KR101308223B1 - Liquid Crystal Display Device Gamma-error - Google Patents

Abstract

The present invention relates to a liquid crystal display device suitable for improving the image quality of moving images.

The liquid crystal display device includes a liquid crystal panel; An input unit for inputting video data; A data driver for supplying pixel driving signals input by the pixels on the liquid crystal panel by one line in response to video data from the input unit; According to how many gray levels of pixel data included in the video data from the input unit are distributed around which gray level, the gamma voltage set which causes the size and the compensation rate of the low gray area of the pixel data to be emphasized to be changed is changed. And a low gradation adaptive gamma voltage generator for supplying the driver.

Gradation, distribution area, distribution, low gradation area, emphasis, compensation

Description

Liquid Crystal Display Device Gamma-error}

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the drawings used in the detailed description of the present invention, a brief description of each drawing is provided.

1A to 1C are characteristic diagrams illustrating gamma error characteristics.

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

3 is a characteristic diagram illustrating gamma characteristics of pixel data corrected by the present invention.

FIG. 4 is a detailed block diagram illustrating in detail the low gray scale adaptive gamma voltage generator of FIG. 2.

5 is a block diagram illustrating a liquid crystal display according to another exemplary embodiment of the present invention.

FIG. 6 is a detailed block diagram illustrating in detail the low gray scale adaptive data compensation unit of FIG. 5.

DESCRIPTION OF THE REFERENCE NUMERALS to the main parts of the drawings "

10: liquid crystal panel 12: gate driver

14: data driver 16: timing control unit

18: low gradation adaptive gamma voltage generator 20,126: delay

22: low gray scale adaptive data compensation unit 100,114: gray scale distribution analysis unit

102,116: correction coefficient determiner 104: programmable gamma voltage generator

110: matrix 112: normal compensation unit

118: low gradation emphasis unit 120: selection unit

122: selection control unit 124: inverse matrix

The present invention relates to a liquid crystal display device capable of faithful reproduction of an image.

Cathode ray tube (hereinafter referred to as "CRT") has been commonly used as a display device until now, but recently, a liquid crystal display device (hereinafter, "LCD") using an active matrix liquid crystal panel as a display screen. Is spreading. The liquid crystal panel included in the LCD displays an image by adjusting the amount of planar light passing from the rear surface through the liquid crystal layer in units of pixels.

In the liquid crystal panel, the amount of light passing through the liquid crystal cell (that is, the luminance of the liquid crystal panel) according to the voltage level (that is, the gradation value of the video data) of the pixel driving signals supplied to the liquid crystal cells arranged in a matrix form is shown in FIG. 1A. It should change linearly, such as LLC, but in practice it will change non-linearly low, such as ULC of FIG. Thus, in the liquid crystal panel, a gamma error occurs, which is an all-optical conversion error that appears when an electrical signal is converted into an optical signal.

To correct this gamma error, the LCD assumes that there are gamma error characteristics such as UDL1 to UDL3 in FIG. 1B for the video data. The LCD uniformly corrects all grayscale values that video data may have in a form in which nonlinear gamma correction characteristics corresponding to the gamma error characteristics UDL1 to UDL3 are selectively applied based on the linear gamma characteristic ULD. do. Since all of the gray scale values that video data can have are gamma-corrected uniformly according to the nonlinear gamma correction characteristic, image degradation occurs in an area of a lower gray scale that becomes larger as the brightness of the image to be displayed becomes darker. In order to improve the deterioration of the image in the lower gray scale region, the gamma error characteristic of the S-shape is assumed as shown in UDL4 of FIG. 1C, and the gamma error characteristic of the S-shape is based on the gamma characteristic (SDL) of the linear characteristic. In some cases, a method of emphasizing and correcting video data of a lower gray level region of the video data has been applied according to a corresponding gamma correction characteristic. In this case, the portion of the image corresponding to the upper gradation region is severely degraded when the lower gradation region is emphasized.

Recently, LCDs have been used not only as screens of notebook computers or as monitors of desktop computers, but also as screens of television receivers. Video data for moving images is mostly input to an LCD used as a video display device of a television receiver.

However, in the case where a moving picture implemented by video data such as television data is displayed, the range of the lower gradations deteriorated in accordance with the brightness of the picture is frequently stretched in the picture displayed by the LCD. As a result, the image quality of the moving image displayed by the LCD is remarkably degraded.

Accordingly, an object of the present invention is to provide a liquid crystal display device suitable for improving the image quality of moving images.

Another object of the present invention is to provide a liquid crystal display device suitable for preventing deterioration in an area of a lower gray level even when the brightness of an image changes.

According to an embodiment of the present invention, a liquid crystal display device includes: a liquid crystal panel; An input unit for inputting video data; A data driver for supplying pixel driving signals input by the pixels on the liquid crystal panel by one line in response to video data from the input unit; According to how many gray levels of pixel data included in the video data from the input unit are distributed around which gray level, the gamma voltage set which causes the size and the compensation rate of the low gray area of the pixel data to be emphasized to be changed is changed. And a low gradation adaptive gamma voltage generator for supplying the driver.

In another embodiment, a liquid crystal display device includes a liquid crystal panel; An input unit for inputting video data; A data driver for supplying pixel driving signals input by the pixels on the liquid crystal panel by one line in response to video data from the input unit; And low gray scale adaptive data for compensating a compensation rate according to a distribution rate of pixel data of a lower gray scale region having a size varying depending on how much gray levels of pixel data included in video data to be transmitted to the data driver are distributed around which gray level. It includes a compensation unit.

Other objects, other advantages and other features of the present invention will become apparent from the detailed description of the preferred embodiments with reference to the accompanying drawings, in addition to the objects of the present invention as described above.

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

2 is a block diagram schematically illustrating a liquid crystal display according to an exemplary embodiment of the present invention. Referring to FIG. 2, the liquid crystal display device includes a gate driver 12 connected to a plurality of gate lines GL1 to GLn on the liquid crystal panel 10 and a plurality of data lines DL1 to DLm on the liquid crystal panel 10. The data driver 14 connected is provided. The plurality of gate lines GL1 to GLn and the plurality of data lines DL1 to DLm are formed on the liquid crystal panel 10 so as to intersect with each other to divide a plurality of pixel regions. Each pixel area of the plurality of pixel regions switches a pixel driving signal to be supplied to a corresponding liquid crystal cell (not shown) from a corresponding data line DL in response to a scan signal on a corresponding gate line GL (not shown). Not formed). The liquid crystal cell adjusts the amount of light passing through the pixel region according to the voltage level of the pixel driving signal to enable an image to be displayed. As a result, a pixel including one thin film transistor and one liquid crystal cell is formed in each pixel area.

The gate driver 12 enables the plurality of gate lines GL1 to GLn for one frame sequentially and exclusively for a predetermined period (that is, for each period of one horizontal sync signal). To this end, the gate driver 12 generates a plurality of scan signals exclusively having enable pulses sequentially shifted for each period of the horizontal synchronization signal. The gate enable pulse included in each of the plurality of scan signals has a width corresponding to the period of the horizontal synchronization signal. The gate enable pulse included in each of the plurality of scan signals is generated once every frame period.

Whenever one of the plurality of gate lines GL1 to GLn is enabled, the data driver 14 corresponds to the number of data lines DL1 to DLm corresponding to one pixel line (ie, one gate line). Pixel driving signals corresponding to the number of pixels arranged in the. Each pixel driving signal corresponding to one line is supplied to a corresponding pixel (ie, a liquid crystal cell) on the liquid crystal panel 10 via a corresponding data line DL. Each of the pixels arranged on one gate line GL passes an amount of light corresponding to a voltage level of the pixel driving signal. In order to generate pixel drive signals for one line, the data driver 14 sequentially inputs one line of pixel data for each period of one horizontal synchronizing signal, and sequentially low-grades the pixel data for one line input thereto. The gamma voltage set from the adaptive gamma voltage generator 18 is used to simultaneously convert an analog pixel driving signal.

The gate driver 12 and the data driver 14 are controlled by the timing controller 16. [ The timing control unit 16 receives a synchronization signal from an external video data source (for example, an image signal demodulation unit included in a television receiving module or a graphics card included in a computer system) not shown via a control transmission line DTL. Enter SYNC. The synchronization signals SYNC supplied from an external video data source include a data clock Dclk, a horizontal synchronization signal Hsync, a vertical synchronization signal Vsync, and the like. The timing controller 16 generates the gate control signals GCS necessary for the gate driver 12 to generate a plurality of scan signals every frame using the synchronization signals SYNC. In addition, the timing controller 16 inputs one line of pixel data sequentially in the data driver 12 every cycle of the horizontal synchronization signal, and converts the sequentially input one line of pixel data into an analog pixel drive signal. Generates data control signals (DCS) necessary to convert and output.

The low gradation adaptive gamma voltage generator 18 is connected to an external video data source (e.g., an image signal demodulator of a television receiver module or a graphics card of a computer system) not shown via a data transmission line DTL. And input video data VDi. In the video data VDi, pixel data are sequentially arranged in frame units (one image unit).

The low gray scale adaptive gamma voltage generator 18 may be emphasized and compensated according to how much gray level values of pixel data included in the video data VDi from the data transmission line DTL are distributed around which gray level. The size and compensation rate of the low gradation region of the pixel data are varied. For example, when most of the pixel data having a gradation value near the middle gradation level among the pixel data of one frame, the low gradation adaptive gamma voltage generator 18 generates the middle gradation of the lower 35% of the pixel data of the frame. A gamma voltage set is generated which causes the pixel data having the gray scale value of the region to be highlighted. In other words, the low gradation adaptive gamma voltage generation unit 18 causes the pixel data having the gray level value of the lower 35% gray level region to be compensated with a larger compensation rate than the pixel data having the gray level value of the remaining upper 65% gray level region. Generate a gamma voltage set. Bosangyul difference of the upper gray scale pixel data of the non-stressed and bosangyul of the pixel data of the low gray level to be emphasized is the number of the pixel data of the gray level value other than the number and the halftone area of the pixel data having a gray level of the halftone region Determined by the ratio. In this case, the low gradation adaptive gamma voltage generator 18 has a gamma voltage set (or gradation change characteristic) similar to VGC1 in FIG. 3. When there is a large amount of pixel data having the gray scale value of the upper gray scale region among the pixel data included in one frame, the low gray scale adaptive gamma voltage generator 18 has the remaining pixel data having the gray scale value of the lower 30% gray scale region. A gamma voltage set is generated to be compensated with a larger compensation rate than pixel data having a gray value of the upper 70% gray area. At this time, the gamma voltage set output from the low gray scale adaptive gamma voltage generator 18 has the same gamma characteristic as that of VGC2 in FIG. 3. As another example, when there are many pixel data having the gray scale value of the lower gray scale region among the pixel data included in one frame, the low gray scale adaptive gamma voltage generation unit 18 may use the gray scale value of the lower 40% gray scale region. The pixel data having? Is compensated with a larger compensation rate than the pixel data having the gray level value of the remaining upper 60% gray level region. The gamma voltage set generated by the low gray scale adaptive gamma voltage generator 18 has the same gamma characteristic as that of VGC3 in FIG. 2. In the low gray scale adaptive gamma voltage generator 18, the gamma voltage set has any one of gamma characteristics such as VGC1 to VGC3 of FIG. 3. In this way, a gamma voltage set having different gamma characteristics according to the distribution gray scale region and distribution diagram of the pixel data is supplied to the data driver 14. Then, the data driver 14 converts the pixel data into an analog type pixel driving signal using a gamma voltage set having a changed gamma characteristic, and thus lower gray levels corresponding to grayscale distribution regions of pixel data such as VGC1 to VGC3 in FIG. 3. The pixel drive signal in the range is emphasized-compensated at a compensation rate according to the distribution of the pixel data. As a result of the compensated pixel driving signal, the image of the lower gray level is highlighted-displayed while preventing the degradation of the image corresponding to the upper gray level in the image displayed on the liquid crystal panel 10. As a result, the image quality of the moving image displayed by the liquid crystal display of the embodiment of the present invention is improved.

In addition, the liquid crystal display according to the exemplary embodiment may further include a delay unit 20 connected between the data transmission line DTL and the data driver 14. The delay unit 20 delays the pixel data to be supplied from the data transmission line DTL toward the data driver 14 by the propagation delay time in the low gradation adaptive gamma voltage generator 18. The period delayed by the delay unit 20 corresponds to a period of one vertical sync signal (that is, one frame period).

FIG. 4 is a detailed block diagram illustrating the low gray scale adaptive gamma voltage generator 18 in FIG. 2 in detail. The low gray scale adaptive gamma voltage generator 18 of FIG. 4 includes a gray scale distribution analyzer 100, a correction coefficient determiner 102, and a programmable gamma voltage generator 104 connected in series with a data transmission line DTL. do. The gray scale distribution analyzer 100 analyzes a histogram of pixel data of one frame to detect how much pixel data is distributed in which gray level region. In other words, the gradation distribution analyzer 100 detects a distribution gradation region and a distribution amount of pixel data of one frame through histometry.

The compensation coefficient determiner 102 applies the sigmoid function to the distribution gray scale region and the distribution amount of the pixel data from the gray scale distribution analyzer 100 and the size and emphasis compensation ratio of the lower gray scale region of the pixel data to be emphasized and compensated. The gamma characteristic of In addition, the correction coefficient determination unit 102 determines a correction coefficient having a logic value that designates a gamma voltage set corresponding to the calculated gamma characteristic.

The programmable gamma voltage generator 104 responsive to the correction coefficient determined by the compensation coefficient determiner 102 generates a gamma voltage set corresponding to a logic value of the correction coefficient among the plurality of gamma voltage sets. The programmable gamma voltage generator 104 analogizes a look-up table in which a set of gamma voltage data corresponding to the number of logic values that a correction factor can have and a gamma voltage data set read from this look-up table. And a digital-to-analog converter for converting to a gamma voltage set in the form. The gamma voltage set generated by the programmable gamma voltage generator 104 has a gamma characteristic of an area having a size corresponding to gray level distribution of pixel data and an emphasis compensation factor according to a distribution of pixel data, as illustrated in VGC1 to VGC3 illustrated in FIG. 2.

5 schematically illustrates a liquid crystal display according to another exemplary embodiment of the present invention. In the liquid crystal display of FIG. 5, the low gray level adaptive data compensation unit 22 connected between the data transmission line DTL and the data driver 14 instead of the low gray level adaptive gamma voltage generator 18 and the delay unit 20. Except for including a has the same configuration as the liquid crystal display of FIG. Although detailed descriptions of the components of FIG. 5 having the same names, the same functions, and the same effects as the components in FIG. 2 are omitted, those skilled in the art will appreciate the liquid crystal display of another exemplary embodiment of the present invention through the description of FIG. 2. It will be easy to understand. In addition, the components of FIG. 5 having the same name, the same function, and the same working effect as those in FIG. 2 will be referred to by the same reference numerals as in FIG.

The low gradation adaptive data compensator 22 selects pixel data of a lower gradation region having a varying size according to how much gradation values of pixel data included in the video data VDi are distributed from the data transmission line. Compensation rate according to distribution is compensated. For example, when most of the pixel data having a gradation value near the middle gradation level among the pixel data of one frame, the low gradation adaptive data compensator 22 is a lower half gradation region of the pixel data of the frame. The pixel data having the gray scale value of is compensated to be larger by the compensation rate corresponding to the pixel data ratio distributed in the area. In other words, the low gray scale adaptive data compensator 22 compensates the pixel data having the gray scale value of the lower 35% gray scale region with a larger compensation rate than the pixel data having the gray scale value of the other upper 65% gray scale region. The number of highlight pixels of bosangyul of the data difference between the non-stressed and bosangyul of the pixel data of the low gray level compensation higher gray level is a gray level value other than the number and the halftone area of the pixel data having a gray level of the halftone region pixel data and Is determined by the ratio of. In this case, the pixel data compensated by the low gradation adaptive data compensator 22 has a gamma characteristic (or gradation change characteristic) similar to that of VGC1 in FIG. 3. When there is a large amount of pixel data having the gray scale value of the upper gray scale region among the pixel data included in one frame, the low gray scale adaptive data compensator 22 determines that the pixel data having the gray scale value of the lower 30% gray scale region is higher than the rest. Compensation is performed at a compensation rate larger than that of pixel data having a gradation value of 70% gradation region. In this case, the pixel data output from the low gray scale adaptive data compensator 22 has the same gamma characteristic as that of VGC2 in FIG. 3. As another example, when there are many pixel data having the gray scale value of the lower gray scale region among the pixel data included in one frame, the low gray scale adaptive data compensator 22 has the gray scale value of the lower 40% gray scale region. The pixel data is compensated with a larger compensation rate than the pixel data having the gray scale value of the remaining upper 60% gray scale region. The pixel data compensated by the low gradation adaptive data compensator 22 has the same gamma characteristic as that of VGC3 in FIG. 3. The pixel data having any one of gamma characteristics such as VGC1 to VGC3 illustrated in FIG. 3 is converted into an analog type pixel driving signal by the data driver 14 and supplied to the liquid crystal panel 10, thereby providing a liquid crystal panel ( 10) Allow an image to be displayed on the screen. The pixel data of the lower gradation region that changes according to the gradation distribution of the pixel data is emphasized and compensated with a compensation rate different from the distribution ratio of the pixel data, thereby preventing deterioration of an image corresponding to the upper gradation in the image displayed on the liquid crystal panel 10. The lower gray level image may be highlighted-displayed. As a result, the image quality of the moving image displayed by the liquid crystal display device according to another embodiment of the present invention is improved.

FIG. 6 is a detailed block diagram illustrating the low gray scale adaptive data compensation unit 22 in FIG. 5 in detail. The low gradation adaptive data compensator 22 of FIG. 6 includes a matrix 110 for inputting video data from an external video source from the data transmission line DTL. The matrix 110 aligns the red, green, and blue pixel data sequentially input from the data transmission line DTL in parallel, and combines the aligned red, green, and blue pixel data to combine luminance pixel data and chromaticity pixel data. Create The luminance pixel data combined by the matrix 110 is supplied to the gradation distribution analyzer 112, and the combined luminance and chroma pixel data are supplied to the normal compensator 112 via the delay unit 126. The normal compensator 112 compensates the gradation value of the pixel data according to the luminance and chroma pixel data from the retarder 126 according to preset correction characteristics so that the pixel data has a linear gamma characteristic as in the LLC of FIG. 1A. To compensate.

The gradation distribution analyzer 114 analyzes the histogram of luminance pixel data for one frame and detects how much luminance pixel data is distributed in which gradation level region. In other words, the gradation distribution analyzer 114 detects the distribution gradation region and the distribution amount of luminance pixel data of one frame through histometry. The gradation distribution area and the distribution diagram analyzed by the gradation distribution analyzer 114 are supplied to the correction coefficient determiner 116. The compensation coefficient determiner 116 applies a sigmoid function to the distribution gradation region and the distribution amount of the luminance pixel data from the gradation distribution analyzer 114 to emphasize and size the lower gradation region of the pixel data to be compensated for. Calculate the reward rate. The enhancement gradation region size and the enhancement compensation ratio determined by the compensation coefficient determination unit 116 are input to the low gradation emphasis unit 118. The low gray level enhancement unit 118 compensates the pixel data of the gray level value of the highlighted gray level region among the first-highlighted luminance and chrominance pixel data from the normal compensator 112 as high as the compensation ratio. The low gradation luminance and chroma pixel data highlighted by the low gradation emphasis unit 118 is supplied to the selection unit 120.

The selector 120 selectively transmits normal compensated luminance and chroma pixel data from the normal compensator 112 and low gray scale luminance and chroma pixel data from the low gray scale emphasis 118 toward the inverse matrix 124. do. The selection control unit 122 controls the selection operation of the selection unit 120 in response to the size of the luminance pixel data from the matrix 110 and the enhancement gradation region from the correction coefficient determination unit 116. When the luminance pixel data has a gray scale value included in the emphasis gray scale region, the selection controller 122 may select the selection unit so that the luminance and chroma pixel data low-graded highlighted by the low gray scale emphasis unit 118 are supplied to the inverse matrix 124. 120). On the contrary, when the luminance pixel data has a gradation value outside of the highlighted gradation region, the selection control unit 122 selects the luminance and chroma pixel data normally compensated by the normal compensation unit 112 to be supplied to the inverse matrix 124. The unit 120 is controlled. As a result, the selector 120 causes the low gradation highlighted luminance and chroma pixel data to be mixed with the normal compensated luminance and chroma pixel data. As shown in FIG. 3, the luminance and chroma pixel data mixed by the selector 120 has a luminance and chroma pixel data of a lower gray scale region that varies according to the gray scale distribution of the luminance pixel data. Has a gamma characteristic compensated for.

The inverse mattress 124 reverse-combines the luminance and chroma pixel data by the selector 120 to restore the red, green, and blue pixel data. The inversely combined red, green, and blue pixel data in inverse matrix 124 is sequentially supplied to data driver 14 of FIG. It is connected between the matrix 110 and the normal compensator 112 to delay the luminance and chroma pixel data to be transmitted from the matrix 110 toward the normal compensator 112. The retarder 126 causes the luminance and chroma pixel data supplied to the normal compensation unit 112 to be synchronized with the signal supplied from the gradation distribution analyzer 114 to the correction coefficient determiner 116. The delay period of the delay unit 126 corresponds to a period of one vertical synchronization signal (that is, one frame period) which is a propagation delay time in the gray scale distribution analyzer 114.

As described above, in the liquid crystal display according to the present invention, the pixel data of the lower gradation region that changes according to the gradation distribution of the pixel data is emphasized and compensated with a compensation ratio different from the distribution of the pixel data. In the image displayed on the liquid crystal panel, the image of the lower gray level may be highlighted-displayed while preventing degradation of the image corresponding to the upper gray level. As a result, the image quality of the moving image displayed by the liquid crystal display device according to the present invention is improved.

As described above, the present invention has been described with reference to the embodiments shown in the drawings, which are merely exemplary, and a person of ordinary skill in the art without departing from the spirit and scope of the present invention. It will be apparent that various modifications, changes, and equivalent other embodiments are possible. Accordingly, the scope of the present invention to be protected should be defined by the appended claims.

Claims (4)

A liquid crystal panel; An input unit for inputting video data; A data driver for supplying pixel driving signals input by the pixels on the liquid crystal panel by one line in response to video data from the input unit; And According to how many gray levels of pixel data included in the video data from the input unit are distributed around which gray level, the gamma voltage set which causes the size and the compensation rate of the low gray area of the pixel data to be emphasized to be changed is changed. A low gradation adaptive gamma voltage generator for supplying a driver, The low gradation adaptive gamma voltage generator includes a gradation distribution analyzer for detecting a distribution gradation region and a distribution map in which pixel data of one frame is distributed, and a distributed gradation region and a distribution diagram and a sigmoid detected by the gradation distribution analyzer. Using a function to generate a correction coefficient determiner for determining the gamma characteristics of the lower gradation region and emphasis compensation ratio of the pixel data to be compensated for compensation, and a gamma voltage set corresponding to the gamma characteristics determined by the correction coefficient determiner 102. And a programmable gamma voltage generator configured to supply the data driver to the data driver. delete A liquid crystal panel; An input unit for inputting video data; A data driver for supplying pixel driving signals input by the pixels on the liquid crystal panel by one line in response to video data from the input unit; And Low gradation adaptive data compensation for compensating a compensation ratio according to a distribution rate of pixel data of a lower gradation region of a size varying depending on how much gradation values of pixel data included in video data to be transmitted to the data driver are distributed near which gradation level Including wealth, The low gradation adaptive data compensator is a normal compensator for compensating a gradation value according to a preset correction characteristic of a matrix combining a luminance component and a chromaticity component from video data from the input unit, and luminance and chroma pixel data from the matrix. And a gradation distribution analyzer for detecting a gradation region and a distribution degree at which the gradation values of the luminance components from the matrix are distributed, and a sigmoid function to the distribution gradation region and the distribution amount of luminance pixel data from the gradation distribution analyzer. A compensation coefficient determiner that calculates a size and an enhancement compensation rate of the lower gray scale region of the pixel data to be emphasized compensated, and an enhanced gray scale region determined by the compensation coefficient determiner among the first-weighted luminance and chrominance pixel data from the normal compensator. To compensate the pixel data of the gradation value as high as the compensation ratio A low gradation enhancement section, a selection section for selectively transferring low gradation luminance and chroma pixel data highlighted by the low gradation enhancement section and normal compensated luminance and chroma pixel data from the normal compensation section toward an inverse matrix; And an inverse matrix for inversely combining video data from luminance and chroma pixel data from a selection unit and supplying the reverse data to the data driver. delete

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