KR20110071384A - Liquid crystal display device and method for driving the same - Google Patents

Abstract

PURPOSE: A liquid crystal display device and a driving method thereof are provided to reduce power consumption by using a second gray scale curve in case of a still image to express gray scales of image data. CONSTITUTION: An image determination unit(100) determines whether images are still images or motion pictures on the basis image data during frame periods. A timing controller(TC) receives, rearranges, and outputs the image data from the image determination unit. First and second gray scale curves express relations among the gray scales of the image data and analog pixel voltages. A data driver(DD) receives the image data from the timing controller. A data driver selects the analog pixel voltage corresponding to the gray scales of the image data during the frame periods.

Description

Liquid crystal display and its driving method {LIQUID CRYSTAL DISPLAY DEVICE AND METHOD FOR DRIVING THE SAME}

The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device and a driving method thereof capable of reducing power consumption.

In general, notebooks are driven in a normally white mode, which causes a high current consumption when a low gray level image is displayed close to the black side. In other words, there is a problem in that a high power consumption is always displayed when an image, for example, a text-based image, in which a plurality of images close to the black are represented.

The present invention has been made to solve the above problems, and it is determined whether the image to be displayed on the screen is a still image or a video, and if it is determined as a still image, image data using a gradation curve having a relatively small maximum gradation voltage It is an object of the present invention to provide a liquid crystal display device and a driving method thereof capable of reducing power consumption by expressing the gray level.

The liquid crystal display according to the present invention for achieving the above object is to display on the screen during these frame periods on the basis of the image data during the predetermined k (k is a natural number of two or more) consecutive frame periods An image discriminating unit determining whether the image is a still image or a moving image; A time controller which receives the image data from the image discriminating unit and rearranges and outputs the image data; And receiving image data from the timing controller and corresponding to the gray level of the image data during the frame periods by using any one of a first gray curve and a second gray curve according to the determination result from the image discriminating unit. And a data driver for selecting and outputting an analog pixel voltage.

The first and second grayscale curves are curves showing a relationship between grayscales of image data and analog pixel voltages; The maximum analog pixel voltage of the second gradation curve is smaller than the maximum analog pixel voltage of the first gradation curve.

The voltage difference between the analog pixel voltages of the second grayscale curve is smaller than the voltage difference between the analog pixel voltages of the first grayscale curve.

The image discriminating unit sets at least one inspection point on the screen, compares image data supplied for k frame periods to at least one unit pixel positioned at the inspection point for each frame period, and compares the image data of each frame period. If they are all the same, the image displayed on the screen during the k frame periods is determined as a still image, whereas if any one of the image data of each frame period is different, the image displayed on the screen during the k frame periods is a video. It is characterized by judging.

The unit pixel comprises a red pixel for displaying a red image, a green pixel for displaying a green image, and a blue pixel for displaying a blue image; Image data supplied to the unit pixel includes red image data supplied to the red pixel, green image data supplied to the green pixel, and blue image data supplied to the blue pixel; The image discriminator compares the total of the red image data, the green image data, and the blue image data supplied to the unit pixel of the inspection point for each frame period during the n frame periods to determine whether the image is the same for the n frame periods. Characterized by judging.

In addition, the driving method of the liquid crystal display device according to the present invention for achieving the above object, during the frame periods based on the image data during the predetermined k (k is a natural number of two or more) consecutive frame periods Determining whether the image is a still image or a moving image to be displayed on a screen; Step B of rearranging and outputting the image data from the step A: receiving the image data from the step B, the frame using any one of the first gradation curve and the second gradation curve according to the determination result from step A And selecting and outputting an analog pixel voltage corresponding to the gray level of the image data during the periods.

The first and second grayscale curves are curves showing a relationship between grayscales of image data and analog pixel voltages; The maximum analog pixel voltage of the second gradation curve is smaller than the maximum analog pixel voltage of the first gradation curve.

The voltage difference between the analog pixel voltages of the second grayscale curve is smaller than the voltage difference between the analog pixel voltages of the first grayscale curve.

The step A may include setting at least one inspection point on the screen; Comparing the image data supplied during the k frame periods to the at least one unit pixel positioned at the inspection point for each frame period; And when the image data of each frame period is all the same, the image displayed on the screen during the k frame periods is determined as a still image, while when any one of the image data of each frame period is different, the k frame periods. And determining an image displayed on the screen as a video.

The unit pixel comprises a red pixel for displaying a red image, a green pixel for displaying a green image, and a blue pixel for displaying a blue image; Image data supplied to the unit pixel includes red image data supplied to the red pixel, green image data supplied to the green pixel, and blue image data supplied to the blue pixel; In step A, the sum of the red image data, the green image data, and the blue image data supplied to the unit pixel of the inspection point is compared for each frame period during the k frame periods to determine whether the image is the same for the k frame periods. Characterized by judging.

The liquid crystal display device and the driving method thereof according to the present invention have the following effects.

According to the present invention, it is determined whether an image to be displayed on the screen is a still image or a moving image. When the image is a still image having a relatively low importance of image quality, the gray scale of the image data is expressed by using a second gray scale curve. Reduce power consumption As a result of this determination, when the image is a moving image having a relatively high importance of image quality, the image quality can be prevented from being degraded by expressing the gray level of the image data using the first gray scale curve.

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

As shown in FIG. 1, a liquid crystal display according to an exemplary embodiment of the present invention includes a plurality of pixel groups PG1 to PGn and a plurality of gate lines GL1 to GLn alternately disposed with each other, and the gate line. Each of the pixel groups so as to be located between the plurality of data lines DL1 to DLm arranged to intersect the pixels GL1 to GLn and the pixel groups PG1 to PGn and adjacent data lines DL1 to DLm. A plurality of pixels PXL formed in the PG1 to PGn to display an image, a gate driver GD to sequentially drive the gate lines GL1 to GLn, and all data each time the gate line is driven. A data driver DD for simultaneously supplying analog pixel voltages to the lines DL1 to DLm, a timing controller TC for controlling the gate driver GD and the data driver DD, and a frame from an external system. Period The image discrimination unit 100 that determines whether the image to be displayed on the screen of the display panel during the frame period is a still image or a moving image based on the image data (R / G / B data) continuously inputted as Include. The image discriminating unit 100 displays an image to be displayed on the screen during these frame periods based on the image data (R / G / B data) during k (k is a natural number of two or more) preset frame periods. It is determined whether the image is a still image or a moving image.

The timing controller TC generates a data control signal DCS and a gate control signal GCS by using the horizontal synchronization signal Hsync, the vertical synchronization signal Vsync, and the clock signal CLK. Supply to driver DD and gate driver GD. The data control signal DCS includes a dot clock, a source shift clock, a source enable signal, a polarity inversion signal, and the like. In addition, the timing controller receives image data (R / G / B data) from the image discriminating unit 100 and rearranges the image data according to timing.

The gate control signal GCS is a signal including a gate start pulse, a gate shift clock, a gate output enable, and the like. The gate control signal GCS is input to the gate driver GD.

The data driver DD samples the image data R / G / B data according to the data control signal DCS from the timing controller TC, and then horizontally samples the sampled image data R / G / B data. Each line is latched by one line for each time period (Horizontal Time: 1H, 2H, ...), and analog pixel voltages corresponding to the latched image data R / G / B data are supplied to the data lines DL1 to DLm. That is, the data driver DD converts the image data R / G / B data from the timing controller TC into an analog pixel signal (data signal) by using a gamma voltage input from the power generator. To DL1 to DLm. In this case, the data driver uses either one of the first grayscale curve and the second grayscale curve according to the determination result from the image discrimination unit 100 to obtain the R / G / B data of the image data during the frame periods. The analog pixel voltage corresponding to the gray level is selected and output. For example, the data driver DD may select one of the first grayscale curve and the second grayscale curve according to the logic state of the discrimination signal IDS from the image discrimination unit 100. Specifically, the data driver DD selects the first gradation curve when the determination signal IDS is high logic, and the data driver DD selects the second gradation curve when the determination signal IDS is low logic. Choose.

The gate driver GD shifts a shift register that sequentially generates scan pulses in response to a gate start pulse among the gate control signals from the timing controller TC, and shifts the voltage of the scan pulses to a voltage level suitable for driving the liquid crystal cell. A level shifter. The gate driver GD sequentially supplies scan pulses to the gate lines GL1 to GLn in response to the gate control signal.

Each pixel PXL is turned on by a scan pulse from a corresponding gate line to switch a pixel voltage from a corresponding data line, and a pixel electrode configured to display an image by receiving the switched pixel voltage from the thin film transistor. It includes. The pixels PXL having such a configuration are formed in the display panel PN.

FIG. 2 is a diagram showing first and second gray scale functions F1 and F2 on which the first and second gray scale curves are based.

As shown in FIG. 2, the first gray scale function F1 takes a function of the form Y = X, and the second gray scale function F2 takes a function of the form Y = aX + B. Here, a is the slope of the first gradation function F1, and this a is (63-B) / 63.

According to the first gray scale function F1, analog pixel voltages of 0 to 63 gray levels are output symmetrically with respect to the input of 0 to 63 gray image data (R / G / B data). On the contrary, according to the second gray scale function F2, analog pixel voltages of 0 to 63 gray levels are asymmetrically output to the input of 0 to 63 gray image data (R / G / B data). According to the first gray scale function F1 of FIG. 2, an analog pixel voltage having the lowest gray scale is output to the input of the lowest gray scale image data R / G / B data, whereas the second gray scale function of FIG. According to F2), it can be seen that an analog pixel voltage having a higher gray level than an analog pixel voltage having the lowest gray level is output to the input of the lowest gray level image data (R / G / B data). If the liquid crystal display device is a normal white driving type liquid crystal display device, the value of the analog pixel voltage for the gray level increases from bright high gray to dark low gray, and thus the second gray scale function (F2) is used. It can be seen that the magnitude of the maximum analog pixel voltage for displaying black by B is smaller than that of the first gray scale function F1. Therefore, when the second gray scale function F2 is used, power consumption by B can be reduced as compared with the first gray scale function F1.

The first gradation curve is generated based on the first gradation function F1, and the second gradation curve is generated based on the second gradation function F2. Looking at it as follows.

FIG. 3 is a diagram illustrating first and second grayscale curves generated based on the first and second grayscale functions F1 and F2 of FIG. 2.

As illustrated in FIG. 3, the first grayscale curve G1 includes a first positive grayscale curve G1_P and a first negative grayscale curve G1_N. Similarly, the second gradation curve G2 includes the second positive gradation curve G2_P and the second negative gradation curve G2_N.

The first and second grayscale curves G1 and G2 are curves representing the relationship between the grayscales of the image data R / G / B data and the analog pixel voltages. That is, the X axis of FIG. 3 is an axis indicating the gray level of the image data (R / G / B data), and the Y axis is an axis indicating the magnitude of the analog pixel voltage. As can be seen in FIG. 3, it can be seen that the pixel voltage of the second grayscale curve G2 corresponding to the same grayscale is different from the pixel voltage of the first grayscale curve G1. Specifically, it can be seen that the pixel voltage of the second grayscale curve G2 is smaller than the pixel voltage of the first grayscale curve G1 corresponding thereto. For example, the maximum analog pixel voltage of the second grayscale curve G2 for displaying black is smaller than the maximum analog pixel voltage of the first grayscale curve G1.

The voltage difference between the analog pixel voltages of the second grayscale curve G2 is smaller than the voltage difference between the analog pixel voltages of the first grayscale curve G1. In other words, when the gray scale of the image data R / G / B data is represented using the first gray scale curve G1, the contrast ratio of the image is relatively improved, but power consumption is increased. On the other hand, when the gray scale of the image data R / G / B data is represented using the second gray curve G2, the contrast ratio of the image is lowered but power consumption is reduced.

 As described above, according to the present invention, it is determined whether the image to be displayed on the screen is a still image or a moving image. When the image is a still image having a relatively low importance of image quality, the image data using the second gradation curve G2 is determined. The power consumption is reduced by expressing the gradation of (R / G / B data). As a result of this determination, when the image is a video having a relatively high importance of image quality, the image quality (R / G / B data) is expressed by using the first gradation curve G1 to prevent the image quality from being lowered. Can be.

4 is a flowchart illustrating a method of driving a liquid crystal display of the present invention.

First, the image data (R / G / B data) for k consecutive k (k is two or more natural numbers) consecutive frame periods is examined (S1), and the image is displayed as a still image to be displayed on the screen during these frame periods. It is determined whether or not the video (S2).

Subsequently, when the image is a still image, the gray scale of the image data R / G / B data is expressed using the second grayscale curve G2 when the determination result from the image discriminating unit 100 is S3. However, when this image is a moving image, the gray scale of the image data R / G / B data is expressed using the first grayscale curve G1 (S2-1).

On the other hand, if it is determined that the image is a moving image, instead of the above-described first gradation curve G1, a gradation curve based on various functions for correcting the moving image quality may be used.

In addition, in the present invention, by combining several functions of controlling the backlight to the image discriminator 100, the image discriminator 100 may be configured to react organically according to the type and nature of the input image data. have.

Here, the principle of image discrimination by the image discriminating unit 100 according to the present invention will be described in detail.

5 and 6 are diagrams for explaining the principle of image discrimination by the image discriminating unit 100 according to the present invention.

As illustrated in FIG. 5, the image discriminating unit 100 sets at least one inspection point TS on the screen SCR, and k-frame periods are included in at least one unit pixel located at the inspection point TS. Image data (R / G / B data) supplied during each frame period is compared for each frame period, and when the image data (R / G / B data) of each frame period is the same, the screen SCR is displayed during the k frame periods. While it is determined that the displayed image is a still image, if any one of the image data (R / G / B data) of each frame period is different, the image displayed on the screen SCR during the k frame periods is a video. To judge.

Here, the unit pixels UX_Odd and UX_Even may include red pixels R_Odd and R_Even for displaying a red image, green pixels G_Odd and G_Even for displaying a green image, and blue pixels B_Odd and B_Even for displaying a blue image. do.

The image data R / G / B data supplied to the unit pixel includes red image data R / G / B data supplied to the red pixel and green image data R / G / B supplied to the green pixel. data) and blue image data (R / G / B data) supplied to the blue pixel.

In this case, the image discriminating unit 100 may transmit red image data (R / G / B data), green image data (R / G / B data), and blue image data (supplied to the unit pixel of the inspection point TS). The total of the R / G / B data) is compared for each frame period during the n frame periods to determine whether the image is the same for the k frame periods.

For example, as illustrated in FIG. 5, nine inspection points TS are formed on the screen SCR of the display panel, and two unit pixels UX_Odd and UX_Even are positioned at each inspection point TS. have. One of the two unit pixels is the odd unit pixel (UX_Odd) to which the odd-numbered image data (R / G / B data) is supplied, and the other is the even-number to which the even-numbered image data (R / G / B data) is supplied. It is a unit pixel UX_Even. Radix unit pixels include radix red pixels (R_Odd), radix green pixels (G_Odd) and radix blue pixels (B_Odd), and even unit pixels include even red pixels (R_Even), even green pixels (G_Even), and even blue pixels. (B_Even) is included.

Radix red image data is supplied to the radix red pixel R_Odd, Radix green image data is supplied to the radix green pixel G_Odd, Radix blue image data is supplied to the radix blue pixel B_Odd, and even red pixel ( Even red image data is supplied to R_Even, even green image data is supplied to even green pixel G_Even, and even blue image data is supplied to even blue pixel B_Even.

6, the radix red image data (R / G / B data), the radix green image data (R / G / B data), and the radix blue, which are located at the first inspection point in the first frame period, are illustrated in FIG. 6. Radix red image data (R / G / B data) and radix green image data (R / G / B data) whose total sum of the image data (R / G / B data) is located at the first inspection point in each of the remaining second to fifth frame periods. / G / B data) and the odd blue image data (R / G / B data), if the sum is equal, the images represented in the radix unit pixels located at the first inspection point during the first to fifth frame periods are all the same. It is judged by the image. Likewise, even red image data (R / G / B data), even green image data (R / G / B data) and even blue image data (R / G) located at the first inspection point in the first frame period. / B data), the sum of the even red image data (R / G / B data), the even green image data (R / G / B data), which are located at the first inspection point in each of the remaining second to fifth frame periods; If the sum of the even blue image data R / G / B data is the same, all of the images represented by the even unit pixel positioned at the first inspection point during the first to fifth frame periods are determined to be the same image. In this case, when the total sum of the data in the odd and even unit pixels is different in any one frame period at this first inspection point, all the images represented by the unit pixels located at the first inspection point are judged to be not identical. do.

In this way, it is checked whether the images at each of the remaining second to ninth inspection points are the same during the first to fifth frame periods, so that each of the nine inspection points is displaying the same image. In this case, the image displayed on the screen SCR during the first to fifth frame periods is finally determined as a still image. However, when any one of these first to ninth inspection points includes another image, the image displayed on the screen SCR during the first to fifth frame periods is finally determined as a moving image.

7 is a view for explaining the effect of the present invention.

FIG. 7A illustrates two kinds of still images when the first gradation curve G1 is applied, and FIG. 7B illustrates two kinds of still images when the second gradation curve G2 is applied. As shown in the figure, it can be seen that the contrast ratio of the image of FIG. 7B is lower than that of the image of FIG. However, both types of images shown in FIG. 7 are still images, and even if the contrast ratio is low, it can be seen that there is no problem in reading the text appearing in the still images.

The present invention described above is not limited to the above-described embodiments and the accompanying drawings, and it is common in the art that various substitutions, modifications, and changes can be made without departing from the technical spirit of the present invention. It will be evident to those who have knowledge of.

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

2 is a diagram showing first and second gray scale functions that are the basis of the first and second gray scale curves.

FIG. 3 is a diagram illustrating first and second grayscale curves generated based on the first and second grayscale functions of FIG. 2. FIG.

4 is a flowchart illustrating a method of driving a liquid crystal display of the present invention.

5 and 6 are views for explaining the principle of image discrimination of the image discriminating unit in the present invention.

7 is a view for explaining the effect of the present invention

Claims (10)

An image discriminating unit for determining whether an image is a still image or a moving image to be displayed on the screen during these frame periods based on image data during k (k is a natural number of two or more) consecutive frame periods; And, A time controller which receives the image data from the image discriminating unit and rearranges and outputs the image data; Image data supplied from the timing controller and an analog pixel corresponding to the gradation of the image data during the frame periods using either one of a first gradation curve and a second gradation curve according to the determination result from the image discriminating unit. And a data driver for selecting and outputting a voltage. The method of claim 1, The first and second grayscale curves are curves showing a relationship between grayscales of image data and analog pixel voltages; And, And the maximum analog pixel voltage of the second gradation curve is smaller than the maximum analog pixel voltage of the first gradation curve. The method of claim 2, And the voltage difference between the analog pixel voltages of the second gradation curve is smaller than the voltage difference between the analog pixel voltages of the first gradation curve. The method of claim 1, The image discriminating unit, At least one inspection point is set on the screen, and image data supplied during k frame periods is compared for each frame period to at least one unit pixel located at the inspection point, and the image data of each frame period is the same. While the image displayed on the screen during the k frame periods is determined as a still image, if any one of the image data of each frame period is different, the image displayed on the screen during the k frame periods is determined as a video. A liquid crystal display device. The method of claim 4, wherein The unit pixel comprises a red pixel for displaying a red image, a green pixel for displaying a green image, and a blue pixel for displaying a blue image; Image data supplied to the unit pixel includes red image data supplied to the red pixel, green image data supplied to the green pixel, and blue image data supplied to the blue pixel; And, The image discriminating unit compares the sum of the red image data, the green image data, and the blue image data supplied to the unit pixel of the inspection point for each frame period during the n frame periods to determine whether the image is the same for the n frame periods. A liquid crystal display device characterized in that the judgment. Determining whether an image is a still image or a moving image to be displayed on the screen during these frame periods, based on image data for k (k is a natural number of two or more) consecutive frame periods; Step B of rearranging and outputting the image data from the step A: The image data is supplied from the step B, and the analog pixel voltage corresponding to the gray level of the image data during the frame periods is obtained using either one of the first gray level curve and the second gray level curve according to the determination result from the step A. And a step (C) of selecting and outputting the liquid crystal display. The method of claim 6, The first and second grayscale curves are curves showing a relationship between grayscales of image data and analog pixel voltages; And, And the maximum analog pixel voltage of the second gradation curve is smaller than the maximum analog pixel voltage of the first gradation curve. The method of claim 7, wherein And the voltage difference between the analog pixel voltages of the second gradation curve is smaller than the voltage difference between the analog pixel voltages of the first gradation curve. The method of claim 6, Step A, Setting at least one inspection point on the screen; Comparing the image data supplied during the k frame periods to the at least one unit pixel positioned at the inspection point for each frame period; And, If the image data of each frame period is all the same, the image displayed on the screen for the k frame periods is determined as a still image, whereas if any one of the image data of each frame period is different, the screen for the k frame periods. And determining the image displayed on the screen as a moving image. The method of claim 9, The unit pixel comprises a red pixel for displaying a red image, a green pixel for displaying a green image, and a blue pixel for displaying a blue image; Image data supplied to the unit pixel includes red image data supplied to the red pixel, green image data supplied to the green pixel, and blue image data supplied to the blue pixel; And, In step A, the sum of the red image data, the green image data, and the blue image data supplied to the unit pixel of the inspection point is compared for each frame period during k frame periods to determine whether the image is identical during k frame periods. Method of driving a liquid crystal display device characterized in that.

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