Image inspecting apparatus, computer-readable recording medium storing a program, image processing apparatus, and image forming apparatus

An inspection image is assumed to contain many abnormalities when a reference image and an inspection image are misaligned. It has been impossible to determine whether the abnormalities are attributed to the inspection image. An image inspecting apparatus includes: a print alignment portion that aligns a print position of a reference image with a print position of an inspection image; an abnormality detector that detects an abnormality in the inspection image based on a difference between the reference image and the inspection image after print positions are aligned; and a print alignment result evaluator that evaluates a print position alignment result from aligning a print position of the reference image with a print position of the inspection image including an abnormality detected based on dispersion of the difference included in an evaluation region around an edge calculated from a printout image included in the reference image.

CROSS-REFERENCE TO RELATED APPLICATIONS

The entire disclosure of Japanese Patent Application No. 2019-7496, filed on Jan. 21, 2019, is incorporated herein by reference in its entirety.

BACKGROUND

Technological Field

The present invention relates to an image inspecting apparatus, a computer-readable recording medium storing a program, an image processing apparatus, and an image forming apparatus.

Description of the Related Art

A conventional image inspection detects an image abnormality by reading an image printed on paper and analyzing the read image. This image inspection detects as an image abnormality such as stain or color deviation occurring on the actual printout image when a difference between an original criterial printout image and an actually detected printout image is larger than or equal to a specified value. When an image is printed on many pages, the image may be printed at a position deviated from the original position. Accurate image alignment is critical. It has been necessary to reliably identify a misaligned image.

As described in Patent Literature 1, for example, a range to determine items to be good can be expanded for a contour where pixel values greatly vary.

CITATION LIST

Patent Literature

Patent Literature 1: JP 2013-224833 A

SUMMARY

Conventionally, a reference image is printed at a correct position on paper. An inspection image is used to inspect the alignment. A difference is found between the inspection image and the reference image. The standard deviation to express dispersion of the differences is used to determine whether the inspection image is correctly aligned. The standard deviation decreases if the reference image and the inspection image match. The standard deviation increases if the reference image and the inspection image mismatch. The standard deviation tends to increase when characters are to be aligned. The standard deviation tends to decrease when images other than characters are to be aligned. Misalignment easily disperses differences between the reference image and the inspection image. The inspection image is assumed to contain many abnormalities. In such a case, an operator to inspect images cannot correctly determine whether an abnormality is caused by stain, for example, detected from the inspection image or results from the misalignment.

The technology disclosed in patent literature 1 presupposes that two images are aligned. By using this technology alone, an operator cannot determine whether two images are correctly aligned.

The present invention has been made in consideration of the foregoing. It is an object of the invention to accurately evaluate the results of aligning the printout of an inspection image based on a reference image.

To embody at least one of the above-described objects, according to an aspect of the present invention, an image inspecting apparatus reflecting one aspect of the present invention includes: a reader that reads an image formed by an image forming apparatus on a recording material and generates an inspection image; a print alignment portion that aligns a print position of a reference image used as a reference for a good-item inspection on an image formed on a recording material with a print position of an inspection image; an abnormality detector that detects an abnormality in the inspection image based on a difference between the reference image and the inspection image after print positions are aligned; and a print alignment result evaluator that evaluates a print position alignment result from aligning a print position of the reference image with a print position of the inspection image including an abnormality detected based on dispersion of the difference included in an evaluation region around an edge calculated from a printout image included in the reference image. The difference is calculated from the inspection image including an abnormality detected.

The above-described image inspecting apparatus represents one mode of the present invention. A computer-readable recording medium storing a program, an image processing apparatus, and an image forming apparatus reflecting one aspect of the present invention are also configured similarly to the above-described image inspecting apparatus.

Description of the embodiments below will clarify issues and configuration other than those mentioned above.

DETAILED DESCRIPTION OF EMBODIMENTS

The description below explains the embodiments of the present invention with reference to the accompanying drawings. However, the scope of the invention is not limited to the disclosed embodiments. The present specification and drawings use the same reference numerals or symbols for constituent elements having substantially the same functions or configurations to omit a duplicate description.

First Embodiment

Configuration of the Image Forming System

With reference toFIG. 1, the description below explains an example configuration of the image forming system according to the first embodiment of the present invention.

FIG. 1is a schematic configuration diagram illustrating an image forming system1according to the first embodiment of the present invention.FIG. 1illustrates the elements and associated elements considered to be necessary for the description of the present invention. The image forming system according to the present invention is not limited to the example illustrated inFIG. 1.

The image forming system1includes an image forming apparatus2and an image inspecting apparatus3. The image forming apparatus2provides an example of the image forming apparatus that forms images on paper based on the electrophotographic system to form images by using static electricity. The image forming apparatus2forms color images on paper based on the tandem type that overlays toner images in four colors such as yellow (Y), magenta (M), cyan (C), and black (K). The image forming apparatus2mainly connects with a PC (Personal Computer)70(seeFIG. 2to be described later) manipulated by an operator via an unshown LAN (Local Area Network). The PC70supplies a job to the image forming apparatus2via the LAN. The image forming apparatus2performs various processes such as an image forming process based on the supplied job.

First, an example configuration of the image forming apparatus2will be described.

The image forming apparatus2includes an image input portion11equipped with an auto document feeder (ADF)12and a manipulation display portion13. The image forming apparatus2also includes a printer portion10equipped with a sheet feed tray20and an image forming portion30.

The image input portion11optically reads an image from a document placed on a platen of the ADF12and applies A/D conversion to the read image to generate image data. The image input portion11can also read an image from a document placed on the platen glass.

The manipulation display portion13is comprised of a display portion mainly including a liquid crystal panel and a manipulation portion mainly including a touch sensor. The display portion and the manipulation portion are integrally formed as a touch panel, for example. The manipulation display portion13generates a manipulation signal representing the contents of manipulation entered by an operator from the manipulation portion and supplies the manipulation signal to a controller50(seeFIG. 2to be described later). Based on a display signal supplied from the controller50, the manipulation display portion13allows the display portion to mainly display the manipulation contents or setup information specified by the operator. The manipulation portion may be provided as a mouse or a tablet and may be configured apart from the display portion.

The sheet feed tray20provides a container that contains sheet Sh where the image forming portion30forms images. The sheet feed tray20contains sheets of different sheet types or basis weights. Sheet Sh represents an example of recording materials. The image forming apparatus2can form images on a plastic sheet as an example of recording materials. The present embodiment provides an example of equipping two sheet feed trays20. However, the number of sheet feed trays20may be one or three or more.

The image forming apparatus2includes a transport path21that transports sheet Sh supplied from the sheet feed tray20to the image inspecting apparatus3. The transport path21includes a plurality of transport rollers to transport sheet Sh.

Downstream of a fixing portion36, the transport path21extends to connect with a transport path41of the image inspecting apparatus3. The transport path21branches downstream of the fixing portion36. One end of the branched transport path21connects with a reversing transport path22that joins the transport path21upstream of the printer portion10. The reversing transport path22includes a reversing portion23that reverses sheet Sh. Sheet Sh, after reversed by the reversing portion23, passes through the reversing transport path22and returns upstream of the transport path21. When sheet Sh is reversed due to a path change, sheet Sh may return to the transport path21downstream of the fixing portion36and then transported to the image inspecting apparatus3.

The image forming portion30includes four image forming units31Y,31M,31C, and31K to form toner images in colors Y, M, C, and K and forms images on sheet Sh. The image forming units31Y,31M,31C, and31K each include unshown chargers, unshown exposers, photosensitive drums32Y,32M,32C, and32K as image carriers, and developers33Y,33M,33C, and33K.

The developers33Y,33M,33C, and33K radiate the light corresponding to an image onto surfaces (outer peripheries) of the photosensitive drums32Y,32M,32C, and32K to form electrostatic latent images on the peripheries of the photosensitive drums. The developers33Y,33M,33C, and33K apply the toner to the electrostatic latent image to form toner images on the photosensitive drums32Y,32M,32C, and32K.

The image forming portion30includes an interim transfer belt34, a secondary transfer portion35, and the fixing portion36. The interim transfer belt34provides a belt onto which images formed on the photosensitive drums32Y,32M,32C, and32K are primarily transferred. The secondary transfer portion35provides a roller that secondarily transfers the toner images onto sheet Sh transported from the transport path21after the toner images in the respective colors are primarily transferred onto the interim transfer belt34.

The fixing portion36is placed downstream in the paper transportation direction of the secondary transfer portion35and performs a fixing process on sheet Sh that is supplied from the image forming portion30and contains a color toner image formed thereon. The fixing portion36heats and pressurizes the transported sheet Sh to fix the image transferred by the image forming portion30onto the surface of sheet Sh. Sheet Sh containing the image fixed by the fixing portion36passes through the transport path21and is transported to the image inspecting apparatus3. Alternatively, sheet Sh passes through the reversing transport path22to be reversed on both sides by the reversing portion23and is then returned to the transport path21upstream in the printer portion10. The printer portion10forms an image on the reverse side of sheet Sh after reversed. The fixing portion36performs the fixing process on sheet Sh that is then transported to the image inspecting apparatus3.

The description below explains an example configuration of the image inspecting apparatus3.

The image inspecting apparatus3inspects whether an image is formed (printed) at the correct position on sheet Sh transported from the image forming apparatus2. An image processing apparatus5attached to the image inspecting apparatus3performs a process on images formed on sheet Sh, namely the image inspection by the image inspecting apparatus3.

The image inspecting apparatus3includes transport paths41,42, and43to transport sheet Sh transported from the image forming apparatus2, a changer44, readers45aand45b, a colorimeter46, and catch trays47and48where sheet Sh is ejected after transported through the transport path41.

The readers45aand45bexemplify image input devices such as an image sensor. For example, the readers45aand45bradiate the light to the surface of sheet Sh and incorporate the reflected light from sheet Sh as image data. Hereinafter, “reading” signifies an operation of the readers45aand45bto incorporate image data on sheet Sh. The reader45areads sheet Sh transported through the transport path41from under the transport path41. The reader45breads sheet Sh transported through the transport path41from above the transport path41. In the description below, the readers45aand45bare generically denoted as a “reader45” to avoid the distinction. The reader45outputs the incorporated image data to the image processing apparatus5.

The colorimeter46exemplifies a color densitometer that reads an image formed on the surface of sheet Sh transported through the transport path41and measures the color density (reflection density) of the image based on image information acquired by reading the image. For example, the colorimeter46can measure the reflected light intensity (spectrum) for each wavelength of light and outputs the density (reflection density) or L*a*b* values of the measured color. For example, the colorimeter46uses a scanner (line sensor) including a plurality of unshown sensors (photoelectric conversion elements) unidimensionally placed all over the paper width direction (orthogonal to the paper transportation direction). When the colorimeter46is configured as a scanner, the scanner moves in the direction (paper transportation direction) orthogonal to the direction of placing the scanner to read an image. The colorimeter46divides a region to read the image into subregions in the form of a mesh and measures the color density of the image formed on sheet Sh in units of the subregions. The colorimeter46outputs information about the measured color density to the image processing apparatus5.

The colorimeter46may be configured as a single sensor that is two-dimensionally moved to measure the color density of an image formed on sheet Sh. Alternatively, the colorimeter46may be configured as a plurality of sensors two-dimensionally placed (in a matrix) to read color densities of all pixels on the sheet in a single measurement.

The image inspecting apparatus3includes the transport paths42and43connected to the transport path41.

The transport path42branches in the middle of the transport path41and ejects sheet Sh inspected by the image processing apparatus5to the catch tray47(an example paper ejector). The catch tray47accepts ejected sheet Sh (also denoted as a “normal sheet”) whose image is identified as being normal by the image processing apparatus5.

The transport path43also branches in the middle of the transport path41and ejects sheet Sh inspected by the image processing apparatus5to the catch tray48(an example paper ejector). The catch tray48accepts ejected sheet Sh (also denoted as an “abnormal sheet”) whose image is identified as being abnormal by the image processing apparatus5.

The changer44changes the direction of transporting sheet Sh so that sheet Sh is transported to one of the transport paths42and43. A mix of normal and abnormal sheets are ejected to only one catch tray47when provided for the image inspecting apparatus3. In this case, normal and abnormal sheets are ejected to be slightly displaced in the direction orthogonal to the ejection direction.

The image inspecting apparatus3transports sheet Sh as a printed matter containing an image formed on both sides or either side of the printed matter. The image inspecting apparatus3reads the image formed by the image forming apparatus2on both sides or either side of sheet Sh and allows the image processing apparatus5to perform a specified inspection.

The present embodiment enables the image forming apparatus2to form images on both sides of sheet Sh and therefore provides an example where the image processing apparatus5inspects both sides of sheet Sh. However, the image processing apparatus5may inspect only one side of sheet Sh transported from an image forming apparatus that can form images on only one side of sheet Sh.

Configuration of the Control System for the Image Forming Apparatus

With reference toFIG. 2, the description below explains an example configuration of the control system for the image forming apparatus2.

FIG. 2is a block diagram illustrating an example configuration of the control system for the image forming apparatus2.

The image forming apparatus2includes a communication I/F portion51, a sheet transporter24, the image input portion11, the image forming portion30, the controller50, a storage portion52, the fixing portion36, and the manipulation display portion13.

The communication I/F portion51provides an interface that uses a network or a dedicated line to transmit and receive data from the PC70as a terminal manipulated by an operator. The communication I/F portion51uses a NIC (Network Interface Card), for example.

Under control of the controller50, the sheet transporter24drives the transport path21, a transport roller (unshown) provided for the reversing transport path22, and the reversing portion23illustrated inFIG. 1.

The controller50includes a CPU (Central Processing Unit)501, a ROM (Read Only Memory)502, a RAM (Random Access Memory)503, and an input image processor504.

The ROM502stores a program executed by the CPU501of the controller50or data used for the execution of the program. The ROM502is used as an example non-transitory computer-readable storage medium that stores a program executed by the CPU501. The ROM502permanently stores the program. The CPU501reads the program saved in the ROM502and thereby controls the components configuring the image forming apparatus2.

The RAM503temporarily stores variables or parameters generated during an arithmetic operation of the CPU501.

An input image is contained in a job entered from the PC70via the communication I/F portion51. The input image processor504performs a specified image process (such as a rasterization process) on the input image to generate image data for printing. The input image processor504also generates image data for printing by performing the image process on image data acquired from a document read from the image input portion11through the use of the ADF12or externally acquired image data. The image data for printing is transmitted to the image forming portion30.

The controller50controls the sheet transporter24to drive the transport roller and transport sheet Sh through the transport path21. When the input image processor504generates image data for printing, the controller50outputs the image data for printing to the image forming portion30. The controller50controls the image forming portion30to form an image on sheet Sh. The controller50controls the fixing portion36to fix the image on sheet Sh.

The controller50receives a manipulation signal from the manipulation display portion13and provides control corresponding to the manipulation signal. The controller50also outputs a display signal to the manipulation display portion13. The manipulation display portion13allows a display panel to display various setup screens to enter various manipulation instructions or setup information and a manipulation screen to display various process results. The information displayed on the manipulation display portion13includes an abnormal image detection result631and an alignment evaluation result632(seeFIG. 3to be described) output from the image inspecting apparatus3.

The storage portion52may store parameters used for the CPU501of the controller50to execute a program or data acquired by executing the program. For example, the storage portion52stores information such as image formation conditions corresponding to density levels. The storage portion52may store a program executed by the CPU501.

Configuration of the Control System for the Image Inspecting Apparatus

The description below explains an example configuration of the control system for the image inspecting apparatus3with reference toFIG. 3.

FIG. 3is a block diagram illustrating an example configuration of the control system for the image inspecting apparatus3.

The image inspecting apparatus3includes a communication I/F portion61, a sheet transporter62, a reader45, and the colorimeter46. The image processing apparatus5is attached to the image inspecting apparatus3and includes a controller60and a storage portion63. The image processing apparatus5includes a storage device4.

The communication I/F portion61provides an interface that uses a network to transmit and receive data from the image forming apparatus2. The communication I/F portion61uses a NIC, for example.

Under control of the controller60, the sheet transporter62drives a transport roller (unshown) provided for the transport path41illustrated inFIG. 1.

As above, the reader45reads images formed on both sides of sheet Sh transported through the transport path41. The present embodiment inspects image data read by the readers45aand45bto align images. Therefore, image data on sheet Sh is described as an “inspection image.” An image as the reference to compare with the inspection image is described as a “reference image.” The reader45reads the reference image in advance. An operator identifies the reference image as being correct in advance. The reader45can read an image formed on sheet Sh by the image forming apparatus2and generate an inspection image603aand a reference image603b. The present embodiment aligns the inspection image and the reference image to inspect whether a printout image is formed at correct positions corresponding to four corners of sheet Sh.

The RAM603of the controller60saves an image read by the reader45as the inspection image603aor the reference image603b. The inspection image603aand the reference image603bmay be saved in the storage portion63mainly including a large-capacity HDD. The inspection image603aand the reference image603bmay contain the information about the color density output from the colorimeter46to the image inspecting apparatus3.

The controller60includes a CPU601, a ROM602, a RAM603, a print alignment portion604, an abnormality detector605, an evaluation region setup portion606, a print alignment result evaluator607, and a sheet ejection destination selector608.

The CPU601reads the program saved in the ROM602and thereby controls the components configuring the image inspecting apparatus3

The ROM602stores a program executed by the CPU601of the controller60or data used for the execution of the program.

The RAM603temporarily stores variables or parameters generated during an arithmetic operation of the CPU601. As above, the RAM603also saves the inspection image603aand the reference image603b. The RAM603also saves a difference image603cand a parameter603d.

The parameter603dincludes various types of values settled by the controller60. For example, the parameter603dincludes values for M pixels and N pixels to settle an evaluation region82inFIG. 6and threshold value Th calculated during the process inFIG. 8to be described later. The print alignment portion604, the abnormality detector605, the evaluation region setup portion606, the print alignment result evaluator607, and the ejection destination selector608perform various processes based on values read from the parameter603d.

The ROM602is used as an example non-transitory computer-readable storage medium that stores a program executed by the CPU601. The ROM602permanently stores the program. The CPU601reads the program saved in the ROM602to provide functions of the print alignment portion604, the abnormality detector605, the evaluation region setup portion606, the print alignment result evaluator607, and the ejection destination selector608.

The print alignment portion604aligns a print position of the inspection image603awith a print position of the reference image603bas the reference of good-item inspection for an image formed on sheet Sh. Based on a document image input to the image forming apparatus2, the print alignment portion604aligns the print position of the inspection image603awith the print position of the reference image603b. The inspection image603ais generated by reading the same printout images formed on a plurality of sheets Sh. When the document size is unchanged, an image contained in the inspection image603ashould maintain the same print position on a plurality of printed matters. Therefore, the print alignment portion604aligns the inspection image603aread from the RAM603with the position of the reference image603bpreviously stored in the RAM603.

The abnormality detector605detects an abnormality in the inspection image603abased on a difference between the reference image603band the inspection image603aafter both print positions are aligned. The difference between the reference image603band the inspection image603ais represented as the difference image603cat the bottom right inFIG. 5to be described later. The abnormality detector605generates one page of the difference image603ccorresponding to one side of sheet Sh where an image is formed after one-side printing. The abnormality detector605generates two pages of the difference image603ccorresponding to both sides of sheet Sh where an image is formed after both side printing. The generated difference image603cis stored in the RAM603.

The abnormality detector605determines the inspection image603ato be normal if there is no difference between the inspection image603aand the reference image603b. For example, the abnormality detector605determines an image to be normal if the image formed on sheet Sh contains no stain or seam. The abnormality detector605determines an image to be abnormal if the image formed on sheet Sh contains stain or seam. The abnormality detector605compares the reference image603bwith the inspection image603agenerated by reading an image formed on sheet Sh to determine whether the image is formed at the correct position on sheet Sh.

When a page contains stain, the inspection image603afor this page differs from the reference image603b. The abnormality detector605compares the inspection image603awith the reference image603band determines the inspection image603ato be abnormal if a difference is found. Then, the abnormality detector605generates an abnormal image detection result631for each job and stores the abnormal image detection result631in the storage portion63. The abnormal image detection result631contains a collection of abnormal images corresponding to the inspection image603adetermined to be abnormal. The abnormal image detection result631is provided as a PDF (Portable Document Format) file, for example. The abnormal image detection result631contains text-format data such as stain position or size and a page number corresponding to the abnormality occurred, namely, factors causing the abnormality detector605to determine the inspection image603ato be abnormal. The abnormal image detection result631may contain the inspection image603adetermined to be abnormal. The abnormal image detection result631may be stored in the RAM603.

Even though the page contains no stain, for example, inaccurate alignment between the inspection image603aand the reference image603bcauses the inspection image603ato be identified as being abnormal. To solve this, the evaluation region setup portion606settles an evaluation region to evaluate an alignment result.

The evaluation region setup portion606defines a first evaluation-exclusion region that diverges from an edge calculated from the reference image603bup to a first specified quantity and disallows the evaluation of a print position alignment result. For example, the edge of a printout image represents part of the printout image such as a contour that maximizes a change rate for pixel values. The evaluation region setup portion606defines an evaluation region that is apart from the first evaluation-exclusion region, diverges from the edge of the printout image up to a second specified quantity larger than the first specified quantity, and allows the evaluation of a print position alignment result. Besides, the evaluation region setup portion606defines a second evaluation-exclusion region that is apart from the second specified quantity and disallows the evaluation of a print position alignment result.

For example, the evaluation region is represented as a belt-like region (evaluation region82) that diverges from the edge of a printout image for a specified distance as illustrated inFIG. 6to be described later. When the abnormality detector605determines the inspection image603ato be abnormal, the print alignment result evaluator607uses the evaluation region to evaluate the alignment of the inspection image603acompared to the reference image603b.

The print alignment result evaluator607evaluates whether the alignment between the reference image603band the inspection image603acauses a correct result. The print alignment result evaluator607calculates the dispersion (such as standard deviation) of differences that are included in the evaluation region around the edge calculated from a printout image included in the reference image603band are calculated from the inspection image603awhere an abnormality is detected. Based on the difference dispersion, the print alignment result evaluator607evaluates a print position alignment result generated by combining the print position of the reference image603bwith the print position of the inspection image603awhere an abnormality is detected. When the quantity of the difference dispersion exceeds specified threshold value Th, for example, the print alignment result evaluator607evaluates that the inspection image603ais misaligned in comparison with the reference image603b. However, when the abnormality detector605does not detect an abnormality contained in the inspection image603a, the print alignment result evaluator607does not evaluate the print position alignment result.

The evaluation region setup portion606generates an evaluation target region (seeFIG. 9to be described) by dividing the difference image603cinto a specified number of regions after the abnormality detector605generates the difference image603cbased on a difference between the reference image603band the inspection image603a. In this case, the print alignment result evaluator607evaluates the misalignment amount of the inspection image603ain comparison with the reference image603bin units of evaluation target regions. When the amount of dispersion of differences calculated in one or more evaluation target regions exceeds threshold value Th, the print alignment result evaluator607evaluates that the inspection image603ais misaligned with the reference image603b.

The print alignment result evaluator607then generates the alignment evaluation result632for each job and saves the alignment evaluation result632in the storage portion63. The alignment evaluation result632is a collection of alignment errors in the inspection image603adetermined to contain a misaligned print position. The alignment evaluation result632is provided as a PDF file, for example. The alignment evaluation result632contains text-format data such as the inspection image603aand the page number of a page determined by the print alignment result evaluator607to be abnormally aligned.

The alignment evaluation result632is stored in the storage portion63and is also transmitted to the external storage device4connected to the image inspecting apparatus3. The storage device4may be provided as USB (Universal Serial Bus) memory, SSD (Solid State Drive), or HDD (Hard Disk Drive) connected to the image inspecting apparatus3. When the alignment evaluation result632is transmitted to the storage device4, an operator can display the alignment evaluation result632stored in the storage device4and confirm the contents. The alignment evaluation result632may be transmitted to and stored in a cloud server or the PC70connected via the communication I/F portion61.

As needed, the controller60transmits the abnormal image detection result631and the alignment evaluation result632read from the storage portion63to the image forming apparatus2or the PC70via the communication I/F portion61. The image forming apparatus2can display the abnormal image detection result631and the alignment evaluation result632on the manipulation display portion13. Therefore, the operator on the image forming apparatus2and the image inspecting apparatus3can confirm the contents of the abnormal image detection result631and the alignment evaluation result632by using the manipulation display portion13. The operator can also confirm the contents of the abnormal image detection result631and the alignment evaluation result632by using the PC70.

The print alignment result evaluator607can direct the image forming apparatus2to perform a “recovery process” via the communication I/F portion61. The recovery process reprints the page corresponding to the inspection image603adetermined to be abnormal. The recovery process can allow the image forming apparatus2to regenerate the image corresponding to the inspection image603athe print alignment result evaluator607evaluated as an “alignment error” indicating the misalignment. The recovery process is performed automatically by the image forming system1or manually by the operator. However, the recovery process, if performed, increases the processing time for the image forming apparatus2. Therefore, the operator to use the image forming system1can previously determine whether to perform the recovery process on the image forming apparatus2when an abnormality is identified.

When configured to perform the recovery process, the image forming apparatus2automatically performs the recovery process on the page corresponding to the inspection image603adetermined to contain an abnormality or an alignment error based on the directive from the print alignment result evaluator607. As above, normal sheets are ejected to the catch tray47and abnormal sheets are ejected to the catch tray48. Therefore, the catch tray47collects only ejected normal sheets that are printed by an initial image formation process or the recovery process.

The sheet ejection destination selector608selects the catch tray (an example ejection destination) for sheet Sh transported via the transport path41based on results from the abnormality detector605and the print alignment result evaluator607. For example, the abnormality detector605determines that an image formed on sheet Sh is not abnormal, namely, normal. Then, sheet Sh is identified as a normal sheet. The sheet ejection destination selector608operates the changer44to transport the normal sheet through the transport path42and ejects the normal sheet to the catch tray47. Meanwhile, the abnormality detector605determines that an image formed on sheet Sh is abnormal. Then, sheet Sh is identified as an abnormal sheet. Sheet Sh is also identified as an abnormal sheet when the print alignment result evaluator607determines that sheet Sh is misaligned. The sheet ejection destination selector608operates the changer44to transport the abnormal sheet through the transport path43and ejects the abnormal sheet to the catch tray48.

The description below explains a method of evaluating the alignment according to the present embodiment with reference toFIGS. 4 through 7.

FIG. 4is an explanatory diagram illustrating how to find a difference between the inspection image603aand the reference image603b.

Graph (1) at the upper part ofFIG. 4illustrates a result of plotting pixel values for the inspection image603aand the reference image603bat the same position in an image. If the inspection image603aand the reference image603bare misaligned, the inspection image603aand the reference image603bare also differently positioned. Therefore, the inspection image603aand the reference image603bare represented as two normal distribution graphs.

Graph (2) at the lower part ofFIG. 4illustrates the difference image603cgenerated by using differences between the inspection image603aand the reference image603b. Pixel values of the difference image603care normalized to take specified values within the range between “0” and “255.” If the difference image603cis monochrome, for example, pixel value “0” represents black and pixel value “255” represents white.

At the left of graph (1), the inspection image603aand the reference image603bdo not overlap. The difference image603cindicates pixel value 0. The difference image603cindicates pixel value 128 at the point where the inspection image603acoincides with the reference image603bin terms of pixel values. At the right of graph (1), the inspection image603aand the reference image603bdo not overlap. The difference image603cindicates pixel value 255. Then, the difference image603cis gradationally represented per pixel values as illustrated inFIG. 5.

If the inspection image603aand the reference image603bare aligned, the inspection image603aand the reference image603bare represented as one normal distribution graph. The difference image603cindicates pixel value 128. The difference image603cis represented with constant density.

FIG. 5is an explanatory diagram illustrating specific examples of the reference image603band the inspection image603a. The description below explains the inspection image603aand the reference image603bread from sheet Sh where an image of character “A” is formed.

The abnormality detector605acquires a difference between the inspection image603aand the previously generated reference image603bto detect an abnormality in the inspection image603a. For example, the reference image603billustrated in the upper part ofFIG. 5contains only character “A.” The inspection image603ais assumed to contain a stain75around character “A.” The reference image603bincludes only character “A” as an example of the printout image. The inspection image603aincludes character “A” and the stain75as an example of the printout image.

When the inspection image603aand the reference image603bare not misaligned and are therefore normally aligned, as illustrated at the bottom left ofFIG. 5, character “A” does not appear in the difference image603cand a stain71with pixel value “255” appears at the positions corresponding to the stain75. Except for the stain71, the difference image603cis generated with the constant density of pixel value “128.” The abnormality detector605determines the inspection image603ato be abnormal based on the stain71appearing in the difference image603c.

When the inspection image603aand the reference image603bare misaligned and are therefore abnormally aligned, as illustrated at the bottom right ofFIG. 5, character “A” appears with the stain71of pixel value “255.” In this case, character “A” is represented as a character72in white of pixel value “255” and a character73in black of pixel value “0.” The abnormality detector605determines the inspection image603ato be abnormal based on the characters72and73in addition to the stain71appearing in the difference image603c.

The characters72and73appearing in the difference image603care all determined as abnormal images without evaluation on the alignment between the reference image603band the inspection image603a. Even if the stain75is not attached to the inspection image603a, misalignment between the reference image603band the inspection image603amay cause the abnormality detector605to determine the inspection image603ato be abnormal. When an abnormality is detected in the inspection image603a, it is necessary to confirm whether the inspection image603ais normally aligned. Standard deviation D (example difference dispersion) is calculated from pixel values of pixels configuring the difference image603cand is used to evaluate whether an alignment result is normal. The difference image603cat the bottom left ofFIG. 5shows a normal alignment result. The difference image603cat the bottom right ofFIG. 5shows an abnormal alignment result. Standard deviation D for the difference image603cat the bottom right is obviously larger than standard deviation D for the difference image603cat the bottom left.

However, the actual alignment somewhat causes differences around the edge due to causes such as dispersion of image distortion during printing. Therefore, the image forming apparatus2permits misalignment of the inspection image603ato a certain degree. It is possible to permit the misalignment by changing difference-based detection levels depending on the vicinity of the printout image edge and regions other than the edge. For example, the misalignment at a level determined to be normal can determine the inspection image603ato be normal. Alignment results are not evaluated at a region adjacent to the character image.

Standard deviation D is unaffected even if misalignment occurs in a uniform image region or an image region that is considerably distant from the edge and contains no printout image. Such a region, if used to evaluate the alignment, decreases the value of standard deviation D and lowers the sensitivity to detect the misalignment. Therefore, the present embodiment does not evaluate alignment results on the region that is considerably distant from the edge of a printout image.

With reference toFIG. 6, the description below explains a range to permit the misalignment of the inspection image603a.FIG. 6is an explanatory diagram illustrating regions used to evaluate alignment results. The description below uses an enlarged version of character “A” contained in the reference image603b. A region to form character “A” is described as a character image region80.

Alignment results are not evaluated in a belt-like region that is adjacent to the edge of character “A” and is formed along character “A.” This region is described as a first evaluation-exclusion region81. The width of the first evaluation-exclusion region81is expressed in the length of N pixels, for example. The size of the first evaluation-exclusion region81is settled based on the amount of misalignment that may occur when character “A” is normally printed. The alignment is evaluated to be correct within the first evaluation-exclusion region81even if character “A” contained in the inspection image603ais misaligned.

Alignment results are evaluated in a belt-like region that is formed along the first evaluation-exclusion region and is described as the evaluation region82. The width of the evaluation region82is expressed in M−N pixels (M>N), for example. An alignment error is evaluated within the evaluation region82when character “A” contained in the inspection image603ais misaligned.

The evaluation region setup portion606can find the evaluation region82based on the maximum size of character “A” that may result from partial variable magnification applied to character “A.” However, an excessive increase in the evaluation region82reduces the sensitivity to evaluate alignment results (or to determine whether the misalignment occurs). The evaluation region setup portion606may previously vary the size of the evaluation region82in various types of images and find the size that starts reducing the sensitivity to evaluate alignment results. This size may be used as the evaluation region82.

Alignment results are not evaluated in a region that is distant from the edge of character “A” by M pixels or more and is described as a second evaluation-exclusion region83. A misprint is likely to occur when character “A” contained in the inspection image603ais misaligned up to the second evaluation-exclusion region83. The abnormality detector605determines the inspection image603ato be abnormal.

FIG. 7is an explanatory diagram illustrating the relationship between the edge of character “A” and threshold value Th.

Enlarged image (1) inFIG. 7shows a partially enlarged part of character “A.” The description below explains changes in pixel values of character “A” along a line90crossing character “A.”

Graph (2) inFIG. 7shows changes in pixel values of character “A.” A solid line91indicates pixel value “255” corresponding to white or the absence of character “A” and pixel value “0” corresponding to black or the presence of character “A.” Threshold value Th is settled to determine the abnormality of the inspection image603a. When the background color of character “A” is white, for example, the left part of graph (2) is also white. When this part contains a stain, for example, the solid line91varies to drop. When threshold value Th “70” is settled for the white part, the inspection image603ais determined to be abnormal if there is darkening or stain corresponding to the pixel value smaller than 70.

When the color of character “A” is black and threshold value Th for the white part is unchanged, character “A” is determined to be stained and the inspection image603ais determined to be abnormal. To solve this, the part of character “A” changes to increase threshold value Th. For example, when threshold value is set to “255,” the character image region of character “A” is assumed to contain no whitish contamination even if the black color is pale or a gray point is mixed in the character image region of character “A.”

To inhibit misalignment of character “A,” threshold value Th1indicated by a broken line is set to rise at the position corresponding to the edge of character “A.” In this case, an alignment error is evaluated even if the inspection image603ais slightly misaligned with the reference image603b.

However, the edge of character “A” is not always clear. The edge of character “A” may be blurred due to noise such as bleeding. In such a case, threshold value Th2is set to gently rise within a specified range on condition that misalignment of character “A” is permitted to a certain degree. The range to raise threshold value Th2is defined to correspond to the length of 1 mm from the edge of character “A.” The length of this range represents the length of M−N inFIG. 6, for example. The inspection image603ais not unconditionally determined to be abnormal in the range to raise threshold value Th2even if noise occurs at the edge of character “A.” As above, changes in the threshold value Th can settle the evaluation region82as illustrated inFIG. 6.

The description below explains an alignment evaluation process performed in the image inspecting apparatus3.

FIG. 8is a flowchart illustrating a process for the image inspecting apparatus3to evaluate the inspection image603a.

The print alignment portion604previously aligns print positions of the inspection image603aread from the RAM603with the reference image603b(S1). The abnormality detector605finds a difference between the reference image603band the inspection image603a(S2), generates the difference image603c, and, based on the difference image603c, determines whether the inspection image603ais abnormal (S3). If the inspection image603ais not abnormal (NO in S3), the abnormality detector605determines the inspection image603ato be normal (S14) and terminates the process.

The sensitivity for differences is reduced around the edge of the reference image603b. If the inspection image603ais abnormal (YES in S3), the stain71appears in the difference image603cas illustrated at the bottom left inFIG. 5. In this case, the evaluation region setup portion606calculates the edge of a printout image such as a character contained in the reference image603b(S4).

The evaluation region setup portion606expands an edge region by N pixels to generate region N (S5) and expands the edge region by M pixels to generate region M (S6). The edge region here denotes a character image region representing character “A” illustrated inFIG. 6and a printout image containing the edge whose alignment result is to be evaluated. Region M corresponds to the range from the edge of character “A” illustrated inFIG. 6to the evaluation region82. Region N corresponds to the range from the edge of character “A” to the first evaluation-exclusion region81.

The evaluation region setup portion606defines misalignment evaluation region A or a region that is included in region M and is not included in region N (S7). Misalignment evaluation region A corresponds to a remainder resulting from subtracting region N from region M, namely, the evaluation region82as illustrated inFIG. 6.

The print alignment result evaluator607divides the difference image603cinto S×T regions (S8). The description below explains the difference image603cdivided into S×T regions with reference toFIG. 9.

FIG. 9is an explanatory diagram illustrating the difference image603cdivided into S×T regions.

The difference image603cis horizontally divided into S (2) and is vertically divided into T (4) to be represented by eight evaluation target regions. For example, a combination of (S, T) is used to represent the evaluation target regions. Evaluation target regions (1, 1), (1, 2), (1, 3), (2, 1), (2, 2), and (2, 3) contain parts of character “A.” However, evaluation target regions (1, 4) and (2, 4) do not contain parts of character “A.”

The present embodiment divides the difference image603cinto S×T evaluation target regions and evaluates the result of aligning the evaluation target regions. For example, when the alignment of inspection image603aincreases misalignment in parts of the inspection image603acontaining a small amount of information (such as regions (1, 4) and (2, 4) in the difference image603cillustrated inFIG. 9), the calculation of standard deviation D for the entire image may decrease the value of standard deviation D.

As illustrated inFIG. 9, the print alignment result evaluator607divides the difference image603cinto eight based on S=2 and T=4 and evaluates the amount of misalignment in the evaluation target regions. The print alignment result evaluator607determines that the inspection image603ais misaligned when standard deviation D exceeds threshold value Th in one or more evaluation target regions.

Returning to the description ofFIG. 8, the print alignment result evaluator607calculates standard deviation D for misalignment evaluation region A in each evaluation target region of the difference image603cthat is divided into a plurality of evaluation target regions in step S8(S9).

The print alignment result evaluator607calculates threshold value Th corresponding to an edge amount of the evaluation target region (S10). A region containing part of character “A” (edge region) is used as the evaluation target region for alignment results. A region not containing part of character “A” is not used as the evaluation target region.

The print alignment result evaluator607changes threshold value Th calculated in step S10depending on the edge amount of a printout image contained in the evaluation target region. The alignment result evaluation according to the present embodiment sometimes causes the evaluation result to generate a larger numeric value (standard deviation D) from a photo image containing an unclear edge having a small edge amount than from an image containing a clear edge. Therefore, threshold value Th may be decreased corresponding to a large amount of the edge contained in an image (such as characters and graphics). Threshold value Th may be increased corresponding to a small amount of the edge contained in an image (such as photos).

The print alignment result evaluator607determines whether there is an evaluation target region satisfying standard deviation D>threshold value Th (S11). If each evaluation target region satisfies standard deviation D≤threshold value Th (NO in S11), the print alignment result evaluator607determines the inspection image603ato be abnormal (S12). The print alignment result evaluator607generates the abnormal image detection result631and then terminates the process.

If there is at least one evaluation target region satisfying standard deviation D>threshold value Th (YES in S11), the print alignment result evaluator607determines the inspection image603aas an alignment error (S13). The print alignment result evaluator607generates the alignment evaluation result632and then terminates the process.

FIG. 10is an explanatory diagram illustrating the display of the alignment evaluation result632. The alignment evaluation result632is saved as a PDF data file, for example.

Proper application software can be used to open the alignment evaluation result632converted into the PDF format. A bookmark is inserted to show the page where an alignment error occurred. The bookmark shows the error content such as “alignment error occurred.” When an operator selects the bookmark, the right part of the screen shows the difference image603cdetermined to cause an alignment error. The operator can confirm the number of alignment errors occurred or the page where the alignment error occurred, for example.

The abnormality detector605may save the abnormal image detection result631as a PDF-format data file. Proper application software may be used to open the abnormal image detection result631to display the inspection image603adetermined to be abnormal. Also, in this case, the operator can select a bookmark showing “abnormal image occurred” and confirm the occurrence of an abnormal image or the page containing the abnormal image occurred, for example.

The image inspecting apparatus3according to the first embodiment described above evaluates the result of aligning the inspection image603abased on the difference image603cgenerated from a difference between the reference image603band the inspection image603a. Misalignment between the reference image603band the inspection image603acan be determined by comparing standard deviation D calculated from the difference image603cwith threshold value Th. As above, the result of aligning the inspection image603ais accurately determined. It is possible to easily determine whether the inspection image603aitself contains an abnormality such as stain or is abnormally aligned.

Whether the result of aligning the inspection image603ais normal is determined based on the evaluation region82(seeFIG. 6) generated from an image such as a character contained in the inspection image603a. Therefore, it is possible to accurately determine the occurrence of an alignment error on the inspection image603a.

As illustrated inFIG. 6, the evaluation region82is represented as a belt-like region surrounding the vicinity of the edge of the printout image. However, the evaluation region82may be separated. Only part of the vicinity of the edge may be used as the evaluation region82. The evaluation region82is defined as being remote from the edge by a specified number of pixels. However, the evaluation region82is defined as being remote from the edge by a specified distance.

A printout image may be distorted depending on the types of sheet Sh. For example, compared to normal paper, a printout image formed on rough paper is more easily distorted than a printout image for the reference image603b. In this case, it is favorable to store a relationship between the type of sheet Sh and the evaluation region size in the parameter603d. The evaluation region setup portion606can change the evaluation region size depending on the printout image distortion that varies with types of sheet Sh.

The reader45previously reads an image formed on sheet Sh. An operator confirms the read image that is then used as the reference image603b. However, the input image processor504processes an input image. The processed input image may be used as the reference image603b.

Standard deviation D may be calculated in terms of the difference image603cas a whole without dividing the difference image603cand may be compared to threshold value Th.

The image inspecting apparatus3includes the image processing apparatus5according to the configuration of the present embodiment. However, the PC70may include the function of the image processing apparatus5. The image processing apparatus5may be separated from the image inspecting apparatus3. An image forming system may be configured by providing a server having the function of the image processing apparatus5. The server may store the inspection image603aand the reference image603bthe image inspecting apparatus3reads from sheet Sh. The server may communicate with the image inspecting apparatus3, perform a good-item inspection on the inspection image603areceived from the image inspecting apparatus3, and transmit an evaluation result to the image inspecting apparatus3or the PC70.

Second Embodiment

The description below explains an example configuration of the image forming system according to the second embodiment of the present invention. The image forming system according to the present embodiment is configured so that an image forming apparatus2A includes the function of the image inspecting apparatus3of the image forming system1illustrated inFIG. 1. Therefore, the image forming system according to the present embodiment includes major processing portions of the controller60in the image inspecting apparatus3according to the above-described embodiment.

FIG. 11is a block diagram illustrating an example configuration of an image forming system1A.

The image forming system1A includes the image forming apparatus2A, the storage device4, and the PC70.

The image forming apparatus2A includes a reader53, a colorimeter54, catch trays55and56, and a changer57in addition to the portions included in the image forming apparatus2illustrated inFIG. 2. The reader53, the colorimeter54, the catch trays55and56, and the changer57have functions comparable to those of the reader45, the colorimeter46, the catch trays47and48, and the changer44included in the image inspecting apparatus3according to the first embodiment.

The reader53and the colorimeter54are placed along the transport path21downstream of the fixing portion36.

The reader53exemplifies an image input device such as an image sensor. After an image is formed on sheet Sh, the reader53reads this sheet Sh from above and from below the transport path21and outputs a read image to a controller50A. The CPU501of the controller50A saves the read image as an inspection image503ain the RAM503.

The colorimeter54measures the color density of the image formed on sheet Sh.

The controller50A includes a print alignment portion505, an abnormality detector506, an evaluation region setup portion507, a print alignment result evaluator508, and a sheet ejection destination selector509in addition to the CPU501, the ROM502, the RAM503, the input image processor504illustrated inFIG. 2. The functions added to the controller50A are similar to those of the print alignment portion604, the abnormality detector605, the evaluation region setup portion606, the print alignment result evaluator607, and the sheet ejection destination selector608illustrated inFIG. 3.

The RAM503saves the inspection image503a, a reference image503b, a difference image503c, and a parameter503d, namely, data having the same contents as the data saved in the RAM603of the image inspecting apparatus3.

The parameter503dprovides various types of values settled by the controller50A. The print alignment portion505, the abnormality detector506, the evaluation region setup portion507, the print alignment result evaluator508, and the sheet ejection destination selector509perform processes related to the above-described embodiments based on preset values read from the parameter503d.

The print alignment portion505aligns a print position of the inspection image503awith a print position of the reference image503bused as a reference for the good-item inspection on an image formed on sheet Sh.

The abnormality detector506detects an abnormality in the inspection image503abased on a difference between the reference image503band the inspection image503awhose print positions are aligned.

The evaluation region setup portion507settles an evaluation region to evaluate a print position alignment result so that the evaluation region departs from the first evaluation-exclusion region and departs from the edge by a second specified quantity larger than the first specified quantity. The evaluation region setup portion507generates an evaluation target region (seeFIG. 9) that divides the difference image into a specified number of segments.

The print alignment result evaluator508determines whether the result of aligning the inspection image503awith the reference image503bis correct. The print alignment result evaluator508evaluates the amount of misalignment between the inspection image503aand the reference image503bin each evaluation target region. The print alignment result evaluator508saves the evaluation result of the alignment as an alignment evaluation result522in the storage portion52.

The sheet ejection destination selector608selects the catch tray for sheet Sh transported through the transport path41according to the results from the abnormality detector506and the print alignment result evaluator508. The changer57is selected according to a directive from the sheet ejection destination selector509to change the paper ejection destination of normal paper and abnormal paper.

Similarly to the above-described image forming system1, the image forming system1A according to the second embodiment described above also determines normality or abnormality of the inspection image603aand evaluates the result of aligning the inspection image603awith the reference image603b. The manipulation display portion13or the PC70can display the abnormal image detection result521and the alignment evaluation result522generated from the pertinent processes. An operator can confirm whether the inspection image503acontains an abnormality or causes an alignment error, based on the displayed abnormal image detection result521and the alignment evaluation result522.

The present invention can accurately evaluate a print position alignment result by limiting an evaluation region to evaluate a result of aligning an inspection image with a reference image.

The present invention is not limited to the above-mentioned embodiments. It is further understood by those skilled in the art that various applications and modifications may be made in the present invention without departing from the spirit and scope thereof described in the appended claims.

For example, the above-mentioned embodiments describe, in detail and specifically, configurations of the apparatuses and the system in order to explain the present invention for simplicity but are not limited to an entity including all the configurations that have been described. The configuration of one of the above-mentioned embodiments can be partially replaced by the configuration of another embodiment. The configuration of one embodiment can be added to the configuration of another embodiment. The configuration of each embodiment can be partially subject to addition, deletion, or replacement of another configuration.

The control lines or the information lines are provided on condition that they are considered necessary for the sake of description. The description does not cover all control lines or information lines as products. Practically, almost all the configurations can be interconnected.

REFERENCE SIGNS LIST