Patent Publication Number: US-10761446-B2

Title: Image forming apparatus and computer-readable recording medium storing program

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. 2018-091697, filed on May 10, 2018, is incorporated herein by reference in its entirety. 
     BACKGROUND 
     Technological Field 
     The present invention relates to an image forming apparatus including a transfer unit for transferring a color toner image onto a sheet, and a computer-readable recording medium storing a program. 
     Description of the Related Art 
     Traditionally, in the field of image forming apparatuses, to suppress the consumption of toner and prevent a reduction in productivity, color correction to be performed using a user real image, which is not an image pattern (correction patch) specially prepared for correction, has been proposed. 
     Patent Literature 1 describes an image processing system including a means for analyzing color components included in image data, a means for identifying a color component to be corrected from the analyzed data, a means for identifying a region in which the identified color component exists, a means for performing measurement based on information of the identified region, and a means for performing color correction based on the obtained information. 
     In addition, Patent Literature 2 describes a technique for extracting portions that are included in a region and in which colors are uniform based on human sensitivity to a difference between colors when a person looks at a user image, allocating a large correction weight to an extracted portion having a large area, and performing color correction. 
     CITATION LIST 
     Patent Literature 
     [Patent Literature 1] Japanese Laid-open Patent Publication No. 2006-270391 
     [Patent Literature 2] Japanese Laid-open Patent Publication No. 2016-178388 
     SUMMARY 
     In the technique described in Patent Literature 2, however, since only portions in which colors are uniform are read, there is a problem that the numbers of colors and gradations able to be used for the color correction are reduced and the accuracy of the color correction is reduced. In addition, in the techniques described in Patent Literature 1 and 2, when a change in a color is detected from a user real image during the execution of a job using a sheet (for example, an embossed sheet) with a surface including recessed and protruding portions, whether the change in the color is caused by the surface with the recessed and protruding portions or caused by a variation in an engine is not clear, both of the causes cannot be distinguished, and the correction may be erroneously performed. 
     A shape of a sheet surface and a change in a color are described below with reference to  FIG. 1  to  FIG. 3 .  FIG. 1  shows an example of a schematic configuration of a general image forming apparatus.  FIG. 2A  to  FIG. 2C  show examples of the shape of the sheet surface and color changes.  FIG. 3  is a graph showing the change in the color due to the sheet surface with recessed and protruding portions. 
     An image forming apparatus  200  shown in  FIG. 1  is of an electrophotographic scheme. The image forming apparatus  200  includes an image forming unit  211 , photoreceptor drums  215 , an intermediate transfer belt  216 , a transferring unit (fixing roller)  218 , a fixer  230 , and an inline sensor  261  (reader). 
     The image forming unit  211  includes image forming units  211 Y,  211 M,  211 C, and  211 K corresponding to basic colors, yellow (Y), magenta (M), cyan (C), and black (K). The image forming units  211 Y,  211 M,  211 C, and  211 K are arranged in this order from an upstream side to a downstream side in a rotational driving direction of the intermediate transfer belt  216 . When the image forming units  211 Y,  211 M,  211 C, and  211 K do not need to be distinguished from each other, the image forming units  211 Y,  211 M,  211 C, and  211 K are collectively referred to as image forming units  211 . The image forming units  211 Y,  211 M,  211 C, and  211 K respectively include developing units  214 . The four photoreceptor drums  215  are installed corresponding to the image forming units  211 Y,  211 M,  211 C, and  211 K, respectively. Color toner images carried by the intermediate transfer belt  216  are transferred onto a sheet S conveyed on a conveyor path  220  at a nip portion between the transferring unit  218  and the intermediate transfer belt  216 . 
     Yellow, magenta, cyan, and black toner images carried by the photoreceptor drums  215  for the respective colors are transferred onto the intermediate transfer belt  216  in a state in which the toner images are aligned. Thus, black toner is more easily transferred onto the sheet than cyan toner. Cyan toner is more easily transferred onto the sheet than magenta toner. Magenta toner is more easily transferred onto the sheet than yellow toner. As shown in  FIG. 2A , when the sheet S, which does not have recessed and protruding portions like a normal sheet, is used, toner of the respective colors is properly transferred onto the sheet from the intermediate transfer belt  216 .  FIG. 2A  shows an example in which cyan toner  201   c , magenta toner  201   m , and yellow toner  201   y  are transferred onto the sheet S (normal sheet). 
     As shown in  FIG. 2B , however, when an embossed sheet with a surface including recessed and protruding portions is used as the sheet S, colors on the printing upstream side are hardly transferred onto the recessed portions of the embossed sheet, and colors change toward the printing downstream side (color change directions are only directions toward the printing downstream side). Alternatively, when a color changes due to not only the recessed and protruding portions of the surface of the sheet S but also the image forming unit  211  (printer engine), a color change direction may be a direction toward the printing upstream side. As shown in  FIG. 3 , when the surface of the sheet S includes the recessed and protruding portions, the phases of the monochromatic toner colors do not change, but it is apparent that the phases of multi-colors, each of which is formed by a combination of multiple toner colors, change toward the printing downstream side (in directions indicated by arrows). 
     As shown in  FIG. 2C , a failure of the transfer of a portion of the yellow toner  201   y  and a failure of the transfer of a portion of the magenta toner  201   m  occur due to the recessed and protruding portions of the surface of the sheet S, the cyan toner  201   c  is deficient (as indicated by a broken line), and colors change toward the printing upstream side. As shown in  FIG. 2B  and  FIG. 2C , when the recessed and protruding portions exist on the surface of the sheet, a color phase of an image transferred to the sheet may vary depending on the recessed and protruding portions of the surface of the sheet. 
     Under such circumstances, a method of removing an effect of the shape of the sheet surface and performing, with high accuracy, a process such as color correction using a result of detecting a real image has been required. 
     To achieve at least one of the abovementioned objects, according to an aspect of the present invention, an image forming apparatus reflecting one aspect of the present invention comprises a transfer body to be rotationally driven, an image forming unit that includes a plurality of developing units that are arranged in series for basic colors in a rotational driving direction of the transfer body and develop toner images of the basic colors based on input image data, and forms the overlapped color toner images on a surface of the transfer body in a state in which the toner images of the basic colors are aligned, and a transferring unit that transfers the color toner images formed on the transfer body onto a sheet. The image forming apparatus further comprises a controller that calculates a difference between color information of the color toner images on the sheet read by a reader and color information of the input image data, calculates a color change direction of the color toner images on the sheet with respect to a color of the input image data based on the difference between the color information, and refers to a table in which color change direction patterns are associated with portions determined to be recessed portions and determines a shape of a surface of the sheet based on information of the color change direction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The advantages and features provided by one or more embodiments of the invention will become more fully understood from the detailed description given hereinbelow and the appended drawings which are given by way of illustration only, and thus are not intended as a definition of the limits of the present invention: 
         FIG. 1  is a diagram showing an example of a schematic configuration of a general image forming apparatus; 
         FIG. 2A  is a diagram showing a first example of a shape of a surface of a sheet and no color change; 
         FIG. 2B  is a diagram showing a second example of the shape of the surface of the sheet and color changes; 
         FIG. 2C  is a diagram showing a third example of the shape of the surface of the sheet and color changes; 
         FIG. 3  is a graph showing color changes caused by recessed and protruding portions of the surface of the sheet; 
         FIG. 4  is a schematic front view showing an example of an entire configuration of an image forming apparatus according to a first embodiment of the invention; 
         FIG. 5  is a block diagram showing an example of a hardware configuration of an image forming apparatus body according to the first embodiment of the invention; 
         FIG. 6  is a diagram showing a table in which color change direction patterns are associated with portions determined to be recessed portions according to the first embodiment of the invention; 
         FIG. 7A  is a diagram showing an example of input image data corresponding to a color change direction pattern ( 1 ); 
         FIG. 7B  is a diagram showing an example of detected data corresponding to a color change direction pattern ( 2 ); 
         FIG. 8A  is a diagram showing an example of color information of a measurement point P 1  of detected data; 
         FIG. 8B  is a diagram showing an example of color information of a measurement point P 2  of detected data; 
         FIG. 9  is a graph showing a color change caused by recessed and protruding portions of the surface of the sheet; 
         FIG. 10  is a diagram showing a result of determining the shape of the sheet; 
         FIG. 11A  is a diagram showing an example of input image data corresponding to the color change direction pattern ( 2 ); 
         FIG. 11B  is a diagram showing an example of detected data corresponding to the color change direction pattern ( 2 ); 
         FIG. 12A  is a diagram showing an example of color information of a measurement point P 3  of detected data; 
         FIG. 12B  is a diagram showing an example of color information of a measurement point P 4  of detected data; 
         FIG. 13  is a graph showing a color change caused by the recessed and protruding portions of the surface of the sheet; 
         FIG. 14  is a diagram showing a result of determining the shape of the sheet; 
         FIG. 15A  is a diagram showing an example of input image data corresponding to a color change direction pattern ( 3 ); 
         FIG. 15B  is a diagram showing an example of detected data corresponding to the color change direction pattern ( 3 ); 
         FIG. 16A  is a diagram showing an example of color information of a measurement point P 5  of detected data; 
         FIG. 16B  is a diagram showing an example of color information of a measurement point P 6  of detected data; 
         FIG. 17  is a graph showing color changes caused by the recessed and protruding portions of the surface of the sheet; 
         FIG. 18  is a diagram showing a result of determining the shape of the sheet; 
         FIG. 19A  is a diagram showing an example of input image data corresponding to a color change direction pattern ( 4 ); 
         FIG. 19B  is a diagram showing an example of detected data corresponding to the color change direction pattern ( 4 ); 
         FIG. 20A  is a diagram showing an example of color information of a measurement point P 7  of detected data; 
         FIG. 20B  is a diagram showing an example of color information of a measurement point P 8  of detected data; 
         FIG. 21  is a graph showing color changes caused by the recessed and protruding portions of the surface of the sheet; 
         FIG. 22  is a diagram showing a result of determining the shape of the sheet; 
         FIG. 23  is a diagram showing read regions (divided regions) generated by dividing a read image acquired from a color toner image on the sheet into a plurality of regions; 
         FIG. 24  is a diagram showing an example in which the shape of the surface of the sheet is determined based on the periodicity of the recessed and protruding portions of the surface of the sheet; 
         FIG. 25A  is a diagram showing an example of a read image in which divided regions are formed so that 3 divided regions are arranged in a vertical direction and 4 divided regions are arranged in a horizontal direction; 
         FIG. 25B  is a diagram showing an example of a result of first determination of a divided region P 1 ; 
         FIG. 25C  is a diagram showing an example of a result of first determination of a divided region P 2 ; 
         FIG. 25D  is a diagram showing an example of a result of second determination of the divided region P 1 ; 
         FIG. 25E  is a diagram showing an example of a result of second determination of the divided region P 2 ; 
         FIG. 26  is a diagram showing an example in which information, which is included in color information of a read image obtained by reading a color toner image on the sheet and indicates a periodic change component corresponding to a component installed in the apparatus and having periodicity, is removed from information to be used for determination according to a second embodiment of the invention; 
         FIG. 27  is a diagram showing an example in which information, which is included in color information of a read image obtained by reading a color toner image on the sheet and corresponds to a low-density portion extending in a conveying direction of the sheet, is removed from the information to be used for the determination; 
         FIG. 28A  is a diagram showing an example of color information of input image data according to a third embodiment of the invention; 
         FIG. 28B  is a flowchart showing an example of color information of detected data (read image); 
         FIG. 28C  is a diagram showing an example of a result of determining the shape of the sheet; 
         FIG. 29  is a flowchart showing a procedure for a process of calculating a correction value by a control device according to a fourth embodiment of the invention; 
         FIG. 30  is a flowchart showing an example of a procedure for a process of determining the shape of the sheet by the control device according to the fourth embodiment of the invention; 
         FIG. 31  is a block diagram showing an example of a hardware configuration of an image forming apparatus according to a fifth embodiment of the invention; 
         FIG. 32  is a flowchart showing an example of a procedure for a process of setting a target by a control device according to the fifth embodiment of the invention; and 
         FIG. 33  is a diagram showing an example of a configuration of main components of an image forming apparatus according to a sixth embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the scope of the invention is not limited to the disclosed embodiments. Constituent elements having substantially the same function or configuration are indicated by the same reference symbol in the present specification and the drawings, and a duplicated description is omitted. 
     1. First Embodiment 
     In a first embodiment of the invention, a color (color phase) change direction of an output image is calculated from information of a difference between a result (read image) of detecting the output image on a sheet with a surface including recessed and protruding portions and input image data, and the recessed and protruding portions of the surface of the sheet are determined based on information of the color change direction. Thus, a change in a color can be corrected without using a detection patch for the sheet such as an embossed sheet or the like which has the surface including the recessed and protruding portions. It may be considered that the recessed and protruding portions of the sheet are relatively different in shape from each other. Hereinafter, a change in a color is referred to as “change” in some cases. 
     [Entire Configuration of Image Forming Apparatus] 
     First, an entire configuration of an image formation system according to the first embodiment of the invention is described.  FIG. 4  is a schematic front view showing an example of an entire configuration of an image forming apparatus according to the first embodiment. 
     The image formation system  1  shown in  FIG. 4  includes an image forming apparatus body  10  and a post-processing device  60 . The image forming apparatus body  10  is, for example, an image forming apparatus of an electrophotographic scheme such as a copy machine. The image forming apparatus is a so-called tandem-type color image forming apparatus that includes an endless intermediate transfer belt  16  (an example of a transfer body) and a plurality of photoreceptor drums (an example of the transfer body) corresponding to basic colors and arranged opposite to the intermediate transfer belt  16  in a vertical direction and forms a full-color image. The image forming apparatus body  10  can form a document image included in a received job on a sheet for each page and perform color correction in parallel with image formation. 
     The image forming apparatus body  10  includes an image forming unit  11 , a sheet conveying unit  20 , a fixing unit  30 , a document reader  40 , and an operation display unit  50  (an example of an operating unit). 
     The image forming unit  11  is an example of an image forming unit and includes an image forming unit  11 Y for forming a yellow (Y) image, an image forming unit  11 M for forming a magenta (M) image, an image forming unit  11 C for forming a cyan (C) image, and an image forming unit  11 K for forming a black (K) image. The Y, M, C, and K colors are basic colors described in the present embodiment. 
     The image forming unit  11 Y includes a photoreceptor drum Y, a charging unit  12 Y installed around the photoreceptor drum Y, an optical writing unit  13 Y having a laser diode  130 Y, a developing device  14 Y (an example of a developing unit), and a drum cleaner  15 Y. Similarly, the image forming units  11 M,  11 C, and  11 K include photoreceptor drums M, C, and K, charging units  12 M,  12 C, and  12 K installed around the photoreceptor drums M, C, and K, optical writing units  13 M,  13 C, and  13 K having laser diodes  130 M,  130 C, and  130 K, developing devices  14 M,  14 C, and  14 K (an example of developing units), and drum cleaners  15 M,  15 C, and  15 K. 
     A surface of the photoreceptor drum Y is uniformly charged by the charging unit  12 Y. A latent image is formed on the photoreceptor drum Y by scanning exposure by the laser diode  130 Y of the optical writing unit  13 Y. The developing device  14 Y visualizes the latent image formed on the photoreceptor drum Y by developing the latent image using toner. By this process, an image (toner image) of a predetermined color corresponding to yellow is formed on the photoreceptor drum Y. 
     Similarly, a surface of the photoreceptor drum M is uniformly charged by the charging unit  12 M. A latent image is formed on the photoreceptor drum M by scanning exposure by the laser diode  130 M of the optical writing unit  13 M. The developing device  14 M visualizes the latent image formed on the photoreceptor drum M by developing the latent image using toner. By this process, a toner image of a predetermined color corresponding to magenta is formed on the photoreceptor drum M. 
     A surface of the photoreceptor drum C is uniformly charged by the charging unit  12 C. A latent image is formed on the photoreceptor drum C by scanning exposure by the laser diode  130 C of the optical writing unit  13 C. The developing device  14 C visualizes the latent image formed on the photoreceptor drum C by developing the latent image using toner. By this process, a toner image of a predetermined color corresponding to cyan is formed on the photoreceptor drum C. 
     A surface of the photoreceptor drum K is uniformly charged by the charging unit  12 K. A latent image is formed on the photoreceptor drum K by scanning exposure by the laser diode  130 K of the optical writing unit  13 K. The developing device  14 K visualizes the latent image formed on the photoreceptor drum K by developing the latent image using toner. By this process, a toner image of a predetermined color corresponding to black is formed on the photoreceptor drum K. When the developing devices  14 Y,  14 M,  14 C, and  14 K are not distinguished from each other, the developing devices  14 Y,  14 M,  14 C, and  14 K are hereinafter referred to as “developing devices  14 ” in some cases. 
     The toner images formed on the photoreceptor drums Y, M, C, and K are sequentially transferred onto predetermined positions on the endless intermediate transfer belt  16  by primary transfer rollers  17 Y,  17 M,  17 C, and  17 K. The toner images, transferred to the intermediate transfer belt  16 , of the colors are transferred by a secondary transferring unit  18  onto the sheet S conveyed by the sheet conveying unit  20  at predetermined time. 
     A fixing unit  30  (an example of a fixing unit) is installed on the side on which the sheet is discharged in the secondary transferring unit  18 . The fixing unit  30  presses and heats the sheet S while conveying the sheet S and fixes the transferred toner images onto the sheet S. The fixing unit  30  is composed of a pair of a heating roller  31  (heating member) and a pressing roller  32  (pressing member). The heating roller  31  includes a heater  33  serving as a heating source for heating the heating roller  31 . The heating roller  31  and the pressing roller  32  can be in contact with each other and are separable from each other. A fixing nip portion is formed as a pressure-contact portion at a position where the heating roller  31  and the pressing roller  32  are in contact with each other. 
     The document reader  40  causes an optical system of a scanning exposure device to scan and expose a document image and causes a line image sensor to read light reflected from the document image to acquire an image signal. The image forming apparatus body  10  may include, on the image forming apparatus body  10 , an automatic document conveying device (not shown) for feeding a document sheet. 
     The operation display unit  50  includes a liquid crystal display (LCD)  51 , a touch panel covering the LCD  51 , various switches, buttons, a numeric keypad, and a group of operational keys. The operation display unit  50  receives an operation of a user and generates an operational signal based on details of the operation. The operation display unit  50  displays, on the LCD  51 , an operational screen based on a display signal received from a control device  100  (refer to  FIG. 6 ). 
     The sheet conveying unit  20  includes a plurality of sheet feeding trays  21  for storing sheets S, and a feeding unit  21   a  for feeding the sheets S stored in the sheet feeding trays  21 . The sheet conveying unit  20  includes a main conveyor path  23  on which the sheets S fed from the sheet feeding trays  21  are conveyed, and a reverse conveyor path  24  for reversing front and back surfaces of each of the sheets S. 
     The sheet conveying unit  20  further includes a switching gate  23   a  at a branching position where the reverse conveyor path  24  is branched from the main conveyor path  23  on the downstream side of the fixing unit  30 . In the image forming apparatus body  10 , an image is formed on a surface that faces upward, of the sheet S that has been conveyed on the main conveyor path  23  and has passed through the secondary transferring unit  18  and the fixing unit  30 . When images are to be formed on both surfaces of the sheet S, the sheet S with a surface that faces upward and on which an image has been formed is conveyed from the main conveyor path  23  to the reverse conveyor path  24  and conveyed from the reverse conveyor path  24  to the main conveyor path  23  so that the surface on which the image has been formed faces downward. By this process, the upper and lower surfaces of the sheet S are reversed and an image can be formed on the other surface facing upward. 
     The post-processing device  60  connectable to the main conveyor path  23  is arranged on a rear side of the image forming apparatus body  10 . The post-processing device  60  performs a post-process on the sheet S on which a toner image supplied from the fixing unit  30  has been formed. The post-processing device  60  includes various post-processing units (not illustrated) such as a sorting unit, a stapling unit, a punching unit, and a folding unit. The post-processing device  60  performs various post-processes on the sheet S discharged from the image forming apparatus body  10  and discharges the sheet S subjected to the post-processes to a sheet discharge tray  25 . 
     An inline sensor  61  (an example of a reader) for reading an image (output image) formed on the sheet S conveyed from the image forming apparatus body  10  is installed above a conveyor path extending from a carrying-in port provided for sheets S and included in the post-processing device  60  to the sheet discharge tray  25 . The inline sensor  61  is installed above the conveyor path and reads an image formed on the upper surface of the conveyed sheet S. 
     As the inline sensor  61 , a line sensor having a plurality of photoelectric conversion elements (not illustrated) arranged in a linear fashion across an entire sheet region extending in a width direction (main scanning direction) of the sheet is used. The width direction of the sheet is perpendicular to a conveying direction of the sheet. Alternatively, as the inline sensor  61 , an image sensor having photoelectric conversion elements arranged in a matrix may be used. The inline sensor  61  irradiates an output image formed on the sheet S with beams emitted from light sources of the photoelectric conversion elements and having beam spots of a predetermined diameter. Then, the inline sensor  61  disperses light reflected from the output image into red (R), green (G), and blue (B) light and acquires information of reflectance of the R, G, and B light to read the output image and detect colors of the read image. 
     As each of the line sensor and the image sensor, a CCD image sensor or a CMOS image sensor (including a MOS image sensor) may be used. While the inline sensor  61  is installed above the conveyor path, another inline sensor may be installed under the conveyor path so that the line sensors read images formed on both surfaces of the sheet S during the time when the sheet S passes through the inline sensors one time. It is sufficient if the inline sensor is installed on the downstream side of the fixing unit  30  in the conveying direction of the sheet S. Thus, the inline sensor  61  may be installed in the image forming apparatus body  10 . 
     [Hardware Configuration of Image Forming Apparatus] 
       FIG. 5  is a block diagram showing an example of a hardware configuration of the image forming apparatus body  10 .  FIG. 5  shows elements necessary for or related to the description of the present embodiment. A control system of the image forming apparatus is not limited to this example. 
     The image forming apparatus body  10  includes a control device  100  (an example of a controller) and a large-capacity storage device  101 . The control device  100  controls the feeding of the sheet S, the formation of an image, and the discharging of the sheet S. The control device  100  includes an arithmetic processing device constituted by a central processing unit (CPU) not illustrated and includes memories such as a random access memory (RAM) and a read only memory (ROM). In the ROM, a program to be executed by the CPU of the control device  100 , data to be used upon the execution of the program, and the like are stored. A micro-processing unit (MPU) may be used instead of the CPU. 
     The large-capacity storage device  101  is an example of a nonvolatile storage unit. In the large-capacity storage device  101 , a parameter to be used when the program is executed by the CPU of the control device  100 , data obtained by executing the program, or the like is stored. In the large-capacity storage device  101 , the program to be executed by the CPU of the control device  100  may be stored. For example, a semiconductor memory, a hard disk, a solid state drive (SSD), an IC card, an SD card, a DVD, or the like is applied to the large-capacity storage device  101 . 
     The control device  100  receives an operational signal from the operation display unit  50  and performs control based on the operational signal. The control device  100  outputs a display signal to the operation display unit  50 . The operation display unit  50  displays, on the LCD  51 , various setting screens for entering various operation instructions and setting information and operational screens for displaying various process results and the like. 
     In addition, the control device  100  acquires color information of a read image detected by the inline sensor  61  of the post-processing device  60  and uses the color information of the read image to perform color correction described later. 
     A communication I/F  102  is an interface that transmits and receives data to and from a personal computer (PC)  120  via a network such as a LAN or a dedicated line. The PC  120  is an operation terminal. As the communication I/F  102 , a network interface card (NIC), a modem, or the like is used, for example. 
     A normal operation (printing operation) of the image forming apparatus body  10  to form an image on the sheet S is described below. The control device  100  controls the sheet conveying unit  20  and causes the sheet conveying unit  20  to transport the sheet S. The control device  100  controls the image forming unit  11  and the secondary transferring unit  18  based on image data acquired by the document reader  40  from a document or input image data acquired from an external and causes the image forming unit  11  and the secondary transferring unit  18  to form an output image (color toner image) on the sheet S. Then, the control device  100  controls the fixing unit  30  to cause the fixing unit  30  to fix the output image onto the sheet S and conveys the sheet S on which the output image has been formed to the post-processing device  60 . The control device  100  controls the post-processing device  60  to cause the post-processing device  60  to discharge the sheet S to the sheet discharge tray  25 . 
     In addition, the control device  100  causes the inline sensor  61  to read the output image formed on the sheet and corrects an imaging parameter (image formation requirement) for each of the basic colors based on color information of the read image. 
     The configuration of the control device  100  is further described below. 
     The control device  100  includes a sheet shape determiner  100   a,  a correction value calculator  100   b , and a table T 1 . In the table T 1 , color change direction patterns are associated with portions determined to be recessed portions (refer to  FIG. 6  in more detail). The CPU of the control device  100  reads the program from the ROM or the large-capacity storage device  101  and executes the read program, thereby enabling functions of the sections. 
     The sheet shape determiner  100   a  calculates a difference between color information of a read image obtained by allowing the inline sensor  61  to read a color toner image on the sheet S and color information of input image data and calculates, from the difference between the color information, a color change direction of the read image obtained from the color toner image with respect to a color of the input image data. Then, the sheet shape determiner  100   a  refers to, based on information of the color change direction, the table T 1  in which the color change direction patterns are associated with the portions determined to be recessed portions, and determines a shape of a surface of the sheet S. The table T 1  may be stored in the ROM not illustrated or the large-capacity storage device  101 . 
     The sheet shape determiner  100   a  determines the shape of the surface of the sheet based on whether the color change direction of the color toner image on the sheet S with respect to the color of the input image data is a color change direction toward the printing upstream side that is the side of a basic color of a developing device  14  arranged on the upstream side in a direction in which the intermediate transfer belt  16  is driven to rotate, or is a color change direction toward the printing downstream side that is the side of a basic color of a developing device  14  arranged on the downstream side in the direction in which the intermediate transfer belt  16  is driven to rotate. 
     The correction value calculator  100   b  calculates a correction value to be used for the image forming unit  11  to correct a color change caused by the image forming unit  11  based on color information of a divided region (refer to  FIG. 23 ) determined to be a protruding portion as the shape of the surface of the sheet S. 
     [Table in Which Color Change Direction Patterns are Associated with Portions Determined to be Recessed Portions] 
       FIG. 6  shows the table T 1  in which the color change direction patterns are associated with the portions determined to be recessed portions. In  FIG. 6 , the portions determined to be recessed portions are set for the four color change direction patterns. Each of the color change direction patterns is determined based on a combination of results of analyzing detected data (color information) of 2 measurement points (corresponding to divide regions shown in  FIG. 23 ). 
     A color change direction pattern ( 1 ) is a pattern in which a color change toward the printing downstream side occurs at one of 2 measurement points and a color change does not occur at the other of the 2 measurement points. In this pattern, a portion determined to be a recessed portion is a portion where the color change toward the printing downstream side occurs. 
     A color change direction pattern ( 2 ) is a pattern in which a color change toward the printing upstream side occurs at one of 2 measurement points and a color change does not occur at the other of the 2 measurement points. In this pattern, a portion determined to be a recessed portion is a portion where the color change does not occur. 
     A color change direction pattern ( 3 ) is a pattern in which only color changes toward the printing downstream side occur at 2 measurement points and the amounts of the color changes are different from each other. In this pattern, a portion determined to be a recessed portion is a portion where the amount of a color change toward the printing downstream side is larger. 
     A color change direction pattern ( 4 ) is a pattern in which only color changes toward the printing downstream side occur at 2 measurement points and the amounts of the color changes are the same. In the case of this pattern, since a recessed portion cannot be identified from the changes in the colors, the recessed portion is estimated from peripheral pixel information (peripheral region information). 
     An example in which the shape of the sheet is determined based on data detected from input image data is described below. When a threshold to be used to determine that a color at a measurement point changes is provided, the threshold may improve the accuracy of determining whether a color change occurs. 
     [Example of Color Change Direction Pattern ( 1 )] 
     First, an example of the color change direction pattern ( 1 ) is described with reference to  FIG. 7A  and  FIG. 7B  to  FIG. 10 .  FIG. 7A  shows an example of input image data corresponding to the color change direction pattern ( 1 ) and  FIG. 7B  shows an example of detected data corresponding to the color change direction pattern ( 1 ).  FIG. 8A  and  FIG. 8B  show examples of color information of measurement points of the detected data.  FIG. 9  is a graph showing a color change caused by the recessed and protruding portions of the surface of the sheet.  FIG. 10  shows a result of determining the shape of the sheet in this example. 
     As shown in  FIG. 7A  and  FIG. 7B , the case where each of the input image data and the detected data (read image) has 21 divided regions formed so that 7 divided regions are arranged in a main scanning direction and 3 divided regions are arranged in an auxiliary scanning direction is described below. The divided regions may be unit pixels, respectively. Each of the divided regions may include a plurality of pixels. An n-th column extending in the main scanning direction is referred to as “n-th main scanning column”, and an m-th row extending in the auxiliary scanning direction is referred to as “m-th auxiliary scanning row”. In the shape of the surface of the sheet used for measurement, first and third auxiliary scanning rows are protruding portions, and a second auxiliary scanning row is a recessed portion. In FIG.  7 A, in color information of the input image data, divided regions included in the third and seventh main scanning columns are of a B color (M with 100% and C with 100%). In  FIG. 7A , divided regions included in the second and sixth main scanning columns, and divided regions in the third to fifth main scanning columns and the first auxiliary scanning row are of a G color (Y with 100% and C with 100%). The other divided regions are of an R color (Y with 100% and M with 100%). A measurement point P 1  exists in the third main scanning column and the second auxiliary scanning row, and a measurement point P 2  exists in the third main scanning column and the third auxiliary scanning row. This example assumes that a color change is not caused by the printer engine (hereinafter referred to “engine”) or the image forming unit  11 . 
     In  FIG. 7B , based on the detected data of the read image, a color change cf occurs in each of divided regions included in the second auxiliary scanning row. Color information (L*a*b* values in this example) of the measurement points P 1  and P 2  is shown in  FIG. 8A  and  FIG. 8B . At the measurement point P 1 , a color phase (Hue) decreases from a theoretical value “34.0” to a measured value “28.3” as indicated by a broken line and a color change toward the printing downstream side is detected. At the measurement point P 2 , theoretical values are equal to measured values, and a color change does not occur. 
     In a graph shown in  FIG. 9 , as indicated by an arrow D 1 , a measured value of the color phase at the measurement point P 1  changes toward the printing downstream side. At the measurement point P 2 , a color change does not occur. 
     As indicated by the result of determining the shape of the sheet in  FIG. 10 , based on the detected data of the 2 measurement points P 1  and P 2 , this example is determined to correspond to the color change direction pattern ( 1 ) in which a color change toward the printing downstream side occurs and a color change does not occur. Since the color change toward the printing downstream side occurs at the measurement point P 1 , the measurement point P 1  is determined to be a recessed portion. If color changes are caused by the image forming unit  11 , the color changes occur at both the measurement points P 1  and P 2 . However, the color change (toward the printing downstream side) occurs only at the measurement point P 1 . 
     [Example of Color Change Direction Pattern ( 2 )] 
     Next, an example of the color change direction pattern ( 2 ) is described with reference to  FIG. 11A  and  FIG. 11B  to  FIG. 14 .  FIG. 11A  shows an example of input image data corresponding to the color change direction pattern ( 2 ) and  FIG. 11B  shows an example of detected data corresponding to the color change direction pattern ( 2 ).  FIG. 12A and 12B  show examples of color information of measurement points of the detected data.  FIG. 13  is a graph showing a color change caused by the recessed and protruding portions of the surface of the sheet.  FIG. 14  shows a result of determining the shape of the sheet in this example. 
     The input image data and the detected data (read image) that are shown in  FIG. 11A  and  FIG. 11B  have the same configuration as those shown in  FIG. 7A  and  FIG. 7B  and each have 21 divided regions formed so that 7 divided regions are arranged in the main scanning direction and 3 divided regions are arranged in the auxiliary scanning direction. The surface of the sheet used for measurement has protruding portions in first and third auxiliary scanning rows and a recessed portion in a second auxiliary scanning row. In addition, color information of the input image data shown in  FIG. 11A  is the same as that shown in  FIG. 7A . A measurement point P 3  exists in a second main scanning column and the second auxiliary scanning row. A measurement point P 4  exists in the second main scanning column and the third auxiliary scanning row. This example assumes that a color change (or a reduction in the amount of attached cyan toner) is caused by the engine or the image forming unit  11 . 
     In  FIG. 11B , a color change cf 1  occurs in each of divided regions included in the first auxiliary scanning row, a color change cf 2  occurs in each of divided regions included in the second auxiliary scanning row and the third to fifth main scanning columns, and a color change cf 3  occurs in each of divided regions included in the third auxiliary scanning row and the first and second main scanning columns and included in the third auxiliary scanning row and the sixth and seventh main scanning columns. Color information (L*a*b* values) of the measurement points P 3  and P 4  is shown in  FIG. 12A  and  FIG. 12B . At the measurement point P 3 , theoretical values are equal to measured values, and a color change does not occur. At the measurement point P 4 , a color phase (Hue) decreases from a theoretical value “158.3” to a measured value “142.3”, and a color change toward the printing upstream side is detected. 
     In a graph shown in  FIG. 13 , as shown in an arrow D 4 , the measured value of the color phase at the measurement point P 4  changes toward the printing upstream side. At the measurement point P 3 , a color change does not occur. 
     As indicated by the result of determining the shape of the sheet in  FIG. 14 , based on the detected data of the 2 measurement points P 3  and P 4 , this example is determined to correspond to the color change direction pattern ( 2 ) in which a color change toward the printing upstream side occurs and a color change does not occur. Since a color change does not occur at the measurement point P 3 , the measurement point P 3  is determined to be a recessed portion. If the sheet S is flat, a C component decreases in amount at each of the measurement points P 3  and P 4  and a color change toward the printing upstream side occurs at each of the measurement points P 3  and P 4 . However, the color change toward the printing upstream side occurs only at the measurement point P 4 . Specifically, a divided region at the measurement point P 4  is likely to be a protruding portion. On the other hand, since the measurement point P 3  is the recessed portion, a C component and a Y component decrease in amount at the measurement point P 3 . Thus, the color change toward the printing upstream side due to the decrease in the amount of the C component and the color change toward the printing downstream side due to the decrease in the amount of the Y component offset each other, and as a result, a color change is hardly seen. 
     [Example of Color Change Direction Pattern ( 3 )] 
     Next, an example of the color change direction pattern ( 3 ) is described with reference to  FIG. 15A  and  FIG. 15B  to  FIG. 18 .  FIG. 15A  shows an example of input image data corresponding to the color change direction pattern ( 3 ) and  FIG. 15B  shows an example of detected data corresponding to the color change direction pattern ( 3 ).  FIG. 16A  and  FIG. 16B  show examples of color information of measurement points of the detected data.  FIG. 17  is a graph shown a color change caused by the recessed and protruding portions of the surface of the sheet.  FIG. 18  shows a result of determining the shape of the sheet in this example. 
     The input image data and the detected data (read image) that are shown in  FIG. 15A  and  FIG. 15B  have the same configuration as those shown in  FIG. 7A  and  FIG. 7B  and each have 21 divided regions formed so that 7 divided regions are arranged in the main scanning direction and 3 divided regions are arranged in the auxiliary scanning direction. The surface of the sheet used for measurement has protruding portions in first and third auxiliary scanning rows and a recessed portion in a second auxiliary scanning row. In addition, as shown in  FIG. 15A , color information of the input image data is the same as that shown in  FIG. 7A . A measurement point P 5  exists in a second main scanning column and the second auxiliary scanning row. A measurement point P 6  exists in the second main scanning column and the third auxiliary scanning row. This example assumes that a color change (or a reduction in the amount of attached yellow toner) is caused by the engine or the image forming unit  11 . 
     In  FIG. 15B , based on the detected data of the read image, a color change cf 1  occurs in each of divided regions included in the first auxiliary scanning row and second to sixth main scanning columns, a color change cf 2 - 1  occurs in each of divided regions included in the second auxiliary scanning row and the first and seventh main scanning columns, a color change cf 2 - 2  occurs in each of divided regions included in the second auxiliary scanning row and the second to sixth main scanning columns, and a color change cf 3  occurs in each of divided regions included in the third auxiliary scanning row and the second to sixth main scanning columns. Color information (L*a*b* values) of the measurement points P 5  and P 6  is shown in  FIG. 16A  and  FIG. 16B . At the measurement point P 5 , a color phase (Hue) increases from a theoretical value “158.3” to a measured value “178.8” as indicated by a broken line, and a color change toward the printing downstream side is detected. At the measurement point P 6 , a color phase (Hue) increases from a theoretical value “158.3” to a measured value “168.3” as indicated by a broken line, and a color change toward the printing downstream side is detected. 
     In a graph shown in  FIG. 17 , as indicated by an arrow D 5 , a measured value of the color phase at the measurement point P 5  significantly changes toward the printing downstream side. In addition, as indicated by an arrow D 6 , a measured value of the color phase at the measurement point P 6  changes toward the printing downstream side. The amounts of the changes at the measurement points P 5  and P 6  are represented by lengths of the arrows D 5  and D 6 . In the present embodiment, since the length of the arrow D 5  is longer than the length of the arrow D 6 , it is apparent that the amount of the change at the measurement point P 5  is larger. 
     As indicated by the result of determining the shape of the sheet in  FIG. 18 , based on the detected data of the 2 measurement points P 5  and P 6 , this example is determined to correspond to the color change direction pattern ( 3 ) in which only color changes toward the printing downstream side occur and the amounts of the changes in the colors are different from each other. In addition, since the amount of the color change toward the printing downstream side at the measurement point P 5  is larger, the measurement point P 5  is determined to be a recessed portion. If a color change is caused by the image forming unit  11 , the amounts of changes in colors at the measurement points P 5  and P 6  are equal to or close to each other. In fact, however, the amount of the change in the color at the measurement point P 5  is larger. This is considered to be due to the fact that the measurement point P 5  is affected by not only the image forming unit  11  but also the shape (recessed portion) of the surface of the sheet. 
     [Example of Color Change Direction Pattern ( 4 )] 
     Next, an example of the color change direction pattern ( 4 ) is described with reference to  FIG. 19A  and  FIG. 19B  to  FIG. 22 .  FIG. 19A  shows an example of input image data corresponding to the color change direction pattern ( 4 ) and  FIG. 19B  shows an example of detected data corresponding to the color change direction pattern ( 4 ).  FIG. 20A  and  FIG. 20B  show examples of color information of measurement points of the detected data.  FIG. 21  is a graph showing a color change caused by the recessed and protruding portions of the surface of the sheet.  FIG. 22  shows a result of determining the shape of the sheet in this example. 
     The input image data and the detected data (read image) that are shown in  FIG. 19A  and  FIG. 19B  have the same configuration as those shown in  FIG. 7A  and  FIG. 7B . Each of the input image data and the detected data has 21 divided regions formed so that 7 divided regions are arranged in the main scanning direction and 3 divided regions are arranged in the auxiliary scanning direction. The surface of the sheet used for measurement has protruding portions in first and third auxiliary scanning rows and a recessed portion in a second auxiliary scanning row. In addition, color information of the input image data shown in  FIG. 19A  and  FIG. 19B  are different from that shown in  FIG. 7A  in that divided regions included in the second auxiliary scanning row and third to fifth main scanning columns are of an R color (Y with 100% and M with 100%). A measurement point P 7  exists in the third main scanning column and the second auxiliary scanning row, and a measurement point P 8  exists in the fourth main scanning column and the second auxiliary scanning row. This example assumes that a color change does not occur due to the engine or the image forming unit  11 . 
     In  FIG. 19B , based on the detected data of the read image, a color change cf occurs in each of divided regions included in the second auxiliary scanning row. Color information (L*a*b* values) of the measurement points P 7  and P 8  is shown in  FIG. 20A  and  FIG. 20B . At the measurement point P 7 , a color phase (Hue) decreases from a theoretical value “34.0” to a measured value “30.1” as indicated by a broken line, and a color change toward the printing downstream side is detected. At the measurement point P 8 , a color phase (Hue) decreases from a theoretical value “34.0” to a measured value “30.1” as indicated by a broken line, and a color change toward the printing downstream side is detected. It is apparent that the amounts of the color changes at the measurement points P 7  and P 8  are the same. 
     In a graph shown in  FIG. 21 , as indicated by an arrow D 7 , a measured value of the color phase at the measurement point P 7  changes toward the printing downstream side. In addition, as indicated by an arrow D 8 , a measured value of the color phase at the measurement point P 8  changes toward the printing downstream side. Since lengths of the arrows D 7  and D 8  are the same, it is apparent that the amounts of the changes at the measurement points P 7  and P 8  are the same. 
     As indicated by the result of determining the shape of the sheet in  FIG. 22 , based on the detected data of the 2 measurement points P 7  and P 8 , this example is determined to correspond to the color change direction pattern ( 4 ) in which only color changes toward the printing downstream side occur and the amounts of the color changes are the same. Since the amounts of the color changes are the same, the measurement points P 7  and P 8  are likely to have the same shape, but a recessed portion cannot be determined based on the color changes. In this case, the sheet shape determiner  100   a  determines the shapes of the measurement points based on information (for example, peripheral pixel information) on the shapes of divided regions existing around the measurement points. 
     [Read Regions (Divided Regions)] 
       FIG. 23  shows read regions (divided regions) generated by dividing a read image acquired from a color toner image on the sheet S into a plurality of regions. As described above, when data (color phase) of the same gradation level exists in regions (either recessed portions or protruding portions) having the same shape, the shapes of the regions cannot be determined based on a color change direction, and the sheet shape determiner  100   a  (refer to  FIG. 5 ) determines (estimates) the shape of a target divided region based on results (shapes) of determining divided regions existing around the target divided region. As shown in  FIG. 23 , a lattice-shaped read region Am is set as a reading unit of the output image (color toner image). In an example shown in  FIG. 23 , the output image is divided into a number m×n of divided regions formed so that a number m of divided regions are arranged in an x direction (main scanning direction) and a number of n divided regions are arranged in a y direction (auxiliary scanning direction). 
     [Determination Based on Periodicity of Recessed and Protruding Portions of Sheet Surface] 
     As a first example of a method of determining the shape of a target divided region based on a result (shape) of determining a divided region existing around the target divided region, a method of determining the shape based on the periodicity of the shape of the surface of the sheet is described below. 
       FIG. 24  shows an example in which the shape of the surface of the sheet is determined based on the periodicity of the recessed and protruding portions of the surface of the sheet. The sheet shape determiner  100   a  analyzes results (color information) of measuring an image read from an output image (color toner image) using a column extending in the x direction (main scanning direction) or a row extending in the y direction (auxiliary scanning direction) and determines the shape of a target region (indicated by ? and to be determined) based on the periodicity of the shape of the analyzed sheet surface. In  FIG. 24 , in the column in the y direction in which the target region to be determined exists, the sheet shape determiner  100   a  determines that regions other than the target region to be determined are determined to be “protruding portions”. Thus, the sheet shape determiner  100   a  determines that the target region is also a protruding portion. 
     Information of the periodicity can be acquired by a method such as user&#39;s manual input using the operation display unit  50  or pre-detection. The information of the periodicity is stored, as the setting of the sheet S stored in a sheet feeding tray  21  of the image forming apparatus body  10 , in the large-capacity storage device  101 . In general, the periodicity of cross-sectional recessed streaks formed on the sheet and the periodicity of cross-sectional protruding streaks formed on the sheet are in a range of 0.3 mm to 5 mm. The information of the periodicity of the shape of the surface of the sheet is described on a packing sheet for the purchased sheet S or the like. 
     [Determination Based on Number of Recessed Portions and Number of Protruding Portions Among Peripheral Divided Regions] 
     As a second example of a method of determining the shape of a target divided region based on a result (shape) of determining a divided region existing around the target divided region, a method of determining the shape based on the number of recessed portions and the number of protruding portions among divided regions existing around the target divided region. 
       FIG. 25A  to  FIG. 25E  show an example of the determination of the shape of the surface of the sheet based on the number of divided regions determined to be recessed portions existing around the target divided region and the number of divided regions determined to be protruding portions existing around the target divided region.  FIG. 25A  shows an example of a read image in which 12 divided regions are formed so that 3 divided regions area arranged in a vertical direction and 4 divided regions are arranged in a horizontal direction. In this case, divided regions P 1  and P 2  existing in the read image are target regions to be determined. Divided regions arranged in the rightmost column are recessed portions, and divided regions that are among the other divided regions and are not the divided regions P 1  and P 2  are protruding portions. A main criterion for the determination is to determine a target divided region based on the shapes of many divided regions existing around the target divided region. For example, when the number of protruding portions existing around the target divided region is larger than the number of recessed portions existing around the target divided region, the target divided region can be determined to be a “protruding portion”. Details are described below. 
       FIG. 25B  shows a result of first determination of the divided region P 1 . Divided regions existing around the divided region P 1  are three “protruding portions” (with reliability of 100%) and one region (divided region P 2 ) indicated by “?”. Thus, the sheet shape determiner  100   a  determines that the divided region P 1  is a “protruding portion” (with reliability of 50%) in the first determination. The present embodiment assumes that a portion is estimated in the first determination with reliability of 50% and estimated in second and later determination with reliability of 50%. The relationships between the percentages and the number of times of the estimation can be arbitrarily set. 
       FIG. 25C  shows a result of first determination of the divided region P 2 . Divided regions existing around the divided region P 2  are two “protruding portions” (with reliability of 100%), one “protruding portion” (with reliability of 50%), and one “recessed portion” (with reliability of 100%). Thus, the sheet shape determiner  100   a  determines that the divided region P 2  is a “protruding portion” (with reliability of 50%) in the first determination. 
       FIG. 25D  shows a result of second determination of the divided region P 1 . The divided regions existing are the divided region P 1  are three “protruding portions” (with reliability of 100%) and one “protruding portion” (with reliability of 50%). Thus, the sheet shape determiner  100   a  determines that the divided region P 1  is a “protruding portion” (with reliability of 100%) in the second determination. 
       FIG. 25E  shows a result of second determination of the divided region P 2 . The divided regions existing around the divided region P 2  are three “protruding portions” (with reliability of 100%) and one “recessed portion” (with reliability of 100%). Thus, the sheet shape determiner  100   a  determines that the divided region P 2  is a “protruding portion” (with reliability of 100%) in the second determination. 
     By repeatedly making the determination in accordance with the criteria for the determination, the shapes of the target divided regions can be estimated. The reliability (accuracy) for the determination can be increased every time the determination is repeatedly made. Divided regions existing around a target divided region may not be divided regions adjacent to the target divided region on the upper, lower, left, and right sides of the target divided region, and a range of divided regions existing around the target divided region (or the number of divided regions existing around the target divided region) may be increased. The shape of a divided region existing in an oblique direction with respect to the target divided region may be used for the determination. 
     According to the aforementioned first embodiment, a difference between color information of a read image obtained by reading a color toner image on the sheet S and color information of input image data is calculated, and a color change direction of the read image obtained by reading the color toner image with respect to a color of the input image data is calculated based on the difference between the color information. Then, the table in which the color change direction patterns are associated with the portions determined to be recessed portions is referred to and the shape of the surface of the sheet is determined. Thus, the color correction can be performed with high accuracy based on color information (detection result) on a user real image while an effect of the shape of the surface of the sheet is removed. Since a special image pattern (detection patch) is not used in the color correction, unnecessary consumption of toner can be suppressed and a reduction in the productivity can be prevented. 
     2. Second Embodiment 
     A second embodiment is an example in which information corresponding to a streak component and an uneven component that are included in color information (measured data) of a read image obtained by reading a color toner image on the sheet S is excluded from information to be used for determination. The image streak rg is an image defect and occurs due to dirt of a laser mirror of an exposure unit, dust attached to a surface of a photoreceptor drum, dirt or damage of the intermediate transfer belt  16 , or the like and leads to a reduction in the accuracy of the shape determination. 
     [Case Where Periodicity Exists in Auxiliary Scanning Direction] 
       FIG. 26  shows an example in which information that is included in color information of a read image obtained by reading a color toner image on the sheet S and indicates a periodic change component corresponding to a component included in the apparatus and having periodicity is excluded from information to be used for determination. In  FIG. 26 , an abscissa indicates a length (centimeters) in the auxiliary scanning direction and an ordinate indicates a value (normalized value) detected by the inline sensor  61 . 
     As shown in  FIG. 26 , a waveform of detected values of the color information is indicated by a solid line, a waveform indicating first decomposition performed to decompose the detected values of the color information into frequencies is indicated by a fine dotted line, and a waveform indicating second decomposition performed to decompose the detected values of the color information into frequencies is indicated by a rough dotted line. The shape is determined by crosschecking the waveforms with the component having the periodicity included in the image forming apparatus body  10 , and excluding a corresponding periodic change component. For example, when a period T of the waveform indicating the first decomposition matches a length of a developing roller, corresponding information among measured data (waveforms of the detected values) is excluded from the information to be used for the determination. The corresponding information may be excluded from the measured data. 
     Thus, the sheet shape determiner  100   a  can exclude information corresponding to a steak component and an uneven component that are caused by the component having the periodicity from the detected color information and determine the shape of the surface of the sheet. This improves the accuracy of determining the shape of the surface of the sheet by the sheet shape determiner  100   a.    
     [Case Where Result of Detecting Low-Density Portion Extending to End of Sheet in Auxiliary Scanning Direction Exists] 
       FIG. 27  shows an example in which information that is included in color information of a read image obtained by reading a color toner image on the sheet S and corresponds to a low-density portion extending in the conveying direction of the sheet S is excluded from information to be used for the determination. 
     In  FIG. 27 , a y direction of the read image indicates the auxiliary scanning direction, and an x direction of the read image indicates the main scanning direction. In addition, a front end of the read image is indicated by E 1  and a rear end of the read image is indicated by E 2 . When a result of detecting a low-density portion extending to the end E 1  corresponding to a sheet end in the auxiliary scanning direction (y direction) exists in the read image shown in  FIG. 27 , an image streak rg (indicated by a dotted line) is regarded to have occurred and is excluded from the information to be used for the determination. Information of this image streak may be excluded from measured data (read image). 
     Thus, the sheet shape determiner  100   a  can exclude, as an image streak, information included in detected color information and corresponding to a low-density portion extending in the conveying direction of the sheet, and determine the shape of the surface of the sheet. This improves the accuracy of determining the shape of the surface of the sheet by the sheet shape determiner  100   a.    
     3. Third Embodiment 
     A third embodiment is an example in which a correction value to be used to correct a change (change caused by the image forming unit  11 ) caused by the engine is calculated from color information of a portion determined to be a protruding portion. 
       FIG. 28A  to  FIG. 28C  show an example in which the correction value to be used to correct a change caused by the image forming unit is calculated from color information of divided regions determined to be protruding portions according to the third embodiment.  FIG. 28A  shows color information of input image data.  FIG. 28B  shows color information of detected data (read image).  FIG. 28C  shows a result of determining the shape of the sheet. The correction value is calculated using color information included in the color information of the detected data and corresponding to the divided regions determined to be the protruding portions and shown in  FIG. 28C . 
     The sheet shape determiner  100   a  determines that a difference between color information, included in the detected data (read image) shown in  FIG. 28B , of divided regions determined to be protruding portions and the color information of the input image data shown in  FIG. 28A  is a change caused by the engine. Then, the sheet shape determiner  100   a  corrects the change caused by the engine. For example, the correction value calculator  100   b  (refer to  FIG. 5 ) converts differences between color space coordinates (L*a*b* values) of protruding portions of the input image data and color space coordinates (L*a*b* values) of the protruding portions of the detected data (read image) to deviations of YMCK values and calculates the correction value based on the deviations of the YMCK values. 
     The difference between the color information may be calculated using RGB values output by the inline sensor  61 . It is, however, desirable that the RGB values be converted to measured values (L*a*b*, CIEXYZ, CIECAM02, and the like) of a device-independent color space and evaluation be performed using the measured color values after the conversion in order to perform the evaluation using the measured color values close to color differences visible by a person. A method of calculating the correction value is not limited. The correction value may be calculated using a known technique. 
     4. Fourth Embodiment 
     As a fourth embodiment, a process obtained by combining the first to third embodiments is described below with reference to  FIG. 29  and  FIG. 30 . 
     [Procedure for Process of Calculating Correction Value] 
       FIG. 29  is a flowchart showing an example of a procedure for a process of calculating the correction value by the control device  100  according to the fourth embodiment of the invention. First, the sheet shape determiner  100   a  causes the inline sensor  61  to read an output image (printed portion) formed on the sheet S based on input image data and causes data of the read image to be stored in the large-capacity storage device  101  (S 1 ). Then, the sheet shape determiner  100   a  decomposes the read image into lattice-shaped read regions Am (refer to  FIG. 23 ) (S 2 ). 
     Then, the sheet shape determiner  100   a  confirms that a streak component and an uneven component are absent in the read image (S 3 ) (refer to  FIG. 26  and  FIG. 27 ). When the streak component and the uneven component exist in the read image (NO in S 3 ), the sheet shape determiner  100   a  removes the streak component and the uneven component from the read image (S 4 ). The streak component and the uneven component may not be removed in step S 4  and may be excluded from information to be used to determine the shape in a process of determining the shape of the sheet in step S 5 . 
     When the streak component and the uneven component do not exist in the read image (YES in S 3 ) or after the process of step S 4 , the sheet shape determiner  100   a  performs the process of determining the shape of the sheet (S 5 ). Then, the correction value calculator  100   b  calculates the correction value from color information of a portion determined to be a protruding portion (S 6 ). After the process of step S 6 , the process of this flowchart is terminated. 
     [Procedure for Process of Determining Shape of Sheet] 
       FIG. 30  is a flowchart showing an example of a procedure for the process of determining the shape of the sheet by the control device  100  according to the fourth embodiment of the invention. This flowchart indicates details of step S 5  shown in  FIG. 29 . 
     First, the sheet shape determiner  100   a  reads color information of the input image data corresponding to the read regions Am (divided regions) of the read image (S 11 ). Then, the sheet shape determiner  100   a  calculates a color change direction of each of the read regions Am with respect to a color of the input image data (S 12 ). The sheet shape determiner  100   a  determines the shape of the surface of the sheet based on the list table (table T 1  shown in  FIG. 6 ) of the color change direction patterns and portions determined to be recessed portions (S 13 ). 
     The sheet shape determiner  100   a  determines whether a read region Am from which the shape of the surface of the sheet cannot be determined is absent (S 14 ). When the read region from which the shape of the surface of the sheet cannot be determined is absent (YES in S 14 ), the sheet shape determiner  100   a  causes information of the shape of the surface of the sheet to be stored in the large-capacity storage device  101  (S 15 ). After the process of step S 15 , the process of this flowchart is terminated. 
     When the read region Am from which the shape of the surface of the sheet cannot be determined exists (NO in S 14 ), the sheet shape determiner  100   a  determines whether a read region Am existing around the read region Am from which the shape of the surface of the sheet cannot be determined has periodicity in terms of the shape of the read region Am (S 16 ). When the read region Am has the periodicity (YES in S 16 ), the sheet shape determiner  100   a  determines the shape of the surface of the sheet based on the periodicity (S 17 ) (refer to  FIG. 24 ). 
     Then, the sheet shape determiner  100   a  determines whether a read region Am from which the shape of the surface of the sheet cannot be determined is absent (S 18 ). The determination is made to confirm whether non-periodic color information is included in the read image. Then, when the read region Am from which the shape of the surface of the sheet cannot be determined is absent (YES in S 18 ), the sheet shape determiner  100   a  causes the process to proceed to step S 15 . 
     When the read region Am does not have the periodicity (NO in S 16 ) or when the read region Am from which the shape of the surface of the sheet cannot be determined exists (NO in S 18 ), the sheet shape determiner  100   a  determines the shape of the surface of the sheet based on the number of recessed portions and the number of protruding portions among peripheral read regions Am (S 19 ). After the process of step S 19 , the sheet shape determiner  100   a  causes the process to proceed to step S 15 . Then, when the answer to the determination of step S 18  is YES or after the process of step S 19 , the sheet shape determiner  100   a  causes information of the shape of the surface of the sheet to be stored in the large-capacity storage device  101  (S 15 ). After the process of step S 15 , the process of this flowchart is terminated. 
     5. Fifth Embodiment 
       FIG. 31  is a block diagram showing a hardware configuration of an image forming apparatus body  10 A according to a fifth embodiment of the invention. The image forming apparatus body  10 A according to the present embodiment is different from the image forming apparatus body  10  ( FIG. 5 ) according to the first embodiment in that the image forming apparatus body  10 A includes a color target setting unit  100   c  of a control device  100 A, instead of the correction value calculator  100   b  of the control device  100 . The color target setting unit  100   c  sets a color target (target color) from color information of a divided region determined to be a protruding portion on the surface of the sheet. 
       FIG. 32  is a flowchart showing an example of a procedure for a process of setting the target by the control device  100 A according to the fifth embodiment. Steps S 21  to S 25  of the flowchart shown in  FIG. 32  are the same as steps S 1  to S 5  of the flowchart shown in  FIG. 29 , and a description thereof is omitted. After the processes of steps S 21  to S 25 , the color target setting unit  100   c  sets a target from color information of a divided region determined to be a protruding portion on the surface of the sheet (S 26 ). 
     In the setting of the target, for example, a color conversion table (also referred to as profile) is corrected. In order to perform color conversion, a device profile (DP) of a target device is required. The DP is also referred to as source profile (also referred to as “target profile”). For example, as the source profile, a profile of an offset printer or a standard profile such as Japan Color is selected. The DP of the device for outputting is referred to as destination profile (also referred to as “printer profile”). A profile of the image forming apparatus (for example, the image forming apparatus body  10 A) for actually outputting a printed material is selected. Input CMYK values are converted to machine-independent values via an A 2 B table of the source profile and converted to other (target) CMYK values via a B 2 A table of the destination profile. 
     According to the aforementioned fifth embodiment, an effect of the shape of the surface of the sheet can be removed and a target can be set from color information (detected results) on a user real image with high accuracy. Since a special image pattern (detection patch) is not used in the color correction, unnecessary consumption of toner can be suppressed and a reduction in the productivity can be prevented. 
     6. Sixth Embodiment 
     Although the aforementioned first to fifth embodiments describe the image forming apparatus system  1  (image forming apparatus bodies  10  and  10 A) that includes the intermediate transfer belt as a transfer body and is of the electrophotographic scheme, the configurations of the image forming apparatus bodies are not limited to those described in the embodiments. It is sufficient if each of the image forming apparatuses has a transferring unit for transferring a color toner image onto a sheet. Specifically, each of the image forming apparatuses according to the embodiments of the invention has a transfer body to be rotationally driven, an image forming unit that includes a plurality of developing units that are arranged in series for the basic colors in a rotational driving direction of the transfer body and develop toner images of the basic colors based on input image data, and forms the overlapped color toner images on a surface of the transfer body in a state in which the toner images of the basic colors are aligned, and a transferring unit that transfers the color toner images formed on the transfer body onto the sheet. The toner may be solid toner or liquid toner. 
     A configuration of an image forming apparatus according to the sixth embodiment is described below. 
       FIG. 33  is a diagram showing an example of a configuration of main components of the image forming apparatus according to the sixth embodiment. The image forming apparatus shown in  FIG. 33  includes an image forming unit  311 , a photoreceptor drum  315  (an example of the transfer body), and a transferring unit  318 . The image forming unit  311  includes 4 developing units  314 Y,  314 M,  314 C, and  314 K for the basic colors (Y, M, C, and K). When the developing units  314 Y,  314 M,  314 C, and  314 K are not distinguished from each other, the developing units  314 Y,  314 M,  314 C, and  314 K are referred to as “developing units  314 ” in some cases. 
     The developing units  314 Y,  314 M,  314 C, and  314 K are arranged opposite to a surface (photoreceptor surface) of the photoreceptor drum  315  in this order from the upstream side to downstream side of a rotational driving direction (clockwise direction) of the photoreceptor drum  315 . After the same image formation region on the surface of the photoreceptor drum  315  is electrically charged and exposed for each of the basic colors so that an electrostatic latent image is formed for each of the basic colors, the developing units  314  develop the electrostatic latent images of the basic colors to form color toner images. Then, the color toner images formed on the surface of the photoreceptor drum  315  are transferred onto the sheet S by the transferring unit  318 . 
     7. Others 
     Although each of the first to sixth embodiments describes an example in which the color correction or the target setting is performed based on results of determining recessed and protruding portions on the surface of the sheet, the embodiments are not limited to the examples. For example, results of determining recessed and protruding portions on the surface of the sheet may be used for density correction, the adjustment of the position of an image, and the adjustment of the amount of varnish to be used for coating in special color printing. 
     Although the first to sixth embodiments describe the image forming apparatuses of the electrophotographic scheme as examples, toner to be used by the image forming apparatuses may be solid toner or liquid toner. In addition, the invention is applicable to an inkjet apparatus using a transfer scheme. 
     The invention is not limited to the embodiments and includes various application examples and modified examples without departing from the spirit of the invention described in the appended claims. 
     The embodiments describe the configurations of the apparatuses and the system in detail and specifically in order to clearly explain the invention. The embodiments are not necessarily limited to the configurations including all the aforementioned constituent elements. In addition, a part of a configuration described in an embodiment among the embodiments may be replaced with a constituent element described in another embodiment among the embodiments. A constituent element described in an embodiment among the embodiments may be added to a configuration described in another embodiment among the embodiments. A constituent element described in any of the embodiments may be added to a configuration described in any of the embodiments, or may be removed from a configuration described in the embodiment, or may be replaced with another constituent element described in any of the embodiments. 
     Some or all of the aforementioned constituent elements, functions, processes, and the like may be enabled by hardware based on, for example, design of an integrated circuit. 
     DESCRIPTION OF REFERENCE SIGNS 
       10 ,  10 A . . . Image forming apparatus body,  11  . . . Image forming unit,  18  . . . Secondary transferring unit,  61  . . . Inline sensor (reader),  100 ,  100 A . . . Control device,  100   a . . . Sheet shape determiner,  100   b . . . Correction Value Calculator,  100   c . . . Color target setting unit, T 1  . . . Table