Patent ID: 12243221

DESCRIPTION OF THE EMBODIMENTS

Embodiments of the present invention will be described hereinafter in detail, with reference to the accompanying drawings. It is to be understood that the following embodiments are not intended to limit the claims of the present invention, and that not all of the combinations of the aspects that are described according to the following embodiments are necessarily required with respect to the means to solve the problems according to the present invention. Also, a plurality of features may be arbitrarily combined. Note that in the following description an external controller may be referred to as an image processing controller, a digital front end, a print server, a DFE, or the like. An image forming apparatus may be referred to as a multifunction peripheral or an MFP.

First Embodiment

FIG.1is a diagram illustrating an overall configuration of a printing system according to a first embodiment of the present invention.

The printing system includes an image forming apparatus101and an external controller102. The image forming apparatus101and the external controller102are connected to each other via an internal LAN105and a video cable106so as to be able to communicate with each other. The external controller102is connected to be capable of communication with a PC103via an external LAN104, and a print instruction can be issued from the PC103to the external controller102.

A printer driver having a function for converting print data into a print description language (e.g., a page description language (PDL)) that can be processed by the external controller102is installed on the PC103. A user of the PC103can issue print instructions from various applications via the printer driver. In such a case, the printer driver transmits the print data to the external controller102based on the print instruction from the user. Upon receiving a print instruction from the PC103, the external controller102performs analysis and rasterization processing of the print data to create image data for printing, inputs the image data into the image forming apparatus101, then performs a print instruction.

Next, the image forming apparatus101will be described.

A plurality of apparatuses having different functions are connected to the image forming apparatus101, which is configured to be capable of complicated printing processes such as bookbinding. A printing apparatus107forms (prints) an image on a sheet conveyed from a paper feeder located at a lower portion of the printing apparatus107using toners. The configuration and the operation principle of the printing apparatus107are as follows. Light rays such as laser beams modulated in accordance with the image data are reflected by a rotating polygonal mirror such as a polygonal mirror and irradiated on the photosensitive drum as scanning light. The electrostatic latent image formed on the photosensitive drum by the laser beam is developed by the toner, and the toner image is transferred to the sheet adhered to the transfer drum. A full color image is formed on a sheet by sequentially executing this series of image forming processes for yellow (Y), magenta (M), cyan (C), and black (K) toners. The sheet on the transfer drum on which the full-color images have been thus formed are conveyed to a fixing unit. The fixing unit includes a roller, a belt, and the like; a heat source such as a halogen heater is incorporated in the roller; and the toner on the sheet to which the toner image has been transferred is dissolved by heat and pressure to fix it to the sheet.

An inserter108can insert, at a desired position, a sheet into a group of sheets printed and conveyed by the printing apparatus107.

A verification apparatus109reads the image of the conveyed sheet and compares it with a preregistered correct image to determine whether the printed image is normal or not.

A large-capacity stacker110is capable of stacking and storing a large number of sheets. A finisher111performs a finishing process on the conveyed sheet. The finishing process includes processing such as stapling, punching, saddle-stitch book binding, and the like, and the sheet bundle on which the finishing process has been performed is discharged to a discharge tray.

Although the printing system ofFIG.1has a configuration in which the external controller102is connected to the image forming apparatus101, the present invention is not limited to the configuration in which the external controller102is connected. That is, the configuration may be such that the image forming apparatus101is directly connected to the external LAN104and the print data is directly transmitted from the PC103to the image forming apparatus101. In this case, data analysis and rasterization processing, then printing processing are performed in the image forming apparatus101.

FIG.2AandFIG.2Bare block diagrams for describing hardware configurations of the image forming apparatus101, the external controller102, and the PC103according to the first embodiment.

First, the configuration of the external controller102will be described with reference toFIG.2A.

The external controller102includes a CPU208, a memory209, an HDD210, a keyboard211, a display212, a LAN I/F (interface)213, a LAN I/F214, and a video I/F215, which are connected via a bus216. The CPU208deploys in the memory209a program stored in the HDD210, executes the deployed program, then performs processing such as receiving print data from the PC103, RIP processing, and transmitting print data to the image forming apparatus101. The memory209has a RAM, stores programs and data required when the CPU208performs various processes, and operates as a work area. The HDD210stores programs and data required for operations such as print processing. The keyboard211is a device for inputting operation instructions to the external controller102. The display212displays information such as an execution application of the external controller102by a still image or moving image video signals. The LAN I/F213connects with the PC103via the external LAN104and communicates a print instruction and the like. The LAN I/F214connects with the image forming apparatus101via the internal LAN105and communicates a print instruction and the like. The video I/F215connects with the image forming apparatus101via the video cable106and communicates image data and the like.

Next, the configuration of the PC103will be described. The PC103includes a CPU201, a memory202, an HDD203, a keyboard204, a display205, and a LAN I/F206, which are connected via a bus207. The CPU201deploys in the memory202a document processing program stored in the HDD203, executes the deployed program, and executes print data creation and a print instruction. The CPU201also comprehensively controls the devices connected to the system bus. The memory202has a ROM, a RAM, and the like; stores programs and data required when the CPU201performs various processes; and operates as a work area of the CPU201. The HDD203stores programs and data required for operations such as print processing. The keyboard204is a device for inputting operation instructions to the PC103. The display205displays information such as an execution application of the PC103by a still image or moving image video signals. The LAN I/F206connects with the external LAN104and communicates a print instruction and the like.

Next, the configuration of the printing apparatus107, the inserter108, the verification apparatus109, the large-capacity stacker110, and the finisher111of the image forming apparatus101will be described with reference toFIG.2B.

The printing apparatus107of the image forming apparatus101includes a communication I/F217, a LAN I/F218, a video I/F220, an HDD221, a CPU222, a memory223, an operation unit224, and a display225. The printing apparatus107further includes a document exposure unit226, a laser exposure unit227, an image forming unit228, a fixing unit229, and a paper feeder230. These components are connected via a system bus231.

The communication I/F217is connected to the inserter108, the verification apparatus109, the large-capacity stacker110, and the finisher111via a communication cable254and performs communication for controlling the respective devices. The LAN I/F218connects with the external controller102via the internal LAN105and communicates a print instruction and the like. The video I/F220connects with the external controller1021via the video cable106and communicates image data and the like.

The HDD221is a storage device in which programs and data are stored. The CPU222deploys in the memory223a program stored in the HDD221, executes the deployed program, and comprehensively performs image processing control and print control. The memory223has a ROM, a RAM, and the like; stores programs and image data required when the CPU222performs various processes; and operates as a work area of the CPU222. The operation unit224receives an input of various settings and an operation instruction from the user. The display225displays the setting information of the image forming apparatus101, the processing status of a print job, and the like.

The document exposure unit226performs a process of reading a document when a copying function or a scanning function is used. That is, the document exposure unit226reads the document by capturing an image with a CCD camera while illuminating the sheet set by the user with an exposure lamp. The laser exposure unit227performs primary charging for irradiating the photosensitive drum with a laser beam to transfer the toner image and laser exposure. In the laser exposure unit227, primary charging in which the surface of the photosensitive drum is charged to a uniform negative potential is first performed. Next, the laser beam is irradiated on the photosensitive drum by the laser driver while adjusting the reflection angle with the polygonal mirror. As a result, the negative electric charges of the irradiated portion are neutralized and an electrostatic latent image is formed. The image forming unit228is a device for transferring toner to a sheet; includes a developing unit, a transfer unit, a toner supply unit, and the like; and transfers the toner on the photosensitive drum to the sheet. In the developing unit, the negatively-charged toner from the developing cylinder is adhered to the electrostatic latent image on the surface of the photosensitive drum, visualizing the electrostatic latent image. The transfer unit performs primary transfer in which a positive potential is applied to the primary transfer roller to transfer the toner on the surface of the photosensitive drum to the transfer belt and secondary transfer in which a positive potential is applied to the transfer roller to transfer the toner on the transfer belt to the sheet. The fixing unit229is a device for melting and fixing the toner on the sheet to the sheet with heat and pressure and includes a heater, a fixing belt, a pressure belt, and the like. The paper feeder230is a device for feeding the sheet, and the operation for feeding and the operation for conveying the sheet are controlled by the rollers and various sensors.

Next, the configuration of the inserter108of the image forming apparatus101will be described. The inserter108of the image forming apparatus101has a communication I/F232, a CPU233, a memory234, and a feed controller235, which are connected via a bus236. The communication I/F232is connected with the printing apparatus107via the communication cable254and performs communication required for control. The CPU233executes a control program stored in the memory234to perform various controls required for paper feeding. The memory234is a storage device in which the control program is stored. Based on an instruction from the CPU233, the feed controller235controls the paper feeder of the inserter108and the feeding and conveyance of the sheet conveyed from the printing apparatus107while controlling the roller and the sensor.

Next, the configuration of the verification apparatus109of the image forming apparatus101will be described.

The verification apparatus109includes a communication I/F237, a CPU238, a memory239, an imaging unit240, an imaging unit256, a display unit241, and an operation unit242, which are connected via a bus243. The communication I/F237is connected with the printing apparatus107via the communication cable254and performs communication required for control. The CPU238executes a control program stored in the memory239to perform various controls required for verification. The memory239has a ROM and a RAM and stores a control program and the like. It is preferable that the memory239has a large-capacity rewritable non-volatile memory for registering a correct image in a non-volatile manner. Based on an instruction from the CPU238, the imaging unit240and the imaging unit256capture the conveyed sheet and read the image printed on the sheet. The CPU238compares the image data obtained by capturing with the imaging unit240and the imaging unit256with the correct image stored in the memory239and determines whether or not the printed image is normal. The display unit241displays a verification result, a setting screen, and the like. The operation unit242is operated by the user and receives an instruction to change the setting of the verification apparatus109, register a correct image, or the like.

The verification apparatus109according to the first embodiment captures the conveyed sheet, two imaging units240and256capturing the left side of the sheet and the right side of the sheet, respectively. In the configuration ofFIG.3to be described later, two cameras331and334are arranged, and these correspond to the imaging unit240and the imaging unit256, respectively. A specific example will be described later.

Next, the configuration of the large-capacity stacker110of the image forming apparatus101will be described.

The large-capacity stacker110has a communication I/F244, a CPU245, a memory246, and a discharge controller247, which are connected via a bus248. The communication I/F244is connected with the printing apparatus107via the communication cable254and performs communication required for control. The CPU245executes a control program stored in the memory246to perform various controls required for paper discharging. The memory246has a ROM, a RAM, and the like and stores a control program and the like. Based on an instruction from the CPU245, the discharge controller247conveys the conveyed sheet to the stack tray, the escape tray, or the subsequent finisher111.

Next, the configuration of the finisher111of the image forming apparatus101will be described.

The finisher111has a communication I/F249, a CPU250, a memory251, a discharge controller252, and a finishing processing unit253, which are connected via a bus257. The communication I/F249is connected with the printing apparatus107via the communication cable254and performs communication required for control. The CPU250executes a control program stored in the memory251to perform various controls required for finishing and paper discharging. The memory251has a ROM, a RAM, and the like and stores a control program and the like. The discharge controller252controls conveyance and discharge of the sheet based on an instruction from the CPU250. The finishing processing unit253performs the finishing process such as stapling, punching, saddle-stitch book binding, based on an instruction from the CPU250.

In the above description, the external controller102and the image forming apparatus101are connected to each other via the internal LAN105and the video cable106but need only be configured to be capable of transmitting and receiving data required for printing, such as a configuration in which they are connected only via the video cable106. In addition, each of the memory202, the memory209, the memory223, the memory234, the memory239, the memory246, and the memory251need only be a storage device for holding data and a program. For example, configuration may be taken where each has been replaced by a volatile RAM, a non-volatile ROM, a built-in HDD, an external HDD, a USB memory, or the like.

FIG.3depicts an overall cross-sectional view illustrating a mechanism of the image forming apparatus101according to the first embodiment.

First, the printing apparatus107will be described. Paper feed decks301and302can accommodate a plurality of various sheets. Each paper feed deck separates and conveys the uppermost sheet of the accommodated sheets to a sheet conveyance path303. To form a color image, developing stations304to307form toner images using Y, M, C, and K colored toners, respectively. The toner image thus formed is primary transferred to an intermediate transfer belt308. The intermediate transfer belt308is driven to rotate clockwise inFIG.3, and the toner image is transferred to the sheet conveyed from the sheet conveyance path303at a secondary transfer position309. The display225displays information for the printing status and setting of the image forming apparatus101. A fixing unit311fixes the toner image on the sheet to the sheet. The fixing unit311includes a pressure roller and a heating roller, and by the sheet to which the toner image is transferred passing between the rollers, the toner is melted and pressure bonded and the toner image becomes fixed to the sheet. The sheet that has passed through the fixing unit311is conveyed to a conveyance path315through a sheet conveyance path312. When further melting and pressure bonding are required for fixing depending on the type of sheet, the sheet that has passed through the fixing unit311is conveyed to a second fixing unit313via the upper sheet conveyance path. The sheet subjected to additional melting and pressure bonding in the second fixing unit313is then conveyed to the conveyance path315through a sheet conveyance path314. When the image forming mode is double-sided, the sheet after fixing is conveyed to a sheet reversing path316; the sheet reversing path316reverses the front and back of the sheet which then is conveyed to a double-sided conveyance path317; and the image is transferred to the second side of the sheet at the secondary transfer position309.

Next, a configuration of the inserter108for inserting a sheet will be described.

The inserter108includes an inserter tray321and causes the sheets fed through a sheet conveyance path322to join the conveyance path315. As a result, it becomes possible to insert a sheet at a desired position in a series of sheets conveyed from the printing apparatus107, then convey the sheets to a succeeding apparatus.

The sheet that has passed through the inserter108is conveyed to the verification apparatus109. Inside the verification apparatus109, the cameras331and334,332and335are arranged in a form in which they are facing each other. The cameras331and334are cameras for reading the top surface of the sheet, and the cameras332and335are cameras for reading the bottom surface of the sheet. The verification apparatus109reads an image of the sheet using the cameras331and334, and332and335at a timing when the sheet conveyed to a sheet conveyance path333reaches a predetermined position, then can determine whether or not the image printed on the sheet is normal. The display unit241displays results of verifications performed by the verification apparatus109and the like.

Next, a configuration of the large-capacity stacker110on which a large number of sheets can be stacked will be described.

The large-capacity stacker110has a stack tray341as a tray on which sheet are stacked. A sheet that has passed through the verification apparatus109is inputted to the large-capacity stacker110through a sheet conveyance path344. The sheet is stacked on the stack tray341from the sheet conveyance path344through a sheet conveyance path345. The large-capacity stacker110also has an escape tray346as a discharge tray. The escape tray346is a discharge tray used for discharging a sheet determined to be a defective sheet by the verification apparatus109. When discharging the sheet to the escape tray346, the sheet is conveyed from the sheet conveyance path344to the escape tray346via a sheet conveyance path347. When conveying the sheet to a post-processing apparatus downstream of the large-capacity stacker110, the sheet is conveyed through a sheet conveyance path348. A reversing unit349is a mechanical unit for reversing the front and back of the sheet. The reversing unit349is used for when stacking sheets on the stack tray341. When stacking the sheets on the stack tray341such that the direction of the inputted sheet and the direction of the sheet at the time of output are the same, the sheet is reversed once in the reversing unit349. When conveying the sheet to the escape tray346or a subsequent post-processing apparatus (finisher111), the sheet is discharged as is without flipping it at the time of stacking, so the reversal operation of the sheet by the reversing unit349is not performed.

The finisher111can perform post-processing on the conveyed sheet in accordance with the function specified by the user. More specifically, the finisher111has a finishing function such as stapling (binding at one place or two places), punching (two holes or three holes), and saddle stitch bookbinding. The finisher111includes two discharge trays351and352, and the sheet bundle on which the finishing process is not to be performed is outputted to the discharge tray351via a sheet conveyance path353. When the finishing process such as stapling is performed, the fed sheet is sent to a processing unit355via a sheet conveyance path354, the finishing function specified by the user is executed, and the sheet is outputted to the discharge tray352. The discharge trays351and352can each be moved up and down, making it possible to move down the discharge tray351and stack on the discharge tray351the sheets on which the finishing process has been performed by the processing unit355. When the saddle stitch bookbinding is designated, a saddle stitching processing unit356performs stapling processing on the center of the sheet bundle, and thereafter, the sheet bundle is folded in two and outputted to a saddle stitch bookbinding tray358via a sheet conveyance path357. The saddle stitch bookbinding tray358has a conveyor-belt configuration and is configured such that the saddle stitch bookbinding bundle stacked on the saddle stitch bookbinding tray358is conveyed to the left side ofFIG.3.

FIG.4Ais a flowchart for describing a process for when the verification apparatus109registers a correct image according to the first embodiment. The process illustrated in the flowchart is achieved by the CPU238of the verification apparatus109executing the above-described program deployed in the memory239.

First, in step S401, the CPU238reads the conveyed sheet (printed sheet) with the imaging units240(camera331) and256(camera334) and stores in the memory239the image data obtained by the reading. Next, the process proceeds to step S402, and the CPU238performs various kinds of image processing (resolution conversion and filtering in the first embodiment) as appropriate on the stored image data. Next, the process proceeds to step S403, and the CPU238performs the process for extracting the feature points of the image data. In this feature point extraction process, feature points are extracted based on various feature amount calculation algorithms (such as Harris Corner Detection, Fast Corner Detection, and AKAZE). Details of the feature point extraction process will be described later. The process proceeds to step S404, and the CPU238stores, as a correct image in the memory239, each of the read image data stored in the memory239and the coordinates of the feature points extracted in step S403, then terminates the process.

FIG.4Bis a flowchart for describing a process for when the verification apparatus109performs verification processing according to the first embodiment. The process illustrated in the flowchart is achieved by the CPU238of the verification apparatus109executing the above-described program deployed in the memory239.

First, in step S411, the CPU238reads the conveyed sheet (printed sheet to be verified) with the imaging units240and256and stores in the memory239the image data (image data to be verified) obtained by the reading, similarly to step S401. Next, the process proceeds to step S412, and the CPU238performs various kinds of image processing (resolution conversion and filtering in the first embodiment) as appropriate on the image data stored in the memory239, similarly to step S402. Next, the process proceeds to step S413, and the CPU238extracts the feature points of the image data, similarly to step S403. Next, the process proceeds to step S414, and the CPU238calculates a geometrical conversion parameter for aligning the read image data with the correct image based on the coordinates of the feature points of the image data to be verified extracted in step S413and the coordinates of the feature points of the correct image extracted and registered in step S403. Here, assuming that the coordinate matrix of the feature points of the image data to be verified is a matrix A, the coordinate matrix of the feature points of the correct image is a matrix B, and the geometrical conversion parameter is a matrix X, the geometrical conversion for alignment is expressed by the following Equation (1).
A·X=BEquation (1)

Assuming that the pseudo-inverse matrix of the matrix A is A−1, the geometrical conversion parameter matrix X is expressed by the following Equation (2).
X=A−1·BEquation (2)

The geometrical conversion parameter is calculated by this Equation (2).

Next, the process proceeds to step S415, and the CPU238aligns the image data to be verified with the correct image by geometrically converting it using the geometrical conversion parameter calculated in step S414. Next, the process proceeds to step S416, and the CPU238obtains for each pixel the difference in the pixels between the correct image and the image data to be verified. Then, the process proceeds to step S417, and the CPU238determines the verification result based on the maximum value of difference between the pixels. That is, here, if the maximum value of the pixel difference is equal to or greater than the threshold value (equal to or greater than the predetermined value), it is determined that the image data to be verified is defective, that is, the sheet on which the image has been printed is a defective (abnormal) sheet, then displays that on the display unit241, for example. When the maximum value of the difference between the pixels is smaller than the threshold value, it is determined that the sheet is a normal sheet.

FIG.5is a diagram for describing examples of the sheet conveyed by the verification apparatus109and an image read by the imaging unit240and the imaging unit256and examples of the coordinates of the feature points according to the first embodiment. InFIG.5, it is assumed that the sheet is conveyed in a direction from the lower side to the upper side inFIG.5in relation to the imaging units240and256.

FIGS.5A,5E, and5Iillustrate examples of arrangement of the imaging unit240and the imaging unit256. Here, the imaging unit240is arranged to read the left side of the sheet to be read that is being conveyed, and the imaging unit256is arranged to read the right side of that sheet. The imaging unit240and the imaging unit256reads an image with an overlapping region where the image is read in an overlapping manner. The overlapping region is between the left end of an imaging area of the imaging unit256and right end of an imaging area of the imaging unit240. The overlapping region needs to overlap across a sufficient region in consideration of the shift in the conveyance of the sheet.

FIGS.5B,5F, and5Jillustrate examples of images of sheets to be read.

FIGS.5C,5G, and5Killustrate examples of images read by the imaging unit240in which only the left side of the sheet has been read.FIGS.5D,5H, and5Lillustrate examples of images read by the imaging unit256in which only the right side of the sheet has been read. At the time of registering the correct image, the CPU238registers, as the correct image in the memory239, the image data obtained by reading the image to be read with the imaging unit240and the imaging unit256. At the time of the verification process, the CPU238compares with the correct image registered in the memory239the image data obtained by reading with the imaging unit240and the imaging unit256.

When the two imaging units240and256are mounted perpendicular to the conveying direction of the sheet as inFIG.5Aand the sheet is conveyed perpendicular to the imaging units as inFIG.5B, ideally the image data obtained by reading with the respective imaging units240and256is read without any deformation. When the printed image on the sheet has three feature points, f0, f1, and f2, the feature points f0and f1are read by the imaging unit240and the feature points f0and f2are read by the imaging unit256as illustrated inFIGS.5C and5D.

Next, in a case where the two imaging units240and256are mounted perpendicular to the conveying direction of the sheet as inFIG.5E, but the sheet is conveyed in a state in which it is tilted relative to the imaging units as inFIG.5Fis considered. In this case, the image data read in a state in which the image is rotated by the amount by which the sheet is tilted is obtained as inFIGS.5G and5H.

Next, in a case where the imaging unit240is mounted tilted relative to the conveying direction of the sheet as inFIG.5I, but the sheet is conveyed perpendicularly relative to the imaging units as inFIG.5Fis considered. In this case, image data read in a state in which an image on the left side of the sheet is deformed (sheared) into a shape of a parallelogram by a tilt angle of the imaging unit240is obtained as inFIGS.5K and5L.

As described above, the image data obtained by reading with the imaging units is deformed in accordance with the conveyance state (angle, main scanning position) of the sheet and the mounting state (offset position, angle) of the imaging units. When the affine transformation is used as the geometrical conversion for aligning with the correct image such deformed read image data, at least three feature points are required. However, depending on the conveyance state of the sheet or the mounting state of the imaging units, there may be cases where the feature points required for affine transformation as illustrated inFIGS.5C and5D, for example, cannot be obtained from the image data obtained by reading with the imaging units.

Therefore, in the first embodiment, in order to calculate the geometrical conversion parameter for the image read by the imaging unit240, the coordinates of the feature point f2read by the imaging unit256are converted, then used. Similarly, in order to calculate the geometrical conversion parameter for the image read by the imaging unit256, the coordinates of the feature point f1read by the imaging unit240are converted, then used. This coordinate conversion will be described with reference toFIG.6.

FIG.6is a flowchart for explaining a process of extracting feature points in steps S403and S413ofFIG.4by the verification apparatus109according to the first embodiment. The process described in the flowchart is achieved by the CPU238of the verification apparatus109executing the program deployed in the memory239. This processing extracts feature points of the read image data for each imaging unit based on the feature amount calculation algorithm.

First, in step S601, based on a feature amount calculation algorithm, the CPU238extracts for each imaging unit feature points of an image corresponding to each imaging unit based on a feature amount of image data obtained by capturing with each imaging unit. Next, in step S602, the CPU238repeats the subsequent processes for all the imaging units. Here, all the imaging units refer to two imaging units240and256in the first embodiment, but the number of the imaging units is not limited to two. Then, in step S603, the CPU238repeats the subsequent processes for all feature points extracted in step S601. Incidentally, in the example of theFIG.5Cand theFIG.5D, all the feature points represent the feature points f0and f1of the image data obtained by the imaging unit240and the feature points f0and f2of the image data obtained by the imaging unit256. Note that the feature point f0is read in an overlapping manner by the imaging units240and256, but in the flowchart ofFIG.6, the processing is performed distinguishing the overlapped feature points as different feature points.

Next, the process proceeds to step S604, and the CPU238determines whether or not the feature point currently being referred to has been read by the imaging unit currently being referred to. As an example, when the imaging unit currently being referred to is the imaging unit240and the feature point currently being referred to is the feature point f2read by the imaging unit256, the determination will be false and the process proceeds to step S605. On the other hand, in the case of the feature points f0and f1read by the imaging unit240, the determination will be true and the process proceeds to step S606. In this way, if the feature point is not read by the currently-referred imaging unit, the process proceeds to step S605, and the CPU238performs a coordinate conversion process of the feature points between the imaging units.

This, in the example of theFIGS.5K and5L, is a process of mapping the feature point f2read by the imaging unit256to the read image data of the imaging unit240. In other words, it is assumed that the feature point f2which the imaging unit240should not be able to read could be read by the imaging unit240. The process, in such a case, converts the coordinates of the feature point f2from the coordinate system of the read image data of the imaging unit256to the coordinate system of the imaging unit240. This mapping can also be done using geometrical conversion. The geometrical conversion parameter necessary for the coordinate conversion process of the feature points is obtained by obtaining the relative attachment positions and angles of the imaging unit240and the imaging unit256by passing a chart image or the like in advance. Incidentally, the parameter for coordinate conversion from the imaging unit240to the imaging unit256, the parameter for coordinate conversion from the imaging unit256to the imaging unit240is separate from each other. Here, the parameter of the imaging unit240for correcting the difference in the attachment position of the imaging unit256is assumed to be measured at the time of shipping, then stored in the verification apparatus109.

The process proceeds to step S606, and the CPU238determines the coordinates of the obtained feature points. Then, in step S607, the CPU238determines whether or not the repetitive process has been completed for all the feature points and if not, returns to step S603. When the process for all the feature points has been completed in this manner, the process proceeds to step S608, the CPU238determines whether the repetitive process has been completed for all the imaging units, and if not, returns to step S602.

As described above, according to the first embodiment, even in a verification apparatus for aligning with a correct image each image data obtained by reading with the plurality of imaging units, it becomes possible to calculate a geometrical conversion parameter by converting the coordinates of the feature points read by the respective imaging units. As a result, even if feature points are unevenly distributed in image data obtained by reading a printed sheet, it is possible to perform alignment processing by geometrical conversion.

Second Embodiment

In the above-described first embodiment, the coordinate conversion process of the feature points in steps S604to S606was performed for all the feature points of the image data obtained by the respective imaging units. However, depending on the printed image, a sufficient number of feature points required for geometrical conversion may be read in one imaging unit. In this case, from the viewpoint of processing speed, a configuration is conceivable in which the process of determining the coordinates of the feature points between the imaging units is omitted. This will be explained as a second embodiment. The configuration and the like of the system according to the second embodiment are the same as those of the first embodiment described above, and therefore description thereof will be omitted.

FIG.7is a flowchart for explaining a process of extracting feature points by a verification apparatus209according to the second embodiment. The process described in the flowchart is achieved by the CPU238of the verification apparatus109executing the above-described program deployed in the memory239. InFIG.7, the same reference numerals are used for the processes common to those in the above-describedFIG.6, and description thereof will be omitted.

In step S701, the CPU238determines whether or not a number of feature points read by the imaging unit are sufficient for calculating the geometrical conversion parameter. If it is determined that the feature points are not sufficient, the process proceeds to step S605and the coordinate conversion process of the feature points between the imaging units is performed. On the other hand, if it is determined that the number of feature points are sufficient for calculating the geometrical conversion parameter, step S605is skipped and the process proceeds to step S606. For example, when an affine transformation is used as a geometrical conversion, at least three feature points are required, and when a projective transformation is used, at least four feature points are required. However, the number of feature points is not limited to these, and the number of feature points having a margin for improving the robustness of the parameter calculation may be set as a threshold value. The number of feature points is made as large as possible, and the coordinates of the extracted feature points are made to distribute evenly over the entire sheet. As a result, even if the read image data is partially deformed due to the conveyance of the sheet, it is possible to suppress alignment error. Therefore, this threshold value is determined from the tradeoff between processing speed and alignment accuracy.

As described above, according to the second embodiment, after a number of feature points necessary for geometrical conversion processing for aligning the images are obtained, the coordinate conversion process of the feature points between the imaging units is omitted. As a result, the speed of verification processing per printed sheet can be improved.

Other Embodiments

Embodiments of the present invention can also be realized by a computer of a system or apparatus that reads out and executes computer executable instructions (e.g., one or more programs) recorded on a storage medium (which may also be referred to more fully as a ‘non-transitory computer-readable storage medium’) to perform the functions of one or more of the above-described embodiment(s) and/or that includes one or more circuits (e.g., application specific integrated circuit (ASIC)) for performing the functions of one or more of the above-described embodiment(s), and by a method performed by the computer of the system or apparatus by, for example, reading out and executing the computer executable instructions from the storage medium to perform the functions of one or more of the above-described embodiment(s) and/or controlling the one or more circuits to perform the functions of one or more of the above-described embodiment(s). The computer may comprise one or more processors (e.g., central processing unit (CPU), micro processing unit (MPU)) and may include a network of separate computers or separate processors to read out and execute the computer executable instructions. The computer executable instructions may be provided to the computer, for example, from a network or the storage medium. The storage medium may include, for example, one or more of a hard disk, a random-access memory (RAM), a read only memory (ROM), a storage of distributed computing systems, an optical disk (such as a compact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™), a flash memory device, a memory card, and the like.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

This application claims the benefit of Japanese Patent Application No. 2020-211561, filed Dec. 21, 2020, which is hereby incorporated by reference herein in its entirety.