JP4835470B2 - Image inspection apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a technique for inspecting the quality of an image formed by an image forming apparatus.

  When the image forming apparatus forms an image corresponding to a document, an original image may not be formed due to unexpected factors. Therefore, some image forming apparatuses have a function of inspecting whether or not an image is normally formed. When such an image forming apparatus forms an image corresponding to a document on a sheet (paper), the image is optically read, and the image on the sheet is inspected by comparing with the document image data on which the image is based. To do.

  Further, when such inspection is performed, there is a problem that the accuracy of the inspection is lowered if a fine image such as a halftone dot or a line is included. This is because the image data obtained by reading the image formed on the sheet and the original image data on which the image is based do not match the fine image even if the image is formed normally. It is because it is easy to produce. In general, such a fine image is not an essential content of a document, and even if there is a mismatch, the inspection result often does not influence.

As a technique for solving the problem caused by a fine image, for example, there is a technique described in Patent Document 1 or 2. Patent Document 1 proposes a technique in which an area corresponding to a character is binarized with a fixed threshold value, an area corresponding to a halftone dot image is binarized with a threshold value according to density, and compared with a base image. Has been. Patent Document 2 proposes a technique for obtaining a signed difference from each corresponding pixel of an image to be compared and inspecting using the result of integration.
JP-A-5-72710 JP-A-10-86344

However, any of the above-mentioned techniques cannot completely solve the problem caused by a fine image, and this image area can still be inconsistent.
The present invention has been made in view of the above circumstances, and an object thereof is to inspect an image including a fine image such as a halftone dot with higher accuracy.

  An image inspection apparatus according to the present invention includes a first acquisition unit configured to acquire first image data including a halftone dot region in an image region, and a second image region corresponding to the image region of the first image data. Second acquisition means for acquiring the image data, detection means for detecting a halftone dot region included in the image area of the first image data acquired by the first acquisition means, and the first acquisition means Comparing means for comparing the image area of the first image data acquired by the second image data and the image area of the second image data acquired by the second acquisition means, the image area of the first image data A comparison means for comparing the image area excluding the halftone dot area detected by the detection means with the image area of the second image data corresponding to the image area, and the comparison result by the comparison means. Output means to output Characterized in that it comprises. According to this invention, even if a mismatch occurs between the halftone dot areas of the first image data and the second image data, the comparison can be performed without including the mismatch in the evaluation.

  In the image inspection apparatus according to the present invention, the first acquisition unit acquires position information representing a position of a halftone dot region included in an image region of the first image data, and the detection unit includes the first The image area at the position represented by the position information acquired by the first acquisition means may be detected as a halftone dot area. For example, when the first image data is image data described in PDL (Page Description Language), the position information can be extracted from the first image data. Alternatively, the position information may be acquired from a host apparatus (printer controller or the like) of the image inspection apparatus.

  The image inspection apparatus according to the present invention includes a first acquisition unit configured to acquire first image data including a plurality of pixel data representing a gradation value and including a halftone dot region in the image region, and a gradation value. Second acquisition means for acquiring second image data comprising a plurality of pixel data representing and having an image area corresponding to the image area of the first image data; and the halftone dot area in the first image data Conversion means for converting the gradation value of the pixel data included in the pixel data and the gradation value of the pixel data of the second image data corresponding to the pixel data into a predetermined value, and the gradation value is converted by the conversion means Comparing means for comparing the image areas of the first and second image data, and output means for outputting a result of comparison by the comparing means. According to this invention, even when the entire image areas of the first and second image data are compared, it is possible not to include the mismatch of the halftone dot areas in the evaluation. Therefore, it is not necessary to determine whether each pixel data can be compared, and the processing can be made efficient in this respect.

  In the image inspection apparatus according to the present invention, the first acquisition unit acquires position information indicating a position of a halftone dot region included in an image region of the first image data, and the conversion unit includes the first A gradation value of pixel data included in a halftone dot area at a position represented by the position information in an image area of the image data, and a gradation value of pixel data of the second image data corresponding to the pixel data. The structure which converts into a predetermined value may be sufficient. For example, when the first image data is image data described in PDL (Page Description Language), the position information can be extracted from the first image data. Alternatively, the position information may be acquired from a host apparatus (printer controller or the like) of the image inspection apparatus.

Note that the present invention can also be specified as an image forming apparatus including the above-described image inspection apparatus and a program that realizes a function executed by the image inspection apparatus. For example, an image forming apparatus according to the present invention includes an acquisition unit that acquires document image data including a halftone dot area in an image region, and an image formation that forms an image according to the document image data acquired by the acquisition unit on a sheet. Means, an image reading means for reading the image formed on the sheet by the image forming means, and generating inspection image data representing the image, and a halftone dot included in the image area of the document image data obtained by the obtaining means Detecting means for detecting an area; and comparing means for comparing an image area of the original image data acquired by the acquiring means with an image area of the inspection image data generated by the image reading means, the original image data An image area excluding a halftone dot area detected by the detection means, and an image area of the inspection image data corresponding to the image area. Comparing means for comparing the bets, it is characterized in that an output means for outputting a result of comparison by the comparing means.
An image forming apparatus according to the present invention includes an acquisition unit that acquires a plurality of pixel data representing a gradation value and includes a halftone dot area in an image area, and an original image acquired by the acquisition unit An image forming unit that forms an image according to data on a sheet, and an image formed on the sheet by the image forming unit is read, and inspection image data including a plurality of pixel data representing the gradation value of the read image is generated. An image reading unit; and a conversion for converting a gradation value of pixel data included in the halftone dot area in the document image data and a gradation value of pixel data of the inspection image data corresponding to the pixel data into a predetermined value A comparison means for comparing the image area of the original image data and the image area of the inspection image data whose gradation values have been converted by the conversion means, and the comparison means. It is characterized in that an output means for outputting a result of the comparison.
In the image forming apparatus as described above, the resolution of the inspection image data generated by the image reading unit is generally lower than the resolution of the original image data or the image formed by the image forming unit. In many cases, a mismatch occurs in an image area including a fine image such as an area. Therefore, when it has such a structure, it can be said that the usefulness of this invention is especially high.

  According to the present invention, an image including a fine image such as a halftone dot can be inspected with higher accuracy.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(1) First Embodiment FIG. 1 is a block diagram showing a configuration of an image forming apparatus 1. As shown in FIG. 1, the image forming apparatus 1 includes an image forming unit 10, an inspection reading unit 20, a control unit 30, a storage unit 40, a UI (User Interface) unit 50, and a communication unit 60. ing.
The image forming unit 10 forms an image on a sheet based on the supplied document image data. The inspection reading unit 20 emits light from a light source, optically reads an image formed on the sheet, and generates image data. The control unit 30 includes a central processing unit (CPU) that controls the entire apparatus, a random access memory (RAM) that provides a work area for work, and a read only memory (ROM) that stores various control programs. Arithmetic processing is performed according to the described procedure. The storage unit 40 includes a storage device such as an HDD (Hard Disk Drive) and stores various data. A UI (User Interface) unit 50 includes a touch panel and various buttons, accepts an operation from a user, and notifies information by an image or sound. The communication unit 60 is an interface device for performing communication via a network. The communication unit 60 receives document image data from an external device such as a computer (not shown) via a network such as a LAN (Local Area Network).

Next, the configuration of the image forming unit 10 and the inspection reading unit 20 will be described with reference to FIG.
The image forming unit 10 includes a plurality of transport rolls 11, an image forming unit 12, and a fixing device 13. The inspection reading unit 20 is provided on the downstream side of the fixing device 13 of the image forming unit 10 and optically reads the sheet on which the document image is formed by the image forming unit 10.

  Here, the configuration of each part of the image forming unit 10 will be described. The plurality of transport rolls 11 transport the sheet in accordance with image formation. The image forming unit 12 forms an image by electrophotography. That is, the image forming unit 12 includes a photosensitive drum, a charging unit, an exposure unit, a developing unit, a transfer unit, and the like, and transfers an image to the sheet with black toner. The photosensitive drum is an image carrier and is a drum-shaped member that rotates around a shaft at a predetermined speed. The charging unit charges the surface of the photosensitive drum to a predetermined potential. The exposure unit irradiates the charged photosensitive drum with a beam to form an electrostatic latent image. The developing unit develops the image by attaching toner to the electrostatic latent image formed on the photosensitive drum. The transfer unit transfers the image developed on the photosensitive drum to a sheet. The fixing device 13 includes a roll member for heating and pressurizing the sheet, and fixes the image transferred to the sheet. With such a configuration, the image forming apparatus 1 stores the supplied document image data in the storage unit 40 and also causes the image forming unit 10 to store an image on a sheet with a predetermined resolution based on the document image data. Let it form. In the present embodiment, it is assumed that the resolution of the image forming unit 10 is 600 dpi (dots per inch). Hereinafter, an image formed by the image forming unit 10 is referred to as a “document image”.

  Next, the configuration of the inspection reading unit 20 will be described. FIG. 3 is a diagram illustrating a device configuration of the inspection reading unit 20. As shown in FIG. 3, the inspection reading unit 20 includes a light source 21, an imaging lens 22, and an image sensor 23.

  The light source 21 irradiates light to a predetermined position of the conveyed white sheet S. The imaging lens 22 images the reflected light from the sheet S at the position of the image sensor 23. The image sensor 23 includes an image sensor that reads an image on the sheet S. The image sensor 23 receives the imaged light, and generates and outputs image data corresponding to the amount of received light. The image data generated by the inspection reading unit 20 is composed of pixel data having a gradation number of “256”. That is, the inspection reading unit 20 represents the density of the original image formed on the sheet according to the magnitude of the pixel data value represented by 8 bits (256 gradations). In the present embodiment, the lightness is higher (brighter) as the gradation value is smaller, and the lightness is lower (darker) as the gradation value is larger. Under such a configuration, the inspection reading unit 20 reads a document image, generates image data representing an image to be inspected, and stores the image data in the storage unit 40. The image to be inspected is hereinafter referred to as “inspection image”, and the image data representing the inspection image is hereinafter referred to as “inspection image data”.

  In the present embodiment, the resolution of the image sensor 23 is lower than the resolution of the image forming unit 10 and is, for example, 200 dpi. This is because if the inspection image data has the same resolution as the original image data, the load when generating and transferring the inspection image data and comparing with the original image data increases.

Here, the document image and the inspection image will be described.
FIG. 4 is a diagram showing a document image A which is an example of a document image formed on a sheet. The document image A is composed of a plurality of characters, symbols, and halftone images, and is formed of black toner. A halftone dot image is a halftone image formed by halftone dots, and is a region indicated by hatching in FIG. The area of the sheet where the toner is not transferred is white because the sheet is exposed as it is.

The document image data that is the basis of the document image is composed of pixel data having a gradation number of “256”. The pixel data indicates white when the gradation value is “0”, black when it is “255”, and indicates halftone, that is, gray when the gradation value is “255”. The resolution of the document image data A is 600 dpi.
In addition, an image area corresponding to a halftone image of each image represented by the document image data and the inspection image data is hereinafter referred to as a “halftone area”.

The control unit 30 executes various image processes for comparing and inspecting the original image data and the inspection image data, in addition to the arithmetic processing for controlling each unit of the image forming apparatus 1. The image processing executed by the control unit 30 is illustrated in FIG. FIG. 5 is a functional block diagram illustrating functions realized by the control unit 30.
In the figure, a reduction processing unit 31, a halftone dot detection unit 32, a halftone dot removal unit 33, and a collation unit 34 are realized by reading and executing a control program stored in a ROM included in the control unit 30.

  The reduction processing unit 31 acquires document image data and inspection image data to be compared from the storage unit 40, and performs a process of reducing the number of gradations of pixel data constituting each of them based on a predetermined threshold value. . In the present embodiment, the reduction processing unit 31 performs a so-called binarization process in which the number of gradations of pixel data is reduced from 256 gradations to 2 gradations. When the reduction processing unit 31 performs binarization processing on the original image data and the inspection image data, the gradation value of the pixel data becomes either “0” or “1”. In the following, a pixel whose pixel data gradation value is “0” is represented in white, and a pixel whose pixel data gradation value is “1” is represented in black.

The halftone dot detection unit 32 detects a halftone dot region existing in the image represented by the original image data and the inspection image data that have been binarized by the reduction processing unit 31. The halftone dot detection unit 32 acquires position information representing the position of a halftone dot region of the original image together with the original image data, and detects a halftone dot region included in the image represented by the inspection image data.
FIG. 6 shows a halftone dot area in the original image data that is the basis of the original image A in FIG. In FIG. 6, the hatched area corresponds to the halftone dot area. The halftone dot detection unit 32 acquires position information that can specify the position of such a halftone dot region. For example, if the document image data is described in PDL (Page Description Language), the halftone dot detection unit 32 interprets the description content of the document image data stored in the storage unit 40 and acquires position information. To do. Alternatively, when the printer controller controls the image forming apparatus 1 as an external device, the halftone dot detection unit 32 may acquire position information from the printer controller. Note that the halftone dot detection unit 32 can also detect a halftone dot region from the relationship with the corresponding position of the document image for the halftone dot region included in the image represented by the inspection image data.

The halftone dot removing unit 33 removes the halftone dot region detected by the halftone dot detecting unit 32 from the image regions represented by the document image data and the inspection image data. Here, “removal” is to convert all the gradation values of the pixel data included in the halftone dot region to a predetermined value “0”, that is, white.
Note that the method of removing the halftone image by the halftone removal unit 33 may be shrinkage processing or masking. As shown in FIG. 7, in the contraction process, when the target pixel is “X” and the pixels in the vicinity 8 are “A” to “H”, the target pixel “X” and the pixels in the vicinity 8 If there is at least one pixel whose tone value is “0”, the tone value of the pixel data of the pixel of interest “X” is set to “0”, and all of the pixel of interest “X” and the vicinity of the surrounding 8 If the gradation value of the pixel data of the pixel of “1” is “1”, the gradation value of the pixel data of the target pixel is “1”. In this way, the halftone dots in the halftone dot region are contracted. The contraction process is not limited to the aspect in which the contraction process is performed by focusing on the pixel of interest and the pixels in the vicinity of the surrounding 8; for example, a 5 × 5 pixel region centered on the pixel of interest, or Further, the contraction process may be performed on a larger area.

  The matching unit 34 compares the document image data and the inspection image data from which the halftone dot area has been removed by the halftone dot removing unit 33, and performs a matching process for obtaining the degree of difference between them. In this collation processing, the collation unit 34 determines whether or not the gradation values of pixels at corresponding positions in each image data match using, for example, a residual sequential test method or the like. The collation unit 34 determines each pixel data and then generates and outputs data indicating the degree of difference between the document image data and the inspection image data. This data is hereinafter referred to as “difference information”.

  With the above configuration, the image forming apparatus 1 forms an image based on the document image data on a sheet, and inspects the sheet on which the image is formed using the inspection reading unit 20 as necessary. The timing at which the image forming apparatus 1 performs the inspection may be when instructed by the user or may be a predetermined cycle. Of course, the inspection may be performed every time the image forming unit 10 forms an image.

FIG. 8 is a flowchart illustrating a procedure of an operation in which the image forming apparatus 1 inspects an image.
Prior to the processing shown in FIG. 8, the control unit 30 supplies the received document image data to the image forming unit 10 to instruct to form an image. In response to this instruction, the image forming unit 10 forms a document image based on the document image data. When a document image is formed on the sheet and the sheet is conveyed to a predetermined position, the inspection reading unit 20 reads this document image as an inspection target and generates inspection image data. And the control part 30 acquires the test | inspection image data produced | generated by the test | inspection reading part 20 (step SA1).

  Subsequently, the control unit 30 performs binarization processing on the inspection image data and the document image data (step SA2). At this time, the control unit 30 compares the gradation value of each pixel data of the inspection image data and the document image data with a predetermined threshold value, and sets the gradation value of the pixel data whose gradation value is equal to or greater than the threshold value to “1”. The tone value of the pixel data whose tone value is less than the threshold value is converted to “0”. That is, the number of gradations of each image data is reduced from “256” to “2”.

  Next, the control unit 30 detects a halftone dot region present in each image represented by the document image data and the inspection image data based on the position information acquired together with the document image data (step SA3). Subsequently, the control unit 30 performs a process of removing the halftone dot area included in the detected document image and the halftone dot area included in the inspection image (step SA4).

  Then, the control unit 30 performs collation processing for comparing the original image data from which the halftone dot area has been removed in step SA4 and the inspection image data (step SA5). The control unit 30 compares the gradation values of the pixel data at corresponding positions with respect to these image data, and specifies pixels having different gradation values. Thereafter, the control unit 30 generates and outputs difference information based on the number of pixels having different gradation values (step SA6). Based on the difference information, the control unit 30 determines whether or not the degree of difference between the document image data and the inspection image data exceeds a predetermined allowable amount (step SA7). If the control unit 30 determines that the degree of difference exceeds a predetermined allowable amount (step SA7; YES), the control unit 30 displays a message “printing error” on the UI unit 50, for example, to the user. Notification is made (step SA8). On the other hand, if the control unit 30 determines that the degree of difference does not exceed the predetermined allowable amount (step SA7; NO), for example, a message “printing normally” is displayed on the UI unit 50. Then, the user is notified (step SA9).

  According to the first embodiment described above, when the image forming apparatus 1 generates the inspection image data obtained by reading the document image, each of the document image data and the inspection image data represented by the position information of the halftone dot area is generated. Remove the halftone area from the image. Then, the image forming apparatus 1 performs collation processing of the document image data and the inspection image data from which the halftone dot area is removed from the image. In this way, the image forming apparatus 1 can accurately remove a halftone dot region that is likely to cause a mismatch, so that the inspection can be performed with high accuracy.

(2) Second Embodiment Next, a second embodiment of the present invention will be described. Note that the present embodiment is similar in apparatus configuration to the above-described first embodiment, and therefore image processing and operations executed by the control unit 30 will be described.

  First, in the second embodiment, image processing executed by the control unit 30 is illustrated in FIG. FIG. 9 is a functional block diagram illustrating a function of inspecting an inspection image realized by the control unit 30. In the figure, the reduction processing unit 31, the differential image data generation unit 35, the region specifying unit 36, and the region removal unit 37 are realized by reading and executing a control program stored in the ROM of the control unit 30. .

  The reduction processing unit 31 acquires document image data and inspection image data to be compared, and performs a process of reducing the number of gradations of pixel data constituting each of them based on a predetermined threshold value. That is, the processing executed by the reduction processing unit 31 is the same as that in the first embodiment.

  The difference image data generation unit 35 compares the gradation values of pixels at corresponding positions of each image data in order to compare the document image data binarized by the reduction processing unit 31 and the inspection image data to obtain a difference. To do. Then, the difference image data generation unit 35 generates data indicating the difference between the gradation values in units of pixels as first difference image data. Note that when the gradation values of the compared pixel data match, the gradation value of the corresponding pixel data of the difference image data is “0”, and when the gradation values are different, the corresponding pixel data The gradation value is “1”. In particular, a pixel represented by black represented by pixel data having a gradation value of “1” in the first difference image data is hereinafter referred to as a “difference pixel”.

FIG. 10 exemplifies document image data W1 and inspection image data W2 for four pixels to be compared, and first difference image data W3 as a result of the comparison. In the figure, the gradation values of the pixel data W _1i (i = 1 to 4) constituting the document image data W1 and the pixel data W _2i constituting the inspection image data W2 are compared and correspond to these. _Assume that the pixel data of the difference image data is W _3i . In the figure, the gradation value of the pixel data of the pixel indicated by hatching is “1”, and the gradation value of the pixel data of the other pixels is “0”.
For example, the gradation value of the pixel data W ₁₁ is "0", since it is also the gradation value of the pixel data W ₂₁ "0", each of the tone values are the same, the first difference image data The gradation value of the pixel data W ₃₁ is “0”. Meanwhile, the gradation value of the pixel data W ₁₂ is "1", because the tone value of the pixel data W ₂₂ is "0", each of the tone values do not match, the pixels of the first difference image data The gradation value of the data W ₃₂ is “1”, which is a difference pixel. Similarly comparing other pixels, the gradation value of the pixel data W ₁₃ is “0” and the gradation value of the pixel data W ₂₃ is “1”. Therefore, the gradation value of the pixel data W ₃₃ is “1”, which is a difference pixel. Since the gradation value of the pixel data W ₁₄ is “1” and the gradation value of the pixel data W ₂₄ is also “0”, the gradation value of the pixel data W ₃₄ is “0”.

  As described above, the first difference image data is image data indicating the position and distribution state of the difference pixels, and has information about the position where the difference between the document image data and the inspection image data occurs. In other words, the region represented by the difference pixel of the first difference image data is a portion where the document image data and the inspection image data are inconsistent, or cannot be expressed due to reading the document image at a low resolution. That is, it corresponds to a halftone dot.

  The area specifying unit 36 acquires position information indicating the position of the halftone dot area of the document image, and specifies an area corresponding to the halftone dot area in the image indicated by the first difference image data.

  The area removing unit 37 generates image data obtained by removing the area specified by the area specifying unit 36 from the first difference image data. This image data is hereinafter referred to as “second difference image data”. Here, “removal” means that all the gradation values of the pixel data included in the area specified by the area specifying unit 36, that is, the area corresponding to the halftone dot area, are converted to a predetermined value “0”, that is, white. It is. That is, the second difference image data is data representing the difference between the document image data and the inspection image data excluding the difference in the area corresponding to the halftone dot area. The process performed by the area removing unit 37 is the same as the process performed by the halftone dot removing unit 33 described above.

FIG. 11 is a flowchart illustrating a procedure of an operation in which the image forming apparatus 1 inspects an inspection image in the present embodiment.
First, the control unit 30 causes the image forming unit 10 to form a document image, and acquires inspection image data generated by the inspection reading unit 20 (step SB1). Then, the control unit 30 performs binarization processing on the document image data and the inspection image data (step SB2). The above operation is the same as that of the first embodiment described above. Next, the control unit 30 compares the binarized inspection image data and the document image data, and generates first difference image data indicating a difference in gradation values (step SB3).

Subsequently, the control unit 30 specifies an area corresponding to a halftone dot area included in the image represented by the first difference image data based on the position information acquired together with the document image data (step SB4). Subsequently, the control unit 30 removes an image area corresponding to the halftone dot area from the image area represented by the first difference image data, and generates second difference image data (step SB5).
And the control part 30 produces | generates and outputs difference information according to the number of the difference pixels contained in the image which 2nd difference image data represents (step SB6). Then, similarly to the first embodiment described above, the control unit 30 determines whether or not the degree of difference between the document image data and the inspection image data exceeds a predetermined allowable amount based on the difference information. (Step SB7). If the control unit 30 determines that the degree of difference exceeds a predetermined allowable amount (step SB7; YES), the control unit 30 displays a message “printing error” on the UI unit 50, for example, to the user. Notification is made (step SB8). On the other hand, if the control unit 30 determines that the degree of difference does not exceed the predetermined allowable amount (step SB7; NO), for example, a message “printing normally” is displayed on the UI unit 50. Then, the user is notified (step SB9).

  According to the second embodiment described above, the image forming apparatus 1 can achieve the same effects as those of the first embodiment described above. In the present embodiment, the image forming apparatus 1 generates first difference image data, generates second difference image data obtained by removing an area corresponding to a halftone dot area from the first difference image data, and generates the second difference image data. The degree of matching between the document image data and the inspection image data is determined based on the difference image data. As a result, the image forming apparatus 1 can compare the original image data and the inspection image data without including a halftone dot region that is likely to cause a mismatch as a comparison target.

(3) Modifications Note that the present invention is not limited to the above-described embodiment, and can be implemented in various modes. Specifically, the following modifications are mentioned, for example. These modifications can be combined as appropriate.

  In the above-described embodiment, the image forming apparatus 1 in which the image inspection apparatus is integrally configured has been described as an example. However, for example, only a configuration corresponding to the image inspection apparatus may be configured as a detachable optional apparatus. In other words, the image inspection apparatus includes the inspection reading unit 20 and the control unit 30 described above, and acquires document image data from an image forming apparatus that is an external device.

  In the above-described embodiment, the image forming apparatus 1 detects the halftone dot area based on the position information acquired together with the document image data. However, the image forming apparatus 1 itself may generate the position information. This is because even if the document image data is supplied to the image forming apparatus 1, the position information of the halftone dot area is not always supplied. In such a case, the image forming apparatus 1 may detect a halftone dot region based on the document image data. Various known methods may be used for detecting the halftone dot region. For example, in the halftone dot area, fine halftone dots are densely arranged with a certain period, and therefore the control unit 30 checks the frequency of the gradation value of each pixel data constituting the image data and the constantness of the period to check the constancy. A point area can be extracted. Then, the control unit 30 may generate position information based on the extracted halftone dot region.

In the first embodiment described above, the control unit 30 performs the binarization process on the document image data and the inspection image data, and then performs the process of detecting and removing the halftone dot region. Each image data may be binarized after processing the region. That is, in the flowchart of FIG. 8, the binarization process has only been completed by step SA5.
In the above-described embodiment, the control unit 30 binarizes the document image data and the inspection image data. However, the control unit 30 may reduce the number of gradations such as 3 gradations or 4 gradations. . That is, a plurality of pieces of pixel data having the number of gradations of 3 or more included in the document image data and the inspection image data are reduced to a predetermined number of gradations of 2 or more, and thereafter the same processing can be performed. Of course, the control unit 30 may not reduce the number of gradations of the pixel data.

  In the first embodiment described above, all the gradation values of the pixel data included in the halftone area are converted to the predetermined value “0” in order to remove the halftone area. May be converted to For example, even if all the gradation values of the pixel data included in the halftone dot area are converted to “1”, there is no difference due to the halftone dot area between the inspection image data and the original image data.

1 is a block diagram illustrating a hardware configuration of an image forming apparatus according to an embodiment of the present invention. 1 is a diagram illustrating an apparatus configuration of an image forming apparatus. It is a figure explaining the structure of a test | inspection reading part. It is a figure which shows an example of a manuscript image. It is a functional block diagram which shows the function implement | achieved by the control part which concerns on 1st Embodiment. FIG. 6 is a diagram illustrating the position of a halftone dot region in a document image. It is a figure explaining a contraction process. It is a flowchart which shows the procedure of the operation | movement which the control part which concerns on the embodiment test | inspects an image. It is a functional block diagram which shows the function implement | achieved by the control part which concerns on 2nd Embodiment. It is a figure explaining a 1st difference image. It is a flowchart which shows the procedure of the operation | movement which the control part which concerns on the embodiment test | inspects an image.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 10 ... Image forming part, 11 ... Conveyance roll, 12 ... Image forming unit, 13 ... Fixing device, 20 ... Inspection reading part, 21 ... Light source, 22 ... Imaging lens, 23 ... Image sensor, 30 Control unit 31 Reduction processing unit 32 Halftone detection unit 33 Halftone dot removal unit 34 Collation unit 35 Difference image data generation unit 36 Area identification unit 37 Area removal unit 40 ... storage unit, 50 ... UI unit, 60 ... communication unit.

Claims (7)

First acquisition means for acquiring first image data including a halftone dot area in the image area;
Second acquisition means for acquiring second image data having an image area corresponding to the image area of the first image data;
Detecting means for detecting a halftone dot area included in the image area of the first image data acquired by the first acquiring means;
Comparing means for comparing the image area of the first image data acquired by the first acquiring means with the image area of the second image data acquired by the second acquiring means, Comparison means for comparing the image area of the image data of the image data excluding the halftone dot area detected by the detection means and the image area of the second image data corresponding to the image area;
An image inspection apparatus comprising: output means for outputting a result of comparison by the comparison means. The first acquisition means includes
Obtaining position information indicating a position of a halftone dot area included in the image area of the first image data;
The detection means includes
2. The image according to claim 1, wherein among the image areas of the first image data, an image area at a position represented by position information acquired by the first acquisition unit is detected as a halftone dot area. Inspection device. A first acquisition unit configured to acquire first image data that includes a plurality of pixel data representing a gradation value and includes a halftone dot area in an image area;
Second acquisition means for acquiring second image data comprising a plurality of pixel data representing a gradation value and having an image area corresponding to the image area of the first image data;
Conversion means for converting a gradation value of pixel data included in the halftone dot area in the first image data and a gradation value of pixel data of the second image data corresponding to the pixel data into a predetermined value When,
Comparing means for comparing the image areas of the first and second image data whose gradation values have been converted by the converting means;
An image inspection apparatus comprising: output means for outputting a result of comparison by the comparison means. The first acquisition means includes
Obtaining position information indicating a position of a halftone dot area included in the image area of the first image data;
The converting means includes
The gradation value of the pixel data included in the halftone dot region at the position represented by the position information in the image region of the first image data, and the gradation of the pixel data of the second image data corresponding to the pixel data The image inspection apparatus according to claim 3, wherein the value is converted into a predetermined value. Obtaining means for obtaining document image data including a halftone dot area in an image area;
Image forming means for forming an image on the sheet according to the document image data acquired by the acquiring means;
An image reading unit that reads an image formed on the sheet by the image forming unit and generates inspection image data representing the image;
Detecting means for detecting a halftone dot area included in the image area of the document image data acquired by the acquiring means;
Comparing means for comparing the image area of the original image data acquired by the acquisition means with the image area of the inspection image data generated by the image reading means, wherein the detecting means is the image area of the original image data. Comparing means for comparing the image area excluding the halftone dot area detected by the image area of the inspection image data corresponding to the image area;
An image forming apparatus comprising: output means for outputting a result of comparison by the comparison means. An acquisition means for acquiring original image data comprising a plurality of pixel data representing gradation values and including a halftone dot area in the image area;
Image forming means for forming an image on the sheet according to the document image data acquired by the acquiring means;
An image reading unit that reads an image formed on the sheet by the image forming unit and generates inspection image data including a plurality of pixel data representing a gradation value of the read image;
Conversion means for converting a gradation value of pixel data included in the halftone dot area in the document image data and a gradation value of pixel data of the inspection image data corresponding to the pixel data into a predetermined value;
Comparison means for comparing the image area of the original image data and the image area of the inspection image data, the gradation values of which have been converted by the conversion means;
An image forming apparatus comprising: output means for outputting a result of comparison by the comparison means. The image forming apparatus according to claim 5, wherein a resolution of an image formed by the image forming unit is different from a resolution of inspection image data generated by the image reading unit.

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