Patent Document

BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention pertains to an image processor, an image forming apparatus, an image forming system comprising these apparatuses, a computer-readable recording medium that records an image forming program, and an image forming method. 
     2. Description of the Related Art 
     Image forming systems have conventionally existed that can be used in the same manner as copying machines, wherein a scanner that reads an original document is connected to a printer that performs printing, and the original document image data read by the scanner is output by means of the printer. In this type of image forming system, various types of scanner/printer combinations are available, and the user can select the scanner and printer based on the functions and performance desired. In addition, image forming systems exist wherein multiple printers and scanners are connected by means of a network. In these image forming systems, the images read from a certain scanner or images created using a personal computer or other apparatus may be output to various printers. 
     However, in the conventional image forming systems, because there are various possible scanner/printer combinations, and because different printers have different output characteristics (reproduced gradation, color reproduction, etc.), variations occur in the quality of the output images. 
     The present invention was created in view of this problem, and an object of the present invention is to eliminate variations in the output image quality that occur due to differences among the printers connected to the image forming system. 
     According to one aspect of the present invention, an image processor that can communicate with an external image forming apparatus includes instruction means for requesting image processing parameter adjustment data from the external image forming apparatus; receiving means for receiving image processing parameter adjustment data from the external image forming apparatus; and means for performing adjustment of an image processing parameter based on the image processing parameter adjustment data received by the receiving means. 
     According to another aspect of the present invention, an image forming apparatus that can communicate with an external image processor comprises data creating means for creating image processing parameter adjustment data; and transmission means for transmitting the image processing parameter adjustment data created by the data creating means to the external image processor. 
     According to another aspect of the present invention, an image forming system comprising includes an image forming apparatus and an image processor. The image processor includes instruction means for requesting image processing parameter adjustment data from the image forming apparatus; receiving means for receiving image processing parameter adjustment data from the image forming apparatus, and image processing means for performing adjustment of an image processing parameter based on the image processing parameter adjustment data received by the receiving means. The image forming apparatus includes data creating means for creating image processing parameter adjustment data, and transmission means for transmitting the image processing parameter adjustment data created by the data creating means to the image processor. 
     The present invention also relates to a computer-readable recording medium on which is recorded an image forming program for an image forming system comprising an image processor and an image forming apparatus. The image forming program comprises a step whereby the image forming apparatus creates image processing parameter adjustment data, a step whereby the image processor requests the image processing parameter adjustment data from the image forming apparatus, a step whereby the image processing parameter adjustment data is transmitted to the image processor, a step whereby the image processing parameter adjustment data sent from the image forming apparatus is received by the image processor, and a step whereby adjustment of an image processing parameter is performed based on the received image processing parameter adjustment data. 
     And, an image forming method for an image forming system having an image processor and an image forming apparatus includes the steps of the image forming apparatus creating image processing parameter adjustment data, the image processor requesting the image processing parameter adjustment data from the image forming apparatus, the image processing parameter adjustment data is transmitted to the image processor, the image processing parameter adjustment data sent from the image forming apparatus is received by the image processor, and performing adjustment of an image processing parameter based on the received image processing parameter adjustment data. 
     In the above descriptions, the image processing parameter may include either a gamma correction table or a color conversion coefficient. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a drawing showing the construction of an image forming system comprising one embodiment of the present invention. 
     FIG. 2 is a flow chart showing the sequence of an automatic adjustment process in which the present invention is applied. 
     FIG. 3 is a drawing showing a pattern data buffer. 
     FIG. 4 is a drawing showing density gamma adjustment patterns. 
     FIG. 5 is a drawing showing color adjustment patterns. 
     FIG. 6 is a block diagram showing the construction of an image processing unit when density gamma adjustment mode is active. 
     FIGS.  7 (A),  7 (B), and  7 (C) are graphs showing an example of printer density reproduction data and of linearization via automatic adjustment. 
     FIG. 8 is a block diagram showing the construction of the image processing unit when color adjustment mode is active. 
     FIG. 9 is a flow chart showing the sequence of the copying operation after automatic adjustment. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows the construction of an image forming system comprising a preferred embodiment of the present invention. 
     This image forming system comprises a scanner  100  and printers  200  connected by means of their respective video interface, P1284 interface and network interface, such that they are capable of bi-directional communication. The original document images are read by a color CCD in the scanner  100  and output as 8-bit R, G, and B image data. After undergoing various processes in an image processor  135  in the scanner  100 , such as RGB to YMCK color conversion, the image data is sent to one of the printers  200 . Although only one printer is illustrated in FIG. 1, there may be several printers connected to the scanner  100 . 
     The scanner  100  has a reading unit  110  equipped with a color CCD, a panel  120  by which instructions are input by the user, and a control board  130 . The control board  130  has a reading control unit  131  that controls the reading unit  110 , a memory  132  that temporarily stores the read image data, a backup RAM  133  that stores the image processing parameters, a memory control unit  134  that controls the memory  132  and the backup RAM  133 , an image processing unit  135  that performs image processing such as logarithmic conversion (conversion from brightness data to density data), UCR/BP processing (undertone elimination and black ink generation), color conversion (conversion to YMCK printing color data), space filter processing such as smoothing (Moire suppression) and MTF correction (sharpening of character and line images), and gamma correction (linearization of the recording density) appropriate for the output characteristics of the printer  200 , a panel control unit  136  that controls the panel  120 , a printer interface control unit  137  that controls the printer interface that allows communication with the printer  200 , and a CPU  138  that performs overall control of the components described above. The reading unit  110  and the control board  130  are connected through SCSI ports, and the panel  120  and the control board  130  are connected by means of a dedicated interface. The interfaces for each printer comprise all of the interfaces capable of bi-directional communication, such as a P1284 interface, a network interface, and a video interface. The image data that has undergone image processing is transmitted to the printer  200  via the video interface. 
     Each printer  200  has a video interface  210  and a nonvideo interface  220 , each of which is capable of communication with the scanner  100 , an engine unit  230  that prints image data received via the video interface  210 , and a CPU  240  that performs overall control of the components mentioned above. The engine unit  230  forms images corresponding to each of the colors of yellow (Y), magenta (M), cyan (C) and black (K), which together form a color image. 
     In the image forming system of the present invention comprising a scanner and printers connected, as described above, image quality data for the images output from the printers  200  is transmitted to the scanner  100 , and variations in the image quality of the output images due to differences among the printers  200  are reduced by automatically adjusting the image processing parameters to have the scanner  100  correct the output images based on the data sent from the printer  200 . 
     FIG. 2 is a flow chart showing the sequence of the automatic adjustment process. Automatic adjustment is begun by the user executing an instruction to begin from the panel  120  (alternatively, automatic adjustment may be performed at regular intervals). Here, possible automatic adjustment modes provided include density gamma adjustment mode (mode number m=0) to automatically adjust for variations in the reproduced density gradation due to differences among the printers, and color adjustment mode (mode number m=1) to automatically adjust for variations in color reproduction. The mode number m may be set by an operator using the panel  20 . The mode number m change is implemented by the CPU  138 . 
     The mode number m may be set by an operator using the panel  120 . The mode number m change is then implemented by the CPU  138 . 
     When an instruction to begin automatic adjustment is issued, the CPU  138  of the scanner  100  determines from the result of communication with the printer  200  whether or not printer initialization has been completed (step S 1 ). If the answer is NO, the CPU  138  waits until initialization of printer  200  is completed, and if the answer is YES, it proceeds to the next step, step S 2 . 
     In step S 2 , it is determined whether the active automatic adjustment mode is density gamma adjustment mode or color adjustment mode. If the active mode is density gamma adjustment mode (YES in step S 2 ), the density gamma adjustment mode patterns shown in FIG. 4 are created and stored in the pattern data buffer in the memory  132  (step S 3 ) (see FIG.  3 ). The density gamma adjustment patterns comprise pattern data comprising combinations of C, M, Y and K values each ranging from the smallest (1) to the largest (255). If the active mode is the color adjustment mode (NO in step S 2 ), the color adjustment patterns shown in FIG. 5 are created and stored in the pattern data buffer in the memory  132  (step S 4 ). The color adjustment patterns consist of pattern data comprising N different combinations of random C, M and Y values. When the storage of pattern data in either step S 3  or step S 4  is completed, the command to begin automatic adjustment is sent to the printer  200  (step S 5 ), and one item of pattern data is selected in step S 6  in accordance with the sequence of pattern data items (pattern 1 to pattern N) set in step S 3  or step S 4 . In step S 7 , the CPU  138  waits for receipt of the density data created by the printer  200  in accordance with the pattern data sent in step S 6  and sent to the printer  200 . 
     On the other hand, if the printer  200  is an electrophotographic printer, a toner image is formed on the photoreceptor based on the received pattern data, the toner image is read by a density detection sensor not shown in the drawings, and density data is thereby obtained. This density data is then sent to the scanner  100 . However, if the printer  200  is an inkjet printer or a thermal transfer printer, the pattern may be created on paper and the density data for this pattern obtained. 
     When the scanner  100  receives the density data from the printer  200  (YES in step S 7 ), the density data is stored in the memory  132  (step S 8 ), and the pattern data number n is incrementally increased (step S 9 ). In step S 10 , it is determined whether the density data for the final pattern data item N has been stored. If the answer in step S 10  is NO, the CPU  138  returns to step S 6  and the density data for the next pattern data is obtained. If the answer is YES, this means that the density data for all of the pattern data has been obtained, and the command to complete automatic adjustment is sent to the printer  200  (step S 11 ). 
     After the density data for all of the pattern data is obtained in this way, in step S 12 , it is determined whether the active automatic adjustment mode is density gamma adjustment mode or color adjustment mode. If it is density gamma adjustment mode (YES in step S 12 ), density reproduction data is created from the density data (step S 13 ), and a new gamma correction lookup table that comprises the image processing parameter is calculated (step S 14 ) so that the printer input values and the read density have a linear relationship, as shown in FIG.  7 (C). 
     If the active automatic adjustment mode is color adjustment mode (NO in step S 12 ), color adjustment data is created (step S 15 ) and a color adjustment parameter that comprises the image processing parameter is calculated from the color adjustment data (step S 16 ). The processes of steps S 13  through S 16  are explained in further detail below. The image processing parameters calculated in steps S 14  and S 16  are stored in the backup RAM  133  (step S 17 ). 
     FIG. 6 is a block diagram showing the construction of the image processing unit  135  where the active automatic adjustment mode is the density gamma adjustment mode (m=0) as shown in the flow chart referred to above. The image processing sequence where the density gamma adjustment mode is active will be explained below with reference to FIG.  6 . 
     The 8-bit R, G, and B image data read and output by the reading unit  110  is stored in the memory  132  in the control board  130 . The R, G, and B image data is then read out from the memory  132  synchronously with each of the YMCK color images printed by the printer  200 , and after logarithmic conversion (conversion from brightness data to density data), UCR/BP processing (undertone elimination and black ink generation), and color conversion (conversion to YMCK printing color data) are performed, space filter processing such as smoothing (Moire suppression) and MTF correction (sharpening of character and line images), and gamma correction (linearization of the recorded density) appropriate for the output characteristics of the printer  200  are performed by the image processing unit  135 . On the other hand, the R, G, and B data read out from the memory  132  is input to an area differentiation unit  139  and area differentiation to distinguish between character areas and photo areas, for example, is performed. Based on the results of this differentiation, the relative amounts of smoothing and MTF correction are alternated for each area, thereby improving image sharpness. The image data processed in this way is input into the printer  200  via the prescribed printer interface, and printing is performed. 
     If the density gamma adjustment mode is active, as described above, the scanner  100  outputs the density gamma adjustment data shown in FIG. 4 to the printer  200  (steps S 5  through S 11 ), creates density reproduction data from the density data received from the printer  200  (step S 13 ), and changes the gamma correction lookup table (LUT) so that this density reproduction data will exhibit a linear relationship between the printer input values and the read density (S 14 ). 
     FIGS.  7 (A),  7 (B), and  7 (C) are graphs showing an example of the density reproduction data obtained from the printer and the linearization performed during automatic adjustment. 
     As shown in FIG.  7 (A), the image density reproduced (read density) generally does not have a linear relationship to the original document density to be reproduced (printer input values). This nonlinearity varies among printers, and variations in density and color are particularly marked in low-density areas. If gamma correction that is adjusted so as to satisfy linearity of only the average values in the drawing is performed with regard to the printer characteristics shown in FIG.  7 (A), the result shown in FIG.  7 (B) is obtained, and variations due to differences among printers remain. In the present invention, the settings of the scanner  100  are corrected so that the output from each printer  200  will exhibit a linear relationship between the printer input values and the read density. By performing this automatic adjustment for each printer  200  as described above, as shown in FIG.  7 (C), image reproduction is attained that comes very close to satisfying this linearity criterion at all times regardless of the differences among the printers  200 , and variations in the output image quality that occur due to differences among conventional printers, printer changes over time and replacement of consumable parts are reduced. 
     FIG. 8 is a block diagram showing the construction of the image processing unit  135  where the active automatic adjustment mode is the color adjustment mode (m=1) as shown in the above flow chart. The image processing sequence where the color adjustment mode is active will be explained below with reference to FIG.  8 . 
     This image processing sequence is basically identical to that shown in FIG.  6 . In other words, the 8-bit R, G, and B image data read and output by the reading unit  110  is stored in the memory  132  in the control board  130 . The R, G, and B image data is then read out from the memory  132  synchronously with the YMCK color images printed by the printer  200 , and after logarithmic conversion, UCR/BP processing and color conversion masking matrix conversion are performed, space filter processing such as smoothing and MTF correction and gamma correction appropriate for the output characteristics of the printer  200  are performed by the image processing unit  135 . On the other hand, the R, G, and B data taken out from the memory  132  is input to the area differentiation unit  139  and area differentiation to distinguish among character areas and photo areas, for example, is performed. Based on the results of this differentiation, the relative amounts of smoothing and MTF correction are alternated for each area, thereby improving image sharpness. The image data processed in this way is input into the printer  200  via a prescribed printer interface, and printing is performed. 
     If the color adjustment mode is active, as described above, the scanner  100  outputs the color adjustment patterns to the printer  200  (steps S 5  through S 11 ), creates color adjustment data from the density data received from the printer  200  (step S 15 ), and changes the color adjustment parameter using this color adjustment data (step S 16 ). 
     Specifically, the color adjustment chart (a chart in which each of YMCK colors has a linear relationship to the density) is read by the reading unit  110 , R, G and B average values are calculated for each patch, and data (color adjustment pattern) is created by performing logarithmic conversion and UCR/BP processing to all of the data (step S 4 ). The data obtained from the logarithmic conversion and UCR/BP processing is termed Data  1  (DR, DG, DB). 
     This Data  1  is then output to the printer  200  in accordance with the sequence outlined in the flow chart of FIG. 2 (steps S 5  through S 11 ), and color adjustment density data is thereby obtained (step S 15 ). This data is termed Data  2 . 
     The color conversion masking matrix is then sought using the smallest square method so that the error between Data  1  and Data  2  will be the smallest (step S 16 ). In other words, A is sought that makes the error between AX and Y the smallest when AX=Y, Data  1  is X and Data  2  is Y in the equation 1 below (color conversion masking matrix conversion equation). 
     Namely, the equation 2 below is obtained using smallest square method curve-fitting.                           Equation                 1        :                                              (                    M11       M12       M13       M14       M15       M16       M17       M18       M19           M21       M22       M23       M24       M25       M26       M27       M28       M29           M31       M32       M33       M34       M35       M36       M37       M38       M39                    )          (                    DR           DG           DG               DR   ×   DG     256                 DG   ×   DB     256                 DR   ×   DB     256                 DR   2     256                 DG   2     256                 DB   2     256                      )       =     (                    C           M           Y                    )                                                                       Equation                 2        :                                            ∑     i   =   0     n                       {                      Ci   -     (       M11   ×     X1   i       +     M12   ×     X2   i       +     M13   ×     X3   i       +     M14   ×     X4   i       +     M15   ×     X5   i       +                         M16   ×     X6   i       +     M17   ×   X7       ,         +   M18     ×     X8   i       +     M19   ×     X9   i           )                      }     2                                               
     M 11  through M 19  that will make the result of this equation 2 the smallest are then sought. M 21  through M 29  and M 31  through M 39  are sought in the same manner and deemed the color conversion masking coefficients. 
     FIG. 9 is a flow chart showing the sequence of the copying operation after automatic adjustment. 
     When the user issues a copy instruction via the panel  120 , the CPU  138  of the scanner  100  reads the image processing parameter stored in the step S 17  described above from the backup RAM  133  (step S 21 ) and sets the read parameter in the image processing unit  135  (step S 22 ). It then begins scanning by means of the reading unit  110  to read the original document, and processes the image data obtained by means of the image processing unit  135  in which the new parameter is set (see FIGS. 6 and 8) (step S 23 ). The processed image data is input to the printer  200  via the prescribed printer interface, whereby printing is begun (step S 24 ). 
     Therefore, using this embodiment, the scanner  100  calculates and stores the scanner image processing parameter for density gamma adjustment or color adjustment and performs image processing using the current scanner image processing parameter when copying is begun. Consequently, the variations in the reproduced gradation and color reproduction that occur due to the differences among printers  200  may be automatically adjusted for on the side of the scanner  100  such that more precise correction is possible and variations in output image quality are further reduced. 
     In addition, not only the variations in output image quality due to the differences among printers  200 , but also the variations in output image quality that occur due to changes in the printers  200  over time or to the replacement of consumable parts may be adjusted for in the same manner. The variations in output image quality are further reduced from this perspective as well. 
     Further, even where different combinations are used for the scanner  100  and printers  200 , the automatic adjustment described above is applicable to reduce the variations in output image quality. 
     Moreover, where image processing is performed using a personal computer and the image data is output to printers  200 , adjustment for the differences among the printers  200  may be performed. 
     The automatic adjustment by the scanner  100  is performed by the CPU  138  executing a prescribed program that describes the processing sequence described above. This prescribed program is provided in the form of a computer-readable recording medium (floppy disk or CD-ROM, for example). This prescribed program may be provided on its own as application software that executes the processing explained above or may be incorporated in the scanner software as one of the scanner functions. This applies where the output from the scanner undergoes image processing by means of a personal computer and is then output to the printers. 
     As explained above, using the present invention, adjustment of image processing parameters is performed in the image processor, and therefore, variations in the reproduced gradation and color reproduction due to the different characteristics of the image forming apparatuses may be automatically adjusted for on the side of the image processor, whereby more precise correction may be performed and the variations in output image quality are further reduced. The variations in output image quality due to changes in the image forming apparatuses over time in the market or to replacement of consumable parts may also be automatically adjusted for. 
     While particular embodiments of the present invention have been illustrated and described herein, the scope of this patent is not limited to the particular illustrated embodiments. The scope of the patent shall be defined by the following claims and equivalents thereto.

Technology Category: g