Patent Publication Number: US-9842550-B2

Title: Display device

Description:
CLAIM OF PRIORITY 
     This U.S. non-provisional patent application claims the priority of and all the benefits accruing under 35 U.S.C. §119 of Korean Patent Application No. 10-2014-0170683, filed on Dec. 2, 2014 in the Korean Intellectual Property Office (“KIPO”), the contents of which are hereby incorporated by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present disclosure relates to a display device capable of preventing a color stain from occurring. 
     Description of the Related Art 
     As one of flat panel displays, a liquid crystal display is widely used in various electric devices, such as a television set, a computer monitor, a notebook computer, a mobile phone, etc., to display an image. 
     The liquid crystal display controls intensity of an electric field applied to a liquid crystal material interposed between two substrates and an amount of light passing through the two substrates to display the image. The liquid crystal display includes a liquid crystal display panel displaying the image and a backlight unit providing the liquid crystal display panel with the light. 
     The backlight unit is classified into an edge-illumination type backlight unit and a direct-illumination type backlight unit according to a position of a light source thereof. The edge-illumination type backlight unit includes a light guide plate and the light source providing the light to a side surface of the light guide plate, and the direct-illumination type backlight unit includes a diffusion plate and a light source disposed under the diffusion plate. 
     SUMMARY OF THE INVENTION 
     The present disclosure provides a display device capable of preventing a color stain from occurring. 
     Embodiments of the inventive concept provide a display device including a backlight unit, a display panel, and a controller. The backlight unit comprises a first light source substrate comprising a plurality of first light sources arranged in a first direction and a second light source substrate disposed adjacent to the first light source substrate in a second direction and comprising a plurality of second light sources arranged in the first direction. The display panel is disposed to be spaced apart from the backlight unit in a third direction substantially perpendicular to the first and second direction and comprising an edge portion defined along at least one side thereof and a plurality of pixels. The controller generates an edge image data corresponding to a plurality of edge pixels disposed in the edge portion among the pixels, wherein the edge image data is generated on the basis of a first angle between the third direction and a first imaginary line connecting the edge pixels and the first light sources and a second angle between the third direction and a second imaginary line connecting the edge pixels and the second light sources 
     The edge portion is disposed in the second direction of the display panel, the display panel includes a center portion disposed adjacent to the edge portion in a fourth direction opposite to the second direction, the second light source substrate is disposed to correspond to the edge portion, and the first light source substrate is disposed adjacent to the second edge light source substrate in the fourth direction to correspond to the center portion. 
     The controller includes a compensation block, and the compensation block compensates for edge image signals corresponding to the edge pixels among image signals provided thereto from the outside on the basis of a compensation value (k 1 ) generated based on the first and second angles to generate edge compensation data and generates the edge image data using the edge compensation data. 
     The compensation value (k 1 ) is generated using cos 2 (⊖ 1 ) and cos 2 (⊖ 2 ), ⊖ 1  denotes the first angle, and ⊖ 2 denotes the second angle. 
     The compensation value (k 1 ) satisfies the following Equation of 
                 k   ⁢           ⁢   1     =       A   ⁡     (       f   ⁡     (     θ   2     )         f   ⁡     (     θ   1     )         )         1   Y         ,         
f(⊖ 1 ) is equal to cos 2 (⊖ 1 ), f(⊖ 2 ) is equal to cos 2 (⊖ 2 ), γ is a gamma tuning value of the display panel, and A is a compensation constant.
 
     The edge image signal includes a red image signal, a green image signal, and a blue image signal, the edge compensation data includes red, green, and blue compensation data, the red and green compensation data are generated by compensation for the red and green image signals on the basis of the compensation value (k 1 ), and the blue compensation data are generated to have a value of the blue image signal. 
     The red and green compensation data are generated by multiplying the compensation value (k 1 ) by the red and green image signals. 
     The edge image data includes an edge red image data, an edge green image data, and an edge blue image data, the edge red and green image data are generated to have values of the red and green image signals when the red or green compensation data has a grayscale value greater than a maximum grayscale value, the edge blue image data is generated by multiplying a reverse compensation value (k 2 ) by the blue compensation data, and the reverse compensation value (k 2 ) satisfies the following Equation of 
     
       
         
           
             
               k 
               ⁢ 
               
                   
               
               ⁢ 
               2 
             
             = 
             
               
                 1 
                 
                   k 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   1 
                 
               
               . 
             
           
         
       
     
     The edge red, green, and blue image data are generated to have the red, green, and blue compensation data respectively when the red and green compensation data have the grayscale value smaller than the maximum grayscale value. 
     The compensation block generates the edge compensation data with reference to a look-up table and the look-up table stores the compensation value (k 1 ) in accordance with the first and second angles. 
     The look-up table includes a first look-up table storing the compensation value (k 1 ) in accordance with the first and second angles and a second look-up table storing the reverse compensation value (k 2 ) in accordance with the first and second angles, and the compensation block refers to the first look-up table when the red and green compensation data have the grayscale value smaller than the maximum grayscale value and refers to the second look-up table when the red or green compensation data have the grayscale value greater than the maximum grayscale value. 
     The first light source emits a yellow light and the second light source emits a blue light. 
     The backlight unit is operated in a time division fashion in synchronization with first and second fields obtained by timely dividing a frame, the first light source emits the yellow light during the first field, and the second light source emits the blue light during the second field. 
     Each of the pixels includes a red sub-pixel including a red color filter, a green sub-pixel including a green color filter, and a transparent sub-pixel including a transmission part. 
     The first light source substrates are operated during the first field and the second light source substrates are operated during the second field. 
     The edge image signal includes a red image signal, a green image signal, and a blue image signal and the edge compensation data includes red, green, and blue compensation data. When the red or green image signal has a grayscale value greater than a maximum grayscale value, the red, green, and blue compensation data are generated to have the red and green image signals, the blue compensation data is generated on the basis of the blue image signal and a reverse compensation value (k 2 ), and the reverse compensation value (k 2 ) satisfies the following Equation of 
     
       
         
           
             
               k 
               ⁢ 
               
                   
               
               ⁢ 
               2 
             
             = 
             
               
                 1 
                 
                   k 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   1 
                 
               
               . 
             
           
         
       
     
     The blue compensation data is generated by multiplying the reverse compensation value (k 2 ) by the blue image signal. 
     A distance between a center of the first light source substrate and a boundary between the edge portion and the center portion is substantially equal to a distance between the boundary and a center of the second light source substrate. 
     According to the above, the edge image signals applied to the edge pixels are compensated on the basis of the first angle with respect to the first light source and the second angle with respect to the second light source. Thus, the color stain may be prevented from occurring on the edge portion. 
    
    
     
       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 showing a display device according to an exemplary embodiment of the present disclosure; 
         FIG. 2  is a view showing a sub-pixel; 
         FIG. 3  is a view showing a principle of realizing a full color image using time and space division schemes; 
         FIG. 4  is a perspective view showing a display panel and a backlight unit shown in  FIG. 1 ; 
         FIG. 5  is a cross-sectional view taken along a line I-I′ shown in  FIG. 4 ; 
         FIG. 6  is a block diagram showing a controller shown in  FIG. 1 ; 
         FIG. 7  is a flowchart showing an operation of a compensation block shown in  FIG. 6 ; 
         FIG. 8  is a view showing first and second look-up table shown in  FIG. 6 ; 
         FIG. 9  is a view showing a compensation value and a reverse compensation value according to first and second angles; 
         FIG. 10  is a flowchart showing performing of a first compensation shown in  FIG. 7 ; and 
         FIG. 11  is a flowchart showing performing of a second compensation shown in  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     It will be understood that when an element or layer is referred to as being “on”, “connected to” or “coupled to” another element or layer, it can be directly on, connected or coupled to the other element or layer or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly connected to” or “directly coupled to” another element or layer, there are no intervening elements or layers present. Like numbers refer to like elements throughout. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the present invention. 
     Spatially relative terms, such as “beneath”, “below”, “lower”, “above”, “upper” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the exemplary term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms, “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “includes” and/or “including”, when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
     Hereinafter, the present invention will be explained in detail with reference to the accompanying drawings. 
       FIG. 1  is a block diagram showing a display device  1000  according to an exemplary embodiment of the present disclosure. 
     Referring to  FIG. 1 , the display device  1000  includes a display panel  200  to display an image, gate and data drivers  110  and  120  to drive the display panel  200 , and a controller  130  to control the gate and data drivers  110  and  120  and a driving scheme of the display panel  200 . 
     The controller  130  receives image signals RGB and control signals CS. The controller  130  converts a data format of the image signals RGB to a data format appropriate to an interface between the data driver  120  and the controller  130  to generate image data ID and applies the image data ID to the data driver  120 . 
     The controller  130  generates a data control signal DCS, e.g., an output start signal, a horizontal start signal, etc., and a gate control signal GCS, e.g., a vertical start signal, a vertical clock signal, a vertical clock bar signal, etc., on the basis of the control signal CS. The data control signal DCS is applied to the data driver  120  and the gate control signal GCS is applied to the gate driver  110 . 
     The gate driver  110  sequentially outputs gate signals in response to the gate control signal GCS provided from the controller  130 . 
     The data driver  120  converts the image data ID to data voltages in response to the data control signal DCS provided from the controller  130 . The data voltages are applied to the display panel  200 . 
     The display panel  200  includes a plurality of gate lines GL 1  to GLn, a plurality of data lines DL 1  to DLm, and a plurality of pixels PX. 
     The gate lines GL 1  to GLn extend in a second direction D 2  and are arranged in a first direction D 1  substantially perpendicular to the second direction D 2  to be substantially parallel to each other. The gate lines GL 1  to GLn are connected to the gate driver  110  to receive the gate signals from the gate driver  110 . 
     The data lines DL 1  to DLm extend in the first direction D 1  and are arranged in the second direction D 2  to be substantially parallel to each other. The data lines DL 1  to DLm are connected to the data driver  120  to receive the data voltages from the data driver  120 . 
     Each pixel PX is connected to a corresponding gate line of the gate lines GL 1  to GLn and a corresponding data line of the data lines DL 1  to DLm. 
     The display device  1000  may further include a backlight unit  300 . The backlight unit  300  receives first and second backlight control signals BCS 1  and BCS 2  generated by the controller  130 . The backlight unit  300  generates a light in response to the first and second backlight control signals BCS 1  and BCS 2  and provides the display panel  200  with the light. 
     Each pixel PX includes a plurality of sub-pixels. Hereinafter, a structure and an operation of one sub-pixel will be described in detail as a representative example. 
       FIG. 2  is a view showing the sub-pixel SPX. 
     Referring to  FIG. 2 , the display panel  200  includes an array substrate AS, an opposite substrate FS, and a liquid crystal layer LL interposed between the array substrate AS and the opposite substrate FS. 
     The sub-pixel SPX includes a transistor TR connected to the second gate line GL 2  and the first data line DL 1 , a liquid crystal capacitor Clc connected to the transistor TR, and a storage capacitor Cst connected to the liquid crystal capacitor Clc in parallel. The storage capacitor Cst may be omitted. 
     The transistor TR is disposed on the array substrate AS. The transistor TR includes a gate electrode connected to the second gate line GL 2 , a source electrode connected to the first data line DL 1 , and a drain electrode connected to the liquid crystal capacitor Clc and the storage capacitor Cst. 
     The liquid crystal capacitor Clc includes a pixel electrode PE disposed on the array substrate AS, a common electrode CE disposed on the opposite substrate FS, and the liquid crystal layer LL disposed between the pixel electrode PE and the common electrode CE. In this case, the liquid crystal layer LL serves as a dielectric substance. The pixel electrode PE is connected to the drain electrode. 
     The common electrode CE is disposed over an entire surface of the opposite substrate FS, but it should not be limited thereto or thereby. The common electrode CE is disposed on the array substrate AS. In this case, at least one of the pixel electrode PE and the common electrode CE may include slits. 
     The storage capacitor Cst includes the pixel electrode PE, a storage electrode (not shown) branched from a storage line (not shown), and an insulating layer disposed between the pixel electrode PE and the storage electrode. The storage line is disposed on the array substrate AS and disposed on the same layer as the second gate line GL 2 . The storage electrode partially overlaps the pixel electrode PE. 
     The sub-pixel SPX further includes a color filter CF displaying one of primary colors. The color filter CF is disposed on the opposite substrate FS, but it should not be limited thereto or thereby. The color filter CF may be disposed on the array substrate AS. 
     The transistor TR is turned on in response to the gate signal provided through the second gate line GL 2 . The data voltage provided through the first data line DL 1  is applied to the pixel electrode PE of the liquid crystal capacitor Clc through the turned-on transistor TR. The common electrode CE is applied with a common voltage. 
     Due to a difference in voltage level between the data voltage and the common voltage, an electric field is formed between the pixel electrode PE and the common electrode CE. Liquid crystal molecules of the liquid crystal layer LL are operated by the electric field formed between the pixel electrode PE and the common electrode CE. A transmittance of the light incident to the liquid crystal layer LL is controlled by the liquid crystal molecules operated by the electric field, and thus a desired image is displayed. 
     The storage line is applied with a storage voltage having a constant voltage, but it should not be limited thereto or thereby. That is, the storage line may be applied with the common voltage. The storage capacitor Cst maintains the voltage charged in the liquid crystal capacitor Clc. 
       FIG. 3  is a view showing a principle of realizing a full color image using time and space division schemes. 
     The sub-pixel may be one of first, second, and third sub-pixels SPX 1 , SPX 2 , and SPX 3  displaying different colors from each other. In the present exemplary embodiment, the first, second, and third sub-pixels SPX 1 , SPX 2 , and SPX 3  are a red sub-pixel, a green sub-pixel, and a transparent sub-pixel, respectively. 
     Areas respectively corresponding to the first, second, and third sub-pixels SPX 1 , SPX 2 , and SPX 3  are referred to as first, second, and third sub-pixel areas SPA 1 , SPA 2 , and SPA 3 . In this case, first and second color filters are respectively disposed in the first and second sub-pixel areas SPA 1  and SPA 2  and a transmission part TP is disposed in the third sub-pixel area SPA 3 . 
     The first color filter is a red color filter RCF that filters the light traveling thereto and transmits only a red light component. The second color filter is a green color filter GCF that filters the light traveling thereto and transmits only a green light component. 
     The backlight unit  300  includes a first light source L 1  and a second light source L 2 . The first light source L 1  emits a first light having a first color and the second light source L 2  emits a second light having a second color different from the first color. 
     As an example, the first and second colors are in a complementary color relation. For instance, a mixed color of the first and second colors may be a white color. 
     In the present exemplary embodiment, the first color is a yellow color and the second color is a blue color. That is, the first and second lights are a yellow light Ly and a blue light Lb, respectively, but they should not be limited thereto or thereby. That is, each of the first and second colors may be one of red, green, magenta, and cyan colors. 
     The first or second light source L 1  or L 2  includes a light emitting diode. The light emitting diode includes a light emitting chip, a fluorescent substance, and a lens part. The fluorescent substance is coated on the light emitting chip to cover the light emitting chip. The lens part covers the light emitting chip and the fluorescent substance. As an example, the first light source L 1  includes a blue light emitting diode to generate the blue light Lb and the second light source L 2  includes a yellow light emitting diode to generate the yellow light Ly. 
     A frame FR is divided into first and second fields FD 1  an FD 2  according to a time sequence. In the first field FD 1 , the first light source L 1  is operated in response to the first backlight control signal BCS 1  and the yellow light Ly is emitted from the first light source L 1 . Then, in the second field FD 2 , the second light source L 2  is operated in response to the second backlight control signal BCS 2  and the blue light Lb is emitted from the second light source L 2 . 
     Accordingly, during the first field FD 1 , the red light component of the yellow light Ly emitted from the yellow light emitting diode transmits through the red color filter RCF and is displayed as a red image IR, and the green light component of the yellow light Ly emitted from the yellow light emitting diode transmits through the green color filter GCF and is displayed as a green image IG. In addition, the yellow light Ly transmits through the transmission part TP and is displayed as a yellow image IY. 
     Then, during the second field FD 2 , the blue light Lb emitted from the blue light emitting diode L 2  transmits through the transmission part TP and is displayed as a blue image IB. However, since the blue light Lb does not transmit through the red and green color filters RCF and GCF, the image is not displayed through the first and second pixel areas PA 1  and PA 2 . 
     As described above, the yellow image IY is displayed during the first field FD 1  by the transmission part TP and the blue image IB is displayed during the second field FD 2  by the transmission part TP. The transmission part TP does not include the color filter, and thus the transmission part TP transmits the yellow and blue lights Ly and Lb without a light loss. Therefore, a light use efficiency of the display device  1000  (refer to  FIG. 1 ) is improved. 
       FIG. 4  is a perspective view showing a display panel  200  and a backlight unit  300  shown in  FIG. 1 . 
     Referring to  FIG. 4 , the backlight unit  300  includes a first light source substrate LS 1 , a second light source substrate LS 2 , and a base BS. Each of the first and second light source substrates LS 1  and LS 2  is provided in a plural number on the base substrate BS. The first and second light source substrates LS 1  and LS 2  are alternately arranged in the second direction D 2 . As an example, the first and second light source substrates LS 1  and LS 2  are arranged in order of the second light source substrate LS 2  the first light source substrate LS 1 / . . . /the second light source substrate LS 2 . 
     The first light source substrate LS 1  has a substantially bar shape elongated in the first direction D 1 . The first light source L 1  is provided in a plural number and the first light sources L 1  are mounted on the first light source substrate LS 1 . The first light source substrate LS 1  includes lines that transmit signals to drive the first light sources L 1 . The first light source substrate LS 1  includes a printed circuit board. 
     The first light sources L 1  are arranged on the first light source substrate LS 1  in a line shape substantially parallel to the first direction D 1 . The first light sources L 1  are connected to each other by the lines of the first light source substrate LS 1  to form one LED string. 
     The first light source substrates LS 1  are connected to a first substrate line SL 1 . The first light source substrates LS 1  receive the first backlight control signal BCS 1  through the first substrate line SL 1 . The first light sources L 1  of the first light source substrates LS 1  are operated during the first field FD 1  (refer to  FIG. 3 ) in response to the first backlight control signal BCS 1 . 
     The second light source substrate LS 2  has a substantially bar shape elongated in the first direction D 1 . The second light source L 2  is provided in a plural number and the second light sources L 2  are mounted on the second light source substrate LS 2 . The second light source substrate LS 2  includes lines that transmit signals to drive the second light sources L 2 . The second light source substrate LS 2  includes a printed circuit board. 
     The second light sources L 2  are arranged on the second light source substrate LS 2  in a line shape substantially parallel to the first direction D 1 . The second light sources L 2  are connected to each other by the lines of the second light source substrate LS 2  to form one LED string. 
     The second light source substrates LS 2  are connected to a second substrate line SL 2 . The second light source substrates LS 2  receive the second backlight control signal BCS 2  through the second substrate line SL 2 . The second light sources L 2  of the second light source substrates LS 2  are operated during the second field FD 2  (refer to  FIG. 3 ) in response to the second backlight control signal BCS 2 . 
     The display panel  200  has a substantially rectangular shape. The display panel  200  includes an edge portion  210  defined along sides substantially parallel to the first direction D 1  among four sides thereof. Accordingly, the edge portion  210  has the rectangular shape elongated along the first direction D 1 . 
     As an example, the display panel  200  includes two edge portions  210  defined therein. One edge portion  210  is defined along the side disposed in the second direction D 2  and the other edge portion  210  is defined along the side disposed in a fourth direction D 4  opposite to the second direction D 2 . A center portion  220  is defined between the edge portions  210 . Since the edge portions  210  have the same structure, hereinafter, the edge portion  210  in the second direction D 2  will be mainly described. 
     Hereinafter, among the pixels PX, the pixels disposed in the edge portion  210  will be referred to as edge pixels EPX and the pixels disposed in the center portion  220  will be referred to as center pixels CPX. 
       FIG. 5  is a cross-sectional view taken along a line I-I′ shown in  FIG. 4 . 
     Referring to  FIGS. 4 and 5 , the display panel  200  includes a boundary  230  defined between the edge portion  210  and the center portion  220 . The boundary  230  is defined as viewed relative to first and second edge light source substrates ELS 1  and ELS 2 . In more detail, the boundary  230  is defined such that a first distance DS 1  between each position on the boundary  230  and a center of the first edge light source substrate ELS 1  is substantially equal to a second distance DS 2  between each position on the boundary  230  and a center of the second edge light source substrate ELS 2 . 
     Here, the second edge light source substrate ELS 2  is disposed at an outermost position in the second direction D 2  of the second light source substrates LS 2 . The second edge light source substrate ELS 2  is disposed under the edge portion  210 . The first edge light source substrate ELS 1  is disposed adjacent to the second edge light source substrate ELS 2  in the fourth direction D 4 . The first edge light source substrate ELS 1  is disposed at an outermost position in the second direction D 2  of the first light source substrates LS 1 . 
     The yellow light Ly, which is emitted from the first light source L 1  of the first edge light source substrate ELS 1  and reaches an arbitrary point Pn of the edge portion  210 , has a first brightness determined by a first angle ⊖ 1 . The first angle ⊖ 1 corresponds to an angle between a first imaginary line IL 1  passing through the arbitrary point Pn and the first light source L 1  of the first edge light source substrate ELS 1  and the third direction D 3 . 
     The first angle this obtained by the following Equation 1. 
                     θ   1     =       tan     -   1       ⁡     (       Xp   +     p   ⁢           ⁢   1       h     )               Equation   ⁢           ⁢   1               
In Equation 1, Xp denotes a distance between the boundary  230  and the arbitrary point Pn, h denotes a distance between the first light source substrate LS 1  and the display panel  200 , and p 1  denotes a distance between a center portion of the first light source L 1  and a point Q at which a third imaginary line IL 3  passing through the boundary  230  and substantially parallel to the third direction D 3  meets the base BS.
 
     The first brightness is proportional to cos 2 (⊖ 1 ). Therefore, as the first angle ⊖ 1  becomes large, the first brightness becomes low. 
     The blue light Lb, which is emitted from the second light source L 2  of the second edge light source substrate ELS 2  and reaches the arbitrary point Pn, has a second brightness determined by a second angle ⊖ 2 . The second angle ⊖ 2  corresponds to an angle between a second imaginary line IL 2  passing through the arbitrary point Pn and the second light source L 2  of the second edge light source substrate ELS 2  and the third direction D 3 . 
     The second angle ⊖ 2  is obtained by the following Equation 2. 
                     θ   2     =       tan     -   1       ⁡     (       Xp   -     p   ⁢           ⁢   2       h     )               Equation   ⁢           ⁢   2               
In Equation 2, p 2  denotes a distance between the point Q and a center portion of the second light source L 2 . Since the first distance DS 1  is equal to the second distance DS 2 , the “p 1 ” is equal to the “p 2 ”.
 
     The second brightness is proportional to cos 2 (⊖ 2 ). Thus, as the second angle ⊖ 2  becomes large, the second brightness becomes low. 
     Since the first and second edge light source substrates ELS 1  and ELS 2  are spaced apart from each other by 2×p 1  (or 2×p 2 ), a difference occurs between the first and second angles ⊖ 1  and ⊖ 2  with respect to the arbitrary point Pn, and as a result, a difference occurs between the first brightness and the second brightness. Accordingly, due to the difference in brightness between the yellow light Ly and the blue light Lb and the difference in color between the yellow light Ly and the blue light Lb, a color stain appears on the edge portion  210 . 
     In more detail, the second angle ⊖ 2  is smaller than the first angle ⊖ 1 . Therefore, since the second brightness is greater than the first brightness, an image that is more bluish than the original image is displayed in the edge portion  210 . 
     However, according to the present exemplary embodiment, the color stain may be prevented from occurring. In detail, as shown in  FIG. 4 , the image data ID includes edge image data EID and center image data CID. The edge image data EID are applied to the edge pixels EPX and compensated on the basis of the first and second angles ⊖ 1  and ⊖ 2  and thus the color stain may be prevented from occurring. Meanwhile, the center image data CID are applied to the center pixels CPX, but not compensated on the first and second angles ⊖ 1  and ⊖ 2 . 
       FIG. 6  is a block diagram showing the controller  130  shown in  FIG. 1  and  FIG. 7  is a flowchart showing an operation of a compensation block shown in  FIG. 6 . 
     Referring to  FIGS. 6 and 7 , the controller  130  includes a compensation block  131 . 
     The compensation block  131  receives the image signals RGB and generates the edge image data EID and the center image data CID. The image signals RGB include a red image signal Ri, a green image signal Gi, and a blue image signal Bi, which respectively include information about a red image, information about a green image, and information about a blue image. 
     The compensation block  131  checks that whether the image signals RGB are the edge image signals corresponding to the edge pixels EPX or the center image signals corresponding to the center pixels CPX (S 1 ). 
     When the image signals RGB are the center image signals, the compensation block  131  generates the center image data CID on the basis of the image signals RGB. In more detail, center red, green, and blue data Rm, Gm, and Bm of the center image data CID are generated to include the red, green, and blue image signals Ri, Gi, and Bi, respectively (S 2 ). 
     When the image signals RGB are the edge image signals, the compensation block  131  checks that whether the red image signal Ri or the green image signal Gi has a grayscale value greater than a maximum grayscale value or not (S 3 ). The maximum grayscale value means the greatest grayscale value represented by each pixel PX, e.g., 255 grayscale value. 
     When the red image signal Ri or the green image signal Gi has the grayscale value smaller than the maximum grayscale value, the compensation block  131  compensates for the image signals RGB on the basis of a compensation value k 1  to generate edge compensation data ECD (S 4 ). Hereinafter, the process of compensating for the image signal on the basis of the compensation value k 1  will be referred to as a first compensation. 
     The compensation value k 1  is generated on the basis of the first and second angles ⊖ 1  and ⊖ 2 . As an example, the compensation value k 1  is generated using cos 2 (⊖ 1 ) and cos 2 (⊖ 2 ). The compensation value k 1  satisfies the following Equation 3. 
                     k   ⁢           ⁢   1     =       A   ⁡     (       f   ⁡     (     θ   2     )         f   ⁡     (     θ   1     )         )         1   Y               Equation   ⁢           ⁢   3               
In Equation 3, f(⊖ 1 ) is equal to cos 2 (⊖ 1 ), f(⊖ 2 ) is equal to cos 2 (⊖ 2 ), γ is a gamma tuning value of the display panel  200 , A is a compensation constant. The gamma tuning value (γ) is to compensate for gamma characteristics of the display panel  200 . The compensation constant (A) is a proportional constant and is to compensate for a variation in amount of the light, which is caused by an optical sheet (not shown) and the display panel  200  of the display device  1000 .
 
     In more detail, red and green compensation data Rc and Gc of the edge compensation data ECD are generated on the basis of the compensation value k 1 . For instance, the red and green compensation data Rc and Gc are generated by multiplying the red and green image signals Ri and Gi by the compensation value k 1 . 
     Blue compensation data Bc of the edge compensation data ECD are generated to have the value of the blue image signal Bi. 
     Then, the compensation block  131  checks that whether the red compensation data Rc or the green compensation data Gc has the grayscale value greater than the maximum grayscale value (S 5 ). 
     When the red compensation data Rc or the green compensation data Gc has the grayscale value smaller than the maximum grayscale value, the compensation block  131  generates the edge image data EID on the basis of the edge compensation data ECD (S 6 ). In more detail, edge red, edge green, and edge blue image data Ro, Go, and Bo of the edge image data EID are generated to have the red, green, and blue compensation data Rc, Gc, and Bc, respectively. 
     When the red image signal Ri or the green image signal Gi has the grayscale value greater than the maximum grayscale value in the checking that whether the red image signal Ri or the green image signal Gi has the grayscale value greater than the maximum grayscale value (S 3 ), the compensation block  131  compensates for the image signals RGB on the basis of a reverse compensation value k 2  to generate the edge image data EID (S 7 ). Hereinafter, the process of compensating for the image signals RGB on the basis of the reverse compensation value k 2  will be referred to as a second compensation. 
     Here, the reverse compensation value k 2  is generated on the first and second angles ⊖ 1  and ⊖ 2 . In the present exemplary embodiment, the reverse compensation value k 2  satisfies the following Equation 4. 
                     k   ⁢           ⁢   2     =     1     k   ⁢           ⁢   1               Equation   ⁢           ⁢   4               
In more detail, the edge blue image data Bo of the edge image data EID are generated on the basis of the reverse compensation value k 2 . For instance, the edge blue image data Bo is generated by multiplying the blue image signal Bi by the reverse compensation value k 2 .
 
     Meanwhile, the edge red image data Ro and the edge green image Go of the edge image data EID are generated to have the values of the red and green image signals Ri and Gi, respectively. 
     In addition, when the red compensation data Rc or the green compensation data Gc has the grayscale value greater than the maximum grayscale value in the checking that whether the red compensation data Rc or the green compensation data Gc has the grayscale value greater than the maximum grayscale value, the compensation block  131  compensates for the image signals RGB on the basis of the reverse compensation value k 2  to generate the edge image data EID (S 7 ). 
     As described above, when the edge image data EID are generated by the first compensation or the second compensation, the color stain appearing on the edge portion  210  (refer to  FIG. 4 ) may be removed. 
     For instance, when the red, green, and blue image signals Ri, Gi, and Bi have the grayscale values of 200, 200, and 200, respectively, the red and green image signals R 1  and Gi are smaller than the maximum grayscale, e.g., 255 grayscale value (S 3 ), and thus first compensation is carried out (S 4 ). As an example, the compensation value k 1  may be about 1.07. The red, green, and blue compensation data Rc, Gc, and Bc generated by carrying out the first compensation (S 4 ) have the grayscale values of 215, 215, and 200, respectively. Since the red and green compensation data Rc and Gc are smaller than 255 grayscale value (S 5 ), the edge red, edge green, and edge blue image data Ro, Go and Bo are generated to have the grayscale values of 215, 215, and 200, respectively (S 6 ). 
     Consequently, the grayscale values of the edge red image data Ro and the edge green image data Go have the grayscale value compensated on the basis of the first and second angles ⊖1 and ⊖2 such that the grayscale values of the edge red image data Ro and the edge green image data Go are greater than 200 grayscale value of the red and green image signals Ri and Gi. The image displayed in the edge pixels EPX in response to the edge red, green, and blue image data Ro, Go, and Bo includes a yellow component much more than that of the original image. Accordingly, the color stain that is bluish and appears on the edge portion  210  is offset and the color stain is removed. 
     On the contrary, when the red, green, and blue image signals Ri, Gi, and Bi have the grayscale values of 255, 255, and 200, respectively, the red and green image signals Ri and Gi are greater than the maximum grayscale value, e.g., 255 grayscale value (S 3 ), and thus the second compensation is carried out. As an example, the reverse compensation value k 2  satisfies the following Equation of 1/compensation value (k 1 )=1/1.07=0.93. The edge red, green, and blue image data Ro, Go, and Bo generated by carrying out the first compensation (S 4 ) have the grayscale values of 200, 200, and 186, respectivley. 
     Consequently, the grayscale value of the edge blue image data Bo has the grayscale value compensated on the basis of the first and second angles ⊖1 and ⊖2 such that the grayscale value of the edge blue image data Bo is smaller than 200 grayscale value of the blue image signals Bi. Thus, the image displayed in the edge pixels EPX in response to the edge red, green, and blue image data Ro, Go, and Bo includes a blue component much less than that of the original image. Accordingly, the color stain that is bluish and appears on the edge portion  210  is removed. 
     As shown in  FIG. 6 , the controller  130  includes a first look-up table LUT 1  and a second look-up table LUT 2 . The compensation block  131  performs the first compensation on the basis of the first look-up table LUT 1  and performs the second compensation on the basis of the second look-up table LUT 2 . 
       FIG. 8  is a view showing the first and second look-up tables LUT 1  and LUT 2  shown in  FIG. 6  and  FIG. 9  is a view showing the compensation value and the reverse compensation value according to the first and second angles ⊖ 1  and ⊖ 2 . 
     Hereinafter, the compensation value k 1  and the reverse compensation value k 2  stored into the first and second look-up tables LUT 1  and LUT 2  will be described in detail with reference to  FIGS. 7 to 9 . 
     The first look-up table LUT 1  stores the compensation value k 1  therein. In more detail, the first look-up table LUT 1  stores the first and second angles ⊖ 1  and ⊖ 2  in accordance with a distance x and the compensation value k 1  as shown in  FIG. 8 . 
     As shown in  FIG. 9 , the distance x corresponds to a distance in the second direction D 2  between a position on the edge portion  210  and the boundary  230 . In more detail, first to n-th distances x 1  to xn are sequentially defined from an end of the edge portion  210  and the boundary  230 . 
     In addition, the first and second angles ⊖ 1  and ⊖ 2  according to the first to n-th distances x 1  to xn are respectively stored in second and third columns of the first look-up table LUT 1 . In more detail, the first angle ⊖ 1  corresponding to the first distance x 1  is ⊖ 11  and the second angle ⊖ 2  corresponding to the first distance x 1  is ⊖ 21 . Similarly, the first angle ⊖ 1  corresponding to the n-th distance xn is ⊖ 1n  and the second angle ⊖ 2  corresponding to the n-th distance xn is ⊖ 2n . 
     The compensation value k 1  according to the first to n-th distances x 1  to xn is stored in a fourth column of the first look-up table LUT 1 . For instance, the compensation value k 1  corresponding to the first distance x 1  is k 11  and the compensation value k 1  corresponding to the n-th distance xn is k 11 . The compensation value k 1  is calculated by substituting the first and second angles ⊖ 1  and ⊖ 2  according to the first to n-th distances x 1  to xn into Equation 3. 
     The second look-up table LUT 2  stores the reverse compensation value k 2 . In more detail, the second look-up table LUT 2  stores the first and second angles ⊖ 1  and ⊖ 2  in accordance with the distance x and the reverse compensation value k 2  as shown in  FIG. 8 . 
     In addition, the first and second angles ⊖ 1  and ⊖ 2  according to the first to n-th distances x 1  to xn are respectively stored in second and third columns of the second look-up table LUT 2 . In more detail, the first angle ⊖ 1  corresponding to the first distance x 1  is ⊖ 11  and the second angle ⊖ 2  corresponding to the first distance x 1  is ⊖ 21 . Similarly, the first angle ⊖ 1  corresponding to the n-th distance xn is ⊖ 1n  and the second angle ⊖ 2  corresponding to the n-th distance xn is ⊖ 2n . 
     The reverse compensation value k 2  according to the first to n-th distances x 1  to xn is stored in a fourth column of the second look-up table LUT 2 . For instance, the reverse compensation value k 2  corresponding to the first distance x 1  is k 21  and the reverse compensation value k 2  corresponding to the n-th distance xn is k 2   n . The reverse compensation value k 2  is calculated by substituting the compensation value k 1  according to the first to n-th distances x 1  to xn into Equation 4. 
       FIG. 10  is a flowchart showing performing of the first compensation shown in  FIG. 7 . 
     Referring to  FIG. 10 , the compensation block  131  (refer to  FIG. 6 ) compensates for the image signals RGB in the unit of each pixel PX (refer to  FIG. 4 ) to generate the edge compensation data ECD. 
     The compensation block  131  obtains the distance x of the pixel PX corresponding to the image signals RGB presently applied thereto (S 8 ). Information about the distance x may be included in the image signals RGB, but it should not be limited thereto or thereby. That is, the compensation block  131  may further include a block that calculates the distance x of the pixel PX corresponding to the image signals RGB using clock signals. 
     Then, the compensation block  131  obtains the compensation value k 1  corresponding to the obtained distance x with reference to the first look-up table LUT 1  (refer to  FIG. 8 ) (S 9 ). 
     After that, the compensation block  131  compensates the image signals RGB on the basis of the compensation value k 1  corresponding to the distance x to generate the edge compensation data ECD. In more detail, the red and green compensation data Rc and Gc are generated by multiplying the compensation value k 1  corresponding to the distance x by each of the red and green image signals R 1  and Gi. Meanwhile, the blue compensation data Bc may be generated to have the value of the blue image signal Bi (S 10 ). 
       FIG. 11  is a flowchart showing performing of the second compensation shown in  FIG. 7 . 
     Referring to  FIG. 11 , the compensation block  131  (refer to  FIG. 6 ) compensates for the image signals RGB in the unit of each pixel PX (refer to  FIG. 4 ) to generate the edge image data EID. 
     The compensation block  131  obtains the distance x of the pixel PX corresponding to the image signals RGB presently applied thereto (S 11 ). 
     Then, the compensation block  131  obtains the reverse compensation value k 2  corresponding to the obtained distance x with reference to the second look-up table LUT 2  (refer to  FIG. 8 ). 
     After that, the compensation block  131  compensates for the image signals RGB on the basis of the reverse compensation value k 2  corresponding to the distance x to generate the edge image data EID. In more detail, the blue image data Bo may be generated by multiplying the reverse compensation value k 2  corresponding to the distance x by the blue image signal Bi. Meanwhile, the edge red and green image data Ro and Go may be generated to have the red and green image signals Ri and Gi, respectively (S 13 ). 
     As described above, since the edge image data EID are generated by compensating for the image signals RGB in accordance with the distance x corresponding to the image signals RGB in the unit of one pixel, a difference in color stain, which is caused by the distance x in the edge portion  210 , may be removed. 
     Although the exemplary embodiments of the present invention have been described, it is understood that the present invention should not be limited to these exemplary embodiments but various changes and modifications can be made by one ordinary skilled in the art within the spirit and scope of the present invention as hereinafter claimed.