Patent Publication Number: US-2016232859-A1

Title: Display apparatus and method of driving the same

Description:
This application claims priority from and the all benefits accruing under 35 U.S.C. §119 from an application earlier filed in the Korean Patent Office as Korean Patent Application No. 10-2015-0021014 filed on Feb. 11, 2015, which is hereby incorporated by reference for all purposes as if fully set forth herein. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a display apparatus and a method of driving the display apparatus. More particularly, example embodiments of the present invention relate to a display apparatus for improving a display quality and a method of driving the display apparatus. 
     2. Description of the Related Art 
     A liquid crystal display (“LCD”) apparatus includes an LCD panel and a driver apparatus configured to drive the LCD panel. The LCD panel includes a plurality of data lines and a plurality of gate lines crossing the data lines. The data lines and the gate lines may define a plurality of pixels. 
     The driver apparatus includes a gate driver configured to output a gate signal to a gate line and a data driver configured to output a data signal to a data line. The driver apparatus may drive the LCD panel in an inversion mode to prevent the LCD panel from being damaged. In the inversion mode, the polarity of a data voltage applied to a pixel may be reversed. 
     In the LCD apparatus, a display defect such as a vertical line may occur by a pixel connection structure and a process deviation. 
     SUMMARY OF THE INVENTION 
     Exemplary embodiments of the present invention provide a display apparatus for improving a display quality. 
     Exemplary embodiments of the present invention provide a method of driving the display apparatus. 
     According to an exemplary embodiment of the present invention, there is provided a display apparatus. The display apparatus includes a display panel comprising a plurality of color sub-pixels which is arranged as a plurality of sub-pixel columns and a plurality of sub-pixel rows, a first pixel column and a second pixel column which comprise a plurality of sub-pixel columns, a luminance controller configured to correct color grayscale data of at least one color sub-pixel included in at least one of the first and second pixel columns by 1-grayscale based on a luminance difference between the first and second pixel columns, and a data driver configured to convert the color grayscale data of the color sub-pixel to a data voltage and to provide the display panel with the data voltage. 
     In an exemplary embodiment, color sub-pixels in a sub-pixel row may be alternately connected to an upper gate line disposed at an upper side of the sub-pixel row and a lower gate line disposed at a lower side of the sub-pixel row, the first pixel column may include color sub-pixels of an even number which are connected to corresponding upper gate lines and consecutively arranged, and the second pixel column may include color sub-pixels of an even number which are connected to corresponding lower gate lines and consecutively arranged. 
     In an exemplary embodiment, the luminance difference may correspond to a grayscale smaller than 1-grayscale. 
     In an exemplary embodiment, the color sub-pixels may include red, green, blue and white sub-pixels. 
     In an exemplary embodiment, the luminance controller may determine at least one of red, green, blue and white grayscale data of the red, green, blue and white sub-pixels so as to compensate for the luminance difference based on a luminance proportion of the red, green, blue and white colors. 
     In an exemplary embodiment, the luminance controller may be configured to correct one of red, green, blue and white grayscale data of the red, green, blue and white sub-pixels in the first pixel column by 1-grayscale, and not to correct red, green, blue and white grayscale data of the red, green, blue and white sub-pixels in the second pixel column. 
     In an exemplary embodiment, the luminance controller may be configured to correct one of red, green, blue and white grayscale data of the red, green, blue and white sub-pixels in the second pixel column by 1-grayscale, and not to correct red, green, blue and white grayscale data of the red, green, blue and white sub-pixels in the first pixel column. 
     In an exemplary embodiment, the luminance controller may be configured to correct color grayscale data of half of a predetermined color sub-pixel in the first pixel column by 1-grayscale, and to correct color grayscale data of half of the predetermined color sub-pixel in the second pixel column by 1-grayscale. 
     In an exemplary embodiment, the luminance controller may be configured to correct white grayscale data of the white sub-pixels in the first pixel column by 1-grayscale, and not to correct red, green, blue and white grayscale data of the red, green, blue and white sub-pixels in the second pixel column. 
     In an exemplary embodiment, the luminance controller may be configured to correct white grayscale data of the white sub-pixels in the second pixel column by 1-grayscale, and not to correct red, green, blue and white grayscale data of the red, green, blue and white sub-pixels in the first pixel column. 
     In an exemplary embodiment, the luminance controller may be configured to correct white grayscale data of half of the white sub-pixels in the first pixel column by 1-grayscale, and to correct white grayscale data of half of the white sub-pixels in the second pixel column by 1-grayscale. 
     According to an exemplary embodiment of the present invention, there is provided a method of driving the display apparatus. The method includes correcting color grayscale data of at least one color sub-pixel included in at least one of first and second pixel columns by 1-grayscale based on a luminance difference between the first and second pixel columns. A display panel comprises a plurality of color sub-pixels which is arranged as a plurality of sub-pixel columns and a plurality of sub-pixel rows. Each of the first and second pixel columns comprises a plurality of sub-pixel columns, and converts the color grayscale data of the color sub-pixel to a data voltage to provide the display panel with the data voltage. 
     In an exemplary embodiment, color sub-pixels in a sub-pixel row may be alternately connected to an upper gate line disposed at an upper side of the sub-pixel row and a lower gate line disposed at a lower side of the sub-pixel row. The first pixel column may include color sub-pixels of an even number which are connected to corresponding upper gate lines and consecutively arranged, and the second pixel column may include color sub-pixels of an even number which are connected to corresponding lower gate lines and consecutively arranged. 
     In an exemplary embodiment, the luminance difference may correspond to a grayscale smaller than 1-grayscale. 
     In an exemplary embodiment, the method may further include correcting one of red, green, blue and white grayscale data of the red, green, blue and white sub-pixels in the first pixel column by 1-grayscale, and not to correcting red, green, blue and white grayscale data of the red, green, blue and white sub-pixels in the second pixel column. 
     In an exemplary embodiment, the method may further include correcting one of red, green, blue and white grayscale data of the red, green, blue and white sub-pixels in the second pixel column by 1-grayscale, and not to correcting red, green, blue and white grayscale data of the red, green, blue and white sub-pixels in the first pixel column. 
     In an exemplary embodiment, the method may further include correcting color grayscale data of half of a predetermined color sub-pixel in the first pixel column by 1-grayscale, and correcting color grayscale data of half of the predetermined color sub-pixel in the second pixel column by 1-grayscale. 
     In an exemplary embodiment, the method may further include correcting white grayscale data of the white sub-pixels in the first pixel column by 1-grayscale, and not correcting red, green, blue and white grayscale data of the red, green, blue and white sub-pixels in the second pixel column. 
     In an exemplary embodiment, the method may further include correcting white grayscale data of the white sub-pixels in the second pixel column by 1-grayscale, and not to correcting red, green, blue and white grayscale data of the red, green, blue and white sub-pixels in the first pixel column. 
     In an exemplary embodiment, the method may further include correcting white grayscale data of half of the white sub-pixels in the first pixel column by 1-grayscale, and correcting white grayscale data of half of the white sub-pixels in the second pixel column by 1-grayscale. 
     According to the present invention, the vertical line defect which corresponds to the luminance difference between the first pixel column, including the color sub-pixels connected to the upper gate line, and the second pixel column, including the color sub-pixels connected to the lower gate line, may be decreased or eliminated. In addition, the color grayscale data of at least one of the red, green, blue and white color sub-pixels included in at least one of the first pixel column and the second pixel column are corrected by the grayscale less than 1-grayscale such that the luminance difference may be decreased or eliminated. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the invention, and many of the attendant advantages thereof, will be readily apparent as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings, in which like reference symbols indicate the same or similar components, wherein: 
         FIG. 1  is a block diagram illustrating a display apparatus according to an exemplary embodiment of the invention; 
         FIG. 2  is a conceptual diagram illustrating a display panel of  FIG. 1 ; 
         FIGS. 3A to 3D  are conceptual diagrams illustrating a luminance difference between first and second pixel columns according to a comparative example embodiment; 
         FIG. 4  is a conceptual diagram illustrating a unit cell for compensating a luminance according to a luminance controller of  FIG. 1 ; 
         FIG. 5  is a conceptual diagram illustrating a method of correcting the luminance difference according to an exemplary embodiment of the invention; 
         FIG. 6  is a conceptual diagram illustrating a method of correcting the luminance difference according to an exemplary embodiment of the invention; and 
         FIG. 7  is a conceptual diagram illustrating a method of correcting the luminance difference according to an exemplary embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, the present invention will be explained in detail with reference to the accompanying drawings. 
       FIG. 1  is a block diagram illustrating a display apparatus according to an exemplary embodiment of the invention, and  FIG. 2  is a conceptual diagram illustrating a display panel of  FIG. 1 . 
     Referring to  FIGS. 1 and 2 , the display apparatus may include a display panel  100  and a panel driving unit  200 . 
     The display panel  100  may include a plurality of data lines DL, a plurality of gate lines GL and a plurality of pixels P. 
     The plurality of data lines DL extends in a first direction D 1  and is arranged in a second direction D 2  crossing the first direction D 1 . 
     The plurality of gate lines GL extends in the second direction D 2  and is arranged in the first direction D 1 . 
     Each of the pixels P may include color sub-pixels of an even number. For example, a pixel P includes a red sub-pixel R, a green sub-pixel G, a blue sub-pixel B and a white sub-pixel W. A color sub-pixel is defined by first and second sides opposite to each other in the first direction D 1  and third and fourth sides opposite to each other in the second direction D 2 . 
     The color sub-pixels are connected to a data line adjacent to one of the first and second sides, and are alternately connected to both gate lines adjacent to the third and fourth sides. 
     For example, as shown in  FIG. 2 , a sub-pixel row is defined by color sub-pixels which are arranged in the first direction D 1  and a sub-pixel column is defined by color sub-pixels which are arranged in the second direction D 2 . 
     A first sub-pixel row SPR 1  includes a first red sub-pixel R 11 , a first green sub-pixel G 11 , a first blue sub-pixel B 11 , a first white sub-pixel W 11 , a second red sub-pixel R 12 , a second green sub-pixel G 12 , a second blue sub-pixel B 12 , a second white sub-pixel W 12 , a third red sub-pixel R 13 , a third green sub-pixel G 13 , a third blue sub-pixel B 13  and a third white sub-pixel W 13 . 
     The first red sub-pixel R 11  is connected to a second gate line GL 2 , which is the lower gate line of both gate lines and to a first data line DL 1 . The first green sub-pixel G 11  is connected to a first gate line GL 1 , which is the upper gate line of both gate lines, and to a second data line DL 2 . The first blue sub-pixel B 11  is connected to the second gate line GL 2  and to a third data line DL 3 . The first white sub-pixel W 11  is connected to the first gate line GL 1  and to a fourth data line DL 4 . 
     The second red sub-pixel R 12  is connected to the first gate line GL 1 , which is the upper gate line of both gate lines, and to a fifth data line DL 5 . The second green sub-pixel G 12  is connected to the second gate line GL 2  and to a sixth data line DL 6 . The second blue sub-pixel B 12  is connected to the first gate line GL 1  and to a seventh data line DL 7 . The second white sub-pixel W 12  is connected to the second gate line GL 2  and to an eighth data line DL 8 . 
     The third red sub-pixel R 13  is connected to the second gate line GL 2 , which is the lower gate line of both gate lines, and to a ninth data line DL 9 . The third green sub-pixel G 13  is connected to the first gate line GL 1  and to a tenth data line DL 10 . The third blue sub-pixel B 13  is connected to the second gate line GL 2  and to an eleventh data line DL 11 . The third white sub-pixel W 13  is connected to the first gate line GL 1  and to a twelfth data line DL 12 . 
     The second sub-pixel row SPR 2  includes a fourth blue sub-pixel B 21 , a fourth white sub-pixel W 21 , a fourth red sub-pixel R 21 , a fourth green sub-pixel G 21 , a fifth blue sub-pixel B 22 , a fifth white sub-pixel W 22 , a fifth red sub-pixel R 22 , a fifth green sub-pixel G 22 , a sixth blue sub-pixel B 23 , a sixth white sub-pixel W 23 , a sixth red sub-pixel R 23  and a sixth green sub-pixel G 23 . 
     The fourth blue sub-pixel B 21  is connected to a third gate line GL 3 , which is the lower gate line of both gate lines, and to the first data line DL 1 . The fourth white sub-pixel W 21  is connected to the second gate line GL 2 , which is the upper gate line of both gate lines, and to the second data line DL 2 . The fourth red sub-pixel R 21  is connected to the third gate line GL 3  and to the third data line DL 3 . The fourth green sub-pixel G 21  is connected to the second gate line GL 2  and to the fourth data line DL 4 . 
     The fifth blue sub-pixel B 22  is connected to the second gate line GL 2 , which is the upper gate line of both gate lines, and to the fifth data line DL 5 . The fifth white sub-pixel W 22  is connected to the third gate line GL 3  and to the sixth data line DL 6 . The fifth red sub-pixel R 22  is connected to the second gate line GL 2  and to the seventh data line DL 7 . The fifth green sub-pixel G 22  is connected to the third gate line GL 3  and to the eighth data line DL 8 . 
     The sixth blue sub-pixel B 23  is connected to the third gate line GL 3 , which is the lower gate line of both gate lines, and to the ninth data line DL 9 . The sixth white sub-pixel W 23  is connected to the second gate line GL 2  and to the tenth data line DL 10 . The sixth red sub-pixel R 23  is connected to the third gate line GL 3  and to the eleventh data line DL 11 . The sixth green sub-pixel G 23  is connected to the second gate line GL 2  and to the twelfth data line DL 12 . 
     As shown in  FIG. 2 , for example, color sub-pixels in a first sub-pixel row SPR 1  may be alternately connected to the upper and lower gate lines. However, the second red sub-pixel R 12 , adjacent to the first white sub-pixel W 11 , is connected to the first gate line GL 1  which is the upper gate line such as the first white sub-pixel W 11 . In addition, the third red sub-pixel R 13 , adjacent to the second white sub-pixel W 12 , is connected to the second gate line GL 2  which is the lower gate line such as the second white sub-pixel W 12 . 
     As described above, by a sub-pixel structure and a process deviation, a first pixel column PC_U, including the first white sub-pixel W 11  and the second red sub-pixel R 12 , displays an image of a relatively high luminance, and a second pixel column PC_L, including the second white sub-pixel W 12  and the third red sub-pixel R 13 , displays an image of a relatively low luminance. Thus, an image displayed on the display panel  100  may have a vertical line defect. 
     The panel driving unit  200  of  FIG. 1  may include a data converter  210 , a luminance controller  230 , a timing controller  250 , a data driver  270  and a gate driver  290 . 
     The data converter  210  is configured to convert first color grayscale data received form an external device to second color grayscale data in correspondence to an RGBW sub-pixel structure of the display panel  100 . For example, the first color grayscale data include red, green and blue grayscale data DS 1  and the second color grayscale data include red, green, blue and white grayscale data DS 2 . 
     The luminance controller  230  is configured to compensate for a luminance difference between images which are respectively displayed on the first pixel column PC_U and the second pixel column PC_L. The images displayed on the first and second pixel columns PC_U and PC_L, respectively, may have a grayscale difference of less than or equal to 1-grayscale. 
     The luminance controller  230  is configured to correct color grayscale data of at least one color of red, green, blue and white sub pixels included in at least one of the first and second pixel columns PC_U and PC_L (DS 3 ), respectively, 
     In addition, the luminance controller  230  is configured to correct color grayscale data in correspondence to at least one color of red, green, blue and white sub pixels included in all of the first and second pixel columns PC_U and PC_L (DS 3 ), respectively, 
     The timing controller  250  is configured to receive an original control signal OCS from the external device. The timing controller  250  is configured to generate a timing control signal for controlling a driving timing of the display panel  100  using the received original control signal OCS. The timing control signal may include a data control signal DCS for controlling a driving timing of the data driver  270  and a gate control signal GCS for controlling a driving timing of the gate driver  290 . 
     The data control signal DCS may include a horizontal synch signal, a vertical synch signal, a load signal, an inversion control signal, a dot clock signal, and so on. The gate control signal GCS may include a vertical start signal, at least one gate clock signal, a gate output enable signal and so on. 
     In addition, the timing controller  250  is configured to correct red, green, blue and white grayscale data (DS 3 ) provided by the luminance controller  230  using various algorithms (DS 4 ). The corrected red, green, blue and white grayscale data (DS 4 ) is provides to the data driver  270 . 
     The data driver  270  is configured to convert the red, green, blue and white grayscale data (DS 4 ) provided by the timing controller  250  into red, green, blue and white data voltages which are analog voltages, and to output the red, green, blue and white data voltages of a positive polarity (+) or a negative polarity (−) based on the inversion control signal. 
     According to the exemplary embodiment, during a frame, color sub-pixels connected to the first and second data lines DL 1  and DL 2 , respectively, receive the data voltage of the positive polarity (+), and color sub-pixels connected to the third and fourth data lines DL 3  and DL 4 , respectively, receive the data voltage of the negative polarity (−). 
     As described above, the data driver  270  is configured to output the data voltages of a repetitive polarity by four data lines to the plurality of data lines of the display panel  100 . 
     The gate driver  290  is configured to generate a gate signal having a gate-on voltage and a gate-off voltage based on the gate control signal, and to output the gate signal to the plurality of gate lines of the display panel  100  along a scan direction. 
       FIGS. 3A to 3D  are conceptual diagrams illustrating a luminance difference between first and second pixel columns according to a comparative example embodiment. 
       FIG. 3A  is a conceptual diagram illustrating when color sub-pixels connected to the lower gate lines as shown in  FIG. 2  are driven, and  FIG. 3B  is a conceptual diagram illustrating when color sub-pixels connected to the upper gate lines, as shown in  FIG. 2 , are driven. 
     Referring to  FIG. 3A , an image displayed on the color sub-pixels SP 1  in the second pixel column PC_L, which are successively connected to the lower gate lines, has a low luminance lower than an image displayed on color sub-pixels SP 2  which are connected to the lower gate lines and adjacent to the color sub-pixels connected to the upper gate lines. 
     Referring to  FIG. 3B , an image displayed on the color sub-pixels SP 3  in the first pixel column PC_U, which are successively connected to the upper gate lines, has a high luminance higher than an image displayed on color sub-pixels SP 4  which are connected to the upper gate lines and adjacent to the color sub-pixels connected to the lower gate lines. 
       FIG. 3C  is a graph diagram illustrating a luminance difference between the first and second pixel columns PC_U and PC_L, respectively, according to a grayscale, and  FIG. 3D  is a graph diagram illustrating a grayscale difference between the first and second pixel columns PC_U and PC_L, respectively, according to a grayscale. 
     Referring to  FIGS. 3C and 3D , the luminance difference between the first and second pixel columns PC_U and PC_L, respectively, is the largest luminance difference in a middle grayscale range. When the luminance difference is converted into the grayscale difference, the grayscale difference between the first and second pixel columns PC_U and PC_L, respectively, has a grayscale difference being smaller than 1-grayscale in the middle grayscale range. 
     The grayscale difference between the first and second pixel columns PC_U and PC_L, respectively, is more than about 0.5-grayscale and less than about 1-grayscale in a range which is from about 40-grayscale to about 160-grayscale. The grayscale difference between the first and second pixel columns PC_U and PC_L, respectively, is less than about 0.5 grayscale in a range which is less than or equal to about 40 grayscale and more than or equal to about 160 grayscale. 
     Thus, when the grayscale difference between the first and second pixel columns PC_U and PC_L, respectively, may be compensated, the luminance difference such as the vertical line defect may be compensated. 
     According to the exemplary embodiment, a grayscale correction value for correcting grayscale date of the pixel may be less than 1-grayscale based on a luminance proportion of red, green, blue and white colors affecting the luminance. 
     The luminance proportion (R:G:B:W) of the red, green, blue and white colors is about (2:7:1:10). When the red grayscale data increase by 1-grayscale, the luminance of the pixel may be increased in correspondence to about (2/20)-grayscale that is 0.1-grayscale. When the green grayscale data increase by 1-grayscale, the luminance of the pixel may be increased in correspondence to about (7/20)-grayscale that is 0.35-grayscale. When the blue grayscale data increase by 1-grayscale, the luminance of the pixel may be increased in correspondence to about (1/20)-grayscale that is 0.05-grayscale. When the white grayscale data increase 1-grayscale, the luminance of the pixel may be increased in correspondence to about (10/20)-grayscale that is 0.5 grayscale. 
     However, when the red grayscale data decrease by 1-grayscale, the luminance of the pixel may be decreased in correspondence to about 0.1-grayscale. When the green grayscale data decrease by 1-grayscale, the luminance of the pixel may be decreased in correspondence to about 0.35-grayscale. When the blue grayscale data decrease by 1-grayscale, the luminance of the pixel may be decreased in correspondence to about 0.05-grayscale. When the white grayscale data decrease by 1-grayscale, the luminance of the pixel may be decreased in correspondence to about 0.5-grayscale. 
       FIG. 4  is a conceptual diagram illustrating a unit cell for compensating a luminance according to a luminance controller of  FIG. 1 . 
     Referring to  FIG. 4 , the unit cell UC includes color sub-pixels which are arranged in a matrix shape such as an 8×2 matrix type. The unit cell UC includes a first red sub-pixel R 1 , a first green sub-pixel G 1 , a first blue sub-pixel B 1 , a first white sub-pixel W 1 , a second red sub-pixel R 2 , a second green sub-pixel G 2 , a second blue sub-pixel B 2  and a second white sub-pixel W 2  which are arranged in a first direction D 1 . The first red sub-pixel R 1  is connected to a lower gate line L, the first green sub-pixel G 1  is connected to an upper gate line U, the first blue sub-pixel B 1  is connected to the lower gate line L, the first white sub-pixel W 1  is connected to the upper gate line U, the second red sub-pixel R 2  is connected to the upper gate line U, the second green sub-pixel G 2  is connected to the lower gate line, the second blue sub-pixel B 2  is connected to the upper gate line, and the second white sub-pixel W 2  is connected to the lower gate line. 
     In addition, the unit cell UC includes a third blue sub-pixel B 3 , a third white sub-pixel W 3 , a third red sub-pixel R 3 , a third green sub-pixel G 3 , a fourth blue sub-pixel B 4 , a fourth white sub-pixel W 4 , a fourth red sub-pixel R 4  and a fourth green sub-pixel G 4 . The third blue sub-pixel B 3  is adjacent to the first red sub-pixel R 1  in a second direction D 2  crossing the first direction D 1  and is connected to a lower gate line L, the third white sub-pixel W 3  is adjacent to the first green sub-pixel G 1  in the second direction D 2  and is connected to an upper gate line U, the third red sub-pixel R 3  is adjacent to the first blue sub-pixel B 1  in the second direction D 2  and is connected to the lower gate line L, the third green sub-pixel G 3  is adjacent to the first white sub-pixel W 1  in the second direction D 2  and is connected to the upper gate line U, the fourth blue sub-pixel B 4  is adjacent to the second red sub-pixel R 2  in the second direction D 2  and is connected to the upper gate line U, the fourth white sub-pixel W 4  is adjacent to the second green sub-pixel G 2  in the second direction D 2  and connected to the lower gate line, the fourth red sub-pixel R 4  is adjacent to the second blue sub-pixel B 2  in the second direction D 2  and is connected to the upper gate line U, and the fourth green sub-pixel G 4  is adjacent to the second white sub-pixel W 2  in the second direction D 2  and is connected to the fourth green sub-pixel G 4 . 
     As shown in  FIG. 4 , the unit cell UC includes a first unit pixel UP 1  including the second red, third green, fourth blue and first white sub-pixels R 2 , G 3 , B 4  and W 1 , respectively, which are connected to the upper gate line and a second unit pixel UP 2  including the first red, fourth green, third blue and second white sub-pixels R 1 , G 4 , B 3  and W 2 , respectively, which are connected to the lower gate line. 
     The first unit pixel UP 1  corresponds to the first pixel column PC_U shown in  FIG. 2  and the second unit pixel UP 2  corresponds to the second pixel column PC_L shown in  FIG. 2 . The first pixel column PC_U displays a relatively high luminance and the second pixel column PC_L displays a relatively low luminance. Thus, in order to compensate for the luminance difference between the first and second pixel columns PC_U and PC_L, respectively, first red, at least one of first green, first blue and first white grayscale correction values r 1 , g 1 , b 1  and w 1 , respectively, is determined for decreasing the luminance of the first unit pixel UP 1 , and at least one of second red, second green, second blue and second white grayscale correction values r 2 , g 2 , b 2  and w 2 , respectively, are determined for increasing the luminance of the second unit pixel UP 2 . 
     For example, a method of calculating the grayscale correction values may include measuring the luminance difference between the first and second pixel columns PC_U and PC_L, respectively, according to the display panel, calculating the grayscale difference in correspondence to the luminance difference between first and second unit pixels UP 1  and UP 2 , respectively, and calculating a grayscale correction value for compensating color grayscale data of at least one of the red, green, blue and white sub-pixels in the first and second unit pixels UP 1  and UP 2 , respectively, based on the grayscale difference. 
     The luminance controller  230  as shown in  FIG. 1  is configured to store the grayscale correction values described above. The luminance controller  230  is configured to correct the color grayscale data of the color sub pixel included in at least one of the first and second pixel columns PC_U and PC_L, respectively, using the grayscale correction value so that the luminance difference between the first and second pixel columns PC_U and PC_L, respectively, may be compensated. 
       FIG. 5  is a conceptual diagram illustrating a method of correcting the luminance difference according to an exemplary embodiment of the invention. 
     Referring to  FIG. 5 , when the grayscale difference corresponding to the luminance difference between the first and second pixel columns PC_U and PC_L, respectively, is 0.5-grayscale, the luminance of the first pixel column PC_U decrease so as to compensate for the grayscale difference of 0.5 grayscale. 
     According to the exemplary embodiment, the luminance controller  230  shown in  FIG. 1  includes a plurality of grayscale correction values for compensating a 0.5-grayscale difference between the first and second pixel columns PC_U and PC_L, respectively, calculated based on the luminance proportion (2:7:1:10) of the red, green, blue and white colors. As shown in  FIG. 4 , the plurality of grayscale correction values includes first red, first green, first blue and first white grayscale correction values r 1 , g 1 , b 1  and w 1 , respectively, corresponding to the first unit pixel UP 1  and second red, second green, second blue and second white grayscale correction values r 2 , g 2 , b 2  and w 2 , respectively, corresponding to the second unit pixel UP 2 . 
     Referring to  FIG. 4 , according to the exemplary embodiment, in order that the high luminance of the first pixel column PC_U decrease by 0.5-grayscale, the white grayscale data of the white sub-pixel included in the first unit pixel UP 1  are decreased by 1-grayscale. The first white grayscale correction value w 1  is determined to be “−1”. Then, the first red, first green and first blue coefficient correction values r 1 , g 1  and b 1 , respectively, corresponding to the first unit pixel UP 1  and the second red, second green, second blue and second white coefficient correction values r 2 , g 2 , b 2  and w 2 , respectively, corresponding to the second unit pixel UP 2  are determined to be “0”. 
     Thus, as shown in  FIG. 5 , the white sub-pixels W included in the first pixel column PC_U of the display panel have a luminance which is decreased by 1-grayscale. Based on the luminance proportion (2:7:1:10), the first pixel column PC_U has the luminance which is decreased by 0.5-grayscale and thus the luminance difference between the first and second pixel columns PC_U and PC_L, respectively, may be decreased or eliminated. 
       FIG. 6  is a conceptual diagram illustrating a method of correcting the luminance difference according to an exemplary embodiment of the invention. 
     Referring to  FIG. 6 , when the grayscale difference corresponding to the luminance difference between the first and second pixel columns PC_U and PC_L, respectively, is 0.5-grayscale, the luminance of the second pixel column PC_L increases to compensate for the grayscale difference of 0.5-grayscale. 
     Referring to  FIG. 4 , according to the exemplary embodiment, in order that the low luminance of the second pixel column PC_L increase by 0.5-grayscale, the white grayscale data of the white sub-pixel included in the second unit pixel UP 2  are increased by 1-grayscale. Thus, the second white grayscale correction value w 2  is determined to be “+1”. Then, the second red, second green and second blue coefficient correction values r 2 , g 2  and b 2 , respectively, corresponding to the second unit pixel UP 2  and the first red, first green, first blue and first white coefficient correction values r 1 , g 1 , b 1  and w 1 , respectively, corresponding to the first unit pixel UP 1  are determined to be “0”. 
     Thus, as shown in  FIG. 6 , the white sub-pixels W included in the second pixel column PC_L of the display panel have a luminance which is increased by 1-grayscale. Based on the luminance proportion (2:7:1:10), the second pixel column PC_L has the luminance which is increased by 0.5-grayscale, and thus the luminance difference between the first and second pixel columns PC_U and PC_L, respectively, may be decreased or eliminated. 
     Table 1 represents grayscale correction values respectively corresponding to various luminance differences according to various exemplary embodiments as follows: 
     
       
         
           
               
             
               
                 TABLE 1 
               
               
                   
               
             
            
               
                 
                   
                     
                     
                         
                         
                     
                   
                 
               
               
                   
               
            
           
         
       
     
     Referring to Table 1, each of exemplary embodiments #1A and #1B has a 0.35-grayscale difference which is a luminance difference between the first and second pixel columns PC_U and PC_L, respectively. According to the exemplary embodiments #1A and #1B, green grayscale data are corrected to compensate for the 0.35-grayscale difference based on the luminance proportion (2:7:1:10) of the red, green, blue and white colors. 
     Referring to  FIG. 4 , according to the exemplary embodiment #1A, green grayscale data of the green sub-pixel included in the first unit pixel UP 1  are decreased by 1-grayscale in order that the luminance of the first pixel column PC_U having a high luminance decreases by 0.35-grayscale. Thus, the first green grayscale correction value g 1  is determined to be “−1”. Then, the first red, first blue and first white coefficient correction values r 1 , b 1  and w 1 , respectively, corresponding to the first unit pixel UP 1  and the second red, second green, second blue and second white coefficient correction values r 2 , g 2 , b 2  and w 2 , respectively, corresponding to the second unit pixel UP 2  are determined to be “0”. 
     Therefore, the green sub-pixel included in the first pixel column PC_U has a low luminance decreased by 1-grayscale and the first pixel column PC_U has a low luminance decreased by 0.35-grayscale. Thus, the luminance difference between the first and second pixel columns PC_U and PC_L, respectively, may be decreased or eliminated. 
     Referring to  FIG. 4 , according to the exemplary embodiment #1B, green grayscale data of the green sub-pixel included in the second unit pixel UP 2  are increased by 1-grayscale in order that the luminance of the second unit pixel UP 2  having a low luminance increases by the 0.35-grayscale. Thus, the second green grayscale correction value g 2  is determined to be “+1”. Then, the second red, second blue and second white coefficient correction values r 2 , b 2  and w 2 , respectively, corresponding to the second unit pixel UP 2  and the first red, first green, first blue and first white coefficient correction values r 1 , g 1 , b 1  and w 1 , respectively, corresponding to the first unit pixel UP 1  are determined to be “0”. 
     Therefore, the green sub-pixel included in the second pixel column PC_L has a high luminance increased by 1-grayscale and the second pixel column PC_L has a high luminance increased by 0.35-grayscale. Thus, the luminance difference between the first and second pixel columns PC_U and PC_L, respectively, may be decreased or eliminated. 
     Each of exemplary embodiments #2A and #2B has a 0.55-grayscale difference which is a luminance difference between the first and second pixel columns PC_U and PC_L, respectively. According to the exemplary embodiments #2A and #2B, green grayscale data are corrected to compensate for the 0.55-grayscale difference based on the luminance proportion (2:7:1:10) of the red, green, blue and white colors. 
     Referring to  FIG. 4 , according to the exemplary embodiment #2A, white and blue grayscale data of the white and blue pixels included in the first unit pixel UP 1  are decreased by 1-grayscale in order that the luminance of the first pixel column PC_U having a high luminance decreases by 0.55-grayscale. Thus, the first white and first blue grayscale correction values w 1  and b 1 , respectively, are determined to be “−1”. Then, the first red and first green coefficient correction values r 1  and g 1 , respectively, corresponding to the first unit pixel UP 1  and the second red, second green, second blue and second white coefficient correction values r 2 , g 2 , b 2  and w 2 , respectively, corresponding to the second unit pixel UP 2  are determined to be “0”. 
     Therefore, the white and blue sub-pixels included in the first pixel column PC_U have a low luminance decreased by 1-grayscale and the first pixel column PC_U has a low luminance decreased by 0.55-grayscale. Thus, the luminance difference between the first and second pixel columns PC_U and PC_L, respectively, may be decreased or eliminated. 
     Referring to  FIG. 4 , according to the exemplary embodiment #2B, white and blue grayscale data of the white and blue sub-pixels included in the second unit pixel UP 2  are increased by 1-grayscale in order that the luminance of the second unit pixel UP 2  having a low luminance increases by 0.55-grayscale. Thus, second white and second blue grayscale correction values w 2  and b 2 , respectively, are determined to be “+1”. Then, the second red and second green coefficient correction values r 2  and g 2 , respectively, corresponding to the second unit pixel UP 2  and the first red, first green, first blue and first white coefficient correction values r 1 , g 1 , b 1  and w 1 , respectively, corresponding to the first unit pixel UP 1  are determined to be “0”. 
     Therefore, the white and blue sub-pixels included in the second pixel column PC_L have a high luminance increased by 1-grayscale and the second pixel column PC_L has a high luminance increased by 0.55-grayscale. Thus, the luminance difference between the first and second pixel columns PC_U and PC_L, respectively, may be decreased or eliminated. 
     Each of exemplary embodiments #3A and #3B has a 0.65-grayscale difference which is a luminance difference between the first and second pixel columns PC_U and PC_L, respectively. According to the exemplary embodiments #3A and #3B, white, red and blue grayscale data are corrected to compensate for the 0.65-grayscale difference based on the luminance proportion (2:7:1:10) of the red, green, blue and white colors. 
     Referring to  FIG. 4 , according to the exemplary embodiment #3A, white, red and blue grayscale data of the white, red and blue pixels included in the first unit pixel UP 1  are decreased by 1-grayscale in order that the luminance of the first pixel column PC_U having a high luminance decreases by 0.65-grayscale. Thus, the first white, first red and first blue grayscale correction values w 1 , r 1  and b 1 , respectively, are determined to be “−1”. Then, the first green coefficient correction value g 1  corresponding to the first unit pixel UP 1  and the second red, second green, second blue and second white coefficient correction values r 2 , g 2 , b 2  and w 2 , respectively, corresponding to the second unit pixel UP 2  are determined to be “0”. 
     Therefore, the white, red and blue sub-pixels included in the first pixel column PC_U have a low luminance decreased by 1-grayscale and the first pixel column PC_U has a low luminance decreased by 0.65-grayscale. Thus, the luminance difference between the first and second pixel columns PC_U and PC_L, respectively, may be decreased or eliminated. 
     Referring to  FIG. 4 , according to the exemplary embodiment #3B, white, red and blue grayscale data of the white, red and blue sub-pixels included in the second unit pixel UP 2  are increased by 1-grayscale in order that the luminance of the second unit pixel UP 2  having a low luminance increases by 0.65-grayscale. Thus, the second white, second red and second blue grayscale correction value w 2 , r 2  and b 2 , respectively, are determined to be “+1”. Then, the second green coefficient correction value g 2  corresponding to the second unit pixel UP 2  and the first red, first green, first blue and first white coefficient correction values r 1 , g 1 , b 1  and w 1 , respectively, corresponding to the first unit pixel UP 1  are determined to be “0”. 
     Therefore, the white, red and blue sub-pixels included in the second pixel column PC_L have a high luminance increased by 1-grayscale and the second pixel column PC_L has a high luminance increased by 0.65-grayscale. Thus, the luminance difference between the first and second pixel columns PC_U and PC_L, respectively, may be decreased or eliminated. 
       FIG. 7  is a conceptual diagram illustrating a method of correcting the luminance difference according to an exemplary embodiment of the invention. 
     As described above, according to previous exemplary embodiments, the luminance of one of the first and second pixel columns PC_U and PC_L, respectively, is compensated for in order to compensate for the luminance difference between the first and second pixel columns PC_U and PC_L, respectively. However, according to an exemplary embodiment, luminance of all of the first and second pixel columns PC_U and PC_L, respectively, is compensated for in order to compensate for the luminance difference between the first and second pixel columns PC_U and PC_L, respectively. 
     For example, the first pixel column PC_U has a luminance higher by 0.25-grayscale than a normal luminance and the second pixel column PC_L has a luminance lower by 0.25-grayscale than the normal luminance. As described above, when the luminance difference between the first and second pixel columns PC_U and PC_L, respectively, is a 0.5-grayscale difference, the luminance of the first pixel column PC_U decreases by the 0.25-grayscale and the luminance of the first pixel column PC_L increases by the 0.25-grayscale according to the exemplary embodiment. 
     In order to decrease the luminance of the first pixel column PC_U by 0.25-grayscale, the luminance controller  230  shown in  FIG. 1  is configured to apply a first white grayscale correction value (w 1 =−1) to color grayscale data in correspondence to half of the white sub-pixels included in the first pixel column PC_U shown in  FIG. 5  for compensating for the luminance difference. Thus, the first pixel column PC_U has a luminance decreased by 0.25-grayscale. 
     In addition, in order to increase the luminance of the second pixel column PC_L by 0.25-grayscale, the luminance controller  230  shown in  FIG. 1  is configured to apply a second white grayscale correction value (w 2 =+1) to color grayscale data in correspondence to half of the white sub-pixels included in the second pixel column PC_L shown in  FIG. 6  for compensating the luminance difference. Thus, the first pixel column PC_U has a luminance increased by 0.25-grayscale. 
     Therefore, the luminance difference between the first and second luminance columns PC_U and PC_L, respectively, may be decreased or eliminated. 
     Although not shown in the figures, various luminance differences according to the previous exemplary embodiments may be decreased or eliminated by compensating for the luminance of all of the first and second luminance columns PC_U and PC_L, respectively, as described above relative to  FIG. 7 . 
     As described above, according to exemplary embodiments of the invention, the vertical line defect which corresponds to the luminance difference between the first pixel column, including the color sub-pixels, connected to the upper gate line, and the second pixel column, including the color sub-pixels connected to the lower gate line, may be decreased or eliminated. In addition, the color grayscale data of at least one of the red, green, blue and white color sub-pixels included in at least one of the first pixel column and the second pixel column are corrected by the grayscale less than 1-grayscale so that the luminance difference may be decreased or eliminated. 
     The foregoing is illustrative of the present invention and is not to be construed as limiting thereof. Although a few exemplary embodiments of the present invention have been described, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of the present invention. Accordingly, all such modifications are intended to be included within the scope of the present invention as defined by the claims. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents but also equivalent structures. Therefore, it is to be understood that the foregoing is illustrative of the present invention and is not to be construed as limited to the specific exemplary embodiments disclosed, and that modifications to the disclosed exemplary embodiments, as well as other exemplary embodiments, are intended to be included within the scope of the appended claims. The present invention is defined by the following claims, with equivalents of the claims to be included therein.