JP5906853B2 - Printing system and image forming apparatus - Google Patents

Description

  The present invention relates to a printing system and an image forming apparatus.

  As a conventional technique described in the publication, after printing an image on a recording material, read image data obtained by reading the image printed on the printed material, and a master image (reference image of the printed material serving as a reference of the read image) ) To detect image defects in printed matter (see Patent Document 1).

JP 2007-33247 A

  An object of the present invention is to suppress erroneous detection of image defects caused by the properties of a recording material to be printed.

Invention of claim 1, wherein a reading means for reading an image forming unit for forming an image based on original image data inputted from outside on a recording material, the image formed on the recording material by said image forming means, wherein In the extracted image data acquired by the acquiring unit, the acquiring unit acquires the property of the recording material by acquiring the gradation value of the extracted image data obtained by extracting a part of the read image data by the reading unit . If the gradation value distribution is narrower than a predetermined reference, the first resolution is selected as the resolution, and if it is wider than the reference, the second resolution lower than the first resolution is selected as the resolution. selection means for, based on said resolution selected by said selecting means and the properties acquired by the acquisition unit, resulting et by reading an image by said reading means And each pixel of the read image data, and correcting means for performing gradation correction, based on the resolution selected by the selection means, and producing means for producing a reference image data from the original image data, from the original image data The created reference image data and the comparison image data obtained by correcting the read image data by the correction unit are collated for each pixel, and the image formed on the recording material by the image forming unit And a detecting means for detecting a defect in the printing system.

According to a second aspect of the present invention, a result of reading an area on the recording material where no image is formed by the image forming unit is input to the obtaining unit as the extracted image data. The printing system according to claim 1 .
According to a third aspect of the invention, the nature, the ground color of the recording material, Kamihada, and claim 1 or 2, wherein the printing system is characterized in that any of a characteristic related to thickness.
Invention of claim 4, wherein the obtaining means, each time an image is formed on the recording material, according to any one of claims 1 to 3, characterized in that to obtain the properties in the recording medium Printing system.
In the invention according to claim 5 , the acquisition unit further creates a lookup table for performing the gradation correction based on the acquired property, and the correction unit uses the lookup table, The printing system according to claim 1 , wherein the gradation correction is performed on each pixel of the read image data.
According to a sixth aspect of the present invention, the image forming means forms an image on the recording material using yellow, magenta, cyan and black color materials, and the reading means is in red, green and blue colors. By reading an image formed on the recording material, red input image data, green input image data, and blue input image data are created as the read image data, and the acquisition means is based on the property. The lookup table corresponding to each of red, green and blue is created, and the correction means uses the lookup table corresponding to each of red, green and blue created in the acquisition means, 6. The printing system according to claim 5 , wherein the gradation correction is performed on each pixel of the red input image data, the green input image data, and the blue input image data.

According to a seventh aspect of the present invention, there is provided image forming means for forming an image on a recording material on the basis of output image data obtained by subjecting original image data input from the outside to first image processing, and the image forming means The reading means for reading the image formed on the recording material by the method, and acquiring the gradation value of the extracted image data obtained by extracting a part of the read image data by the reading means, thereby acquiring the properties of the recording material When the gradation value distribution in the extracted image data acquired by the acquisition unit acquired by the acquisition unit is narrower than a predetermined reference, the first resolution is selected as the resolution, and when the distribution is wider than the reference based on the selection means and the resolution selected by said properties acquired by the acquisition means and the selecting means for selecting the second resolution lower than the first resolution as the resolution Applied to each pixel of the read image data obtained by reading an image by said reading means, and correcting means for performing gradation correction, said the original image data, the correction based on the resolution selected by said selection means And a reference image data creating means for creating reference image data by performing a second image processing different from the first image processing, and a method for detecting defects in an image formed on the recording material by the image forming means. An output unit that outputs the reference image data created by the reference image data creation unit and the comparison image data obtained by correcting the read image data by the correction unit. It is.

The output image data is defined in a first color space, the read image data is defined in a second color space different from the first color space, and the reference image data and the comparison 8. The image forming apparatus according to claim 7 , wherein the image data is defined in a third color space having a reproduction color gamut wider than the first color space and the second color space.

According to the first aspect of the present invention, it is possible to suppress erroneous detection of an image defect caused by unevenness of a recording material to be printed with an image, as compared with a case where this configuration is not provided.
According to the second aspect of the invention, as compared with the case not having this constitution, more accurately, it is possible to obtain the properties of the recording material.
According to the third aspect of the present invention, it is possible to acquire the property of the recording material that affects the density characteristics of the read image data.
According to the fourth aspect of the present invention, even when images are continuously formed on recording materials having different properties as compared with the case where the present configuration is not provided, it is caused by the properties of the recording material. It is possible to suppress erroneous detection of image defects.
According to the fifth aspect of the present invention, gradation correction suitable for the recording material can be performed each time as compared with the case where this configuration is not provided.
According to the sixth aspect of the present invention, the density characteristics in the comparison image data are different from those in the output image data even when the full color image is printed and read as compared with the case without this configuration. It can be close to the characteristics.
According to the seventh aspect of the present invention, it is possible to suppress erroneous detection of image defects caused by the unevenness of the recording material to be printed with an image, as compared with the case where the present configuration is not provided.
According to the eighth aspect of the present invention, compared to the case where the present configuration is not provided, even if the original image data includes a pixel outside the input color gamut that can be read by the reading unit, it is formed on the recording material. The accuracy of the inspection of the obtained image can be ensured.

1 is a diagram illustrating a configuration of a printing system. It is a figure which shows the structure of a printing apparatus. FIG. 3 is a diagram illustrating a configuration of an image reading unit provided in the printing apparatus. It is a figure which shows the structure of the CCD image sensor provided in the image reading part. It is a block diagram which shows the function structure of a setting apparatus. FIG. 2 is a block diagram illustrating a functional configuration of a printing apparatus. FIG. 3 is a block diagram illustrating a functional configuration of a background correction setting unit and a collation read image creation unit provided in a control unit of the printing apparatus. It is a block diagram which shows the function structure of an inspection apparatus. It is a figure for demonstrating the read image data for 1 line in the main scanning direction obtained by reading the various paper (without an image) in a different state with an image reading part. FIG. 6 is a diagram (continued) for explaining read image data for one line in the main scanning direction obtained by reading various sheets (no image) in different states by an image reading unit. FIG. 4 is a diagram for explaining a print area of an image on a sheet. (A) is a figure for demonstrating the structure of a background image acquisition area, (b) is for demonstrating an example of the gradation distribution (histogram) based on each gradation value acquired from the background image acquisition area. FIG. It is a figure for demonstrating the procedure of the printing and test | inspection in the printing system of this Embodiment. It is a flowchart for demonstrating the flow of the process which a base | substrate correction | amendment setting part performs among the procedures of printing and a test | inspection in a printing system. It is a flowchart for demonstrating the flow of the process which the reading image preparation part for collation performs among the procedures of printing and a test | inspection in a printing system. It is a figure for demonstrating an example of the structure of the LUT for background correction | amendment produced in the LUT production | generation part, and used by the gradation conversion part. FIG. 4 is a conceptual diagram for explaining a relationship between an original image for printing obtained from an original image, a sheet to be printed on the original image for printing, and a printed matter obtained by printing the original image for printing on a sheet. . It is a conceptual diagram for explaining the relationship between a read image obtained by reading a printed matter, a background image obtained from the read image, and a collation read image obtained based on the read image and the background image. Relationship between the collation read image, the collation original image obtained based on the same original image as the collation read image, and the collation read image obtained based on the same original image and the difference image of the collation original image It is a conceptual diagram for demonstrating.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
FIG. 1 is a diagram illustrating a configuration of a printing system to which the exemplary embodiment is applied.
The printing system according to the present embodiment includes a printing apparatus 1 that prints an image on paper, a setting apparatus 2 that sets image data (original image data) to be printed by the printing apparatus 1 and its printing conditions, and a printing apparatus 1. Are provided with an inspection device 3 for inspecting the contents of an image (printed image) printed on a sheet, and a network 4 for connecting the printing device 1, the setting device 2 and the inspection device 3 to each other.

FIG. 2 is a diagram illustrating a configuration of the printing apparatus 1. The printing apparatus 1 of the present embodiment is a plateless printing apparatus that prints an image using an electrophotographic method.
The printing apparatus 1 has a so-called tandem configuration and includes a plurality of image forming units 10Y, 10M, 10C, and 10K that form toner images of respective color components by an electrophotographic method. The printing apparatus 1 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like, and each apparatus and operation of each unit (image processing is performed) constituting the printing apparatus 1. A control unit 100 for controlling (including). Here, the plurality of image forming units 10Y, 10M, 10C, and 10K form yellow, magenta, cyan, and black images, respectively.

  The printing apparatus 1 also includes an intermediate transfer belt 20 that sequentially transfers (primary transfer) the color component toner images formed by the image forming units 10Y, 10M, 10C, and 10K, and holds the toner images. And a secondary transfer device 30 that collectively transfers (secondary transfer) the toner image on the transfer belt 20 to a sheet P (an example of a recording material) formed in a rectangular shape.

  Here, each of the plurality of image forming units 10Y, 10M, 10C, and 10K includes a photosensitive drum 11 that is rotatably mounted. In each of the image forming units 10Y, 10M, 10C, and 10K, around the photosensitive drum 11, a charging device 12 that charges the photosensitive drum 11 and the photosensitive drum 11 are exposed to write an electrostatic latent image. An exposure device 13 and a developing device 14 that visualizes the electrostatic latent image on the photosensitive drum 11 with a corresponding color toner are provided. Further, in each of the image forming units 10Y, 10M, 10C, and 10K, a primary transfer device 15 that transfers each color component toner image formed on the photosensitive drum 11 to the intermediate transfer belt 20, and a residual on the photosensitive drum 11 A drum cleaning device 16 for removing toner is provided.

  Next, the intermediate transfer belt 20 is provided so as to be stretched over three roll members 21 to 23 that are rotatably provided. Of these three roll members 21 to 23, the roll member 22 drives the intermediate transfer belt 20. The roll member 23 is disposed opposite to the secondary transfer roll 31 with the intermediate transfer belt 20 interposed therebetween, and the secondary transfer device 30 is configured by the secondary transfer roll 31 and the roll member 23. A belt cleaning device 24 for removing residual toner on the intermediate transfer belt 20 is provided at a position facing the roll member 21 across the intermediate transfer belt 20.

  Further, in the printing apparatus 1, the first transport path R1 through which the paper P transported toward the secondary transfer apparatus 30 passes, and the second transport path R2 through which the paper P after passing through the secondary transfer apparatus 30 passes. A third transport path R3 is provided which branches from the second transport path R2 downstream of the fixing device 50 (described later) and extends below the first transport path R1 to guide the paper P to the first transport path R1 again. It has been. Of the paper P transported along the second transport path R2, those not guided to the third transport path R3 are discharged to the outside of the printing apparatus 1 and stacked on a paper stacking unit (not shown).

  Further, the printing apparatus 1 includes a paper transport unit 40 that transports the paper P along the first transport path R1, the second transport path R2, and the third transport path R3. The paper transport unit 40 is provided on the downstream side in the transport direction of the paper P with respect to the first paper supply device 40A for supplying the paper P to the first transport route R1 and the first paper supply device 40A. And a second paper supply device 40B for supplying paper P to R1. The first paper supply device 40A and the second paper supply device 40B have the same structure, and each of the first paper supply device 40A and the second paper supply device 40B has a paper storage portion for storing the paper P. 41, a take-out roll 42 for taking out and transporting the paper P stored in the paper storage unit 41 is provided. Here, the first paper supply device 40A and the second paper supply device 40B can store different sizes and orientations and different types of paper P.

  Further, the paper transport unit 40 includes a plurality of transport rolls 43 that transport the paper P in each of the first transport path R1, the second transport path R2, and the third transport path R3. Furthermore, the paper transport unit 40 includes a belt transport unit 44 that transports the paper P that has passed through the secondary transfer device 30 to the fixing device 50 side in the second transport path R2.

  In addition, the printing apparatus 1 further includes a fixing device 50 that fixes the image secondarily transferred onto the paper P by the secondary transfer device 30 on the second transport path R2. The fixing device 50 includes a heating roll 50A that is heated by a built-in heater (not shown) and a pressing roll 50B that presses the heating roll 50A. In the fixing device 50, the paper P passes between the heating roll 50A and the pressing roll 50B, whereby the paper P is heated and pressurized, and the image on the paper P is fixed to the paper P.

  In the following description, the image forming units 10Y, 10M, 10C, and 10K, the intermediate transfer belt 20, the secondary transfer device 30, the paper transport unit 40, and the fixing device 50 are collectively referred to as the image forming unit 10. .

  In the printing apparatus 1 of the present embodiment, an image can be printed on the first surface of the paper P supplied from the first paper supply device 40A or the like, and in addition, an image can be printed on the second surface of the paper P. Be able to. More specifically, in this printing apparatus 1, the front and back of the paper P that has passed through the fixing device 50 after the image is transferred to the first surface is reversed by being conveyed via the third conveyance path R3. The sheet P with the front and back reversed is supplied to the secondary transfer device 30 again. Then, the image is transferred onto the second surface of the paper P by the secondary transfer device 30. Thereafter, the sheet P passes through the fixing device 50 again, and the transferred image is fixed on the sheet P. As a result, an image is formed not only on the first side of the paper P but also on the second side.

  In the printing apparatus 1 according to the present embodiment, the second transport path R2 is located downstream of the fixing device 50 in the transport direction of the paper P, and between the second transport path R2 and the third transport path R3. An image reading unit 60 that reads an image printed on the paper P through secondary transfer and fixing is provided upstream of the branching unit in the conveyance direction of the paper P. The image reading unit 60 reads an image on the surface of the sheet P passing through the secondary transfer device 30 on the side facing the intermediate transfer belt 20, that is, the surface on which the image was secondarily transferred immediately before. It is configured.

FIG. 3 is a diagram illustrating a configuration of the image reading unit 60 provided in the printing apparatus 1. Here, FIG. 3 shows a cross-sectional configuration of the image reading unit 60 as viewed from the near side in FIG. In the following description, the conveyance direction of the paper P (the direction from the left side to the right side in the drawing) is the sub-scanning direction SS, and the direction orthogonal to the conveyance direction of the paper P (the direction from the front side to the back side in the drawing). Is called the main scanning direction FS.
Here, a first guide 45 and a second guide 46 for guiding the sheet P to be conveyed are formed on the downstream side of the fixing device 50 shown in FIG. The sheet P is transported in the second transport path R <b> 2 formed between the first guide 45 and the second guide 46.

  The image reading unit 60 is arranged above the first guide 45, that is, on the side facing the image forming surface of the conveyed paper P, and is imaged below the second guide 46. An opposing portion 62 arranged to face the portion 61, and a fan that is disposed above the first guide 45 and upstream of the imaging unit 61 in the sheet conveying direction, and blows air into the second conveying path R2. It has the ventilation part 63 which has.

  Among these, the imaging unit 61 has a first housing 71 in which a space is formed and an opening 71a is formed in a lower portion facing the second transport path R2, and has light transmittance with respect to visible light. A light transmissive member 72 fitted into the opening 71a is provided. A part of the first housing 71 functions as a transport path forming unit that forms a part of the second transport path R <b> 2 together with the first guide 45. In addition, the imaging unit 61 includes a first light source 73 that emits light to the second transport path R2 side via the light transmissive member 72 below the inside of the first housing 71 and above the light transmissive member 72. And a second light source 74 that is disposed on the downstream side of the first light source 73 in the transport direction of the paper P and irradiates light to the second transport path R <b> 2 side through the light transmissive member 72. ing. Further, the imaging unit 61 is irradiated from the first light source 73 and the second light source 74 to the paper P conveyed in the second conveyance path R2 via the light transmissive member 72, and the reading position RP of the paper P The first mirror 75a, the second mirror 75b, and the third mirror 75c that further reflect the light reflected from the lens, the lens system 76 that reduces the optical image incident from the third mirror 75c, and the light emitted from the lens system 76 is received. And a CCD (Charge Coupled Device) image sensor 77 for photoelectric conversion. That is, in this example, the image reading unit 60 forms an optical image on the CCD image sensor 77 using a so-called reduction optical system. In FIG. 3, the lens system 76 is shown as a single lens, but the lens system 76 may be configured by a combination of a plurality of lenses.

  On the other hand, the facing portion 62 has a space formed therein, and is rotatable inside the second housing 81, the second housing 81 having an opening 81a formed in an upper portion facing the second transport path R2. A reading reference member 82 that is arranged and read by the imaging unit 61 and used for calibration of the imaging unit 61 and the like is provided. Here, the reading reference member 82 has an octagonal cross section, and is arranged with one of the outer surfaces exposed to the opening 81a. That is, each outer surface of the reading reference member 82 can be disposed at a reading position RP by the imaging unit 61. Further, on the outer peripheral surface of the reading reference member 82, for example, a white reference surface 82a on which a white reference member is formed, a black reference surface (without reference numeral) on which a black reference member is formed, and a Y reference on which a yellow reference member is formed. Surface (no reference), M reference surface (not indicated) on which a magenta reference member is formed, C reference surface (not indicated) on which a cyan reference member is formed, a reading exposure surface 82b exposed when reading paper P, and the like Is formed. In the present embodiment, the reading exposure surface 82b is black as in the black reference surface. The white reference plane, black reference plane, Y reference plane, M reference plane, C reference plane, reading exposure plane, and the like are wider in the main scanning direction FS and the sub-scanning direction SS than the imaging area by the imaging unit 61. It is formed.

FIG. 4 is a diagram for explaining the configuration of the CCD image sensor 77 provided in the imaging unit 61.
The CCD image sensor 77 has a sensor substrate 77a formed in a rectangular shape, and three line sensors 77R, 77G, and 77B mounted side by side on the sensor substrate 77a. In the following description, these three line sensors 77R, 77G, and 77B are referred to as a red line sensor 77R, a green line sensor 77G, and a blue line sensor 77B, respectively. The red line sensor 77R, the green line sensor 77G, and the blue line sensor 77B are each disposed so as to extend in the main scanning direction FS. The red line sensor 77R, the green line sensor 77G, and the blue line sensor 77B are arranged side by side in the sub-scanning direction SS. Each of the red line sensor 77R, the green line sensor 77G, and the blue line sensor 77B is configured by arranging k photodiodes PD in a straight line (for example, k = 8000 in the present embodiment). The red line sensor 77R, the green line sensor 77G, and the blue line sensor 77B are provided with color filters for transmitting different wavelength components. However, the CCD image sensor 77 is not limited to this, and may be constituted by a two-dimensional area sensor that reads RGB colors. In place of the CCD image sensor 77, a CMOS image sensor may be used.

FIG. 5 is a block diagram showing a functional configuration of the setting device 2 shown in FIG. The setting device 2 of the present embodiment is configured by a computer device including a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like. Here, the setting device 2 performs a data process for inputting data to the printing device 1 when executing a job for continuously printing and outputting an image on one or a plurality of sheets P based on a single instruction. Front End).
The setting device 2 includes an original image creation unit 201, a user interface (UI) 202, and a transmission / reception unit 203.

  The original image creation unit 201 creates “original image data” that can be interpreted by the printing apparatus 1 based on, for example, input image data input from the outside.

  The UI 202 receives input of various settings required for printing when the printing apparatus 1 executes printing based on the original image data. Here, examples of the settings received via the UI 202 include a color space for defining original image data, and a resolution for executing printing based on the original image data. However, color space and resolution information may already be included in the input image data. In the following description, the color space of the original image data is referred to as “set color space”, and the resolution of the original image data is referred to as “set resolution”. In this example, the set color space is defined in the RGB color space. The UI 202 displays an image based on data sent from the printing apparatus 1 and the inspection apparatus 3 shown in FIG. 1 via the network 4 on a display (not shown).

  The transmission / reception unit 203 transmits / receives various data to / from the printing apparatus 1 and the inspection apparatus 3 illustrated in FIG.

FIG. 6 is a block diagram illustrating a functional configuration of the printing apparatus 1 illustrated in FIGS. 1 and 2.
The printing apparatus 1 according to the present embodiment controls an image forming unit 10 that prints an image on a sheet P, an image reading unit 60 that reads a printed image on the sheet P, and the image forming unit 10 and the image reading unit 60. And a control unit 100. Further, the control unit 100 includes a transmission / reception unit 101, a printing original image creation unit 102, a collation original image creation unit 103, a background correction setting unit 104, and a collation read image creation unit 105.

  The transmission / reception unit 101 as an example of output means transmits / receives various data to / from the setting device 2 and the inspection device 3 illustrated in FIG.

  Based on the original image data input from the setting device 2 via the transmission / reception unit 101, the printing original image creation unit 102 generates “printing original image data as an example of output image data corresponding to the image forming unit 10. Is created. Here, when creating the printing original image data from the original image data, the printing original image creating unit 102 sets the color space (“output”) corresponding to the color material of the image forming unit 10 as the set color space of the original image data. Color space). In this example, the output color space as an example of the first color space is defined in the CMYK color space corresponding to the color materials of the image forming unit 10 (in this example, cyan, magenta, yellow, and black). Further, when creating the printing original image data from the original image data, the printing original image creating unit 102 sets a resolution (referred to as “output resolution”) based on the setting resolution of the original image data. The output resolution may be set to the same value as the set resolution or may be set to a value different from the set resolution.

  The image forming unit 10 as an example of an image forming unit prints an image (printed image) based on the output color space and the output resolution on the paper P using the printing original image data created by the printing original image creating unit 102. And output as printed matter.

  The image reading unit 60 as an example of a reading unit and an acquisition unit reads a print image on the paper P using three line sensors 77R, 77G, and 77B (see FIG. 4). Then, the image reading unit 60 creates “read image data” based on the reading results input from the line sensors 77R, 77G, and 77B. Here, when the image reading unit 60 creates read image data from the read result of the print image, the color space of the read image data is a color space (“input” corresponding to the read color of each line sensor 77R, 77G, 77B. Color space). In this example, the input color space as an example of the second color space is RGB corresponding to the colors (in this example, red, green, and blue) of the line sensors 77R, 77G, and 77B constituting the image reading unit 60. Defined in color space. Further, the image reading unit 60 sets a resolution (“input resolution”) based on the reading result when generating the reading image data from the reading result of the print image. The input resolution is determined by the arrangement interval of a plurality of sensors constituting each line sensor, the reading period of each line sensor, the conveyance speed of the paper P, and the like, and may be the same value as the output resolution. However, the output resolution may be different.

An original image creation unit 103 for collation as an example of the reference image data creation unit is based on the original image data input from the setting device 2 via the transmission / reception unit 101, and a reference for use in an image defect inspection described later. Thus, “verification original image data” as an example of the reference image data is created. Here, when the collation original image creation unit 103 creates collation original image data from the original image data, the set color space of the original image data is changed to a color space corresponding to the inspection of the image defect (“inspection color space”). Called). In this example, the inspection color space as an example of the third color space is defined in a CIELAB (hereinafter, sometimes referred to as L ^* a ^* b ^* ) color space. Further, when creating the matching original image data from the original image data, the matching original image creating unit 103 sets the set resolution to a resolution corresponding to the inspection of the image defect as necessary (referred to as “inspection resolution”). Convert to In this example, the original image data for comparison is created from the original image data. However, the present invention is not limited to this. For example, the original image data for verification is obtained from the original image data for printing obtained based on the original image data. Image data may be created.

  The background correction setting unit 104, based on the read image data input from the image reading unit 60, as an example of the nature of the paper P in the printed matter, the background color of the paper P, the paper surface (background) of the paper P, the paper P The background that is present in the read image data due to the characteristics relating to the thickness of the paper (including basis weight and transparency) (hereinafter, these properties of the paper P are simply referred to as “background”). Various correction data used for correction to remove the influence of the above are set. The specific contents of the correction data will be described later.

  Based on the read image data input from the image reading unit 60, the collated read image creating unit 105 uses “a collated read image as an example of comparison image data that serves as a reference for use in the inspection of image defects to be described later. Data ”. Further, the collated read image creating unit 105 performs correction based on various correction data set by the background correction setting unit 104 when creating collated read image data based on the read image data. Here, the collated read image creation unit 105 converts the input color space of the read image data into the inspection color space described above when creating the collated read image data from the read image data. In addition, the collated read image creating unit 105 converts the input resolution to the above-described inspection resolution as necessary when creating collated read image data from the read image data. Here, in the present embodiment, both the background correction setting unit 104 and the verification read image creation unit 105 have a function as a correction unit.

  The collation original image creation unit 103 described above sets the correction data set by the background correction setting unit 104 when creating collation original image data based on the original image data (or print original image data). Correction based on

FIG. 7 is a block diagram illustrating functional configurations of the background correction setting unit 104 and the matching read image creation unit 105 provided in the control unit 100 of the printing apparatus 1.
Among these, the background correction setting unit 104 includes a shading correction unit 1041, an inspection resolution determination unit 1042, and an LUT creation unit 1043. In the background correction setting unit 104 (shading correction unit 1041) of the present embodiment, background image data obtained by extracting a part of the area from the read image data created by the image reading unit 60 is stored. Entered. Here, the background image data as an example of the extracted image data includes a plurality of pixels that are continuous in each of the main scanning direction FS and the sub-scanning direction SS. Details of the background image data will be described later.

  The shading correction unit 1041 performs shading correction on the background image data input from the image reading unit 60. Here, the shading correction data used in the shading correction unit 1041 is obtained by using the first light source 73 and the white light source surface 82a of the reading reference member 82 at the reading position RP in the image reading unit 60 shown in FIG. This is obtained based on the light reception results of the three line sensors 77R, 77G, and 77B when the second light source 74 is irradiated with light.

  The inspection resolution determination unit 1042 is based on the background image data subjected to the shading correction, and the matching original image data created by the matching original image creation unit 103 and the matching read image data created by the matching read image creation unit 105 It is determined whether or not to change the inspection resolution set in common to both from the reference value. The resolution change information (resolution conversion instruction) determined by the inspection resolution determination unit 1042 includes the collation original image creation unit 103, the resolution conversion unit 1052 provided in the collation read image creation unit 105, and LUT creation. To the unit 1043.

  The LUT creation unit 1043 uses the paper P when the collation read image creation unit 105 creates collation read image data from the read image data based on the background image data subjected to the shading correction and the resolution change information. A background correction LUT (Look Up Table) used for gradation conversion for removing the influence of the background is created. In this example, the background correction LUT created by the LUT creation unit 1043 has a relationship of RGB (input) → RGB (output). The background correction LUT created by the LUT creation unit 1043 is output to a gradation conversion unit 1053 provided in the collation read image creation unit 105.

  On the other hand, the verification read image creation unit 105 includes a shading correction unit 1051, a resolution conversion unit 1052, a gradation conversion unit 1053, and a color space conversion unit 1054. The read image data itself output from the image reading unit 60 is input to the collated read image creating unit 105 (shading correction unit 1051) of the present embodiment.

  The shading correction unit 1051 performs shading correction on the read image data input from the image reading unit 60. Here, the shading correction data used in the shading correction unit 1051 is the same as that used in the shading correction unit 1041 of the background correction setting unit 104.

  When the resolution conversion unit 1052 receives a resolution conversion instruction from the inspection resolution determination unit 1042 provided in the background correction setting unit 104, the resolution (reading resolution) of the read image data subjected to the shading correction is a reference. Resolution conversion is performed so that the resolution is lower than the value (inspection resolution). If no resolution conversion instruction is received, the resolution conversion unit 1052 does not perform resolution conversion.

  The gradation conversion unit 1053 applies the background correction LUT created by the LUT creation unit 1043 of the background correction setting unit 104 to the read image data subjected to shading correction and resolution conversion according to an instruction. And gradation conversion is performed.

  The color space conversion unit 1054 converts the read image data after gradation conversion input from the gradation conversion unit 1053 into an inspection color space, and sends the obtained read image data for collation to the transmission / reception unit 101. Output toward.

  In the example shown in FIG. 7, the shading correction unit 1041 is provided in the background correction setting unit 104, and the shading correction unit 1051 is provided in the matching read image creation unit 105, and shading correction is performed individually. It is not limited to this. For example, when the configuration in which the image reading unit 60 performs shading correction first is employed, the shading correction unit 1041 and the shading correction unit 1051 are not necessary.

FIG. 8 is a block diagram showing a functional configuration of the inspection apparatus 3 shown in FIG. The inspection device 3 according to the present embodiment is configured by a computer device including a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like. The inspection device 3 inspects the presence or absence of image defects in the printed image printed on the paper P by the printing device 1.
The inspection apparatus 3 includes a transmission / reception unit 301, an image collation unit 302, and an image defect determination unit 303.

  The transmission / reception unit 301 transmits / receives various data to / from the printing apparatus 1 and the setting apparatus 2 illustrated in FIG.

  The image matching unit 302 performs pixel-by-pixel processing on both the matching original image data and the matching read image data obtained based on the common original image data input from the printing apparatus 1 via the transmission / reception unit 301. The pixel value is collated.

  The image defect determination unit 303 determines the presence / absence of an image defect in the print image printed on the paper P based on the common original image data based on the collation result by the image collation unit 302. The determination result is sent to the setting device 2 via the transmission / reception unit 301. Here, in the present embodiment, the image collation unit 302 and the image defect determination unit 303 provided in the inspection apparatus 3 function as detection means.

Here, the relationship between the state of the paper P and the image data read by the image reading unit 60 will be described.
FIGS. 9 and 10 are diagrams for explaining read image data for one line in the main scanning direction FS obtained by reading various sheets P (no image) in different states by the image reading unit 60. . In this example, it is assumed that the above-described shading correction has already been performed on each read image data.

  First, FIG. 9A illustrates read image data in the case where white thick paper is used as the paper P. FIG. 9B illustrates read image data when white thin paper is used as the paper P. Further, FIG. 9C illustrates read image data when gray thick paper is used as the paper P.

  On the other hand, FIG. 10A illustrates read image data (same as FIG. 9A) when white thick paper is used as the paper P. FIG. 10B illustrates read image data when a light pink thick paper is used as the paper P. Further, FIG. 10C illustrates read image data in the case where white embossed paper (which has been subjected to uneven processing) is used as the paper P.

  In FIGS. 9A to 9C and FIGS. 10A to 10C, the image reading unit 60 shown in FIG. 3 reads the image at the reading position RP in order to reproduce the image reading conditions when printing is performed. A reading exposure surface 82b (presenting black) of the reference member 82 is disposed. In each of FIGS. 9A to 9C and FIGS. 10A to 10C, the horizontal axis indicates the position in the main scanning direction FS at the reading position RP. In each lower row, the positional relationship between the reading exposure surface 82b of the reading reference member 82 and the paper P is shown, and in each upper row, input from the red line sensor 77R (R input) as read image data. ), The input from the green line sensor 77G (G input) and the input from the blue line sensor 77B (B input) are shown as respective gradation values. In this example, it is assumed that each pixel is expressed by 256 gradations (8 bits). Further, in each of the R input, the G input, and the B input, it means that “255” as the maximum value is the brightest and “0” as the minimum value is the darkest. . In the following description, a portion where the reading exposure surface 82b is hidden by the presence of the sheet P on the reading exposure surface 82b when viewed from above the reading position RP (on the CCD image sensor 77 side) is described as “ A region where the reading exposure surface 82b is exposed due to the absence of the sheet P on the reading exposure surface 82b is referred to as an “exposing surface facing region”. In this example, the sheet facing area is located at the center in the main scanning direction FS, and the exposed surface facing area is located at both ends in the main scanning direction FS as viewed from the sheet facing area.

  First, read image data obtained when white thick paper is used as the paper P shown in FIG. 9A will be described. In this example, in each of the R input, the G input, and the B input, the gradation value corresponding to the exposed surface facing area is 0, and the gradation value corresponding to the paper facing area is 255. Note that the gradation value corresponding to the paper facing area is 255 because the whiteness (color tone) of the paper P made of white thick paper and the whiteness of the white reference surface 82 a provided on the reading reference member 82 are the same. This is the case.

  Next, read image data obtained when white thin paper is used as the paper P shown in FIG. 9B will be described. In this example, in each of the R input, the G input, and the B input, the gradation value corresponding to the exposed surface facing area is 0, and the gradation value corresponding to the sheet facing area is white thick paper. It is smaller than 230. This is because when the reading exposure surface 82b exhibiting black color is used and a white thin paper is used as the paper P, the reading exposure surface 82b is seen through the paper P. This results in substantially gray, and as a result, the substantial color tone of the paper P including the influence of the reading exposure surface 82b does not match the color tone of the white reference surface 82a. However, since gray is an achromatic color, the magnitudes of the gradation values of the R input, the G input, and the B input in this case are common.

  Next, read image data obtained when gray thick paper is used as the paper P shown in FIG. 9C will be described. In this example, in each of the R input, the G input, and the B input, the gradation value corresponding to the exposed surface facing area is 0, and the gradation value corresponding to the sheet facing area is white thick paper. 190 which is even smaller than that. This is because the color tone of the paper P made of gray thick paper does not match the color tone of the white reference surface 82a. However, since gray is an achromatic color, the magnitudes of the gradation values of the R input, the G input, and the B input in this case are common.

  Furthermore, the read image data obtained when using light pink thick paper as the paper P shown in FIG. 10B will be described. In this example, the gradation value corresponding to the exposed surface facing area is 0 in each of the R input, the G input, and the B input. However, regarding the gradation value corresponding to the paper facing area, the R input is 230 smaller than that of white thick paper, and the G input and B input are 200 smaller than the R input. This is because the color tone of the paper P made of light pink thick paper does not match the color tone of the white reference surface 82a. Here, since the light pink color is a chromatic color, the gradation values of the R input, the G input, and the B input in this case are not common.

  Finally, read image data obtained when white embossed paper is used as the paper P shown in FIG. 10C will be described. In this example, the gradation value corresponding to the exposed surface facing area is 0 in each of the R input, the G input, and the B input. However, with respect to the gradation value corresponding to the paper facing area, in the R input, G input, and B input, there are alternately portions of 255 and 200 respectively. This is because, due to the unevenness provided on the surface of the paper P, the color tone of the convex portion matches the color tone of the white reference surface 82a, while the color tone of the concave portion and the color tone of the white reference surface 82a do not substantially match. caused by. However, since white is an achromatic color, the magnitudes of the gradation values of the R input, G input, and B input in this case are common to the concave and convex portions.

  In FIGS. 9 and 10, in order to help the understanding of the invention, an ideal state, that is, a state where the paper P is flat along the main scanning direction FS and has no color unevenness (in the embossed paper shown in FIG. 10C). Is an example in which the concave portions and the convex portions periodically exist along the main scanning direction FS and the depths of the concave portions are uniform. However, since there may be variations in the actual paper P, there may be some variation in the input values (gradation values) of each pixel along the main scanning direction FS.

  In this description, whether the paper P is “thick paper” or “thin paper” is determined based on whether the back surface is transparent through the paper P. In other words, “thick paper” means that the back surface is not transparent through the paper P, and “thin paper” means that the back surface is transparent through the paper P.

  FIG. 11 is a diagram for explaining an image printing area on the paper P. FIG. In the printing apparatus 1 of the present embodiment, the image forming unit 10 prints an image on the paper P. At this time, the print image based on the original image data (actually the original image data for printing) is printed on the paper P. Is printed in the central area excluding the edges of the four sides. In the following description, an outer edge of a region where a print image can be printed on the paper P is referred to as a setting frame F (indicated by a broken line in the drawing). In addition, on the paper P, an area inside the setting frame F, that is, an area where a print image can be printed is referred to as an in-frame area Ai, and an area outside the setting frame F, ie, an area where the print image cannot be printed, is referred to as an outside frame area Ao.

  In this embodiment, the image reading unit 60 reads both the in-frame area Ai and the out-of-frame area Ao on the paper P, thereby obtaining read image data for one page. Here, in the present embodiment, as described above, when the image reading unit 60 performs image reading, the reading exposure surface 82b exhibiting black is arranged at the reading position RP. For this reason, as described with reference to FIGS. 9 and 10, the outer edge of the out-of-frame area Ao, that is, the end position of the paper P (the boundary between the paper facing area and the exposed surface facing area) is determined based on the reading results of each RGB color. It can be easily discriminated, and the inner data can be extracted as read image data for one page.

  Further, in the present embodiment, among the read image data for one page obtained in this way, the data present in the background image acquisition area Ag set in a rectangular shape in the out-of-frame area Ao is converted to the control unit 100. Are extracted as background image data to be used by the background correction setting unit 104 (see FIG. 7). In this example, a part of the out-of-frame area Ao that is upstream in the main scanning direction FS and upstream in the sub-scanning direction SS is set as the background image acquisition area Ag.

  FIG. 12A is a diagram for explaining the structure of the background image acquisition area Ag, and FIG. 12B is a gradation distribution (histogram) based on each gradation value obtained from the background image acquisition area Ag. It is a figure for demonstrating an example.

  As shown in FIG. 12A, the background image acquisition region Ag in the present embodiment includes M × N pixels that are M consecutive in the main scanning direction FS and N consecutive in the sub-scanning direction. Yes. That is, the base image acquisition area Ag is composed of a plurality of pixels.

  Further, when a histogram is created with the horizontal axis representing the gradation values of a plurality of pixels constituting the background image acquisition area Ag and the vertical axis representing the frequency of each gradation value, as shown in FIG. Various patterns are obtained depending on the state. Here, in FIG. 12B, the gradation distribution (shown by a solid line in the figure) obtained when the first paper Pa made of white thick paper is used as the paper P, and the white thin paper or The gradation distribution (indicated by a broken line in the figure) obtained when the second paper Pb made of gray thick paper is used, and the floor obtained when the third paper Pc made of white embossed paper is used as the paper P. A tone distribution (indicated by a dashed line in the figure) is illustrated.

  In the case of the first paper Pa (white thick paper), the gradation distribution is a pattern having a sharp peak on the high gradation side. In the case of the second paper Pb (white thin paper or gray thick paper), the gradation distribution has a sharp peak on the middle gradation side between the high gradation side and the low gradation side according to the density. It becomes the pattern which has. On the other hand, in the case of the third paper Pc (white embossed paper), the gradation distribution has a broad pattern with a peak collapsed compared to the above two.

  FIG. 13 is a diagram for explaining printing and inspection procedures in the printing system according to the present embodiment. In the following, the operation of each device constituting the printing system and the exchange of data between the devices will be described with reference to FIG.

  Original image data (set color space (RGB in this example) and set resolution (300 dpi in this example)) created by the setting device 2 (not shown) is input to the printing original image creation unit 102 of the printing device 1. Is done. Accordingly, the printing original image creation unit 102 generates printing original image data (output color space (CMYK in this example), output resolution (600 dpi in this example)) based on the original image data (RGB, setting resolution). create.

  In the printing apparatus 1, the printing original image data (CMYK, output resolution) created by the printing original image creating unit 102 is input to the image forming unit 10. Accordingly, the image forming unit 10 prints an image including each color of CMYK on the paper P and outputs it as a printed matter. Subsequently, the image reading unit 60 provided in the printing apparatus 1 reads the print image on the paper P. The image reading unit 60 then reads the read image data (input color space (RGB in this example), input resolution (300 dpi in this example)) based on the reading results using the three line sensors 77R, 77G, and 77B. Create

  Further, in the printing apparatus 1, background image data (RGB, input resolution) obtained by extracting a part of the read image data created by the image reading unit 60 is input to the background correction setting unit 104. Accordingly, the background correction setting unit 104 outputs a resolution conversion instruction as necessary, and creates a background correction LUT used for background correction. Details of specific processing executed by the background correction setting unit 104 will be described later.

Furthermore, in the printing apparatus 1, the read image data (RGB, input resolution) created by the image reading unit 60 is input to the collated read image creating unit 105. Accordingly, the collated read image creation unit 105 uses the read image data (RGB, input resolution) and the correction data (resolution conversion instruction, background correction LUT) input from the background correction setting unit 104. Then, the verification read image data (L ^* a ^* b ^* , inspection resolution (300 dpi (reference value) or 150 dpi)) is created. The details of the specific processing executed by the verification read image creation unit 105 will be described later.

On the other hand, the same original image data (RGB, set resolution) as that used for the current printing is input to the collation original image creation unit 103 of the printing apparatus 1. Accordingly, the collation original image creation unit 103 performs collation original image data (inspection color space (L ^* a ^* b ^{* in} this example), inspection resolution (in this example) based on the original image data (RGB, set resolution). Then, 300 dpi or 150 dpi)) is created. Here, the original image creation unit 103 for collation sets the inspection resolution of the original image data for collation to 300 dpi when the correction data (resolution conversion instruction) has not been received from the background correction setting unit 104, and the background correction setting unit 104 When correction data (resolution conversion instruction) is received, the verification resolution of the original image data for verification is converted to 150 dpi.

Subsequently, in the inspection apparatus 3, the original image data for verification (L ^* a ^* b ^* , inspection resolution) output from the verification original image creation unit 103 of the printing apparatus 1 obtained based on the same original image data. The collated read image data (L ^* a ^* b ^* , inspection resolution) output from the collated read image creating unit 105 of the printing apparatus 1 is input to the image collating unit 302. Accordingly, the image collating unit 302 collates the original image data for collation (L ^* a ^* b ^* , inspection resolution) and the read image data for collation (L ^* a ^* b ^* , inspection resolution) for each pixel. Do. As a collation method in the image collation unit 302, for example, for the original image data for collation (L ^* a ^* b ^* , inspection resolution) and the read image data for collation (L ^* a ^* b ^* , inspection resolution), two-dimensional There is a method of obtaining difference image data (L ^* a ^* b ^* , inspection resolution) by calculating, for each pixel, a pixel value difference between pixels existing at the same position on the coordinates.

  In the inspection apparatus 3, the collation result (difference image data) by the image collation unit 302 is input to the image defect determination unit 303. Accordingly, the image defect determination unit 303 determines the presence / absence of an image defect in the printed image printed on the paper P based on the collation result. As an image defect determination method by the image defect determination unit 303, for example, there is a method of detecting the occurrence of an image defect when the magnitude of the difference in the collation result is larger than a predetermined reference value. Here, when the occurrence of an image defect is detected, the determination result is transmitted to the setting device 2. In the setting device 2, an image for notifying the occurrence of an image defect is displayed on the UI 202 (see FIG. 3).

FIG. 14 is a flowchart for explaining the flow of processing executed by the background correction setting unit 104 shown in FIG. 7 in the printing and inspection procedures in the printing system.
In the background correction setting unit 104, first, the shading correction unit 1041 acquires background image data from the image reading unit 60 (step 101), and executes shading correction on the acquired background image data (step 102).

  Next, the inspection resolution determination unit 1042 is based on the gradation value of each pixel constituting the background image data subjected to the shading correction by the shading correction unit 1041, for example, a histogram (see FIG. 12B). (Gradation distribution) is created (step 103). Then, the inspection resolution determination unit 1042 determines whether or not the obtained gradation distribution has a wide range, that is, a pattern close to the third sheet Pc shown in FIG. 12B (step 104). When an affirmative determination (Yes) is made in step 104, the inspection resolution determination unit 1042 determines the resolution for the LUT creation unit 1043, the collation original image creation unit 103, and the collation read image creation unit 105 (resolution conversion unit 1052). A conversion instruction (instruction to change the inspection resolution from 300 dpi (reference value) to 150 dpi) is output (step 105). On the other hand, if a negative determination (No) is made in step 104, the inspection resolution determination unit 1042 proceeds directly to the next step 106 without outputting a resolution conversion instruction.

  Subsequently, the LUT creation unit 1043 creates a background correction LUT based on the background image data subjected to the shading correction by the shading correction unit 1041 (step 106), and the created background correction LUT is used as a collation read image. The data is output to the creation unit 105 (gradation conversion unit 1053) (step 107). If a resolution conversion instruction has been received from the inspection resolution determination unit 1042 in step 105, the LUT creation unit 1043 creates a background correction LUT corresponding to the resolution conversion instruction.

  Then, it is determined whether or not the next page, that is, the next printed matter exists (step 108). If an affirmative determination (Yes) is made in step 108, the process returns to step 101 to continue the processing for the background image data obtained from the printed material on the next page. On the other hand, if a negative determination (No) is made in step 108, a series of processing is completed.

FIG. 15 is a flowchart for explaining the flow of processing executed by the verification read image creation unit 105 shown in FIG. 7 in the printing and inspection procedures in the printing system.
In the collated read image creation unit 105, first, the shading correction unit 1051 acquires read image data from the image reading unit 60 (step 201), and executes shading correction on the acquired read image data (step 202).

  Next, the resolution conversion unit 1052 determines whether or not there is a resolution conversion instruction from the inspection resolution determination unit 1042 provided in the background correction setting unit 104 (step 203). If the determination in step 203 is affirmative (Yes), the resolution conversion unit 1052 reduces the resolution of the read image data subjected to the shading correction by the shading correction unit 1041 (in this example, the input resolution is Resolution conversion is executed (step 204), which is 300 dpi (same as the reference value of the inspection resolution, which is 150 dpi). On the other hand, when a negative determination (No) is made in step 203, the resolution conversion unit 1052 proceeds to the next step 205 as it is without executing resolution conversion.

  Subsequently, the gradation conversion unit 1053 is provided in the background correction setting unit 104 for the read image data subjected to the shading correction by the shading correction unit 1041 (or the read image data subjected to further resolution conversion). The tone conversion is executed using the background correction LUT received from the LUT creation unit 1043 (step 206). Here, the background image data which is the basis of the background correction LUT used for gradation conversion is included in the read image data to be subjected to gradation conversion.

Then, the color space conversion unit 1054 performs color space conversion for converting the input image space, that is, the RGB color space, to the inspection color space, that is, the L ^* a ^* b ^* color space, on the read image data that has been subjected to the gradation conversion. (Step 207), and the obtained read image data for verification is output to the transmission / reception unit 101 (Step 208).

  Then, it is determined whether or not the next page, that is, the next printed matter exists (step 209). If an affirmative determination (Yes) is made in step 209, the process returns to step 201 to continue the processing for the read image data obtained from the printed matter on the next page. On the other hand, if a negative determination (No) is made in step 209, a series of processing is completed.

FIG. 16 is a diagram for explaining an example of the background correction LUT created by the LUT creation unit 1043 shown in FIG. 7 and used by the gradation conversion unit 1053.
Here, FIG. 16A is set as the contents of the background image data of each color of RGB when white thick paper is used as the paper P described with reference to FIGS. 9A and 10A. The relationship with the background correction LUT is shown. FIG. 16B illustrates the relationship between the background image data contents of RGB colors and the background correction LUT set when white thin paper is used as the paper P described with reference to FIG. 9B. Is shown. Further, FIG. 16C shows the relationship between the background image data contents of RGB colors and the background correction LUT set when gray thick paper is used as the paper P described with reference to FIG. 9C. Is shown. Furthermore, FIG. 16D shows the background correction LUT and the contents of the background image data for each color of RGB when the thin paper is used as the paper P described with reference to FIG. Shows the relationship. FIG. 16E shows the contents of the background image data for each color of RGB and the background correction LUT set when white embossed paper is used as the paper P described with reference to FIG. Showing the relationship.

  Note that the gradation values of each of the RGB colors shown in FIGS. 16A to 16E are average gradations obtained by averaging the gradation values of each color for each color in a plurality of pixels constituting the background image data. Value. For example, when embossed paper is used as the paper P, as described with reference to FIG. 10C, the gradation value fluctuates (distributes) according to the unevenness present on the paper P. However, by averaging the gradation values of a plurality of pixels for each color, the influence of shading caused by unevenness present on the paper P is reduced.

  The background correction LUT also includes a red conversion table in which R (red) input gradations (before conversion) and output gradations (after conversion) are associated with each other for each RGB color, and an input floor of G (green). A green conversion table that associates a tone (before conversion) and an output gradation (after conversion), and a blue that associates an input gradation (before conversion) and an output gradation (after conversion) of B (blue) Conversion table. In this example, in order to simplify the description, the relationship between the input gradation and the output gradation is expressed by a linear expression in each of the red conversion table, the green conversion table, and the blue conversion table. Take the case as an example.

  For example, in the example shown in FIG. 16A, the gradation value of each color of RGB in the background image data is 255. Therefore, for each color of RGB, the red conversion table, the green conversion table, and the blue conversion table are set so that the input gradation value 0 becomes the output gradation value 0 and the input gradation value 255 becomes the output gradation value 255. Is created. In this case, tone correction is not substantially performed.

  For example, in the example shown in FIG. 16B, the gradation value of each color of RGB in the background image data is 230. For this reason, for each color of RGB, the red conversion table, the green conversion table, and the blue conversion table so that the input gradation value 0 becomes the output gradation value 0 and the input gradation value 230 becomes the output gradation value 255. Is created.

  For example, in the example shown in FIG. 16C, the gradation value of each color of RGB in the background image data is 190. For this reason, for each color of RGB, the red conversion table, the green conversion table, and the blue conversion table so that the input gradation value 0 becomes the output gradation value 0 and the input gradation value 190 becomes the output gradation value 255. Is created.

  For example, in the example shown in FIG. 16D, in the background image data, the R color gradation value is 230, and the G color and B color gradation values are 200, respectively. Therefore, for the R color, a red conversion table is created so that the input gradation value 0 becomes the output gradation value 0 and the input gradation value 230 becomes the output gradation value 255, and for the G color and the B color. The green conversion table and the blue conversion table are created so that the input gradation value 0 becomes the output gradation value 0 and the input gradation value 200 becomes the output gradation value 255.

  For example, in the example shown in FIG. 16E, the gradation value of each color of RGB in the background image data is 180 respectively. For this reason, for each color of RGB, the red conversion table, the green conversion table, and the blue conversion table so that the input gradation value 0 becomes the output gradation value 0 and the input gradation value 180 becomes the output gradation value 255. Is created.

Finally, the printing and inspection procedures in the printing system according to the present embodiment will be described with specific examples.
FIG. 17 illustrates the relationship between the printing original image obtained from the original image, the paper P to be printed on the printing original image, and the printed material obtained by printing the printing original image on the paper P. It is a conceptual diagram for. 17A shows the original image for printing, FIG. 17B shows the paper P, and FIG. 17C shows the printed matter. In this example, it is assumed that the printing original image shown in FIG. 17A is a character image of “Aiueo”, and white thin paper is used as the paper P shown in FIG.
The printed matter obtained in this case is in a state where the back surface of the paper P can be seen through. In the printed matter shown in FIG. 17C, the image “Aiueo” is printed in the in-frame area Ai, but no image is printed in the out-of-frame area Ao.

  FIG. 18 is a conceptual diagram for explaining the relationship between a read image obtained by reading a printed matter, a background image obtained from the read image, and a collation read image obtained based on the read image and the background image. It is. Here, FIG. 18A shows a read image, FIG. 18B shows a background image, and FIG. 18C shows a collation read image. In this example, since the paper P constituting the printed material is a white thin paper, the background portion (the portion where the background of the paper P is exposed) in the read image exhibits the black color that was the background at the time of reading. It is gray because of the reading exposure surface 82b (see FIG. 3). Here, in the present embodiment, the background correction setting unit 104 and the matching read image creation unit 105 perform background correction using the background image. Therefore, in the obtained matching read image, blank thin paper is used. The effect due to the use of as the paper P is removed.

  FIG. 19 shows a difference between a collation read image, a collation original image obtained based on the same original image as the collation read image, and a collation read image and collation original image obtained based on the same original image. It is a conceptual diagram for demonstrating the relationship with an image. Here, FIG. 19A shows a matching read image (the same as FIG. 18C), FIG. 19B shows a matching original image, and FIG. 19C shows a difference image. Yes. In this example, since the influence of the background image that has existed due to the background of the paper P is removed from the collated read image, as shown in FIG. The difference image obtained as the difference between the collation read image and the collation original image obtained on the basis of the above becomes an empty state. That is, the state of the paper P in the printed matter is less likely to affect the difference image.

  In this embodiment, since the acquisition of the background image data and the background correction based on the background image data are performed for each page of the printed matter output from the image forming unit 10, for example, the first provided in the printing apparatus 1. The first paper supply device 40A and the second paper supply device 40B store paper P having different states, and the supply source of the paper P is supplied to the first paper supply device 40A and the second paper supply during a series of printing operations. Even when switching to and from the apparatus 40B, the influence of errors in the background correction can be reduced.

  In the present embodiment, the background correction is performed based on the background image data extracted from the read image data obtained by reading the paper P on which the print image is recorded, that is, the printed material. However, the present invention is not limited to this. For example, via the UI 202 provided in the setting device 2, the type of the paper P (the thickness of the paper P, the color of the paper P, the paper texture of the paper P, etc.) to be used in the job to be executed is set as the background correction setting unit 104. In accordance with the type of the acquired paper P, determination regarding resolution conversion and creation of a background correction LUT may be performed.

  In this embodiment, the background correction LUT for each color used in the background correction is set by a linear expression. However, the present invention is not limited to this, and a secondary expression or more may be used. Also, a direct look up table (DLUT) may be used.

  Further, in the present embodiment, even when printing is performed using a paper P colored in a chromatic color (for example, light pink) or an embossed paper P, the background correction and color conversion are performed to perform the reading for verification. Although image data has been created, in the case of this type of paper P, the influence of the background may not be completely removed. Therefore, when using paper P colored chromatic (for example, light pink) or embossed paper P, data indicating that the reliability of the read image data for verification is not high is added. It is good to leave.

  Furthermore, in the present embodiment, the case where a full-color image is formed using the image forming unit 10 has been described. However, the present invention is not limited to this. For example, when a monochrome image is formed using only black In addition, the technique of this embodiment can be applied.

DESCRIPTION OF SYMBOLS 1 ... Printing apparatus, 2 ... Setting apparatus, 3 ... Inspection apparatus, 4 ... Network, 10 ... Image formation part, 60 ... Image reading part, 100 ... Control part, 101 ... Transmission / reception part, 102 ... Original image creation part for printing, DESCRIPTION OF SYMBOLS 103 ... Original image creation part for collation, 104 ... Background correction setting part, 105 ... Reading image creation part for collation, 201 ... Original image creation part, 202 ... UI, 203 ... Transmission / reception part, 301 ... Transmission / reception part, 302 ... Image collation , 303 ... Image defect determination unit, 1041 ... Shading correction unit, 1042 ... Inspection resolution determination unit, 1043 ... LUT creation unit, 1051 ... Shading correction unit, 1052 ... Resolution conversion unit, 1053 ... Tone conversion unit, 1054 ... Color Spatial conversion section, P ... paper

Claims (8)

Image forming means for forming an image based on original image data input from the outside on a recording material;
Reading means for reading an image formed on the recording material by the image forming means;
Obtaining means for obtaining the properties of the recording material by obtaining a gradation value of the extracted image data obtained by extracting a part of the read image data by the reading means;
When the gradation value distribution in the extracted image data acquired by the acquisition unit is narrower than a predetermined reference, the first resolution is selected as the resolution, and when the distribution is wider than the reference, the resolution is selected as the resolution. Selecting means for selecting a second resolution lower than the first resolution;
Correction that performs gradation correction on each pixel of the read image data obtained by reading the image by the reading unit based on the property acquired by the acquiring unit and the resolution selected by the selecting unit Means,
Creating means for creating reference image data from the original image data based on the resolution selected by the selecting means;
The reference image data created from the original image data and the comparison image data obtained by correcting the read image data by the correction unit are collated for each pixel, and the recording material is used by the image forming unit. And a detecting unit for detecting a defect in the image formed on the printing system. Wherein the acquiring means, among the read image data, wherein said image forming means result of reading an area where no image is formed by the recording material, according to claim 1, wherein the input as the extraction image data Printing system. The printing system according to claim 1 , wherein the property is one of characteristics relating to a ground color, a paper surface, and a thickness of the recording material. The printing system according to claim 1 , wherein the acquisition unit acquires the property of the recording material every time an image is formed on the recording material. The acquisition unit further creates a lookup table for performing the gradation correction based on the acquired property,
The printing system according to claim 1 , wherein the correction unit performs the gradation correction on each pixel of the read image data using the lookup table. The image forming means forms an image on the recording material using yellow, magenta, cyan and black color materials,
The reading unit reads an image formed on the recording material in red, green, and blue colors, so that red input image data, green input image data, and blue input image data are used as the read image data. Create
The acquisition means creates the lookup table corresponding to each of red, green and blue based on the property,
The correction means uses the lookup table corresponding to each of red, green, and blue created by the acquisition means, and uses the red input image data, the green input image data, and the blue input image data. The printing system according to claim 5 , wherein the gradation correction is performed on each of the pixels. Image forming means for forming an image on a recording material based on output image data obtained by performing first image processing on original image data input from outside;
Reading means for reading an image formed on the recording material by the image forming means;
Obtaining means for obtaining the properties of the recording material by obtaining a gradation value of the extracted image data obtained by extracting a part of the read image data by the reading means;
When the gradation value distribution in the extracted image data acquired by the acquisition unit is narrower than a predetermined reference, the first resolution is selected as the resolution, and when the distribution is wider than the reference, the resolution is selected as the resolution. Selecting means for selecting a second resolution lower than the first resolution;
Correction that performs gradation correction on each pixel of the read image data obtained by reading the image by the reading unit based on the property acquired by the acquiring unit and the resolution selected by the selecting unit Means,
Reference image data creating means for creating reference image data by performing correction based on the resolution selected by the selection means on the original image data and performing second image processing different from the first image processing; ,
In order to detect defects in the image formed on the recording material by the image forming means, the reference image data created by the reference image data creating means and the read image data are corrected by the correcting means. An image forming apparatus including output means for outputting the comparison image data obtained in the above. The output image data is defined in a first color space, the read image data is defined in a second color space different from the first color space, and the reference image data and the comparison image data are defined in the first color space. The image forming apparatus according to claim 7 , wherein the image forming apparatus is defined by a space and a third color space having a reproduction color gamut wider than the second color space.

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