JP5361837B2 - Shading inspection apparatus, image forming apparatus, and shading inspection method - Google Patents

Description

  The present invention relates to a shading inspection apparatus, an image forming apparatus, and a shading inspection method, and includes a shading inspection apparatus used for shading inspection, an image forming apparatus such as a copying machine, a facsimile machine, and a multifunction peripheral (MFP: Multi Function Peripheral) equipped with the same. And improvement of the shading inspection method.

  Conventionally, this type of image forming apparatus rotates based on image data read from a CCD (charge coupled device) sensor by irradiating light on a document or image data read from a contact type sensor such as a CIS (contact image sensor). A latent image is formed on the surface of the photosensitive member, a toner image is formed from the latent image with toner supplied from a toner cassette, the toner image is transferred to a conveyed sheet, and the toner is transferred to the sheet through a heat fixing unit. A configuration in which the sheet is heated and fixed and discharged is well known.

  In addition, due to variations in components and functional causes, a shading phenomenon in which the density and luminance of image data for each line read from a CCD sensor or CIS sensor is not uniform is likely to occur, and CCD There is also a concern that dust or the like adheres to the sensor or CIS sensor surface and the same phenomenon occurs.

  In particular, in an image forming apparatus, during maintenance after shipment, image data obtained by reading a test sheet is displayed, and shading inspection is performed by determining whether a white line or a black line is generated on the display image. When a white line or the like is generated, the reading surface of the CCD sensor or CIS sensor is cleaned or the sensor itself is replaced.

  In particular, the CIS sensor is often used for reading the back side when reading on both sides, and is a sensor that reads an image in close contact with the surface of the document. Therefore, shading is likely to occur due to dust adhering to the surface, and shading inspection is important. is there.

  Conventionally, as a shading inspection method, for example, a shading inspection method disclosed in Japanese Patent Laid-Open No. 2007-267078 (Patent Document 1) has been proposed.

  This patent document 1 is a shading inspection method for reading a band having a predetermined density on a test chart and detecting a line from the image of the read band. The first average value of pixels belonging to a target pixel column and the target pixel Calculating a second average value of pixels belonging to a plurality of columns in the vicinity of the column, and determining that the shading data is abnormal when the first average value is not within an allowable range from the second average value. The detection of the line is possible with the same margin both near the center and at the end.

JP 2007-267078 A

  However, in Patent Document 1 described above, as described in the specification, it is necessary to previously install inspection software on a personal computer externally connected to the image forming apparatus, and a personal computer is required for inspection. In addition, it is time consuming and the detection of white lines, color lines, and the like is likely to be complicated, and processing time is required. Therefore, there is room for further improvement in performing accurate shading inspection with a simple configuration.

  The present invention has been made to solve such a problem, and is provided with a shading inspection apparatus, an image forming apparatus, and a shading inspection method capable of being mounted on an image forming apparatus and capable of simple and reliable shading inspection. For the purpose of provision.

  In order to solve such a problem, a shading inspection apparatus according to claim 1 of the present invention includes a document reading unit that optically reads a surface image of a fed document and acquires image data, and the read image data. A histogram is created when the image is a gray document, a threshold value for converting the image data from the gray document into a monochrome binary image is created from the histogram, and the image data from the gray document is converted into a monochrome binary image based on the created threshold value. An image conversion unit for converting to an image and a printing unit for printing the converted monochrome binary image as shading data are provided.

  A shading inspection apparatus according to a second aspect of the present invention includes a document reading unit that optically reads a surface image of a fed document and obtains image data, and displays a histogram when the read image data is a gray document. A threshold for creating and converting the image data from the gray document into a monochrome binary image from the histogram, and an image conversion unit for converting the image data from the gray document into a monochrome binary image based on the created threshold; And a display unit for displaying the converted monochrome binary image on the screen.

  A shading inspection apparatus according to a third aspect of the present invention has a configuration in which the document reading unit has a contact-type reading sensor that reads image data in close contact with the document.

  A shading inspection apparatus according to claim 4 of the present invention is configured such that the image conversion unit creates a histogram relating to a single color in image data of a read gray original.

  An image forming apparatus according to a fifth aspect of the present invention includes the shading inspection apparatus according to any one of the first to fourth aspects, and includes an image forming unit that forms an image of the read image data. Yes.

  A shading inspection method according to a sixth aspect of the present invention includes a document reading process for feeding a gray document and optically reading the inspection gray image on the surface to obtain image data, and an image relating to the read gray document. A histogram creation process for creating a histogram from data, a threshold creation process for creating a threshold for converting image data related to the gray original into a black and white binary image from the histogram, and image data related to the gray original based on the created threshold An image conversion process for converting to a binary image; and a printing process for printing the converted monochrome binary image as shading data.

  A shading inspection method according to a seventh aspect of the present invention includes a document reading process of feeding a gray document and optically reading the inspection gray image on the surface to obtain image data, and an image related to the read gray document. A histogram creation process for creating a histogram from data, a threshold creation process for creating a threshold for converting image data related to the gray original into a monochrome binary image from the histogram, and image data relating to the gray original based on the created threshold An image conversion process for converting to a monochrome binary image; and a display process for displaying the converted monochrome binary image on a screen.

  In the shading inspection method according to an eighth aspect of the present invention, the document reading process uses a contact-type reading sensor that reads image data in close contact with the document.

  In the shading inspection method according to claim 9 of the present invention, the image conversion process creates a histogram relating to a single color in the image data of the read gray original.

  In such a shading inspection apparatus and a shading inspection method according to claims 1 and 6 of the present invention, a gray original is fed, and a gray image for inspection on the surface is optically read to obtain image data. A histogram is created from image data relating to a gray document, a threshold value for converting the image data relating to the gray document into a monochrome binary image is created from the histogram, and the image data relating to the gray document is converted into a monochrome binary image based on the threshold value. Since it is converted and the black and white binary image is printed and displayed as shading data, it can be mounted on an image forming apparatus, and a simple and reliable shading inspection can be performed.

  In the shading inspection apparatus and the shading inspection method according to the second and seventh aspects of the present invention, a gray original is fed, an inspection gray image on the surface is optically read to obtain image data, and the read gray original is read. A histogram is created from the image data, a threshold value for converting the image data relating to the gray original into a monochrome binary image is created from the histogram, and the image data relating to the gray original is converted into a monochrome binary image based on the created threshold value. Since the binary image obtained by re-converting the monochrome binary image is output and the converted monochrome binary image is displayed on the screen, a simple and reliable shading inspection can be performed by the preview function without consuming print toner or the like. In addition, it becomes possible to easily determine the cause of white stripes or black stripes.

  In the shading inspection apparatus and the shading inspection method according to the third and eighth aspects of the present invention, the document reading process is performed using the contact-type reading sensor that closely contacts the document and reads the image data. It is easy to detect dust or the like that easily adheres to the surface of the sensor to be read.

  In the shading inspection apparatus and the shading inspection method according to the fourth and ninth aspects of the present invention, a histogram relating to a single color in the image data of the read gray original is created. Implementation is possible.

1 is a block diagram showing an embodiment of an image forming apparatus equipped with a shading inspection apparatus according to the present invention. It is a principal part block diagram which shows the principal part of the shading test | inspection apparatus which concerns on this invention. FIG. 3 is a diagram illustrating an operation panel unit of the image forming apparatus according to the present invention. It is a figure explaining operation | movement of the shading test | inspection apparatus which concerns on this invention. It is a figure explaining operation | movement of the shading test | inspection apparatus which concerns on this invention. It is a flowchart explaining operation | movement of the shading test | inspection apparatus which concerns on this invention. It is a figure explaining the operation | movement regarding another structure of the shading test | inspection apparatus which concerns on this invention.

  Embodiments of a shading inspection apparatus, an image forming apparatus, and a shading inspection method according to the present invention will be described below with reference to the drawings. The shading inspection apparatus and the shading inspection method of the present invention will be described in the process of describing the image forming apparatus of the present invention.

  FIG. 1 is a block diagram showing an embodiment of an image forming apparatus A according to the present invention.

  The image forming apparatus A includes a document reading unit 3, a storage unit 5, an operation panel unit 7, a printing unit 9, and a transmission / reception unit 11 with the main control unit 1 as a center, and constitutes, for example, a multifunction peripheral (MFP). . Note that the image forming apparatus A has a configuration other than this, but since it is not the gist of the present invention, description and illustration are omitted.

  The document reading unit 3 is a scanner that optically reads the double-sided image from the automatically fed document 13 and generates image data as will be described later, and image data for each page under the control of the main control unit 1. Is stored in the storage unit 5. Details of the document reading unit 3 will be described later.

  The storage unit 5 stores read image data from the document reading unit 3 and received image data (to be described later) from the transmission / reception unit 11 under the control of the main control unit 1, and also reads and writes the operation program of the main control unit 1. Possible, for example, a hard disk.

  The operation panel unit 7 is arranged on the upper part of the main body case 15 shown in FIG. 2 (not shown in FIG. 2), and is known as a display unit capable of displaying various operation states under the control of the main control unit 1. It has a function as an input unit such as a liquid crystal display panel and a touch switch for receiving an operation instruction of the apparatus.

  For example, as shown in FIG. 3, the operation panel unit 7 is associated with various operation instructions and selection keys 7a such as printing (copying) processing, printer processing, scanner processing, facsimile transmission / reception processing, etc. In addition to the publicly known numeric keypad 7b, start key 7c, stop key 7d for inputting setting change of setting items, the display panel unit 7e for displaying the operation status of the apparatus is provided.

  The display panel 7e is provided with an inspection start key 7f for starting a shading inspection on one side (front surface) of the document 13 and an inspection start key 7g for starting a shading inspection on the opposite surface (back surface).

  The start key 7c can be used to input the reading of the document 13, and the stop key 7d can be used to input an instruction to stop reading the document 13. The inspection start keys 7f and 7g can be used to start the shading inspection.

  The printing unit 9 is arranged in the main body case 15 of FIG. 2, and although not shown in detail, a plurality of paper feeding units on which paper is set and the above-described image data are developed into print image image data from the toner cassette. A color or monochrome printing engine as an image forming unit having a transfer unit (rotating photoreceptor) that develops toner with toner and transfers a toner image onto a sheet, and a fixing unit that fixes a transferred image on the transferred sheet It is.

  The transmission / reception unit 11 in FIG. 1 is an interface unit that transmits / receives information such as various image data to / from an information processing apparatus B such as a computer via a network NT according to a predetermined protocol.

  The main control unit 1 includes a CPU, a ROM that stores an operation program for the CPU, and a working RAM (none of which are shown), and includes the document reading unit 3, the storage unit 5, and the operation described above. While controlling the panel part 7, the printing part 9, the transmission / reception part 11, etc., the function part (not shown) of the image forming apparatus A is controlled. Other functions will be described later.

  Next, the document reading unit 3 described above will be described with reference to FIG.

  In FIG. 2, transparent contact glasses 17 and 19 are arranged on the upper side of the main body case 15. The contact glass 17 has an elongated rectangular shape, and is in the main scanning direction of the document 13 to be read (perpendicular to the conveyance direction of the document). In the direction of the main body case 15.

  The contact glass 19 has a rectangular shape larger than the size of the document 13 and is disposed so as to extend in the direction opposite to the contact glass 17 from the vicinity of the contact glass 17.

  Inside the main body case 15, immediately below the contact glass 17, a line-shaped light source 21 made of, for example, a light-emitting diode that emits light toward the document 13 positioned on the contact glass 17, and the contact glass 17 side. A reading unit 27 is formed which includes a mirror 23 that receives and reflects the reflected light and a storage portion 25 that stores these mirrors.

  The reading unit 27 is connected to a moving unit 29 disposed inside the main body case 15. The reading unit 27 starts from a position immediately below the contact glass 17 and extends along the contact glass 19 in parallel to the right end in the figure. While moving intermittently at the timing, the moving part 29 is controlled to reciprocate so as to return toward the start when it reaches the end.

  In the main body case 15, mirrors 31 and 33, a condenser lens 35, and a first reading unit 37 are arranged on the optical axis of the reflected light from the mirror 23 to form an optical system.

  The first reading unit 37 is composed of, for example, a CCD line sensor, and is based on the reflected light from the reading unit 27 that is bent and guided by the mirrors 31 and 33 and collected by the condenser lens 35. The image data converted into the digital signal is output to the arithmetic unit 39.

  The calculation unit 39 performs various filter processing calculations and processing operations such as enlargement / reduction on the digital image data from the first reading unit 37 and the second reading unit 51 to be described later, via the main control unit 1. The data is output to the storage unit 5.

  An automatic document feeder 41 is placed on the main body case 15 so as to cover the contact glasses 17 and 19, and the end portion is fixed to the main body case 15 by a hinge mechanism (not shown) so that it can be displaced in a fan shape. .

  The automatic document feeder 41 has a main body 43 positioned above the contact glass 17, and a document tray 45 and a paper discharge tray 47 extending from the main body 43 are positioned above the contact glass 19.

  A plurality of moving units serving as a moving unit that feeds the document 13 from the document tray 45, conveys the document 13 in a loop through the vicinity of the reading unit 27, and discharges it to the sheet discharge tray 47 in the main body 43 of the automatic document conveyance unit 41. The conveying roller 49 is arranged.

  In the main body 43, a second reading unit 51 is disposed in the vicinity of the reading unit 27. The second reading unit 51 is composed of, for example, a line sensor type CIS sensor, and has a function of directly reading a document image by contacting the back surface of the conveyed document 13 and outputting digital image data to the calculation unit 39. ing.

  The plurality of transport rollers 49 are rotationally controlled by a reading control unit 53 described later, and the reading control unit 53 is a part of the function of the main control unit 1 described above and has the following functions. Yes.

  That is, the reading control unit 53 performs reading control of the document reading unit 3 so that the document 13 is read page by page based on an instruction input from the start key 7 c or the stop 7 d, and stores read image data in the storage unit 5. In addition, it has a function of controlling the reading stop of the document 13 with respect to the document reading unit 3.

  The reading control unit 53 has a function of controlling execution of reading of the original 13 with respect to the original reading unit 3 when the start of shading inspection is instructed by the inspection start key 7f or 7g. In this case, the first or second reading unit 37 or 51 has a function of controlling output of image data to the main control unit 1.

  Next, the function of the main control unit 1 described above will be further described with reference to FIG.

  The main control unit 1 has a function as the image conversion unit 55 in addition to the functions described above.

  That is, the image conversion unit 55 determines whether the read image data obtained from the document reading unit 3 is a gray document under a situation where the shading test start is instructed by the inspection start key 7f or 7g. When it is determined that there is a histogram, a histogram relating to the gray original image data is created, and a threshold value for converting the image data from the gray original into a monochrome binary image is created from the histogram.

  FIG. 4 shows a histogram relating to gray original image data. For example, if the CIS sensor is in a normal state without dust or the like, the normal characteristic of the mountain shape, which is a collection of normal data, as shown by the solid line in FIG. If dust or the like is attached to a part of the line, it becomes an abnormal characteristic of a mountain shape that is a collection of abnormal data as shown by the broken line in FIG.

  The image conversion unit 55 has a function of creating a threshold value corresponding to the created histogram characteristics, and for inverting and converting individual pixels forming each line of gray original image data into a monochrome binary image. Yes. As the threshold value, for example, a value obtained by returning a certain interval from the highest peak portion (the portion with the most data) of the normal characteristic histogram is determined as the threshold value.

  The image conversion unit 55 converts the individual pixels of the image data relating to the gray original into a black and white binary image based on the created threshold value, and outputs the converted black and white binary image to the printing unit 9. It also has a function to control printing.

  For example, each pixel of gray original image data has 256 gradations between white and black, and when the normal characteristic of the solid line in FIG. 4 is obtained as a histogram, the gradation of 128 gradations or more with 128 gradations as a threshold value. All the gradation areas are converted to black pixels, and all gradation areas less than 126 gradations are converted to white pixels.

  On the other hand, when the abnormal characteristic of the broken line in FIG. 4 is obtained, the threshold value is not changed by that, and pixel conversion is performed by determining the threshold value with reference to the gradation having the largest data in the normal characteristic histogram. Thus, if white stripes are detected during reading, it can be clearly output by binarization processing.

  For this reason, when the abnormal characteristic shown by the broken line in FIG. 4 is obtained, the gradation area somewhat darker than the normal characteristic is also converted into white pixels, so that dust or the like adheres to the second reading unit 51 (CIS sensor). The vicinity of the current pixel is converted into a white pixel, which tends to be clear.

  That is, when dust is attached to the CIS sensor, the gray portion is read in white due to the characteristics of the CIS sensor. Therefore, in the histogram in which the abnormal characteristic is seen, the abnormal characteristic portion itself has a threshold value. Since the white portion is determined and the other portions are output in black, the white lines are emphasized and clear.

  FIG. 5A shows a state in which shading data that has been inverted and converted into a black and white binary image in a state where dust or the like is not attached in the second reading unit 51 (CIS sensor) is printed on a sheet by the printing unit 9, and FIG. Fig. 5 shows a state in which the printing unit 9 prints and displays the shading data inverted and converted into a black and white binary image in a state where dust or the like is attached in the second reading unit 51 (CIS sensor).

  Note that FIG. 5B exaggerates the vicinity of the pixel corresponding to the portion to which dust or the like is attached as a white pixel region, and the white pixel region is not necessarily displayed wide.

  Next, the operation of the shading inspection apparatus according to the present invention will be briefly described with reference to the flowchart of FIG.

  As an example, an example will be described in which an inspection gray original 13 having a gray density on both sides or the entire side of a sheet is fed and the gray density plane is read by the second reading unit 51.

  When the inspection gray document 13 is set on the document tray 45 of the automatic document conveying section 41 and the inspection key 7g of the operation panel section 7 is touched to start the shading inspection, the reading control section 53 controls in step S1. The roller 49 feeds the gray original 13 from the original tray 45, conveys it in a loop, and discharges it to the discharge tray 47.

  In this process, the second reading unit 51 directly reads the back image of the conveyed gray document 13 and outputs the inspection gray image to the main control unit 1 via the calculation unit 39 (document reading process).

  In the next step S2, the image conversion unit 55 creates a histogram from the read gray document image data (histogram creation process). In step S3, the image conversion unit 55 converts the gray document image data into a monochrome binary image. Is created from the histogram (threshold creation processing).

  Further, in step S4, the image conversion unit 55 converts the gray original image data into a black and white binary image (image conversion processing) based on the created threshold value, and the black and white binary image is converted into shading data as shown in FIG. The image conversion unit 55 controls the printing unit 9 to perform printing (printing process).

  Therefore, when no dust or the like is attached to the second reading unit 51, an image whose entire surface is converted to a black image is printed as shown in FIG. 5A, and dust or the like is attached to the second reading unit 51. In the state, as shown in FIG. B, an image in which a portion to which dust or the like is attached is converted into a white image is printed on the paper.

  Such a process constitutes the shading inspection method of the present invention.

  Then, the service staff or user of the image forming apparatus A observes the printed sheet, and if white streaks or the like are displayed in the printed image, the second reading unit 51 is contaminated. The CIS sensor reading surface is cleaned and dust is removed or the CIS sensor itself is replaced.

  As described above, the shading inspection apparatus according to the present invention includes a document reading unit 3 including a contact-type reading sensor that closely contacts a fed document and optically reads the surface image to acquire image data, and the read image data. Is a gray document, a histogram is created, a threshold for converting image data from the gray document into a monochrome binary image is created from the histogram, and image data from the gray document is converted into a monochrome binary based on the created threshold An image conversion unit 51 that converts to an image, and a printing unit 9 that prints the converted monochrome binary image as shading data are provided.

  Therefore, by observing the printed paper, it becomes easy to determine the stain on the reading unit forming the original reading unit 3, and a reliable shading inspection can be performed easily and in a short time, and a shading inspection function is provided for image formation. It can be mounted on the device A. In particular, it is useful for reading gray originals.

  In addition, since the dust adhering to the CIS sensor or the like forming the second reading unit 51 is easily displayed as a white streak, it is easy for service personnel and users to determine whether or not the CIS sensor needs to be replaced.

  In the shading inspection apparatus of the present invention, the document reading unit 3 is not limited to a contact type reading sensor that is in close contact with a document and reads a surface image thereof. Is particularly useful because it easily adheres dust or the like to the surface.

  Needless to say, the shading inspection apparatus according to the present invention is applicable not only to the inspection and detection of dirt in the second reading unit 51 but also to the inspection and detection of dirt in the first reading unit 37.

  Further, in the shading inspection apparatus of the present invention, if the histogram in the image data of the read gray original is created as a histogram relating to a single color, an accurate shading inspection can be performed even if the configuration and processing are simplified. A configuration is also possible in which a histogram relating to a plurality of colors in the data is created.

  Further, the gray density of the gray original for inspection is arbitrary, but a density of about 128 gradations is preferable from the viewpoint of obtaining a clear image.

  Incidentally, the above-described shading inspection apparatus of the present invention is configured to print image data converted from a gray original to a monochrome binary image, but the present invention is not limited to this.

  That is, a document reading unit 3 including a contact-type reading sensor that closely contacts a fed document and optically reads the surface image to acquire image data, and a histogram of the read image data when the read image data is a gray document. A threshold value for creating and converting the image data from the gray document into a monochrome binary image from the histogram, and an image conversion unit 55 for converting the image data from the gray document into a monochrome binary image based on the created threshold value; Further, a configuration including a display panel unit (display unit) 7e for displaying the converted monochrome binary image on the screen is also possible.

  According to such a configuration, since the image data converted from the gray original to the monochrome binary image is displayed on the display panel unit 7e, simple and reliable shading can be performed by the preview function without consuming toner or the like by the printing unit 9. The inspection can be performed, and the cause of white stripes or black stripes can be determined.

  In FIG. 7A, the image conversion unit 55 converts the gray original image data into a black and white binary image based on the created threshold (image conversion processing), and the black and white binary image is displayed on the display panel unit 7e as shading data. Indicates the status (display processing).

  Therefore, it is possible for the service person to check for the presence of white stripes without using the printing toner in the image forming apparatus A and without consuming the printing toner purchased by the user. There is no need for printing on the side, and the processing speed is expected to improve, and the maintenance work period is also shortened.

  In this regard, in the configuration in which the converted monochrome binary image data is printed by the printing unit 9 as shading data, as shown in FIG. 7B, one sheet so that the density image above the threshold is black based on the read gray original. It will print on the eye paper.

  However, with the printed first sheet, it may be difficult to determine whether the white streak is caused by the document reading unit 3 or the transfer unit 9 in the printing unit 9, for example. It is necessary to reverse the black and white image data again, print it on the second sheet, and check whether the black and white are reversed at the same position on the first and second sheets.

  In such a configuration, naturally, the amount of consumption of printing toner is large. In particular, since white stripes are detected, toner consumption increases during printing of the first sheet. However, the display panel unit 7e uses a monochrome binary image as shading data. This can be improved in the image display configuration, the processing speed can be improved, and the confirmation time for the service person can be shortened.

  In FIG. 7B, the image conversion unit 55 converts the gray original image data into a black and white binary image based on the created threshold (image conversion processing), and the black and white binary image is printed by the printing unit 9 as shading data. And the second sheet on which the converted black-and-white binary image is inverted and converted again by the image conversion unit 55, and white pixels are converted to black pixels and black pixels are converted to white pixels again. ing.

  If the image forming apparatus A is configured by including the shading inspection method of the present invention and the above-described shading inspection apparatus, the same effect as the above-described shading inspection apparatus can be obtained.

1 Main control unit 3 Document reading unit 5 Storage unit 7 Operation panel unit (display unit, input unit)
7a selection key 7b numeric keypad 7c start key 7d stop key 7e display panel section 7f, 7g inspection start key 9 printing section (image forming section)
11 Transmission / Reception Unit 13 Document 15 Body Case 17, 19 Contact Glass 21 Light Source 23, 31, 33 Mirror 25 Storage Unit
27 Reading unit 29 Moving section 35 Condensing lens 37 First reading section 39 Calculation section 41 Automatic document conveying section 43 Main body section 45 Document tray 47 Paper discharge tray 49 Roller 51 Second reading section 53 Reading control section 55 Image conversion section A Image forming apparatus B Information processing apparatus NT Network

Claims (9)

A document reading unit that optically reads a surface image of a fed document and acquires image data;
A histogram is created when the read image data is a gray document, a threshold value for converting the image data from the gray document into a black and white binary image is created from the histogram, and the gray value is based on the created threshold value. An image conversion unit for converting the image data from the original into a monochrome binary image;
A printing unit that prints the converted monochrome binary image as shading data;
A shading inspection apparatus comprising: A document reading unit that optically reads a surface image of a fed document and acquires image data;
A histogram is created when the read image data is a gray document, a threshold value for converting the image data from the gray document into a black and white binary image is created from the histogram, and the gray value is based on the created threshold value. An image conversion unit for converting the image data from the original into a monochrome binary image;
A display unit for displaying the converted monochrome binary image on a screen;
A shading inspection apparatus comprising:   The shading inspection apparatus according to claim 1, wherein the document reading unit includes a contact-type reading sensor that contacts the document and reads the image data.   The shading inspection apparatus according to claim 1, wherein the image conversion unit creates the histogram relating to a single color in the image data of the read gray original.   An image forming apparatus comprising the shading inspection apparatus according to claim 1, further comprising an image forming unit that forms an image of the read image data. A document reading process for feeding a gray document and optically reading a gray image for inspection on the surface to obtain image data;
A histogram creation process for creating a histogram from the image data relating to the read gray document;
A threshold value creating process for creating a threshold value for converting the image data relating to the gray document into a monochrome binary image from the histogram;
An image conversion process for converting the image data relating to the gray document into a black and white binary image based on the created threshold;
Print processing for printing the converted monochrome binary image as shading data;
A shading inspection method comprising: A document reading process for feeding a gray document and optically reading a gray image for inspection on the surface to obtain image data;
A histogram creation process for creating a histogram from the image data relating to the read gray document;
A threshold value creating process for creating a threshold value for converting the image data relating to the gray document into a monochrome binary image from the histogram;
An image conversion process for converting the image data relating to the gray document into a black and white binary image based on the created threshold;
Display processing for displaying the converted monochrome binary image on a screen;
A shading inspection method comprising:   8. The shading inspection method according to claim 6, wherein the document reading process uses a contact-type reading sensor that contacts the document and reads the image data.   The shading inspection method according to claim 6, wherein the image conversion processing creates the histogram relating to a single color in the image data of the read gray original.

Images