KR101616924B1 - Liquid Crystal Display device - Google Patents

Abstract

A liquid crystal display device is disclosed.

A liquid crystal display according to the present invention includes: a liquid crystal display panel in which a plurality of gate lines and a plurality of data lines are arranged to display an image; a gate driver for driving the plurality of gate lines; And a data brightness analyzer for obtaining a transfer function using the histogram analysis and modulating a luminance component of the data signal, wherein the data brightness analyzer comprises: A histogram is obtained using the brightness component of the image, and a cumulative density function is obtained through the histogram to find a brightness region occupied by the image.

Luminance, histogram, transfer function, cumulative distribution function, contrast

Description

[0001] The present invention relates to a liquid crystal display device,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display (LCD), and more particularly, to a liquid crystal display capable of improving image quality by using a transfer function for improving contrast through brightness analysis of an input image.

In general, the contrast of an image means the difference between the bright and dark areas in the image, that is, the contrast ratio. The larger the contrast ratio, the higher the contrast. An image with a high contrast can be said to be an image with high clarity because the difference between bright and dark areas in the image is clear. Accordingly, when an image having a low contrast is subjected to image processing and converted into an image having a high contrast, a high-quality image can be obtained by improving the sharpness of the image.

As one of image processing techniques for improving the sharpness of images with low contrast, there is known a technique of stretching an image histogram. Images with high contrast are widely distributed at each image level of the histogram. That is, an image having a high contrast has an appropriate number of frequencies in a bright region and a dark region, so that a histogram of an image having a high contrast has a frequency distribution widely distributed over the entire image level.

On the other hand, since the difference between the bright region and the dark region is small in the low-contrast image, the histogram has a frequency distribution in a relatively narrow region of the image level. If the histogram of the low-contrast image is modified so as to widely distribute the frequency distribution in a narrow region, an image having a large difference between the bright region and the dark region can be generated. The extension of the frequency distribution of the histogram in this manner is called stretching of the histogram.

The histogram stretching technique of this image can improve the sharpness of the image when it is applied to the image acquired under the general conditions. However, when applying the batch histogram stretching technique to the images obtained in some special conditions, Thereby degrading the image quality. For example, when there is a very bright light source in the image, that is, when there is a saturated area, or when the image is composed of monochrome series and the distribution of the histogram is very narrow, or when the distribution of the histogram is high (bright side) Or when the histogram stretching is applied to the image shifted to the lower image level side (dark side), the sharpness of the image may not be improved or the image may be distorted.

The present invention provides a liquid crystal display device capable of analyzing a histogram component of an input image to find an area where most of the image is located and obtaining a transfer function based on the area, thereby improving the contrast ratio. .

A liquid crystal display according to an embodiment of the present invention includes a liquid crystal display panel in which a plurality of gate lines and a plurality of data lines are arranged to display an image, a gate driver for driving the plurality of gate lines, A data driver for supplying a data signal corresponding to the image and a data brightness analyzer for obtaining a transfer function using histogram analysis of the input image and modulating a luminance component of the data signal, The analyzer obtains a histogram using the luminance component of the image, obtains a cumulative density function through the histogram, and finds a brightness region occupied by the image.

A liquid crystal display (LCD) device according to the present invention analyzes a histogram component of an input image, finds a region (for example, 90%) where most of the image is located, obtains a transfer function based on the region, The image quality can be improved.

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

1 is a view illustrating a liquid crystal display device according to an embodiment of the present invention.

1, a liquid crystal display according to an exemplary embodiment of the present invention includes a plurality of gate lines GL1 to GLn and a plurality of data lines DL1 to DLm, A gate driver 110 for supplying a scan signal to the gate lines GL1 to GLn and a data line DL1 to DLm for supplying a scan signal to the gate lines GL1 to GLn, A timing controller 130 for controlling the gate driver 110 and the data driver 120 and a common voltage Vcom for supplying the common voltage Vcom to the liquid crystal display panel 100. [ And a voltage generating unit 150.

In addition, the liquid crystal display according to the embodiment of the present invention further includes a data brightness analyzer 140 for analyzing the brightness of the data signal from the timing controller 130 using the histogram analysis.

In the liquid crystal display panel 100, liquid crystal is formed between two glass substrates, and a plurality of gate lines GL1 to GLn and a plurality of data lines DL1 to DLm cross each other on the lower glass substrate. The thin film transistors TFT formed at the intersections of the plurality of gate lines GL1 to GLn and the plurality of data lines DL1 to DLm are connected to the data lines DL1 to DLn in response to scan signals from the gate lines GL1 to GLn, DLm to the liquid crystal cell Clc.

To this end, the gate electrode of the thin film transistor TFT is connected to the gate lines GL1 to GLn, and the source electrode thereof 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.

A storage capacitor Cst for holding the voltage of the liquid crystal cell Clc is formed on the lower glass substrate of the liquid crystal display panel 100. The storage capacitor Cst may be formed between the liquid crystal cell Clc and the previous gate line or may be formed between the liquid crystal cell Clc and another common line.

On the upper glass substrate of the liquid crystal display panel 100, color filters of R, G, and B colors corresponding to the respective pixel regions where the thin film transistors (TFT) are formed, and the gate lines GL1 to GLn, A black matrix for covering the data lines DL1 to DLm and the thin film transistors (TFT), and a common electrode covering both of them.

The gate driver 110 correspondingly supplies a plurality of scan signals to the plurality of gate lines GL1 to GLn in response to a gate control signal GCS from the timing controller 130. [ The plurality of scan signals cause the plurality of gate lines GL1 to GLn to be sequentially enabled for one horizontal synchronous signal period. The gate driver 110 may include a plurality of gate driver integrated circuits.

In response to the data control signals DCS from the timing controller 130, the data driver 120 generates a plurality of pixel data voltages each time one of the plurality of gate lines GL1 to GLn is enabled And supplies them to the plurality of data lines DL1 to DLm on the liquid crystal display panel 100, respectively. The data driver 120 may include a plurality of data driver ICs.

The timing controller 130 receives synchronization signals (Vsync, Hsync) supplied from an external system (for example, a graphics module of a computer system or a video demodulation module of a television receiving system, not shown) A gate control signal GCS for controlling the gate driver 110 and a data control signal DCS for controlling the data driver 120 are generated using a clock signal DE and a clock signal CLK.

In addition, the timing controller 130 arranges image data (Data) input from an external system and supplies the aligned data to the data driver 120. [

The common voltage generator 150 generates a common voltage Vcom using a power supply voltage Vdd applied from a power supply unit not shown and supplies the common voltage Vcom to the common electrode of the liquid crystal display panel 100, .

The data brightness analyzer 140 analyzes a histogram component of an input image, finds an area where most of the image is located, and obtains a transfer function based on the area, thereby modulating the brightness of the input image.

2, the data brightness analyzer 140 includes a first color space converter 141 for separating input image data (V-data, RGB) into a luminance component and a chrominance component, And a histogram analyzing unit 143 for performing histogram analysis using the luminance component separated by the first color space converting unit 141.

In addition, the data brightness analyzer 140 generates a transfer function using the histogram analyzed by the histogram analyzer 143, modulates the luminance component of the input image using the generated transfer function, A chrominance component compensator 149 for compensating the separated chrominance component so as to correspond to the modulation of the luminance component of the input image, and a chrominance compensator 149 for combining the modulated luminance component and the chrominance component And a second color space conversion unit 147 for outputting the image data as image data.

The first color space conversion unit 141 separates the image data (V-data) input from the timing controller 130 into a luminance component (Y) and a color difference component. The luminance component Y separated by the first color space transforming unit 141 is supplied to the histogram analyzing unit 143. The chrominance components separated by the first color space transformer 141 are supplied to the chrominance compensator 149.

나누어 히스토그램을 구한다. 예를 들어, N=3인 경우 총 8개의 구간으로 나누어 히스토그램을 구한다. 이는 하나의 예일 뿐 N의 값은 얼마든지 변경이 가능하다. The histogram analyzer 143 calculates the histogram of the input image using the luminance component. In consideration of the hardware size of the liquid crystal display device, the histogram analyzer 143 calculates the input luminance region

Divide to obtain histogram. For example, if N = 3, the histogram is divided into eight sections. This is only one example, but the value of N can be changed at any time.

The histogram analyzer 143 obtains the histogram by dividing the histogram into a plurality of luminance regions, obtains a cumulative density function thereof, and determines an image brightness level using a predetermined value among 80 to 100% of all the displayed pixels do.

FIG. 3 is a diagram showing the search for a section belonging to the 90% point of the cumulative density function obtained by the histogram analyzing unit of FIG.

As shown in FIGS. 2 and 3, the histogram analyzer 143 (FIG. 2) finds the histogram of the input image and obtains the cumulative density function of the histogram to find 90% of the cumulative density function. The 90% point of the cumulative density function means that most of the luminance information of the input image is distributed below the histogram area corresponding to the 90% cumulative density function.

The histogram area corresponding to the 90% cumulative density function is 7.

The histogram analyzer 143 obtains the histogram using the luminance component separated from the first color space transformer 141, obtains the cumulative density function using the histogram, A histogram area corresponding to 100% point is found. A histogram area corresponding to 80 to 100% of the cumulative density function is provided to the transfer function generation and application unit 145. At this time, the histogram area corresponding to 80 to 100% of the cumulative density function means the image brightness level.

The transfer function generating and applying unit 145 obtains a transfer function according to the image brightness level obtained by the histogram analyzing unit 143 and applies the transfer function to the input brightness component. A process of generating a transfer function according to an image brightness level in the transfer function generating and applying unit 145 will be described with reference to FIG.

As shown in Table 1 below, the transfer function generating and applying unit 145 includes Shift Amount for shifting the transfer function in the negative direction according to the image brightness level and Shift Amount for shifting the transfer function in the negative direction, The corresponding information is preset.

Image brightness level (brightness area) Histogram upper bound value Shift Amount Histo. One 32 16 Histo. 2 64 32 Histo. 3 96 48 Histo. 4 128 64 Histo. 5 160 80 Histo. 6 192 96 Histo. 7 224 112 Histo. 8 225 128

The Shift Amount value is set to have a value corresponding to one half of the histogram upper limit boundary value that is differently applied according to the image brightness level and belongs to the image brightness level. However, the Shift Amount value can be set to any value.

For example, if the image brightness rating is Histo. 3, the histogram upper boundary value is 96 gray, and the Shift Amount value is 48 gray.

4 is a diagram illustrating a process of generating a transfer function in the transfer function generating and applying unit of FIG.

As shown in FIGS. 2 and 4A, the transfer function generating and applying unit 145 generates a transfer function of an input luminance component having a linear characteristic. The transfer function of the linear characteristic shifts the dynamic range in the negative direction by the Shift Amount value shown in Table 1, as shown in FIG. 4 (b).

For example, if the image brightness level determined by the histogram analyzer 143 is Histo. 7, the transfer function generating and applying unit 145 shifts the transfer function of the input luminance component having a linear characteristic by 112 grams in the negative direction.

Then, the transfer function generating and applying unit 145 calculates a slope of the transfer function of the input luminance component having a linear characteristic shifted by 112 g in the negative direction, As shown in Fig.

At this time, the transfer function generating and applying unit 145 sets threshold values (th +, th-) to determine the gradients differently in order to prevent the gray scale saturation that may occur in the low gray scale and the high gray scale.

 The slope of the transfer function of the input luminance component having a linear characteristic shifted by 112 g in the negative direction can be divided into a and b. a is the slope of the transfer function corresponding to the intermediate gradation, and b is the slope of the transfer function corresponding to the low gradation and the high gradation.

The slope a is obtained by the equation Y1 = aX.

Here, by controlling the slope of Y1, that is, the variable a, the contrast of the image of the intermediate group can be adjusted. Since a is located in the first and third quadrants through the origin (0, 0), it can be understood that the value a is larger than 1.

The slope of b can be obtained by the following equations (1) and (2).

Y2 = bX + c

Y3 = bX + d

Here, Y2 is a formula for obtaining a transfer function corresponding to a high gradation, and Y3 is a formula for obtaining a transfer function corresponding to a low gradation.

By controlling the variable b, which is the slope of Y2 and Y3, it is possible to prevent gradation saturation that may occur during contrast stretching at high gradations and low gradations.

The value of b is determined to be in a range of greater than 0 and less than 1.

At this time, the variable c is determined by c? (A-b) * th + and the variable d is determined by d? (A-b) * th-.

The variables c and d determine the slope of Y1 and Y2 and determine the Threshold (th +, th-) value corresponding to the boundary between the contrast stretching region and the saturation region. The variables a, b, c, and d may be determined differently depending on the image brightness level.

By determining the inclination (a, b) of the transfer function corresponding to the high gradation, the low gradation and the intermediate gradation through the above process, the input (a, b) having a linear characteristic shifted by 112 grams in the negative direction The transfer function of the luminance component is modified.

As shown in FIG. 4 (d), the transfer function having a slope modified by each gradation is shifted in the positive direction as much as shifted in the negative direction. The transfer function shifted in the positive direction becomes the transfer function finally generated in the transfer function generating and applying unit 145.

The transfer function generation and application unit 145 applies the finally generated transfer function to the input luminance component separated from the first color space conversion unit 141. [ The contrast of the input luminance component is improved by the transfer function. The luminance component having improved contrast in the transfer function generating and applying unit 145 is output to the second color space converting unit 147.

The transfer function finally generated by the transfer function generating and applying unit 145 is supplied to the chrominance compensation unit 149. [

The chrominance component compensator 149 applies the transfer function output from the transfer function generating and applying unit 145 to the chrominance component separated by the first color space transformer 141, As shown in FIG. The chrominance component compensated by the chrominance component compensator 149 is output to the second color space converter 147.

The second color space converter 147 combines the luminance component and chrominance component applied to the transfer function into RGB data and outputs the combined data to the data driver 110 of FIG.

The data driver 110 provides the data to the data lines DL1 to DLm of the LCD panel 100 using the data output from the second color space converter 147. [ As a result, the liquid crystal display panel 100 displays an image with improved image quality.

As described above, the liquid crystal display device according to the present invention analyzes the histogram using the luminance component of the input image, finds the image brightness region where most of the image is located, and calculates a transfer function ) Can be obtained and the contrast of the input image can be improved to improve the image quality.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, the true scope of the present invention should be determined by the technical idea of the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view illustrating a liquid crystal display device according to an embodiment of the present invention. FIG.

FIG. 2 is a detailed circuit diagram of the data brightness analyzer of FIG. 1. FIG.

FIG. 3 is a diagram illustrating the search for a section belonging to a 90% point of the cumulative density function obtained by the histogram analyzing unit of FIG. 2;

4 is a diagram illustrating a process of generating a transfer function in the transfer function generating and applying unit of FIG. 2;

BRIEF DESCRIPTION OF THE DRAWINGS FIG.

100: liquid crystal display panel 110: gate driver

120: Data driver 130: Timing controller

140: Data luminance analysis unit 141: First color space conversion unit

143: Histogram analysis unit 145: Transfer function generation and application unit

147: second color space converter 149: chrominance component compensator

150: common voltage generator

Claims (6)

A liquid crystal display panel in which a plurality of gate lines and a plurality of data lines are arranged to display an image; A gate driver for driving the plurality of gate lines; A data driver for supplying a data signal corresponding to the image to the plurality of data lines; And And a data brightness analyzer for obtaining a transfer function using the histogram analysis of the input image and modulating the luminance component of the data signal, Wherein the data brightness analyzer obtains a histogram using the brightness component of the image and obtains a cumulative density function through the histogram to find a brightness region occupied by the image, Wherein the data brightness analyzer comprises: A first color space converter for separating the input image into a luminance component and a chrominance component; A histogram analyzer for analyzing the histogram using the separated luminance components; A transfer function generating and applying unit for generating the transfer function using the analyzed histogram and modulating a luminance component of the input image using the transfer function; A chrominance compensation unit for applying chrominance components separated by the first color space transform unit to the transfer function to compensate for the luminance component modulated by the transfer function generating and applying unit; And a second color space converter for combining the luminance component modulated by the transfer function generating and applying unit and the chrominance component compensated by the chrominance compensation unit into image data. delete delete The method according to claim 1, Wherein the histogram analyzer calculates a histogram using the input luminance component and calculates a cumulative density function using the calculated histogram. 5. The method of claim 4, Wherein the histogram analyzing unit determines an image brightness level occupying 80% to 100% of the displayed image using the cumulative density function. 6. The method of claim 5, Wherein the transfer function generating and applying unit obtains a transfer function having a different slope according to the image brightness level determined by the histogram analyzing unit.

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