KR20050055158A - Liquid crystal display and driving method thereof - Google Patents

Abstract

Disclosed are a liquid crystal display and a driving method thereof capable of maximizing the luminance of a local image included in an input image.

According to an aspect of the present invention, there is provided a method of driving a liquid crystal display, comprising: determining a driving method of each local image selected from an input digital image; Generating a control signal according to the determined driving scheme; And driving the liquid crystal panel according to the control signal.

Therefore, when the local image requires the maximum luminance, the local image may be driven in a hold manner, thereby obtaining a brighter brightness value than the conventional impulse method.

Description

Liquid crystal display and driving method thereof

The present invention relates to a liquid crystal display, and more particularly, to a liquid crystal display and a driving method thereof capable of maximizing the luminance of a local image included in an input image.

In general, a liquid crystal display (LCD) is an apparatus for displaying an image because each pixel of a liquid crystal panel in front of the liquid crystal panel selectively transmits the light generated from the light source at the rear side as a kind of an optical switch. That is, in the related art, the brightness is controlled by adjusting the intensity of an electron beam through which a cathode ray tube (CRT) is scanned, whereas the liquid crystal display controls the brightness of a screen by controlling the intensity of light generated from a light source.

Meanwhile, with the development of technology, technology for displaying a moving image as well as displaying a still image is in the spotlight. However, it is difficult to implement a moving image in a liquid crystal display device used for various display media. That is, since the response speed of the liquid crystal is slower than one frame period, the liquid crystal display maintains a voltage (for example, an image signal or data voltage) charged in the liquid crystal for one frame and then applies a new voltage in the next frame. Drag on the screen, that is, motion blur occurs.

FIG. 1A illustrates a light intensity over time in a general CRT, and FIG. 1B illustrates a light density over time in a general liquid crystal display.

As shown in FIG. 1A, the CRT is driven in an impulse manner, whereas as shown in FIG. 1B, the liquid crystal display is driven in a hold manner, thereby causing a drag of a screen when a video is implemented. In this hold method, actual image data is displayed in synchronization with gate pulses applied to the respective gate lines, and the actual image data displayed in this way is displayed with the backlight turned on for one frame.

At present, an impulse method for removing the screen drag phenomenon has been proposed in the LCD.

The impulse method of the liquid crystal display includes a data blinking method and a scanning backlight method.

FIG. 2A is a diagram for describing a general data blocking method, and FIG. 2B is a diagram for explaining a general scanning backlight method.

As shown in FIG. 2A, the data blinking method divides a width of a gate pulse sequentially applied to each gate line in half, so that one gate line B is included in a gate pulse of a first region having a width of the divided gate pulse. Real image data is applied to the second line, and black data is applied to another gate line (A-line) different from the one gate line (B-line) to the gate pulse of the second region of the width of the divided gate pulse. Will be. At this time, when viewed from the other gate line (A-line), actual image data is maintained for a predetermined time in one frame, and then black data is also maintained for a predetermined time. Here, when the width of the gate pulse has a response speed of 21us based on XGA, the first region and the second region are divided at the same ratio. In this case, each line (eg, an A-line) may secure one frame at a specific ratio (such as 7: 3 or 6: 4). The data blinking method is also called a black data insertion method.

On the other hand, in the scanning backlight method, as shown in FIG. 2B, instead of inputting actual image data for each width of the gate pulse sequentially applied to each gate line, a plurality of backlights are sequentially turned on / off, thereby providing impulse. The drive is made. For example, a gate pulse is applied to one gate line, and actual image data is applied to data lines crossing on the selected gate line. In this case, the backlight which is in charge of the pixel area defined by the gate line and the data lines is turned on for a predetermined time and then turned off. Therefore, the actual data is displayed for a predetermined time when the backlight is turned on, and then the impulse driving is performed by not displaying the actual data for the predetermined time when the backlight is turned off.

By using the above-described driving method, that is, the data blinking method and the scanning backlight method, the liquid crystal display may be driven in an impulse manner to remove the blurring of the screen.

On the other hand, when an image is displayed on the screen by the LCD, the luminance of each pixel included in the image is different from each other. Due to the luminance difference of each pixel, the screen may be locally bright and dark.

In particular, there is a portion of the local image that requires maximum brightness.

However, as described above, when the liquid crystal display is driven in an impulse manner, the actual image is displayed only for a predetermined time during one frame, so that the portion where the maximum luminance is to be displayed is not displayed at the maximum luminance. There was a problem that the image quality is reduced.

Accordingly, the present invention has been made to solve the above problems, and the liquid crystal display capable of maximizing the luminance of the portion requiring the maximum luminance by driving the local image that requires the maximum luminance when driving in an impulse manner. It is an object of the present invention to provide an apparatus and a driving method thereof.

According to a preferred embodiment of the present invention for achieving the above object, the liquid crystal display device, the control unit for determining the driving method of each local image selected from the input digital image; A data driver for supplying the control signal and the digital image to the data lines according to the driving method; A gate driver for sequentially supplying a control signal and a gate signal to gate lines according to the driving method; And a liquid crystal panel having a plurality of pixels two-dimensionally disposed along the gate lines and the data lines.

Here, the driving method is determined by comparing the average luminance value of the selected local image with a predetermined threshold value. That is, when the average luminance value of the selected region image is larger than a predetermined threshold, the selected region image is required to have the maximum luminance, and accordingly, a hold method is determined, and the average luminance value of the selected region image is a predetermined threshold value. In a smaller case, the selected local image does not require the maximum luminance, and thus may be determined by an impulse method.

According to another preferred embodiment of the present invention, a method of driving a liquid crystal display device includes: determining a driving method of each local image selected from an input digital image; Generating a control signal according to the determined driving scheme; And driving the liquid crystal panel according to the control signal.

The determining of the driving method may include: dividing the input digital image into a plurality of local images having a macroblock including at least one pixel; Comparing an average luminance value obtained from each of the divided plurality of regional images with a predetermined threshold value; And determining a driving method of each of the plurality of local images according to the comparison result.

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

3 is a view showing a schematic configuration of a liquid crystal display of the present invention. 4 is a diagram illustrating a detailed configuration of a controller in the liquid crystal display of FIG. 3.

Referring to FIG. 3, the liquid crystal display of the present invention includes a digital video card 1 for converting an analog image into a digital image, and a controller 2 for determining a driving method of each local image selected from the digital image. And a data driver 3 for supplying the control signal and the digital image according to the driving method to the data lines DL, and the control signal and the gate signal according to the driving method to the gate lines GL. And a liquid crystal panel (4) having a gate driver (5) for supplying a plurality of pixels, and a plurality of pixels two-dimensionally disposed along the gate lines (GL) and the data lines (DL).

The digital video card 1 converts an analog input image into a digital video image and detects synchronization signals V and H included in the input image.

As shown in FIG. 4, the control unit 2 includes a maximum luminance checking unit 11, a driving method determination unit 13, and a timing control unit 15.

The maximum luminance checking unit 11 receives a digital video image and a synchronization signal (V, H) from the digital video card 1, and divides the digital image into a plurality of local images having at least one pixel. The local image may be divided into macroblock units of 2 pixels * 2 pixels, 4 pixels * 4 pixels, or 8 pixels * 8 pixels. In this case, each pixel included in the macroblock unit has a unique luminance value. In this case, the maximum luminance checking unit 11 obtains a luminance average value of each pixel included in the macroblock, and when the luminance average value exceeds a predetermined threshold, peak brightness is required for the local image. It will be selected as an area. In this case, when the average luminance value does not exceed a predetermined threshold, the local image corresponding to the average luminance value may be selected as an area where maximum luminance is not required.

Alternatively, as described above, when the local image is not divided into macroblocks and the luminance value of each pixel is compared with a predetermined threshold and the predetermined threshold is exceeded, the pixel may be selected as an area requiring maximum luminance. It may be.

Any of the two methods described above may be used, but only a region where maximum luminance is required from the digital image is selected.

As such, when the maximum luminance check unit 11 determines whether the maximum luminance is required for each region image, information about each region image is provided to the driving method determiner 13. Here, the information about the local image means information about whether the maximum luminance is required for the local image. As described above, the maximum luminance checking unit 11 may determine whether the maximum luminance is required for each local image.

The driving method determination unit 13 determines the driving method of the corresponding local image based on the information on the local image provided from the maximum luminance checking unit 11. For example, the local image requiring the maximum luminance among the regional images provided by the maximum luminance checking unit 11 may be determined by the hold method, and the local image that does not require the maximum luminance may be determined by the impulse method. Accordingly, when it is determined that the local image is driven by the hold method, the driving method determination unit 13 generates '0' as a control signal for controlling the local image, and the local image is driven by an impulse method. If it is determined to be, to generate a '1' as a control signal for controlling the local image.

For example, as shown in FIG. 5, in order to display P1 to P9 pixels on a screen in a 3 pixel * 3 pixel area image, the first, second and third gate lines GL1, GL2, and GL3 are displayed. Assume that a gate pulse is applied, and a data signal is applied to the first, second and third data lines DL1, DL2, and DL3. In this case, when the local image is identified as a region requiring maximum luminance, the driving method determiner 13 generates a control signal '1' for the local image. Accordingly, the local image is driven through the first, second and third gate lines GL1, GL2 and GL3 and the first, second and third data lines DL1, DL2 and DL3. The luminance of can be maximized compared to the impulse method.

The timing controller 15 controls and drives a control signal (0 or 1) according to each local image by using the control signal provided from the driving method determination unit 13 and the synchronization signals V and H detected from the digital image. Generate and output signals Dclk and GSP. Here, Dclk is a dot clock signal for providing to the data driver 3 and GSP is a gate start pulse for providing to the gate driver 5. Accordingly, the data driver 3 is provided with the digital image, a control signal according to the determined driving method, a dot clock signal, and the like, and the gate driver 5 provides a control signal and a gate start pulse according to the determined driving method. And the like.

The gate driver 5 sequentially generates gate signals in response to the gate start pulse GSP input based on the control signal 1 or 0 provided from the controller 2 to the gate lines DL. Supply it. In response to the gate signal input from the gate driver 5, the video data on the data line DL is supplied to the pixel electrode of the liquid crystal cell Clc by the switching element TFT.

The data driver 3 receives a dot clock Dclk from the controller 2 together with digital image video data of control signals 1 or 0, red (R), green (G), and blue (B). . The data driver 3 gamma-compensates digital video data of red (R), green (G), and blue (B) in synchronization with a dot clock (Dclk), converts the analog video into analog data, and converts the data lines into data lines (line by line). DL).

In the liquid crystal panel 4, liquid crystal is injected between two glass substrates, and the gate lines GL and the data lines DL are formed to be perpendicular to each other on the lower glass substrate. A switching element for selectively supplying an image input from the data lines DL to the liquid crystal cell Clc is formed at the intersection of the gate lines GL and the data lines DL. To this end, a gate line GL is connected to a gate terminal of the switching element TFT, and a data line DL is connected to a source terminal of the switching element TFT.

In the liquid crystal display device provided as described above, it is preferable that the liquid crystal panel 4 is basically driven in an impulse manner.

In this case, the impulse method may use any one of a data blinking method and a scanning backlight method as described above.

Therefore, when it is determined by the driving method determination unit 13 in the impulse method, it is driven in one of the data blinking method or the scanning backlight method. In this case, when the maximum luminance is required for a specific area image and the control signal '1' is outputted when the maximum brightness is required, the drive mode is driven in the hold mode when driving the specific area image.

For example, in the case of a data blinking method, the actual image data is applied to the specific local image for a predetermined time period of one frame, and then instead of the black data when a predetermined time elapses, that is, when the black data is applied. Image data is applied. Here, the actual image data may have a luminance value of the original image data or a luminance value that is brighter than that.

In addition, in the case of the scanning backlight method, the backlight is turned on for a predetermined time in one frame with respect to the specific area image, and the backlight is continuously turned on when a predetermined time elapses, that is, when the backlight needs to be turned off.

The driving method of the liquid crystal display device provided as above is demonstrated.

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

3, 4 and 6, a digitally converted image and a synchronization signal from the digital video card 1 are input to the controller 2 (S 21).

The controller 2 divides the digital image into a plurality of local images (S 22). In this case, the size of the local image may be any one of one pixel, two pixels * 2 pixels, three pixels * 3 pixels, and four pixels * 4 pixels.

An average luminance value of pixels included in the divided local image is calculated. Here, the average luminance value means a value obtained by dividing the luminance values of individual pixels included in the divided local image by the number of pixels. The average luminance value of the regional image calculated as described above is compared with a predetermined threshold value (S 23). Here, the predetermined threshold indicates a reference value for determining whether the maximum luminance value is required, and is preferably set at 80 to 90% of the maximum luminance value.

As a result of the comparison by S 23, when the average luminance value of the divided region image is larger than a predetermined threshold value, the maximum luminance is required for the divided region image (S 24). On the contrary, when the average luminance value of the divided region image is smaller than a predetermined threshold, the maximum luminance is not required for the divided region image (S 27).

S 23, S 24, and S 27 may be performed on all local images.

In this way, the driving method is determined depending on whether the maximum luminance is required by S 24 and S 27. That is, when the maximum luminance is required for the region image, the region image is determined to be driven by the hold method (S 25). When the maximum luminance is not required for the region image, the region image is an impulse. It is determined to be driven in a manner (S 28).

As such, when each driving method is determined according to whether the maximum luminance is required for the local image, a control signal according to the corresponding driving method is generated. That is, when it is determined by the hold method by S 25, the control signal '1' is generated (S 26), and when it is determined by the impulse method by S 28, the control signal '0' is generated (S 29). ).

In this case, the control signal is generated for each pixel included in the local image. For example, as shown in FIG. 5, when a local image having a size of 3 pixels * 3 pixels is driven in a hold manner because a maximum luminance is required, the control signal starts from all pixels included in the local image, that is, P1. All control signals of '1' are generated for P9.

On the other hand, the controller 2 generates a gate start pulse GSP and a dot clock signal Dclk based on the synchronization signal (S30).

The control unit 2 provides the control signal and the gate start pulse to the gate driver 5, and provides the control signal, the dot clock signal and the digital image to the data driver 3.

At this time, the liquid crystal panel 4 is basically driven by an impulse method. That is, the gate driver 5 sequentially applies a predetermined gate signal to each gate line GL in response to the gate start pulse.

The data driver 3 gamma-compensates the digital image in response to the dot clock signal Dclk in synchronization with gate signals applied to the respective gate lines GL, and gamma-corrected image data, that is, actual image data. Is applied to the data lines DL.

Here, the actual image data is applied for a predetermined time in one frame. Then, black data for not displaying the actual image data is applied for the remaining time. In this case, when the control signal is '1' as the corresponding local image is required as the maximum brightness is required, the gate lines GL and the data lines for displaying the pixels included in the local image are displayed. DL) continuously applies real image data for one frame section or turns on the backlight continuously for one frame section, and drives the corresponding local image for which maximum luminance is required (S 31). ). Herein, in the case of the local image requiring the maximum luminance, the actual image data preferably has a luminance value of the original image data or higher.

If the local image is determined by the impulse method because the maximum luminance is not required, and the control signal '0' is generated, the local image is driven by the existing impulse method. That is, in the data blinking method, actual image data may be applied for a predetermined time in one frame, and black data may be applied for the remaining time. In addition, in the case of the scanning backlight method, the backlight may be turned on for a predetermined time in one frame, and the backlight may be turned off for the remaining time.

Therefore, in the case of the local image where maximum luminance is required, the region that does not require maximum luminance is driven by continuously applying real image data when the black data is applied or by holding the backlight to turn on the backlight continuously. By displaying brighter than the image, there is an effect that can maximize the maximum brightness more.

For example, as shown in FIG. 7A, when the local luminance of a portion of the digital image is required to have the maximum luminance, the actual image data of the digital image is displayed on the entire screen area for a predetermined time period in one frame. . In this case, as shown in FIG. 7B, when the maximum luminance is required for the region image of the predetermined portion, the region image of the predetermined portion is applied to the remaining region except for a predetermined time period, that is, the black data is applied. For example, the maximum luminance of the local image may be maximized by continuously applying real image data using the hold method or by continuously turning on the backlight.

As described above, according to the present invention, by selecting a local image for which the maximum luminance is required in the digital image and driving the selected local image by a hold method instead of an impulse method, the maximum luminance of the local image can be maximized. The effect is expected.

In addition, such a driving method can realize a video almost similar to that of a conventional CRT, and is expected to have an effect of improving dynamic brightness and dynamic contrast ratio performance.

FIG. 1A illustrates light intensity over time in a typical CRT. FIG.

1B is a view for explaining the density of light with time in a typical liquid crystal display;

2A is a diagram for explaining a general data blinking scheme.

2B is a view for explaining a general scanning backlight method.

3 is a view showing a schematic configuration of a liquid crystal display of the present invention.

4 is a diagram illustrating a detailed configuration of a controller in the liquid crystal display of FIG. 3.

5 is a view for explaining a local image in the liquid crystal display of FIG. 3.

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

7A and 7B are exemplary views illustrating a state in which a local image requiring maximum luminance in FIG. 3 is maximized by a hold method.

<Name of the code for the main part of the drawing>

1: digital video card 2: control unit

3: data driver 4: liquid crystal panel

5: Gate driver 11: Maximum luminance check unit

13 driving method determination unit 15 timing control unit

Claims (10)

A controller configured to determine a driving method of each local image selected from the input digital image; A data driver for supplying the control signal and the digital image to the data lines according to the driving method; A gate driver for sequentially supplying a control signal and a gate signal to gate lines according to the driving method; And A liquid crystal panel having a plurality of pixels two-dimensionally disposed along the gate lines and the data lines. Liquid crystal display comprising a. The liquid crystal display of claim 1, wherein the local image is selected in macroblock units including at least one pixel. The liquid crystal display of claim 1, wherein the driving method is determined by comparing an average luminance value of the selected local image with a predetermined threshold value. The liquid crystal of claim 1 or 3, wherein when the average luminance value of the selected region image is larger than a predetermined threshold, the selected region image is required to have a maximum luminance, and accordingly, the liquid crystal is determined in a hold manner. Display. The method of claim 1 or 3, wherein when the average luminance value of the selected local image is smaller than a predetermined threshold, the selected local image is not required to have a maximum luminance, and accordingly, is determined by an impulse method. LCD display device. The liquid crystal display of claim 5, wherein the impulse method is one of a data blinking method and a scanning backlight method. Determining a driving method of each local image selected from the input digital image; Generating a control signal according to the determined driving scheme; And Driving the liquid crystal panel according to the control signal Method of driving a liquid crystal display device comprising a. The method of claim 7, wherein determining the driving method, Dividing the input digital image into a plurality of local images having a macroblock including at least one pixel; Comparing an average luminance value obtained from each of the divided plurality of regional images with a predetermined threshold value; And Determining a driving method of each of the plurality of local images according to the comparison result; Method of driving a liquid crystal display device comprising a. The method of claim 8, wherein when the average luminance value is larger than a predetermined threshold, the local image is required to have a maximum luminance, and accordingly, is determined in a hold manner. The method of claim 8, wherein when the average luminance value is smaller than a predetermined threshold, the local image is not required to have a maximum luminance, and accordingly, an impulse method is determined.