Abstract:
An image forming device includes an input unit to receive binary data for each color being input; a generation unit to generate an synthesis window, by applying a window of a predetermined size to each of the binary data for each color and synthesizing each window region; an image process unit to expand an image, by applying a plurality of sub windows to the synthesis window; and a control unit to detect an edge region of the expanded image, extract dots corresponding to the edge region from the binary data for each color, and carry out reinforcement or deletion of the dots. Accordingly, the quality of an image deteriorated by color disagreement is improved by software.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of Korean Application No. 2007-5601, filed Jan. 18, 2007, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    Aspects of the present invention relate to an image forming device and a method therefore, and more particularly, to an image forming device that compensates image disagreement by software and improves the quality of an image and a method thereof. 
         [0004]    2. Description of the Related Art 
         [0005]    As electronic technologies are developed, peripheral devices such as printers, scanners, and the like, are widely and actively used. Specifically, as many manufacturing companies have competitively participated in printer development, laser printers have replaced dot printers and inkjet printers that were used in the past because of the considerably improved print quality and print speed and lower noise level of the laser printer. The term “laser printer” refers to a printer that uses a laser light beam modulated as an image signal to transfer an image to a photosensitive unit. Thereafter, toner is adhered to the photosensitive unit and transferred onto a printable medium (such as, for example, printing paper) to form the image on the printable medium. The toner is fixed on the printable medium by high heat and pressure. 
         [0006]    A laser printer performs the operation of printing an image through a printing process typically divided into charging, writing, developing, transferring, fusing and the like. The term “charging” refers to a process of applying a high voltage (about 7000V) to a charger to form a negative charge on the surface of the photosensitive unit by a corona discharge. The term “writing” refers to a process of scanning the laser beam over the surface of the photosensitive unit with the negative charge to selectively neutralize or reverse the negative charge in an image-wise manner, and thus to form a latent image on the surface of the photosensitive unit. The term “developing” refers to a process of adhering toner particles with a negative charge onto the latent image on the surface of the photosensitive unit. The term “transferring” refers to a process of applying a predetermined transferring voltage to a transfer unit when a printable medium is passed between the photosensitive unit and the transfer unit, to form a positive charge on the back side of the printable medium so that the negatively charged toner particles adhered on the surface of the photosensitive unit (i.e., drum) are attracted to the printable medium. The term “fusing” refers to a process of completely fusing the toner formed on the printable medium by applying proper heat and pressure. Through these processes, an image is output to be formed on the printable medium. 
         [0007]    Specifically, these days, color laser printers have been widely used. A color laser printer expresses a color image, typically using four colored toners, cyan (C), magenta (M), yellow (Y) and black (K), collectively referred to as “CMYK.” In a color laser printer, to print a clear image, four photosensitive units are used and a printing process is performed with respect to each color of toner. Further, to display each colored toner at an accurate position, an intermediate transfer belt (ITB) can be used to transfer a color image onto a printable medium by a two-step process. 
         [0008]    In an image forming apparatus that forms a color image using the intermediate transfer belt, a plurality of photosensitive units and the like, each type of toner should be accurately superposed and transferred at the same position onto the printable medium. That is, in forming color images using separate C, M, Y and K toners, at least one or more tonor colors are superposed to display one image color. To display an accurate image color, each toner image has to be accurately transferred to an accurate position. 
         [0009]    However, as the number of printings increases, there is a problem in that image disagreement may occur. In image disagreement, a position to which toner is transferred is misaligned by an operation error between transfer units. That is, when each transfer unit cannot transfer the toner at the same position, an edge part of the image is blurred. This becomes a problem in printing a black text region, since all colors of C, M, Y and K are superposed to print the black text region. However, when the image disagreement occurs, a particular color may be prominent at an edge region of the black text, causing the text boundary to be blurred. 
         [0010]    To prevent the aforementioned problems, a conventional technology in this field uses an automatic color calibration function. That is, a color calibration process is automatically performed periodically. When an image forming apparatus prints about N sheets of printed matters, and the image transferred by each transfer unit of is misaligned by about X dots, the printer calibrates colors by adjusting the transfer position by the X dots regularly after printing the N sheets of prints. This is called the automatic color calibration process. However, when the color calibration process is performed, a lot of toner is consumed when performing the color calibration process. Accordingly, the amount of used toner increases. Moreover, since a user cannot use the image forming apparatus during the period in which a color calibration is performed, this approach may cause any inconvenience to the user. 
       SUMMARY OF THE INVENTION 
       [0011]    Aspects of the present invention relate to an image forming apparatus that applies a window to binary data of a color in order to understand the characteristics of an image, processes an edge region of the image accordingly, compensates for image disagreement by software, and minimizes the use of memory capacity, and a method thereof. 
         [0012]    According to an aspect of the present invention, there is provided an image forming device, comprising an input unit to receive binary data for each color being input; a generation unit to generate an synthesis window, by applying a window of a predetermined size to each of the received binary data for each color and synthesizing each window region; an image process unit to conditionally expand an image within the synthesis window along a directionality of the image existing within the synthesis window, by applying a plurality of sub windows to the synthesis window; and a control unit to detect an edge region of the expanded image, extract dots corresponding to the edge region from the binary data for each color, and carry out reinforcement or deletion of the dots corresponding to the edge region. 
         [0013]    According to an aspect of the present invention, the image forming device may further comprise an image forming unit to perform an image forming operation, by using each of the binary data for each color in which the dots corresponding to the edge region are reinforced or deleted. 
         [0014]    According to an aspect of the present invention, the generation unit may comprise a window application unit to have each pixel constituting each of the binary data for each color as a target pixel and apply a window of n×m in size, wherein n and m are any natural numbers, to the target pixel; and a synthesis unit to synthesize windows of the binary data for each color, in an OR-type manner, and to generate an synthesis window to display all pixels existing within each window of the binary data for each color. 
         [0015]    Further, according to an aspect of the present invention, the image process unit may comprise an operation unit to calculate a characteristic value for each of the sub windows representing the characteristic of an image existing within each of the sub windows, by applying each of the sub windows to the synthesis window; a condition storing unit to store conditions for expansion, considering the directionality depending on the characteristic value; and an expansion unit to expand the image by adding pixels in the target pixel region when it is determined that the calculated characteristic value satisfies the conditions for expansion. 
         [0016]    In this case, according to an aspect of the present invention, the operation unit may apply first, second, third and fourth sub windows respectively positioned at each corner region of the synthesis window, a fifth sub window crossing the center of the synthesis window widthwise, and a sixth sub window crossing the center of the synthesis window lengthwise; wherein, when the number of pixels existing in one of the first, second, third and fourth sub windows is at or above a predetermined threshold number of pixels, the operation unit may calculate the characteristic value of the one of the first, second, third and fourth sub windows as ‘1’, and when the number of pixels existing in the one of the first, second, third and fourth sub windows is below the predetermined threshold number of pixels, the operation unit may calculate the characteristic values of the one of the first, second, third and fourth sub windows as ‘0’; and when pixels exist at both sides of the center pixel in one of the fifth and sixth sub windows, the operation unit may calculate the characteristic value of the one of the fifth and sixth sub windows as ‘1’, and when pixel is absent at one or both sides of the center pixel in the one of the fifth and sixth sub windows, the operation unit may calculate the characteristic value of the one of the fifth and sixth sub windows as ‘0’. 
         [0017]    Further, according to an aspect of the present invention, the condition storing unit may store the conditions for expansion as follows: 
         [0018]    1) C1 &amp; C2 &amp; C3=1 
         [0019]    2) C3 &amp; C4 &amp; C5=1 
         [0020]    3) C1 &amp; C3 &amp; C6=1 
         [0021]    4) C2 &amp; C4 &amp; C6=1 
         [0022]    5) C1 &amp; C4=1 
         [0023]    6) C2 &amp; C3=1. 
         [0024]    In the conditions for expansion, C1, C2, C3, C4, C5 and C6 respectively refer to the characteristic values of the first, second, third, fourth, fifth and sixth sub windows. 
         [0025]    According to an aspect of the present invention, the characteristic value may be the number of pixels existing within the sub window or the distribution of the pixels existing therein. 
         [0026]    According to an aspect of the present invention, the binary data for each color may include C, M, Y and K color binary data. In this case, only when a rate of K color dots included in the edge region is at or above a predetermined threshold rate, the control unit may reinforce the dots positioned at the edge region on the K color binary data and delete the dots positioned at the edge region on the C, M and Y color binary data. 
         [0027]    According to another aspect of the present invention, there is provided an image forming device, comprising an image process unit to conditionally expand an image along a directionality of the image according to synthesized color binary data; and a control unit to detect an edge region of the expanded image, extract dots corresponding to the edge region from the color binary data and carry out reinforcement or deletion of the dots corresponding to the edge region 
         [0028]    According to another aspect of the present invention, there is provided an image forming method comprising generating a synthesis window, by applying a window of a predetermined size to each of binary data for each color and synthesizing each window region; conditionally expanding an image along the directionality of the image existing in the generated synthesis window, by applying a plurality of sub windows to the synthesis window; and detecting an edge region of the expanded image, extracting dots positioned in the edge region from the binary data for each color, and carrying out reinforcement or deletion of the extracted dots. 
         [0029]    According to an aspect of the present invention, the image forming method may further comprise: performing an image forming operation, by using each of the binary data for each color in which the dots positioned in the edge region are reinforced or deleted. 
         [0030]    According to an aspect of the present invention, the generating may comprise: selecting each pixel constituting each of the binary data for each color as a target pixel, and applying a window being n×m in size, wherein n and m are any natural numbers, to the target pixel; and synthesizing windows of the binary data for each color, in an OR-type manner and generating an synthesis window that displays all pixels existing within each window. 
         [0031]    According to an aspect of the present invention, the conditional expanding may comprise calculating a characteristic value representing the characteristic of an image existing within the sub windows, by applying the sub windows to the synthesis window; and expanding the image by adding pixels to the target pixel region when it is determined that the calculated characteristic value satisfies one of the conditions for expansion considering the directionality depending on the characteristic value. 
         [0032]    According to an aspect of the present invention, the calculating of the characteristic value may comprise: applying first, second, third and fourth sub windows respectively positioned at each corner region of the synthesis window, a fifth sub window crossing a center of the synthesis window widthwise, and a sixth sub window crossing the center of the synthesis window lengthwise; calculating the characteristic values for each sub window independently, wherein, for the first, second, third and fourth sub windows, the characteristic value of a sub window is ‘1’ when the number of pixels existing in the sub window is at or above a predetermined threshold number of pixels, and the characteristic value of the sub window is ‘0’ when the number of pixels existing in the sub window is below the predetermined threshold number of pixels; and wherein, for the fifth and sixth sub windows, the characteristic value of a sub window is ‘1’ when pixels exist at both sides of the center pixel in the sub window the characteristic value is ‘0’ when all pixels are absent at one or both sides of the center pixel in the sub window. 
         [0033]    In this case, according to an aspect of the present invention, the conditions for expansion may be as follows: 
         [0034]    1) C1 &amp; C2 &amp; C3=1 
         [0035]    2) C3 &amp; C4 &amp; C5=1 
         [0036]    3) C1 &amp; C3 &amp; C6=1 
         [0037]    4) C2 &amp; C4 &amp; C6=1 
         [0038]    5) C1 &amp; C4=1 
         [0039]    6) C2 &amp; C3=1. 
         [0000]    In the conditions for expansion, C1, C2, C3, C4, C5 and C6 respectively refer to the characteristic values of the first, second, third, fourth, fifth and sixth sub windows. 
         [0040]    Further, according to an aspect of the present invention, the characteristic value may be the number of pixels existing within the sub window or the distribution of the pixels existing therein. 
         [0041]    According to an aspect of the present invention, the binary data for each color may include C, M, Y and K color binary data. In this case, wherein, when a rate of K color dots included in the edge region is at or above a predetermined threshold rate, the detecting may comprise reinforcing the dots positioned at the edge region on the K color binary data and deleting the dots positioned at the edge region on the C, M and Y color binary data. 
         [0042]    Additional aspects and/or advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0043]    These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
           [0044]      FIG. 1  is a block diagram of an image forming apparatus according to an embodiment of the present invention; 
           [0045]      FIG. 2  is a block diagram describing the image forming apparatus of  FIG. 1  in more detail; 
           [0046]      FIG. 3  is a schematic view illustrating a process of applying a window to binary data for each color; 
           [0047]      FIGS. 4A-4D  are schematic views of a result of applying the window to the binary data for each color; 
           [0048]      FIG. 5  is a schematic view of a synthesis window; 
           [0049]      FIGS. 6A-6F  are schematic views of a plurality of sub windows; 
           [0050]      FIG. 7  is a schematic view of a result of applying the sub windows of  FIG. 6  to the synthesis window of  FIG. 4 ; 
           [0051]      FIG. 8  is a schematic view of an image being expanded to a target pixel; 
           [0052]      FIG. 9A  shows an image displayed by the binary data for each color; 
           [0053]      FIG. 9B  shows the expanded image data; 
           [0054]      FIG. 9C  is a schematic view of an edge region of the expanded image data; 
           [0055]      FIGS. 10A and 10B  are schematic before and after views illustrating an example of a final image form with the edge region in which K color dots are reinforced and the other color dots are deleted; 
           [0056]      FIG. 11  is a flow chart describing an image forming method according to an exemplary embodiment of the present invention; and 
           [0057]      FIG. 12  is a flow chart describing a more particular example of the image forming method of  FIG. 11 . 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0058]    Reference will now be made in detail to the present embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present invention by referring to the figures. 
         [0059]      FIG. 1  is a block diagram of an image forming device according to an embodiment of the present invention. In  FIG. 1 , the image forming device comprises an input unit  110 , a generation unit  120 , an image process unit  130  and a control unit  140 . While not shown, it is to be understood that the apparatus can include additional capabilities, such as copying, faxing and/or scanning in other aspects of the invention. 
         [0060]    Binary data for each color are input in the input unit  110 . A video controller (not shown) of the image receives an 8-bit color image of cyan (C), magenta (M), yellow (Y) and black (K) and performs a halftone process, to generate the each color binary data. The input unit  110  receives the binary data for each color undergoing the halftone process and being input by the video controller. Specifically, the binary data for each color may be the binary data for C, M, Y and K colors. While the image forming device is described in the context of C, M, Y, and K colors, it is to be understood that other colors and/or other numbers of colors can be used. 
         [0061]    The generation unit  120  applies a window of a predetermined size to e color binary data for each color. Thereafter, the generation unit  120  generates a synthesis window by synthesizing each window region. Specifically, the generation unit  120  applies the window, which can be represented as n×m (width×length) to each of the C, M, Y and K binary data. Thereafter, the generation unit  120  generates the synthesis window displaying all pixels that are within each window in an OR-type manner. 
         [0062]    The image process unit  130  applies a plurality of sub windows to the generated synthesis window to determine the directionality of an image existing in the synthesis window. Further, the image process unit  130  performs an operation of expanding the image along the determined directionality. The sub windows can be set in the position and size to most effectively indicate the directionality of the image included in the single synthesis window. For example, when the synthesis window has the size of n×m, the sub windows may be set to have the size of (n−a)×(m−b) and to be positioned at each corner region. In this case, two sub windows crossing a center region of the synthesis window lengthwise and widthwise may be additionally applied, in addition to four sub windows each positioned in each corner region. However, it is to be understood that other locations and/or numbers of sub windows can be used. 
         [0063]    The image process unit  130  determines the directionality of the image within the synthesis window, by checking the number of pixels existing within each sub window and the distribution of the pixels. Accordingly, when it is determined that the image is formed in a desired direction and when there is any deficient region in the direction of the image, the image process unit  130  expands the image by adding pixels to the deficient region. 
         [0064]    The control unit  140  detects an edge region of the image expanded by the image process unit  130 . When the deficient region of the image is filled by the image process unit  130 , the edge region of the image can become smooth. Accordingly, the control unit  140  extracts the edge region from the binary data of each color and performs a process of reinforcing or deleting the dots belonging to the edge region based on the binary data of each color. 
         [0065]    Specifically, the control unit  140  performs the process of reinforcing K color dots in the edge region extracted from the K color binary data and performs the process of deleting C, M and Y color dots in the edge region extracted from the C, M and Y color binary data. When the image is formed using binary data of each color processed in the above-described manner, dots of various colors are prevented from being prominently displayed in the edge region of the black text, and the boundary of the black text is clearly processed to improve the degree of definition. 
         [0066]      FIG. 2  is a block diagram illustrating, in more detail, an example of the constitution of the image forming device of  FIG. 1 . In  FIG. 2 , the image forming device further comprises an image forming unit  150 . In  FIG. 2 , one image forming unit  150  is illustrated for clarity. However, the image forming unit may comprise various types of components, such as four photosensitive units and transfer units, an intermediate transfer belt, and the like. 
         [0067]    While not required in all aspects, the shown input unit  110  includes an interface unit  111  and a storage unit  112 . The interface unit  111  receives binary data of each color being input from the video controller (not show) and stores the binary data in the storage unit  112 . 
         [0068]    The generation unit  120  includes a window application unit  121  and a synthesis unit  122 . The window application unit  121  applies a window to each of the color binary data. A process of applying the window will be described with reference to  FIG. 3  and  FIGS. 4A-4D . 
         [0069]    In  FIG. 3 , the window application unit  121  applies the window to one side of the color binary data. The window application unit  121  has each pixel of the color binary data as a target pixel and applies the window, which is n×m in size (wherein, n and m are any natural numbers), to the target pixel. In  FIG. 3 , a window of a 5×5 size is applied by way of example. That is, after one window W 1 - 1  is applied to one side of the color binary data “quick”, subsequent windows W 1 - 2 , W 1 - 3 , . . . , W 2 - 1 , . . . are sequentially applied. 
         [0070]      FIGS. 4A to 4D  are a schematic views illustrating an example of the result of applying the window to the C, M, Y and K color binary data, respectively. In  FIG. 4 , when one window is applied at the same position of the C, M, Y and K color binary data  201 ,  202 ,  203  and  204 , three dots for each of C, M and Y colors are included in each of the C, M and Y color binary data  201 ,  202  and  203  ( FIGS. 4A to 4C , respectively), and twelve dots for K color are included in the K color binary data  204  ( FIG. 4D ). 
         [0071]    When the window for binary data for each color is obtained, the synthesis unit  122  synthesizes the obtained windows, in an OR-type manner, to generate a synthesis window displaying all pixels existing within each window as shown, for example, in  FIG. 5 . That is, when all windows illustrated in  FIGS. 4A to 4D  are synthesized, the synthesis window of  FIG. 5  is produced. 
         [0072]    The image process unit  130  includes an operation unit  131 , a condition storing unit  132  and an expansion unit  133 . The operation unit  131  applies a plurality of sub windows to the synthesis window and calculates a characteristic value representing the characteristic of the image existing within the sub windows. The size, position, shape and the like of the sub window may be determined by a manufacturer or a user, considering the size and shape and the like of the synthesis window. 
         [0073]      FIGS. 6A to 6F  are schematic view of example of the sub windows. In  FIGS. 6A to 6F , the operation unit  131  applies a total of six sub windows. That is, when the 5×5 synthesis window is generated, the number of dots included within the synthesis window totals twenty-five. Accordingly, the size of the sub window in use may be set to be below 5×5 in size. 
         [0074]    In  FIG. 6A , a first sub window  310  is formed in a regular square which is positioned at the upper left corner of the synthesis window (relative to the drawing) and which is 3×3 in size. A second sub window  320  ( FIG. 6B ), a third sub window  330  ( FIG. 6C ) and a fourth sub window  340  ( FIG. 6D ) are respectively positioned at the upper right corner, the lower left corner and the lower right corner of the synthesis window and have the same shape and same size as those of the first sub window  310 . 
         [0075]    In addition, a fifth sub window  350  ( FIG. 6E ) and a sixth sub window  360  ( FIG. 6F ) may be used together. The fifth sub window  350  crosses the center point of the synthesis window. That is, the dot a 13  corresponding to the target pixel, lengthwise and is 1×5 in size. The sixth sub window  360  crosses the center point of the synthesis window widthwise and is 5×1 in size. 
         [0076]    The operation unit  131  calculates the characteristic values of the sub windows  310 ,  320 ,  330 ,  340 ,  350  and  360  independently, considering the number of pixels existing within the sub windows  310 ,  320 ,  330 ,  340 ,  350  and  360  or the distribution of the pixels. When the number of the pixels existing within one of the first, second, third and fourth sub windows  310 ,  320 ,  330  and  340  is at or above a threshold number of pixels, the characteristic value of that sub window is calculated as ‘1’. If the number of pixels is not above the threshold number, the characteristic values of that sub window is calculated as ‘0’. 
         [0077]    When pixels exist on both sides of the center pixel in sub window  350  or  360 , the characteristic values of that sub window  350  and  360  is calculated as ‘1’. When pixels do not exist at either side of the center pixel in sub window  350  or  360 , the characteristic value of that sub window  350  and  360  is calculated as ‘0’. That is, the method of calculating the characteristic values of the first, second, third, fourth, fifth and sixth sub windows  310 ,  320 ,  330 ,  340 ,  350  and  360  are represented in the following formula: 
         [0000]    
       
         
               
             
               
               
             
           
               
                   
               
               
                 Formula 1 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 If the number of pixels within the first sub window ≧  Th, 
               
               
                   
                 then C1=1, else C1=0 
               
               
                   
                 If the number of pixels within the second sub window ≧  Th, 
               
               
                   
                 then C2=1, else C2=0 
               
               
                   
                 If the number of pixels within the third sub window ≧  Th, 
               
               
                   
                 then C3=1, else C3=0 
               
               
                   
                 If the number of pixels within the fourth sub window ≧  Th, 
               
               
                   
                 then C4=1, else C4=0 
               
               
                   
                 If (a11 or a12) and (a14 or a15) = 1, then C5=1, else C5=0 
               
               
                   
                 If (a3 or a8) and (a18 or a23) = 1, then C6=1, else C6=0 
               
               
                   
                   
               
             
          
         
       
     
         [0078]    In the Formula 1, “C1” through “C6” respectively refer to the characteristic values of the first, second, third, fourth, fifth and sixth sub windows. The value “Th” refers to the threshold number of pixels, which can be user-selected. 
         [0079]    When the characteristic values for the sub windows  310 ,  320 ,  330 ,  340 ,  350  and  360  have been obtained by the operation unit  131 , the expansion unit  133  verifies whether conditions for expansion stored in the condition storing unit  132  are satisfied. The conditions for expansion of the image region are represented in the following formula: 
         [0000]      C1 &amp; C2 &amp; C3=1 
         [0000]      C3 &amp; C4 &amp; C5=1 
         [0000]      C1 &amp; C3 &amp; C6=1 
         [0000]      C2 &amp; C4 &amp; C6=1 
         [0000]      C1 &amp; C4=1 
         [0000]      C2 &amp; C3=1  Formula 2 
         [0080]    When any one of the conditions in the above-described formula 2 is satisfied, the expansion unit  133  expands the image region to the target pixel. If none of the conditions for expansion are satisfied, the expansion unit  133  does not expand the image region to the target pixel. 
         [0081]      FIG. 7  is a schematic view for explaining a process of applying each sub window to the synthesis window of  FIG. 5 . A process of expanding the image region in the synthesis window of  FIG. 5  will be described, assuming that Th is ‘5’. When the first sub window  310  is applied to the synthesis window of  FIG. 5 , four pixels exist within the first sub window  310 . Therefore, since the number of the pixels existing within the first sub window  310  is below ‘5’, the characteristic value of the first sub window  310  is ‘0’. 
         [0082]    Next, since seven pixels exist within the second sub window  320 , the characteristic value of the second sub window  320  is ‘1’. Likewise, the characteristic value of the third sub window  330  is ‘0’, and the characteristic value of the fourth sub window  340  is ‘1’. 
         [0083]    Next, in the fifth sub window  350 , since no pixels exist at the positions of a 11  and a 22 , the characteristic value thereof is ‘0’. However, in the sixth sub window  360 , since the pixels exist in all positions a 3 , a 8 , a 18  and a 23 , the characteristic value thereof is ‘1’. 
         [0084]      FIG. 7  illustrates only the sub windows with the characteristic value ‘1,’ that is, the second, fourth and sixth sub windows  320 ,  340  and  360 . Accordingly, the condition of C2 &amp; C4 &amp; C6=1 is satisfied. Since this is the fourth condition of the above-described Formula 2, the expansion unit  133  decides the expansion to the target pixel. 
         [0085]      FIG. 8  illustrates a state of the image expanded to the target pixel by the expansion unit  133 . In this manner, whether or not to expand to the target pixel included in each window is determined depending on the directionality of the pixels around the target pixel. Consequently, the deficient region inside the image or the edge region is filled. 
         [0086]    The control unit  140  detects the edge region of the expanded image. An algorithm of detecting an edge region is well known. Thereafter, the control unit  140  extracts dots positioned in the edge region from binary data of each color stored in the storage unit  112 , to perform the process of reinforcing or deleting dots. Accordingly, the control unit  140  controls the image forming unit  150  to perform a process of forming an image by using binary data of each color with the processed edge region. The image forming unit  150  is capable of displaying the binary data of each color as an image through a plurality of photosensitive units and transfer units and the like. 
         [0087]    The control unit  140  is capable of additionally performing a process of determining whether the pertinent image is a black text or a color text, based on the number of K color dots existing in the detected edge region. 
         [0088]    That is, in the case of black text, the control unit  140  clarifies the boundary by reinforcing the K color and deleting the other colors in the edge region and then prints the image through the image forming unit  150 . 
         [0089]    In the case of the color text, since the colors are naturally displayed in the edge region, the control unit  140  does not perform the reinforcing or deleting process. The control unit  140  controls the image forming unit  150  to form the image by using the binary data of each color stored in the storage unit  112 . 
         [0090]      FIGS. 9A through 9C  are schematic views showing how a shape of an image may be changed in the process of detecting the edge region by expanding the image. In  FIG. 9A , the binary data one color is indicated. In the color binary data of  FIG. 9A , it is noted that some deficient regions exist in the region forming the image. 
         [0091]    Next,  FIG. 9B  illustrates the image after being expanded by the image process unit  130 . As illustrated in  FIG. 9B , most of the deficient regions are filled as the image is expanded, to clarify the edge region. When the edge region is derived in this state, a clear edge region is obtained as shown in  FIG. 9C . The control unit  140  applies the obtained edge region to the binary data of each color, to reinforce the K color dots and to delete the C, M and Y color dots in the edge region part. Thereby, colors other than black are prevented from being displayed around the boundary of black text. 
         [0092]      FIGS. 10A and 10B  are a schematic before and after views of text with a processed edge region. In  FIG. 10A , before the edge region of the text is processed, different colors are displayed in many of the edge regions, or deficient regions exist therein. However, when the control unit  140  performs the edge region process, the dots of various colors positioned in the edge region are deleted and the deleted region and deficient regions are reinforced by the K color dots, so that the text with the clear boundary shown in  FIG. 10B  is obtained. However, since the region finally processed by the control unit  140  corresponds to the edge region of the binary data of each color, the internal region displays the original image by the superposition of the binary data of each color. This is because color disagreement is typically not noticeable in an internal region and becomes a noticeable problem only in the edge region. Therefore, color superposition is performed in the internal region to reproduce the black region as it is, and the control unit  140  may process only the edge region. 
         [0093]      FIG. 11  is a flow chart describing an image forming method according to another embodiment of the present invention. In  FIG. 11 , in operation S 1110 , a window is applied to the binary data for each color, to generate a synthesis window. Since the method of processing the synthesis window is already described, in detail, with respect to  FIGS. 3 through 5 , no further description thereof will be presented. 
         [0094]    In operation S 1120 , a plurality of sub windows are applied to the generated synthesis window, to expand an image according to the directionality of the image. Since the method of applying the sub windows and the method of expanding the image are already described, in detail, with respect to  FIGS. 6A-F  through  FIG. 8 , no further description thereof will be presented. 
         [0095]    In operation S 1130 , an edge region of the expanded image is detected. In operation S 1140 , dots positioned in the edge region are reinforced or deleted on the binary data for each color accordingly. 
         [0096]      FIG. 12  is a flow chart that describes, in more detail, the image forming method according to the embodiment of  FIG. 11 . In  FIG. 12 , in operation S 1210 , binary data for each color are input in a video controller and the like. Unlike the conventional art, since the binary data not the 8-bit data are input according to an aspect of the invention, the use of memory is significantly reduced. Specifically, in the example used to describe the present embodiment, C, M, Y and K color binary data are input. 
         [0097]    In operation S 1215 , a window is applied to each of the binary data being input, and in operation S 1220 , a synthesis window is generated in an OR-type manner. In operation S 1225 , a plurality of sub windows are applied to the generated synthesis window. In operation S 1230 , a characteristic value of each sub window is calculated. The characteristic value of each sub window can be calculated through Formula 1 described above according to an aspect of the invention, but can be otherwise defined. 
         [0098]    When the characteristic value has been calculated, in operation S 1235 , it is determined whether the calculated characteristic value satisfies conditions for expansion. For example, the conditions for expansion may be those represented in Formula 2, described above. If the calculated value does not satisfy the condition for expansion, the method with respect to the generated synthesis window is ended. 
         [0099]    If the conditions for expansion are satisfied, in operation S 1240 , the image of the synthesis window is expanded, to fill a deficient region positioned in the edge region and the like of the image. 
         [0100]    In operation S 1245 , the edge region of the expanded image is detected, and in operation S 1250 , the number of K color dots in the edge region is verified. In operation S 1255 , it is checked whether a rate of the verified number of K color dots is at or above a predetermined threshold rate. When the number of K color dots is at or above the threshold rate, the image is considered as a black text, and when the rate of K color dots is below the threshold rate, the image is considered as a color text. For example, when the threshold rate is predetermined as 70%, the total number of dots positioned in the edge region is  100 , and the number of K color dots is 70 or above, the image is recognized as the black text. However, when the number of K color dots is below 70, the image is recognized as the color text. 
         [0101]    Therefore, when the image is recognized as the color text, any additional process is not performed with respect to the binary data of each color being input and stored, so that the binary data of each color are maintained as they are. 
         [0102]    However, when the image is recognized as the black text (that is, when the rate of the K color dots included is at or above the threshold rate) in operation S 1260 , the K color is reinforced and the other colors are deleted in the edge region. In operation S 1265 , an image forming process is performed by using the binary data of each color to reinforce or delete color dots of each edge region accordingly. Consequently, the boundary of the black text becomes clearly defined and any other colors are prevented from being prominently displayed in the boundary. 
         [0103]    As described above, in accordance with the image forming device and method of the embodiments of the present invention, even though a color disagreement may occur, the edge region can be processed using software, to prevent the quality of an image from deteriorating due to a color disagreement. Specifically, the boundary of a composite black text displayed by the superposition of various colors can be processed to be clearer. Furthermore, in accordance with the image forming device and method, since the edge region is processed using the binary data for each color, a low capacity memory can be used for the processing of the edge region. 
         [0104]    Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in this embodiment without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.