KR20110024481A - Liquid crystal display and method for eliminating afterimage - Google Patents

Abstract

PURPOSE: A liquid crystal display and a method for eliminating an afterimage are provided to prevent motion blur by improving the sharpness at interface through interface detection of an input stop image. CONSTITUTION: In a liquid crystal display and a method for eliminating an afterimage, an interface detection unit(130) calculates the luminance difference of an image signal at each region. The interface detection unit detects the interface of an image block. A motion vector detector(150) measures a block and the degree of special position movement. The motion vector detector detects the motion vector of the image. An FRC conversion unit(160) converts a frame rate according to the movement of the image based on the motion vector.

Description

Liquid Crystal Display and method for eliminating afterimage}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display and an afterimage removing method, and more particularly, to a liquid crystal display and an afterimage removing method controlling a sharpness gain at a boundary portion of an input still image to prevent image distortion. .

In the recent information society, display elements are a visual information transmission medium, and their importance is ever more emphasized, and many kinds of flat panel displays have been developed.

The flat panel display device includes a liquid crystal display (LCD), a field emission display (FED), a plasma display panel (PDP), an electroluminescence (EL), and an organic light (OLED). Emitting Diodes).

Among such flat panel display devices, liquid crystal display devices tend to be gradually widened due to their light weight, thinness, and low power consumption. In line with this trend, liquid crystal displays are being used for portable computers such as notebook PCC, office automation equipment, audio / video equipment, and indoor / outdoor advertising display devices. It is rapidly developing into anger.

Typically, a liquid crystal display device displays an image by adjusting light transmittance of pixel cells according to a video signal. Such a liquid crystal display device includes a liquid crystal panel (Liguid Crystal Display Panel) in which pixel cells are arranged in a matrix form between two glass substrates to display an image, and a backlight unit (Back Light Unit) for irradiating light to the liquid crystal panel. And a driving device for supplying a driving signal for driving the liquid crystal panel.

Here, the light source may be classified into a side light type and a direct type according to an arrangement method of a light source included in the backlight unit. In the direct type, a light source such as a plurality of fluorescent lamps is arranged on the rear surface of the liquid crystal panel to directly irradiate light over the entire surface of the liquid crystal panel. Such a direct type method is advantageous in the application of a large LCD due to the high uniformity and brightness of light irradiated onto the liquid crystal panel.

In addition, the lamp of the direct type backlight unit is always driven to supply light of uniform intensity to the entire rear surface of the liquid crystal panel, and the liquid crystal panel controls the transmittance of light supplied from the lamp to express an image. However, the liquid crystal panel has an afterimage, i.e., motion blur, which is attracted to an image represented by the liquid crystal panel by the time when the liquid crystal molecules are arranged vertically and horizontally according to the electric field applied between the two array substrates. Motion Blur) occurs.

In particular, in order to realize a high quality moving picture, the LCD device must be driven at a high speed of 60 Hz or more every second, thereby increasing the amount of frames. Since the liquid crystal molecules must be changed in electric field in proportion to the amount of the frame, the afterimage phenomenon due to the delay of the response speed of the liquid crystal molecules becomes more serious, and thus the motion blur is also increased.

The present invention is to provide a method and a liquid crystal display device for preventing afterimages by controlling the sharpness (gain) on the boundary portion by detecting the edge of the input image.

Technical problems to be achieved by the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned above will be clearly understood by those skilled in the art from the following description. Could be.

According to an aspect of the present invention, there is provided a liquid crystal display device including: a boundary detector for detecting a boundary portion of an image block by obtaining a luminance difference value from an image signal for each frame region; A motion vector detector for detecting a motion vector of an image by measuring a degree of positional movement with respect to the divided blocks for each frame; and an FRC converter for converting a frame rate according to the degree of motion of the image based on the detected motion vector. And a sharpness gain by amplifying an edge luminance value of an edge of an image block boundary of the converted frame rate at a predetermined ratio.

The edge gain control unit may further include an edge gain control unit configured to amplify an edge luminance value of the block boundary portion of the frame detected by the edge detector at a predetermined ratio to control the sharpness gain.

The apparatus further includes a frame area determiner configured to divide the input frame into a plurality of screen areas including a predetermined number of blocks including N * M pixels, and determine the divided image area.

The boundary detector detects the boundary portion when the luminance change value between the pixels of each frame region is equal to or greater than a reference value.

The boundary detector uses a boundary detection algorithm that converts an input image signal between a spatial coordinate (R, G, B) system or a (Y, U, V) system.

The boundary detector analyzes a color difference part of the input image signal.

The motion vector detector uses a motion prediction error value such as Sum of Absolute Difference (SAD) or Mean Absolute Difference (MAD) to measure the similarity of positional movement in space with the divided blocks for each frame.

The FRC converter generates an interpolated frame based on the detected motion vector between the previous frame and the current frame.

The gain adjusting unit may set an amplification ratio in a range of 10 to 20% of an edge luminance value of a block boundary portion of the detected frame.

The present invention also provides a method for removing afterimages of a liquid crystal display, the method comprising: detecting a boundary portion of an image block by obtaining a luminance difference value from an image signal for each frame region; Detecting a motion vector of the image by measuring a degree of spatial position movement with the divided blocks for each frame; and converting a frame rate according to the degree of motion of the image based on the detected motion vector. The sharpness gain is adjusted by amplifying the edge luminance value of the boundary of the image block of the converted frame rate at a predetermined ratio.

The frame area is characterized by consisting of a predetermined number of blocks including N * M pixels.

The detecting of the boundary portion of the image block may include detecting the boundary portion when the luminance change value between pixels of each frame region is equal to or greater than a reference value.

The detecting of the boundary portion of the image block uses a boundary detection algorithm that converts an input image signal between a spatial coordinate (R, G, B) system or a (Y, U, V) system.

The detecting of the boundary portion of the image block may analyze the color difference portion of the input image signal.

The detecting of the motion vector of the image uses a motion prediction error value such as Sum of Absolute Difference (SAD) or Mean Absolute Difference (MAD) to measure the similarity of the positional movement in space.

Converting the frame rate generates an interpolated frame based on the detected motion vector between the previous frame and the current frame.

The adjusting of the sharpness gain may include setting an amplification ratio in a range of 10 to 20% of the edge luminance value.

The present invention has an effect of reducing the motion picture response time and preventing motion blur by increasing the sharpness gain at the boundary portion by detecting the edge of the input still image.

The objects, features and advantages of the present invention will be more readily understood by reference to the accompanying drawings and the following detailed description. In describing the present invention, when it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the subject matter of the present invention, the description thereof will be omitted.

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

 The liquid crystal display device includes a liquid crystal panel 210 including a pixel region formed for each region defined by a plurality of gate lines GL1 to GLm and a plurality of data lines DL1 to DLn, and a plurality of gate lines GL1. A gate driver 230 including a plurality of gate driver ICs 232 sequentially supplying the gate scan signal to the GLm), and input image data R, G, and B to the gate control signal GCS. Converting and aligning the data driver 220 including the data driver IC 222 which supplies the plurality of data lines DL1 to DLn so as to be synchronized with the image data R, G, and B from the outside. And a plurality of lamps and optical members to supply light to the data driver 220, and to supply light to the control unit 170 for controlling the driving of the gate driver 230 and the data driver 220. Backlight unit composed of And an inverter 260 for supplying a driving voltage to the plurality of lamps constituting the backlight unit 50.

Although not shown, a common gamma voltage Vcom is applied to a reference gamma voltage generator for generating and supplying a reference gamma voltage to the data driver 220, a driving voltage for driving each device, and a common electrode of the liquid crystal panel 210. It includes a voltage generator for supplying.

The liquid crystal panel 210 includes a transistor array substrate and a color filter array substrate bonded to each other, a spacer for maintaining a constant cell gap between the two array substrates, and a liquid crystal filled in a space provided by the spacer.

The liquid crystal panel 210 includes a thin film transistor (hereinafter, referred to as TFT) formed in a pixel region (pixel) defined by m gate lines GL1 to GLm and n data lines DL1 to DLn. And a pixel cell connected to the TFT. The TFT supplies the analog image data signals from the data lines DL1 to DLn to the pixel cells in response to the gate scan signals from the gate lines GL1 to GLm.

The pixel cell includes the common electrode facing the liquid crystal with the liquid crystal interposed therebetween and the pixel electrode connected to the TFT, so that the pixel cell can be equivalently represented by the liquid crystal capacitor. The pixel cell includes a storage capacity for maintaining the analog image data signal charged in the liquid crystal capacitor until the next analog image data signal is charged. The pixel cell is supplied with a common voltage Vcom to the common electrode.

The TFT includes a gate electrode connected to the gate lines GL1 to GLm, a source electrode connected to the data lines DL1 to DLn, and a drain electrode connected to the pixel electrode. Red (R), green (G), and blue (B) color filters are vertically arranged on the color filter array substrate of the liquid crystal panel 210 to form a matrix.

The image quality improvement unit 100 extracts the boundary detection and the motion vector from the frame unit of the input image signal, changes the frame rate, amplifies the luminance value of the detected boundary portion, and outputs the corrected image data in which the sharpness gain is adjusted. do.

In addition, the image quality improvement unit 100 performs signal processing for image quality improvement such as noise reduction (NR) and color tone enhancement (CTE) with respect to the frame of the input image signal. That is, the image quality improvement unit 100 attenuates noise generated during decoding or noise existing from the generation of the input image signal and performs signal processing to increase the color of the image.

The controller 170 arranges the image data R, G, and B input from the image quality improving unit 100 in units of frames, and supplies the aligned image data in the frame units to the data driver 220. In addition, the controller 170 uses the dot clock DLCK, the data enable signal DE, and the horizontal and vertical synchronization signals Hsync and Vsync input from the outside, and the data control signal DCS and the gate control signal GCS. ) To control driving timing of each of the data driver 220 and the gate driver 230.

Here, the data control signal DCS includes a source shift clock (SSC), a source start pulse (SSP), a polarity control signal (POL), and a source output signal (SOE). The gate control signal GCS includes a gate start pulse GSP, a gate shift clock GSC, a gate output enable GOE, and the like. In addition, the controller 170 includes an inverter controller 172 for controlling the inverter 260 which supplies a driving voltage to the lamps of the backlight unit 250.

The inverter 260 sequentially drives a plurality of lamps within one frame according to a control signal input from the inverter controller 172.

In addition, the controller 170 arranges the image data stored in units of frames so as to be synchronized with the driving frequency (60 Hz) of the liquid crystal panel 210 and supplies the same to the data driver 220. In addition, the liquid crystal panel is controlled at a frequency of 60 Hz to control the inverter controller 172 to generate a control signal to match the image data of the first frequency (60 Hz) to drive the image data of the second frequency (120 Hz). Applied to the inverter 260. Here, the second frequency is in the range of 61 Hz to 120 Hz, and in particular, is defined as a driving frequency, for example, 75 Hz, 90 Hz, 105 Hz, 120 Hz, which is currently applied to the liquid crystal display.

The gate driver 230 includes a shift register that sequentially generates a gate scan signal in response to the gate control signal GCS from the controller 170. The gate driver 230 sequentially applies a gate scan signal to the m gate lines GL1 to GLm in response to the gate control signal GCS input from the controller 170, thereby providing the respective gate lines GL1. Turn on the TFT connected to ~ GLm). In this case, the gate driver 230 determines the high level voltage and the low level voltage of the gate scan signal according to the input gate high voltage VGH and the gate low voltage VGL.

In response to the data control signal DSC supplied from the controller 170, the data driver 220 outputs an analog image data signal corresponding to a line corresponding to the data line DL1 to DLn every time the gate scan signal is supplied. To feed. At this time, the data driver 220 inverts the polarity of the analog image data signal supplied to the data lines DL1 to DLn in response to the polarity control signal POL.

Since the liquid crystal panel 210 does not emit light by itself, it requires a separate light source such as a lamp. In order to irradiate light onto the liquid crystal panel 210, the backlight unit 250 including a plurality of lamps and optical members is used, and in the case of the liquid crystal panel 210 expressing a full HD quality, 23 (± 1) lamps will be used.

2 is a block diagram illustrating a liquid crystal display device having an afterimage removing function according to an exemplary embodiment of the present invention.

The frame buffer 110 stores image signals in units of frames from a predetermined external image source.

The frame area determiner 120 determines a divided image area by dividing a frame applied from the frame buffer 110 into a plurality of screen areas including a predetermined number of blocks including N * M pixels.

The boundary detector 130 detects the boundaries of the image block by analyzing the luminance and the chrominance part from the image signal for each frame region divided by the frame region determiner 120. In this case, the boundary detector 130 determines the boundary area when the luminance change value between the pixels in the analyzed frame is equal to or greater than the reference value. Here, the boundary detector 130 may be a hardware module or a software module.

Specifically, each pixel in the color image may be represented by a three-dimensional vector in the color space. The color space can be represented by a number of different coordinate systems, such as (Y, U, V), (R, G, B), (X, Y, Z) and (I, H, S) color space coordinate system. Of these coordinate systems, the (I, H, S) system is the closest to the human perception. In the present invention, the boundary detection unit 130 represents an input image signal as a (R, G, B) system or a (Y, U, V) system so that the (R, G, B) system or ( Using the boundary detection algorithm that performs the conversion between the Y, U, and V) systems, the luminance difference and the chrominance part of the input image signal are analyzed and detected as the block boundary part of the frame when the luminance and chrominance difference between the pixels is greater than or equal to the reference value. .

The boundary gain control unit 140 controls the sharpness gain by amplifying the edge luminance value of the block boundary portion of the frame detected by the boundary detector 130 at a predetermined ratio. Here, the amplification ratio of the edge luminance value is amplified in the range of 10-20% of the edge luminance value.

The motion vector detector 150 generates a motion vector from the block boundary portion of the frame determined by the frame region determiner 120. Here, since the motion vector is calculated in the convex unit for each frame, the motion vector detection unit 150 divides the frame image from blocks of a predetermined size, and blocks the reference position of each block and moves the spatial position with respect to the previous frame block. Can be estimated as a motion vector. In this case, the motion vector detector 150 may use a motion prediction error value such as sum of absolute difference (SAD) or mean absolute difference (MAD) to measure the similarity of position movement.

The FRC converter 160 converts the frame rate according to the degree of motion of the image based on the motion vector detected by the motion vector detector 150. Here, the frame rate refers to the number of frames of the video signal displayed on the screen for one second, and the unit of the frame rate is Hz. The frame rate convertor converts a frequency of an input video signal according to an output standard. For example, to convert a 50Hz video signal to 100Hz, a new interpolation frame is inserted between original frames. . When inserting such an interpolation frame, the FRC converter 160 generates an interpolation frame based on the detected motion vector between the previous frame and the current frame.

In addition, according to the present invention, the FRC converter 160 applies the sharpness gain value obtained by amplifying the edge luminance value of the block boundary portion of the frame from the boundary gain control unit 140 at a predetermined ratio to the converted frame rate. Create

The LCD module 200 converts an image signal input from the FRC converter 160 into a data signal and a gate signal and outputs the data signal to the liquid crystal panel.

3 is an exemplary view illustrating measurement of a motion picture response time (MPRT) according to an embodiment of the present invention.

The video quality measuring apparatus 300 measures the video quality affected by the response speed by detecting the light generated from the frame f of the input image displayed on the liquid crystal display under test. In this case, it is recognized that the gray level P of the image displayed on the LCD is changed by the optical sensor provided in the moving image quality measuring device 300. In detail, the CCD camera c of the moving picture quality measuring apparatus 300 captures the boundary surface movement, ie, the gray level change, of the image displayed on the LCD at a fixed position.

FIG. 4 is a graph illustrating a video response time (MPRT) measurement according to an exemplary embodiment of the present invention, ie, an edge width calculated according to a change in gray level of an image displayed on a liquid crystal display. In FIG. 4, the X axis is the time shutter scale (Time_Shutter_Scale) and the Y axis is the luminance. The luminance edge width corresponding to the lower amplitude 10% (W1) to the upper amplitude 90% (W2) among the amplitudes of the graph generated according to the video response time (MPRT) measurement is calculated as the response time T. As a result of measuring the video response time (MPRT), the 60Hz normal video shows 14-16ms response time and the 120Hz video shows 8 ~ 10ms drag.

Among the graphs shown in FIG. 5, the 'S' graph shown to be increased from the lower left to the upper right is a case where the luminance level is increased, and the 'inverse S' graph shown to be reduced from the upper left to the lower right is the luminance. This is the case when the level is reduced. In particular, FIG. 5B is a graph illustrating a video response time (MPRT) measurement by applying sharpness gain by amplifying a boundary luminance value (S) according to an embodiment of the present invention.

6 (a, b) are exemplary diagrams illustrating a video response time (MPRT) measurement using boundary marginal gains according to an embodiment of the present invention.

The video quality measuring apparatus 300 measures the video quality according to the response speed of the liquid crystal display, and considers the gray level of the image displayed on the liquid crystal display in consideration of the brightness of the image having the '256' level from the 0 level to the 255 level. Measure video quality by dividing into 7 levels. FIG. 6A shows a drag phenomenon of an average of 8.9 ms (t1) of a 120Hz image generated by converting a frame rate to generate an interpolated frame. On the other hand, according to the present invention, the 120Hz image to which the sharpness gain is applied by amplifying the edge luminance value (S) exhibits a response time of an average of 7.3 ms (t2), thereby reducing drag.

7 is a flowchart illustrating a method of removing an afterimage of a liquid crystal display according to an exemplary embodiment.

The video signal is received from an external video source (S7001). The input video signal is temporarily stored in units of frames.

The input frame is divided into a plurality of screen regions including a predetermined number of blocks including N * M pixels, and the divided image region for each frame is determined (S7002).

The boundaries of the image block are detected by analyzing the luminance and the chrominance part from the divided image signals for each frame region (S7003). In this case, when the luminance change value between the pixels in the analyzed frame is greater than or equal to the reference value, it is determined as the boundary part.

The motion vector of the input image is extracted by measuring the degree of positional movement with respect to the divided blocks for each frame (S7004).

The frame rate is converted according to the degree of motion of the image based on the extracted motion vector (S7005). The frame rate conversion (FRC) converts the frequency output standard of the input video signal to insert a new interpolation frame between the original frames.

The edge luminance value of the boundary of the image signal of the converted frame rate is amplified by a predetermined ratio to enhance the sharpness gain to improve image quality (S7006).

On the other hand, the terms used in the present invention (terminology) are terms defined in consideration of functions in the present invention, which may vary according to the intention or custom of the skilled person in the relevant field, the definitions of which are used throughout the present invention. It should be based on.

The present invention is not limited to the above-described embodiments and may be variously modified and changed by those skilled in the art, which are included in the spirit and scope of the present invention as defined in the appended claims.

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

2 is a block diagram illustrating a liquid crystal display having an afterimage removing function according to an exemplary embodiment of the present invention.

3 is an exemplary view showing a video response time (MPRT) measurement according to an embodiment of the present invention

4 is a graph showing a video response time (MPRT) measurement according to an embodiment of the present invention

5 (a, b) is a graph showing a video response time (MPRT) measurement to which the marginal side gain is applied according to an embodiment of the present invention

6 (a, b) is an exemplary view showing a video response time (MPRT) measurement to apply the boundary side gain in accordance with an embodiment of the present invention

7 is a flowchart illustrating a method of removing an afterimage of a liquid crystal display according to an exemplary embodiment of the present invention.

* Description of the symbols for the main parts of the drawings *

100. Picture quality improvement unit 110. Frame buffer

120. Frame area determination unit 130. Boundary detection unit

140. Boundary gain controller 150. Motion vector extractor

160. FRC conversion unit 170. control unit

200.LCD module 210.LCD panel

220. Data Driver 230. Gate Driver

240. Inverter 250. Backlight unit

Claims (17)

Detecting a boundary portion of an image block by obtaining a luminance difference value from an image signal for each frame region; Detecting a motion vector of an image by measuring a degree of positional movement with respect to the divided blocks for each frame; and And converting a frame rate according to the degree of motion of the image based on the detected motion vector. The sharpness gain is adjusted by amplifying the edge luminance value of the boundary portion of the image block of the converted frame rate at a predetermined ratio. The method of claim 1, And the frame area is composed of a predetermined number of blocks including N * M pixels. The method of claim 1, Detecting the boundary portion of the image block, And detecting a boundary portion when a luminance change value between pixels of each frame area is equal to or greater than a reference value. The method of claim 1, Detecting the boundary portion of the image block, A boundary detection algorithm for converting an input image signal between a spatial coordinate (R, G, B) system or a (Y, U, V) system is used. The method of claim 1, Detecting the boundary portion of the image block, The afterimage removal method of the liquid crystal display device characterized by analyzing the chrominance part of an input video signal. The method of claim 1, The detecting of the motion vector of the image comprises using a motion prediction error value such as Sum of Absolute Difference (SAD) or Mean Absolute Difference (MAD) to measure the similarity of the positional movement in space. How to get rid of afterimages on display devices. The method of claim 1, The converting of the frame rate may include generating an interpolation frame based on a detected motion vector between a previous frame and a current frame. The method of claim 1, The adjusting of the sharpness gain may include setting an amplification ratio in a range of 10 to 20% of the edge luminance value. A boundary detector for detecting a boundary portion of the image block by obtaining a luminance difference value from an image signal for each frame region; A motion vector detector for detecting a motion vector of an image by measuring a degree of positional movement with respect to the divided blocks for each frame; and A FRC converter configured to convert a frame rate according to the degree of motion of the image based on the detected motion vector, And a sharpness gain by amplifying an edge luminance value of the boundary of the image block of the converted frame rate at a predetermined ratio. The method of claim 9, And a boundary gain control unit configured to control the sharpness gain by amplifying the edge luminance values of the block boundary portions of the frame detected by the boundary detector at a predetermined ratio. The method of claim 9, And a frame area determination unit for dividing an input frame into a plurality of screen areas including a predetermined number of blocks including N * M pixels, and determining the divided image area. The method of claim 9, And the boundary detector detects the boundary portion when the luminance change value between the pixels of each frame area is equal to or greater than a reference value. The method of claim 9, And the edge detector uses a boundary detection algorithm for converting an input image signal between a spatial coordinate (R, G, B) system or a (Y, U, V) system. The method of claim 9, And the boundary detector analyzes a chrominance portion of an input image signal. The method of claim 9, The motion vector detection unit uses a motion prediction error value such as sum of absolute difference (SAD) or mean absolute difference (MAD) to measure the similarity of positional movement in space with the divided blocks for each frame. A liquid crystal display device. The method of claim 9, And the FRC converter generates an interpolated frame based on the detected motion vector between the previous frame and the current frame. The method of claim 10, And the gain control unit sets an amplification ratio in a range of 10 to 20% of an edge luminance value of a block boundary portion of the detected frame.

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