Patent Publication Number: US-9406002-B2

Title: Processing device that corrects pixels of an edge-portion correction area of a print image

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority based on 35 USC 119 from prior Japanese Patent Application No. 2014-106380 filed on May 22, 2014 entitled “PROCESSING DEVICE”, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This disclosure relates to an image processing device, and is suitable for application to color electrophotographic printers (hereinafter also referred to as color printers), for example. 
     2. Description of Related Art 
     A conventional color printer is provided with five image drum units arranged in a row. Four of these image drum units form toner images with toners of four different colors, i.e., cyan, magenta, yellow, and black, which are base colors for the formation of a print image, and the remaining one image drum unit forms a toner image of the same pattern as that of a base color portion of a print image with toner of one color, such as clear or white, which is a special color for the formation of a print image. Then, the color printer forms a print image in which the special color is laid over the base colors in such a way that the toner images of the base colors formed by the four image drum units and the toner image of the special color formed by the one image drum unit are transferred sequentially one over another in that order and fixed to a surface of a medium to be printed (print medium). Alternatively, the color printer forms a print image in which the base colors are laid over the special color in such a way that the toner images of the base colors formed by the four image drum units are transferred sequentially one over another and fixed to a surface of a print medium, and then the toner image of the special color formed by the one image drum unit is transferred and fixed thereto (see Patent Literature 1, for example). 
     [Patent Literature 1] Japanese Patent Application Publication No. 2010-152209 (pp. 7, 8, and 14, and FIG. 1) 
     SUMMARY OF THE INVENTION 
     A conventional color printer forms a print image in which the special color is laid over the base colors or a print image in which the base colors are laid over the special color by laying toner images of five colors, one over another, on a surface of a print medium. However, in some color printers, the toner images are transferred onto the surface of the print medium while being misaligned relative to their ideal transfer positions depending on factors such as the assembly precision of the printer. In this case, the color printer has a problem that the special color spreads out from under the base colors and stands out, or the base colors spread out from under the special color and stand out in an edge portion of the print image formed on the surface of the printed medium, which deteriorates the quality of the print image. 
     An objective of an embodiment of the invention is to provide an image processing device capable of reducing deterioration in the quality of a print image. 
     An aspect of the invention is an image processing device that includes a correction processor configured to correct print image data by correcting an edge-portion correction area in an edge portion of a print image based on the print image data, the area extending along image edge expressed with a ground color and an upper color laid over the ground color in the edge portion. According to the above aspect of the invention, in the image edge portion of the print image based on the print image data, it is possible to make the width of the ground color narrower than the width of the upper color such that the area of the ground color retreats toward the center of the image from the image edges, or to lower the density of the ground color. By doing so, even if the ground color and the upper color are misaligned with each other in the edge portion of the print image when the image is formed on the surface of the print medium, it is possible to prevent the ground color from spreading out from under the upper color or make the ground color spreading out from under the upper color less likely to stand out. Thereby, the deterioration in the quality of the print image can be reduced. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic side view illustrating the internal configuration of a color printer according to the invention. 
         FIG. 2  is a block diagram illustrating the circuit configuration of the color printer according to embodiment 1. 
         FIG. 3  is a block diagram of functional circuit blocks for explaining first image processing executed by a first controller. 
         FIG. 4  is a schematic diagram for explaining the detection of a boundary correction area of a print image. 
         FIG. 5  is a schematic diagram for explaining a first area detection range with respect to a print image. 
         FIG. 6  is a schematic diagram for explaining the detection of an edge-portion correction area for a bordered mode of a print image. 
         FIG. 7  is a schematic diagram for explaining a first correction processing performed on a print image. 
         FIG. 8  is a schematic diagram for explaining the formation of a print image on a surface of a print medium based on corrected print image data. 
         FIGS. 9A to 9C  are schematic sectional views for explaining the misregistration of a ground color and an upper color in the case of forming a print image in a conventional color printer. 
         FIGS. 10A to 10C  are schematic sectional views for explaining the misregistration of a ground color and an upper color in the case of forming a print image in the color printer according to embodiment 1. 
         FIG. 11  is a flowchart illustrating a boundary correction area detection processing procedure. 
         FIG. 12  is a flowchart illustrating a first edge-portion correction area detection processing procedure. 
         FIG. 13  is a flowchart illustrating a first correction processing procedure. 
         FIG. 14  is a block diagram illustrating the circuit configuration of a color printer according to embodiment 2. 
         FIG. 15  is a block diagram of functional circuit blocks for explaining a second image processing executed by a second controller. 
         FIG. 16  is a schematic diagram for explaining the detection of an edge-portion correction area for a borderless mode of a print image. 
         FIGS. 17A to 17C  are schematic sectional views for explaining the misregistration of a ground color and an upper color in the case of forming a print image in a conventional color printer. 
         FIGS. 18A to 18C  are schematic sectional views for explaining the misregistration of a ground color and an upper color in the case of forming a print image in the color printer according to embodiment 2. 
         FIG. 19  is a flowchart illustrating a second edge-portion correction area detection processing procedure. 
         FIG. 20  is a flowchart illustrating a second correction processing procedure. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Descriptions are provided hereinbelow for embodiments based on the drawings. In the respective drawings referenced herein, the same constituents are designated by the same reference numerals and duplicate explanation concerning the same constituents is omitted. All of the drawings are provided to illustrate the respective examples only. 
     Note that the description is provided in the following order: (1) Embodiment 1, (2) Embodiment 2, and (3) Other Embodiments. 
     (1) Embodiment 1 
     (1-1) Internal Configuration of a Color Printer 
     In  FIG. 1 , throughout the description, reference numeral  1  denotes color printer  1  of a secondary transfer type according to the invention. Color printer  1  includes, for example, printer chassis  2  of substantially a box shape whose front surface  2 A is a right edge surface in the drawing. Incidentally, in the following description, an upward direction denoted by arrow al in the drawing when color printer  1  is viewed while facing front surface  2 A is also referred to as a printer upward direction and a direction opposite the upward direction is also referred to as a printer downward direction. These directions are also referred to as a printer upward/downward direction collectively when these need not be particularly distinguished from each other or both of these are meant. In addition, in the following description, a forward direction denoted by arrow b 1  in the drawing when color printer  1  is viewed while facing front surface  2 A is also referred to as a printer forward direction and a direction opposite the forward direction is also referred to as a printer backward direction. These directions are also referred to as a printer forward/backward direction collectively when these need not be particularly distinguished from each other or both of these are meant. Further, in the following description, a leftward direction denoted by arrow c 1  in the drawing when color printer  1  is viewed while facing front surface  2 A is also referred to as a printer leftward direction and a direction opposite the leftward direction is also referred to as a rightward direction. These directions are also referred to as a printer leftward/rightward direction collectively when these need not be particularly distinguished from each other or both of these are meant. Furthermore, in the following description, a rotation direction denoted by arrow dl in the drawing, which is about an axis parallel with the printer leftward/rightward direction, is also referred to as one rotation direction and a direction opposite this direction is also referred to as the other rotation direction. 
     Manipulation panel  4  having various manipulation keys, a touch screen, and the like is disposed in, for example, a front edge portion of upper surface  2 B of printer chassis  2 . Moreover, in upper surface  2 B, printer chassis  2  is provided with medium delivery section  2 BX that places thereon a rectangular medium to be printed (print medium  5 ), for example, having a print image formed thereon and delivers it to the user. Medium ejection port  2 BY is formed in a rear inner wall of this medium delivery section  2 BX. On the other hand, image formation section  7  for forming a print image on a surface of print medium  5  is disposed in a central portion of printer chassis  2 . Image formation section  7  includes five, namely, a first to fifth, image formation units  10  to  14 , transfer unit  15 , and fixation unit  16 , for example. 
     First to fifth image formation units  10  to  14  are detachably attached to be arranged in a row in the printer rearward direction. In this respect, four rear image formation units, namely, second to fifth image formation units  11  to  14 , each hold toner as a developer of any of the four colors, i.e., black (K), yellow (Y), magenta (M), and cyan (C), for example, which are base colors for the formation of a print image, such that image formation units  11  to  14  hold the colors different from each other. Meanwhile, one foremost image formation unit, namely, first image formation unit  10  holds toner of white (W), for example, which is a special color for the formation of a print image. First to fifth image formation units  10  to  14  are configured to respectively form electrostatic latent images on the surfaces of first to fifth photoconductive drums  20  to  24 , which are image carriers that rotate in the one rotation direction, by irradiating respectively the surfaces of the photoconductive drums with exposure light using first to fifth LED (light emitting diode) heads  25  to  29 , which are exposure units that are controlled based on corresponding color components of a print image, and then form toner images, which are developer images, by developing the electrostatic latent images with toner. Note that, first image formation unit  10  may be replaced with a unit holding a toner of clear (CL) which is a special color, for example, since this unit is attachable to and detachable from printer chassis  2 . 
     In transfer unit  15 , endless transfer belt  33  is stretched around belt drive roller  30 , driven roller  31 , and backup roller  32  that rotate in the other rotation direction. Transfer unit  15  is configured to transfer, sequentially one over another, the toner images of first to fifth photoconductive drums  20  to  24  onto the surface of transfer belt  33  between belt drive roller  30  and driven roller  31  with five primary transfer rollers  34  to  38 , and transfer the toner images on transfer belt  33  onto the surface of print medium  5  with secondary transfer roller  39  facing backup roller  32 . Note that transfer unit  15  has cleaning blade  40  provided in its rear end portion such that one end portion of cleaning blade  40  is pressed against the surface of transfer belt  33 . Thereby, transfer unit  15  can remove toner, which remains un-transferred on the surface of print medium  5 , from the surface of transfer belt  33  by use of cleaning blade  40 . The fixation unit is configured to apply heat and pressure on the toner image transferred on the surface of print medium  5  by transfer unit  15 , and thus melt and fix the toner image to the surface of print medium  5  to form a print image thereon. 
     In addition, medium supply section  43  is disposed inside printer chassis  2  in its lower end portion. Medium supply section  43  is configured to feed one print medium  5  at a time with feed roller  42  from media cassette  41  that is loaded with print media  5 . Note that color printer  1  can use various print media  5 , such as white plain paper and plain paper of colors other than white of a predefined medium size, and transfer paper for printing on a T-shirt, for formation of a print image by loading these various print media  5  in media cassette  41 . Moreover, a transport section for medium supply  44  is provided inside printer chassis  2  in its front lower end portion. Transport section for medium supply  44  is configured to transport print medium  5  fed from media cassette  41  to image formation section  7  through a transport path for the medium supply. Further, a transport section for medium ejection  45  is provided inside printer chassis  2  in its rear end portion. The transport section for medium ejection  45  is configured to transport print medium  5  fed from fixation unit  16  to medium ejection port  2 BY through a transport path for the medium ejection. Furthermore, a transport section for medium resupply  46  is provided inside printer chassis  2  between image formation section  7  and medium supply section  43 . The transport section for medium resupply  46  is configured to transport print medium  5  fed from fixation unit  16  back to the transport section for medium supply  44  through a transport path for the medium resupply. Besides, separator  47  is disposed inside printer chassis  2 . Separator  47  is configured to change the path to transport print medium  5  fed from fixation unit  16  between the transport path for medium ejection and the transport path for medium resupply. 
     In the situation where first image formation unit  10  holding white toner is attached to color printer  1  and plain paper of white or another color is loaded in media cassette  41  as print medium  5 , for example, the printer forms toner images of black, yellow, magenta, and cyan on the surfaces of second to fifth photoconductive drums  21  to  24  with second to fifth image formation units  11  to  14  and forms a white toner image, having substantially the same pattern as that of a black, yellow, magenta, and cyan portion of a print image, on the surface of first photoconductive drum  20  with first image formation unit  10 , then transfers the toner images onto the surface of transfer belt  33  one over another in the order of cyan, magenta, yellow, black, and white, and then transfers the toner images of five colors, thus formed on transfer belt  33 , onto a surface of a plain paper sheet that is transported from medium supply section  43  through the transport path for medium supply. Further, after color printer  1  forms a print image represented with the base colors and the special color by fixing the toner images of five colors to the surface of the plain paper sheet with fixation unit  16 , it transports the plain paper sheet to medium ejection port  2 BY through the transport path for medium ejection and ejects it to medium delivery section  2 BX. Here, color printer  1  transfers the toner images of five colors, thus transferred on the surface of transfer belt  33 , upside down onto the surface of the plain paper sheet. As a result, the white toner image is interposed between the surface of the plain paper sheet and the toner images of the base colors, and white serves as a foundation for the base colors in the print image. Thereby, thanks to white serving as the foundation for the base colors, color printer  1  can represent the print image with the base colors as clear as their original colors no matter which of a white plain paper sheet and a plain paper sheet of another color is used as print medium  5  on which the print image is formed. 
     On the other hand, in the situation where first image formation unit  10  holding white toner is attached to color printer  1  and transfer paper is loaded in media cassette  41  as print medium  5 , the printer forms toner images on the surfaces of second to fifth photoconductive drums  21  to  24  with second to fifth image formation units  11  to  14 . and transfers the toner images onto the surface of transfer belt  33  one over another in the order of cyan, magenta, yellow, and black, and then transfers the toner images of four colors, thus formed on transfer belt  33 , onto a surface of a transfer paper sheet that is transported from medium supply section  43  through the transport path for medium supply. Note that, in this event, color printer  1  changes a medium transport path with separator  47  to supply the transfer paper sheet, which is fed from fixation unit  16  with a print image represented only with the base colors formed thereon, to image formation section  7  again by way of the transport path for medium resupply and the transport path for medium supply, in this order. While the sheet is being resupplied, color printer  1  forms a white toner image, having substantially the same pattern as that of a black, yellow, magenta, and cyan portion of a print image, on the surface of first photoconductive drum  20  with first image formation unit  10  and transfers the toner image onto the surface of transfer belt  33 . Then, the printer transfers the toner image, thus formed on transfer belt  33 , onto the surface of the resupplied transfer paper sheet such that the toner image is laid over the print image on the surface of the sheet. After color printer  1  forms a print image represented with the special color as well as the base color by fixing the white toner image to the print image on the surface of the transfer paper sheet with fixation unit  16 , the printer changes the medium transport path again with separator  47  and thereby transports the transfer paper sheet to medium ejection port  2 BY through the transport path for medium ejection and ejects it to medium delivery section  2 BX. In this case, color printer  1  forms the print image by transferring and fixing the toner image of the base colors on the surface of the transfer paper sheet, and then transferring and fixing the toner image of white as the special color. Thus, the base colors can be coated with white in the print image. Because the transfer with the transfer paper sheet is made by bringing the print image on that surface into contact with the surface of a T-shirt, color printer  1  can make white serve as a foundation for the base colors when the print image is transferred onto a T-shirt by way of the transfer paper sheet. Thereby, thanks to white serving as the foundation for the base colors, color printer  1  can represent the print image with the base colors as clear as their original colors no matter which of a white T-shirt and a T-shirt of another color is used as the medium on which the print image is transferred. 
     On the other hand, in the situation where first image formation unit  10  holding clear toner is attached to color printer  1  and plain paper of white or another color is loaded in media cassette  41  as print medium  5 , for example, the printer forms a print image by transferring and fixing toner images of the base colors to the surface of a plain paper sheet and then transferring and fixing thereto a toner image of clear as the special color, as in the case of forming a print image on the surface of a transfer paper sheet. Thereby, color printer  1  can gloss the base colors by coating the base colors with the color of clear in the print image formed on the surface of the plain paper sheet. In this way, color printer  1  can form a print image in the bordered printing mode on the surface of any of various print media  5 , for example, such that the base colors and the special color are laid in the order predefined according to the type of print medium  5 . 
     Meanwhile, as described above, when color printer  1  forms a print image represented with the base colors and white as the special color on the surface of a plain paper sheet as print medium  5 , the special color serves as the foundation for the base colors. Further, when color printer  1  forms a print image represented with the base colors and white as the special color on the surface of a transfer paper sheet as print medium  5 , the special color is located on the base colors on the transfer paper sheet, but as in the above case, the special color serves as the foundation for the base colors in the state where the print image is transferred on the surface of a T-shirt. Furthermore, when color printer  1  forms a print image represented with the base colors and the color of clear as the special color on the surface of a plain paper sheet as print medium  5 , the special color is located on the base colors, and the base colors serve as the foundation for the special color. Hence, in the following description, depending on the type of print medium  5  on which a print image is to be formed and the type of the special color used to represent the print image, white as the special color which serves as the foundation for the base colors in the print image and the base colors which serve as the foundation for the color of clear as the special color in the print image are also called a ground color as appropriate, and the base colors which are located on white as the special color serving as the foundation for the base colors in the print image and the color of clear as the special color which is located on the base colors serving as the foundation for the special color are also called an upper color as appropriate. 
     (1-2) Circuit Configuration of the Color Printer 
     Next, the circuit configuration of color printer  1  is described using  FIG. 2 . In color printer  1 , storage unit  51  such as a hard disc drive or a ROM (Read Only Memory), a memory (not illustrated) such as a RAM (Random Access Memory) serving as a work area for first controller  50 , and manipulation panel  4  described above are connected to first controller  50 , such as a CPU (Central Processing Unit) or a microprocessor. Moreover, first image input unit  52  and head controller  53  are connected to first controller  50 . First image input unit  52  is configured to load image data of an image to be printed from the outside and generate print image data of the print image having an image size slightly smaller than the size of the print medium for use in bordered printing, for example. Head controller  53  is configured to control first to fifth LED heads  25  to  29  described above. Note that, first image input unit  52  is capable of loading image data of an image to be printed that is stored in, for example, an external memory such as a USB (Universal Serial Bus) memory or a memory card attached to color printer  1 . Alternatively, first image input unit  52  is also capable of loading image data of an image to be printed from, for example, an imaging device connected to color printer  1  by wire or wireless, such as a digital still camera or a mobile information terminal equipped with a camera function. Still alternatively, first image input unit  52  is also capable of loading image data of an image to be printed from, for example, an information processing device connected to color printer  1  by wire or wireless, such as a personal computer. 
     First controller  50  is configured to load various programs such as a base program, a first image processing program, and a variety of application programs previously stored in storage unit  51  from the storage unit to the memory as appropriate, and expand these in the memory. Further, first controller  50  is configured to exert an overall control on color printer  1  according to the various programs thus developed in the memory, and execute predetermined arithmetic processing, various processing in response to manipulation commands inputted through manipulation panel  4 , and the like. With these functions, at the time of forming a print image, first controller  50  drives image formation section  7 , medium supply section  43 , and the like for forming a print image, executes image processing on print image data given by first image input unit  52 , and sends corrected print image data thus obtained to head controller  53 . In this event, based on the corrected print image data given by first controller  50 , head controller  53  generates second to fifth head control data corresponding to color components of cyan, magenta, yellow, and black of the print image, and generates first head control data corresponding to a color component of white or clear of the print image. In addition, under control of first controller  50 , head controller  53  sends each of first to fifth head control data to a corresponding one of first to fifth LED heads  25  to  29  at a predetermined timing. In this way, in first to fifth image formation units  10  to  14 , first controller  50  can drive first to fifth LED heads  25  to  29  to form electrostatic latent images on the surfaces of first to fifth photoconductive drums  20  to  24  based on first to fifth head control data, and form toner images by developing the electrostatic latent images with toner. Further, first controller  50  can form a print image on the surface of print medium  5  as described above based on the toner images formed by first to fifth image formation units  10  to  14 . 
     Meanwhile, in some color printers, toner images on the surfaces of first to fifth photoconductive drums  20  to  24  are transferred onto the surface of transfer belt  33  while being misaligned relative to their ideal transfer positions depending on factors such as assembly precision of the printer. In this case, because the toner images of five colors on transfer belt  33  are transferred and fixed to the surface of print medium  5  while being misaligned with each other in color printer  1 , such misregistration leads to a misregistration of the ground color and the upper color laid one over another in a print image. This eventually makes the ground color spread out from under the upper color in an edge portion and a central portion of the print image. Further, in color printer  1 , depending on factors such as its assembly precision, there is tendency that the misregistration of the ground color and the upper color laid one over another in the print image increases and a larger portion of the ground color spreads out from under the upper color in the case of forming a print image. This happens in such a way that a toner image of a special color on transfer belt  33  is transferred and fixed to the surface of print medium  5 . Then toner images of base colors on the belt are transferred and fixed thereto; or in the case of forming a print image in such a way that toner images of the base colors on the belt are transferred and fixed to the surface of print medium  5  and then a toner image of the special color on the belt is transferred and fixed thereto. This is as compared to the case of forming a print image in such a way that toner images of the base colors and a toner image of the special color on the belt are transferred and fixed to the surface of print medium  5  at the same time. Incidentally, in the following description, an image formation method of forming a print image in such a way that toner images of the base colors and a toner image of the special color on transfer belt  33  are transferred and fixed to the surface of print medium  5  at the same time is also referred to as a first image formation method. An image formation method of forming a print image in such a way that toner images of the base colors on transfer belt  33  are transferred and fixed to a surface of print medium  5  and then a toner image of the special color on transfer belt  33  is transferred and fixed thereto is also referred to as a second image formation method. 
     To deal with such a phenomenon, color printer  1  previously detects, for example, the amount of first misregistration estimated to occur between the ground color and the upper color, laid one over another, when a print image is formed in the bordered printing mode on the surface of print medium  5  with the first image formation method and the ground color spreads out from under the upper color in this print image. In addition, based on the amount of the first misregistration, color printer  1  assigns, as appropriate, a block-shaped first pixel search range for searching pixels to be corrected in the print image, for example. Further, based on the amount of the first misregistration and the image size of the print image, the color printer assigns, as appropriate, a first area detection range for detecting an edge-portion area to be corrected in an edge portion of the print image for bordered printing (hereinafter, such an area is also referred to as an edge-portion correction area for bordered mode). The first area detection range is in the shape of a frame going around the print image along the edges of the image. Thus, first controller  50  stores, in storage unit  51 , first pixel search range information indicating the first pixel search range and first area detection range information indicating the first area detection range. Besides, color printer  1  also previously detects, for example, the amount of second misregistration estimated to occur between the ground color and the upper color, laid one over another, when a print image is formed in the bordered printing mode on a surface of print medium  5  with the second image formation method and the ground color spreads out from under the upper color in this print image. In addition, based on the amount of the second misregistration, color printer  1  assigns, as appropriate, a block-shaped second pixel search range for searching pixels to be corrected in the print image for bordered printing, for example. Further, based on the amount of the second misregistration and the image size, a second area detection range in the shape of a frame, going around the print image along the edges of the image, is determined for detecting an edge-portion correction area for the bordered mode in an edge portion of the print image. Thus, first controller  50  stores, in storage unit  51 , second pixel search range information indicating the second pixel search range and second area detection range information indicating the second area detection range. 
     Incidentally, the amount of the first misregistration is detected as the first misregistration distance represented with pixels and the first misregistration direction, for example. When the amount of the first misregistration is used for assignment of the first pixel search range, a reference length for the search range assignment is obtained by doubling the first misregistration distance in the first misregistration direction, and the reference length for search range assignment is divided into a main-direction component length in a main-scanning direction of the print image and a sub-direction component length in a sub-scanning direction. In this way, the first pixel search range is assigned in the shape of a square or a rectangular block whose lengths in the main-scanning direction and in the sub-scanning direction are equal to the main-direction component length and the sub-direction component length of the reference length for search range assignment, respectively. Meanwhile, when the amount of the first misregistration is used for the assignment of the first area detection range, the first misregistration distance in the first misregistration direction is directly used as a reference length for detection of the range assignment and is divided into a main-direction component length in the main-scanning direction of the print image and a sub-direction component length in the sub-scanning direction. In this way, the first area detection range is assigned in the shape of a frame whose width between strip-shaped portions on one and the other image-edge sides in the main-scanning direction of the print image (hereinafter, such edges are also referred to as image left/right edges collectively and such portions are also referred to as left/right strip-shaped portions collectively) is equal to the main-direction component length of the reference length for detection of the range assignment and whose width between strip-shaped portions on one and the other image-edge sides in the sub-scanning direction (hereinafter, such edges are also referred to as image top/bottom edges collectively and such portions are also referred to as top/bottom strip-shaped portions collectively) is equal to the sub-direction component length of the reference length for detection range assignment. In other words, the first area detection range is assigned in the shape of a frame whose widths between the left/right strip-shaped portions and between the top/bottom strip-shaped portions are equal to or different from each other. Besides, the second pixel search range and the second area detection range are assigned in the same manner as the first pixel search range and the first area detection range based on the amount of the second misregistration detected as a second misregistration distance represented with pixels and a second misregistration direction. Note, however, that a portion of the ground color spreading out from under the upper color tends to be larger in the second image formation method than in the first image formation method as described above. Thus, in response to that tendency, the second pixel search range and the second area detection range are assigned so that they may be wider in at least one of the main-scanning direction and the sub-scanning direction than the first pixel search range and the first area detection range. 
     With the configuration above, upon receiving print image data from first image input unit  52  in the formation of a print image, first controller  50  executes a first image processing by using the first pixel search range, the first area detection range, the second pixel search range, and the second area detection range to prevent the ground color from spreading out from under the upper color throughout the print image (i.e., in an edge portion and a central portion of the image). In fact, first controller  50  executes the first image processing according to the first image processing program stored in storage unit  51  by using the print image data generated by first image input unit  52 . With reference to  FIG. 3 , print image data generation processing executed by first image input unit  52  is described specifically below, and besides, while various functions that first controller  50  implements according to the first image processing program are indicated by functional circuit blocks for the sake of convenience, the first image processing that first controller  50  executes according to the first image processing program is described specifically below as the processing executed by the functional circuit blocks. 
     In this case, when a command to display a setting screen is made at any timing by the user through manipulation panel  4 , for example, setting unit  61  of first spread-out correction unit  60  retrieves setting screen data from storage unit  51 , and sends it to manipulation panel  4  to display the setting screen in response to the command. Setting unit  61  thereby makes the user input the type of print medium  5  loaded in media cassette  41  and a color of toner held by first image formation unit  10  (i.e., white or clear as the special color) at this time on the setting screen through manipulation panel  4 . Setting unit  61  then detects an image formation method (i.e., any of the first image formation method and the second image formation method) to be used in the formation of a print image and the types of the ground color and the upper color. Then, setting unit  61  makes a setting such that all parts of first spread-out correction unit  60  (i.e., boundary correction area detector  62 , first edge-portion correction area detector  63 , and first correction processor  64 ) execute a processing according to the image formation method and the types of the ground color and the upper color thus detected. In this event, setting unit  61  also sets first image input unit  52  to generate print image data of a print image represented with the types of ground color and the upper color thus detected. Incidentally, setting unit  61  is capable of detecting an image formation method and the types of the ground color and the upper color not only upon input on the setting screen as described above, but also, for example, upon notification from an information processing device connected to color printer  1 , such as a personal computer, if the image data of an image to be printed is given from the image processing device to first image input unit  52 . Note that, hereinbelow, print image data generation processing and first image processing applied to the print image data that are executed when a print image in which white serves as the ground color is formed on a surface of a plain paper sheet as print medium  5  according to the setting made by setting unit  61  are described specifically. Then described are the print image data generation processing and first image processing applied to the print image data that are executed when a print image in which white serves as the ground color is formed on a surface of a transfer paper sheet as print medium  5  according to the setting made by setting unit  61 , and the print image data generation processing and first image processing applied to the print image data that are executed when a print image in which the base colors serve as the ground color (that is, the color of clear serves as the upper color) is formed on a surface of a plain paper sheet as print medium  5  according to the setting made by setting unit  61 . The events are described in this order. 
     In the case where a print image, in which white serves as the ground color, is formed on the surface of a plain paper sheet, upon loading image data of an image to be printed from the outside, first image input unit  52  generates print image data of the print image represented with the colors of cyan, magenta, yellow, black, and white based on the loaded image data. In this event, first image input unit  52  stores, in the print image data for every pixel of the print image, five kinds of pixel values represented by normalizing the densities of cyan, magenta, yellow, black, and white into values from “0” to “255” respectively based on the pattern of the print image. In fact, the pixel value of cyan for each pixel becomes “0” when the color of cyan is not used to represent the pixel, and becomes a value larger than “0” according to its density when the color of cyan is used to represent the pixel. The same holds for the pixel values of magenta, yellow, black, and white for each pixel. Note, however, that, in order to make white serve as the ground color only for a base color portion in the print image, for every pixel of the print image, first image input unit  52  sets the pixel value of white at a value larger than “0,” more preferably at “255” indicating the highest density for the purpose of fully exploiting its function as the ground color if at least one of the pixel values of cyan, magenta, yellow, and black is equal to a value larger than “0,” and sets the pixel value of white at “0” if all of the pixel values of cyan, magenta, yellow, and black are equal to “0.” Accordingly, in the print image, a colored area is an area including only pixels in each of which the pixel value of white is larger than “0” and at least one of the pixel values of cyan, magenta, yellow, and black is larger than “0.” Further, in the print image, a colorless area is an area including only pixels in each of which all the pixel values of cyan, magenta, yellow, black, and white are equal to “0.” First image input unit  52  generates the print image data in this manner and sends it to boundary correction area detector  62 . 
     Upon receiving the print image data from first image input unit  52 , boundary correction area detector  62  retrieves first pixel search range information from storage unit  51  and executes boundary correction area detection processing according to the setting made by setting unit  61 . In this event, as illustrated in  FIG. 4 , while shifting first pixel search range SE 1  in the main-scanning direction or in the sub-scanning direction sequentially on a pixel-by-pixel basis on print image IM 1  which is based on the print image data, boundary correction area detector  62  makes every pixel in print image IM 1  positioned at the center of first pixel search range SE 1  sequentially one at a time to designate the pixel as focused pixel P 51 . First pixel search range SE 1  is indicated by the first pixel search range information and is formed of a square of five pixels (in the main-scanning direction)×five pixels (in the sub-scanning direction), for example. In addition, every time boundary correction area detector  62  designates each pixel as focused pixel PS 1  on print image IM 1  one at a time, it judges whether or not both conditions where focused pixel PS 1  is a pixel of colorless area AR 1  and where at least one of pixels PN 1  located around focused pixel PS 1  in first pixel search range SE 1  (hereinafter, such pixels are also referred to as neighboring pixels) is a pixel of colored area AR 2  are satisfied on the basis of the five kinds of pixel values of focused pixel PS 1  and the five kinds of pixel values of each of neighboring pixels PN 1 . As a result of the judgment, if focused pixel PS 1  is a pixel of colored area AR 1  and at least one of neighboring pixels PN 1  is a pixel of colored area AR 2 , boundary correction area detector  62  judges that focused pixel PS 1  at this time is a pixel to be corrected for boundary correction (hereinafter, such pixel is also referred to as a boundary correction pixel). In contrast, if focused pixel PS 1  is a pixel of colorless area AR 1  but all of neighboring pixels PN 1  are pixels in colorless area AR 1  as well, boundary correction area detector  62  judges that focused pixel PS 1  at this time is a pixel not to be corrected (non-correction pixel). Further, if all of focused pixel PS 1  and neighboring pixels PN 1  are pixels in colored area AR 2 , boundary correction area detector  62  judges that focused pixel PS 1  at this time is a non-correction pixel as in the above case. In this manner, based on the judgment result, boundary correction area detector  62  detects a boundary area to be corrected (boundary correction area) which is a boundary portion between colorless area AR 1  and colored area AR 2  in print image IM 1  and is formed of boundary correction pixels. Note that boundary correction area detector  62  generates boundary correction area detection data indicating a boundary correction area while judging, one at a time, whether each of pixels in print image IM 1  is a boundary correction pixel or a non-correction pixel. Specifically, boundary correction area detector  62  stores data in the boundary correction area detection data such that it associates a value of “1” indicating a boundary correction pixel with a pixel in print image IM 1  if judging that the pixel is a boundary correction pixel, and such that it associates a value of “0” indicating a non-correction pixel with a pixel in print image IM 1  if judging that the pixel is a non-correction pixel. Upon detecting a boundary correction area, boundary correction area detector  62  sends first edge-portion correction area detector  63  the boundary correction area detection data together with the print image data. 
     Upon receiving the boundary correction area detection data together with the print image data from boundary correction area detector  62 , first edge-portion correction area detector  63  retrieves first area detection range information from storage unit  51  and executes first edge-portion correction area detection processing according to the setting made by setting unit  61 . In this event, as illustrated in  FIG. 5 , first edge-portion correction area detector  63  designates every pixel in print image IM 1  based on the print image data as a focused pixel sequentially one at a time. Then, every time first edge-portion correction area detector  63  designates each pixel as a focused pixel on print image IM 1  one at a time, it judges whether or not the focused pixel is a pixel of colored area AR 2  and also whether or not the focused pixel is a pixel within first area detection range DE 1  on the basis of first area detection range DE 1  and the five kinds of pixel values of the focused pixel, first area detection range DE 1  being indicated by the first area detection range information and having left/right strip-shaped portions of the same width and top/bottom strip-shaped portions of the same width, for example. Note that first edge-portion correction area detector  63  may judge that a focused pixel is a pixel within first area detection range DE 1  if the coordinates of the focused pixel satisfy at least one of four kinds of conditions represented by the following formulae (1) to (4):
 
 x&lt;W 1  (1);
 
 y&lt;W 1  (2);
 
 x≧X 1− W 1  (3); and
 
 y≧Y 1− W 1  (4),
 
     where: X 1  and Y 1  indicate the horizontal size and the vertical size of print image IM 1  represented with the number of pixels in the main-scanning direction and in the sub-scanning direction, respectively, with the left upper corner of the print image used as point of origin OP 1  (0, 0). W 1  indicates the width of each of the left/right strip-shaped portions and the top/bottom strip-shaped portions of first area detection range DE 1  represented by the number of pixels thereof; and (x, y) indicates the coordinates of the focused pixel. Then, as illustrated in  FIG. 6 , if the focused pixel is a pixel of colored area AR 2  and is also a pixel within first area detection range DE 1 , first edge-portion correction area detector  63  judges that this focused pixel is a pixel to be corrected for image edge-portion correction (hereinafter, such pixel is also referred to as an edge-portion correction pixel). In contrast, if the focused pixel is a pixel of colorless area AR 1 , first edge-portion correction area detector  63  judges that this focused pixel is a non-correction pixel irrespective of whether or not this focused pixel is a pixel within first area detection range DE 1 . Further, if the focused pixel is a pixel of colored area AR 2  but is a pixel outside first area detection range DE 1 , first edge-portion correction area detector  63  also judges that this focused pixel is a non-correction pixel. In this manner, based on the judgment result, first edge-portion correction area detector  63  detects the edge-portion correction area for bordered mode AR 3 , which extends along the edges of the image formed by edge-portion correction pixels, in colored area AR 2  located in left/right edge portions and top/bottom edge portions of print image IM 1 . Incidentally,  FIG. 6  illustrates an example where all of the image left/right edge portions and the image top/bottom edge portions are colored area AR 2  and thus first area detection range DE 1  overlapping these portions are detected directly as an edge-portion correction area for bordered mode AR 3 . Note that first edge-portion correction area detector  63  generates edge-portion correction area detection data indicating an edge-portion correction area for bordered mode AR 3  while judging, one at a time, whether each of the pixels in print image IM 1  is an edge-portion correction pixel or a non-correction pixel. Specifically, first edge-portion correction area detector  63  stores data in the edge-portion correction area detection data such that it associates a value of “1” indicating an edge-portion correction pixel with a pixel in print image IM 1  if judging that the pixel is an edge-portion correction pixel. It associates a value of “0” indicating a non-correction pixel with a pixel in print image IM 1  if judging that the pixel is a non-correction pixel. Upon detecting an edge-portion correction area for bordered mode AR 3 , first edge-portion correction area detector  63  sends first correction processor  64  the edge-portion correction area detection data together with the print image data and the boundary correction area detection data. 
     Upon receiving the boundary correction area detection data and the edge-portion correction area detection data together with the print image data from first edge-portion correction area detector  63 , first correction processor  64  retrieves first pixel search range information from storage unit  51  and executes first correction processing according to the setting made by setting unit  61 . In this event, as illustrated in  FIG. 7 , while shifting first pixel search range SE 1  (not illustrated in  FIG. 7 ) indicated by the first pixel search range information in the main-scanning direction or in the sub-scanning direction sequentially on a pixel-by-pixel basis on print image IM 1  which is based on the print image data, first correction processor  64  designates every pixel in print image IM 1  as focused pixel PS 1  at the center of first pixel search range SE 1  sequentially one at a time, for example. In addition, every time first correction processor  64  designates each pixel as a focused pixel PS 1  on print image IM 1  one at a time, it judges whether or not focused pixel PS 1  is an edge-portion correction pixel and whether or not the focused pixel is a boundary correction pixel on the basis of the edge-portion correction area detection data and the boundary correction area detection data. As a result of the judgment, if focused pixel PS 1  is an edge-portion correction pixel, first correction processor  64  replaces, with “0,” only the pixel value of white out of the five kinds of pixel values of this focused pixel PS 1  (i.e., edge-portion correction pixel). Meanwhile, if focused pixel PS 1  is a boundary correction pixel, out of the pixel values exclusive of the pixel value of white among the five kinds of pixel values of focused pixel PS 1  (i.e., boundary correction pixel), first correction processor  64  changes the pixel value of cyan from its original value of “0” to the largest value among the pixel values of cyan that neighboring pixels PN 1  in first pixel search range SE 1  respectively have. In the same way, first correction processor  64  changes each of the pixel values of magenta, yellow, and black that this focused pixel PS 1  (i.e., a boundary correction pixel) has from its original value of “0” to the largest value among the pixel values of the corresponding color that neighboring pixels PN 1  in first pixel search range SE 1  respectively have. Note that, if focused pixel PS 1  is a non-correction pixel (that is, focused pixel PS 1  is neither an edge-portion correction pixel nor a boundary correction pixel), first correction processor  64  leaves the five kinds of pixel values of this focused pixel PS 1  unchanged. 
     Thereby, first correction processor  64  can correct print image IM 1  so that edge-portion correction area for bordered mode AR 3  extending along the edges of print image IM 1  may be represented only with the upper color, and thus, in an edge portion of print image IM 1 , it can make the width of the ground color narrower than the width of the upper color, laid over the ground color, such that the area of the ground color retreats toward the center of the image from the image edges. In addition, first correction processor  64  can correct print image IM 1  so that boundary correction area AR 4  in a central portion of print image IM 1  may be represented only with the upper color, and thus it can make the width of the upper color wider than the width of the ground color laid under the upper color in a central portion of print image IM 1 . Then, first correction processor sends the print image data of print image IM 1 , whose edge-portion correction area for bordered mode AR 3  and boundary correction area AR 4  are corrected, to output image processor  65  as corrected print image data. Incidentally, upon receipt of the corrected print image data from first correction processor  64 , output image processor  65  performs a predetermined processing, such as a tone correction processing and a value reduction processing using a dithering technique, an error diffusion technique, or the like, on the corrected print image data, and sends the resultant data to subsequent head controller  53 . 
     In this manner, as illustrated in  FIG. 8 , color printer  1  forms print image IM 1  in the state where the edge-portion correction area for bordered mode AR 3  and boundary correction area AR 4  are corrected, in a print area slightly smaller than the surface of print medium  5  and in the bordered printing mode where a fringe portion of the print medium on the surface thereof is entirely left unprinted. In the meantime, a conventional color printer does not perform the first image processing at all on the print image data as done in embodiment 1=. Hence, when a print image in which white serves as ground color GC 1  is formed on a surface of print medium  5 , for example, upper color UC 1  having a width equal to ground color GC 1  is laid over the ground color, as illustrated in  FIG. 9A . Thus, if upper color UC 1  and ground color GC 1  laid one over another in a print image on print medium  5  are misaligned with each other in the conventional color printer, ground color GC 1  spreads out from under upper color UC 1 , as illustrated in  FIGS. 9B and 9C . As a result, in the conventional color printer, ground color GC 1  which should be originally hidden under upper color UC 1  and invisible in the print image turns visible and stands out, which deteriorates the quality of the print image. On the other hand, color printer  1  according to embodiment 1 corrects edge-portion correction area for bordered mode AR 3  and boundary correction area AR 4  in print image IM 1  based on print image data so that, in prospect of such misregistration, the width of upper color UC 2  laid over ground color GC 2  may be widened relative to the width of ground color GC 2 , as illustrated in  FIG. 10A . Thus, when print image IM 1  in which white serves as ground color GC 2  is formed on a surface of print medium  5  in color printer  1 , for example, it is possible to lay upper color UC 2  with a width wider than ground color GC 2  over the ground color. By doing so, even if upper color UC 2  and ground color GC 2  laid one over another in print image IM 1  on print medium.  5  are misaligned with each other in color printer  1 , it is possible to prevent ground color GC 2  from spreading out from under upper color UC 2 , as illustrated in  FIGS. 10B and 10C . Accordingly, in color printer  1 , ground color GC 2  which should be originally hidden under upper color UC 2  and invisible in the print image can be kept invisible even when these colors are misaligned with each other, so that the deterioration in the quality of print image IM 1  can be prevented. 
     Next, in the case where print image IM 1  in which white as the special color serves as the ground color is formed on a surface of a transfer paper sheet, the configuration of the print image data itself of print image IM 1  is no different from the configuration of the print image data described above; thus, upon loading image data of an image to be printed from the outside, first image input unit  52  generates print image data similar to the above print image data based on the loaded image data, and sends it to boundary correction area detector  62 . Upon receiving the print image data from first image input unit  52 , boundary correction area detector  62  retrieves second pixel search range information from storage unit  51  in this case according to the setting made by setting unit  61 , but executes the boundary correction area detection processing as in the above case using the second pixel search range information. Boundary correction area detector  62  thereby detects boundary correction area AR 4  in print image IM 1  based on the print image data, and sends first edge-portion correction area detector  63  the boundary correction area detection data together with the print image data. Upon receiving the boundary correction area detection data together with the print image data from boundary correction area detector  62 , first edge-portion correction area detector  63  retrieves second area detection range information from storage unit  51  in this case according to the setting made by setting unit  61 , but executes the first edge-portion correction area detection processing as in the above case using the second area detection range information. First edge-portion correction area detector  63  thereby detects edge-portion correction area for bordered mode AR 3  in print image IM 1  based on the print image data, and sends first correction processor  64  the edge-portion correction area detection data together with the print image data and the boundary correction area detection data. Upon receiving the boundary correction area detection data and the edge-portion correction area detection data together with the print image data from first edge-portion correction area detector  63 , first correction processor  64  retrieves second pixel search range information from storage unit  51 , in this case according to the setting made by setting unit  61 , but executes the first correction processing as in the above case using the second pixel search area information. First correction processor  64  thereby corrects boundary correction area AR 4  as well as edge-portion correction area for bordered mode AR 3  of print image IM 1 . First correction processor  64  then sends the print image data of print image IM 1  thus corrected to output image processor  65  as corrected print image data. 
     In the meantime, when print image IM 1  is formed on a surface of a transfer paper sheet in color printer  1  based on the corrected print image data, white having a width narrower than the width of the base colors is laid over the base colors on the transfer paper sheet and hence the base colors spread out from under white. However, if print image IM 1  is transferred onto a T-shirt by way of the transfer paper sheet, white serves as the ground color and the base colors, being wider than white, are laid over white as described above. Thereby, in color printer  1 , even if the upper color and the ground color laid one over another in print image IM 1  on the transfer paper sheet are misaligned with each other, it is possible to prevent the ground color from spreading out from under the upper color in the state where print image IM 1  is transferred on a T-shirt. Accordingly, in color printer  1 , the ground color which should be originally hidden under the upper color and invisible on a T-shirt being a final target for the formation of print image IM 1  can be kept invisible even when these colors are misaligned with each other, so that the deterioration in the quality of print image IM 1  can be prevented. 
     Next, in the case where print image IM 1  in which the base colors serve as the ground color (that is, the color of clear as the special color serves as the upper color) is formed on the surface of a plain paper sheet, upon loading image data of an image to be printed from the outside, first image input unit  52  generates print image data of print image IM 1  represented with the colors of cyan, magenta, yellow, black, and clear based on the loaded image data. In this event, first image input unit  52  stores, in the print image data for every pixel of print image IM 1 , five kinds of pixel values represented by normalizing the densities of cyan, magenta, yellow, black, and clear into values from “0” to “255” respectively. Note that, as in the case of the print image in which white serves as the ground color described above, each of the pixel values of cyan, magenta, yellow, and black for each pixel becomes when the corresponding color is not used to represent the pixel, and becomes a value larger than “0” according to its density when the corresponding color is used to represent the pixel. Further, in order to make the color of clear serve as the upper color for glossing the base colors in print image IM 1 , for every pixel of print image IM 1 , first image input unit  52  sets the pixel value of clear at a value larger than “0,” more preferably at “255” indicating the highest density for the purpose of achieving sufficient gloss if at least one of the pixel values of cyan, magenta, yellow, and black is equal to a value larger than “0,” and sets the pixel value of clear at “0” if all of the pixel values of cyan, magenta, yellow, and black are equal to “0.” Accordingly, in print image IM 1  in which the base colors serve as the ground color, a colored area is an area including only pixels in each of which the pixel value of clear is larger than “0” and at least one of the pixel values of cyan, magenta, yellow, and black is larger than “0,” and a colorless area is an area including only pixels in each of which all the pixel values of cyan, magenta, yellow, black, and clear are equal to “0.” First image input unit  52  generates the print image data in this manner and sends it to boundary correction area detector  62 . 
     Upon receiving the print image data from first image input unit  52 , boundary correction area detector  62  retrieves second pixel search range information from storage unit  51  according to the setting made by setting unit  61  and executes the boundary correction area detection processing as in the above case. Boundary correction area detector  62  thereby detects boundary correction area AR 4  in print image IM 1  based on the print image data, and sends first edge-portion correction area detector  63  the boundary correction area detection data together with the print image data. Upon receiving the boundary correction area detection data together with the print image data from boundary correction area detector  62 , first edge-portion correction area detector  63  retrieves second area detection range information from storage unit  51  according to the setting made by setting unit  61  and executes the first edge-portion correction area detection processing as in the above case. First edge-portion correction area detector  63  thereby detects the edge-portion correction area for bordered mode AR 3 , which extends along the edges of the image, in print image IM 1  based on the print image data, and sends first correction processor  64  the edge-portion correction area detection data together with the print image data and the boundary correction area detection data. Upon receiving the boundary correction area detection data and the edge-portion correction area detection data together with the print image data from first edge-portion correction area detector  63 , first correction processor  64  retrieves second pixel search range information from storage unit  51  according to the setting made by setting unit  61  and executes a first correction processing. In this event, as in the above case, while shifting the second pixel search range sequentially on a pixel-by-pixel basis on print image IM 1 , first correction processor  64  designates every pixel in print image IM 1  as a focused pixel sequentially one at a time, and judges whether or not the focused pixel is an edge-portion correction pixel and whether or not the focused pixel is a boundary correction pixel. As a result of the judgment, if the focused pixel is an edge-portion correction pixel, out of the five kinds of pixel values of this focused pixel (i.e., edge-portion correction pixel), first correction processor  64  changes each of the pixel values of cyan, magenta, yellow, and black, excluding the pixel value of clear from its original value larger than “0,” to “0” because the base colors serve as the ground color in print image IM 1 . Thereby, first correction processor  64  can correct print image IM 1  so that edge-portion correction area for bordered mode AR 3  extending along the edges of print image IM 1  may be represented only with the color of clear as the upper color, and thus, in an edge portion of the image, it can make the width of the base colors as the ground color narrower than the width of the color of clear as the upper color, laid over the ground color, such that the area of the ground color retreats toward the center of the image from the image edges. In addition, if the focused pixel is a boundary correction pixel, out of the five kinds of pixel values of this focused pixel (i.e., boundary correction pixel), first correction processor  64  changes only the pixel value of clear from its original value of “0” to a value larger than “0,” for example, “255.” Thereby, first correction processor  64  can make the width of the color of clear as the upper color wider than the width of the base colors as the ground color laid under the upper color in a central portion of print image IM 1 . Then, first correction processor  64  sends the print image data of print image IM 1  corrected in the above manner to output image processor  65  as corrected print image data. Thus, when print image IM 1  represented with the base colors as the ground color and the color of clear as the upper color is formed on the surface of print medium  5  in color printer  1 , it is possible to lay the color of clear wider than the ground color laid over the ground color. By doing so, even if the base colors and the color of clear laid one over another in print image IM 1  on print medium  5  are misaligned with each other in color printer  1 , it is possible to prevent the base colors from spreading out from under the color of clear. Accordingly, in color printer  1 , even if the color of clear and the base colors are misaligned with each other in print image IM 1 , it is possible to avoid the generation of base color portions that cannot be coated with the color of clear and gloss the base colors exactly, and thus to prevent the deterioration in the quality of print image IM 1 . 
     (1-3) First Image Processing 
     Next, with the flowcharts illustrated in  FIGS. 11 to 13 , a description is given of boundary correction area detection processing procedure RT 1 , first edge-portion correction area detection processing procedure RT 2 , and first correction processing procedure RT 3  that first controller  50  executes as part of a first image processing procedure according to the first image processing program. Upon receiving print image data from first image input unit  52 , first controller  50  starts boundary correction area detection processing procedure RT 1  illustrated in  FIG. 1  according to the first image processing program. Upon starting boundary correction area detection processing procedure RT 1 , in step SP 1 , first controller  50  designates one of the pixels in print image IM 1  as focused pixel PS 1 , and judges whether or not both conditions where this focused pixel PS 1  is a pixel of colorless area AR 1  and where any pixel of colored area AR 2  exists within a pixel search range (i.e., among neighboring pixels PN 1  in first pixel search range SE 1  or the second pixel search range which are located around focused pixel PS 1 ) are satisfied. If a positive result is obtained in step SP 1 , it indicates that the width of the upper color laid over the ground color can be made wider than the width of the ground color in a central portion of print image IM 1  by making such a correction that focused pixel PS 1  may be represented with the upper color. Thus, if a positive result is obtained in step SP 1 , first controller  50  proceeds to step SP 2  to judge that this focused pixel PS 1  is a boundary correction pixel of boundary correction area AR 4 , and proceeds to next step sp 3 . In contrast, if a negative result is obtained in step SP 1 , it indicates that focused pixel PS 1  is a pixel relatively away from a boundary between colorless area AR 1  and colored area AR 2 , and therefore the width of the upper color laid over the ground color cannot be made wider than the width of the ground color in the central portion of print image IM 1  even by making such a correction that focused pixel PS 1  may be represented with the upper color. Thus, if a negative result is obtained in step SP 1 , first controller  50  proceeds to step SP 4  to judge that this focused pixel PS 1  is a non-correction pixel outside boundary correction area AR 4 , and proceeds to step SP 3 . In step SP 3 , first controller  50  judges whether or not the judgment on all the pixels in print image IM 1  is over, and goes back to step SP 1  if a negative result is obtained. When first controller  50  finishes judging all the pixels in print image IM 1  to be either a boundary correction pixel or a non-correction pixel, it detects boundary correction area AR 4  based on the judgment result. Then, if a positive result is obtained in step SP 3 , first controller  50  proceeds to next step SP 5  to terminate boundary correction area detection processing procedure RT 1 . 
     When first controller  50  finishes boundary correction area detection processing procedure RT 1 , it subsequently starts first edge-portion correction area detection processing procedure RT 2  illustrated in  FIG. 12  according to the first image processing program. Upon starting first edge-portion correction area detection processing procedure RT 2 , in step SP 11 , first controller  50  designates one of the pixels in print image IM 1  as a focused pixel, and judges whether or not this focused pixel is a pixel of colored area AR 2  and also a pixel within an area detection range (i.e., first area detection range DE 1  or the second area detection range) extending along the edges of the image. If a positive result is obtained in step SP 11 , it indicates that the width of the ground color can be made narrower than the width of the upper color, laid over the ground color, in an edge portion of print image IM 1  such that the area of the ground color retreats toward the center of the image from the image edges by making such a correction that the focused pixel may be represented with the upper color. Thus, if a positive result is obtained in step SP 11 , first controller  50  proceeds to step SP 12  to judge that this focused pixel is an edge-portion correction pixel of the edge-portion correction area for bordered mode AR 3 , and proceeds to next step SP 13 . In contrast, if a negative result is obtained in step SP 11 , it indicates that the focused pixel is a pixel relatively away from the edge portion of print image IM 1 , and therefore the width of the ground color cannot be made narrower than the width of the upper color, laid over the ground color, in the edge portion of print image IM 1  such that the area of the ground color retreats toward the center of the image from the image edges even if such a correction is made that the focused pixel may be represented with the upper color. Thus, if a negative result is obtained in step SP 11 , first controller  50  proceeds to step SP 14  to judge that this focused pixel is a non-correction pixel outside the edge-portion correction area for bordered mode AR 3 , and proceeds to step SP 13 . In step SP 13 , first controller  50  judges whether or not the judgment on all the pixels in print image IM 1  is over, and goes back to step SP 11  if a negative result is obtained. When first controller  50  finishes judging all the pixels in print image IM 1  to be either an edge-portion correction pixel or a non-correction pixel, it detects the edge-portion correction area for bordered mode AR 3  based on the judgment result. Then, if a positive result is obtained in step SP 13 , first controller  50  proceeds to next step SP 15  to terminate first edge-portion correction area detection processing procedure RT 2 . 
     When first controller  50  finishes first edge-portion correction area detection processing procedure RT 2 , it subsequently starts first correction processing procedure RT 3  illustrated in  FIG. 13  according to the first image processing program. Upon starting first correction processing procedure RT 3 , in step SP 21 , first controller  50  designates one of the pixels in print image IM 1  as focused pixel PS 1 , and judges whether or not this focused pixel PS 1  is an edge-portion correction pixel. If a positive result is obtained, first controller  50  proceeds to step SP 22  to correct the edge-portion correction area for bordered mode AR 3  such that the pixel value of the ground color of the edge-portion correction pixel is replaced with “0,” and then proceeds to the next step SP 23 . In contrast, if focused pixel PS 1  is any of a boundary correction pixel and a non-correction pixel, and thus a negative result is obtained in step S 21 , first controller  50  proceeds to step SP 24  to judge whether or not this focused pixel PS 1  is a boundary correction pixel. If a positive result is obtained in SP 24 , first controller  50  proceeds to step SP 25  to correct boundary correction area AR 4  such that the pixel value of the upper color of the boundary correction pixel is replaced with a value larger than “0,” and then proceeds to next step SP 23 . On the other hand, if focused pixel PS 1  is a non-correction pixel which should be excluded from the correction target and a negative result is obtained in step SP 23 , first controller  50  proceeds to step SP 23 . In step SP 23 , first controller  50  judges whether or not the correction on the edge-portion correction area for bordered mode AR 3  and boundary correction area AR 4  in print image IM 1  is over. If a negative result is obtained in step SP 23  because there is a pixel not yet judged to be an edge-portion correction pixel nor judged to be a boundary correction pixel or not and therefore the correction on edge-portion correction area for bordered mode AR 3  and boundary correction area AR 4  is not over, first controller  50  goes back to step SP 21 . Then, if a positive result is obtained in step SP 23  because the correction on edge-portion correction area for bordered mode AR 3  and boundary correction area AR 4  is over, first controller  50  proceeds to next step SP 26  to terminate first correction processing procedure RT 3 . 
     (1-4) Operation and Effect of Embodiment 1 
     In color printer  1  having the above configuration, first controller  50  loads print image data, and detects the edge-portion correction area for bordered mode AR 3  in an edge portion of print image IM 1  based on the print image data. The edge-portion correction area for bordered mode extends along the edges of the image represented with the ground color and the upper color laid one over another. Then, in color printer  1 , first controller  50  corrects print image IM 1  based on the print image data so that edge-portion correction area for bordered mode AR 3  may be represented only with the upper color, and thereby generates corrected print image data. 
     With the above configuration, color printer  1  can make the width of the ground color narrower than the width of the upper color, laid over the ground color, in the edge portion of print image IM 1  based on the print image data such that the area of the ground color retreats toward the center of the image from the image edges. Accordingly, even if the ground color and the upper color laid one over another are misaligned with each other in an edge portion of the image when print image IM 1  is formed on a surface of print medium  5  in color printer  1 , it is possible to avoid a situation where the ground color spreads out from under the upper color on the surface of print medium  5  (or on a T-shirt on which print image IM 1  is eventually formed), that is, avoid a visible misregistration of the upper color and the ground color, and thus to prevent the deterioration in the quality of print image IM 1 . 
     In addition, in color printer  1 , first controller  50  detects boundary correction area AR 4  adjacent to colored area AR 2  in a central portion of print image IM 1  based on print image data, and corrects boundary correction area AR 4  so that this area may be represented with the upper color. By doing so, color printer  1  can make the width of the upper color in colored area AR 2  wider than the width of the ground color laid under the upper color in the central portion of print image IM 1  based on the print image data. Accordingly, in color printer  1 , it is also possible to avoid a situation where the ground color spreads out from under the upper color in a central portion of print image IM 1  when print image IM 1  is formed on a surface of print medium  5 , and thus to prevent the deterioration in the quality of print image IM 1  further reliably. Moreover, in color printer  1 , first controller  50  corrects boundary correction area AR 4  such that, for each pixel of boundary correction area AR 4 , the pixel value of the upper color that this pixel has is replaced with the largest value among the pixel values of the upper color that pixels in a pixel search range, including the pixel as a center pixel, respectively have. Accordingly, in a central portion of the image, color printer  1  can expand a portion of colored area AR 2 , being a boundary with colorless area AR 1 , while hardly changing the color thereof. Thus, color printer  1  can also prevent the deterioration in the image quality which would otherwise be caused if the upper color portion of colored area AR 2  expanded by the correction on boundary correction area AR 4  turns to a color significantly different from its original color. 
     Moreover, color printer  1  stores first area detection range DE 1  in storage unit  51  as first area detection range information, first area detection range DE 1  having a width assigned according to the amount of the first misregistration of the ground color and the upper color in the case of forming print image IM 1  on a surface of print medium  5  with the first image formation method, and stores a second area detection range in storage unit  51  as second area detection range information. The second area detection range has a width assigned according to the amount of the second misregistration of the ground color and the upper color in the case of forming print image IM 1  on a surface of print medium  5  with the second image formation method. Further, when color printer  1  forms print image IM 1  with the first image formation method, first controller  50  detects the edge-portion correction area for bordered mode AR 3  in first area detection range DE 1  extending along the edges of the image. and corrects it in print image IM 1  based on the print image data. Furthermore, when color printer  1  forms print image IM 1  with the second image formation method, first controller  50  detects the edge-portion correction area for bordered mode AR 3  in the second area detection range extending along the edges of the image and corrects it in print image IM 1  based on print image data. Accordingly, irrespective of which of the first image formation method and the second image formation method color printer  1  uses to form print image IM 1  on a surface of print medium  5 , color printer  1  can narrow the width of the ground color in an edge portion of print image IM 1  based on print image data such that the area of the ground color retreats toward the center of the image from the image edges by the amount of correction according to the amount of first misregistration or the amount of second misregistration. Thus, even if the amount of misregistration of the ground color and the upper color varies depending on which method is used to form print image IM 1  on a surface of print medium  5 , the color printer can adequately avoid a situation where the ground color spreads out from under the upper color in print image IM 1  on the surface of print medium  5  (or on a T-shirt on which print image IM 1  is eventually formed), and thus prevent the deterioration in the quality of print image IM 1 . 
     (2) Embodiment 2 
     (2-1) Internal Configuration of Color Printer 
     Next, a description is given of the internal configuration of color printer  70  ( FIG. 1 ) according to embodiment 2. Color printer  70  is not only capable of forming a print image on the surface of print medium  5  in the bordered printing mode, but also capable of forming a print image thereon in the borderless printing mode where the whole front surface of print medium  5  is used as a print area without any border portion left on the surface. Note, however, that, although the circuit configuration of color printer  70 , to be described later, differs from the circuit configuration of color printer  1  according to embodiment 1 described above in order to enable the formation of a print image in the borderless printing mode, the internal configuration of color printer  70  is the same as the internal configuration of color printer  1  according to embodiment 1. Accordingly, the internal configuration of color printer  70  according to embodiment 2 is understood with reference to the description on the internal configuration of color printer  1  according to embodiment 1 described with  FIG. 1 , and is therefore not described here. 
     (2-2) Circuit Configuration of Color Printer 
     Next, the circuit configuration of color printer  70  is described with  FIG. 14  in which portions that are corresponding to those of  FIG. 2  are given reference numerals that are the same as those of  FIG. 2 . Color printer  70  has the same configuration as in the case of embodiment 1 except that second controller  71  such as a CPU or a microprocessor, storage unit  72  such as a hard disc drive or a ROM, and second image input unit  73  are provided in place of first controller  50 , storage unit  51 , and first image input unit  52  according to embodiment 1 described above. Thus, second controller  71  is configured to load various programs, such as a base program and a variety of application programs previously stored in storage unit  72 , from the storage unit to a memory (not illustrated) as appropriate, and expand these in the memory. Further, second controller  71  is configured to exert an overall control on color printer  70  according to the various programs thus developed in the memory, and execute a predetermined arithmetic processing, that includes various processing in response to manipulation commands inputted through manipulation panel  4 , and the like. Thereby, second controller  71  can form a print image on a surface of print medium  5 . 
     Meanwhile, second image input unit loads image data of an image to be printed from the outside in the same manner as first image input unit  52  according to embodiment 1. Then, in the case of forming a print image on a surface of print medium  5  in the bordered printing mode, second image input unit  73  generates print image data of the print image having an image size slightly smaller than the size of the print medium for use in bordered printing as in the case of first image input unit  52  described above. Alternatively, in the case of forming a print image on a surface of print medium  5  in the borderless printing mode, second image input unit  73  generates print image data of the print image having an image size slightly larger than the size of the print medium for use in borderless printing, for example. Note that, in the case where a print image is formed on a surface of print medium  5  with the first image formation method, for example, print image data generated by second image input unit  73  for use in borderless printing is assigned, as appropriate, such an image size (hereinafter, such a size is also referred to as a first borderless image size) that an edge portion of the image extends beyond the top and bottom edges and the left and right edges of the surface of print medium  5  by an equal width or different widths according to the amount of first misregistration. Alternatively, in the case where a print image is formed on a surface of print medium  5  with the second image formation method, print image data generated by second image input unit  73  for use in borderless printing is assigned, as appropriate, such an image size (hereinafter, such a size is also referred to as a second borderless image size) that an edge portion of the image extends beyond the top and bottom edges and the left and right edges of the surface of print medium  5  by an equal width or different widths according to the amount of the second misregistration. Note, however, that, since there is tendency that a larger portion of the ground color spreads out from under the upper color with the second image formation method than with the first image formation method as described above, the second borderless image size is assigned so as to be wider than the first borderless image size in at least one of the main-scanning direction and the sub-scanning direction. 
     Thus, in storage unit  72 , second controller  71  stores the above-mentioned first pixel search range information and second pixel search range information, and stores the above-mentioned first area detection range information and second area detection range information for use in processing print image data for bordered printing. In addition, according to the amount of the first misregistration, the first borderless image size, and the size of the medium (medium size), color printer  70  assigns, as appropriate, a third area detection range being in the shape of a frame going around a print image along the edges of the image, being an area extending beyond print medium  5 , and being used to detect an edge-portion area to be corrected in an edge portion of the print image of the first borderless image size (hereinafter, such an area is also referred to as an edge-portion correction area for borderless mode). Likewise, in an edge portion of a print image of the second borderless image size, color printer  70  assigns, as appropriate, a fourth area detection range, which is an area extending beyond print medium  5  and is used to detect an edge-portion correction area for the borderless mode, according to the amount of the second misregistration, the second borderless image size, and the medium size. Note that the third area detection range and the fourth area detection range are each in the shape of a frame whose widths between left/right strip-shaped portions and between top/bottom strip-shaped portions are equal to, or different from, each other as in the case of the first area detection range and the second area detection range, and they are assigned so that the fourth area detection range may be wider than the third area detection range. Thus, in storage unit  72 , second controller  71  stores third area detection range information indicating the third area detection range and fourth area detection range information indicating the fourth area detection range. Note that, in storage unit  72 , second controller  71  stores first borderless image size information indicating the first borderless image size represented with the number of pixels in the main-scanning direction and in the sub-scanning direction, and also stores second borderless image size information indicating the second borderless image size represented with the number of pixels in the main-scanning direction and in the sub-scanning direction. 
     Storage unit  72  stores therein a second image processing program having a configuration different from the first image processing program according to embodiment 1 described above. With the configuration above, upon receiving print image data from second image input unit  73  in the formation of a print image, second controller  71  executes second image processing by using the first and second pixel search range and the first to fourth detection range as appropriate to prevent the ground color from spreading out from under the upper color throughout the print image (i.e., in an edge portion and a central portion of the image). Thus, with  FIG. 15 , in which portions that are corresponding to those of  FIG. 3  are given reference numerals that are the same as those of  FIG. 3 , print image data generation processing executed by second image input unit  73  is described specifically below. Besides, while various functions that second controller  71  implements according to the second image processing program are indicated by functional circuit blocks for the sake of convenience, the second image processing that second controller  71  executes according to the second image processing program is described specifically below as the processing executed by the functional circuit blocks. 
     In this case, in the same manner as setting unit  61  according to embodiment 1 described above, setting unit  76  of second spread-out correction unit  75  detects an image formation method and the type of the ground color and the upper color. Then, setting unit  76  makes a setting such that all parts of second spread-out correction unit  75  (i.e., boundary correction area detector  62 , second edge-portion correction area detector  77 , and second correction processor  78 ) execute processing according to the image formation method and the type of the ground color and the upper color thus detected, and such that second image input unit  73  generates print image data of a print image represented with the ground color and the upper color thus detected. Further, at the time of forming a print image for example, setting unit  76  lets the user direct a printing mode at this time (i.e., either of the bordered printing mode and the borderless printing mode) on a setting screen displayed on manipulation panel  4 . Then, if the formation of a print image in the bordered printing mode is directed by the user, setting unit  76  makes a setting such that second image input unit  73  generates print image data for a bordered printing in addition to the above setting. On the other hand, if the formation of a print image in the borderless printing mode is directed by the user, setting unit  76  retrieves first borderless image size information or second borderless image size information from storage unit  72  depending on which image formation method (i.e., the first image formation method and the second image formation method) is used at this time and sends it to second image input unit  73 . At the same time, setting unit  76  makes a setting such that second image input unit  73  generates print image data for borderless printing in addition to the above setting. Incidentally, if image data of an image to be printed is given to second image input unit  73  from an information processing device connected to color printer  70 , setting unit  76  may direct that the information processing device direct a printing mode besides letting the user direct a printing mode on the setting screen. 
     Meanwhile, second image input unit  73  generates print image data for bordered printing or print image data for borderless printing according to the setting made by setting unit  76 , and sends boundary correction area detector  62  the print image data and printing mode information indicating whether the print image data is for bordered printing or for borderless printing irrespective of whichever print image data is generated. However, second image input unit  73  generates print image data for bordered printing in the same manner as first image input unit  52  according to embodiment 1 described above. Thus, in the following description, only the process of generating print image data for borderless printing is described as to the processing executed by second image input unit  73 . In addition, upon receiving print image data and printing mode information from second image input unit  73 , boundary correction area detector  62  detects a boundary correction area based on the print image data and sends a boundary correction area detection data to second edge-portion correction area detector  77  together with the print image data and the printing mode information. However, boundary correction area detector  62  executes boundary correction area detection processing as in the case of embodiment 1, described above, irrespective of which of print image data for bordered printing and print image data for borderless printing boundary correction area detector  62  retrieves. Thus, a specific description on the processing of printing boundary correction area detector  62  is omitted. Further, upon retrieving print image data and printing mode information, together with boundary correction area detection data from boundary correction area detector  62 , second edge-portion correction area detector  77  judges a printing mode based on the printing mode information. Then, second edge-portion correction area detector  77  executes the same processing as the first edge-portion correction area detection processing executed by first edge-portion correction area detector  63  if the judged printing mode is the bordered printing mode, but executes a processing different from the first edge-portion correction area detection processing if the judged printing mode is the borderless printing mode. Thus, in the following description, as to the processing executed by second edge-portion correction area detector  77 , the processing executed when the judged printing mode is the bordered printing mode is not described, and only the processing executed when the judged printing mode is the borderless printing mode is described. Furthermore, second correction processor  78  executes the same processing irrespective of whether the printing mode is the bordered printing mode or the borderless printing mode. Thus, in the following description, as to the processing executed by second correction processor  78 , only the processing executed when the printing mode is the borderless printing mode is described, and the processing executed when the printing mode is the bordered printing mode is not described. 
     In the case where a print image in which white serves as the ground color is formed on a surface of a plain paper sheet in the borderless printing mode, upon loading image data of an image to be printed from the outside, second image input unit  73  generates print image data of the print image having the first borderless image size and represented with the colors of cyan, magenta, yellow, black, and white based on the loaded image data. In this event, for example, for a portion of the print image which entirely overlaps the surface of print medium  5 , second image input unit  73  stores, in the print image data for every pixel of that portion, five kinds of pixel values represented by normalizing the densities of cyan, magenta, yellow, black, and white into values from “0” to “255” respectively based on the pattern of the print image, in the same manner as first image input unit  52  according to embodiment 1 described above. On the other hand, for an area of the print image which extends beyond the print medium, second image input unit  73  stores, in the print image data for every pixel of that area, five kinds of pixel values of “0” indicating that none of the colors of cyan, magenta, yellow, black, and white is used for representing the pixel, for example. Second image input unit  73  sends the print image data generated in this manner to boundary correction area detector  62  together with the printing mode information indicating the borderless printing mode applied at this time. Then, upon receiving the boundary correction area detection data together with the print image data and the printing mode information from boundary correction area detector  62 , second edge-portion correction area detector  77  executes second edge-portion correction area detection processing and judges a printing mode applied at this time (i.e., the borderless printing mode in this case). In addition, second edge-portion correction area detector  77  retrieves first pixel search range information and third area detection range information from storage unit  72  according to the setting made by setting unit  76  as well as the judgment result. In this event, as illustrated in  FIG. 16 , while shifting first pixel search range SE 1  indicated by the first pixel search range information in the main-scanning direction or in the sub-scanning direction sequentially on a pixel-by-pixel basis on print image IM 2  which is based on the print image data, second edge-portion correction area detector  77  makes every pixel in print image IM 1  positioned at the center of first pixel search range SE 1  sequentially one at a time to designate the pixel as focused pixel P 51 . In addition, every time second edge-portion correction area detector  77  designates each pixel as a focused pixel PS 1  on print image IM 1  one at a time, it judges whether or not both conditions where focused pixel PS 1  is a pixel of extension area AR 5  and where at least one of neighboring pixels PN 1  is a pixel of colored area AR 2  are satisfied on the basis of a third area detection range (not illustrated) indicated by the third area detection range information and having widths between left/right strip-shaped portions and between top/bottom strip-shaped portions that are equal to each other, for example, and five kinds of pixel values of each of neighboring pixels PN 1  in first pixel search range SE 1 . Note that second edge-portion correction area detector  77  may judge that focused pixel PS 1  is a pixel of extension area AR 5  being the third area detection range if the coordinates of focused pixel PS 1  satisfy at least one of four kinds of conditions represented with the following formulae (5) to (8):
 
 x&lt;W 2  (5);
 
 y&lt;W 2  (6);
 
 x≧X 2− W 2  (7); and
 
 y≧Y 2− W 2  (8),
 
     where: X 2  and Y 2  indicate the horizontal size and the vertical size represented with the number of pixels in the main-scanning direction and in the sub-scanning direction, respectively, with the left upper corner of print image IM 2  used as the point of origin. W 2  indicates the width of each of image left/right edge portions and image top/bottom edge portions of extension area AR 5  represented with the number of pixels thereof; and (x, y) indicates the coordinates of focused pixel PS 1 . Then, if a focused pixel is a pixel of extension area AR 5  and at least one of neighboring pixels PN 1  is a pixel of colored area AR 2 , second edge-portion correction area detector  77  judges that this focused pixel PS 1  is an edge-portion correction pixel. In contrast, if focused pixel PS 1  is a pixel outside extension area AR 5 , second edge-portion correction area detector  77  judges that this focused pixel PS 1  is a non-correction pixel irrespective of whether or not any of neighboring pixels PN 1  is a pixel of colored area AR 2 . Further, if focused pixel PS 1  is a pixel of extension area AR 5  but all of neighboring pixels PN 1  are pixels in colorless area AR 1 , second edge-portion correction area detector  77  also judges that this focused pixel PS 1  is a non-correction pixel. In this manner, based on the judgment result, second edge-portion correction area detector  77  detects an edge-portion correction area for the borderless mode, which is formed of edge-portion correction pixels and adjacent to colored area AR 2  on the central side of the image, in extension area AR 5  of print image IM 2 . Note that second edge-portion correction area detector  77  generates edge-portion correction area detection data indicating the edge-portion correction area for the borderless mode while judging, one at a time, whether each of the pixels in print image IM 2  is an edge-portion correction pixel or a non-correction pixel. Specifically, second edge-portion correction area detector  77  stores data in the edge-portion correction area detection data such that it associates a value of “2” indicating an edge-portion correction pixel with a pixel in print image IM 2  if judging that the pixel is an edge-portion correction pixel, and such that it associates a value of “0” indicating a non-correction pixel with a pixel in print image IM 2  if judging that the pixel is a non-correction pixel. Note that second edge-portion correction area detector  77  stores a value of “2,” indicating an edge-portion correction pixel of an edge-portion correction area for the borderless mode, in the edge-portion correction area detection data if detecting the edge-portion correction area for the borderless mode in print image IM 2  for borderless printing in the above manner, but stores a value of “1,” indicating an edge-portion correction pixel of an edge-portion correction area for bordered mode, in the edge-portion correction area detection data if detecting the edge-portion correction area for bordered mode in the print image for bordered printing. Second edge-portion correction area detector  77  thereby makes the edge-portion correction area detection data recognizable as to which of the edge-portion correction area for the bordered mode and the edge-portion correction area for the borderless mode the edge-portion correction area detection data indicates. Then, upon detecting the edge-portion correction area for the borderless mode in this manner, second edge-portion correction area detector  77  sends the edge-portion correction area detection data to second correction processor  78  together with the print image data and the boundary correction area detection data. 
     Upon receiving the boundary correction area detection data and the edge-portion correction area detection data, together with the print image data from second edge-portion correction area detector  77 , second correction processor  78  retrieves first pixel search range information from storage unit  72  and executes second correction processing according to the setting made by setting unit  76 . In this event, while shifting first pixel search range SE 1  (not illustrated in  FIG. 7 ) indicated by the first pixel search range information in the main-scanning direction or in the sub-scanning direction sequentially on a pixel-by-pixel basis on print image IM 2  which is based on the print image data, second correction processor  78  designates every pixel in print image IM 2  as a focused pixel PS 1  at the center of first pixel search range SE 1  sequentially one at a time, for example. In addition, every time second correction processor  78  designates each pixel as a focused pixel PS 1  on print image IM 2  one at a time, it judges whether or not focused pixel PS 1  is an edge-portion correction pixel of the edge-portion correction area for the borderless mode, whether or not the focused pixel is an edge-portion correction pixel of the edge-portion correction area for the bordered mode, and whether or not the focused pixel is a boundary correction pixel of the boundary correction area. As a result of the judgment, if focused pixel PS 1  is an edge-portion correction pixel of the edge-portion correction area for the borderless mode, second correction processor  78  changes the pixel value of white that this focused pixel PS 1  (i.e., boundary correction pixel) has from its original value of “0” to the largest value among the pixel values of white that neighboring pixels PN 1  in first pixel search range SE 1  respectively have. In the same way, second correction processor  78  changes each of the pixel values of cyan, magenta, yellow, and black that this focused pixel PS 1  (i.e., boundary correction pixel) has from its original value of “0” to the largest value among the pixel values of the corresponding color that neighboring pixels PN 1  in first pixel search range SE 1  respectively have. Note that, if focused pixel PS 1  is a boundary correction pixel, second correction processor  78  changes the pixel values of cyan, magenta, yellow, and black except for the pixel value of white among the five kinds of pixel values of this focused pixel PS 1  (i.e., boundary correction pixel) in the same manner as first correction processor  64  according to embodiment 1 described above. On the other hand, if focused pixel PS 1  is a non-correction pixel (that is, focused pixel PS 1  is neither an edge-portion correction pixel nor a boundary correction pixel), second correction processor  78  leaves the five kinds of pixel values of this focused pixel PS 1  unchanged. Incidentally, second correction processor  78  corrects an edge-portion correction pixel in the above manner when receiving print image data for borderless printing from second edge-portion correction area detector  77 , but processes an edge-portion correction pixel in the same manner as first correction processor  64  according to embodiment 1 described above when receiving print image data for bordered printing from second edge-portion correction area detector  77 . In this manner, second correction processor  78  corrects print image IM 2  for borderless printing so that the edge-portion correction area for the borderless mode extending along the edges of the image may be represented with the ground color and the upper color laid one over another, and thus widens the width of colored area AR 2  in the edge portion of the image such that colored area AR 2  expands toward the edges of the image from an area having the medium size in the image. Then, second correction processor  78  sends the print image data of print image IM 2  thus corrected to output image processor  65  as corrected print image data. 
     Thereby, color printer  70  can form print image IM 2 , whose edge-portion correction area for the borderless mode and boundary correction area are corrected, in the borderless printing mode on the entire surface of print medium  5  on the basis of the corrected print image data. Note that, in this event, an edge portion of a toner image is left un-transferred on the surface of transfer belt  33  when transfer unit  15  transfers the toner image onto the surface of print medium  5  from the surface of transfer belt  33  in color printer  70  because the first borderless image size of print image IM 2  based on the corrected print image data is larger than the medium size. However, such residual toner can be removed with cleaning blade  40 . Meanwhile, when forming a print image on a surface of print medium  5  in the borderless printing mode, a conventional color printer generates print image data of the print image having an image size equal to the medium size. Thus, as illustrated in  FIG. 17A , as long as the conventional color printer can form a print image on a surface of print medium  5  such as a plain paper sheet without any misalignment of the print image itself relative to the surface, for example, it is possible to lay ground color GC 3  and upper color UC 3  of the same width one over another in a colored area in an edge portion of the image while aligning them along an edge of the sheet. However, as illustrated in  FIG. 17B , because the conventional color printer does not perform the second image processing as in embodiment 2 on print image data at all, ground color GC 3  spreads out from under upper color UC 3  if ground color GC 3  and upper color UC 3  laid one over another are misaligned with each other in the colored area in the edge portion of the image, which deteriorates the quality of the print image. Further, as illustrated in  FIG. 17C , if the print image itself is misaligned relative to the surface of print medium  5  in the conventional color printer, ground color GC 3  and upper color UC 3  are moved away from the edge of the sheet and the color of the sheet (i.e., the color of print medium  5 ) turns visible in addition to the upper color, which still deteriorates the quality of the print image. On the other hand, color printer  70  according to embodiment 2 generates print image data of print image IM 2  of the first borderless image size larger than the medium size, and corrects an edge-portion correction area for the borderless mode, extending along the edges of the image, in print image IM 2  based on the print image data to widen the width of colored area AR 2  in an edge portion of the image such that colored area AR 2  expands toward the edges of the image from an area having the medium size in the image. Thus, as illustrated in  FIG. 18A , when color printer  70  forms print image IM 2  on a surface of print medium  5  such as a plain paper sheet, for example, and if there is no misalignment of the print image itself relative to the surface, it is possible to make a part of ground color GC 4  and upper color UC 4  laid one over another spread out beyond the edge of the sheet in the edge portion of the image, and thereby to prevent ground color GC 4  and the color of the sheet from becoming visible. Further, as illustrated in  FIG. 18B , even if ground color GC 4  and upper color UC 4  laid one over another are misaligned with each other in the edge portion of the image in color printer  70 , it is possible to make ground color GC 4  spread out from under upper color UC 4  outside the edge of the sheet, and thereby to prevent ground color GC spreading out from under upper color UC 4  from becoming visible. Furthermore, as illustrated in  FIG. 18C , even if print image IM 2  itself is misaligned relative to the surface of print medium  5  in color printer  70 , it is possible to make ground color GC 4  and upper color UC 4  laid one over another aligned along the edge of the sheet in the edge portion of the image, and thereby to prevent ground color GC 4  and the color of the sheet from becoming visible in this case as well. 
     Next, in the case where print image IM 2  in which white as the special color serves as the ground color is formed in the borderless printing mode on the surface of a transfer paper sheet, upon loading image data of an image to be printed from the outside, second image input unit  73  generates print image data similar to the above case except that the size of the print image (the second borderless image size in this case) as well as the width of an extension area of the image are different, and sends it to boundary correction area detector  62  together with printing mode information. Then, upon receiving boundary correction area detection data as well as the print image data and the printing mode information from boundary correction area detector  62 , second edge-portion correction area detector  77  executes second edge-portion correction area detection processing and judges a printing mode (i.e., the borderless printing mode in this case) based on the printing mode information. Further, second edge-portion correction area detector  77  retrieves the second pixel search range information and the fourth area detection range information from storage unit  72  in this case according to the setting made by setting unit  76  as well as the judgment result, but executes the second edge-portion correction area detection processing similar to the above to detect an edge-portion correction area for the borderless mode. Second edge-portion correction area detector  77  then sends edge-portion correction area detection data to second correction processor  78  together with the print image data and the boundary correction area detection data. Upon receiving the boundary correction area detection data and the edge-portion correction area detection data as well as the print image data from second edge-portion correction area detector  77 , second correction processor  78  retrieves the second pixel search range information from storage unit  72  according to the setting made by setting unit  76 , but executes the second correction processing similar to the above to generate corrected print image data and sends it to output image processor  65 . 
     Next, in the case where print image in which the base colors serve as the ground color (that is, the color of clear as the special color serves as the upper color) is formed in the borderless printing mode on the surface of a plain paper sheet, upon loading image data of an image to be printed from the outside, second image input unit  73  generates print image data similar to the above case except that the pixel value of clear instead of the pixel value of white is stored in each pixel, and sends it to boundary correction area detector  62  together with printing mode information. Then, upon receiving boundary correction area detection data as well as the print image data and the printing mode information from boundary correction area detector  62 , second edge-portion correction area detector  77  executes a second edge-portion correction area detection processing and judges a printing mode (i.e., the borderless printing mode in this case) based on the printing mode information. Further, second edge-portion correction area detector  77  retrieves the second pixel search range information and the fourth area detection range information from storage unit  72  according to the setting made by setting unit  76  as well as the judgment result, and executes the second edge-portion correction area detection processing similar to the above to detect an edge-portion correction area for the borderless mode. Second edge-portion correction area detector  77  then sends edge-portion correction area detection data to second correction processor  78  together with the print image data and the boundary correction area detection data. Upon receiving the boundary correction area detection data, the edge-portion correction area detection data and the print image data from second edge-portion correction area detector  77 , second correction processor  78  retrieves the second pixel search range information from storage unit  72  according to the setting made by setting unit  76 , and executes the second correction processing similar to the above to generate corrected print image data and sends it to output image processor  65 . 
     (2-3) Second Image Processing 
     Next, with the flowcharts illustrated in  FIGS. 19 and 20  in which portions that are correspond to those of  FIGS. 12 and 13  are given reference numerals that are the same as those of  FIGS. 12 and 13 , a description is given of second edge-portion correction area detection processing procedure RT 4  and second correction processing procedure RT 5  that second controller  71  executes as part of a second image processing procedure according to the second image processing program. Note that boundary correction area detection processing procedure RT 1 , that second controller  71  executes as part of the second image processing procedure, is similar to that in the case of embodiment 1, and therefore is not described. When first controller  50  finishes boundary correction area detection processing procedure RT 1 , it subsequently starts second edge-portion correction area detection processing procedure RT 4  illustrated in  FIG. 19  according to the second image processing program. Upon starting second edge-portion correction area detection processing procedure RT 4 , in step SP 31 , second controller  71  judges whether or not the printing mode at this time is the borderless printing mode, and proceeds to step SP 32  if a positive result is obtained. Then, in step SP 32 , second controller  71  designates one of the pixels in a print image as a focused pixel PS 1 , and judges whether or not both conditions are satisfied as to where this focused pixel PS 1  is a pixel of extension area AR 5 , and where any pixel of colored area AR 2  exists within a pixel search range (i.e., among neighboring pixels PN 1  in first pixel search range SE 1  or the second pixel search range which are located around focused pixel PS 1 ). If a positive result is obtained in step SP  32 , it indicates that focused pixel PS 1  is located near colored area AR 2  in an edge portion of the image and therefore the width of colored area AR 2  can be widened toward the edges of the image (i.e., toward the outside of print medium  5 ) by correcting the pixel values of focused pixel PS 1  so that the focused pixel may be represented with the ground color and the upper color. Thus, if a positive result is obtained in step SP 32 , second controller  71  proceeds to step SP 33  to judge that this focused pixel PS 1  is an edge-portion correction pixel of the edge-portion correction area for the borderless mode, and proceeds to next step SP 34 . In contrast, if a negative result is obtained in step SP 32 , it indicates that focused pixel PS 1  is relatively away from colored area AR 2  in the edge portion of the image, and therefore the width of colored area AR 2  cannot be widened toward the edges of the image even by correcting the pixel values of focused pixel PS 1  so that the focused pixel may be represented with the ground color and the upper color. Thus, if a negative result is obtained in step SP 32 , second controller  71  proceeds to step SP 35  to judge that this focused pixel PS 1  is a non-correction pixel outside the edge-portion correction area for the borderless mode, and proceeds to step SP 34 . Note that, if a negative result is obtained in step SP 31  because the printing mode at this time is the bordered printing mode, second controller  71  proceeds to step SP 11  and executes the processing in step SP 11 , then executes the processing in step SP 12  or the processing in step SP 14 , and then proceeds to step SP 34 . In step SP 34 , second controller  71  judges whether or not the judgment on all the pixels in the print image is over, and goes back to step SP 31  if a negative result is obtained. When second controller  71  finishes judging all the pixels in the print image to be either an edge-portion correction pixel or a non-correction pixel, it detects the edge-portion correction area for the borderless mode or edge-portion correction area for bordered mode AR 3  based on the judgment result. Then, if a positive result is obtained in step SP 34 , second controller  71  proceeds to next step SP 36  to terminate second edge-portion correction area detection processing procedure RT 4 . 
     When second controller  71  finishes second edge-portion correction area detection processing procedure RT 4 , it subsequently starts second correction processing procedure RT 5  illustrated in  FIG. 20  according to the second image processing program. Upon starting second correction processing procedure RT 5 , in step SP 41 , second controller  71  designates one of the pixels in the print image as a focused pixel PS 1 , and judges whether or not this focused pixel PS 1  is an edge-portion correction pixel of the edge-portion correction area for the borderless mode. If a positive result is obtained, second controller  71  proceeds to step SP 42 . Then, in step SP 42 , second controller  71  corrects the edge-portion correction area for the borderless mode so that all of the five kinds of pixel values of the edge-portion correction pixel of the edge-portion correction area for the borderless mode may be replaced with a value larger than “0,” and proceeds to next step SP 43 . In contrast, if a negative result is obtained in step SP 41 , second controller  71  proceeds to step SP 44  to judge whether or not focused pixel PS 1  is an edge-portion correction pixel of the edge-portion correction area for the bordered mode. If a positive result is obtained in step SP 44 , second controller  71  executes the processing in step SP 22  and then proceeds to step SP 43 . Alternatively, if a negative result is obtained in step SP 44 , second controller  71  executes the processing in step SP 24 , and then executes the processing in step SP 25  and proceeds to step SP 43  or proceeds to step SP 43  without executing the processing in step SP 25 . In step SP 43 , second controller  71  judges whether or not the correction is over on the edge-portion correction area for borderless mode and boundary correction area AR 4  in the print image or the correction on edge-portion correction area for bordered mode AR 3  and boundary correction area AR 4  in the print image. If a negative result is obtained in step SP 43  because there is a pixel not yet judged to be an edge-portion correction pixel or not nor judged to be a boundary correction pixel or not and therefore the correction is not over, second controller  71  goes back to step SP 41 . Then, if a positive result is obtained in step SP 43  because the correction on the edge-portion correction area for the borderless mode and boundary correction area AR 4  in the print image or the correction on the edge-portion correction area for bordered mode AR 3  and boundary correction area AR 4  in the print image is over, second controller  71  proceeds to next step SP 45  to terminate second correction processing procedure RT 5 . 
     (2-4) Operation and Effect of Embodiment 2 
     When color printer  70  having the above configuration forms print image IM 2  in the borderless printing mode, second image input unit  73  generates print image data of print image IM 2  which has an image size larger than the medium size and in which colorless extension area AR 5  extends beyond an area having the medium size in the image. Then, in color printer  70 , second controller  71  generates corrected print image data by detecting the edge-portion correction area for the borderless mode, which extends along the edges of the image adjacent to colored area AR 2 , in extension area AR 5  of print image IM 2  which is based on the print image data, and then making such a correction that the detected area may be represented with the ground color and the upper color laid one over another. 
     With the configuration above, color printer  70  can widen the width of colored area AR 2  in print image IM 2  based on the print image data such that colored area AR 2  expands toward the edges of the image from an area having the medium size in the image. Accordingly, even if print image IM 2  itself is misaligned relative to the surface of print medium  5  or the upper color and the ground color laid one over another in the edge portion of print image IM 2  are misaligned with each other when color printer  70  forms print image IM 2  on a surface of print medium  5  in the borderless printing mode, it is possible to avoid a situation where the color of print medium  5 , which should be originally hidden under print image IM 2  and invisible, turns visible or where the ground color spreading out from under the upper color is visible. Because it is possible to avoid this type situation, it is thus possible to prevent the deterioration in the quality of print image IM 2 . 
     In addition, in color printer  70 , second controller  71  corrects the edge-portion correction area for the borderless mode such that, for each pixel of the edge-portion correction area for borderless mode, each of the pixel values of the pixel is replaced with the largest value among the corresponding pixel values of one or more pixels of colored area AR 2  in the pixel search range, including the pixel as a center pixel. Accordingly, color printer  70  can expand a portion of colored area AR 2 , being a boundary with the edge-portion correction area for the borderless mode, toward the edge-portion correction area for the borderless mode while hardly changing the color thereof. Thus, color printer  1  can also prevent a deterioration in the image quality which would otherwise be caused if the portion of colored area AR 2  expanded by the correction on the edge-portion correction area for the borderless mode turns to a color different from its original color. 
     (3) Other Embodiments 
     (3-1) Other Embodiment 1 
     Note that, in embodiments 1 and 2 described above, the description is given of the case where an edge-portion correction area for the borderless mode is corrected such that each of the pixel values of the ground color and the upper color that each pixel of the edge-portion correction area for borderless mode has is replaced with the largest value among the pixel values of the corresponding one of the ground color and the upper color that pixels in a pixel search range including the pixel as a center pixel respectively have. However, not limited thereto, the invention may be so configured that the edge-portion correction area for the borderless mode is corrected such that each of the pixel values of the ground color and the upper color that each pixel of the edge-portion correction area for borderless mode has is replaced with the average value of the pixel values of the corresponding one of the ground color and the upper color that pixels in a pixel search range including the pixel as a center pixel respectively have. With the above configuration as well, the invention can expand a portion of colored area AR 2  on a central side of the image, being a boundary with the edge-portion correction area for the borderless mode, toward the edge-portion correction area for the borderless mode while hardly changing the color thereof. Alternatively, the invention may be so configured that the edge-portion correction area for borderless mode is corrected to be represented only with the upper color such that only the pixel value of the upper color that each pixel of the edge-portion correction area for borderless mode has is replaced with the largest value among the pixel values of the upper color that pixels in a pixel search range including the pixel as a center pixel respectively have, or replaced with the average value of the pixel values of the upper color that pixels in the pixel search range including the pixel as a center pixel respectively have. With the above configuration as well, the invention can achieve an effect similar to that in embodiment 2 described above. 
     (3-2) Other Embodiment 2 
     Further, in embodiments 1 and 2 described above, the description is given of the case where an edge-portion correction area for the bordered mode is corrected such that the pixel value of the ground color that each pixel of the edge-portion correction area for bordered mode has is replaced with “0.” However, not limited thereto, the invention may be so configured that the edge-portion correction area for the bordered mode is corrected such that the pixel value of the ground color that each pixel of the edge-portion correction area for the bordered mode has is replaced with the average value of the pixel values of the ground color that pixels in a pixel search range including the pixel as a center pixel respectively have, or is replaced with a predetermined value which is selected within a range that a pixel value can take (i.e., from “0” to “255”) excluding the smallest value and the largest value. With the above configuration, the invention can prevent a situation where, when the width of colored area AR 2  including the edge-portion correction area for the bordered mode is relatively narrow in an edge portion of an image, for example, the width of the ground color in colored area AR 2  is further narrowed and the ground color becomes unable to fully exert its foundation function, which would otherwise be caused if the pixel value of the ground color that each pixel of the edge-portion correction area for bordered mode has is replaced with “0.” Besides, in the case where the pixel value of the ground color that each pixel of an edge-portion correction area for the bordered mode has, is replaced with the average value of the pixel values of the ground color that pixels in a pixel search range including the pixel as a center pixel respectively have, the invention may set the pixel search range wider than the width of the edge-portion correction area for bordered mode. By doing so, when colorless area AR 1  abuts on the edge-portion correction area for the bordered mode, for example, the pixel value of the ground color that each pixel of the edge-portion correction area for the bordered mode has, can be made smaller than the largest value within a range that this value can take. As a result, although the ground color spreads out from under the upper color if the ground color and the upper color laid one over another are misaligned with each other in an edge portion of a print image when the image is formed on a surface of print medium  5 , the invention can make the density of the spread-out portion relatively low to make this portion less likely to stand out, so that the deterioration in the quality of the print image can be reduced. In addition, in the case where the pixel value of the ground color that each pixel of the edge-portion correction area for the bordered mode has is replaced with a predetermined value which is selected within a range that a pixel value can take excluding the smallest value and the largest value, even if the predetermined value is set as small as possible, the invention can make the ground color, which spreads out from under the upper color when a print image is formed on a surface of print medium  5 , less likely to stand out and thus can reduce the deterioration in the quality of the print image. 
     (3-3) Other Embodiment 3 
     Further, in embodiments 1 and 2 described above, the description is given of the case where a boundary correction area adjacent to colored area AR 2  is detected in colorless area AR 1  located in a central portion of a print image and corrected such that the pixel value of the upper color that each pixel of the boundary correction area has is replaced with the largest value among the pixel values of the upper color that pixels in a pixel search range including the pixel as a center pixel respectively have. However, not limited thereto, the invention may be so configured that a boundary correction area adjacent to colored area AR 2  is detected in colorless area AR 1  located in a central portion of a print image and corrected such that the pixel value of the upper color that each pixel of the boundary correction area has is replaced with the average value of the pixel values of the upper color that pixels in a pixel search range including the pixel as a center pixel respectively have. With the above configuration as well, the invention can expand a portion of colored area AR 2  in a central portion of the image, being a boundary with the boundary correction area, toward the boundary correction area while hardly changing the color thereof. Alternatively, the invention may be so configured that a boundary correction area adjacent to colorless area AR 1  is detected in colored area AR 2  located in the central portion of the print image and corrected such that the pixel value of the ground color that each pixel of the boundary correction area has is replaced with “0.” With the above configuration as well, the invention can narrow the width of the ground color in colored area AR 2  relative to the width of the upper color laid over the ground color, and accordingly this makes it possible to avoid the situation where the ground color spreads out from under the upper color of colored area AR 2  in the central portion of print image IM 1  when the image is formed on a surface of print medium  5 . Still alternatively, the invention may be so configured that, when a boundary correction area is detected in colored area AR 2  located in the central portion of the print image, the boundary correction area is corrected such that the pixel value of the ground color that each pixel of the boundary correction area has is replaced with the average value of the pixel values of the upper color that pixels in a pixel search range including the pixel as a center pixel respectively have. With the above configuration, the invention can prevent a situation where, when the width of colored area AR 2  is relatively narrow, for example, the width of the ground color is further narrowed and the ground color becomes unable to fully exert its foundation function, which would otherwise be caused if the pixel value of the ground color is replaced with “0.” 
     (3-4) Other Embodiment 4 
     Further, in embodiments 1 and 2 described above, the description is given of the case where an edge-portion correction area for the bordered mode, or an edge-portion correction area for the borderless mode, is detected in a print image after a boundary correction area is detected. However, not limited thereto, the invention may be so configured that the boundary correction area is detected in the print image after the edge-portion correction area for the bordered mode or the edge-portion correction area for the borderless mode is detected, or may be so configured that the boundary correction area as well as the edge-portion correction area for the bordered mode or the edge-portion correction area for the borderless mode are detected in a time-sharing processing or at the same time. 
     (3-5) Other Embodiment 5 
     Further, in embodiments 1 and 2 described above, the description is given of the case where, while sequentially designating each of pixels in a print image as a focused pixel, first controller  50  or second controller  71  judges whether this focused pixel is an edge-portion correction pixel or a non-correction pixel to detect an edge-portion correction area for the borderless mode or an edge-portion correction area for the bordered mode. However, not limited thereto, the invention may be so configured as follows, for example. Specifically, first image input unit  52  or second image input unit  73  divides print image data into data segments on several-lines by several-lines basis, further divides each of the data segments into block data segments, and sends each of the block data segments to first controller  50  or second controller  71  together with information on the position of the block data segment in the print image data. Then, according to the position information loaded together with the block data segments, first controller  50  or second controller  71  detects an edge-portion correction area for the borderless mode or an edge-portion correction area for the bordered mode on a block-by-block basis while selectively using the block data segments along the edges of the image. With the above configuration, the invention can reduce the processing of the load placed when first controller  50  or second controller  71  executes the first edge-portion correction area detection processing or the second edge-portion correction area detection processing. 
     (3-6) Other Embodiment 6 
     Further, in embodiments 1 and 2 described above, the description is given of the case where first controller  50  and second controller  71  execute the first and second image processing procedures, described above with  FIGS. 11 to 13  and  FIGS. 19 and 20 , according to the first and second image processing programs stored in storage units  51  and  72  in advance. However, not limited thereto, the invention may be so configured that first controller  50  and second controller  71  of color printers  1  and  70  execute the first and second image processing procedures with the first and second image processing programs installed via a computer-readable storage medium storing therein the first and second image processing programs, or with the first and second image processing programs installed from the outside using a wired/wireless communication medium such as a local area network, the Internet, or a digital satellite broadcast. Incidentally, a computer-readable storage medium through which to install the first and second image processing programs in color printers  1  and  70  to make them executable may be implemented by a package medium such as a flexible disc, a CD-ROM (Compact Disc-Read Only Memory), or a DVD (Digital Versatile Disc), or may be implemented by a semiconductor memory, a magnetic disc, or the like storing therein various programs temporarily or permanently. Further, a wired/wireless communication medium such as a local area network, the Internet, or a digital satellite broadcast may be used as a unit that stores the first and second image processing programs in a computer-readable storage medium. Furthermore, the first and second image processing programs may be stored in a computer-readable storage medium via various communication interfaces such as a router and a modem. 
     (3-7) Other Embodiment 7 
     Further, in embodiments 1 and 2 described above, the description is given of the case where the image processing device according to the invention is applied to color printers  1  and  70  of secondary transfer type described above with  FIGS. 1 to 20 . However, not limited thereto, the invention is widely applicable to other image processing devices of various configurations including a color printer of primary transfer type, an MFP (Multi-Function Peripheral), a facsimile machine, a multifunction device, a copier, and an information processing device such as a computer. 
     (3-8) Other Embodiment 8 
     Further, in embodiments 1 and 2 described above, the description is given of the case where each of first controller  50  and second controller  71  described above with  FIGS. 1 to 20  is employed as an edge-portion correction area detector that detects an edge-portion correction area in an edge portion of a print image based on print image data, the edge-portion correction area extending along the edges of the image represented with the ground color and the upper color laid one over another. However, not limited thereto, the invention may widely employ other edge-portion correction area detectors having various configurations including an edge-portion correction area detection circuit having a hardware configuration for detecting an edge-portion correction area in an edge portion of a print image based on print image data, the edge-portion correction area extending along the edges of the image represented with the ground color and the upper color laid one over another. 
     (3-9) Other Embodiment 9 
     Further, in embodiments 1 and 2 described above, the description is given of the case where print image data of a print image described above with  FIGS. 1 to 20  having an image size smaller than the medium size is employed as print image data of a print image in an edge portion of which an edge-portion correction area that extends along the edges of the image represented with the ground color and the upper color laid one over another is detected. However, not limited thereto, the invention may widely employ other various kinds of print image data having various configurations including print image data of a print image having the same image size as the medium size and print image data that stores for each pixel various pixel values, with which whether the pixel is to be represented with the ground color and/or the upper color or not can be set, in place of, or in addition to, pixel values representing the densities. 
     (3-10) Other Embodiment 10 
     Further, in embodiments 1 and 2 described above, the description is given of the case where each of first controller  50  and second controller  71  described with  FIGS. 1 to 20  is employed as a correction processor that corrects an edge-portion correction area of a print image. However, not limited thereto, the invention may widely employ other correction processors having various configurations including a correction processing circuit having a hardware configuration for correcting an edge-portion correction area of a print image. 
     The invention may be used for image processing devices including an electrophotographic color printer, an MFP, a facsimile machine, a multifunction device, a copier, and an information processing device. 
     The invention includes other embodiments in addition to the above-described embodiments without departing from the spirit of the invention. The embodiments are to be considered in all respects as illustrative, and not restrictive. The scope of the invention is indicated by the appended claims rather than by the foregoing description. Hence, all configurations including the meaning and range within equivalent arrangements of the claims are intended to be embraced in the invention.