Patent Publication Number: US-2022214637-A1

Title: Image forming apparatus and control method thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of U.S. patent application Ser. No. 16/713990, filed on Dec. 13, 2019, which claims priority from Japanese Patent Application No. 2018-246039 filed Dec. 27, 2018, which are hereby incorporated by reference herein in their entireties. 
    
    
     BACKGROUND 
     Field 
     The present disclosure relates to calibration control in an image forming apparatus. 
     Description of the Related Art 
     When an electrophotographic image forming apparatus is continuously used, the density of an image printed on a sheet fluctuates due to various factors. Examples of factors that cause a fluctuation in image density include a deterioration level of parts of the image forming apparatus, an environment (temperature, humidity) where the image forming apparatus is placed, and consumables such as toners and sheets that are used in printing by the image forming apparatus. 
     Thus, calibration is executed so that the image forming apparatus prints an image with a target density. Specifically, correction data is generated using a color difference between a result of reading a test pattern acquired by printing a patch image on a medium, such as a sheet, and the target density. 
     Japanese Patent Application Laid-Open No. 2007-329929 discusses an image forming apparatus that efficiently generates correction data by causing a scanner to read a test pattern on a document conveyed by an automatic document conveyance apparatus (auto document feeder (hereinafter, referred to as “ADF”)). 
     Japanese Patent Application Laid-Open No. 2002-59626 discusses an image forming apparatus that includes an ADF and generates correction data using a result of reading a test pattern on a document conveyed by the ADF. Further, an image forming apparatus that does not include an ADF and generates correction data using a result of reading a test pattern on a document placed on a platen glass is also discussed. 
     SUMMARY 
     It has now been determined that in a method of reading a document conveyed by an ADF, an operation of opening and closing a document pressing plate is unnecessary, unlike that in a method of reading a document placed on a platen glass, and thus the operation burden on a user in reading a plurality of documents continuously at once is reduced, wherein in the method of reading a document placed on a platen glass, the reading accuracy is sometimes higher than that in the method of reading a document conveyed by an ADF. In view thereof, it has now been determined that it would be desirable to include the two reading methods in a single image forming apparatus and select one of the reading methods that is suitable for an intended purpose of use by the user. 
     According to an aspect of the present disclosure, an image forming apparatus includes an image forming unit and a reading unit. The image forming unit is configured to form an image. The reading unit has a first reading mode, in which a document conveyed by a conveyance unit is read, and a second reading mode, in which a document placed on a platen glass is read. The image forming apparatus also includes a detection unit configured to detect placement of a test document on the reading unit, and a correction data generation unit configured to determine, based on a result of the detection by the detection unit, to execute a first correction mode, in which correction data is generated using a result of reading the test document in the first reading mode, or a second correction mode, in which correction data is generated using a result of reading the test document in the second reading mode, and generate correction data in the determined correction mode. 
     Further features of the present disclosure will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a system block diagram illustrating an image forming apparatus according to an exemplary embodiment of the present disclosure. 
         FIG. 2  illustrates a scanner unit according to an exemplary embodiment of the present disclosure. 
         FIG. 3  is a block diagram illustrating a control unit that controls the scanner unit according to an exemplary embodiment of the present disclosure. 
         FIG. 4  is a flowchart illustrating an operation according to a first exemplary embodiment of the present disclosure. 
         FIG. 5  illustrates an operation mode determination method according to an exemplary embodiment of the present disclosure. 
         FIGS. 6A, 6B, 6C, and 6D  illustrate an example of a screen display according to the first exemplary embodiment of the present disclosure. 
         FIG. 7  is a flowchart illustrating an operation according to a second exemplary embodiment of the present disclosure. 
         FIGS. 8A, 8B, and 8C  illustrate an example of a screen display according to the second exemplary embodiment of the present disclosure. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Various exemplary embodiments of the present disclosure will be described in detail below with reference to the drawings. 
     It should be noted that the below-described exemplary embodiments are not intended to limit the scope of the claimed invention and that not every combination of features described in the exemplary embodiments is always essential to a technical solution of the invention. 
       FIG. 1  is a block diagram illustrating a control unit  115  of an image forming apparatus according to a first exemplary embodiment. Each component of the control unit  115  is connected to a system bus  101  and/or an image bus  110 . A read-only memory (ROM)  102  stores a system boot program. Further, system software configured to realize each unit according to the present exemplary embodiment is stored on the ROM  102  or an accumulation memory  105  and executed by a central processing unit (CPU)  103 . A random access memory (RAM)  104  is a system work area for software execution by the CPU  103  and is also an image memory configured to temporarily store image data while the image data is processed. The accumulation memory  105  is used as an internal storage. Data read by a scanner unit  112 , image data, and system software are stored. The accumulation memory  105  includes a hard disk drive (HDD) or solid state drive (SSD). A local area network (LAN) interface (I/F) unit  106  is an I/F unit configured to connect to a LAN and performs information input/output with a device connected to the LAN. A line I/F unit  107  is an I/F unit configured to connect to a wide area network (WAN) and performs information input/output with a device connected to the WAN. The above-described configurations are provided on the system bus  101 . An input/output (IO) control unit A  109  is a bus bridge that connects the system bus  101  and the image bus  110 , which transfers image data at high speed, and converts a data configuration for the system bus  101 . The image bus  110  includes an all-purpose bus such as a Peripheral Component Interconnect (PCI) bus, Institute of Electrical and Electronics Engineers (IEEE) 1394 bus, or PCI Express (PCIEx) bus. The below-described configurations are provided on the image bus  110 . The scanner unit  112  and a printer unit  113 , which are image input/output devices, and an image processing unit  111  are connected, and synchronous/asynchronous conversion of image data is performed. The image processing unit  111  includes a plurality of application-specific integrated circuits (ASICs) configured to perform image processing, such as resolution conversion, compression/decompression, and binary multi-value conversion, on input image data and output image data. An operation unit control unit B  108  for image data is an interface unit between the control unit  115  and an operation unit (user interface (hereinafter, referred to as “UI”))  114  and outputs image data to be displayed on the operation unit  114  to the operation unit  114 . Further, the operation unit control unit B  108  is also configured to transmit information input to the operation unit  114  by a system user to the CPU  103 . The operation unit control unit B  108  is an I/F unit via which software controls the operation unit  114 , which includes a display apparatus and a keypad apparatus. In the present exemplary embodiment, the operation unit  114  includes a liquid crystal display (LCD) touch panel and analyzes a video graphics array (VGA) signal output from the operation unit control unit B  108  and displays the VGA signal. 
       FIG. 2  is a cross-sectional side view illustrating an internal configuration of a document feeder (DF) unit  200  of the scanner unit  112 . The DF unit  200  includes a document tray  201  for stacking a document to be read. A document sensor  203 , two document guides  202 , and a document size detection sensor  204  are provided on the document tray  201 . The document sensor  203  detects whether there is a document. If the document sensor  203  detects a document on a sheet conveyance path, the detected document is conveyed. The two document guides  202  are aligned in a lengthwise direction of the document (vertical to a document conveyance direction), and a document stacked on the document tray  201  is conveyed by three rollers, a pickup roller  205 , a conveyance roller  207 , and a sheet discharge roller  209 . The pickup roller  205  is a roller that conveys the document stacked on the document tray  201  into the document conveyance path in the DF unit  200 . The conveyance roller  207  conveys the document conveyed into the document conveyance path by the pickup roller  205 . The sheet discharge roller  209  conveys the document conveyed by the conveyance roller  207  to a sheet discharge tray  211 . Further, the document conveyed by the pickup roller  205  is detected by a document passing detection sensor  206 , and whether the first document has passed is determined based on the time of the detection. Further, all the conveyance roller  207 , the pickup roller  205 , and the sheet discharge roller  209  are driven by a stepping motor (illustration thereof is omitted). Sub-scan thinning processing in the DF unit  200  is realized by setting driving pulses of the conveyance roller  207 , the pickup roller  205 , and the sheet discharge roller  209  to twice the frequency. The document conveyed by the DF unit  200  is read by a contact image sensor (CIS)  210  via a DF reading window  208 , the CIS  210  being provided to a sensor unit  212  located under the DF reading window  208 . The sensor unit  212  is freely movable in a sub-scan direction and also in a direction that is the same as the document conveyance direction in which the document is conveyed from the conveyance roller  207  toward the sheet discharge roller  209 . The DF reading window  208  has a length in the sub-scan direction, and the CIS  210  can be moved to a desired position within the length range and can read the document at the moved position. The CIS  210  includes a photoelectric conversion element, such as a charge-coupled device (CCD), and simultaneously performs First In First Out (FIFO) accumulation of an image from each element and generation of a control signal for controlling the FIFO accumulation and the CCD. The CIS  210  is generally realized by a plurality of photoelectric conversion elements arranged in a line. 
     Further, the scanner unit  112  includes a platen glass  213 . In a case where a document is to be read via the platen glass  213 , it is also possible to open a document pressing plate  214 , place the document on the platen glass  213 , close the document pressing plate  214 , and then read the document while moving the sensor unit  212  having the CIS  210  in the sub-scan direction. 
     Further, the CIS  210  is also configured to detect whether a document is set on the platen glass  213 . When the document pressing plate  214  is closed, the CIS  210  reads a portion of the document under the platen glass  213 . The CIS  210  analyzes the read image and determines whether a document is set. As this is a publicly-known technique, detailed description thereof will be omitted. 
     In the present exemplary embodiment, a method of reading a document placed on the document tray  201  while conveying the document in a state where the sensor unit  212  having the CIS  210  is fixed is referred to as “ADF reading mode” (first reading mode). Further, a method of reading a document placed on the platen glass  213  by moving the sensor unit  212  is referred to as “pressing-plate reading mode” (second reading mode). 
       FIG. 3  illustrates blocks in which hardware for controlling the scanner unit  112  based on a scanner unit control application program is integrated, and the blocks are included in the scanner unit  112 . The scanner unit  112  is controlled based on the scanner unit control application program that is executed on a CPU  301  of a scanner control unit  300  in the description below. Alternatively, an application program for controlling the scanner unit  112  can be executed by the CPU  103  of the control unit  115 . The scanner control unit  300  includes the CPU  301 , a RAM  302 , a clock (CLK) control unit  303 , a ROM  304 , a motor controller unit  305 , and a CCD control unit  307 . The scanner unit control application program is stored on the ROM  304  and executed by the CPU  301 . The CLK control unit  303  distributes a clock to each block. The CLK control unit  303  includes a crystal oscillator and a phase-locked loop (PLL) element. The crystal oscillator generates a clock, and the PLL element multiplies and divides the clock generated by the crystal oscillator. The scanner unit control application configured to control the scanner control unit  300  outputs a control clock from the CLK control unit  303  to the motor controller unit  305 , the CCD control unit  307 , and the RAM  302  according to an instruction in scanning The blocks further perform multiplication and division according to the clock input from the CLK control unit  303  and generate a control clock for a motor that rotates the CCD element and various rollers. The instruction for scanning contains information such as color/monochrome distinction information and resolution information, and the scanner unit control application changes a setting of the PLL of the CLK control unit  303  based on the content of the instruction. By changing the setting of the PLL, frequencies of various clocks are changed to change a reading speed. Image data read by the CIS  210  is accumulated on the ROM  304 . 
     An operation of a calibration function will be described in detail below. In the present exemplary embodiment, generation of correction data for use in image density adjustment will be described below as an example. The present exemplary embodiment, however, is not limited to the described example and is also applicable to calibration, such as image position adjustment or density non-uniformity adjustment, in which a patch image is printed on a sheet and a scanner unit reads the patch image and correction data is generated using the reading result. 
     Next, a process of generating correction data for use in density adjustment according to the present exemplary embodiment will be described below with reference to  FIG. 4 . In the present exemplary embodiment, a case where three documents (charts) on which a predetermined test pattern is printed are printed, the printed test documents are read, and correction data is generated using the reading result will be described. 
     The number of test documents needed is generally determined based on the type of a dither pattern that is used by an image forming apparatus in image forming, because correction data needs to be generated with respect to each dither pattern that is used in executing image processing. Thus, an image forming apparatus that can use a plurality of dither patterns needs to generate correction data for each of the dither patterns. The correction data is generated using a result of reading a single test document printed using a dither pattern. Thus, in a case where correction data is to be generated for three dither patterns (e.g., low lines per inch, high lines per inch, error diffusion), three test documents are needed. Further, in another exemplary embodiment, a plurality of dither patterns can be used to print on a single test document. In this case, the number of test documents needed is reduced. The number of test documents can be determined based on the number of dither patterns as described above, or the processing can be performed using a number of test documents needed to generate correction data corresponding to a selected dither pattern. 
     A program of the control unit  115  for the flowchart is stored on the ROM  102  of the control unit  115  and is read to the RAM  104  and executed by the CPU  103 . 
     In step S 401 , a sheet feeding cassette of the printer unit  113  that stores a sheet on which a test document is to be printed is selected via the operation unit  114  based on a user instruction to execute calibration. 
     Next, in step S 402 , an instruction to execute printing is received via the operation unit  114 . In step S 403 , three test documents are printed based on the instruction. In a case where correction data is generated, the test documents are output using different dither patterns generated by the image processing unit  111 . As this technique is publicly known, detailed description thereof is omitted. Further, a color/shape patch pattern from which each test document can be distinguished can be printed on a margin portion so that which dither pattern is used in outputting the read test document can be determined. Further, a number that specifies a document number can be printed on a margin so that the user can distinguish each test document with ease. 
     In step S 404 , an area for a variable number N is reserved on the RAM  104 , and the variable number N is initialized to zero. Further, an area for a used flag for each test document for identifying a used test document for generating correction data is reserved, and the used flag is initialized to a value that indicates an unused state. 
     In step S 405 , a screen is displayed on the operation unit  114  to prompt the user to set the test documents output in step S 403  at a desired document placement position on the platen glass  213  or the document tray  201  of the ADF. The user having seen the displayed screen sets the printed test documents at a desired document placement position. 
     In step S 406 , an instruction to start reading the test document is received via the operation unit  114 . 
     In step S 407 , the CPU  103  transmits an inquiry about document detection information, which indicates whether a document is detected on the document tray  201  of the ADF and/or the platen glass  213 , to the CPU  301  via the IO control unit A  109 . The inquiry about document detection information does not have to be at this timing. For example, document detection information about the platen glass  213  can be acquired when the test document is set on the platen glass  213  and the document pressing plate  214  of the platen glass  213  is closed after step S 405 . Alternatively, the order of steps S 406  and  5407  can be reversed, and in a case where no document is detected on the platen glass  213  and the document tray  201  of the ADF, a document reading start instruction is not received. 
     In step S 408 , an operation mode in subsequent steps is determined based on the document detection information acquired in step S 407 . Details of the determination will be described below with reference to  FIG. 5 . In a case where a document placed on the document tray  201  of the ADF is detected, correction data is generated in a first correction mode. In the first correction mode, a test document is read in a first reading mode (ADF reading mode). Specifically, a plurality of test documents placed on the document tray  201  of the ADF is read based on one reading instruction. Then, a plurality of pieces of correction data corresponding to the respective test documents is generated using density information acquired by reading the test documents. Specifically, generation of correction data is started after all the test documents are read. On the other hand, in a case where a document placed on the platen glass  213  is detected, correction data is generated in a second correction mode. In the second correction mode, a test document is read in a second reading mode (pressing-plate reading mode). Correction data corresponding to the test document is generated using density information acquired by reading the single test document placed on the platen glass  213 . The series of processing is executed each time a single test document is read. Specifically, the test document reading processing and the correction data generation processing are repeatedly executed a plurality of times. 
     In a case where it is determined that an error has occurred (ERROR in step S 408 ), the processing proceeds to step S 409 . In a case where it is determined that the ADF reading mode (first reading mode) is to be performed (ADF READING MODE in step S 408 ), the processing proceeds to step S 410 . In a case where it is determined that the pressing-plate reading mode (second reading mode) is to be performed (PRES SING-PLATE READING MODE in step S 408 ), the processing proceeds to step S 415 . 
     In step S 409 , a screen that prompts the user to place the test document again appropriately is displayed on the operation unit  114 . 
     In step S 410 , the test documents placed on the document tray  201  of the ADF are sequentially conveyed, a scanner controller reads the test documents, and images acquired by reading the test documents are transferred to the control unit  115 . Then, the CPU  103  analyzes whether the transferred images are suitable for use in generation of correction data. For example, in a case where a luminance pattern is not detected from the images acquired by reading the test documents, a case where appropriate test documents are not used, and a case where the test documents are printed in an inappropriate state, the CPU  103  determines that the transferred images are not suitable for use in generation of correction data. 
     In step S 411 , in a case where it is determined that all the three images acquired by reading the three test documents can be used in generation of correction data in step S 410  (YES in step S 411 ), the processing proceeds to step S 412 . On the other hand, in a case where it is determined that one or more of the three images acquired by reading the three test documents cannot be used in generation of correction data (NO in step S 411 ), the processing proceeds to step S 413 . 
     In step S 412 , the images acquired by reading the three test documents in step S 410  are analyzed, and a correction table for use in correcting a density of an image to be printed is generated. Based on a difference between a value obtained by converting a luminance value of a read image to a density value and a target value stored on the RAM  104 , a density correction table which is to be used in image processing a printed image and stored on the RAM  104  is generated (updated). As this technique is publicly known, detailed description thereof will be omitted. 
     In step S 413 , a screen that prompts the user to place the test document again appropriately is displayed on the operation unit  114 . 
     In step S 414 , a screen that indicates that correction data is generated is displayed on the operation unit  114 , and the processing of generating correction data for use in density adjustment is ended. 
     In step S 415 , the single test document placed on the platen glass  213  is read by the scanner controller, and an image acquired by reading the test document is transferred to the control unit  115 . Then, the CPU  103  analyzes the transferred image. The image analysis is like that in step S 410 . 
     However, in a case where it is determined that the test document that has been previously used in generation of correction data is read again as a result of analyzing the patch for test document determination described above in the description of step S 403  and comparing the patch with the used flag provided for each test document on the RAM  104 , it is determined that the images cannot be used in generation of correction data. Alternatively, the patch for test document determination described above in the description of step S 403  can be analyzed, and in a case where the test documents are inappropriate test documents, it may be determined that an error has occurred. For example, in a case where N=0, it is determined that the test document is for use in generation of correction data for a first dither pattern. In a case where N=1, it is determined that the test document is for use in generation of correction data for a second dither pattern. In a case where N=2, it is determined that the test document is for use in generation of correction data for a third dither pattern. 
     In step S 416 , if it is determined that the read image can be used in generation of correction data in step S 415  (YES in step S 416 ), the processing proceeds to step S 417 . If it is determined that the read image cannot be used in correction (NO in step S 416 ), the processing proceeds to step S 422 . 
     In step S 417 , the image acquired in step S 415  is analyzed, and a correction table for use in correcting a density of an image to be printed is generated. Based on a value obtained by converting a luminance value of a read image to a density value and a target value stored on the RAM  104 , a density correction table to be used in image processing on a printed image and stored on the RAM  104  is generated (updated). Further, a flag for the test document that is used in generation of correction data among the used flags provided for each test document on the RAM  104  is set to a used state. As this technique is publicly known, detailed description thereof is omitted. 
     In step S 418 , one is added to the variable number N stored on the RAM  104 . 
     In step S 419 , in a case where the variable number N is three or greater, it is determined that correction data has been generated using the three test documents (YES in step S 419 ), and the processing proceeds to step S 414 . Otherwise (NO in step S 419 ), the processing proceeds to step S 420 . 
     In step S 420 , a screen that prompts the user to set the Nth document on the platen glass  213  is displayed on the operation unit  114 . 
     In step S 421 , an instruction to start reading the test document is received via the operation unit  114 . 
     In step S 422 , a screen that prompts the user to place the test document again appropriately is displayed on the operation unit  114 . 
     In step S 423 , in a case where the variable number N is one, the processing proceeds to step S 405  so that the test document is removed from the platen glass  213  and placed on the ADF. In a case where the variable number N is two or greater, the processing proceeds to step S 420  so that the generation of correction data by reading from the platen glass  213  is continued. Further, the determination in step S 423  can be skipped. In this case, the processing proceeds from step S 422  to step S 420 . 
     Alternatively, the processing of generating correction data for use in density adjustment that is executed in the flowchart can be cancelled based on an instruction to the operation unit  114  in steps  5405  and  5420 . 
     Next, a method for the operation mode determination in step S 408  will be described below with reference to  FIG. 5 . 
       FIG. 5  is a table that illustrates a process of determining an operation in step S 408  based on information that indicates whether a document is detected on the platen glass  213  and/or the document tray  201  of the ADF. In a case where a document is detected on the platen glass  213  and no document is detected on the document tray  201  of the ADF, the processing proceeds from step S 408  to step S 410 . Specifically, the test document is read in the pressing-plate reading mode, and correction data is generated in the second correction mode. On the other hand, in a case where no document is detected on the platen glass  213  and a document is detected on the document tray  201  of the ADF, the processing proceeds from step S 408  to step S 411 . Specifically, the test document is read in the ADF reading mode, and correction data is generated in the first correction mode. 
     In a case where a document is detected on the platen glass  213  and on the document tray  201  of the ADF, or in a case where no document is detected on the platen glass  213  and on the document tray  201  of the ADF, it is determined that an error has occurred, and the processing proceeds from step S 408  to step S 409 . 
     Alternatively, in the case where a document is detected on the platen glass  213  and on the document tray  201  of the ADF, the operation unit  114  displays a screen that prompts the user to select whether a test document is to be read via the platen glass  213  or the ADF (the first reading mode or the second reading mode). Then, the test document is read in the user-selected mode. Further, in another exemplary embodiment, in the case where a test document is detected on the platen glass  213  and on the document tray  201  of the ADF, reading can be executed from predetermined one of the platen glass  213  and the document tray  201  of the ADF. For example, reading from the ADF is prioritized as in a copy function, or reading from one of the platen glass  213  and the document tray  201  of the ADF that is preset on the operation unit  114  is prioritized. 
     Next, an example of a screen that is displayed on the operation unit  114  will be described below with reference to  FIGS. 6A to 6D . 
       FIG. 6A  illustrates an example of a screen that is displayed in steps S 405  and S 406 . The screen prompts the user to set three test documents on the document tray  201  of the ADF or set the first test document on the platen glass  213 . Although not illustrated in  FIG. 6A , an item for designating a test document placement method (orientation, front/back) and the number of test documents can be displayed on the screen. At the press of a “START READING” button, step S 406  is executed. 
       FIG. 6B  illustrates an example of a screen that is displayed in steps S 420  and S 421 . The screen prompts the user to set a test document to be read next on the platen glass  213 . The example is a case where N=2, and the displayed phrase is changed depending on the number of test documents to be set based on the value of N. At the press of the “START READING” button, step S 421  is executed. In a case where a “CANCEL” button is pressed on the screen, the processing of generating correction data for use in density adjustment is ended. 
       FIG. 6C  illustrates an example of a screen that is displayed in step S 409 . The screen prompts the user to check the test document placement method in order to resolve an error due to a test document detection state illustrated in  FIG. 5 . At the press of a “RETURN” button, the processing proceeds to step S 405 . 
       FIG. 6D  illustrates an example of a screen that is displayed in steps S 413  and S 422 . Since the read image is not suitable for use in generation of correction data, an item for checking whether the read document is a test document and an item for checking whether the print state of a test document with no defects are displayed to prompt the user to check the items. At the press of the “RETURN” button, the processing proceeds to step S 405  or S 423 . 
     As described above, a test document reading method is determined based on document detection results acquired from the platen glass  213  and the document tray  201  of the ADF, and a process of generating density correction data is determined. Thus, calibration is performed by an appropriate process using a test document placed at a desired position by the user. 
     Further, when the user places a test document at a desired placement position on the platen glass  213  or the document tray  201  of the ADF, an appropriate process for generating correction data is automatically determined, so that the bother of inputting a setting in advance by the user can be omitted. 
     In the first exemplary embodiment, an example in which a process of generating density correction data is determined based on the area where a placed test document is detected, i.e., based on the test document reading mode, is described. 
     In a second exemplary embodiment, a configuration that the reading mode can be changed during correction data generation will be described below. This increases the freedom and flexibility of test document reading, so that an image forming apparatus the calibration function of which can be used as desired by the user can be provided. 
     Points that are described in the first exemplary embodiment with reference to  FIGS. 1, 2, and 3  are like those in the second exemplary embodiment, so that description thereof will be omitted. 
     A process of generating correction data for use in density adjustment according to the present exemplary embodiment will be described below with reference to  FIG. 7 . In this example, three test documents are printed and read and correction is performed. The number of test documents is not limited to three, and a required number of test documents for generation of desired correction data can be used. Description of points that are like those in  FIG. 4  is omitted. 
     In step S 701 , a screen that prompts the user to set the test documents output in step S 403  at a desired reading portion is displayed on the operation unit  114 . A correction-data-generated flag is referred to. Details thereof are illustrated in  FIGS. 8A, 8B, and 8C . Then, in a case where correction data is not successfully generated using each result of reading the test documents, if the first correction mode using the ADF reading mode is being executed, a screen is displayed to prompt the user to set the three test documents on the document tray  201  of the ADF. On the other hand, if the second correction mode using the pressing-plate reading mode is being executed, a screen is displayed to prompt the user to set the first test document on the platen glass  213 . 
     Further, in a case where the processing returns to step S 701  after correction data is successfully generated using at least one of the test documents in either one of the reading modes, an instruction is changed as described below. 
     If the first correction data mode using the ADF reading mode is being executed, an instruction to set a (single or plurality of) test document (s) that has not been used in generation of correction data on the document tray  201  of the ADF is provided. 
     On the other hand, if the second correction data mode using the pressing-plate reading mode is being executed, an instruction to set one of the other test documents that have not been read for generation of correction data on the platen glass  213  is provided. 
     In step S 702 , the test documents are conveyed in the order in which the test documents are placed on the document tray  201  of the ADF, the conveyed test documents are read by the scanner controller, and images acquired by reading the test documents are transferred to the control unit  115 . Then, the CPU  103  analyzes whether the transferred images are suitable for use in generation of correction data. For example, in a case where a luminance pattern is not detected from the images acquired by reading the test documents, a case where appropriate test documents are not used, and a case where the test documents are printed in an inappropriate state, the CPU  103  determines that the transferred images are not suitable for use in generation of correction data. Further, the CPU  103  refers to a document detection flag, and if a test document is previously used to generate correction data, the CPU  103  determines that the used test document is not suitable for use as an image for generation of correction data. 
     In step S 703 , if the CPU  103  determines that one or more of the test documents read in step S 702  can be used in generation of correction data (YES in step S 703 ), the processing proceeds to step S 704 . Otherwise (NO in step S 703 ), the processing proceeds to step S 413 . In another exemplary embodiment, if the CPU  103  determines that all the test documents read in step S 702  can be used in generation of correction data, the processing proceeds to step S 703 . Otherwise, the processing proceeds to step S 413 . 
     In step S 704 , the CPU  103  analyzes each image determined as an image that can be used in generation of correction data among the images of the test documents read in step S 702 , and executes correction data generation processing. Details of the correction data generation processing are like those in step S 412 , so that description thereof will be omitted. 
     In step S 705 , the number of test documents on which correction has been performed is added to the variable number N stored on the RAM  104 . 
     Next, an example of a screen that is displayed on the operation unit  114  will be described below with reference to  FIGS. 8A, 8B, and 8C . A screen like that described above with reference to  FIGS. 6A to 6D  is displayed in a case of an error, so description thereof will be omitted. 
       FIG. 8A  illustrates an example of a screen that is displayed in steps S 406  and S 407  in a case where correction data has not been successfully generated. A screen that prompts the user to set the three test documents on the document tray  201  of the ADF or the first test document on the platen glass  213  is displayed. Although not illustrated in  FIG. 8A , an item for designating a test document placement method and the number of test documents can be displayed. At the press of the “START READING” button, step S 407  is executed. 
       FIG. 8B  illustrates an example of a screen that is displayed in steps S 406  and S 407  in a case where the first test document is read via the platen glass  213  and correction data is successfully generated. The correction-data-generated flag is referred to, and since the first test document for which corresponding correction data has been successfully generated is unnecessary, the screen prompts the user to place the second and third test documents on the document tray  201  of the ADF. This point is a difference from  FIG. 8A . In an alternative configuration, the screen can always prompt the user to place the three test documents on the document tray  201  of the ADF. In this case, as described above in the description of step S 702 , the test document for which correction data is successfully generated is not a correction target, so that no issue arises. 
       FIG. 8C  illustrates an example of a screen that is displayed in steps S 406  and S 407  in a case where the second and third test documents are read via the ADF and correction data is successfully generated. The correction-data-generated flag is referred to, and the screen prompts the user to set the first test document for which correction data has not yet been successfully generated on the document tray  201  of the ADF or the platen glass  213 . 
     In the second exemplary embodiment, the screen prompts the user to set the three test documents on the document tray  201  of the ADF, as in the first exemplary embodiment. However, for example, in a case where the user intends to set all the three test documents on the document tray  201  of the ADF but sets only two of the test documents, the two test documents are read in the ADF reading mode and correction data is generated in the first correction mode in the present exemplary embodiment. Then, the remaining single test document is separately read in the pressing-plate reading mode and correction data is generated in the second correction mode. (It is also possible to read the test document in the ADF reading mode and generate correction data in the first correction mode). 
     Further, the user who needs highly-accurate correction data only for a specific dither pattern and wishes to efficiently generate correction data for the remaining dither patterns can use the two correction modes in generating correction data. Specifically, the test document that corresponds to correction data corresponding to the specific dither pattern is set on the platen glass  213  and is read in the pressing-plate reading mode. In this way, the test document is read with great accuracy, so that highly-accurate correction data is generated. 
     Further, the test documents that correspond to correction data corresponding to the remaining dither patterns are set on the document tray  201  of the ADF and read in the ADF reading mode. In this way, the test documents are efficiently read, so that the burden on the user that is involved in generation of correction data is reduced. 
     According to the exemplary embodiments of the present disclosure, when the user places a chart that is a document with a test pattern printed thereon at a desired document placement position, a correction mode in which calibration is to be executed is automatically determined based on the placement position. In this way, calibration is executed by a process in the mode that is automatically determined based on the document placement position. 
     Other Embodiments 
     Embodiment(s) of the present disclosure can also be realized by a computer of a system or apparatus that reads out and executes computer executable instructions (e.g., one or more programs) recorded on a storage medium (which may also be referred to more fully as a ‘non-transitory computer-readable storage medium’) to perform the functions of one or more of the above-described embodiment(s) and/or that includes one or more circuits (e.g., application specific integrated circuit (ASIC)) for performing the functions of one or more of the above-described embodiment(s), and by a method performed by the computer of the system or apparatus by, for example, reading out and executing the computer executable instructions from the storage medium to perform the functions of one or more of the above-described embodiment(s) and/or controlling the one or more circuits to perform the functions of one or more of the above-described embodiment(s). The computer may comprise one or more processors (e.g., central processing unit (CPU), micro processing unit (MPU)) and may include a network of separate computers or separate processors to read out and execute the computer executable instructions. The computer executable instructions may be provided to the computer, for example, from a network or the storage medium. The storage medium may include, for example, one or more of a hard disk, a random-access memory (RAM), a read only memory (ROM), a storage of distributed computing systems, an optical disk (such as a compact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™), a flash memory device, a memory card, and the like. 
     While the present disclosure has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.