysis within a first dimming range in which a data compensation algorithm can be skipped. If the input image is identical to a specific image including a black region of a predetermined size or more, The dimming value of the first blocks corresponding to the first blocks is lowered from the first determined value to the minimum value outside the first dimming range and the dimming value of the second blocks neighboring the first blocks is set to be smaller than the first determined value within the first dimming range Lower.

Accordingly, 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 device according to an embodiment of the present invention;
Fig. 2 is a circuit diagram showing equivalently a part of a pixel array of the liquid crystal display panel shown in Fig. 1. Fig.
FIGS. 3A and 3B illustrate examples in which the brightness of the surface light source is divided into blocks. FIG.
4 is a block diagram showing a detailed configuration of a dimming control unit according to the present invention;
5 is a flow chart showing a dimming value adjustment operation in the dimming control section;
6 is a diagram showing an example of block division and its driving;

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

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

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

In the liquid crystal display panel 10, a liquid crystal layer is formed between two glass substrates. As shown in FIG. 2, a plurality of data lines 14a to 14d and a plurality of gate lines 15a to 15d are crossed on the lower glass substrate of the liquid crystal display panel 10. The liquid crystal cells Clc are arranged in a matrix form in the liquid crystal display panel 10 by the intersection structure of the data lines 14a to 14d and the gate lines 15a to 15d. A thin film transistor (TFT), a pixel electrode 1 of a liquid crystal cell Clc connected to a thin film transistor (TFT), a storage capacitor Cst, and the like 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. The common electrode 2 is formed on an upper glass substrate in a vertical electric field driving mode such as a TN (Twisted Nematic) mode and a VA (Vertical Alignment) mode. The common electrode 2 is formed of an IPS (In Plane Switching) mode, an FFS (Fringe Field Switching) Is formed on the lower glass substrate together with the pixel electrode 1 in the same horizontal electric field driving system. On the upper glass substrate and the lower glass substrate of the liquid crystal display panel 10, a polarizing plate is attached and an alignment film for forming a pre-tilt angle of the liquid crystal is formed on the inner surface in contact with the liquid crystal.

The data driver 12 includes a shift register for sampling a clock signal, a register for temporarily storing digital video data (RGB), a data register for storing data for one line in response to a clock signal from a shift register, A digital / analog converter for selecting the positive / negative gamma voltage under reference to the gamma reference voltage corresponding to the digital data value from the latch, the positive / negative gamma voltage converted by the positive / negative gamma voltage 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, and the like. The data driver 12 latches the digital video data RGB under the control of the timing controller 11 and outputs the latched digital video data RGB to the positive polarity / Polarity analog data voltages and supplies them to the data lines 14. [

The gate driver 13 is composed of a plurality of gate driver ICs each including a shift register, a level shifter for converting an output signal of the shift register into a swing width appropriate for TFT driving 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 the digital video data RGB input from the system board on which the external video source is mounted according to the resolution of the liquid crystal display panel 10 and supplies the digital video data RGB to the data driver 12. The timing control unit 11 receives 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, DCLK from the system board , GDC). The timing controller 11 inserts an interpolation frame between the frames of the input video signal input at a frame frequency of 60 Hz and multiplies the data timing control signal DDC and the gate timing control signal GDC to 60 x N It is possible to control the operations of the data driver 12 and the gate driver 13 at a frame frequency of Hz.

The backlight unit includes a light guide plate portion 20 and a plurality of light sources 24 for irradiating light to the side surfaces of the light guide plate portion 20. In addition, the backlight unit includes a plurality of optical sheets stacked between the light guide plate portion 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 the 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 divided driving can be implemented in various forms. 3A, when the light sources 24 are disposed on the right and left sides of the light guide plate portion 20, the light guide plate portion 20 may be divided vertically. 3B, when the light sources 24 are disposed on the upper and lower sides of the light guide plate unit 20, the light guide plate unit 20 can be divided in the right and left direction.

Such an edge type backlight unit capable of local dimming is disclosed in Korean Patent Application No. 10-2009-0028154 (2009.04.01), Korean Patent Application No. 10-2009-0028162 (2009.04.01 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), Korea Patent Application No. 10-2009-0073372 (2009.08.10), and Korean Patent Application No. 10-2009-0082899 (2009.09.03).

The dimming control unit 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 block size units by using various image analysis techniques. The dimming control unit 16 determines the dimming value of the light sources 24 for local dimming according to the image analysis result. The dimming control unit 16 partially down-adjusts the predetermined dimming value for each block and outputs the dimming value as a local dimming signal LDIM when the input image is the same as a predetermined image including a predetermined area, do.

The light source driving unit 22 adjusts the current intensity separately supplied to the light sources 24 under the control of the dimming control unit 16. The light source driver 22 supplies the light sources 24 of the 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, While adjusting the supply current of the light sources 24 responsible for the blocks corresponding to the dark portion of the display image displayed on the liquid crystal display panel 10 to a relatively low level.

4 is a block diagram showing a detailed configuration of the dimming control unit 16 according to the present invention. 5 is a flow chart showing a dimming value adjustment operation in the dimming control section 16. 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 determination unit 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, The input image RGB is analyzed on the basis of the sizes of the light source blocks LBL1 to LBL8 and RBL1 to RBL8 and a representative value of each block including at least one of the mode, (D1 to D16) for individually controlling the brightness of the light sources 24 are determined within the first dimming range (S10). If the representative value for each block is high, the dimming value determining unit 161 increases the on-duty of the dimming value of the corresponding light source block within the first dimming range. On the contrary, if the representative value for each block is low, And 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 the data compensation algorithm can be omitted, that is, on duty 50% to on duty 100%. 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 a brightness that is insufficient as in the prior art. The present invention determines the dimming values (D1 to D16) for each block within the first dimming range as described above. Therefore, it is possible to prevent a conventional problem, that is, a halo effect or flickering, The compensation logic of the second embodiment is unnecessary, which is effective to reduce the manufacturing cost.

The dimming value adjuster 162 compares the input image RGB with a specific image stored in the memory 163 in advance to determine whether the input image RGB is the same or not. The specific image includes a black area of a predetermined size or larger like a letter box (S20). Therefore, a specific image may be a 21: 9 image including a letter box, or a 4: 3 image including a letter box.

The dimming value adjusting unit 162 adjusts the dimming values D1, D8, and R8 of the first blocks LBL1, LBL8, RBL1, and RBL8 corresponding to the black region (letter box) D9, and D16 to a minimum value outside the first dimming range (S30). Here, the minimum value indicates either on duty 0% to 1.5%. The dimming value adjuster 162 of the present invention adjusts the dimming values D1, D8, D9 and D16 of the first blocks LBL1, LBL8, RBL1 and RBL8 corresponding to the black area (letterbox) Adjusting to the minimum value solves the problem that the contrast ratio of the black area such as letterbox is lowered when the dimming value per block is increased as a whole in order to omit the image processing process.

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, And is adjusted downward within the dimming range (S40). In the case of an edge type backlight unit that utilizes the property that the light advances straight in the light guide plate even when the local dimming method is applied, there is an undesirable influence between neighboring blocks due to light interference or the like. Therefore, if the dimming values D2, D7, D10, D15 of the second blocks LBL2, LBL7, RBL2, RBL7 adjacent to the black region are adjusted downward within the first dimming range, Much easier.

When the input image RGB is the same as the previously stored specific image, the dimming value adjusting unit 162 adjusts the dimming value of the first and second blocks to be lower than a value determined within the first dimming range, And supplies the dimming value for each block to the dimming value output unit 164. If the input image RGB is different from the previously 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 inputted from the dimming value adjusting unit 162 to the light source driving unit 22 as the local dimming signal LDIM (S50).

As described above, according to the present invention, a dimming value for each block is first determined within a first dimming range in which a data compensation algorithm can be skipped based on image analysis, and then a specific image including a black region of a predetermined size or larger The dimming value of the first blocks corresponding to the black region is lowered from the first determined value to the minimum value outside the first dimming range and the dimming value of the second blocks neighboring the first blocks is set to be within the first dimming range Lower than the first determined value.

Accordingly, 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.

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.

10: liquid crystal display panel 11: timing controller
12: Data driver 13: Gate driver
16: dimming control unit 22: light source driving unit
24: light sources 161: dimming value determination unit
162: a dimming value adjustment unit 164: a dimming value output unit

Claims (10)

A liquid crystal display panel;
A backlight unit that includes a plurality of light sources for supplying light to at least one side of the light guide plate and divides the surface light source irradiated to the liquid crystal display panel into a plurality of blocks;
A dimming value determining unit for determining a dimming value for each block for individually controlling the brightness of the light sources within a first dimming range by analyzing an input image in units of blocks; And
And a dimming value adjusting unit adjusting the dimming value of the first blocks corresponding to the black area to a minimum value outside the first dimming range when the input image is the same as a specific image including a black area of a predetermined size or more. Display device. The method according to claim 1,
Wherein the dimming value adjusting unit comprises:
And adjusts the dimming value of the second blocks adjacent to the first blocks in the first dimming range. The method according to claim 1,
Wherein the specific image including the black region of the predetermined size or larger is a 21: 9 image including a letter box, or a 4: 3 image including a letter box. The method according to claim 1,
Wherein the dimming value adjusting unit comprises:
Wherein the input image is compared with the specific image stored in advance in the memory to determine whether the input image is the same or not. 3. The method of claim 2,
The first dimming range indicates an on duty of 50% to an on duty of 100%
Wherein the minimum value indicates any one of on duty 0% to 1.5%. A method of driving a liquid crystal display device having a liquid crystal display panel and a backlight unit dividing a surface light source irradiated on 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, ,
Determining a dimming value for each block for controlling the luminance of the light sources within a first dimming range by analyzing an input image in units of blocks; And
And adjusting the dimming value of the 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 method according to claim 6,
Further comprising adjusting the dimming value of the second blocks adjacent to the first blocks within the first dimming range. The method according to claim 6,
Wherein the specific image including the black region of the predetermined size or larger is a 21: 9 image including a letter box, or a 4: 3 image including a letter box. The method according to claim 6,
And comparing the input image with the specific image stored in advance in the memory to determine whether the two images are the same or not. 8. The method of claim 7,
The first dimming range indicates an on duty of 50% to an on duty of 100%
Wherein the minimum value indicates any one of on duty 0% to 1.5%.

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