Patent Publication Number: US-9898814-B2

Title: Image inspection apparatus, image inspection method, and control program of image inspection apparatus

Description:
This application is a continuation application of U.S. application Ser. No. 14/026,393, filed Sep. 13, 2013, which claims priority pursuant to 35 U.S.C. §119 to Japanese Patent Applications Nos. 2012-203583, filed on Sep. 14, 2012, and 2013-165585, filed on Aug. 8, 2013, in the Japan Patent Office. The entire contents of the above-identified applications are incorporated herein by reference. 
    
    
     BACKGROUND 
     Technical Field 
     The present invention relates to an image inspection system and an image inspection method, and more particularly to setting of inspection thresholds used for determining defects in image. 
     Background Art 
     Conventional inspections of printed matter such as printed papers are conducted by visual inspection, but inspection apparatuses have been introduced to conduct the inspections as a post-processing operation of the offset printing. As for the inspection apparatus, the printed matters are visually inspected by an operator to select a printed matter having satisfactory image quality, and then the selected printed matter is scanned to generate a master image to be used as a reference image. The master image and inspection target printed matter are compared with each other by scanning the inspection target printed matter, and based on difference between the master image and the inspection target, defect of the inspection target printed matter can be determined. 
     However, the printing apparatuses of digital to press such as image forming apparatuses using electrophotography typically print images with a small volume, and also print different images for each page (i.e. variable printing), in which generating a master image from printed matter as a reference image is not efficient. In this type of image forming apparatuses, the master image can be generated from print data to efficiently conduct the inspection for the variable printing. 
     In this image inspection process, the defect of printed matter can be determined based on the above mentioned difference level. Specifically, scanned images prepared by scanning sheets printed with images and the master image generated from the print data are compared, in which positions and sizes of comparing images are matched and then the comparing images are compared for each pixel based on a given threshold. 
     JP-2008-003876-A discloses an image inspection process for an inkjet printer, which can verify inspection precision for the image inspection. Specifically, defects that may likely occur for the inkjet printer are artificially printed on sheets, the sheets having printed with the artificial defects are inspected, and then it is verified whether the inspection can be conducted effectively. 
     The above mentioned threshold used for comparing the images affect the inspection precision, therefore effective thresholds need to be set for high precision inspection. JP-2008-003876-A discloses a configuration to determine whether the inspection is conducted effectively using thresholds such as thresholds set in advance, in which suitable thresholds are not set automatically. 
     SUMMARY 
     In one aspect of the present invention, an image inspection apparatus for inspecting an image output on a recording medium by scanning the output image as a scanned image Is devised. The image inspection apparatus includes an inspection reference image generator to obtain data of an output-target image used by the image forming apparatus to conduct an image forming operation, and to generate an inspection reference image using the data of the output-target image, the inspection reference image to be used for an image inspection of the scanned image; an image inspection unit to determine whether the scanned image includes a defect based on a comparison result obtained by comparing a difference between the inspection reference image and the scanned image with a given threshold; and a threshold determiner to determine the given threshold. The threshold determiner controls generation of the inspection reference image having a normal image condition to be used for determining the given threshold. The threshold determiner computes a difference between the inspection reference image and the scanned image obtained by scanning a threshold setting image prepared by adding an artificial defect to the inspection reference image. The threshold determiner determines the given threshold based on the difference between the scanned image and the inspection reference image. 
     In another aspect of the present invention, a method of inspecting an image output on a recording medium by an image forming apparatus Is devised. The method comprising the steps of: obtaining data of an output-target image input to the image forming apparatus; forming a threshold setting image on the recording medium using the image forming apparatus, the threshold setting image prepare-able by adding an artificial defect to the output-target image; generating an inspection reference image using the data of the output-target image; scanning the threshold setting image formed on the recording medium to obtain a scanned image of the threshold setting image; computing a difference between the scanned image and the inspection reference image by comparing the scanned image and the inspection reference image; and determining a threshold based on the difference between the scanned image and the inspection reference image, the determined threshold to be compared with the difference between the scanned image and the inspection reference image to determine whether the scanned image includes a defect. 
     In another aspect of the present invention, a non-transitory computer-readable carrier medium storing a program that, when executed by a computer, causes the computer to execute a method of inspecting an image output on a recording medium by an image forming apparatus is devised. The method comprising the steps of obtaining data of an output-target image input to the image forming apparatus; forming a threshold setting image on the recording medium using the image forming apparatus, the threshold setting image prepare-able by adding an artificial defect to the output-target image; generating an inspection reference image using the data of the output-target image; scanning the threshold setting image formed on the recording medium to obtain a scanned image of the threshold setting image; computing a difference between the scanned image and the inspection reference image by comparing the scanned image and the inspection reference image; and determining a threshold based on the difference between the scanned image and the inspection reference image, the determined threshold to be compared with the difference between the scanned image and the inspection reference image to determine whether the scanned image includes a defect. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the disclosure and many of the attendant advantages and features thereof can be readily obtained and understood from the following detailed description with reference to the accompanying drawings, wherein: 
         FIG. 1  shows a schematic configuration of an image forming system including an inspection apparatus according to an example embodiment; 
         FIG. 2  shows an example block diagram of a hardware configuration of the inspection apparatus according to an example embodiment; 
         FIG. 3  shows an example block diagram of an engine controller, a print engine and an inspection apparatus according to an example embodiment; 
         FIG. 4  shows a schematic mechanical configuration of a print processing unit according to an example embodiment; 
         FIG. 5  shows an example block diagram of master image processing unit according to an example embodiment; 
         FIG. 6  is a flowchart of process of a threshold determination process according to an example embodiment; 
         FIGS. 7A, 7B and 7C  show examples of output images used for a threshold determination process according to an example embodiment; 
         FIG. 8  shows an example of setting of artificial defects according to an example embodiment; 
         FIG. 9  shows an example of a computation result of discrete threshold computed for a plurality of artificial defects according to an example embodiment; 
         FIG. 10  is a flowchart of process of computing discrete threshold according to an example embodiment; 
         FIGS. 11A and 11B  show examples of threshold selection screens according to an example embodiment; 
         FIG. 12  shows another example of threshold selection screen according to an example embodiment; 
         FIGS. 13A and 13B  show schematic configurations of systems according to another example embodiment; 
         FIG. 14  shows a schematic configuration of a system according to another example embodiment; 
         FIG. 15  schematically shows a process of comparing images for inspection according to an example embodiment; and 
         FIG. 16  schematically shows an example of threshold setting according to an example embodiment. 
     
    
    
     The accompanying drawings are intended to depict exemplary embodiments of the present invention and should not be interpreted to limit the scope thereof. The accompanying drawings are not to be considered as drawn to scale unless explicitly noted, and identical or similar reference numerals designate identical or similar components throughout the several views. 
     DETAILED DESCRIPTION 
     A description is now given of exemplary embodiments of the present invention. It should be noted that although such terms as first, second, etc. may be used herein to describe various elements, components, regions, layers and/or sections, it should be understood that such elements, components, regions, layers and/or sections are not limited therefore because such terms are relative, that is, used only to distinguish one element, component, region, layer or section from another region, layer or section. Thus, for example, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the present invention. 
     In addition, it should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present invention. Thus, for example, as used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. Moreover, the terms “includes” and/or “including”, when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     Furthermore, although in describing views shown in the drawings, specific terminology is employed for the sake of clarity, the present disclosure is not limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that have a similar function, operate in a similar manner, and achieve a similar result. Referring now to the drawings, apparatuses or systems according to example embodiments are described hereinafter with reference to  FIGS. 1 to 25 . 
     In this disclosure, an image forming system includes an inspection apparatus, in which a master image and an scanned image obtained by scanning an image output by an image forming operation are compared to inspect an output (e.g., printed image) of the image forming operation, and based on the a comparison result, thresholds used to determine defect in an image, matched to inspection precision desired by a user, can be settable easily and preferably. 
       FIG. 1  shows an example configuration of an image forming system according to an example embodiment. As shown in  FIG. 1 , the image forming system includes, for example, a digital front end (DFE)  1 , an engine controller  2 , a print engine  3  and an inspection apparatus  4 . Based on a received print job, the DFE  1  generates bitmap data, which is image data to be output (i.e., output-target image), and outputs the generated bitmap data to the engine controller  2 . 
     Based on the bitmap data received from the DFE  1 , the engine controller  2  controls the print engine  3  to conduct an image forming operation. Further, the engine controller  2  transmits the bitmap data received from the DFE  1  to the inspection apparatus  4 , wherein the bitmap data is used as data of original information for preparing an inspection reference image to be used for inspection at the inspection apparatus  4  when the inspection apparatus  4  inspects an output result of an image forming operation of the print engine  3 . 
     Under the control of the engine controller  2 , the print engine  3  conducts an image forming operation on a recording medium such as paper using the bitmap data, and scans an output paper such as a paper printed with an image using a scanner, and inputs the scanned image data to the inspection apparatus  4 . The recording medium may be, for example, a sheet such as paper, film, plastic sheet, and any material that can be used for outputting (i.e., forming) an image by an image forming operation. Based on the bitmap data input from the engine controller  2 , the inspection apparatus  4  generates a master image. Then, the inspection apparatus  4  compares the scanned image data, input from the print engine  3 , and the generated master image to conduct an image inspection of output image, in which the inspection apparatus  4  is used as an image inspection apparatus. 
     A description is given of a hardware configuration of the engine controller  2 , the print engine  3  and the inspection apparatus  4  according to an example embodiment with reference to  FIG. 2 . Further, as for the inspection apparatus  4 , engines for scanner and printer may be added to the hardware configuration shown in  FIG. 2 .  FIG. 2  shows a block diagram of an example hardware configuration of the inspection apparatus  4 . The engine controller  2  and the print engine  3  may have a hardware configuration similar to the inspection apparatus  4  shown in  FIG. 2 . 
     As shown in  FIG. 2 , the inspection apparatus  4  can be configured similarly to information processing apparatuses such as general servers, and personal computers (PC), or the like. Specifically, the inspection apparatus  4  includes a central processing unit (CPU)  10 , a random access memory (RAM)  20 , a read only memory (ROM)  30 , a hard disk drive (HDD)  40 , and an interface (I/F)  50 , connectable to each other via a bus  90 . Further, the  1 /F  50  is connectable to a liquid crystal display (LCD)  60 , an operation unit  70 , and a specific device  80 . 
     The CPU  10  is a computing processor or unit which controls the inspection apparatus  4  as a whole. The CPU  10  can be configured with various types of processors, circuits, or the like, such as a programmed processor, a circuit, and an application specific integrated circuit (ASIC), used singly or in combination. The RAM  20  is a volatile memory, to which data or information can be written and read at high speed, and is used as a working memory when the CPU  10  processes data or information. The ROM  30  is a non-volatile memory used as a read only memory, and stores programs such as firmware or the like. The HDD  40  is a non-volatile storage device, to and from which data or information can be written and read, and stores operating system (OS), management or control software programs, application software programs, various data, or the like. 
     The I/F  50  can be used to connect various types of hardware and network to the bus  90 , and controls such connection. The LCD  60  is a user interface to display information, with which the status of the inspection apparatus  4  can be checked by a user. The operation unit  70  is a user interface such as a keyboard, a mouse, etc., with which information can be input to the inspection apparatus  4  by the user. 
     The specific device  80  may be disposed as hardware to conduct a specific capability or function for each of the engine controller  2 , the print engine  3  and the inspection apparatus  4 . For example, as for the print engine  3 , the specific device  80  may be a plotter to conduct an image forming operation on sheets, and a scanner to scan images output on the sheets. Further, as for the engine controller  2  and the inspection apparatus  4 , the specific device  80  may be a specific computing circuit to conduct high speed image processing, and the specific device  80  may be, for example, an application specific integrated circuit (ASIC). 
     In the above hardware configuration, software programs stored in a storage area such as the ROM  30 , the HDD  40 , or an optical disk can be read and loaded to the RAM  20 , and the CPU  10  runs such programs to control various units, with which a software-executing controller can be configured. With a combination of such software-executing controller and hardware, a functional block to operate the engine controller  2 , the print engine  3  and the inspection apparatus  4  can be configured. In an example embodiment, at least one of the units is implemented as hardware or as a combination of hardware/software. 
       FIG. 3  shows an example block diagram of the engine controller  2 , the print engine  3  and the inspection apparatus  4 . As shown in  FIG. 3 , the engine controller  2  includes, for example, a data obtainer  201 , an engine control unit  202  and a bitmap transmitter  203 . Further, the print engine  3  includes, for example, a print processing unit  301  and a scanner  302 . Further, the inspection apparatus  4  includes, for example, a scanned image obtainer  401 , a master image processing unit  402 , an inspection control unit  403  and an inspection unit  404 . The inspection unit  404  can be used as an image inspection unit that compares images for inspection. 
     Upon obtaining the bitmap data from the DFE  1  by the data obtainer  201 , the engine control unit  202  and the bitmap transmitter  203  are operated. The bitmap data is information of pixels composing an image to be output by an image forming operation, and the data obtainer  201  can function as a pixel information obtainer. Based on the bitmap data transferred from the data obtainer  201 , the engine control unit  202  instructs the print engine  3  to conduct an image forming operation, in which the engine control unit  202  can function as an output execution control unit. The bitmap transmitter  203  transmits the bitmap data, obtained by the data obtainer  201 , to the inspection apparatus  4 . 
     The print processing unit  301  obtains the bitmap data input from the engine controller  2 , conducts an image forming operation to a sheet, and outputs a printed sheet. Therefore, the print processing unit  301  can function as an image forming apparatus. The print processing unit  301  can use any types of image forming mechanism including, for example, the electrophotography, the inkjet method, or the like. The scanner  302  scans an image formed on the sheet by conducting a printing operation by the print processing unit  301 , and outputs scanned data to the inspection apparatus  4 . The scanner  302  is, for example, a line scanner disposed along a transport route of sheet output by the print processing unit  301 , in which the scanner  302  scans the transported sheet face to read an image formed on the sheet. 
     A description is given of mechanical configurations of the print processing unit  301  and the scanner  302  with reference to  FIG. 4 . As shown in  FIG. 4 , the print processing unit  301  includes, for example, image forming units  106 BK,  106 M,  106 C,  106 Y and a transport belt  105  of an endless movement unit, in which the image forming units  106 BK,  106 M,  106 C,  106 Y are disposed along the transport belt  105 , which is referred to as the tandem type. Specifically, the image forming units  106 BK,  106 M,  106 C,  106 Y (electrophotography processing units) are disposed along the transport belt  105  from the upstream side of a transport direction of the transport belt  105 . An intermediate transfer image is formed on the transport belt  105 , and transferred to a recording medium such as a sheet  104 , which is separated and fed from a sheet tray  101  using a sheet feed roller  102  and a separation roller  103 . 
     The internal configuration is common for the image forming units  106 BK,  106 M,  106 C,  106 Y except color of toner image, which means the image forming unit  106 BK forms black image, the image forming unit  106 M forms magenta image, the image forming unit  106 C forms cyan image, and the image forming unit  106 Y forms yellow image. Hereinafter, the image forming unit  106 BK is described as the representative of the image forming units  106 BK  106 M,  106 C,  106 Y. Each members composing the image forming units  106 BK  106 M,  106 C,  106 Y may be attached with BK, M, C, Y as required. 
     The transport belt  105  is an endless belt extended by a drive roller  107  and a driven roller  108 . The drive roller  107  can be rotated by a drive motor. The drive motor, the drive roller  107  and the driven roller  108  can be collectively function as a drive unit for the transport belt  105  which is the endless movement unit. 
     When forming images, the image forming unit  106 BK transfers black toner image to the rotating transport belt  105 . The image forming unit  106 BK includes, for example, a photoconductor drum  109 BK used as a photoconductor, a charger  110 BK disposed near the photoconductor drum  109 BK, a development unit  112 BK, a photoconductor cleaner, and a decharger  113 BK. Further, an optical writing unit  111  irradiates light for each of the photoconductor drums  109 BK,  109 M,  109 C,  109 Y (hereinafter, photoconductor drum  109 ). 
     When forming images, an outer face of the photoconductor drum  109 BK is charged uniformly by the charger  110 BK in a dark environment, and then an electrostatic latent image for black image is formed on the photoconductor drum  109 BK by irradiating light from a light source for black image in the optical writing unit  111 . The development unit  112 BK develops the electrostatic latent image using black toner, and then black toner image is formed on the photoconductor drum  109 BK. 
     The black toner image is transferred to the transport belt  105  at a transfer position of the photoconductor drum  109 BK and the transport belt  105  by a transfer unit  115 BK, in which the photoconductor drum  109 BK and the transport belt  105  may contact or be the closest with each other. With this transfer, the black toner image is formed on the transport belt  105 . Upon completing the transfer of black toner image, the photoconductor cleaner removes toner remaining on the outer face of the photoconductor drum  109 BK, and then the photoconductor drum  109 BK is decharged by the decharger  113 BK to prepare for a next image forming operation. 
     The transport belt  105  transferred with the black toner image by the image forming unit  106 BK is transported to the image forming unit  106 M, next to the image forming unit  106 B, by rotating the transport belt  105 . Similar to the image forming process at the image forming unit  106 BK, the image forming unit  106 M forms magenta toner image on the photoconductor drum  109 M, and the magenta toner image may be superimposed and transferred on the black toner image. 
     The transport belt  105  having the transferred black toner image and magenta toner image is then transported to the image forming units  106 C,  106 Y. Similar to the image forming unit  106 BK, cyan toner image formed on the photoconductor drum  109 C, and yellow toner image formed on the photoconductor drum  109 Y may be superimposed and transferred on the black toner image and magenta toner image, with which the intermediate transfer image of full color is formed on the transport belt  105 . 
     The sheet  104  stacked in the sheet tray  101  is fed from the top sheet, and the intermediate transfer image formed on the transport belt  105  is transferred on the sheet  104  at a transfer position that the transport belt  105  and the sheet  104  contact or be the closest with each other in the transport route, with which an image is formed on the sheet  104 . The sheet  104  formed with the image is transported to a fusing unit  116  to fuse the image on the sheet  104 , and then ejected from the image forming apparatus. 
     In the fusing unit  116 , the toner image transferred on the sheet  104  is fused by heat, in which water included in the sheet  104  is vaporized when the sheet  104  is passing through the high temperature fusing unit  116 , with which the sheet  104  shrinks and therefore the image size on the sheet  104  may be come smaller than the image size of original image. When the scanner  302  scans the shrink sheet  104 , the scanned image smaller than the original image may be generated. 
     Further, when the duplex printing is conducted, the sheet  104  having the fused image is transported to an inverting route to invert the faces of the sheet  104 , and then the sheet  104  is transported to the transfer position again. The sheet  104  having the fused image on one face or both faces is transported to the scanner  302 . Then, the scanner  302  scans one face or both faces, with which a scanned image, which is an inspection target image, is generated. 
     A description is given of the inspection apparatus  4  by referring  FIG. 3  again. The scanned image obtainer  401  obtains the scanned image data generated by scanning the sheet face by the scanner  302  in the print engine  3 , and inputs the scanned image data as an inspection target image to the inspection unit  404 . As described above, the master image processing unit  402  obtains the bitmap data input from the engine controller  2 , and generates a master image as an inspection reference image to be compared with the inspection target image. Therefore, based on the output-target image, the master image processing unit  402  is used as an inspection reference image generator that generates the master image as the inspection reference image to be used for inspecting the scanned images. The generation process of master image by the master image processing unit  402  will be described later. 
     The inspection control unit  403  controls the inspection apparatus  4  as a whole, and each unit in the inspection apparatus  4  is operated under the control of the inspection control unit  403 . Further, in an example embodiment, the inspection control unit  403  includes, for example, a master image generation controller  403   a , an image comparison inspection controller  403   b , a threshold determination processing unit  403   c  and a user interface (UI) controller  403   d  as shown in  FIG. 3 . The inspection unit  404  is used as an image inspection unit that compares the scanned image data, input from the scanned image obtainer  401 , and the master image, generated by the master image processing unit  402 , to determine whether a desired image forming operation is conducted. The inspection unit  404  may be configured with the above mentioned ASIC or the like to compute a great amount of data with high speed processing. 
     A description is given of the master image processing unit  402  with reference to  FIG. 5 .  FIG. 5  shows an example block diagram of the master image processing unit  402 . As shown in  FIG. 5 , the master image processing unit  402  includes, for example, a binary/multi-value converter  421 , a resolution level converter  422 , a color converter  423  and a master image outputting unit  424 . The master image processing unit  402  can be devised as the specific device  80  (see  FIG. 2 ) devised by a combination of hardware and software such as the ASIC controlled by software. The inspection unit  404  and the master image processing unit  402  can be configured using the ASIC as described above. Further, the inspection unit  404  and the master image processing unit  402  can be configured using a software module executable by the CPU  10 . 
     The binary/multi-value converter  421  conducts a binary/multi-value converting process to a binary format image expressed binary such as color/non-color to generate a multi-valued image. The bitmap data is information input to the print engine  3 . The print engine  3  conducts an image forming operation based on binary format image for each color of cyan, magenta, yellow, black (CMYK). Because the scanned image data, which is the inspection target image, is a multi-valued image composed of multi-gradient image of the three primary colors of red, green and blue (RGB), a binary format image is initially converted to a multi-valued image by the binary/multi-value converter  421 . The multi-valued image is, for example, an image expressed by 8-bit for each CMYK. 
     Further, the print engine  3  conducts an image forming operation based on binary format image for each of CMYK, and the master image processing unit  402  includes the binary/multi-value converter  421  but not limited hereto. For example, when the print engine  3  conducts an image forming operation based on multi-valued image, the binary/multi-value converter  421  can be omitted. 
     The resolution level converter  422  conducts a resolution level conversion process to match a resolution level of multi-valued image generated by the binary/multi-value converter  421  to a resolution level of the scanned image data (i.e., inspection target image). Because the scanner  302  generates scanned image data, for example, with the resolution level of 200 dots per inch (dpi), the resolution level converter  422  converts a resolution level of multi-valued image generated by the binary/multi-value converter  421  to 200 dpi. 
     The color converter  423  obtains the image having converted with the resolution level by the resolution level converter  422  and conducts a color converting process. Because the scanned image data is RGB-format image as described above, the color converter  423  converts the CMYK-format image having converted with the resolution level by the resolution level converter  422  to the RGB-format image, with which a multi-valued image of 200 dpi expressed with 8-bit for each of RGB (total 24 bits) for each pixel is generated. 
     The master image outputting unit  424  outputs the master image, generated by using the binary/multi-value converter  421 , the resolution level converter  422  and the color converter  423 , to the inspection control unit  403 . Based on the master image obtained from the master image processing unit  402 , the inspection control unit  403  instructs the inspection unit  404  to conduct an image comparing process to obtain a comparison result. 
     Referring back to  FIG. 4 , the inspection unit  404  compares the scanned image data and the master image expressed with 8-bit for each of RGB (total 24 bits) as described above for each corresponding pixel, and computes difference of pixel values for each of RGB for each pixel. Based on the comparison of the computed difference and a threshold, the inspection unit  404  determines whether a defect occurs to the scanned image data. Therefore, the inspection unit  404  can function as an image inspection unit to determine defect of the scanned image data based on difference of the inspection reference image and the scanned image data. Further, the difference computed for each of pixels can be correlated for each of pixel positions and can be configured as a differential image. 
     Further, the difference and the threshold can be compared by the inspection unit  404  as follows. For example, values of the difference computed for each of pixels are summed for a given area of an image as a total value, and the total value is compared with the threshold, which is set to be compared with the total value. The given area for summing values of the difference of each of pixels is, for example, a 20-dot square area. In an example embodiment, the threshold is a value set for the total difference value of the given area (hereinafter, defect determination unit area) obtainable by summing values of the difference. The inspection unit  404  can output information of position of the defect determination unit area on an image having a total difference exceeding the threshold, wherein this position information can be used as information indicating presence of defect in the scanned image data. The position information in the image is defined by, for example, coordinate information on the image. 
     When comparing the scanned image and the master image, the scanned image is divided into a plurality of areas as shown in  FIG. 15 . The inspection unit  404  superimposes each divided area to a corresponding area of the master image to compute a difference of pixel value of each pixel such as difference of density. Further, a position of superimposing the divided area to the master image is shifted left/right and up/down to determine a position that the computed difference becomes the smallest and the smallest difference is used as a comparison result. Each one of the divided areas shown in  FIG. 15  can be used as the above described defect determination unit area. 
     Further, the above described threshold can be provided by register setting to the inspection unit  404  configured as, for example, ASIC. The inspection control unit  403 , which is configured by executing a program using the CPU  10 , writes a threshold, set as shown in  FIG. 17 , to the register provided to designate a threshold for the inspection unit  404 , with which the above described threshold can be set. 
     Further, in another method, each pixel is determined as normal or defect based on a comparison result of the difference computed for each pixel and the threshold, and the count number of pixels determined as defect and the threshold set for the count number are compared. 
     In the system according to an example embodiment, when setting thresholds used for the image comparing process by the inspection unit  404 , thresholds matched to inspection precision, which may be desired by a user, can be set easily, and therefore, each of the modules included in the inspection control unit  403  can be used to determine the above mentioned threshold using each unit of the inspection apparatus  4 . A description is given of a process of setting the threshold with reference to  FIG. 6 . 
       FIG. 6  is a flowchart of process of setting threshold according to an example embodiment. As shown in  FIG. 6 , when setting the threshold, under the control of the engine controller  2 , the print engine  3  conducts a printing operation for images used for setting thresholds (hereinafter, referred to as threshold setting image) (S 601 ).  FIGS. 7A to 7C  show examples of threshold setting images according to an example embodiment. As for the threshold setting images,  FIG. 7A  shows reference image pattern  701 , which is an image having normal image condition not added artificial defects, and the reference image pattern is used to determine thresholds. As shown in  FIG. 7A , the reference image pattern  701  can be drawn and formed in 4 rows in the horizontal direction or the X direction, and 5 lines in the vertical direction or the Y direction for given color mark. The images of  FIG. 7A  can be output as a first image using the print engine  3  under the control of the engine controller  2 . 
     By contrast,  FIGS. 7B and 7 ( c ) show threshold setting images prepared by adding a plurality of different artificial defects to the above described reference image of normal image condition.  FIG. 7B  show images prepared by adding artificial defects having different color densities to the above described reference image pattern (hereinafter, density-changed defect pattern  702 ). As shown in  FIG. 7B , the density-changed defect pattern  702  can be prepared by adding different artificial defects to each one of marks arranged in the X direction and the Y direction. The images of  FIG. 7B  can be output as a second image using the print engine  3  under the control of the engine controller  2 . 
     As for the density-changed defect pattern, each mark arranged in the X direction is added with artificial defects of different colors, and each mark arranged in the Y direction is added with artificial defects of different densities. Therefore, the images of  FIG. 7B  are images added with a plurality of artificial defect having different colors and density levels.  FIG. 8  shows an example of information referred by the engine control unit  202  of the engine controller  2  when outputting the density-changed defect pattern  702  shown in  FIG. 7B  (hereinafter, density-changed defect pattern information). Further, information of the density-changed defect pattern of  FIG. 8  can be stored, for example, in a storage included in the engine controller  2  such as the RAM  20 , ROM  30 , HDD  40 , and/or an external storage. 
     In  FIG. 8 , PC, PM, PY and PK are values indicating colors such as C, M, Y, K for the pattern. As shown in  FIG. 8 , as for the density-changed defect pattern information, each pattern arranged in 4 rows in the X direction and 5 lines in the Y direction is set with color information of artificial defects. For example, as a pattern for the first line/first row, PC is added with d 1 , and as for other M, Y, K in the first line, the same value of color are added with as artificial defect, in which d 1  is added to PM at the second row, to PY at the third row, and to PK at the fourth row, with which artificial defects having colors different from the original pattern can be prepared. 
     Further, as shown in  FIG. 8 , adding values can be changed such as +d 1 , +d 2 , +d 3  - - - in the Y direction, in which the greater the value of n of d n , the greater the density, which means, in the Y direction, color density becomes thicker by adding values of artificial defects. The change of density is indicated in  FIG. 7B  by using line patterns such as dot line, dashed line, or the like. 
     When outputting the density-changed defect pattern shown in  FIG. 7B , the engine control unit  202  obtains settings for an range for changing density, and determines a value of d n  shown in  FIG. 8  based on the obtained settings for the range. The settings for the range may include values that may be set for the engine control unit  202  in advance, or set manually by a user when outputting the density-changed defect pattern. 
     The d n  can be obtained using the following formula (1) by setting the lower limit d m  and the upper limit d M  for the settings of the range.
 
 d   n   =d   m +¼( d   M   −d   m )× n   (1)
 
     Based on the computation using the above formula (1), the range of from d m  to d M  can be divided equally, for example, by five values of d 1  to d 5 , and can be used as the adding values of density. 
       FIG. 7C  show images prepared by adding artificial defects having different line width to the above described reference image pattern (hereinafter, width-changed defect pattern  703 ). Similar to the density-changed defect pattern, as shown in  FIG. 7C , the width-changed defect pattern  703  can be prepared by adding different artificial defects to each one of marks arranged in the X direction and the Y direction. Similar to the images of  FIG. 7B , the images of  FIG. 7C  are images added with a plurality of artificial defect different in color and width. The images of  FIG. 7C  can be output as a third image using the print engine  3  under the control of the engine controller  2 . Similar to the density-changed defect pattern  702 , as for the width-changed defect pattern  703 , each mark arranged in the X direction is added with artificial defects of different colors, and each mark arranged in the Y direction is added with artificial defects of different width. 
     Similar to the density-changed defect pattern, the engine control unit  202  changes width of artificial defects within a set range for changing width of artificial defects shown in  FIG. 7C . The range of changing width can be computed using the above formula (1) as d n  of width of artificial defects. Further, the engine control unit  202  stores the computed d n  to be used for a later processing. 
     Further, in an example embodiment, the engine control unit  202  can generate bitmap data used for an image forming operation of the patterns shown in  FIG. 7A  to  FIG. 7C , but the DFE  1  can generate bitmap data. 
     In the process at S 601 , the engine controller  2 , the print engine  3  and the inspection apparatus  4  respectively conduct the above described operations, in which the engine controller  2  transmits the bitmap data to the inspection apparatus  4 , and data of the scanned image, generated in the print engine  3  by scanning the output sheet using the scanner  302 , is input to the inspection apparatus  4 . Then, when setting the thresholds, based on the bitmap data input from the engine controller  2 , the inspection apparatus  4  generates a master image based on bitmap data of the first image (S 602   a ), and selects and obtains data of scanned image of the second image and the third image (S 602   b ). 
     In the process at S 602   a , among bitmap data of the first, second and third images input from the engine controller  2 , the master image generation controller  403   a  of the inspection control unit  403  controls the master image processing unit  402  to generate a master image only for the first image. The master image is used as the inspection reference image as described above. The master image is also referred to as a normal reference image used for inspection, and the normal reference image is used as the inspection reference image for the preparing the above described threshold setting image. 
     Further, in the process at S 602   b , the image comparison inspection controller  403   b  of the inspection control unit  403  controls the scanned image obtainer  401  to discard the scanned image data of the first image from the scanned image data of the first, second and third images input from the print engine  3 , and obtains the scanned image of the second image and the third image. The scanned image data is image data obtained by scanning the above described threshold setting image, wherein scanned image data is also referred to as defect scanned image. 
     Then, the image comparison inspection controller  403   b  of the inspection control unit  403  controls the inspection unit  404  to compare the above described master image of first image and the scanned image of the second and third images (image comparing process) to compute the above described difference for each of the second image and the third image to obtain a differential image (S 603 ). In S 603 , a difference between the master image and the scanned image data is computed for each of a plurality of artificial defects having different colors and levels shown in  FIG. 7B  and  FIG. 7C . 
     Upon obtaining the differential image for the second image and the third image with respect to the master image, as explained with reference to  FIGS. 7A to 7C , the threshold determination processing unit  403   c  of the inspection control unit  403  computes a threshold to detect an artificial defect artificially added in each of marks arranged in rows and lines as defect (S 604 ). In the process of S 604 , as shown in  FIG. 9 , threshold such as th 11 , th 12  - - - can be computed for each of marks arranged in 4 rows in the X direction and 5 lines in the Y direction. In S 604 , based on the difference generated for each one of a plurality of artificial defects having different colors and levels, a threshold to be used for determining each one of the plurality of artificial defects as defect can be computed, and the each computed threshold is referred to as discrete threshold. Further, information shown in  FIG. 9  can be stored, for example, in a storage included in the inspection unit  404  such as the RAM  20 , ROM  30 , HDD  40 , and/or an external storage. 
       FIG. 9  shows an example of a table including discrete thresholds. In an example embodiment, a discrete threshold is set for each mark included in the second image and the third image. Therefore, the table shown as  FIG. 9  can be generated for each of the second image and the third image. 
     A description is given of a detail of S 604  ( FIG. 6 ) with reference to  FIG. 10 . As shown in  FIG. 10 , the threshold determination processing unit  403   c  sets a starter threshold (S 1001 ) at first. The starter threshold is a threshold that any types of defect are not extracted as defect, which means that even if a total difference value for the defect determination unit area is great, a value greater than the total difference value for the defect determination unit area is set as the starter threshold, with which no defect is determined as defect. 
     Upon setting the starter threshold, the threshold determination processing unit  403   c  controls the inspection unit  404  to conduct a defect determination process based on the set threshold (S 1002 ). In S 1002 , a defect determination process is conducted for each area displaying each mark shown in  FIG. 7A  to  FIG. 7C . By contrast, in a normal determination process, a defect determination process is conducted for an entire image. Therefore, the number of target pixels becomes different between the determination at S 1002  and the determination for the normal determination process, therefore the population parameter of computed difference valued becomes different. To cope with the change of population parameter, the threshold to be applied at S 1002  is adjusted in view of a ratio of the number of pixels of entire image and the number of pixels of an area displaying each mark. Further, the starter threshold set at S 1001  can be set to a value corresponding to the number of pixels of an area displaying each mark. 
     If each area displaying a mark is determined as current defect based on the determination result of S 1002  (S 1003 : YES), the threshold determination processing unit  403   c  registers or sets a currently-used threshold as a threshold for the area determined as current defect to the table shown in  FIG. 9  (S 1004 ). With this processing, each discrete threshold such as th 11 , th 12  and so on shown in  FIG. 9  can be registered. 
     Upon completing S 1004 , the threshold determination processing unit  403   c  checks whether a threshold is set for all of areas (S 1005 ). If the threshold is set for all of areas as shown in  FIG. 9  (S 1005 : YES), the process ends. By contrast, if no area is determined as current defect when S 1002  is conducted (S 1003 : NO), or if the threshold is not yet set for all of areas (S 1005 : NO), the threshold determination processing unit  403   c  changes a value of the threshold to increase the probability to be determined as defect (S 1006 ), and repeats the process from S 1002 . 
     In an example embodiment, the threshold determination processing unit  403   c  can change values of threshold gradually to increase the probability to be determined as a defect, and repeats the defect determination process until all of areas are determined as defect. With this processing, as explained with reference to  FIGS. 7B and 7C , thresholds matched to an actual defect determination process can be determined based on thresholds used for extracting various artificial defects having different levels. Further, in an example embodiment, because the defects can be determined based on the scanned image data generated by the scanner  302 , thresholds matched to the images scanned real time by the scanner  302  can be set. 
     Further, as described above, the threshold applied at S 1002  is different from the threshold to determine a defect for an entire image. Therefore, if a threshold set at the concerned timing is multiplied by the number of pixels and the multiplied threshold is used as a threshold at S 1002 , a threshold set to a table at S 1004  is a threshold set at the concerned timing. By contrast, if a threshold set at the concerned timing is used as a threshold at S 1002 , a threshold set to a table at S 1004  is a threshold obtained by multiplying the threshold set at the concerned timing by the number of pixels. 
     Further, in the defect determination process, a ratio of the number of pixels having difference greater than a given value with respect to the total number of pixels can be used as information for the defect determination process. If the ratio such as percentage is set as a threshold, the same threshold can be used even if the population parameter of pixels, to be inspected, changes. 
     Upon completing the process of S 604 , the UI controller  403   d  controls a display unit to display a graphical user interface (GUI), which is used by a user to set a threshold, and the inspection control unit  403  receives a selection result input by a user&#39;s operation (S 605 ). The GUI displayed in S 605  is referred to as a threshold selection screen hereinafter, and  FIG. 11A  and  FIG. 11B  show examples of threshold selection screens. The threshold selection screens shown in  FIG. 11A  and  FIG. 11B  can be displayed on a display unit such as the LCD  60  connected to the inspection apparatus  4 .  FIG. 11A  shows an initial screen of GUI displayed in S 605 , which means a screen before a user&#39;s selection operation. 
     As shown in  FIG. 11A , the threshold selection screen displays images of the density-changed defect pattern and the width-changed defect pattern described with reference to  FIGS. 7B and 7C . These images can be displayed using, for example, the second image and the third image obtained by the scanned image obtainer  401 . The user can select one or more marks to be identified as defect on the screen shown in  FIG. 11A . 
     When selecting the mark on the screen shown in  FIG. 11A , the user operates the screen, but the mark is selected by looking the output sheet (i.e., not selected on the screen), in which the user can determine the defect based on the defect actually output on the sheet.  FIG. 11B  shows an example screen when images to be identified as defect are selected by the user. As shown in  FIG. 11B , the mark selected by the user is displayed on the screen with high-lighted condition such as encircling frame. 
     When the mark is selected as described above, the UI controller  403   d  obtains the selection result, and the threshold determination processing unit  403   c  can set a threshold to detect each mark as defect by referring the table shown in  FIG. 9 . Specifically, when the UI controller  403   d  receives the user&#39;s selection at S 605 , the threshold determination processing unit  403   c  extracts a discrete threshold, corresponding to the defect selected by the user shown in  FIG. 11B , from the table shown in  FIG. 9 . In this process, the UT controller  403   d  recognizes one or more defects selected by an operation to the screen shown in  FIG. 11A  by a user. 
     Specifically, when one or more marks are selected as defect as shown in  FIG. 11B , the threshold determination processing unit  403   c  obtains information of arrangement position of the selected defect on the image, and identifies the arrangement in X direction and the arrangement in Y direction indicated in the table of  FIG. 9 . Then, the threshold determination processing unit  403   c  extracts information of threshold corresponding to the arrangement position of the selected defect such as th 11 , th 21  and so on from the table shown in  FIG. 9 . 
     Upon extracting the discrete thresholds for the selected defects ( FIG. 11B ) from the table of  FIG. 9 , the threshold determination processing unit  403   c  determines a finally-set threshold based on the extracted discrete thresholds (S 606 ). In S 606 , among the extracted discrete thresholds corresponding to the marks selected by the user as to-be-determined as defect, the threshold determination processing unit  403   c  determines one of the discrete thresholds as the finally-set threshold, in which a discrete threshold having the strictest threshold is determined as the finally-set threshold. When the strictest threshold is set as the finally-set threshold, the greater number of marks can be determined as defect. The threshold determined with this process can be stored as the threshold setting as shown in  FIG. 16 , and when the inspection unit  404  conducts an inspection by comparing images, a threshold can be provided to the inspection unit  404  by writing the threshold as a register value by the inspection control unit  403 . 
     Upon determining the finally-set threshold, the threshold determination processing unit  403   c  determines whether re-adjustment is required based on the user&#39;s operation (S 607 ), in which the UI controller  403  obtains an operation instruction input by the user. In S 607 , the threshold determination processing unit  403   c  controls a display unit such as the LCD  60  connected to the inspection apparatus  4  to display a screen for selecting whether the re-adjustment is required, and determines whether the re-adjustment is required based on the user&#39;s operation to the screen. 
     If the re-adjustment is not required (S 607 : NO), the threshold determination processing unit  403   c  ends the process. By contrast, if the re-adjustment is required (S 607 : YES), the threshold determination processing unit  403   c  instructs the engine controller  2  to repeat the steps from S 601  and controls the inspection apparatus  4 , in which as described above, the inspection control unit  403  designates a range of changing density and/or width of the density-changed defect pattern or the width-changed defect pattern. Specifically, the threshold determination processing unit  403   c  can designate d n  for the mark having the maximum value d M  and the minimum value d m  for each discrete threshold extracted at S 605 . 
     As described above, the d n  computed for each mark can be stored in the storage included in the engine controller  2  such as the RAM  20 , ROM  30 , HDD  40 , and/or the external storage. Therefore, the threshold determination processing unit  403   c  can designate “d n ” for each of the density-changed defect pattern and the width-changed defect pattern to the engine control unit  202  by only notifying a position in the Y direction of a mark corresponding to the above described maximum value and minimum value. 
     Further, at S 605 , a discrete threshold can be extracted for each of the density-changed defect pattern and the width-changed defect pattern. Therefore, the threshold determination processing unit  403   c  designates d n  for a mark corresponding to the maximum value and the minimum value of each discrete threshold extracted at S 605  for each of the density-changed defect pattern and the width-changed defect pattern. 
     When the process of S 601  is to be conducted repeatedly, the mark added with the artificial defect corresponding to the maximum value and the minimum value of the discrete threshold, extracted by the process at S 605  by already conducting the threshold setting process once, can be formed as the density-changed defect pattern and the width-changed defect pattern. By conducting the process of  FIG. 6  for the second image and the third image, the threshold can be set more precisely. 
     In the system of an example embodiment, images displaying defects having changed the defect level step-wisely as shown in  FIGS. 7B and 7C  are prepared. By conducting the defect determination process by changing the thresholds step-wisely, discrete thresholds that can detect each of defects having step-wisely changed defect levels can be obtained. Then, the user checks a sheet printed with a given pattern with eyes to select one or more marks to be determined as defect, and determines the finally-set threshold based on the discrete threshold correlated to the selected marks. With this processing, when the image inspection is conducted based on a comparison result obtained by comparing an image generated by scanning an image output by an image forming operation and a master image, the setting of threshold used for determining the defect can be conducted easily and preferably based on the comparison result. 
     Further, in the above described example embodiment, when setting the thresholds, for example, a printing operation of images shown in  FIGS. 7A to 7C  is conducted. With this configuration, for example, a process of changing a range of to-be-set threshold (e.g. S 607  in  FIG. 6 ) can be conducted repeatedly. If the process of changing a range of threshold is not required, bitmap data of image shown in  FIG. 7A  is input to the master image processing unit  402 , and a known scan-use chart having the images similar to the images shown in  FIGS. 7B and 7C  can be scanned by the scanner  302  of the print engine  3 , with which the above described operation can be conducted. 
     Further, in the above described example embodiment, as shown in  FIGS. 11A and 11B , the second image and the third image are displayed on a screen, from which a user can select marks intuitively based on visual information displayed on the screen but not limited hereto. For example, a user can select marks from a list shown in  FIG. 12 , wherein the list includes position information of marks in the X direction and the Y direction, which may be indicated as text information. 
     Further, in the above described example embodiment, as shown in  FIGS. 7B / 7 C and  FIGS. 11A / 11 B, the density-changed defect pattern and width-changed defect pattern are displayed on the screen by arranging marks having different color and levels of artificial defects with a given order, with which a user can easily select an allowable defect in view of the level of artificial defects. Further, the density-changed defect pattern and width-changed defect pattern can be displayed on the screen by arranging marks having different color and levels of artificial defects randomly (i.e., not arranged with a given order), with which a user can select marks without preconception. 
     Further, as explained with reference to  FIGS. 7B and 7C , in an example embodiment, the density-changed defect pattern and the width-changed defect pattern can be reproduced using a plurality of artificial defects having different levels for each of cyan, magenta, yellow and black (CMYK). Because of human perception on colors may differ for each person, the level of artificial defects that can be allowed or not for each one of colors may be different for each person. 
     For example, as for a relatively pale color such as Y, one user may allow a mark corresponding to PY+d 4  shown in  FIG. 8  (i.e., only a mark corresponding to PY+d 5  is selected as to-be-determined defect) while the same user may select marks corresponding to from PK+d 1  to PK+d 5  (i.e., all of marks shown in  FIG. 8 ) as the to-be-determined defect for K. In this case, a threshold set for the mark corresponding to PK+d 1  becomes the strictest value. If this strictest value is applied, the defect of Y that the user determines as allowable may be determined as defect. 
     In this case, the inspection unit  404  can set thresholds step-wisely to enhance the user&#39;s convenience. Specifically, the finally set threshold may include a first threshold and a second threshold, in which the first threshold is set to determine defect without confirmation by a user, and the second threshold is set to determine defect based on a selection of a user. 
     In this case, at S 605  ( FIG. 6 ), the threshold determination processing unit  403   c  extracts the strictest value as a threshold corresponding to the selected mark for each of artificial defects of each of colors, that is for each of rows in the table shown in  FIG. 9 . Then, among the thresholds extracted for each of colors, the threshold determination processing unit  403   c  sets a value having a broadest allowable range as the first threshold, with which a smaller number of defects are determined as defect, and sets the strictest value as the second threshold, with which a greater number of defects are determined as defect. 
     In this processing, if a defect is determined as defect when the threshold having the broadest allowable range is applied, a user may detect the same defect as defect by visual confirmation with a higher probability, therefore the defect is determined as defect without the confirmation by the user. Further, if a defect is determined as defect when the threshold having the narrowest allowable range is applied, it is not clear whether the user may detect the same defect as defect by visual confirmation, therefore the defect is determined as defect based on the confirmation by the user, with which the defect determination precision can be enhanced. 
     Further, when the setting process of thresholds is conducted repeatedly as explained with reference for S 607  ( FIG. 6 ), the threshold determination processing unit  403   c  can designate the value of d n  such as d m  and d M  of d n  as the value corresponding to the first threshold and the second threshold. 
     Further, in the above described example embodiment, as explained with reference to  FIGS. 11A / 11 B and S 605  ( FIG. 6 ), upon the visual confirmation of artificial defects by the user, a mark is selected, with which the inspection apparatus  4  can determine the finally-set threshold based on the threshold corresponding to the selected mark. With this configuration, the allowable level of defect determination can be set easily based on the user&#39;s visual confirmation. 
     Further, even without the user&#39;s selection operation, by setting the threshold based on a difference between a normal image such as the first image shown in  FIG. 7A  and artificial defect images such as the second and third images shown in  FIGS. 7B and 7C , which are images added with artificial defects, the threshold corresponding to the condition of the scanner  302  can be set. Therefore, by omitting the process of S 605  ( FIG. 6 ), the threshold can be set automatically based on the difference between the master image generated for the normal image and the scanned image data of the image added with artificial defects. 
     Further, in the above example embodiment, as shown in  FIG. 1 , the DFE  1 , the engine controller  2 , the print engine  3  and the inspection apparatus  4  are separate apparatuses with each other. The DFE  1 , the engine controller  2  and the print engine  3  shown in  FIG. 1  can be included in image forming apparatuses such as printers, which are not image forming apparatuses for commercial printing machines such as production printers. 
     For example, as shown in  FIG. 13A , the inspection apparatus  4  can be connected to a printer having the DFE  1 , the engine controller  2  and the print engine  3 . Further, as shown in  FIG. 13B , a printer having the DFE  1 , the engine controller  2 , the print engine  3  and the inspection apparatus  4  can be configured as one printer. 
     Further, in the above example embodiment, the DFE  1 , the engine controller  2 , the print engine  3  and the inspection apparatus  4  are connected with each other via a local interface such as universal serial bus (USB), peripheral component interconnect express (PCIe) or the like to configure the system. However, the inspection apparatus  4  is not required to be placed at the same site of the DFE  1 , the engine controller  2  and the print engine  3 , but the inspection apparatus  4  can be provided as an application for the system, for example, via a network. 
       FIG. 14  shows one example configuration that the function of the inspection apparatus  4  is provided via the network, in which the engine controller  2  and the print engine  3  may be connected to the inspection apparatus  4  via a public line  5  such as the Internet. The engine controller  2  and the print engine  3  can transmit information to the inspection apparatus  4  via the public line  5 . Further, the inspection apparatus  4  can transmit an inspection result to the engine controller  2  via the public line  5 . In this configuration, the inspection apparatus  4  is not required at a user site, with which an initial cost of the user can be reduced. 
     Further, in the configuration shown in  FIG. 14 , the user cannot control the inspection apparatus  4  directly because the function of the inspection apparatus  4  is provided via the network. In this configuration, the screens shown in  FIGS. 11A / 11 B and  FIG. 12  and other screens for controlling the inspection apparatus  4  can be displayed on an information processing apparatus such as a personal computer (PC) connectable to the network via a web browser, with which the user can use the system similar to the above example embodiment. 
     Further, in the above example embodiment, the first image, the second image and the third image are formed on different sheets, but not limited hereto. For example, the first image, the second image, and the third image can be formed on the same sheet, in which the master image processing unit  402  generates a master image by extracting an area displaying the first image, and further, the scanned image obtainer  401  extracts an area displaying the second image and the third image from the scanned image, and uses the extracted area as the scanned image data for the inspection target. 
     Further, in the above example embodiment, the levels of artificial defect can be changed by changing the defect density and/or defect range (e.g., width of defect), but not limited thereto. For example, other parameters of image can be used and changed as required. Further, in the above example embodiment, each parameter can be changed separately, but parameters can be changed with some combinations. 
     Further, in the above example embodiment, when the threshold determination process is conducted, the modules used for the normal inspection process such as the master image processing unit  402 , the inspection unit  404  or the like can be controlled by the master image generation controller  403   a  and the image comparison inspection controller  403   b , and the threshold determination processing unit  403   c  and the UI controller  403   d  can be operated based on information obtained by the control, with which the modules can collectively function as a threshold determiner. With this configuration, the configuration of apparatus can be simplified by using each module effectively. Further, because the same or similar modules used for the normal inspection process can be used for the above example embodiment, the threshold can be effectively determined under the same or similar condition of the normal inspection process, but the configuration is not limited hereto. 
     For example, some specific modules can be employed for the master image generation controller  403   a  and the image comparison inspection controller  403   b  of the above example embodiment, in which a master image generation module and an image comparison inspection module specifically employed for the threshold determination process can be provided, which means an inspection reference image generation unit that generates an inspection reference image having normal image condition to be used for the image inspection, and an image comparison inspection unit that computes a difference between the scanned image of the threshold setting image and the inspection reference image can be provided. 
     Further, in the above example embodiment, the threshold determination processing unit  403   c  and the UI controller  403   d  are configured in the inspection control unit  403 , but the configuration is not limited hereto. For example, a specific module for the threshold determination processing unit  403   c  and a specific module for the UI controller  403   d  can be provided separately from the inspection control unit  403 . 
     In the above described example embodiment, an image inspection can be conducted by comparing an image obtained by scanning an image output by an image forming operation and a master image, and based on a comparison result, setting of threshold used to determine defect can be conducted easily and preferably. 
     The present invention can be implemented in any convenient form, for example using dedicated hardware, or a mixture of dedicated hardware and software. The present invention may be implemented as computer software implemented by one or more networked processing apparatuses. The network can comprise any conventional terrestrial or wireless communications network, such as the Internet. The processing apparatuses can compromise any suitably programmed apparatuses such as a general purpose computer, personal digital assistant, mobile telephone (such as a Wireless Application Protocol (WAP) or 3G-compliant phone) and so on. Since the present invention can be implemented as software, each and every aspect of the present invention thus encompasses computer software implementable on a programmable device. 
     The computer software can be provided to the programmable device using any storage medium, carrier medium, carrier means, or digital data carrier for storing processor readable code such as a flexible disk, a compact disk read only memory (CD-ROM), a digital versatile disk read only memory (DVD-ROM), DVD recording only/rewritable (DVD-R/RW), electrically erasable and programmable read only memory (EEPROM), erasable programmable read only memory (EPROM), a memory card or stick such as USB memory, a memory chip, a mini disk (MD), a magneto optical disc (MO), magnetic tape, a hard disk in a server, a solid state memory device or the like, but not limited these. 
     The hardware platform includes any desired kind of hardware resources including, for example, a central processing unit (CPU), a random access memory (RAM), and a hard disk drive (HDD). The CPU may be implemented by any desired kind of any desired number of processor. The RAM may be implemented by any desired kind of volatile or non-volatile memory. The HDD may be implemented by any desired kind of non-volatile memory capable of storing a large amount of data. The hardware resources may additionally include an input device, an output device, or a network device, depending on the type of the apparatus. Alternatively, the HDD may be provided outside of the apparatus as long as the HDD is accessible. In this example, the CPU, such as a cache memory of the CPU, and the RAM may function as a physical memory or a primary memory of the apparatus, while the HDD may function as a secondary memory of the apparatus. 
     In the above-described example embodiment, a computer can be used with a computer-readable program, described by object-oriented programming languages such as C++, Java (registered trademark), JavaScript (registered trademark), Perl, Ruby, or legacy programming languages such as machine language, assembler language to control functional units used for the apparatus or system. For example, a particular computer (e.g., personal computer, work station) may control an information processing apparatus or an image processing apparatus such as image forming apparatus using a computer-readable program, which can execute the above-described processes or steps. In the above described embodiments, at least one or more of the units of apparatus can be implemented in hardware or as a combination of hardware/software. In example embodiment, processing units, computing units, or controllers can be configured with using various types of processors, circuits, or the like such as a programmed processor, a circuit, an application specific integrated circuit (ASIC), used singly or in combination. 
     Numerous additional modifications and variations are possible in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the disclosure of the present invention may be practiced otherwise than as specifically described herein. For example, elements and/or features of different examples and illustrative embodiments may be combined each other and/or substituted for each other within the scope of this disclosure and appended claims.