JP2018146359A - Image forming device, control method thereof, and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique for generating an image feature amount that makes highly accurate diagnosis possible when abnormality occurs in an image forming device.SOLUTION: The image forming device outputs a diagnostic chart in which each pixel is formed with a concentration that corresponds to predetermined luminance (e.g., 50%) (S301), and acquires its scanned image (S302). The image forming device applies a conversion process capable of converting pixels of predetermined luminance to pixels of maximum luminance (100%) or minimum luminance (0%) to each pixel of the luminance data acquired from the scanned image and thereby performing the conversion process of the scanned image, and generates an image feature amount on the basis of the post-conversion luminance data (S306).SELECTED DRAWING: Figure 3

Description

  The present invention relates to an image forming apparatus, a control method thereof, and a program.

  In an image forming apparatus such as an electrophotographic MFP (multifunction peripheral), when a problem occurs in the quality of a formed image, an inspection image (for example, a diagnostic chart) is output, and based on the read result of the output image A technique for diagnosing an image forming apparatus is known. For example, Patent Document 1 proposes a fault diagnosis system that acquires a scan image of an image output by a printer, calculates an image feature amount based on the acquired scan image, and diagnoses a fault location using a predetermined diagnosis model. ing.

  When statistical data storing the correspondence between the image feature amount and the failure location as described above is used as a diagnosis model, it is possible to diagnose the failure location by a known method such as Bayesian estimation. In addition, by accumulating data relating to cases that occurred in the past as statistical data, learning of a diagnostic model can be realized and the accuracy of diagnosis can be improved.

Japanese Patent No. 4687614

  When the image forming apparatus is diagnosed by the above-described method, if the density of the diagnostic chart is close to the density of the portion where the image defect has occurred (for example, a stripe having a density higher or lower than the surrounding pixels), the image There is a possibility that highly accurate diagnosis cannot be performed in the forming apparatus.

  The present invention has been made in view of the above problems. An object of the present invention is to detect a streak image generated in an inspection image with high accuracy.

  The present invention can be realized as an image forming apparatus, for example. An image forming apparatus according to an aspect of the present invention includes an image forming unit that forms an image on a sheet, an inspection image that is formed on the sheet by controlling the image forming unit, and the inspection image that is output from the reading device. A control unit that acquires a reading value for each corresponding pixel; an offset unit that offsets the reading value for each pixel so that the reading value of the representative pixel becomes a predetermined value among the reading values for each pixel; Determining means for determining whether or not a streak occurs in the inspection image based on a read value of the target pixel and a read value of another pixel different from the target pixel among the offset read values for each It is characterized by having.

  According to the present invention, a streak image generated in an inspection image can be detected with high accuracy.

Block diagram showing a system configuration example The flowchart which shows the procedure of the image processing by the image processing part 114 Flow chart showing the procedure of diagnostic imaging processing The figure which shows the example of a detection of the image defect based on the conversion process of a scanned image Diagram showing an example of a diagnostic chart The figure which shows the example of the operation screen relevant to an image diagnosis process

  Below, the form for implementing this invention is demonstrated using drawing. The following embodiments do not limit the invention according to the claims, and all combinations of features described in the embodiments are not necessarily essential to the solution means of the invention.

[First Embodiment]
<Configuration of MFP>
FIG. 1 is a block diagram illustrating a configuration example of a system in the present embodiment. An MFP (Multi Function Printer) 101 forms (prints) an image on a recording material such as a sheet (paper) using toners of cyan (C), magenta (M), yellow (Y), and black (K). The image forming apparatus. The MFP 101 has not only a printing function but also a reading function for reading a document image (scanning) to generate a scanned image. The MFP 101 is connected to a network compatible device such as a PC 124 and a server (server device) 128 via a network 123 such as a LAN or the Internet. The PC 124 can transmit print data to the MFP 101 using the printer driver 125.

  The MFP 101 includes a controller 102, a printer (printing device) 115, a display device 118, a scanner (reading device) 119, an input device 120, a storage device 121, and a network interface (I / F) 122 connected to the controller 102. Is provided. The controller 102 includes a CPU 103. The network I / F 122 can communicate with external devices such as the PC 124 and the server 128 and receive data such as print data from the PC 124. The controller 102 includes a CPU 103, a renderer 112, an image processing unit 114, and an image diagnostic unit 126. The controller 102 further includes a RAM and a ROM (not shown). The CPU 103 controls the entire MFP 101 by reading the control program stored in the ROM in the storage device 121 or the controller 102 into the RAM and executing it.

  The controller 102 performs the following image processing. The interpreter 104 of the CPU 103 interprets the PDL (page description language) portion of the print data received from the PC 124 via the network 123 and the network I / F 122 and generates intermediate language data 105. The intermediate language data 105 is input to a CMS (Color Management System) 106 or 109 according to the setting by the printer driver 125.

  The CMS 106 performs color conversion of the intermediate language data 105 using the source profile 107 and the destination profile 108 to generate intermediate language data (after CMS) 111. The source profile 107 converts a device-dependent color space such as RGB or CMYK into a device-independent color space such as L * a * b * (hereinafter referred to as Lab) or XYZ determined by the CIE (International Lighting Commission). This is a profile for conversion. XYZ is a device-independent color space like Lab, and expresses colors with three types of stimulus values. The destination profile 108 is a profile for converting a device-independent color space into a CMYK color space depending on the device (printer 115).

  On the other hand, the CMS 109 performs color conversion of the intermediate language data 105 using the device link profile 110 to generate intermediate language data (after CMS) 111. The device link profile 110 is a profile for directly converting a device-dependent color space such as RGB or CMYK into a CMYK color space depending on the device (printer 115). In the present embodiment, the CMS (106 and 109) is divided according to the type of the profile (107, 108 and 110), but a plurality of types of profiles may be handled by one CMS. The type of profile is not limited to the example given in the present embodiment, and any type of profile may be used as long as the device-dependent CMYK color space of the printer 115 is used.

  The renderer 112 generates a raster image 113 from the intermediate language data 111 generated by the CPU 103. The image processing unit 114 performs image processing to be described later on the raster image 113 or the scan image generated by the scanner 119. The image diagnosis unit 126 is based on a scan image obtained by reading the diagnostic chart output by the printer 115 with the scanner 119 when a problem occurs in the quality of the image printed by the printer 115 (print quality). Perform image diagnostic processing.

  The printer 115 forms an image on a sheet using C, M, Y, and K toners. The printer 115 is controlled by the controller 102 and includes a paper feeding unit 116 that feeds sheets and a paper discharge unit 117 that discharges sheets on which images are formed. The scanner 119 includes an ADF (Auto Document Feeder), optically reads an image of a document, generates a scan image, and outputs it. The scanner 119 is used for various processes such as a scan process, a copy process, an image transmission process, and an image diagnosis process.

  The display device 118 is a UI (user interface) that displays an instruction to the user or the state of the MFP 101. The input device 120 is a UI for receiving input from the user. Note that some of the input devices are configured by touch panels and are integrated with the display device 118. The storage device 121 is a storage device such as an HDD that stores data processed by the controller 102 or data received by the controller 102.

  The server 128 is connected to the MFP 101 via the network 130. The network 130 is connected to the network 123. Although the server 128 is connected only to the MFP 101 in FIG. 1, a plurality of MFPs may be connected.

  The server 128 includes estimation databases (DB) 129 and 132 and a corresponding content estimation unit 131. The estimation DB 129 is a DB for summing up information that associates correspondence contents by a service person and the feature amount obtained by the image diagnosis unit 126 when a problem occurs in print quality in the MFP 101. The correspondence content estimation unit 131 estimates the correspondence content from the feature amount obtained by the image diagnosis unit 126 using the statistical data of the estimation DB 129. The more statistical data, the better the accuracy of estimation by the correspondence content estimation unit 131, and it becomes possible to determine the correspondence content without requiring judgment by a service person. The estimation DB 132 is a DB for aggregating data different from the estimation DB 129.

<Image Processing by Image Processing Unit 114>
Next, the image processing executed by the image processing unit 114 will be described with reference to FIG. FIG. 2 is a flowchart illustrating a procedure of image processing performed by the image processing unit 114 on the scanned image generated by the raster image 113 or the scanner 119. 2 is realized by processing by an ASIC (Application Specific Integrated Circuit) (not shown) provided in the image processing unit 114.

  In step S <b> 201, the image processing unit 114 determines whether the processing target image (received image data) is a scan image generated by the scanner 119 or a raster image 113. If the image to be processed is a raster image 113 bitmap-developed by the renderer 112, the image processing unit 114 is a CMYK image converted into CMYK depending on the printer device by the CMS. Proceed with the process. On the other hand, if the image to be processed is a scanned image, the image processing unit 114 proceeds with the process to S202 because the image is an RGB image.

  In step S202, the image processing unit 114 performs color conversion processing on the RGB image to generate a common RGB image. The common RGB image is defined in an RGB color space that does not depend on a device, and can be converted into a device-independent color space such as Lab by calculation.

  Thereafter, in S203, the image processing unit 114 performs filter processing on the common RGB image. When the filter processing is completed, in S204, the image processing unit 114 performs background removal processing on the image after the filter processing, thereby removing the ground color component from the image. In step S205, the image processing unit 114 generates a CMYK image by performing color conversion processing on the image on which the background removal processing has been performed.

  In step S <b> 206, the image processing unit 114 corrects the gradation characteristics of each color of C, M, Y, and K using a 1D-LUT (one-dimensional lookup table). Finally, the image processing unit 114 performs halftone processing such as screen processing and error diffusion processing to generate a CMYK image (binary), and ends the processing.

<Image diagnosis processing>
Next, an image diagnosis process executed by the CPU 103 will be described with reference to FIG. FIG. 3 is a flowchart showing the procedure of the image diagnosis processing according to the present embodiment. The processing of each step in FIG. 3 may be realized by the CPU 103 reading and executing a control program stored in a ROM or storage device 121 (not shown) in the controller 102, or by processing by an ASIC. Also good.

  The image diagnosis process is a process executed by a user or serviceman using the input device 120 when a problem occurs in the print quality of the printer 115, and is executed by the CPU 103 using the image diagnosis unit 126. . In the present embodiment, an example is shown in which an image feature amount used for diagnosing an abnormality in which a portion (black stripe) having a higher density than surrounding pixels is generated in an image formed by the printer 115 is shown. Note that the image feature amount is, for example, a parameter relating to the position where a streak image is generated in the diagnostic chart 500 shown in FIG. 5, the type of streak image (white streak or black streak), the density of the streak image, and the thickness of the streak image. It is. The diagnostic chart 500 corresponds to an inspection image.

  First, in S301, the CPU 103 controls the printer 115 to form (print) a diagnostic chart (inspection image) on a sheet. The diagnostic chart is an image in which each pixel is formed with a density corresponding to a predetermined luminance. FIG. 5 shows an example of a diagnostic chart. The diagnostic chart 500 of FIG. 5 is composed of, for example, halftone images of CMYK colors formed on a single sheet (paper) of A4 size at a density corresponding to a luminance of 50% with respect to the maximum luminance. Has been. That is, the diagnostic chart 500 is composed of pixels having a uniform density throughout the longitudinal direction of the sheet. Note that the density of the diagnostic chart may be a density corresponding to a luminance other than 50%.

  In step S <b> 302, when the sheet on which the diagnostic chart is formed is set in the scanner 119, the CPU 103 controls the scanner 119 to optically read the inspection image and generate image data. Thereby, the CPU 103 acquires the image data of the scanned image corresponding to the diagnostic chart.

  Thereafter, in S303, the CPU 103 controls the image diagnosis unit 126 to perform a scan image analysis process. Specifically, the CPU 103 acquires luminance data including the luminance value of each pixel corresponding to the image data generated by the scanner 119. In step S <b> 304, the CPU 103 controls the image diagnostic unit 126 to determine whether an image defect (black stripe) is detected in the diagnostic chart 500.

  Here, an image defect detection method will be described. The image diagnostic unit 126 calculates the average value of the luminance values of all the pixels included in the band image in the band image for each color included in the diagnostic chart 500. Next, the image diagnosis unit 126 compares the average luminance value of the band image with the luminance value for each pixel included in the band image. At this time, if the difference between the average luminance value and the luminance value of the target pixel is larger than the threshold, the image diagnosis unit 126 sets a determination value “1” for the target pixel. On the other hand, if the difference between the average luminance value and the target luminance value is equal to or smaller than the threshold value, the image diagnosis unit 126 sets a determination value “0” for the target pixel. Then, after setting the determination values for all the pixels, the image diagnosis unit 126 determines whether or not the pixels for which the determination value “1” is set are arranged in a line. If pixels whose difference from the average luminance value is larger than the threshold are arranged in a line, the image diagnosis unit 126 determines that a streak image is generated in the band image. Further, the CPU 103 generates an image feature amount of the scanned image based on the obtained luminance data.

  If an image defect is detected in S304, the CPU 103 advances the process to S308. In step S308, the CPU 103 stores the image feature amount generated in step S303 in the storage device 121, and ends the process. In this case, the CPU 103 displays the screen 600 of FIG. Further, the CPU 103 may notify the user of the detection result of the image defect as a result of the image diagnosis based on the diagnostic chart.

  On the other hand, if no image defect is detected in S304, the CPU 103 advances the process to S305. Here, for example, when the density of the diagnostic chart is close to the density of the portion where the image defect has occurred (black stripe), the image defect may not be detected by the analysis processing in S303. In such a case, the CPU 103 performs the processing of S305 to S307 in order to perform analysis processing with higher accuracy.

  In step S305, the CPU 103 controls the image diagnosis unit 126 to perform scan image conversion processing (offset processing). Specifically, the CPU 103 obtains a conversion process capable of converting a pixel having a predetermined luminance (50% in this example) into a pixel having the maximum luminance (100%) or the minimum luminance (0%) in S303. By applying it to each pixel of the luminance data, a scan image conversion process is performed. The CPU 103 generates an image feature amount based on the converted luminance data.

  In the above-described conversion processing, the luminance of a pixel that does not cause an image defect (not changed from the density corresponding to 50% luminance) among the pixels constituting the scan image is set to the maximum luminance (100%) or the minimum luminance. Convert to (0%). Thereby, it is possible to make the pixel in which the image defect has occurred stand out from the surrounding pixels. For the conversion of each pixel, a difference value (+ 50% or −50% in this example) of a predetermined brightness (50% in this example) with respect to the maximum brightness (100%) or the minimum brightness (0%) is calculated in S303. This can be realized by the process of adding to the luminance value of each pixel of the luminance data acquired in (1).

  For example, by converting a pixel with no image defect into a pixel having the maximum luminance (100%), it is possible to detect a portion (black stripe) having a higher density than the surrounding pixels in the image formed by the printer 115. become. That is, it is possible to diagnose an abnormality in which a portion having a higher density than the surrounding pixels is generated, and it is possible to generate an image feature amount used for such diagnosis. On the other hand, by converting pixels with no image defects into pixels with the minimum luminance (0%), it is possible to detect a portion (white streak) having a lower density than the surrounding pixels in the image formed by the printer 115. become. That is, it is possible to diagnose an abnormality in which a portion having a density lower than that of surrounding pixels is generated, and it is possible to generate an image feature amount used for such diagnosis.

  In the present embodiment, an example is shown in which image diagnosis processing (first diagnosis) is performed for an abnormality in which an image formed by the printer 115 has a portion (black stripe) having a higher density than the surrounding pixels. In the second embodiment, an example of image diagnosis processing (second diagnosis) for an abnormality in which an image formed by the printer 115 has a lower density (white stripes) than surrounding pixels is shown. Note that by setting the corresponding luminance to about 50% (50% or a density close to 50%) so that the density of each pixel in the diagnostic chart becomes an intermediate density, either black stripes or white stripes are set. Diagnosis can be performed, and more accurate diagnosis can be performed.

  Here, the CPU 103 may select which of the first diagnosis and the second diagnosis described above is performed according to a user instruction via the input device 120. In that case, the CPU 103 displays the screen 610 of FIG. 6 on the display device 118, for example, and accepts selection of the first diagnosis (selection of the button 612) or selection of the second diagnosis (selection of the button 611) from the user. In the present embodiment, it is assumed that the button 612 is selected by the user on the screen 610.

  FIG. 4A shows an example of the conversion process in S305 according to the present embodiment. When each pixel of the diagnostic chart is formed with a density corresponding to a brightness of 50% with respect to the maximum density (100%) as in this example, the brightness data conversion process is as shown in FIG. As shown, it can be realized easily. Here, pixels formed at a density corresponding to 50% luminance included in the diagnostic chart 500 correspond to representative pixels. Specifically, the CPU 103 generates a duplicate image (duplicate data) 402 of the scan image (luminance data) 401 and adds the luminance value of the corresponding pixel in the duplicate image 402 to the luminance value of each pixel of the scan image 401. Thus, the composite image 403 is acquired. In this way, the CPU 103 acquires the composite image 403 by adding the duplicate value to the read value (luminance value) for each pixel of the scan image. By this conversion processing, as shown in FIG. 4A, in the synthesized image 403, a portion other than the black stripe 400 generated in the scanned image 401 becomes white. On the other hand, the black stripe 400 does not become white but stands out from surrounding pixels.

  In step S <b> 306, the CPU 103 controls the image diagnosis unit 126 to determine whether or not a streak image is generated in the diagnostic chart 500 based on the luminance data (composite image 403) converted by the conversion process described above. A determination process for determining

  Here, the determination process will be described. The image diagnostic unit 126 calculates an average value of the luminance values of all the pixels converted in the conversion process. Next, the image diagnosis unit 126 compares the average luminance value after conversion with the luminance value after conversion for each pixel. At this time, if the difference between the average luminance value and the luminance value of the target pixel is larger than the threshold, the image diagnosis unit 126 sets a determination value “1” for the target pixel. On the other hand, if the difference between the average luminance value and the target luminance value is equal to or smaller than the threshold value, the image diagnosis unit 126 sets a determination value “0” for the target pixel. Then, after assigning determination values to all the pixels, the image diagnosis unit 126 determines whether or not the pixels having the determination value “1” are arranged in a line. If pixels whose difference from the average luminance value is larger than the threshold are arranged in a line, the image diagnosis unit 126 determines that a streak image is generated in the band image. Further, the CPU 103 generates an image feature amount based on the luminance data (composite image 403) generated by the conversion process.

  After that, in S307, the CPU 103 displays the result of the determination process on the display device 118, thereby notifying the user of the result of the diagnosis process. Finally, in step S308, the CPU 103 stores the image feature amount generated in step S306 in the storage device 121, and ends the process. Note that the CPU 103 may transmit the image feature amount to the server 128 for diagnosis of an abnormality of the MFP 101 or determination of corresponding contents by a service person.

  As described above, in the MFP 101 of this embodiment, the printer 115 forms an image on a sheet. The CPU 103 controls the printer 115 to form an inspection image on the sheet, and acquires a read value (luminance value) for each pixel corresponding to the inspection image (diagnosis chart) output from the scanner 19. The CPU 103 offsets the read value for each pixel so that the read value of the representative pixel becomes a predetermined value among the read values for each pixel. This offset processing corresponds to the scan image conversion processing in S303, and the predetermined value corresponds to the luminance value of the maximum luminance or the minimum luminance. Further, the CPU 103 determines whether or not a streak has occurred in the inspection image based on the read value of the target pixel among the offset read values for each pixel and the read value of another pixel different from the target pixel. judge. According to this embodiment, when an abnormality occurs in the MFP 101, a streak image can be detected with high accuracy.

[Second Embodiment]
In the second embodiment, an image diagnosis process for an abnormality in which an image formed by the printer 115 has a portion (white streak) having a lower density than surrounding pixels will be described. In the present embodiment, for the sake of simplification of explanation, the description will focus on the parts different from the first embodiment.

  In the present embodiment, the CPU 103 performs image diagnosis processing in the procedure shown in the flowchart of FIG. 3 as in the first embodiment. However, the scan image conversion process in S305 is different from that of the first embodiment.

  FIG. 4B shows an example of the conversion process in S305 according to the present embodiment. When each pixel of the diagnostic chart is formed with a density corresponding to 50% of luminance with respect to the maximum density (100%) as in this example, the luminance data conversion processing is as shown in FIG. As shown, it can be realized easily. Specifically, the CPU 103 generates a duplicate image (duplicate data) 412 of the scan image (luminance data) 411. Further, the CPU 103 adds the luminance value of the corresponding pixel in the duplicate image 412 to the luminance value of each pixel of the scan image 411 and subtracts it by the luminance value of the maximum luminance (100%) to obtain the composite image 413. . As described above, the CPU 103 obtains the composite image 413 by adding the duplicate value to the read value (luminance value) for each pixel of the scanned image and subtracting the read value with the luminance value of the maximum luminance. By this conversion processing, as shown in FIG. 4B, in the composite image 413, the portion other than the white stripe 410 generated in the scan image 411 becomes black. On the other hand, the white stripe 410 does not become black and stands out from surrounding pixels.

  In step S <b> 306, the CPU 103 performs a determination process for determining whether or not a streak image is generated in the diagnostic chart 500 based on the luminance data (the composite image 413) converted by the conversion process described above. Here, since the determination process is the same as that of the first embodiment, the description thereof is omitted. Further, the CPU 103 generates an image feature amount based on the luminance data (composite image 413) generated by the conversion process. After that, in S307, the CPU 103 displays the result of the determination process on the display device 118, thereby notifying the user of the result of the diagnosis process.

  Finally, in S308, the CPU 103 stores the image feature amount in the storage device 121, and ends the process, as in the first embodiment. Note that the CPU 103 may transmit the image feature amount to the server 128 for diagnosis of an abnormality of the MFP 101 or determination of corresponding contents by a service person.

  As described above, according to the present embodiment, a streak image can be detected with high accuracy as in the first embodiment.

[Other Embodiments]
The present invention supplies a program that realizes one or more functions of the above-described embodiments to a system or apparatus via a network or a storage medium, and one or more processors in a computer of the system or apparatus read and execute the program This process can be realized. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

101: MFP (image forming apparatus), 102: controller, 103: CPU, 114: image processing unit, 115: printer, 119: scanner, 121: storage device, 122: network I / F, 126: image diagnostic unit

Claims (14)

Image forming means for forming an image on a sheet;
Control means for controlling the image forming means to form an inspection image on the sheet and obtaining a read value for each pixel corresponding to the inspection image output from the reading device;
Offset means for offsetting the read value for each pixel so that the read value of the representative pixel becomes a predetermined value among the read values for each pixel;
Judgment to determine whether or not streaks occur in the inspection image based on the read value of the target pixel among the offset read values for each pixel and the read value of another pixel different from the target pixel Means,
An image forming apparatus comprising: The predetermined value is a luminance value of maximum luminance,
The offset means performs processing capable of converting the representative pixel into the pixel having the maximum luminance,
The image forming apparatus according to claim 1, wherein the determination unit determines whether or not a streak having a density higher than that of surrounding pixels is generated in the inspection image formed by the image forming unit. . The luminance of the representative pixel is 50% of the maximum luminance,
The image forming apparatus according to claim 2, wherein the offset unit adds a duplicate value of the read value to the read value for each pixel. The predetermined value is a luminance value of minimum luminance,
The offset means performs processing capable of converting the representative pixel into the pixel having the minimum luminance,
The image forming apparatus according to claim 1, wherein the determination unit determines whether or not a streak having a density lower than that of surrounding pixels is generated in the inspection image formed by the image forming unit. . The luminance of the representative pixel is 50% of the maximum luminance,
The image forming apparatus according to claim 4, wherein the offset unit adds a duplicate value of the read value to the read value for each pixel and subtracts the luminance value of the maximum luminance. The predetermined value is a luminance value of maximum luminance,
The offset means adds a difference value of the luminance of the representative pixel with respect to the maximum luminance to the read value for each pixel,
The image forming apparatus according to claim 1, wherein the determination unit determines whether or not a streak having a density higher than that of surrounding pixels is generated in the inspection image formed by the image forming unit. . The predetermined value is a luminance value of minimum luminance,
The offset means adds a difference value of the luminance of the representative pixel with respect to the minimum luminance to the read value for each pixel,
The image forming apparatus according to claim 1, wherein the determination unit determines whether or not a streak having a density lower than that of surrounding pixels is generated in the inspection image formed by the image forming unit. . A first diagnosis for an abnormality in which a streak having a density higher than that of surrounding pixels is generated in the inspection image formed by the image forming unit, and a second diagnosis for an abnormality in which a stripe having a density lower than that of surrounding pixels is generated. And further comprising selection means for selecting one according to a user instruction,
The offset means is
When the first diagnosis is selected by the selection unit, the reading value for each pixel is offset so that the reading value of the representative pixel becomes the luminance value of the maximum luminance among the reading values for each pixel. ,
When the second diagnosis is selected by the selection unit, the reading value for each pixel is offset so that the reading value of the representative pixel becomes the luminance value of the minimum luminance among the reading values for each pixel. The image forming apparatus according to claim 1. The offset means is
When the first diagnosis is selected, the difference value of the luminance of the representative pixel with respect to the maximum luminance is added to the read value for each pixel,
The image forming apparatus according to claim 8, wherein when the second diagnosis is selected, a difference value of the luminance of the representative pixel with respect to the minimum luminance is added to the read value for each pixel. The luminance of the representative pixel is 50% of the maximum luminance,
The offset means is
When the first diagnosis is selected, a duplicate value of the read value is added to the read value for each pixel,
9. The method according to claim 8, wherein when the second diagnosis is selected, a duplicate value of the read value is added to the read value for each pixel, and the luminance value of the maximum luminance is subtracted. Image forming apparatus. 11. The apparatus according to claim 1, further comprising a generation unit configured to generate an image feature amount used for diagnosis of the image forming apparatus based on the offset read value for each pixel. Image forming apparatus. 12. The transmission apparatus according to claim 11, further comprising: a transmission unit configured to transmit the image feature amount generated by the generation unit to an external server device for a diagnosis process for diagnosing an abnormality of the image forming apparatus. Image forming apparatus. A method for controlling an image forming apparatus including an image forming unit that forms an image on a sheet,
Controlling the image forming unit to form an inspection image on the sheet, and obtaining a reading value for each pixel corresponding to the inspection image output from the reading device;
Offsetting the read value for each pixel so that the read value of the representative pixel becomes a predetermined value among the read values for each pixel;
A step of determining whether or not a streak is generated in the inspection image based on a read value of the target pixel among the offset read values for each pixel and a read value of another pixel different from the target pixel. When,
A control method for an image forming apparatus, comprising:   A program for causing a computer to execute each step of the control method for the image forming apparatus according to claim 13.