Abstract:
In a method of processing data of a display apparatus, red, green and blue data are gamut mapped as red, green, blue and white data. The red, green, blue and white data are reconstructed by means of subpixel rendering to generate metameric sets dot pixels composed for example of one such dot pixel having red and green color components and another such dot pixel having blue and white color components such that when the metameric set dot pixels is lit up it produces a white colored region on the display apparatus and when un-lit it appears as contrastingly dark colored region on the display apparatus. By selectively forcing one metameric set of dot pixels to be un-lit, the method allows an immediately adjacent metameric set of dot pixels to be lit-up as a contrasting white region on the display apparatus.

Description:
PRIORITY STATEMENT 
     This application claims priority under 35 U.S.C. §119 to Korean Patent Application No. 2009-125951, filed on Dec. 17, 2009 in the Korean Intellectual Property Office (KIPO), the contents of which application are herein incorporated by reference in their entirety. 
     BACKGROUND 
     1. Field of Disclosure 
     The present disclosure of invention relates to a method of processing data and a display apparatus for performing the method. More particularly, the present disclosure relates to a method of processing image data signals for thereby improving expression of a sharp edged glyph such as an alphabetic character and a display apparatus for performing the method. 
     2. Description of Related Technology 
     Generally, a flat panel display apparatus may include a matrix of light outputting picture element units (pixel or subpixel units) such as the liquid crystal shuttered units of a liquid crystal display (LCD) panel. The LCD panel is caused to display a desired image using a selective light transmittance characteristic of its liquid crystal material and color filters as well as using a backlight providing assembly disposed underneath to provide light for controlled passage through the LCD panel. A conventional LCD panel has a striped RGB structure. The striped RGB structure includes red, green and blue subpixels, and each of the red, green and blue subpixels is arranged to form a continuous stripe of the subpixel&#39;s color in either the column that the respective R, G, B subpixel resides in or in the row of the subpixel&#39;s residence. The conventional RGB triad has a capability of providing its own full gamut spectrum of colors as well as a capability of providing a white light when the metameric triad of RGB primary colors are lit up according to an appropriate drive mix (e.g., all turned on to maximum drive). 
     Recently, so-called Pentile™ RGBW structures have been developed that feature a screen-populating, repeating group having red, green, blue and white subpixels. See for example U.S. 2008/0030526 (Brown Elliott et al.: Methods and Systems for Sub-Pixel Rendering with Adaptive Filtering) which disclosure is incorporated herein by reference. The Pentile™ RGBW structure may be advantageously used to decrease the number of subpixels actually present in the display area of the flat panel while providing an apparent resolution equal to or greater than that of a striped RGB structure having many more subpixels. Since the RGBW repeating group of the Pentile™ structure includes one or more white subpixels and these do not use a light-reducing color filter, an LCD panel having such an RGBW structure tends to have higher light transmittance efficiency when displaying unsaturated colors or black and white images so that luminance of the backlight assembly may be accordingly decreased to thereby reduce power consumption of the display apparatus. For example, for a display apparatus that is used in an office environment where black on white background typing is desired, black characters may be displayed on a white board background where the white board background is produced at least partly by the white subpixels, so that power consumption may be remarkably reduced relative to a display using only the striped RGB structure (and having corresponding R, G and B; light suppressing color filters). However, due to the discrete nature in which the RGBW subpixels are spatially arranged, the display apparatus having the RGBW structure may not display the character (or another glyph having slanted sharp edges, etc.) as an image that is perceived to be a smoothly formed one. 
       FIGS. 1A and 1B  are respective conceptual diagrams showing how an alphabetic character “A” might be respectively displayed as a black filled glyph on a first display panel having the conventional striped RGB structure and on a second display panel having an RGBW structure (in this case an 8-cell RGBW repeating group). 
     Referring to  FIGS. 1A and 1B , while the attempted display of the character “A” on the first display panel (RGB structured) is smoothly displayed, the attempted display of the same character “A” on the second display panel (RGBW structured) can appear distorted when the white board generating algorithm tries to make maximal use of the white subpixels and color balancing and the character “A” is therefore not always smoothly displayed on the display panel having the RGBW structure. More specifically, and comparing it to the idealized “A” shown in  FIG. 1A , the RGBW formed “A” of  FIG. 1B  suffers from drawbacks such as that, some regions of the “A” character which should not be displayed as black are displayed as black, and some regions of the “A” character which should be displayed as black instead displayed as white. Yet more specifically, consider the interior white area of the capitol “A” glyph immediately below the apex of the “A”. In  FIG. 1A  this interior white area is displayed as two RGB triads lit up in a column and surrounded by black. However, in  FIG. 1B  this interior white area consists of one horizontal RGB triad in one row and just one lit-up W subpixel in the row below. Color balancing for providing a fully white color is thus preserved. However the shape of the intended “A” glyph is not preserved. Accordingly, the characters are not always smoothly displayed as originally intended on the display panel having the RGBW structures. 
     DEFINITIONS 
     Traditionally, terms such as “pixel” and “subpixel” have provided sufficient means for expressing the functions of basic picture elements in a conventional stripe RGB display structure. However, with the advent of newer types of picture element structures it sometimes becomes desirable to be able to express other concepts. The term “metameric” as used herein refers to a plurality of adjacent light emitting units that are individually drivable to output corresponding luminosities in respective wavelength bands including at least one combination that can appear as white light to the human visual system. Adjacent red and cyan light emitting elements, for example, can define a metameric pair. Adjacent blue and yellow light emitting elements can also define a metameric pair. Adjacent RGB light emitting elements can define a metameric triad. Because the human visual system has been shown to perceive spatial resolution differently if tested with only adjacent black and white light emitting elements as compared to adjacent colored elements (where black/white resolution tends to be finer than color versus adjacent color resolution), it is sometimes desirable to speak in terms of picture elements that affect black/white resolution. The term “dot pixel” will be used herein. More specifically, reference will be made herein to a blueish-white “dot pixel” (also denoted as: BW Dp) that is capable of outputting adjacent lights that appear to be blueish-white to the human visual system and reference will be made herein to a yellowish-white “dot pixel” (also denoted as: YW Dp) that is capable of outputting adjacent lights that appear to be yellowish-white (or even just simply yellow) to the human visual system. The yellowish-white “dot pixel” (YW Dp) will also be referenced herein at times as a Red-Green dot pixel (also denoted as: RG Dp). The non-white colors, blueish-white and yellowish-white, will be referenced herein at times as off-white colors. An immediately adjacent combination of different off-white dot pixels, namely, a blueish-white “dot pixel” and a yellowish-white “dot pixel” (B+W Dp and Y+W Dp) may be capable of outputting adjacent lights that appear to be white-white (or more simply, white) to the human visual system. Thus, one can have a metameric pair of adjacent off-white dot pixels (a BW Dp adjacent to a YW Dp). Reasons for such additional definitions will become clearer from the below detailed descriptions. 
     SUMMARY 
     The present disclosure of invention provides a method of processing image data signals for thereby improving expression of sharp edged glyphs (e.g., alphabetic characters) when the latter are displayed on a display panel having an RGBW repeating group structure. 
     The present disclosure of invention also provides a display apparatus for performing the above-mentioned method. 
     According to one aspect of the present disclosure, there is provided a machine-implemented and automated method of processing the image data signals of a display apparatus so as to reduce or eliminate the aforementioned problem. In the method, supplied red, green and blue input data signals are re-mapped into a gamut space having red, green, blue and white data components as its primary light providing elements. The gamut-mapped red, green, blue and white data are rendered by way of area resampling onto coverage areas of respective dot pixels, where in one embodiment, the dot pixels include blueish-white dot pixels (BW DP&#39;s) immediately adjacent to yellowish-white dot pixels (YW DP&#39;s; where the latter are also at times referred to herein as RG Dp&#39;s). When a clean black line is to be rendered by the display, where the line is vertical or horizontal, a selective algorithm automatically sets to a predetermined black grayscale level an immediately adjacent first pair consisting of a BW Dp and a YW Dp so that corresponding other adjacent pairs of the BW Dp&#39;s and YW Dp&#39;s neighboring the first pair may be lit-up as white light outputting pairs in sharp contrast to the blackened first pair of metameric off-white dot pixels. In one embodiment, the decision to selectively force adjacent pairs of the BW Dp&#39;s and YW Dp&#39;s to be the predetermined black grayscale level is automatically made based on the input red, green and blue data signals. In one embodiment, the algorithm bypasses the forced blackening of the first pair of metameric dot pixels (Dp&#39;s) when they are automatically detected to be part of a predetermined checkerboard pattern. 
     According to another aspect of the present disclosure, there is provided a method of processing data of a display apparatus. In the method, red, green and blue data are gamut mapped as red, green, blue and white data. The red, green, blue and white data are area resampled to align with BW Dp&#39;s and YW Dp&#39;s of the display apparatus. The display apparatus includes a blue shifting module and a subpixel rendering module. 
     According to still another aspect of the present disclosure, a display apparatus includes a display panel, a light source part and a data processing circuit. The display panel includes a first dot pixel having red and green subpixels and a second dot pixel having blue and white subpixels. The dot pixels are selectively activated to display different kinds of image including images with horizontal and/or vertical black lines. The light source part provides backlighting light to the display panel. The data processing circuit automatically forces the first and second kinds of dot pixels (BW Dp&#39;s and YW Dp&#39;s) to a predetermined black grayscale level based on input red, green and blue data. The data processing circuit includes a gamut mapping part and a subpixel rendering part. The gamut mapping part maps the red, green and blue data as red, green, blue and white data. The subpixel rendering part uses area resampling to reconstruct the gamut mapped data to align with coverage areas of the first and second kinds of dot pixels (BW Dp&#39;s and YW Dp&#39;s) of the display apparatus. 
     According to still another aspect of the present disclosure, a display apparatus includes a display panel, a light source part and a data processing circuit. The display panel includes a dot pixel having red and green subpixels or blue and white subpixels. The dot pixel displays an image. The light source part provides light to the display panel. The data processing circuit includes a gamut mapping part and a subpixel rendering part. The gamut mapping part maps red, green and blue data as red, green, blue and white data. The subpixel rendering part selectively applies a blue shift algorithm processing a color change between adjacent data smoothly to the red, green, blue and white data. The subpixel rendering part reconstructs the red, green, blue and white data to generate red and green data or blue and white data using the adjacent data adjacent to the red, green, blue and white data. 
     According to a method of automatically processing data and a display apparatus for performing the method, input red, green and blue data having a grayscale that is within a predetermined threshold of a predetermined black grayscale and are corresponding to a sharp edged glyph such as an alphabetic character are automatically found and their corresponding dot pixels (BW Dp&#39;s and YW Dp&#39;s) of the display apparatus are selectively forced to have the predetermined black grayscale if they are not part of a predetermined checkerbox pattern. 
     In addition, when the red, green, blue and white data are in a region where the character is displayed, a blue shift algorithm may be selectively bypassed so as to improve the expression of the character. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features and advantages of the present disclosure will become more apparent by describing in detailed example embodiments with reference to the accompanying drawings, in which: 
         FIGS. 1A and 1B  are conceptual diagrams respectively illustrating a character “A” displayed on a display panel having a conventional RGB structure and an RGBW structure; 
         FIG. 2  is a plan view illustrating a display apparatus according to an example embodiment in accordance with the disclosure; 
         FIG. 3  is a block diagram illustrating a data processing circuit of  FIG. 2 ; 
         FIGS. 4A and 4B  are conceptual diagrams illustrating operation of a subpixel rendering part of  FIG. 3 ; 
         FIG. 5  is a flowchart illustrating a method of processing data by the data processing circuit of  FIG. 2 ; 
         FIGS. 6A and 6B  are conceptual diagrams illustrating a dot-check patterned artifact; 
         FIGS. 7A and 7B  are conceptual diagrams illustrating a method of determining the dot-check patterned artifact of  FIGS. 6A and 6B ; 
         FIGS. 8A to 8C  are conceptual diagrams illustrating various patterns displayed on the display apparatus of  FIG. 2 ; 
         FIG. 9  is a block diagram illustrating a data processing circuit according to another example embodiment in accordance with the disclosure; 
         FIG. 10  is a flowchart illustrating a method of processing data by a data processing circuit of  FIG. 9 ; 
         FIG. 11  is a block diagram illustrating a data processing circuit according to still another example embodiment in accordance with the disclosure; 
         FIG. 12  is a conceptual diagram illustrating operation of a subpixel rendering part of  FIG. 11 ; and 
         FIG. 13  is a flowchart diagram illustrating a method of processing data by the data processing circuit of  FIG. 11 . 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure is provided more fully hereinafter with reference to the accompanying drawings, in which example embodiments are shown. The present teachings may, however, be embodied in many different forms and should not be construed as limited to the example embodiments set forth herein. Rather, these example embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the present teachings to those skilled in the pertinent art. In the drawings, the sizes and relative sizes of layers and regions may be exaggerated for clarity. 
     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 numerals 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, third 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 disclosure. 
     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 example embodiments only and is not intended to be limiting of the present disclosure. 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 “comprises” and/or “comprising,” 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. 
     Example embodiments are described herein with reference to cross-sectional illustrations that are schematic illustrations of idealized example embodiments (and intermediate structures) of the present teachings. As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, example embodiments should not be construed as limited to the particular shapes of regions illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. For example, an implanted region illustrated as a rectangle will, typically, have rounded or curved features and/or a gradient of implant concentration at its edges rather than a binary change from implanted to non-implanted region. Likewise, a buried region formed by implantation may result in some implantation in the region between the buried region and the surface through which the implantation takes place. Thus, the regions illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the actual shape of a region of a device and are not intended to limit the scope of the present teachings. 
     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 disclosure most closely pertains. 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 teachings will be provided in more detail with reference to the accompanying drawings. 
       FIG. 2  is a plan schematic view illustrating a display apparatus according to a first example embodiment  50 . 
     Referring to  FIG. 2 , the display apparatus  50  according to the present example embodiment includes a timing controller  101 , a data processing circuit  100 , a display panel  200 , a data lines driver  300 , a gate lines driver  400 , a backlighting light source part  500  and a light source driver circuit  600 . 
     The timing controller  101  controls driving timings of the data lines driver  300  and of the gate lines driver  400  based on one or more synchronization signals received from outside (from the left in  FIG. 2 ). 
     The data processing circuit  100  receives conventional striped RGB data from outside (from the left in  FIG. 2 ) and responsively generates image rendering red, green, blue and white data signals: Rro, Gro, Bro and Wro (see  FIG. 3 ) based on the red, green and blue data signals R, G and B received from the outside. In the illustrated example the RGBW repeating group has an 8-cell structure shown at the center of the display area of substrate  200  and by way of further example, the data processing circuit  100  may generate red and green subpixel driving signals (e.g., Rro and Gro) corresponding to differently located ones of the red subpixels and the green subpixels, Rp and Gp provided in the illustrated 8-cell RGBW repeating group. However if a not fully saturated color is to be produced, the data processing circuit  100  may additionally generate blue and white subpixel driving signals (e.g., Bro and Wro) corresponding to differently located ones of the blue and white subpixels, Bp and Wp, provided in the illustrated 8-cell RGBW repeating group based on how much of a white light component is present the originally supplied, RGB signal. In addition, in some embodiments (so-called, dynamically backlit LCD panels) the data processing circuit  100  may further generate one or more luminance control signals for controlling a corresponding one or more luminance levels output from respective parts of the light source part  500  based on how much of a white light component is present the originally supplied, RGB signal. 
     As mentioned, the display panel  200  has an RGBW structure including red, green, blue and white subpixels Rp, Gp, Bp and Wp (two independently drivable instances of each in the example of  FIG. 2 ). The illustrated 8-cell RGBW repeating group may be viewed as comprising a diagonally opposed pair of blueish-white dot pixels (BW Dp&#39;s) and a diagonally opposed pair of yellowish-white dot pixels (YW Dp&#39;s). As mentioned above, a combination of a BW Dp and an adjacent YW Dp may be activated to appear to provide white-white output light (BW+YW=WW) in that screen location. The illustrated display panel  200  includes a plurality of data lines DL, a plurality of gate lines GL crossing with the data lines DL. The display area of panel  200  is substantially tessellated with copies of the 8-cell repeating group, which repeating group is filled with four, adjacent “dot pixels”, Dp&#39;s, where each such dot pixel consists of two yellow-producing capable or blue-white producing capable subpixels. In other words, each of the dot pixels Dp contains either a pair of red and green subpixels, Rp and Gp, or a pair of blue and white subpixels, Bp and Wp. In the illustrated example, a size (area) of a dot pixel Dp(RG) or Dp(BW) respectively including red and green subpixels Rp and Gp or blue and white subpixels Bp and Wp is roughly the same as that of a conventional RGB metameric “pixel” that consists of adjacent red, green and blue subpixels in a comparable RGB striped structure. 
     The data driver  300  converts the red, green, blue and white digital data signals Rro, Gro, Bro and Wro into red, green, blue and white data voltages, and provides the red, green, blue and white data voltages to the data lines DL of the substrate  200 . 
     The gate driver  400  sequentially provides row-activating gate signals such as in one at a time sequence to the gate lines GL. 
     The light source part  500  includes a light source generating light. The light source part  500  provides the light to the display panel  200 . The light source may include one or more fluorescent lamps or one or more different kinds of light emitting diodes (LEDs) in edge lighting or backlighting configuration. 
     The light source driver  600  controls driving of the light source part  500 . The light source driver  600  may control luminance of the light provided to the display panel  200  based on the luminance control signal outputted from the data processing circuit  100 . 
       FIG. 3  is a block diagram illustrating details of one embodiment of the data processing circuit  100  of  FIG. 2 . 
     Referring to  FIGS. 2 and 3 , the data processing circuit  100  includes an input gamma function transformer (or generator)  110 , a gamut mapping part  120 , a luminance controller  130 , a scaler  140 , a clamping part  150 , a subpixel rendering part  160 , a first line memory buffer  165 , a second line memory buffer  171 , a black setting part  175  and a dithering part  180 . 
     As is known to those skilled in the art, conventional RGB input data is provided as not-linearly distributed value encodings (encoded brightness signals). In order to transform these into linearly distributed value encodings (luminance encodings); a so-called input gamma function transform is generally performed. The input gamma generator  110  of the illustrated embodiment includes a red transform lookup table LUT 1 , a green transform lookup table LUT 2  and a blue transform lookup table LUT 3 . The input gamma generator  110  outputs m-bit wide, linearized red data Rin, m-bit wide, linearized green data Gin and m-bit wide, linearized blue data Bin based on the supplied n-bit wide, nonlinearized red data R, n-bit wide, nonlinearized green data G and n-bit wide, nonlinearized blue data B using the red, green and blue lookup tables LUT 1 , LUT 2  and LUT 3 . The n and m are natural numbers and n&lt;m. For example, n may be 8-bits wide and m may be 12-bits wide. 
     The gamut mapping part  120  maps the m-bit wide, linearized red, green and blue data signals Rin, Gin and Bin into an alternate gamut space defined by corresponding m-bit wide, and still linearized red, green, blue and white data Ro, Go, Bo and Wo (where it is to be noted here that Wo is an added color component corresponding to the less conventional RGBW structure). 
     The gamut mapping part  120  receives the red, green and blue data signals Rin, Gin and Bin. The red, green and blue data signals Rin, Gin and Bin may be paired to represent dot data pairs corresponding to respective dot pixels (Dp&#39;s). The gamut mapping part  120  generates the red, green, blue and white data Ro, Go, Bo and Wo based on the red, green and blue data Rin, Gin and Bin. 
     In one embodiment, the gamut mapping part  120  calculates and generates as an internal signal, a white ratio signal WR according to exemplary Equation 1 as follows. 
     
       
         
           
             
               
                 
                   
                     White 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     
                       Ratio 
                       ⁡ 
                       
                         ( 
                         WR 
                         ) 
                       
                     
                   
                   = 
                   
                     
                       
                         L 
                         W 
                       
                       
                         
                           L 
                           R 
                         
                         + 
                         
                           L 
                           G 
                         
                         + 
                         
                           L 
                           B 
                         
                       
                     
                     = 
                     
                       m 
                       2 
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     1 
                   
                   ] 
                 
               
             
           
         
       
     
     Here, L R  is the output red luminance level, L G  is the green luminance level, L B  is the blue luminance level and L W  is the output white luminance level. 
     The gamut mapping part  120  may generates the red, green, blue and white data Ro, Go, Bo and Wo based on a white ratio value WR (=m 2 ) that satisfies below Equation 2. 
     
       
         
           
             
               
                 
                   
                       
                   
                   ⁢ 
                   
                     [ 
                     
                       Equation 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       2 
                     
                     ] 
                   
                 
               
             
             
               
                 
                   
                       
                   
                   ⁢ 
                   
                     
                       2 
                       ⁢ 
                       Ro 
                     
                     = 
                     
                       
                         Rin 
                         ⁡ 
                         
                           ( 
                           
                             1 
                             + 
                             
                               m 
                               2 
                             
                           
                           ) 
                         
                       
                       - 
                       
                         2 
                         ⁢ 
                         
                           m 
                           2 
                         
                         ⁢ 
                         Wo 
                       
                     
                   
                 
               
             
             
               
                 
                   
                       
                   
                   ⁢ 
                   
                     
                       2 
                       ⁢ 
                       Go 
                     
                     = 
                     
                       
                         Gin 
                         ⁡ 
                         
                           ( 
                           
                             1 
                             + 
                             
                               m 
                               2 
                             
                           
                           ) 
                         
                       
                       - 
                       
                         2 
                         ⁢ 
                         
                           m 
                           2 
                         
                         ⁢ 
                         Wo 
                       
                     
                   
                 
               
             
             
               
                 
                   
                       
                   
                   ⁢ 
                   
                     
                       2 
                       ⁢ 
                       Bo 
                     
                     = 
                     
                       
                         Bin 
                         ⁡ 
                         
                           ( 
                           
                             1 
                             + 
                             
                               m 
                               2 
                             
                           
                           ) 
                         
                       
                       - 
                       
                         2 
                         ⁢ 
                         
                           m 
                           2 
                         
                         ⁢ 
                         Wo 
                       
                     
                   
                 
               
             
             
               
                 
                   
                       
                   
                   ⁢ 
                   
                     
                       
                         2 
                         ⁢ 
                         
                           m 
                           2 
                         
                         ⁢ 
                         Wo 
                       
                       = 
                       
                         
                           ( 
                           
                             
                               2 
                               ⁢ 
                               Rin 
                             
                             + 
                             
                               5 
                               ⁢ 
                               Gin 
                             
                             + 
                             Bin 
                           
                           ) 
                         
                         8 
                       
                     
                     , 
                   
                 
               
             
             
               
                 
                   
                     
                       
                         max 
                         ⁡ 
                         
                           ( 
                           
                             Rin 
                             , 
                             Gin 
                             , 
                             Bin 
                           
                           ) 
                         
                       
                       ⁢ 
                       
                         ( 
                         
                           1 
                           + 
                           
                             m 
                             2 
                           
                         
                         ) 
                       
                     
                     - 
                     1 
                   
                   ≤ 
                   
                     2 
                     ⁢ 
                     
                       m 
                       2 
                     
                     ⁢ 
                     Wo 
                   
                   ≤ 
                   
                     
                       min 
                       ⁡ 
                       
                         ( 
                         
                           Rin 
                           , 
                           Gin 
                           , 
                           Bin 
                         
                         ) 
                       
                     
                     ⁢ 
                     
                       ( 
                       
                         1 
                         + 
                         
                           m 
                           2 
                         
                       
                       ) 
                     
                   
                 
               
             
           
         
       
     
     The luminance controller  130  then responsively determines a luminance level to be provided by the light source part  500  using a histogram based on the red, green, blue and white data Ro, Go, Bo and Wo generated by the gamut mapping part  120 . Compared to a conventional display panel having just the striped RGB structure, the display panel  200  according to the present example embodiment further includes the white subpixel so that the display panel  200  has a higher white light emission efficiency. Thus, the light source part  500  may be driven at a relatively lower luminance level, and power consumption of the display apparatus may be comparatively decreased. 
     The scaler  140  redetermines grayscale levels of the red, green, blue and white data Ro, Go, Bo and Wo generated in the gamut mapping part  120  based on the luminance level(s) determined as the output(s) for the luminance control part  130 . In other words, the actual luminance output of each pixel unit is the combination of the intensity of backlighting provided for that pixel unit and the percentage of light that will be passed through the liquid crystal layer based on how the liquid crystal cell is driven. The scaler  140  determines the new liquid crystal cell drive amount based on the setting of the backlighting amount. 
     Sometimes the scaler produces drive results (Ro*, Go*, Bo*, Wo*) that exceed the drive capabilities of the LCD panel either on the low luminance end or the high illustrated end of the capabilities spectrum. The clamping part  150  responsively compensates the red, green, blue and white data Ro*, Go*, Bo* and Wo* determined in the scaler  140  so that, for example, pure saturated color output is slightly sacrificed and some white component is added in that location when the light source part  500  is being driven with a very low luminance level and the desired level of saturated-only color cannot therefore be produced in that screen location. 
     The first line memory buffer  165  stores the post-clamping data (Ro′, Go′, Bo′, Wo′) outputted from the clamping part  150  on a display line-by-line basis so that a previous line is stored in the first line memory buffer  165  when data for a next subsequent display line arrives through the pipeline. For example, the first line memory buffer  165  may store adjacent data adjacent to the red, green, blue and white data Ro′, Go′, Bo′ and Wo′ so that a next described, subpixel rendering part  160  can use both previous line luminance values and current line luminance values to re-render the display drive signals on a subpixel rendering basis (e.g., area resampling and luminance redistribution based on the area resampling as well as optional color rebalancing and luminance channel filtering). 
     The subpixel rendering part  160  reconstructs the red, green, blue and white data Ro′, Go′, Bo′ and Wo′ to thereby generate rendered red and green data Rr and Gr or blue and white data Br and Wr using the adjacent data adjacent to the red, green, blue and white data Ro, Go, Bo and Wo stored in the first line memory buffer  165  according to a pixel structure of the display panel  200 . 
     The second line memory buffer  171  stores yet further history about the red, green and blue data R, G and B which are input as data into the LUTs  110 . 
     The black setting part  175  (also referenced herein as the black re-establishing part  175 ) determines whether the pre-gamma converted, brightness levels specified by the red, green and blue data R, G and B stored in the second line memory buffer  171  include brightness levels corresponding to a predefined black grayscale level. If the red, green and blue data R, G and B do not include the predefined black grayscale level, then the black re-establishing part  175  outputs the red and green data Rr* and Gr* or the blue and white data Br* and Wr* outputted from the subpixel rendering part  160  as they are, without any alteration. 
     On the other hand, if the red, green and blue brightness data R, G and B retained by the second line memory buffer  171  indicate that a full black luminance was originally intended, the black re-establishing part  175  further analyzes the data to automatically determine whether the red, green and blue brightness data R, G and B define a black dot pattern corresponding to a predetermined dot-check pattern, where this is done using adjacent data adjacent the red, green and blue data R, G and B which are stored in the second line memory buffer  171 . 
     If the red, green and blue data R, G and B do not include the black dot configuration according to the predetermined dot-check pattern, the black setting part  175  sets the grayscale level of the red and green data Rr and Gr or the blue and white data Br and Wr outputted from the subpixel rendering part  160  as the predetermined black grayscale level. On the other hand, if the red, green and blue data R, G and B include the black dot data having the predetermined dot-check pattern, the black setting part  175  outputs the red and green data Rr* and Gr* or the blue and white data Br* and Wr* outputted from the subpixel rendering part  160  as they are, without any alteration; in other words, without over-writing and thus re-establishing the original full black level. 
     The dithering part  180  is optimal and it may perform temporal and/or spatial gray-scale dithering for the red and green data Rr and Gr or the blue and white data Br and Wr which are processed to m-bit type. The dithering part  180  outputs n-bit red and green data Rro and Gro or n-bit blue and white data Bro and Wro, where n is less than m. Stated otherwise; if the output RGBWr* from the black re-establishing part  175  calls for a higher degree of gray scale precision per subpixel than the LCD panel can deliver in a single instant; say 12-bits of gray scale resolution per subpixel (m=12) where the LCD panel can only deliver, say, 8-bits of gray scale resolution per subpixel in a single instant (n=8), then one or both of temporal and spatial gray-scale dithering are provided by the dithering part  180  such that the average human visual system perceives the desired higher gray scale resolution on per subpixel or per dot pixel basis. 
       FIGS. 4A and 4B  are conceptual diagrams providing an example of how area resampling may be carried out by the subpixel rendering part of  FIG. 3 . 
     In  FIG. 4A , each circle (e.g., P 1 , P 2 , etc.) represents a light-outputting point light source and the usually diamond shaped area (e.g., A 1 ) surrounding that point light source (e.g., P 1 ) represents a coverage area assigned to that point light source. As can be seen in  FIG. 4A , the point light sources (circles P 1 , P 2 , etc.) are regularly distributed and their correspondingly assigned coverage areas (generally diamond shaped areas) are defined by virtual lines drawn equidistant between the regularly spaced apart point light sources (circles P 1 , P 2 , etc.). 
     Also in  FIG. 4A , each non-diamond square (e.g., D 11 , D 12 ) represents an input or source-data dot pixel. That is, for each RGBW set output by the gamut mapping part  120  of  FIG. 3 , there is a corresponding source-data dot pixel location represented by one of the non-diamond squares (e.g., D 11 , D 12 ) shown in  FIG. 4A . Not all the source-data dot pixel locations are shown. This is done to avoid illustrative clutter. Some of the source-data dot pixels (e.g., D 11 , D 12 , D 13 , D 14 ) are overlaid on the map of the display screen point light sources (e.g., circle P 1 ) such that these source-data dot pixels (e.g., D 11 , D 12 , D 13 , D 14 ) are shared by multiple diamond shaped areas (e.g., A 1 ) of corresponding, on display, point light sources (circles). More specifically, each of source-data dot pixels D 11 , D 12 , D 13 , and D 14  must distribute its intended luminance contribution four ways, namely, to the diamond areas on its left and right and to the diamond areas above and below it. What is not shown in  FIG. 4A , but will be shown in  FIG. 4B  is that a source-data dot pixel (e.g., D 0  of  FIG. 4B ) can come to be overlaid in the center of a diamond shaped areas (e.g., A 1 ); in which case, that source-data dot pixel (e.g., D 0 ) does not spread its intended luminance contribution elsewhere, but rather contributes its luminance value only to the point light source (e.g., P 1 ) that owns that diamond shaped area (e.g., A 1 ). In a case where a plurality of source-data dot pixels (e.g., D 0 , D 11 , D 12 , D 13 , D 14 ) come to be overlaid both inside and across the boundaries of a given diamond shaped areas (e.g., A 1 ), the intended luminance contributions of each are normalized (in one embodiment) so that the sum of contribution percentages is 100%. This is accomplished for example in the luminance contribution kernel filter of  FIG. 4B  by assigning 50% weight to the fully-inside-the-area source-data dot pixel (D 0 ) and by assigning 12.5% weight to the one-quarter inside-the-area source-data dot pixels (D 1 , D 2 , D 3 , D 4 ). 
     Referring to further details of  FIG. 4A , a circular point P 1  represents the display screen construct that is intended to generate a corresponding one of red, green, blue or white point source output based on the contribution of surrounding source-data dot pixels (e.g., D 11 , D 12 , D 13 , D 14 ) disposed adjacent to the circular point P 1 . As mentioned, the usually diamond shaped area (e.g., A 1 ) assigned to the circular point P 1  represents the coverage area of that circular point P 1 . 
       FIG. 4A  also shows an alternate way of looking at how much contribution each source-data dot pixel (e.g., D 44 ) is intended to make to the circular points (e.g., P 4 , P 5 , P 6  and P 7 ) over whose domains the given source-data dot pixel (e.g., D 44 ) is overlaid. A diamond shaped area A 44  is assigned to corresponding source-data dot pixel D 44  and the percentage of overlay of that area A 44  over the coverage areas (e.g., A 1 ) of the circular points (e.g., P 4 , P 5 , P 6  and P 7 ) is computed. This alternate way of viewing the situation is more general in that the way that a geometrically scaled pattern of source-data dot pixels can overlay a predetermined pattern of on-screen, point light sources (e.g., P 1 ) can vary depending on the actual design of the subpixel repeating groups of the display. In  FIG. 4A , each Red subpixel in the 8-cell Pentile repeating group may map to a corresponding on-screen, point light source (e.g., P 1 ). Alternatively or additionally, each lumina dot pixel (Dp) such as each RG dot pixel may map to a corresponding on-screen, point light source (e.g., P 1 ). Similarly, by shifting the illustrated dashed square one step left or right, it can be seen that each BW dot pixel may map to a corresponding on-screen, point light source (circle). It should be apparent that each BW dot pixel may be used to serve as a blueish-white light outputting point. While not as clearly apparent, each RG dot pixel may be used (in combination with a Blue subpixel lent from an adjacent dot) to serve as a white light outputting point (BW+YW=WW). 
     Referring to the specifics of  FIG. 4B , shown there is an example of a luminance channel filtering kernel that may be used as part of a subpixel rendering algorithm to remap input definitions of white light source areas (e.g., A 44 ) into corresponding luminance outputs to be provided by the on-screen, point light source (circles). In  FIG. 4B , the non-Pentile RGBW structure denoted as D 0  (and which consists of the red, green, blue and white data components identified as Ro, Go, Bo and Wo) is deemed to be at a center of a nine pixel area that happens to overlay the coverage area of a Pentile dot pixel (either an RG dot pixel or a BW dot pixel). In accordance with area resampling rules, the contributions weighting kernel is used to assign 12.5% contributions from the North, South, East and West side non-Pentile RGBW structures (D 1 -D 4 ) and to assign 50% contribution from the central non-Pentile RGBW structure (D 0 ) so as to thereby determine the drive signal to be applied to the corresponding Pentile dot pixel (either an RG dot pixel or a BW dot pixel). 
     If a location of the central (D 0 ) red, green, blue and white data Ro, Go, Bo and Wo resampled using the adjacent dot data D 1 , D 2 , D 3  and D 4  corresponds to even numbered dots of the display panel  200 , the red, green, blue and white data Ro, Go, Bo and Wo are reconstructed to generate red and green data Rr and Gr. If the location of the central (D 0 ) red, green, blue and white data Ro, Go, Bo and Wo resampled using the adjacent dot data D 1 , D 2 , D 3  and D 4  corresponds to odd numbered dots of the display panel  200 , the red, green, blue and white data Ro, Go, Bo and Wo are reconstructed to generate blue and white data Br and Wr. 
       FIG. 5  is a flowchart diagram illustrating a method of processing data signals of the data processing circuit of  FIG. 2 .  FIGS. 6A and 6B  are conceptual diagrams illustrating possible dot-check patterned artifacts. 
     Referring to  FIGS. 3 and 5 , the input gamma generator  110  generates m-bit wide, linearized red, green and blue value encoded data signals: Rin, Gin and Bin based on n-bit wide, nonlinearized red, green and blue value encoded data signals R, G and B (step S 110 ). The number of bits per subpixel in the m-bit red, green and blue data Rin, Gin and Bin is greater than that of the n-bit red, green and blue data R, G and B. The second line memory buffer  171  stores the n-bit wide red, green and blue value encoded data signals R, G and B. 
     The gamut mapping part  120  generates m-bit red, green, blue and white data Ro, Go, Bo and Wo based on the m-bit red, green and blue data Rin, Gin and Bin (step S 120 ). 
     The luminance controller  130  determines a luminance level of the light source part  500  using a histogram based on the m-bit red, green, blue and white data Ro, Go, Bo and Wo corresponding to a frame. 
     The scaler  140  redetermines grayscale levels of its respectively output m-bit red, green, blue and white data signals, Ro*, Go*, Bo* and Wo* based on the luminance level (step S 130 ). 
     The clamping part  150  compensates the pure color element of its respectively output m-bit red, green, blue and white data signals, Ro′, Go′, Bo′ and Wo′ according to the luminance level of the light source part  500  (step S 140 ). 
     The subpixel rendering part  160  generates the m-bit red and green data Rr and Gr or the m-bit blue and white data Br and Wr using the red, green, blue and white data Ro′, Go′, Bo′ and Wo′ and the adjacent data adjacent to the red, green, blue and white data Ro, Go, Bo and Wo stored in the first line memory buffer  165  according to an RGBW structure of the display panel  200  (step S 150 ). 
     The black setting part  175  determines whether all grayscale levels of the n-bit red, green and blue data R, G and B stored in the second line memory buffer  171  are substantially equal to “0” which represents the predetermined black grayscale level in one embodiment, (step S 161 ). If all grayscale levels of the n-bit red, green and blue data R, G and B are substantially equal to “0”, the black setting part  175  determines whether the n-bit red, green and blue data R, G and B include black dot data having a predetermined dot-check pattern (step S 163 ). 
     If the n-bit red, green and blue data R, G and B do not include the black dot data having the predetermined dot-check pattern, the black setting part  175  sets the m-bit red and green data Rr and Gr to “0” (the YW Dp equal to 0) or the m-bit blue and white data Br and Wr to “0” (the BW Dp equal to 0) to thereby represent the corresponding black grayscale level (step S 171 ). 
     On the other hand, if at least one of the grayscale levels of the red, green and blue data R, G and B is not equal to “0” in the step S 161 , the black setting part  175  outputs the m-bit red and green data Rr and Gr or the m-bit blue and white data Br and Wr generated in the subpixel rendering part  160  as they are (as is), without any alteration (step S 175 ). 
     In addition, if the n-bit red, green and blue data R, G and B include the black dot data having the predetermined dot-check pattern in the step S 163 , the black setting part  175  outputs the m-bit red and green data Rr and Gr or the m-bit blue and white data Br and Wr generated in the subpixel rendering part  160  as they are (as is), without any alteration (step S 175 ). 
     Referring to  FIG. 6A , shown is a first predetermined pattern which can be simply referred to as Checkerboard-wise Lit-up YW Dp&#39;s (turned on yellowish-white dot pixels). In the Checkerboard-wise Lit-up YW Dp&#39;s pattern, the BW Dp&#39;s (blueish-white dot pixels) are turned off and thus display a black pattern portion BK of the Checkerboard pattern. On the other hand, the red and green subpixels Rp and Gp are lit up so as to display the white portion of the Checkerboard pattern as turned on YW Dp&#39;s (which display yellow instead of white). 
     Referring next to  FIG. 6B , shown is a second predetermined pattern which can be simply referred to as Checkerboard-wise Lit-up BW Dp&#39;s (turned on blueish-white dot pixels). In this second pattern, the red and green subpixels Rp and Gp display the black pattern BK portion of the Checkerboard pattern. The Lit-up BW Dp&#39;s have a relatively lower luminance than an ideal WW Dp (white-white dot pixel, not shown) and thus, the intended 50% black and 50% white texture may not be clearly displayed. Similarly, in the case of  FIG. 6A , the YW Dp&#39;s (which display yellow instead of white) have a slightly different luminosity effect than the ideal WW Dp (white-white dot pixel, not shown) and thus, the intended 50% black and 50% white texture may not be clearly displayed. 
     In accordance with the present disclosure, a test is automatically carried out for detecting either one of the first and second patterns of respective  FIGS. 6A and 6B . When either the Checkerboard-wise Lit-up YW Dp&#39;s pattern is detected ( FIG. 6A ) or the Checkerboard-wise Lit-up BW Dp&#39;s pattern is detected ( FIG. 6B ) and a Black Re-establishing operation is indicated to be possible by the black setting part  175 , the Black Re-establishing operation is automatically suppressed and instead, the m-bit red and green data Rr and Gr or the m-bit blue and white data Br and Wr outputted from the subpixel rendering part  160  are displayed as they are, without any alteration. 
     The dithering part  180  performs dithering for the m-bit red and green data Rr and Gr or the m-bit blue and white data Br and Wr to generate the n-bit red and green data Rro and Gro or the blue and white data Bro and Wro (step S 180 ). 
       FIGS. 7A and 7B  are conceptual diagrams illustrating a method of automatically determining whether the dot-check patterned artifacts of  FIG. 6A  or  6 B are present. 
     Referring to  FIGS. 3 ,  5  and  7 A, the second line memory buffer  171  may be a single line memory buffer. The second line memory buffer  171  is storing red, green and blue data R, G and B corresponding to a (k−1)-th horizontal line (the previous row) when the black setting part  175  receives data corresponding to the k-th horizontal line. Herein, k is a natural number. 
     The black setting part  175  automatically determines that the dot-check patterned artifacts of  FIG. 6A  or  6 B will be generated based on the dot data D stored in the second line memory buffer  171  and adjacent data such as a first dot data D 1 , a second dot data D 2  and a third dot data D 3  disposed adjacent to the dot data D, when grayscale levels of the red and green data Rr and Gr corresponding to the dot data D are substantially equal to “0” which represents the black grayscale level and thus indicates that the black re-establishing part  175  will be trying to re-establish a more pure black downstream in the pipeline. 
     For example, when all of the first dot data D 1  and the third dot data D 3  disposed in a diagonal direction forming a check pattern with respect to the dot data D are substantially equal to “0” and the second dot data D 2  are not equal to “0,” the black setting part  175  determines the dot data D as the black dot data having the dot-check pattern. Accordingly, the black setting part  175  performs the step S 175 . 
     In contrast, when the first dot data D 1  and the third dot data D 3  are not equal to “0” and the second dot data D 2  are substantially equal to “0,” the black setting part  175  determines the dot data D not to be the black dot data having the dot-check pattern. Accordingly the black setting part  175  performs the step S 171 . 
     Referring to  FIGS. 3 ,  5  and  7 B, the second line memory buffer  171  including a double line memory buffer is explained. The second line memory buffer  171  stores red, green and blue data R, G and B corresponding to a (k−1)-th horizontal line and a k-th horizontal line, when the black setting part  175  receives data corresponding to the k-th horizontal line. 
     The black setting part  175  determines a dot-check pattern based on the dot data D stored in the second line memory buffer  171  and adjacent data such as a first dot data D 1 , a second dot data D 2  and a third dot data D 3  disposed adjacent to the dot data D, when grayscale levels of the red and green data Rr and Gr corresponding to the dot data D are substantially equal to “0” which represents the black grayscale level. 
     For example, when at least one of the first, second and the third dot data D 1 , D 2  and D 3  is substantially equal to “0” which represents the black grayscale level, the black setting part  175  determines the dot data D not to be the black dot data having the dot-check pattern. Accordingly, the black setting part  175  performs the step S 171 . 
     In contrast, when all of the first, second and third dot data D 1 , D 2  and D 3  are not equal to “0,” the black setting part  175  determines the dot data D as the black dot data having the dot-check pattern. Accordingly the black setting part  175  performs the step S 175 . 
       FIGS. 8A to 8C  are conceptual diagrams illustrating examples of various patterns displayed on the Pentile RGBW display apparatus of  FIG. 2  when the checkerboard testing algorithm of the present disclosure is used.  FIG. 8A  is a conceptual diagram illustrating a black text displayed on the display apparatus of  FIG. 2  except this time, unlike  FIG. 1B , the interior white area below the apex of the “A” consists of a lit-up BW Dp in a first row and a lit-up YW Dp in the row below it where each of the lit up Dp&#39;s forms part of a respective checkerboard pattern at least in the horizontal row direction. 
       FIG. 8B  is a conceptual diagram illustrating a horizontal white stripes pattern displayed on the display apparatus of  FIG. 2  that preserves white color balance.  FIG. 8C  is a conceptual diagram illustrating a vertical white stripes pattern displayed on the display apparatus of  FIG. 2  that also preserves white color balance. 
     Referring to the specifics of  FIG. 8A , due to the nature of the 8-cell repeating group. the red and green subpixels R and G (also known herein as the YW Dp&#39;s) are repeatedly arranged in a zig-zag shape and the blue and white subpixels B and W (also known herein as the BW Dp&#39;s) are also repeatedly arranged in a zig-zag shape in a region adjacent to the black text TX. Each white subpixel W may alone display as a white dot region. Also, every triad of adjacent red, green, and blue subpixels R, G and B, in combination, may display as a white region. In addition, each YW Dp in combination with an adjacent BW Dp may be both lit up to thereby display as a white region. By using variations of these techniques, a desired shape of a black filled glyph (e.g., a text glyph, TX) may be displayed with a desired shape on a white background without distortion. 
     Referring to  FIG. 8B , this shows the RGB triad approach wherein red, green, blue and white subpixels R, G, B and W are repeatedly arranged in a horizontal direction and lit up as such, so that a horizontal stripe pattern adjacent to a black horizontal line HL is displayed with white. Therefore, the horizontal black line pattern may easily be displayed without distortion. 
     Referring to  FIG. 8C , this shows the BW+YW=WW approach wherein a two-subpixel wide white vertical line may be formed. In other words, red, green, blue and white subpixels R, G, B and W are repeatedly arranged in the vertical direction, so that a vertical stripe pattern adjacent to a black vertical line VL is displayed with white. Therefore, the vertical black line pattern may be easily displayed without distortion. Review of  FIG. 8A  will show that the black “A” glyph is formed of a combination black horizontal and vertical lines where the black lines are bounded on left and right sides thereof by lit-up combinations of BW+YW=WW dot pixels. 
     Accordingly, expression of sharp edged glyphs such as alphabetic characters may be improved on an RGBW Pentile organized display screen. 
     Hereinafter, the same reference numerals will be used to refer to the same or like parts as those described in above example embodiment, and any repetitive detailed explanation will be omitted or briefly explained. 
       FIG. 9  is a block diagram illustrating a second data processing circuit according to another example embodiment of the present disclosure. 
     Referring to  FIGS. 2 and 9 , the illustrated data processing circuit  100 A includes an input gamma generator  110 , a gamut mapping part  220 , a luminance controller  130 , a scaler  140 , a clamping part  150 , a subpixel rendering part  260 , a line memory buffer  165  and a dithering part  180 . In this case, there is no discrete black setting part  175  or second line buffer  171 . 
     The input gamma generator  110  includes a red lookup table LUT 1 , a green lookup table LUT 2  and a blue lookup table LUT 3 . The input gamma generator  110  outputs m-bit red data Rin, m-bit green data Gin and m-bit blue data Bin based on the n-bit red data R, n-bit green data G and n-bit blue data B using the red, green and blue lookup tables LUT 1 , LUT 2  and LUT 3 . The n and m are natural numbers and n&lt;m. 
     The gamut mapping part  220  is different from  120  of  FIG. 3 . The different gamut mapping part  220  generates m-bit red, green, blue and white data Ro, Go, Bo and Wo based on the m-bit red, green and blue data Rin, Gin and Bin according to the above Equations 1 and 2 with a slight modification such that its solutions can include all black sections. For example, if all of grayscale levels of the red, green and blue data Rin, Gin and Bin are substantially equal to “0” (near zero in accordance with a predetermined nearness threshold) which represents a black grayscale level, the gamut mapping part  220  sets grayscale levels of the m-bit red, green, blue and white data Ro, Go, Bo, Wo corresponding to the red, green and blue data Rin, Gin and Bin to a black grayscale level. In contrast, if grayscales of the red, green and blue data Rin, Gin and Bin are not substantially equal to “0” (spaced apart from zero by more than the predetermined nearness threshold), the gamut mapping part  220  generates the m-bit red, green, blue and white data Ro, Go, Bo and Wo according to Equations 1 and 2. 
     The luminance controller  130  determines a luminance level of the light source part  500  using a histogram based on the red, green, blue and white data Ro, Go, Bo and Wo generated in the gamut mapping part  220 . 
     The scaler  140  redetermines grayscale levels of the red, green, blue and white data Ro*, Go*, Bo* and Wo* generated in the gamut mapping part  220  based on the luminance level determined in the luminance control part  130 . 
     The clamping part  150  compensates the red, green, blue and white data Ro*, Go*, Bo* and Wo* determined in the scaler  140  so that the clamping part  150  compensates a pure color element sacrificed when the light source part  500  is driven with the low luminance level by the luminance controller  130 . 
     The line memory buffer  165  stores data outputted from the clamping part  150 . For example, the line memory buffer  165  may store adjacent data adjacent to the red, green, blue and white data Ro′, Go′, Bo′ and Wo′. 
     The subpixel rendering part  260  reconstructs the red, green, blue and white data Ro′, Go′, Bo′ and Wo′ to generate subpixel rendered red and green data Rr and Gr or blue and white data Br and Wr using the subpixel rendering algorithm explained above with reference for example to  FIGS. 4A and 4B . 
     For example, if the grayscale levels of the red, green, blue and white data Ro, Go, Bo and Wo include a black grayscale level, the subpixel rendering part  260  determines whether the red, green, blue and white data Ro, Go, Bo and Wo are black dot data having a dot-check pattern using adjacent data adjacent to the red, green, blue and white data Ro, Go, Bo and Wo. If the red, green, blue and white data Ro, Go, Bo and Wo are not the black dot data having the dot-check pattern, the subpixel rendering part  260  sets grayscale levels of the red and green data Rr and Gr or the blue and white data Br and Wr corresponding to the red, green, blue and white data Ro, Go, Bo, Wo to a black grayscale level. In contrast, if the red, green, blue and white data Ro, Go, Bo and Wo are the black dot data having the dot-check pattern, the subpixel rendering part  260  reconstructs the red, green, blue and white data Ro, Go, Bo and Wo to generate the red and green data Rr and Gr or the blue and white data Br and Wr using the subpixel rendering algorithm explained above with reference to  FIGS. 4A and 4B . 
     The dithering part  180  performs dithering for the red and green data Rr and Gr or the blue and white data Br and Wr which are processed to an m-bit type, and thus outputs n-bit red and green data Rro and Gro or n-bit blue and white data Bro and Wro. 
       FIG. 10  is a flowchart diagram illustrating a method of processing data signals of the second data processing circuit of  FIG. 9 . 
     Referring to  FIGS. 9 and 10 , the input gamma generator  110  generates m-bit red, green and blue data Rin, Gin and Bin based on n-bit red, green and blue data R, G and B (step S 210 ). 
     The gamut mapping part  220  determines whether all grayscale levels of the red, green and blue data Rin, Gin and Bin are equal to “0” which represents a black grayscale level (step S 220 ). If all grayscale levels of the red, green and blue data Rin, Gin and Bin are substantially equal to “0,” the gamut mapping part  220  sets grayscale levels of the m-bit red, green, blue and white data Ro, Go, Bo and Wo corresponding to the red, green and blue data Rin, Gin and Bin to “0” which represents a black grayscale level (step S 223 ). In contrast, if the grayscale levels of the red, green and blue data Rin, Gin and Bin are not equal to “0,” the gamut mapping part  220  generates the m-bit red, green, blue and white data Ro, Go, Bo and Wo according to Equations 1 and 2 (step S 225 ). 
     The luminance controller  130  determines a luminance level of the light source part  500  using a histogram based on the m-bit red, green, blue and white data Ro, Go, Bo and Wo corresponding to a frame. 
     The scaler  140  redetermines grayscale levels of the m-bit red, green, blue and white data Ro*, Go*, Bo* and Wo* based on the luminance level (step S 230 ). 
     The clamping part  150  compensates the pure color element of the m-bit red, green, blue and white data Ro′, Go′, Bo′ and Wo′ according to the luminance level of the light source part  500  (step S 240 ). 
     The subpixel rendering part  260  includes a part that automatically bypasses subpixel rendering for dot check conditions. More specifically, the subpixel rendering part  260  determines whether all grayscale levels of the red, green, blue and white data Rin, Gin, Bin and Win are substantially equal to “0” which represents a black grayscale level (step S 250 ). If all grayscale levels of the red, green, blue and white data Rin, Gin, Bin, and Win, are substantially equal to “0,” the subpixel rendering part  260  determines whether the red, green, blue and white data Ro, Go, Bo and Wo are black dot data having a dot-check pattern using adjacent data adjacent to the red, green, blue and white data Ro, Go, Bo and Wo (step S 253 ). 
     If the red, green, blue and white data Rin, Gin, Bin, and Win, are not the black dot data having the dot-check pattern, the subpixel rendering part  260  sets the grayscale levels of the red and green data Rr and Gr to “0” (thus forcing the corresponding YW Dp equal to zero) or sets the blue and white data Br and Wr corresponding to the red, green, blue and white data Rin, Gin, Bin and Win to “0” (thus forcing the corresponding BW Dp equal to zero) which represents the black grayscale level (step S 255 ). Subpixel rendering step S 257  is bypassed. In contrast, if the red, green, blue and white data Rin, Gin, Bin and Win are the black dot data but do not have the dot-check pattern, the subpixel rendering part  260  reconstructs the red, green, blue and white data Ro, Go, Bo and Wo using the normal subpixel rendering algorithm to thereby generate the red and green data Rr and Gr or the blue and white data Br and Wr using the subpixel rendering algorithm explained above with reference for example to  FIGS. 4A and 4B  (step S 257 ). 
     The dithering part  180  performs dithering for the m-bit red and green data Rr and Gr or the m-bit blue and white data Br and Wr provided from the subpixel rendering part  260  to generate n-bit red and green data Rro and Gro or n-bit blue and white data Bro and Wro (step S 280 ). 
     In the present example embodiment, the data outputted from the clamping part  150  and stored in the line memory buffer  165  are used to determine whether the red, green, blue and white data Ro, Go, Bo and Wo are the black dot data having the dot-check pattern. Although not shown in figures, an additional line memory buffer storing data outputted from the subpixel rendering part  260  may be used to determine whether the red, green, blue and white data Rin, Gin, Bin, and Win, are the black dot data having the dot-check pattern. In this case, the additional line memory buffer storing the data from the subpixel rendering part  260  may be a single line memory buffer or a double line memory buffer as explained above with reference to  FIGS. 7A and 7B . 
     According to the second example embodiment, the black text, the black horizontal pattern and the black vertical pattern displayed on the display apparatus may be displayed without distortion as shown in  FIGS. 8A ,  8 B and  8 C. In addition, the function of the gamut mapping part  220  and the subpixel rendering part  260  may be modified to decrease the number of memories. 
       FIG. 11  is a block diagram illustrating a third data processing circuit according to still another example embodiment of the present disclosure. 
     Referring to  FIG. 11 , the data processing circuit  100 B includes an input gamma generator  110 , a gamut mapping part  120 , a luminance controller  130 , a scaler  140 , a clamping part  150 , a subpixel rendering part  360 , a line memory buffer  165  and a dithering part  180 . 
     The input gamma generator  110  includes a red lookup table LUT 1 , a green lookup table LUT 2  and a blue lookup table LUT 3 . The input gamma generator  110  outputs m-bit red data Rin, m-bit green data Gin and m-bit blue data Bin based on the n-bit red data R, n-bit green data G and n-bit blue data B using the red, green and blue lookup tables LUT 1 , LUT 2  and LUT 3 . The n and m are natural numbers and n&lt;m. 
     The gamut mapping part  120  generates m-bit red, green, blue and white data Ro, Go, Bo and Wo based on the m-bit red, green and blue data Rin, Gin and Bin according to Equations 1 and 2. 
     The luminance controller  130  determines a luminance level of the light source part  500  using a histogram based on the red, green, blue and white data Ro, Go, Bo and Wo generated in the gamut mapping part  120 . 
     The scaler  140  redetermines grayscale levels of the red, green, blue and white data Ro, Go, Bo and Wo generated in the gamut mapping part  120  based on the luminance level determined in the luminance control part  130 . 
     The clamping part  150  compensates the red, green, blue and white data Ro*, Go*, Bo* and Wo* determined in the scaler  140  so that the clamping part  150  compensates a pure color element sacrificed when the light source part  500  is driven with the low luminance level by the luminance controller  130 . 
     The line memory buffer  165  stores data outputted from the clamping part  150 . For example, the line memory buffer  165  may store adjacent data adjacent to the red, green, blue and white data Ro′, Go′, Bo′ and Wo′. 
     The subpixel rendering part  360  includes a blue timing shift algorithm module (BSA) and a subpixel rendering algorithm module (SPRA) explained above with reference to  FIGS. 4A and 4B . The BSA module operates to generate smoother images near edges of the screen when processing natural image color combinations and displaying various nonartificial color images. Although the BSA smoothly processes the color combination in a natural colorful display, the BSA can generate an artifact in a sharp edged glyph (e.g., text) editing display including black and white colors. 
     The subpixel rendering part  360  according to the present example embodiment automatically tests different regions of the display image to thereby determine whether a display region is a text display region or a natural color mix display region by applying a 3 by 3 data determining block to the red, green, blue and white data Ro′, Go′, Bo′ and Wo′ outputted from the clamping part  150  and the adjacent data stored in the line memory buffer  165 . If a grayscale level of a dot data to which the 3 by 3 data determining block is applied is “0” which represents a black grayscale and/or “255” which represents a white grayscale in an 8-bit system, the sub pixel rendering part  360  determines the display region as being the text display region so that the sub pixel rendering part  360  only applies the SPRA instead of applying both of the BSA and the SPRA. In contrast, if the grayscale level of the dot data to which the 3 by 3 data determining block is applied includes a grayscale level except for the black and white grayscale levels, the sub pixel rendering part  360  determines the display region as being the natural color display region so that the sub pixel rendering part  360  applies both of the BSA and the SPRA. 
     The dithering part  180  performs dithering for the red and green data Rr and Gr or the blue and white data Br and Wr which are processed to the m-bit type, and outputs n-bit red and green data Rro and Gro or n-bit blue and white data Bro and Wro. 
       FIG. 12  is a conceptual diagram illustrating operation of the subpixel rendering part of  FIG. 11 . 
     Referring to  FIGS. 11 and 12 , the subpixel rendering part  360  determines whether the dot data D are data in a text display region or in a color display region by applying a 3 by 3 data determining block to the dot data D including the red, green, blue and white data Ro, Go, Bo and Wo outputted from the clamping part  150  and adjacent dot data stored in the line memory buffer  165 . 
     For example, the adjacent dot data include first dot data D 1  disposed adjacent to the dot data D in a first direction, second dot data D 2  disposed adjacent to the dot data D in a second direction, third dot data D 3  disposed adjacent to the dot data D in a third direction and fourth dot data D 4  disposed adjacent to the dot data D in a fourth direction. 
     The 3 by 3 determining block applies a weight of “1” to central dot data and four adjacent dot data to upper, lower, left and right directions from the central dot data, and “0” to four adjacent dot data to diagonal directions from the central dot data. For example, the 3 by 3 determining block applies “1” to the dot data D and the first, second, third and fourth dot data D 1 , D 2 , D 3  and D 4 . 
     The maximum grayscale values and the minimum grayscale values of the dot data D and the first, second, third and fourth dot data D 1 , D 2 , D 3  and D 4  are respectively calculated by Equation 3.
 
MAX=MAXIMUM( Rg,Gg,Bg,Wg ),
 
MIN=MINIMUM( Rg,Gg,Bg,Wg )  [Equation 3]
 
Herein, Rg is a grayscale level of red data, Gg is a grayscale level of green data, Bg is a grayscale level of blue data, and Wg is a grayscale level of white data.
 
     If the maximum grayscale values and the minimum grayscale values are “0” or “255” in an 8-bit system, or “0” and “255,” the subpixel rendering part  360  determines the dot data D as the data in the text display region. If the dot data D are determined as the data in the text display region, the sub pixel rendering part  360  only applies just the SPRA instead of applying both of the BSA and the SPRA. 
     In addition, if the maximum grayscale values and the minimum grayscale values include the grayscale level except for “0” and “255,” the subpixel rendering part  360  determines the dot data D as the data in the color display region. If the dot data D are determined as the data in the color display region, the sub pixel rendering part  360  applies both of the BSA and the SPRA. 
       FIG. 13  is a flowchart diagram illustrating a method of processing data of the data processing circuit of  FIG. 11 . 
     Referring to  FIGS. 11 ,  12  and  13 , the input gamma generator  110  generates m-bit red, green and blue data Rin, Gin and Bin based on n-bit red, green and blue data R, G and B (step S 310 ). 
     The gamut mapping part  120  generates m-bit red, green, blue and white data Ro, Go, Bo and Wo based on the m-bit red, green and blue data Rin, Gin and Bin (step S 320 ). 
     The luminance controller  130  determines a luminance level of the light source part  500  using a histogram based on the m-bit red, green, blue and white data Ro, Go, Bo and Wo corresponding to a frame. 
     The scaler  140  redetermines grayscale levels of the m-bit red, green, blue and white data Ro*, Go*, Bo* and Wo* based on the luminance level (step S 330 ). 
     The clamping part  150  compensates the pure color element of the m-bit red, green, blue and white data Ro′, Go′, Bo′ and Wo′ according to the luminance level of the light source part  500  (step S 340 ). 
     The subpixel rendering part  360  determines whether the red, green, blue and white data Ro′, Go′, Bo′ and Wo′ are data in a text display region by applying the 3 by 3 data determining block to the red, green, blue and white data Ro′, Go′, Bo′ and Wo′ and the data stored in the line memory buffer  165  (step S 350 ). 
     As shown in  FIG. 12 , if the grayscale level of the five dot data to which the 3 by 3 data determining block is applied includes a grayscale level except for “0” which represents the black grayscale level and “255” which represents the white grayscale level in an 8-bit system, the sub pixel rendering part  360  applies the BSA to the red, green, blue and white data Ro′, Go′, Bo′ and Wo′ (step S 360 ). The subpixel rendering part  360  reconstructs the red, green, blue and white data Ro′, Go′, Bo′ and Wo′ to generate red and green data Rr and Gr or blue and white data Br and Wr using the SPRA explained above with reference to  FIGS. 4A and 4B  (step S 370 ). 
     In contrast, if the grayscale level of the five dot data to which the 3 by 3 data determining block is applied is substantially equal to “0” which represents the black grayscale level and/or “255” which represents the white grayscale level in an 8-bit system, the subpixel rendering part  360  reconstructs the red, green, blue and white data Ro, Go, Bo and Wo to generate red and green data Rr and Gr (a YW Dp) or blue and white data Br and Wr (a BW Dp) using the SPRA (step S 370 ) instead of using both of the SPRA and the BSA. In the present example embodiment, although the BSA is applied prior to the SPRA, the SPRA may be applied prior to the BSA. 
     The dithering part  180  performs dithering for the m-bit red and green data Rr and Gr or the m-bit blue and white data Br and Wr to output the n-bit red and green data Rro and Gro or the blue and white data Bro and Wro (step S 380 ). 
     According to the present example embodiment, the black text, the black horizontal pattern and the black vertical pattern may be displayed without distortion as shown in  FIGS. 8A ,  8 B and  8 C. In addition, the subpixel rendering part  360  is modified, so that the number of memories may be decreased and the operation of the method according to the present example embodiment may be simplified respectively comparing to the previous example embodiments of  FIGS. 2 and 9 . 
     As described above, according to the present disclosure of invention, a black text may be displayed without distortion by setting grayscale levels of red and green data (the YW dot pixels) or blue and white data (the BW dot pixels) corresponding to input red, green and blue data R, G and B including a black grayscale level to a black grayscale level. In addition, if the red, green, blue and white data Ro, Go, Bo and Wo are the data in a text display region, a blue shift algorithm may be selectively not applied so that a black text may be displayed without distortion. 
     The foregoing is illustrative of the present teachings and is not to be construed as limiting thereof. Although a few example embodiments of the present disclosure of invention have been described, those skilled in the art will readily appreciate from the foregoing that many modifications are possible in the example embodiments without materially departing from the novel teachings and advantages of the present disclosure. Accordingly, all such modifications are intended to be included within the scope of the present teachings. 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 functionally equivalent structures. Therefore, it is to be understood that the foregoing is illustrative of the present teachings and is not to be construed as limited to the specific example embodiments disclosed, and that modifications to the disclosed example embodiments, as well as other example embodiments, are intended to be included within the scope of the teachings.