KR20110070233A - Backlight unit, method for driving local dimming of liquid crystal display device using the same and apparatus thereof - Google Patents

Abstract

PURPOSE: A backlight unit, a method for driving local dimming of a liquid crystal display device using the same and apparatus thereof are provided to improve dimming effect by optimizing the size and shape of a block. CONSTITUTION: In a backlight unit, a method for driving local dimming of a liquid crystal display device using the same and apparatus thereof, The backlight unit comprises a plurality of point light sources, a plurality of local dimming blocks(B1~Bn), and a plurality of regions. A plurality of local dimming blocks divides the point light sources and driving them. A plurality of local dimming blocks has a different size. A plurality of regions divides a plurality of local dimming block by sizes thereof. The regions are arranged in progressing direction from the center of the backlight unit to the outer edge thereof.

Description

BACKLIGHT UNIT, METHOD FOR DRIVING LOCAL DIMMING OF LIQUID CRYSTAL DISPLAY DEVICE USING THE SAME AND APPARATUS THEREOF}

The present invention relates to a liquid crystal display, and more particularly, to a backlight unit capable of optimizing the size and shape of a block to improve a dimming effect, and a method and apparatus for driving a local dimming of a liquid crystal display using the same.

Recently, a flat panel display such as a liquid crystal display (LCD), a plasma display panel (PDP), an organic light emitting diode (OLED) display, or the like is mainly used as an image display device. .

The liquid crystal display device includes a liquid crystal panel for displaying an image through a pixel matrix using electrical and optical characteristics of liquid crystals having anisotropy such as refractive index and dielectric constant, a driving circuit for driving the liquid crystal panel, and a backlight unit for irradiating light to the liquid crystal panel. It is provided. Each pixel of the liquid crystal display implements grayscale by controlling the light transmittance transmitted from the backlight unit through the liquid crystal panel and the polarizer to vary the direction of the liquid crystal array according to the data signal.

In the liquid crystal display, the luminance of each pixel is determined by the product of the luminance of the backlight unit and the light transmittance of the liquid crystal according to data. In order to improve contrast ratio and reduce power consumption, the liquid crystal display uses backlight dimming that analyzes an input image, controls backlight brightness by adjusting dimming values, and compensates data. For example, the backlight dimming method for reducing power consumption reduces power consumption of the backlight unit by decreasing backlight brightness with dimming value and increasing brightness with data compensation.

Recently, the backlight unit uses an LED backlight using a light emitting diode (LED) as a light source, which has advantages of high brightness and low power consumption as compared to a conventional lamp. Since the LED backlight can be controlled by location, the LED backlight may be driven by a local dimming method that divides into a plurality of blocks and controls luminance by blocks. The local dimming method divides the backlight and the liquid crystal panel into a plurality of blocks and analyzes data on a block-by-block basis to determine local dimming values and compensate data, thereby further improving contrast ratio and further reducing power consumption.

In general, in the conventional local dimming method, the LED backlight unit is equally divided into m × n, for example, 7 × 5 local dimming blocks as shown in FIG. 1 to block according to an average pixel level (APL). Very low brightness is controlled. However, in the conventional local dimming method, even though the image has the same average pixel level as shown in FIG. 1, the bright image as shown in FIG. In addition to the increase in power consumption, there is a problem in that the image quality is deteriorated due to the reduction in the contrast ratio. This is because the conventional local dimming block is designed around an image in which a bright image extends from the center to the outside. In fact, as shown in FIG. 1B, when a bright image is located at the outer side of the screen, that is, at the center of the screen of the dark image, outer blocks having a uniform size in the backlight are driven by unnecessary red lines. In addition to increasing power consumption, there is a problem in that the image quality is deteriorated due to a decrease in the contrast ratio.

SUMMARY OF THE INVENTION An object of the present invention is to provide a backlight unit capable of improving the dimming effect by optimizing the size and shape of a block and a method and apparatus for driving a local dimming of a liquid crystal display using the same.

In order to solve the above problems, the backlight unit according to the present invention comprises a plurality of point light source; A plurality of local dimming blocks which drive the plurality of point light sources and have different sizes; And a plurality of areas obtained by dividing the plurality of local dimming blocks by the size, wherein the plurality of areas are arranged along a direction from the center of the backlight unit toward the outside.

The size of the local dimming block gradually decreases from the center of the backlight unit toward the outer side. The areas of each of the plurality of areas are the same, the area of the local dimming block is different for each of the areas, and the area of the local dimming block is the same in each area.

When the backlight unit is divided into n (where n is a natural number) areas, and the size ratio of the local dimming block included in each of the n areas is defined as B1, B2, ..., Bn, The ratio of the local dimming block size between the regions is as follows.

In accordance with another aspect of the present invention, there is provided a method of driving a local dimming device, the method comprising: detecting a representative gray value of each block by analyzing an image in units of blocks corresponding to the local dimming block of the backlight unit; Determining a dimming value for each block according to the representative gray level value for each block; And controlling the luminance of the unit of the backlight for each local dimming block by using the dimming value for each block.

In addition, the local dimming driving method of the present invention comprises the steps of: calculating a gain value by light quantity analysis using the pre-stored light profile data of the backlight unit and the dimming value for each block; Compensating the input data with the calculated gain value; Displaying the compensated data on the liquid crystal panel.

The local dimming driving device of the liquid crystal display according to the present invention comprises: the backlight unit; The liquid crystal panel which displays an image using light from the backlight unit; A local dimming driver for analyzing input image data in units of blocks corresponding to the local dimming block of the backlight unit to determine and output a dimming value for each local dimming block; And a backlight driver configured to drive the backlight unit in units of the local dimming block by using a block-specific dimming value from the local dimming driver.

The local dimming driver may be further configured to calculate a gain value by light quantity analysis using the pre-stored light profile data of the backlight unit and the dimming value for each block, and further correct the input image data with the calculated gain value; The liquid crystal display according to the present invention further includes a panel driver which displays the corrected data on the liquid crystal panel.

The method and apparatus for driving a local dimming of a backlight unit and a liquid crystal display using the same according to the present invention divide a backlight unit into a plurality of areas in which the size of the local dimming block is gradually reduced from the center toward the outer side, thereby brightening the image on the outside of the screen. Even if it is located, it can minimize the unnecessary driving of the backlight. Therefore, the present invention can optimize the effect of reducing power consumption by local dimming driving and can improve image quality by improving the contrast ratio.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

In the backlight unit according to the present invention, the size of the local dimming block is designed differently according to the position. As shown in FIG. 1, when the backlight unit is divided and driven into a plurality of local dimming blocks having the same size, a bright image as shown in (B) is located outside the screen. This is because driving consumes more power. Therefore, in the backlight unit of the present invention, the size of the local dimming block positioned at the outer side of the screen is smaller than the size of the local dimming block positioned at the center of the screen. In other words, in the backlight unit of the present invention, the size of the local dimming block gradually decreases from the center of the screen toward the outer side. On the other hand, for this purpose, if the size of the outermost block is randomly reduced in the number of the same local dimming block, the size of the local dimming block which is located relatively in the center may increase, and thus the dimming effect may be inefficient. Therefore, in the backlight unit of the present invention, while reducing the size of the local dimming block from the center toward the outer side, the ratio of the size of the local dimming block that can optimize the power consumption reduction according to the APL is to be derived.

First, an ideal local dimming, ie, a local dimming state of one pixel unit, is assumed and the relationship between the image pattern size and the APL will be described. 2 shows a white and a black image pattern, respectively, and graphically shows changes in APL according to the size of the image pattern.

FIG. 2 (A) shows a case where the APL gradually increases as the size of the white image pattern increases from the center of the screen toward the outer side, and (B) shows that the size of the black image pattern increases from the center of the screen to the outside. This is a case where APL gradually decreases while increasing. In general, APL refers to the number of pixels having a peak (white) luminance on the screen, that is, the area occupied by the white pixels on the screen. The pattern size refers to a portion in which the backlight unit is turned on in the local dimming state of an ideal pixel unit. In FIG. 2C, the X-axis represents the size ratio of the white and black image patterns, and when the horizontal and vertical lengths are assumed to be 1, the X-axis represents the size ratio of the image pattern, and the Y-axis represents APL.

Referring to FIG. 2C, the APL increases proportionally according to the size of the white image pattern shown in (A), or the APL decreases proportionally according to the size of the black image pattern shown in (B). It can be seen that not. In order to compensate for this, in the present invention, the size of the local dimming block is differently designed step by step according to the position.

If the size of the white image pattern gradually increases from the center of the screen toward the outer side as shown in (A), the APL for the size of the white image pattern is the square of the size (X) of the white image pattern as shown in Equation 1 below. That is, it is proportional to the area X ² of the white image pattern. Accordingly, as the horizontal (or vertical) size X of the white image pattern increases as shown in (C), the APL increases in a parabolic form.

APL = X ²

When the size of the black image pattern gradually increases from the center of the screen toward the outer side as shown in (B), the APL for the size of the black image pattern is squared of the size (X) of the black image pattern as shown in Equation 2 below. That is, it is inversely proportional to the area (X ² ) of the black image pattern. Therefore, as the horizontal (or vertical) size X of the black image pattern increases as shown in (C), the APL decreases in the form of an inverted parabola.

APL = 1-X ²

In FIG. 2C, the point where the graph of the APL relationship with respect to the size of the white image pattern intersects the graph of the APL relationship with respect to the size of the black image pattern is a point for optimizing the dimming effect. Therefore, in the present invention, in order to find a point for optimizing the APL according to the size of the white image pattern and the black image pattern, the plurality of regions of the backlight unit are divided into a plurality of regions and the size relationship of the blocks for each region is derived.

The backlight unit according to the present invention is divided into n (n is a natural number) regions in which the size of the local dimming blocks B1 to Bn gradually decreases from the center to the outer side as shown in FIG. 3, and local dimming between n regions. The size ratio of the blocks B1 to Bn is set to have a relational expression as shown in Equation 3 below. Equation 3 below is derived on the assumption that APL is proportional to the square of the block size (Bn ² ) when the ratio of the size of the local dimming block is defined as Bn in each region, so that the aspect ratio of the block is kept constant.

4 illustrates an example in which the backlight unit according to the present invention is divided into three regions. The backlight unit illustrated in FIG. 4 is divided into first to third regions X, Y, and Z, and the size ratio of local dimming blocks in the first to third regions X, Y, and Z is B1, B2. , Defined as B3. The local dimming blocks are arranged such that the same number is included in the first to third regions X, Y, and Z along a diagonal line. If the areas of the first to third regions X, Y, and Z are equal to each other, the size ratio B1: B2: B3 of the local dimming block between the first to third regions X, Y, and Z is optimized. The size of the local dimming block can be determined. The size ratio B1: B2: B3 of the local dimming block between the first to third regions X, Y, and Z decreases from the center toward the outer side. In FIG. 4, when the total width is assumed to be 1, the widths of the first to third regions X, Y, and Z are 1 / n (n = 3), and thus can be summarized as in Equation 4 below.

When the backlight unit is divided into n regions as shown in FIG. 3 and the size of the local dimming block is reduced in n steps from the center to the outer side as shown in FIG. 3, it can be generalized as shown in Equation 3 above.

As described above, the backlight unit according to the present invention divides the area of the local dimming blocks B1 to Bn step by step into n (n is a natural number) area from the center to the outside, even if a bright image is located on the outside of the screen. By minimizing the unnecessary driving of the backlight, it is possible to optimize the reduction of power consumption by local dimming driving and to improve the image quality by improving the contrast ratio.

5 is a graph comparing power consumption before and after applying the backlight unit according to the present invention. In FIG. 5, as shown in FIG. 4, when the backlight unit is divided into first to third regions X, Y, and Z, that is, when n = 3, power consumption according to APL is compared with a conventional backlight unit. From the graph shown, it can be seen that the power consumption (blue line) of the present invention is reduced than the conventional power consumption (red line).

6 is a diagram schematically illustrating a liquid crystal display using a backlight unit according to an exemplary embodiment of the present invention.

The liquid crystal display shown in FIG. 6 analyzes the input image data by a plurality of blocks to determine a local dimming value and to compensate for the data, and a panel driver to output data from the local dimming driver 12. The LED backlight unit 40 is driven block by block based on the timing controller 20 for supplying to the 22 and controlling the drive timing of the panel driver 22 and the local dimming value for each block from the local dimming driver 10. And a liquid crystal panel 28 driven by the data driver 24 and the gate driver 26 of the panel driver 22. Here, the local dimming driver 10 may be embedded in the timing controller 20.

The backlight unit 40 uses a direct-type LED backlight in which a plurality of point light sources, that is, a plurality of LEDs are arranged to face the liquid crystal panel 28, is divided and driven into a plurality of local dimming blocks to provide light to the liquid crystal panel 28. Investigate. As described above, the LED backlight is driven by being divided into a plurality of regions having different sizes of the local dimming block. The LED array is designed to gradually reduce the size of the local dimming blocks B1 to Bn in n areas from the center of the screen toward the outer side. In particular, the area of each of the n areas is set equal to each other, and the ratio of the size of the local dimming blocks B1 to Bn between the n areas decreases from the center to the outside while maintaining the relation as shown in Equation 3 above. It is designed to optimize the reduction of power consumption by local dimming drive.

The local dimming driver 10 detects a representative gray level value for each block by analyzing data for each of a plurality of blocks using the input image data and the synchronization signal. In this case, since the size of the block for image analysis corresponds to the size of the local dimming block of the backlight unit 40 described above, the size of the image analysis block is also the same as the size of the local dimming block from the center of the screen toward the outside. It will gradually decrease. The local dimming driver 10 determines a dimming value corresponding to the representative gray level value for each block and outputs the dimming value to the backlight driver 30. In this case, the local dimming driver 10 uses a lookup table in which the dimming value is preset according to the representative gray level value for each block. In addition, the local dimming driver 10 calculates a gain value by light quantity analysis using the pixel-specific light amount data from the memory and the local dimming value of each block, and compensates the input data with the calculated gain value to the timing controller 20. Output

The timing controller 20 aligns the output data from the local dimming driver 10 and outputs the data to the data driver 24, which is the panel driver 22. In addition, the timing controller 20 adjusts the driving timing of the data driver 24 using a plurality of synchronization signals input from the local dimming driver 12, that is, a vertical synchronization signal, a horizontal synchronization signal, a data enable signal, and a dot clock. A data control signal for controlling and a gate control signal for controlling the driving timing of the gate driver 26 are generated, and the data control signal and the gate control signal are output to the data driver 24 and the gate driver 26, respectively. Meanwhile, the timing controller 20 adds an overshoot value or an undershoot value to modulate data according to the data difference between adjacent frames in order to improve the response speed of the liquid crystal (not shown). It may further include.

The panel driver 22 includes a data driver 24 for driving the data line DL of the liquid crystal panel 28, and a gate driver 26 for driving the gate line GL of the liquid crystal panel 28.

The data driver 24 converts the digital image data from the timing controller 24 into an analog data signal (pixel voltage signal) using a gamma voltage in response to the data control signal from the timing controller 20 to form a liquid crystal panel 28. Is supplied to the data line DL.

The gate driver 26 sequentially drives the gate line GL of the liquid crystal panel 28 in response to the gate control signal from the timing controller 20.

The liquid crystal panel 28 displays an image through a pixel matrix in which a plurality of pixels are arranged. Each pixel implements a desired color by using a combination of red, green, and blue sub-pixels that adjust light transmittance by varying liquid crystal arrays according to luminance compensated data signals. Each subpixel includes a thin film transistor TFT connected to a gate line GL and a data line DL, a liquid crystal capacitor Clc and a storage capacitor Cst connected in parallel with the thin film transistor TFT. The liquid crystal capacitor Clc charges the data signal supplied to the pixel electrode through the thin film transistor TFT and the difference voltage between the common voltage Vcom supplied to the common electrode and drives the liquid crystal according to the charged voltage to thereby transmit light. Adjust. The storage capacitor Cst keeps the voltage charged in the liquid crystal capacitor Clc stable.

The backlight driver 30 drives the backlight unit 40 block by block according to the dimming value for each block from the local dimming driver 10 to adjust the brightness of the backlight unit 40 for each block. When the backlight unit 40 is divided and driven into a plurality of ports, the backlight unit 40 may include a plurality of backlight drivers 30 for independently driving the plurality of ports. The backlight driver 30 drives the backlight unit 40 for each block by generating a PWM signal having a duty ratio corresponding to the dimming value for each block for each block and supplying an LED driving signal corresponding to the generated PWM signal for each block. . The backlight driver 30 sequentially drives the light emitting blocks by using the local dimming values input from the local dimming driver 10 in the block connection order to control the backlight luminance for each block.

Accordingly, the liquid crystal display according to the present invention displays input image data as a product of the backlight luminance controlled for each block and the light transmittance controlled by the compensated data in the liquid crystal panel.

FIG. 7 is a block diagram illustrating a detailed configuration of the local dimming driver shown in FIG. 6.

The local dimming driver 10 shown in FIG. 7 includes an image analyzer 11, a dimming value determiner 12, a dimming value corrector 16, a memory 13, a gain value calculator 14, and data compensation. The part 15 is provided.

In the memory 13, dimming values for the representative gray level values for each block are stored in advance in the form of a look-up table, and light profile data for the light source of the local dimming block is stored in advance.

The image analyzer 11 analyzes input image data in units of a local dimming block of the backlight to detect a representative gray level value for each block, and outputs the representative gray level value for each block to the dimming value determiner 12. In detail, the image analyzer 11 detects the maximum value for each pixel in the input image data, divides the maximum value for each pixel into predetermined block units, and adds and averages the average value for each block as a representative gray level value for each block. In this case, since the size of the block for image analysis corresponds to the size of the local dimming block of the backlight unit 40 described above, the size of the image analysis block is also the same as the size of the local dimming block from the center of the screen toward the outside. It will gradually decrease.

The dimming value determiner 12 determines and outputs a local dimming value for each block corresponding to the representative gray level value for each block from the image analyzer 11. The dimming value determiner 12 uses a lookup table that stores the dimming value characteristics of the representative grayscale values for each block stored in the memory 13, for each block corresponding to the representative grayscale values for each block from the image analyzer 11. Select and output the dimming value.

The gain value calculating unit 14 uses the light source profile stored in the memory 13, that is, the light amount data for each pixel and the local dimming value for each block from the dimming value determiner 12 to reach the current pixel. 2 The total light amount is calculated, and a gain value is calculated and output as the ratio of the first and second total light amounts. The gain value calculator 14 uses the light amount data for each pixel from the memory 13 to present the sum of the light amount data reaching the current pixel from a light source of a plurality of blocks adjacent to the current input pixel when the entire backlight is at maximum luminance. It calculates with the 1st total light quantity of a pixel. In addition, the gain value calculating unit 14 multiplies and sums each of the light amount data reaching the current pixel from the light sources of the plurality of blocks by multiplying local dimming values for each block, and thus neighboring multiple blocks when the luminance of the backlight is adjusted for each block according to the local dimming value. To calculate the second total amount of light reaching the current pixel. The gain value calculator 14 calculates a ratio of the second total light amount to the first total light amount of the current pixel and outputs the ratio of the second total light amount as the gain value of the current pixel.

The data compensator 15 compensates and outputs the luminance of the current pixel data by multiplying the gain value from the gain value calculator 14 by the gain value calculated by the input data of the current pixel.

As described above, the liquid crystal display according to the present invention divides the backlight unit into n (n is a natural number) regions in which the size of the local dimming blocks B1 to Bn decreases step by step from the center to the outer side, thereby brightening the image on the screen. Even when located outside, the unnecessary driving of the backlight can be minimized to further reduce power consumption by local dimming and improve image quality.

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

1 is a view showing a conventional local dimming driving method.

FIG. 2 is a diagram illustrating changes in APL according to white and black image patterns and their sizes. FIG.

3 is a diagram illustrating a divided structure of a backlight unit according to an exemplary embodiment of the present invention.

4 is a diagram illustrating a structure in which a backlight unit is divided into three regions according to an exemplary embodiment of the present invention.

5 is a graph showing the power consumption before and after the application of the backlight unit according to the present invention.

6 is a view showing a liquid crystal display using the backlight unit according to an embodiment of the present invention.

FIG. 7 is a diagram illustrating an internal configuration of the local dimming driver shown in FIG. 6.

Claims (8)

A plurality of point light sources; A plurality of local dimming blocks which drive the plurality of point light sources and have different sizes; A plurality of regions obtained by dividing the plurality of local dimming blocks by the size; And the plurality of areas are arranged along a direction from the center of the backlight unit toward the outside. The method according to claim 1, And a size of the local dimming block gradually decreases from the center of the backlight unit toward the outer side. The method according to claim 2, And an area of each of the plurality of regions is the same, an area of the local dimming block is different for each of the regions, and an area of the local dimming block is the same in each of the regions. The method of claim 3, When the backlight unit is divided into n (where n is a natural number) areas, and the size ratio of the local dimming block included in each of the n areas is defined as B1, B2, ..., Bn, And the ratio of the local dimming block size between the regions is as follows.

Detecting a representative gray value of each block by analyzing an image in units of blocks corresponding to the local dimming block of the backlight unit of claim 1; Determining a dimming value for each block according to the representative gray level value for each block; And controlling the luminance of the unit of the backlight for each local dimming block by using the dimming value for each block. The method according to claim 5, Calculating a gain value through light quantity analysis using light profile data of the backlight unit stored in advance and dimming value of each block; Compensating the input data with the calculated gain value; And displaying the compensated data on a liquid crystal panel. The backlight unit according to any one of claims 1 to 4; A liquid crystal panel which displays an image using light from the backlight unit; A local dimming driver for analyzing input image data in units of blocks corresponding to the local dimming block of the backlight unit to determine and output a dimming value for each local dimming block; And a backlight driver for driving the backlight unit in units of the local dimming block by using a block-specific dimming value from the local dimming driver. The method of claim 7, The local dimming driver calculates a gain value by light quantity analysis using the pre-stored light profile data of the backlight unit and the dimming value for each block, and further corrects the input image data with the calculated gain value; And a panel driver which displays the corrected data on the liquid crystal panel.

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