KR20080057605A - Liquid crystal display and method of driving the same - Google Patents

Abstract

An LCD device and a driving method thereof are provided to display clear images by modulating data corresponding to a center portion of respective blocks based on analyzed histogram. An LCD(Liquid Crystal Display) device includes an LCD panel(150), a block histogram analyzer, a block conversion function selector, a block data stretching unit, data and gate drivers(130,140), and a timing controller(110). The block histogram analyzer analyzes a histogram on input images displayed in the LCD panel for every block. The block conversion function selector selects a conversion function for data stretching according to luminance distribution analyzed in the block histogram analyzer. The block data stretching unit modulates data of the input images corresponding to a center portion of respective blocks using the selected conversion function. The data driver supplies data, converted through the block data stretching unit, to the LCD panel. The gate driver supplies scan pulses to the LCD panel. The timing controller supplies the modulated data to the data driver and controls the data and gate drivers.

Description

Liquid crystal display and driving method thereof {LIQUID CRYSTAL DISPLAY AND METHOD OF DRIVING THE SAME}

1 is a block diagram illustrating a data stretching apparatus in a general liquid crystal display.

2 is a block diagram illustrating an internal configuration of a liquid crystal display according to an exemplary embodiment of the present invention.

3 is a block diagram illustrating a detailed configuration of an adaptive data stretching unit illustrated in FIG. 2.

4 is a diagram illustrating a method of analyzing a histogram on a block-by-block basis for an input image of a liquid crystal display according to an exemplary embodiment of the present invention.

FIG. 5 is a graph illustrating a histogram of a result of analyzing one block in an input image of a liquid crystal display according to an exemplary embodiment of the present invention.

6 is a graph illustrating various types of transform functions according to an embodiment of the present invention.

7 to 9 are diagrams for explaining various conversion functions shown in FIG. 6 according to the frequency distribution for each luminance.

10 is an explanatory diagram for describing a driving method of stretching data using a transform function according to an exemplary embodiment of the present invention.

11 is a flowchart illustrating a method of stretching data in a method of driving a liquid crystal display according to an exemplary embodiment of the present invention.

(Explanation of symbols for the main parts of the drawing)

110: timing controller 120: adaptive data stretching unit

130: data driver 140: gate driver

150: liquid crystal display panel 121: block histogram analysis unit

122: conversion function selection unit for each block 123: data stretching processing unit for each block

121a: blocks

The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device and a driving method thereof, which are adaptively optimized for an input image displayed on a liquid crystal display in consideration of ambient luminance.

In general, a liquid crystal display (LCD) displays an image by adjusting light transmittance of liquid crystal cells according to a video signal.

In such a liquid crystal display device, an active matrix type liquid crystal display device is advantageous in realizing a video because active control of a switching element is possible.

Thin film transistors (TFTs) are mainly used as switching elements used in active matrix liquid crystal displays.

In recent years, the liquid crystal display has been expanding its application field from display devices and monitors of office equipment to televisions.

Accordingly, manufacturers of liquid crystal display devices have invested a lot in image quality improvement to realize image quality comparable to that of a conventional cathode ray tube (CRT). As a part of this, a method of improving contrast and brightness by using data stretching has been proposed.

1 is a block diagram illustrating a data stretching apparatus in a general liquid crystal display.

The conventional data stretching device functions to improve the brightness of an input image by stretching input digital video data input to a timing controller from an external system.

Referring to FIG. 1, a conventional data stretching apparatus includes a histogram analysis / on screen display (OSD) input unit 11, a stretching curve selector 12, and a plurality of data stretching curves 13A to 13N. Include.

The histogram analysis / OSD input unit 11 analyzes a histogram, that is, a frequency distribution for each luminance, of the input digital video data RGB (IN) by one frame, and then calculates the calculated histogram result. The OSD stretching selection command selected by the user is supplied to the stretching curve selector 12.

The stretching curve selecting unit 12 selects any one of the N data stretching curves 13A to 13N according to the histogram result from the histogram analysis / OSD input unit 11 or the OSD stretching selection command.

The plurality of data stretching curves 13A to 13N store different stretching curves, and the input digital video data RGB (IN) input from the stretching curve selecting unit 12 is stored in the corresponding data stretching curves 13A to 13N. Modulate accordingly.

Each of the plurality of data stretching curves 13A to 13N is configured as a lookup table and stored in a memory, and the input digital video data RGB (IN) input from the stretching curve selector 12 is used as an address. The corresponding stretch data is output as output data RGB (OUT).

However, the conventional data stretching apparatus has a problem in that image quality is deteriorated due to input digital video data RGB (IN) that is difficult to be optimized by preset data stretching curves.

In particular, in the case of the input image in which the dark image and the bright image part exist together, the luminance of the dark image or the bright image decreases or increases, so that there is a problem that compensation is not properly performed.

For example, in the case of an input image having a star in the night sky, when the data is stretched by analyzing the histogram, the star decreases in brightness.

This is because the data is stretched after simply analyzing the entire screen, even if the histogram is analyzed by one frame, detailed image expression is difficult.

Accordingly, an aspect of the present invention is to provide a liquid crystal display and a driving method thereof capable of realizing a clear image by adaptively compensating brightness for a specific region of an input image in consideration of ambient luminance.

Further technical problems to be achieved by the present invention are not limited to the above-mentioned technical problems, and other technical problems not mentioned above are clearly understood by those skilled in the art from the following description. It can be understood.

According to another aspect of the present invention, there is provided a liquid crystal display device including: a liquid crystal display panel; a block-by-block histogram analyzer for analyzing a histogram in units of nxn blocks on an input image displayed on the liquid crystal display panel; A block function conversion unit for selecting a conversion function for data stretching according to the frequency distribution of each luminance analyzed by the analysis unit, and modulating the data of the input image corresponding to the center of each block by using the selected conversion function. A block data stretching processor, a data driver for supplying data converted by the block data stretching processor, a gate driver for supplying scan pulses to the liquid crystal display panel, and a block for data stretching for each block Drive the modulated data to the data Fed to, and a timing controller for controlling the data driver and the gate driver.

According to an exemplary embodiment of the present invention, a method of driving a liquid crystal display includes analyzing a histogram in units of nxn blocks with respect to an input image, selecting a conversion function for stretching data according to a frequency distribution of each luminance in the histogram, Modulating data corresponding to a central portion of each block by using a conversion function, and displaying the modulated data on a liquid crystal display panel.

Specific details of other embodiments are included in the detailed description and the drawings. Advantages and features of the present invention and methods for achieving them will be apparent with reference to the embodiments described below in detail with the accompanying drawings. Like reference numerals refer to like elements throughout.

Hereinafter, a liquid crystal display according to an exemplary embodiment of the present invention will be described in detail with reference to the accompanying drawings.

2 is a block diagram illustrating an internal configuration of a liquid crystal display according to an exemplary embodiment of the present invention.

Referring to FIG. 2, a liquid crystal display according to an exemplary embodiment of the present invention supplies data to a liquid crystal display panel 150 on which an input image is displayed and to data lines DL1 to DLm of the liquid crystal display panel 150. The data driver 130 for controlling the gate driver 140 for supplying scan pulses to the gate lines GL1 to GLn of the liquid crystal display panel 150, and stretching the input digital video data RGB by adaptive data stretching. An adaptive data stretching unit 120 and a timing controller 110 for supplying stretched digital video data R0G0B0 to the data driver 130 and controlling the data driver 130 and the gate driver 140 are included.

In the liquid crystal display panel 150, liquid crystal is formed between two upper and lower glass substrates, and the data lines DL1 to DLm and the gate lines GL1 to GLn are orthogonal to each other on the lower glass substrate. The thin film transistor TFT formed at the intersection of the data lines DL1 to DLm and the gate lines GL1 to GLn may receive data in response to scan pulses of the gate lines GL1 to GLn. Data input through the lines DL1 to DLm is supplied to the liquid crystal cell Clc.

For this purpose, the gate electrode of the thin film transistor TFT is connected to the gate lines GL1 to GLn, and the source electrode is connected to the data lines DL1 to DLm. The drain electrode of the thin film transistor TFT is connected to the pixel electrode of the liquid crystal cell Clc. In addition, a storage capacitor Cst is formed on the lower glass substrate of the liquid crystal display panel 150 to maintain the voltage of the liquid crystal cell Clc. The storage capacitor Cst may be formed between the liquid crystal cell Clc and the front gate lines GL1 to GLn, or may be formed between the liquid crystal cell Clc and a separate common line.

The data driver 130 receives the stretched digital video data R1G1B1 from the timing controller 110 in response to the data control signal DCS supplied from the timing controller 110, and stretches the digital video data R1G1B1. Is supplied to the data lines DL1 to DLm of the liquid crystal display panel 150 to be synchronized with the scan pulse under the control of the timing controller 110.

The gate driver 140 is connected to the gate lines GL1 to GLn by sequentially supplying scan pulses to the gate lines GL1 to GLn in response to the gate control signal GDC from the timing controller 110. Each thin film transistor TFT is turned on to select the liquid crystal cells Clc of one horizontal line to which the pixel voltage of the data, that is, the analog gamma compensation voltage, is to be supplied. Then, the data generated from the data driver 130 is supplied to the liquid crystal cell Clc of the horizontal line selected by the scan pulse.

The adaptive data stretching unit 120 analyzes the histogram of the input digital video data RGB applied to the timing controller 110 in units of blocks, and performs stretching according to the frequency distribution for each luminance in the histogram of each block unit. Select the conversion function for In addition, the stretched data R0G0B0 is output by adaptively processing data stretching for a specific region of each block by comparing a frequency distribution including a stretching range and a reference fraction determined according to a predetermined algorithm.

Accordingly, the adaptive data stretching unit 120 analyzes the histogram in units of blocks in the input image of each screen, and in particular, reduces the brightness of the specific region by stretching the data in consideration of the specific region (median value) of each block with the ambient luminance. To compensate for the increase.

The adaptive data stretching unit 120 may be built in the timing controller 110.

3 is a block diagram illustrating a detailed configuration of an adaptive data stretching unit illustrated in FIG. 2.

Referring to FIG. 3, the adaptive data stretching unit 120 according to an exemplary embodiment of the present invention has a large block histogram analyzer 121, a block transform function selector 122, and a block data stretch processor 123. ).

In this case, the block-by-block histogram analyzer 121, the block-by-block conversion function selector 122, and the block-by-block data stretching processor 123 may both be embedded in the timing controller 110, and at least one of them is embedded. May be

The histogram analyzer 121 for each block analyzes the histogram in units of blocks of size n × n with respect to the input image.

4 is a diagram illustrating a method of analyzing a histogram on a block-by-block basis for an input image of a liquid crystal display according to an exemplary embodiment of the present invention.

Referring to FIG. 4, the histogram analysis unit 121 for each block determines the size of the block 121a with respect to the input image, moves the determined block 121a at regular intervals, and displays the histogram for the entire screen. Analyze

Here, the number of blocks 121a depends on the size of one screen or the size of the block 121a.

In addition, the size n x n of the block 121a varies depending on the size of the input image and the size of the histogram to be analyzed, and typically 3 x 3 and 5 x 5 are used.

In addition, the movement of the block 121a in one screen is performed in one direction such as right or left, lower side, or upper side from the starting point, and the movement interval may be made in units of pixels.

As shown in the drawing, when the moving intervals of the blocks 121a are shifted by one pixel interval, the blocks 121a may overlap each other.

The histogram analyzed in this manner is as follows.

FIG. 5 is a graph illustrating a histogram of a result of analyzing one block in an input image of a liquid crystal display according to an exemplary embodiment of the present invention.

In the illustrated histogram graph, the luminance component having a range of 0 to 255 is represented as the X axis, and the Y axis represents a frequency distribution indicating how many pixels having luminance values corresponding to the X axis are in blocks of size n x n.

For example, in the dark input image, the low luminance data having low brightness is more than the high luminance data. In contrast, in the bright input image, the high luminance data having the high brightness is larger than the low luminance data.

Looking at the graph, as a result of analyzing the histogram for any one block, it can be seen that there are many pixels having luminance values between 128 and 160.

Referring back to FIG. 3, the block-by-block transform function selector 122 of the adaptive data stretching analyzer 120 according to an embodiment of the present invention is a result calculated by the block-by-block histogram analyzer 121. The conversion function for data stretching is selected according to the frequency distribution by luminance.

The upper limit value Pmax and the lower limit value Pmin of the luminance value are input from the outside as a reference for selecting the conversion function.

In this case, the conversion function is derived by connecting slopes proportional to the total number of pixel data (total frequency) in each of the plurality of blocks. This can be derived through an equation in real time for each input image.

The slope of the conversion function is an output luminance value / input luminance value, and as the total frequency included in each block range increases, the slope increases, and thus the gray scale expression power increases.

In addition, the conversion function is classified into a normal mode, a high brightness mode, and a low brightness mode according to the frequency distribution of the histogram. The shape of the conversion function varies according to the normal mode, the high brightness mode, and the low brightness mode.

FIG. 6 is a graph illustrating various types of conversion functions according to an embodiment of the present invention. As shown in FIG. 6, the conversion functions A, B, and C are different according to the high brightness mode, the low brightness mode, and the normal mode. Can be.

7 to 9 are diagrams for explaining various conversion functions shown in FIG. 6 according to the frequency distribution for each luminance.

Specifically, FIG. 7 is a graph showing a high brightness mode, FIGS. 8A and 8B are graphs showing a low brightness mode, and FIG. 9 is a graph showing a normal mode.

Referring to FIG. 7, the X axis represents a luminance value, and the Y axis represents a frequency corresponding to each luminance value of the X axis.

As can be seen from the graph, in the high luminance mode, a condition where the frequency HFN having a luminance value greater than or equal to the upper limit Pmax is greater than the predetermined reference frequency when compared with the preset upper limit Pmax and the lower limit Pmin. Satisfies.

Here, the reference frequency is an average frequency having a luminance value higher than or equal to the upper limit value Pmax, and is used as a comparison target of the frequency HFN having a luminance value higher than or equal to the upper limit reference value Pmax.

In the low luminance mode, the frequency LFN1 having a luminance value equal to or lower than the reference lower limit value Pmax as shown in FIG. 8A is larger than the preset reference frequency or equal to or lower than the reference lower limit value Pmin as shown in FIG. 8B. This is the case where the frequency LFN2 having the luminance value equal to or greater than the reference upper limit value Pmax is larger than the preset reference frequency.

The normal mode does not satisfy both the conditions of the high luminance mode and the low luminance mode, and as shown in FIG. 9, the frequency NFN having a luminance value larger than the lower limit Pmin and smaller than the upper limit Pmax is shown in FIG. 9. It is larger than the set standard frequency.

10 is an explanatory diagram for describing a driving method of stretching data using a transform function according to an exemplary embodiment of the present invention.

Referring to FIG. 3, the block-specific data stretching processor 123 of the adaptive data stretching unit 120 according to an embodiment of the present invention uses the transform function selected from the above-described transform function type to determine the block size of each block. Modulate the data corresponding to the center part.

For example, as a result of analyzing the histogram of one block of the input image as shown in FIG. 10, a conversion function having a slope of S for five sections is selected, and the luminance value x_in of the input pixel is Assume a value between x_2 and x_3.

Then, the input luminance value is converted by the following equation.

y_out = slope_3 * (x_in-x2) + y2

Here, y_out is an output value for the luminance value x_in of the input pixel, and according to the equation, the luminance value x_in is converted into y_out.

In the same manner as above, the data of the x_in value of the input image is converted and y_out is output, and the output y_out is converted again with ultraviolet light (UV) to display on the screen.

That is, the block data stretching processing unit 123 does not convert all the pixels included in the nxn block, but modulates only the pixels corresponding to the center of the nxn blocks, thereby adapting them in consideration of the surrounding environment (luminance and contrast ratio) of the specific region. To compensate for the brightness.

When such modulation is performed on the screen, the image brightness can be expressed by increasing the luminance and dynamic range of the input image.

Accordingly, the liquid crystal display according to the exemplary embodiment of the present invention selects a conversion function based on the nxn block, maps only the median value of the nxn block to the selected conversion function, and modulates the contrast ratio of the display image by outputting the input brightness value. By making it larger, a more natural and clear image can be realized.

Hereinafter, a driving method of the liquid crystal display according to the exemplary embodiment of the present invention will be described.

11 is a flowchart illustrating a method of stretching data in a method of driving a liquid crystal display according to an exemplary embodiment of the present invention.

Referring to FIG. 11, in a first step S1, a histogram is analyzed in units of n × n blocks with respect to an input image.

In this step, the size of a block is determined as an area for analyzing the histogram with respect to the input image, and the histogram is analyzed while moving at regular intervals in units of blocks.

The movement interval is composed of pixel intervals, and for detailed image representation, it is preferable to overlap the blocks before the movement and the blocks after the movement. This is not to modulate the data of the entire block in consideration of the ambient luminance, but to modulate only the data for the center portion of the block, so that the modulated center portions are adjacent to each other as much as possible.

Next, in step S2, a transform function for stretching data is selected according to the frequency distribution for each luminance in the histogram calculated in the previous step.

In detail, the upper limit and the lower limit of the luminance value are preset in the calculated histogram, and the frequency distribution of three sections divided based on the set upper limit and the lower limit is calculated.

Thereafter, the frequency of the three sections divided by the reference upper limit and the reference lower limit is compared with a predetermined reference frequency, and then a conversion function is selected according to the comparison result.

Here, the conversion function is classified into a normal mode, a high brightness mode, and a low brightness mode according to the frequency distribution of the histogram.

Therefore, when the frequency having the luminance value equal to or greater than the reference upper limit is larger than the preset reference frequency, the conversion function of the high luminance mode is selected.

Alternatively, when a frequency having a luminance value less than or equal to a reference upper limit is greater than a predetermined reference frequency or a frequency having a luminance value less than or equal to a reference lower limit and greater than or equal to a predetermined reference frequency is greater than a predetermined reference frequency, select a low luminance mode conversion function. do.

Alternatively, when a frequency having a luminance value larger than the reference lower limit and smaller than the reference upper limit is larger than a predetermined reference frequency, the conversion function of the normal mode is selected.

Next, in step S3, data corresponding to the center of each block is modulated by using the selected transform function.

In this case, instead of converting all pixels included in the block having the size of nxn, only the pixels corresponding to the center portion of the block of nxn are modulated, thereby adaptively compensating the brightness in consideration of the surrounding environment (luminance and contrast ratio) for a specific region. do.

When such modulation is performed on the entire screen, the luminance and dynamic range of the input image are enlarged to enable natural and detailed image representation.

Finally, in step S4, the modulated data is applied to the data lines through the timing controller and the data driver of the liquid crystal display to display the data on the liquid crystal display panel.

Although embodiments of the present invention have been described above with reference to the accompanying drawings, those skilled in the art to which the present invention pertains may implement the present invention in other specific forms without changing the technical spirit or essential features thereof. I can understand that.

Therefore, since the embodiments described above are provided to completely inform the scope of the invention to those skilled in the art, it should be understood that they are exemplary in all respects and not limited. The invention is only defined by the scope of the claims.

According to the present invention, the liquid crystal display according to the present invention analyzes the histogram of the input image in units of nxn blocks, selects a conversion function based on the reference image, and then maps only the median value of the nxn blocks to the conversion function, thereby outputting an input luminance value. By modulating in, the luminance and dynamic range of the display image can be enlarged to realize a more detailed and clear image.

Claims (16)

A liquid crystal display panel; A block-by-block histogram analyzer for analyzing a histogram in units of n x n blocks with respect to the input image displayed on the LCD panel; A block function conversion unit for selecting a conversion function for data stretching according to the frequency distribution for each luminance analyzed by the block histogram analyzer; A block data stretching processor for modulating data of an input image corresponding to a center portion of each block by using the selected conversion function; A data driver for supplying data converted by the block-by-block data stretching processor to the liquid crystal display panel; A gate driver supplying a scan pulse to the liquid crystal display panel; And A timing controller for supplying the modulated data to the data driver by the data stretching unit for each block and controlling the data driver and the gate driver Liquid crystal display comprising a. The method of claim 1, The block-specific histogram analyzer determines the size of the block unit with respect to the input image, and analyzes the entire input image while moving the block unit at regular intervals. The method of claim 2, And the block unit moves at pixel intervals. The method of claim 1, The block function conversion unit selection unit, And one of a normal mode, a high luminance mode, and a low luminance mode according to the frequency distribution for each luminance analyzed by the histogram analyzer for each block. The method of claim 4, wherein The high brightness mode is a liquid crystal display, characterized in that the frequency having a luminance value equal to or greater than a reference upper limit is greater than a predetermined reference frequency. The method of claim 4, wherein The low luminance mode is characterized in that the frequency having a luminance value less than or equal to the reference lower limit is greater than a predetermined reference frequency or the frequency having a luminance value less than or equal to the lower limit and more than or equal to the reference upper limit is greater than a predetermined reference frequency. Liquid crystal display. The method of claim 4, wherein And the normal mode is a case in which a frequency having a luminance value greater than the reference lower limit and smaller than the reference upper limit is greater than a predetermined reference frequency. The method of claim 1, And wherein the block-by-block histogram analyzer, the block-by-block conversion function selector, or the block-by-block data stretching processor are embedded in the timing controller. Analyzing the histogram with respect to the input image in units of n x n blocks; Selecting a conversion function for stretching data according to a frequency distribution of each luminance in the histogram; Modulating data corresponding to a central portion of each block by using the selected conversion function; And Displaying the modulated data on a liquid crystal display panel; Method of driving a liquid crystal display comprising a. The method of claim 9, Analyzing the histogram, And determining the size of the block unit with respect to the input image, and analyzing the entire input image while moving the block unit at regular intervals. The method of claim 10, The analyzing of the histogram comprises moving the block unit at pixel intervals. The method of claim 9, Selecting the conversion function, Setting a reference upper limit value and a reference lower limit value of the luminance value in the histogram, calculating a frequency distribution of three sections divided based on the reference upper limit value and the reference lower limit value; Comparing the frequency of three sections divided by the reference upper limit value and the reference lower limit value with a predetermined reference frequency; and Selecting a conversion function according to the comparison result Method of driving a liquid crystal display comprising a. The method of claim 12, The selecting of the conversion function according to the comparison result may include selecting one of a normal mode, a high brightness mode, and a low brightness mode. The method of claim 13, Selecting a conversion function according to the comparison result, And selecting the high luminance mode when a frequency having a luminance value equal to or greater than the upper limit is greater than a predetermined reference frequency. The method of claim 13, Selecting a conversion function according to the comparison result, Selecting the low luminance mode when a frequency having a luminance value less than or equal to the reference lower limit is greater than a preset reference frequency or a frequency having a luminance value less than or equal to the reference lower limit and more than a reference upper limit is greater than a preset reference frequency. A drive method of a liquid crystal display device. The method of claim 13, Selecting a conversion function according to the comparison result, And the normal mode is selected when a frequency having a luminance value greater than the reference lower limit and smaller than the reference upper limit is greater than a preset reference frequency.

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