WO2019198431A1

WO2019198431A1 - Image reading irregularity correction method, image reading device, image formation device, and image reading irregularity correction program

Info

Publication number: WO2019198431A1
Application number: PCT/JP2019/011121
Authority: WO
Inventors: 完司永島
Original assignee: 富士フイルム株式会社
Priority date: 2018-04-12
Filing date: 2019-03-18
Publication date: 2019-10-17

Abstract

Provided is an image reading irregularity correction method in which first shading correction information for correcting image irregularity relating to shading is calculated using the following: image information obtained as a result of using a predetermined bright reference plate as an image to be read when forming an image in an imaging unit for converting an image to be read formed by a plurality of pixels coated with a filter film into image information; and image information obtained from the imaging unit while in a predetermined dark reference state. A predetermined spatial frequency is extracted from a correction result obtained by using the first shading correction information to correct image information obtained by using the imaging unit to form an image in which an image of a printed article having a predetermined color and a predetermined density is blurred, and second shading correction information for correcting reading density irregularity in each pixel of the imaging unit with respect to the predetermined color and the predetermined density is thereby calculated. A correction unit uses the first shading correction information and the second shading correction information to correct image information obtained as a result of using the imaging unit to form an image of an image to be read.

Description

Image reading unevenness correction method, image reading apparatus, image forming apparatus, and image reading unevenness correction program

The present disclosure relates to an image reading unevenness correction method, an image reading apparatus, an image forming apparatus, and an image reading unevenness correction program.

The image reading apparatus generally performs shading correction in order to correct variations in the output of each pixel of the imaging unit. In the shading correction, the white reference plate is read and corrected. However, the accuracy (non-uniformity) of the white reference plate is a problem.

Japanese Patent Laid-Open No. 6-291945 discloses illumination means for illuminating a document, a solid-state image sensor in which light receiving elements are arranged in a line, and an imaging optical system for forming an image of the document on the solid-state image sensor. In an image reading apparatus having a shading correction plate, the optical system is defocused by a diffusion plate or the like when an image is formed on the solid-state imaging device.

However, in Japanese Patent Laid-Open No. 6-291945, the influence of non-uniformity of the shading correction plate can be suppressed by defocusing and reading the shading correction plate, but the variation due to the spectral characteristics of each pixel is suppressed. There is room for improvement.

An object of the present disclosure is to provide an image reading unevenness correction method, an image reading apparatus, an image display apparatus, an image forming apparatus, and an image reading unevenness correction program capable of correcting variations caused by spectral characteristics of each pixel of an imaging unit. And

An image reading unevenness correction method according to the present disclosure includes a plurality of pixels coated with a filter film, and a bright reference plate predetermined in an imaging unit that converts an image to be read formed on the plurality of pixels into image information. The first shading correction information for correcting light / dark image unevenness using image information obtained by forming an image as an image to be read and image information obtained from the imaging unit in a predetermined dark reference state From the correction result calculated by the first calculation unit and corrected by the first shading correction information, the image information obtained by blurring the image of the printed matter with the predetermined color and the predetermined density and forming the image on the imaging unit is determined in advance. By extracting the predetermined spatial frequency, the second calculation unit calculates second shading correction information for correcting the reading density unevenness of each pixel of the imaging unit with respect to the predetermined color and the predetermined density. 1 With over fading correction information and the second shading correction data, the correction unit image information obtained by imaging the imaging unit images to be read is correct.

In addition, the image reading unevenness correction method according to the present disclosure forms an image to be read on the imaging unit in order to blur the image of the printed matter with a predetermined color and a predetermined density onto the imaging unit. A blurring unit that blurs an image formed on the imaging unit may be inserted between the lens and the imaging unit.

In the image reading unevenness correction method of the present disclosure, the blurring portion may be a diffusing member or a lens diffusing plate.

Further, in the image reading unevenness correction method of the present disclosure, the blurring unit includes a reflecting mirror that adjusts the length of the optical path, and a condenser lens, and the length of the optical path that constitutes the Keller illumination system in which the imaging lens is a collector lens. By arranging each so as to be, the image formed on the imaging unit may be blurred.

Further, in the image reading unevenness correcting method of the present disclosure, the blurring unit includes a condenser lens, adjusts the length of the optical path, and configures the Keller illumination system using the imaging lens as a collector lens, thereby connecting to the imaging unit. The image to be imaged may be blurred.

Further, in the image reading unevenness correcting method of the present disclosure, the blurring unit includes a reflecting mirror that adjusts the length of the optical path, a fly array lens, a collimator lens, and a condenser lens, and a Keller illumination system using the imaging lens as a collector lens By arranging each of them so as to have the length of the optical path constituting the image, the image formed on the imaging unit may be blurred.

Further, in the image reading unevenness correction method of the present disclosure, the blurring unit includes a fly array lens and a condenser lens, adjusts the length of the optical path, and configures the Keller illumination system using the imaging lens as a collimator lens. The image formed on the imaging unit may be blurred.

In addition, the image reading unevenness correction method of the present disclosure calculates the second shading correction information for each of a plurality of predetermined colors and a plurality of types of predetermined density printed matter, and sets the density to a density other than the plurality of types of densities. On the other hand, it may be calculated by interpolation.

In addition, the image reading unevenness correction method of the present disclosure performs extraction of a predetermined spatial frequency using a high-pass filter or a band-pass filter.

An image reading apparatus according to the present disclosure includes a plurality of pixels coated with a filter film, an imaging unit that converts an image to be read formed on the plurality of pixels into image information, and a predetermined bright reference plate. First shading correction information for correcting light and dark image unevenness is calculated using image information obtained by forming an image on the imaging unit and image information obtained from the imaging unit in a predetermined dark reference state. 1 a calculation unit, a blur imaging unit that blurs an image to be read and forms an image on the imaging unit, and a blurred printed image having a predetermined color and a predetermined density, and an image formed by the imaging unit is blurred By extracting a predetermined spatial frequency from the correction result obtained by correcting the image information obtained by forming an image on the imaging unit with the first shading correction information, each of the imaging unit for a predetermined color and a predetermined density is extracted. Compensates for pixel reading density unevenness An image obtained by forming an image to be read on the imaging unit on the basis of the calculation results of the second calculation unit for calculating the second shading correction information and the first calculation unit and the second calculation unit A correction unit that corrects information.

In the image reading device of the present disclosure, the blur imaging unit includes a blur unit that blurs an image formed on the imaging unit between the imaging lens that forms an image to be read on the imaging unit and the imaging unit. By inserting the image, the image to be read may be blurred and formed on the imaging unit.

In the image reading device of the present disclosure, the blurring unit may be a diffusing member or a lens diffusing plate.

In the image reading apparatus of the present disclosure, the blurring unit includes a reflecting mirror that adjusts the length of the optical path, and a condenser lens, and has a length of the optical path that constitutes a Keller illumination system in which the imaging lens is a collector lens. By disposing each, the image formed on the imaging unit may be blurred.

In the image reading device of the present disclosure, the blurring unit includes a condenser lens, adjusts the length of the optical path, and forms an image on the imaging unit by configuring a Keller illumination system using the imaging lens as a collector lens. The image may be blurred.

Further, in the image reading device of the present disclosure, the blurring unit includes a reflector that adjusts the length of the optical path, a fly array lens, a collimator lens, and a condenser lens, and constitutes a Keller illumination system in which the imaging lens is a collector lens The image formed on the imaging unit may be blurred by arranging each of them so as to have the length of the optical path.

Further, in the image reading apparatus of the present disclosure, the blurring unit includes a fly array lens and a condenser lens, adjusts the length of the optical path, and configures a Keller illumination system using the imaging lens as a collimator lens. The image formed on the image may be blurred.

In the image reading apparatus of the present disclosure, the second calculation unit calculates the second shading correction information for each of a plurality of predetermined colors and a plurality of predetermined densities of printed matter, The second shading correction information may be calculated for each density by interpolation.

In addition, the image reading device of the present disclosure performs extraction of a predetermined spatial frequency using a high-pass filter or a band-pass filter.

The image forming apparatus according to the present disclosure includes an image forming unit that forms an image on a recording medium and the image reading device according to the present disclosure, and binds an image formed on the recording medium by the image forming unit to the imaging unit. Image information converted by imaging is corrected by a correction unit.

Also, the image reading unevenness correction program of the present disclosure causes a computer to function as the first calculation unit and the second calculation unit in the image reading device of the present disclosure.

Also, the image reading unevenness correction program of the present disclosure causes the computer to function as the first calculation unit, the second calculation unit, and the correction unit in the image reading apparatus of the present disclosure.

According to the present disclosure, it is possible to correct variations caused by the spectral characteristics of each pixel of the imaging unit.

1 is a configuration diagram illustrating an example of an overall configuration of an image forming apparatus according to an exemplary embodiment. It is a perspective view which shows schematic structure of the in-line sensor which concerns on this embodiment. It is a block diagram which shows the structure of the control system of the in-line sensor which concerns on this embodiment. It is a figure which shows an example of the reading result which imaged and read the printed matter of the predetermined density | concentration of yellow with the diffusion member, and imaged on the imaging part. It is a figure which shows the result of having applied the low-pass filter to the reading result of FIG. 4A. It is a figure which shows the result of having applied the band pass filter by further applying a high pass filter with respect to FIG. 4B. It is a figure which shows the result of having produced | generated and corrected the 2nd shading correction information from the result of applying a band pass filter. 6 is a flowchart illustrating an example of a flow of processing performed by a reading control device of the image forming apparatus according to the present embodiment. It is a figure which shows schematic structure of the 1st example which smoothes distribution of the reading light imaged on the imaging part which concerns on this embodiment. It is a figure which shows schematic structure of the 2nd example which smoothes distribution of the reading light imaged on the imaging part which concerns on this embodiment. It is a figure which shows schematic structure of the 3rd example which smoothes distribution of the reading light imaged on the imaging part which concerns on this embodiment. It is a figure which shows schematic structure of the 4th example which smoothes distribution of the reading light imaged on the imaging part which concerns on this embodiment.

Hereinafter, embodiments of the technology of the present disclosure will be described in detail with reference to the drawings. Note that this embodiment does not limit the present disclosure.

First, the overall configuration of an image forming apparatus to which the technology of the present disclosure is applied will be described. FIG. 1 is a configuration diagram showing an example of the overall configuration of the image forming apparatus according to the present embodiment.

The image forming unit 11 of the image forming apparatus 10 includes a head 72M (magenta), 72K (black), and 72C on a recording medium 24 (sometimes referred to as “paper” for convenience) held on the drawing drum 70 of the drawing unit 16. The image forming apparatus forms a desired color image by ejecting ink from each of (cyan) and 72Y (yellow). The image forming apparatus 10 of the present embodiment employs a two-liquid reaction system in which a processing liquid is applied onto the recording medium 24 before ink ejection, and the processing liquid and the ink liquid are reacted to form an image on the recording medium 24. This is an applied image forming apparatus. In the following description, the CMYK symbols may be omitted when referring to all of them without distinction.

As shown in FIG. 1, the image forming unit 11 mainly includes a paper feeding unit 12, a processing liquid applying unit 14, a drawing unit 16, a drying unit 18, a fixing unit 20, and a discharging unit 22.

The paper feed unit 12 supplies the recording medium 24 to the treatment liquid application unit 14. The paper feed unit 12 is provided with a paper feed tray 50 for storing the recording medium 24, and the recording medium 24 is fed from the paper feed tray 50 to the processing liquid applying unit 14 one by one.

In the image forming apparatus 10 according to the present embodiment, a plurality of types of recording media 24 having different paper types and sizes (paper sizes) can be used as the recording medium 24. The paper supply unit 12 may include a plurality of paper trays that separately collect various recording media and may automatically switch the paper to be sent to the paper supply tray 50 from the plurality of paper trays. It is also possible for the operator to select or replace the paper tray. In this embodiment, a sheet (cut paper) is used as the recording medium 24. However, a configuration in which a continuous paper (roll paper) is cut into a necessary size and fed is also possible. The medium used as the recording medium 24 is not particularly limited, and examples thereof include high-quality paper, coated paper, and paper mainly composed of cellulose such as art paper.

The processing liquid application unit 14 applies the processing liquid to the recording surface of the recording medium 24. The treatment liquid contains a color material aggregating agent that agglomerates the color material in the ink applied by the drawing unit 16, and the ink is separated from the color material and the solvent when the treatment liquid comes into contact with the ink. Promoted.

As shown in FIG. 1, the treatment liquid application unit 14 includes a paper feed drum 52, a treatment liquid drum 54, and a treatment liquid application device 56. The processing liquid drum 54 rotates while holding the recording medium 24 on the outer peripheral surface, and conveys the recording medium 24. A treatment liquid coating device 56 is provided outside the treatment liquid drum 54 at a position facing the outer peripheral surface. The processing liquid application device 56 includes a processing liquid container in which the processing liquid is stored, and applies the processing liquid stored in the processing container to the recording medium 24 while measuring.

The recording medium 24 to which the processing liquid is applied by the processing liquid applying unit 14 is transferred from the processing liquid drum 54 to the drawing drum 70 of the drawing unit 16 through the intermediate transport unit 26.

The drawing unit 16 includes a drawing drum 70, a sheet pressing roller 74, and heads 72M, 72K, 72C, and 72Y. The recording medium 24 is conveyed in a state where the recording surface is held outwardly on the outer peripheral surface of the drawing drum 70, and ink is applied to the recording surface from the

heads

72M, 72K, 72C, 72Y.

The

heads

72M, 72K, 72C, 72Y of the present embodiment are full-line type ink jet heads each having a length corresponding to the maximum width of the image forming area in the recording medium 24. On the ink ejection surface, a nozzle row in which a plurality of nozzles for ink ejection are arranged over the entire width of the image forming area is formed.

The treatment liquid application unit 14 causes the ink droplets of the corresponding color to be ejected from each of the

heads

72M, 72K, 72C, and 72Y toward the recording surface of the recording medium 24 held on the drawing drum 70. The ink comes into contact with the processing liquid previously applied to the recording surface. When the ink comes into contact with the treatment liquid, the color material dispersed in the ink is aggregated to form an aggregate of the color material. Thereby, the color material flow on the recording medium 24 is prevented, and an image is formed on the recording surface of the recording medium 24.

In this embodiment, the four-color configuration of CMYK is exemplified, but the combination of the ink color and the number of colors is not particularly limited, and light ink, dark ink, special color ink, and the like are added as necessary. May be. For example, it is possible to add a head for ejecting light-colored ink such as light cyan and light magenta, and the arrangement order of the color heads is not particularly limited.

The recording medium 24 on which the image is formed by the drawing unit 16 is transferred from the drawing drum 70 to the drying drum 76 of the drying unit 18 through the intermediate conveyance unit 28.

The drying unit 18 dries moisture contained in the solvent separated by the aggregation action of the color material. As shown in FIG. 1, the drying unit 18 includes a drying drum 76 and a solvent drying device 78. The recording medium 24 is conveyed while being held on the outer peripheral surface of the drying drum 76 with the recording surface facing outward. The solvent drying device 78 is disposed at a position facing the outer peripheral surface of the drying drum 76, and blows warm air toward the recording medium 24.

The recording medium 24 that has been dried by the drying unit 18 is transferred from the drying drum 76 to the fixing drum 84 of the fixing unit 20 via the intermediate conveyance unit 30.

The fixing unit 20 is provided with a halogen heater 86, a fixing roller 88, and an inline sensor 90 as an image reading device on the outer peripheral surface of the fixing drum 84. The recording medium 24 is conveyed while being held on the outer peripheral surface of the fixing drum 84 with the recording surface facing outward.

The halogen heater 86 preheats the recording medium 24. The fixing roller 88 heats and presses the recording medium 24.

The in-line sensor 90 is for measuring a check pattern, a moisture content, a surface temperature, a gloss level, and the like for an image fixed on the recording medium 24. For example, the in-line sensor 90 uses a line sensor, an area sensor, or the like. The image fixed to 24 is read.

As shown in FIG. 1, a discharge unit 22 is provided following the fixing unit 20. The discharge unit 22 includes a discharge tray 92, and a transfer drum 94, a conveyance belt 96, and a stretching roller 98 are provided between the discharge tray 92 and the fixing drum 84 of the fixing unit 20. The recording medium 24 is sent to the conveying belt 96 by the transfer drum 94 and discharged to the discharge tray 92.

Although not shown in FIG. 1, the image forming apparatus 10 according to the present exemplary embodiment includes a processing liquid for the ink loading unit that supplies ink to each head 72 and the processing liquid application unit 14 in addition to the above configuration. A head maintenance unit for cleaning each head 72 (wiping of the discharge surface, purging, nozzle suction, etc.), a position detection sensor for detecting the position of the recording medium 24 on the paper transport path, and each part of the apparatus The temperature sensor etc. which detect the temperature of this are provided.

Subsequently, the inline sensor 90 as an image reading apparatus according to the present embodiment will be described. FIG. 2 is a perspective view illustrating a schematic configuration of the inline sensor 90 according to the present embodiment.

As shown in FIG. 2, the in-line sensor 90 includes a pair of light sources 38, an imaging lens 36, a diffusion member 34 as a blurring unit, an imaging unit 32, and a white reference plate 40 as a predetermined bright reference plate. It is configured. The predetermined bright reference plate is, for example, a reference plate having a predetermined brightness or higher, and is not limited to the white reference plate 40, but may be replaced with a bright reference plate other than white. Good.

The pair of light sources 38 are arranged on the conveyance path of the paper to be read by the inline sensor 90 and illuminate the paper. Specifically, the pair of light sources 38 are elongated in a direction orthogonal to the paper transport direction. The length of the irradiation range of the light source 38 is an irradiation range having a width wider than the width of the paper to be conveyed. Further, the pair of light sources 38 are arranged symmetrically with respect to the optical axis reflected by the paper and directed toward the imaging lens 36. The illumination of the paper is not limited to the pair of light sources 38, and may be a single light source or a plurality of three or more light sources. Moreover, as a light source, it is possible to apply a semiconductor light source (for example, LED etc.) or a discharge lamp.

The imaging lens 36 images the light irradiated from the pair of light sources 38 and reflected by the paper on the imaging unit 32.

The imaging unit 32 is formed on a sheet by a line sensor in which photoelectric conversion elements such as CCD (Charge-Coupled-Devices) and CMOS (Complementary Metal-Oxide-Semiconductor) are arranged in a line in a direction crossing the sheet conveyance direction. Read the image. In the present embodiment, an example in which the imaging unit 32 applies a color line sensor in which line sensors corresponding to three colors of red (R), green (G), and blue (B) are arranged in three rows will be described. This is not a limitation. For example, an area sensor in which photoelectric conversion elements are two-dimensionally arranged may be applied.

The diffusing member 34 is configured such that light from the pair of light sources 38 is reflected by the paper and can enter and exit an optical path (hereinafter sometimes referred to as a reading optical path) that goes to the imaging unit 32 via the imaging lens. Yes. When the diffusing member 34 is on the reading optical path, the light to be read is diffused by the diffusing member 34 so that the image to be read is blurred and formed on the imaging unit 32, and the reading light is smoothed. Since the diffusing member 34 is a light diffusing member, a light diffusing effect can be obtained even if it is inserted between the reading object and the imaging lens 36 or between the imaging lens 36 and the imaging unit 32. When the light is diffused at a position far from the unit 32, the amount of light reaching the imaging unit 32 is reduced. Therefore, it is desirable to dispose it between the imaging lens 36 and the imaging unit 32 and immediately before the imaging unit 32. As a result, the image to be read is blurred, the fine density distribution is also blurred, and the reading light is smoothed. In this embodiment, an example in which an image to be read is blurred by the diffusing member 34 will be described. However, the present invention is not limited to this. For example, a configuration in which at least one position of the imaging unit 32 and the imaging lens 36 is moved is applied as a blur imaging unit, and imaging is performed by moving at least one of the imaging unit 32 and the imaging lens 36 and shifting the focus. The image formed on the unit 32 may be blurred. Alternatively, a lens diffusion plate (LSD: Light レンズ Shaping 板 Diffusers, Luminit) may be used instead of the diffusing member 34.

The white reference plate 40 can enter and exit the reading position of the imaging unit 32, and the white reference plate 40 is moved to the reading position of the imaging unit 32 during shading correction preparation for creating shading correction information for correcting density unevenness. Let On the other hand, the white reference plate 40 is retracted from the conveyance path when reading an image of a sheet.

Next, the configuration of the control system of the inline sensor 90 will be described. FIG. 3 is a block diagram illustrating a configuration of a control system of the inline sensor 90 according to the present embodiment.

The inline sensor 90 is controlled by the reading control device 42. The reading control device 42 is configured by a computer in which a CPU (Central Processing Unit) 42A, a ROM (Read Only Memory) 42B, a RAM (Random Access Memory) 42C, and an input / output port 42D are connected to a bus 42E. The reading control device 42 corresponds to a first calculation unit, a second calculation unit, and a correction unit.

The ROM 42B stores various programs and information for controlling the inline sensor 90. The inline sensor 90 is controlled by developing the program stored in the ROM 42B in the RAM 42C and executing it by the CPU 42A.

A pair of light sources 38, a diffusing member driving unit 44, a white reference plate driving unit 46, and an imaging unit 32 are connected to the input / output port 42D.

As described above, the light source 38 is turned on to illuminate the paper to be read, and the light emitted from the light source 38 is reflected by the paper and imaged on the imaging unit 32 via the imaging lens 36. .

The diffusing member driving unit 44 moves the diffusing member 34 on the reading optical path of the imaging unit 32 and blurs an image formed on the imaging unit 32. In the present embodiment, the diffusing member 34 is retracted from the reading optical path of the imaging unit 32 when generating first shading correction information described later. On the other hand, when calculating second shading correction information to be described later, the diffusing member 34 is moved onto the reading optical path of the imaging unit 32 to blur the image formed on the imaging unit 32.

The white reference plate drive unit 46 drives the white reference plate 40 to move and retract the white reference plate 40 to the reading position of the imaging unit 32.

The imaging unit 32 reads the image to be read by forming an image formed on the sheet to be read, and generates image information representing the read image. Then, the imaging unit 32 performs A / D (analog / digital) conversion or the like on the generated image information and outputs it to the reading control device 42.

The reading control device 42 controls the light source 38, the diffusing member driving unit 44, the white reference plate driving unit 46, and the imaging unit 32 to generate correction information such as shading correction for correcting the reading characteristics of the imaging unit 32. The image information read by the imaging unit 32 is corrected using the correction information.

By the way, in general shading correction, the image information obtained by reading the white reference plate 40 (or read in a predetermined bright state) and the image obtained by reading the black reference plate (or read in a predetermined dark reference state). Shading correction information is generated from the information. Then, density unevenness is corrected using this, and image information with uniform reading characteristics is acquired. As the shading correction information, when reading a color image, white illumination or mixed illumination of R, G, and B is used. However, the white reference plate 40 has substantially uniform reflection spectral characteristics in the visible light region. It is a thing. On the other hand, a color image reading target is printed using inks such as cyan (C), magenta (M), and yellow (Y). Among these inks, a relatively dark image with one color ink or When relatively thin images are printed, the reflection characteristics in the visible light region are often not proportional to the wavelength in these images. This is particularly noticeable when the density is expressed by the density of dots, as in the case of forming an image by inkjet. The image information read in a predetermined dark reference state is image information read in a state where light is not incident on the imaging unit 32 (or a predetermined dark state), and the black reference plate is read. Includes image information.

On the other hand, the color imaging unit 32 has spectral sensitivity variation (sensitivity difference with respect to each wavelength) for each pixel. The larger the variation, the more the corresponding pixel cannot be corrected sufficiently only by the light / dark shading correction, and the color density may be uneven.

In particular, in the present embodiment, a line sensor is used, and one pixel is used for reading one column of pixels arranged in a direction orthogonal to the width direction (pixel arrangement direction) of the line sensor, so that the spectral sensitivity variation is large. If there is a pixel, this influence becomes linear color density unevenness. Furthermore, when pixels having a large variation in spectral sensitivity are continuously present in the pixel row, or when a plurality of pixels are present in a relatively close range, strip-shaped color density unevenness occurs. On the other hand, when the area sensor is applied, color density unevenness corresponding to a pixel having a large variation on a one-to-one basis. Both are problems in image quality, and appropriate correction is necessary to obtain a good image.

Here, in the present embodiment, when the characteristics of the imaging unit 32 in which uneven color density occurs are examined, there are pixels that are solidified in a certain section on the imaging unit 32 and have uneven color density. In these pixels, when shading correction is performed using a light and dark reference and an achromatic color (gray) of brightness between the white reference plate 40 and the black reference is read, color density unevenness does not occur, but a specific color is not generated. When read, uneven color density occurred.

Actually, the color density unevenness occurred when the reading object printed with colors including yellow and yellow inks of various brightness (for example, red and green) was subjected to shading correction.

In the yellow optical density D (≈1.2), the difference in the output of the imaging unit 32 between the portion with uneven color density and the portion without uneven color density is about 1 to 1.5 in 8-bit data (value range 0 to 255). There was a difference. The direct cause of the color density unevenness is estimated to be that the pixel with the blue filter for reading yellow has a lighter color filter than the other pixels in the pixel having the color density unevenness. It is thought that the thickness error is caused.

Furthermore, as a reason for the occurrence of uneven color density in yellow, in the case of yellow, a blue filter is provided for the change in density of yellow compared to other colors (magenta, cyan, black in color printing ink). It is mentioned that the output change of the imaging unit 32 is small. In particular, the output change of the image pickup unit 32 provided with the blue filter even when the density of yellow is changed at medium to high density is compared with the output change of the image pickup unit 32 provided with the green filter for other colors, for example, magenta. Small. In this density range, if an output difference of the imaging unit 32 provided with the blue filter is caused by a thickness error of the color filter, the density difference of yellow is relatively detected as compared with other colors. Concentration unevenness becomes more noticeable.

In order to remove the influence of the thickness error of the filter film such as the color filter of the imaging unit 32 and obtain a good reading result, it is necessary to measure and correct the reading unevenness of the imaging unit 32 with high accuracy.

However, since the ink (coloring material, dye, pigment, etc.) differs depending on the printed material to be read, the spectral characteristics with respect to reflected light or transmitted light also differ. Therefore, it is desirable to obtain correction information with higher accuracy by creating a correction printed matter that can be regarded as a reference of a specific color having a uniform density with an actual printed matter, and measuring this.

However, in many actual printed materials, in order to express the difference in density, printing having a fine “image structure” such as a halftone dot or a dither matrix is performed. Further, the printing itself includes unevenness due to non-uniformity. In addition, the paper has fine irregularities on the surface, papermaking unevenness, etc., which also affect the density distribution.

Therefore, even if the illumination is completely uniform, the printed matter has a fine density distribution. Therefore, when viewed microscopically, the density distribution is not uniform. Therefore, in a state where the optical adjustment is performed so as to read the reading target and the image is in focus, the “fine density distribution” is read by the imaging unit 32. If the “fine density distribution” is read, it is difficult to distinguish between the density distribution of the printed matter and the spectral sensitivity unevenness of the imaging unit 32, and it is impossible to correctly measure the reference density of a specific color.

That is, by performing reading using a printed matter having a reference density using the original ink to be read and the light source 38, the spectral sensitivity unevenness of each pixel of the imaging unit 32 at a predetermined reference density is accurately measured. It is necessary to. However, as described above, the fine density distribution of the printed matter is read together, and it is a problem that the spectral sensitivity unevenness for each pixel and the fine density distribution of the printed matter cannot be separated.

Therefore, in the present embodiment, first shading correction information for correcting light and dark image unevenness is calculated. Further, a predetermined spatial frequency is obtained from a correction result obtained by correcting image information obtained by blurring an image of a printed matter having a predetermined color and a predetermined density and forming the image on the imaging unit 32 with the first shading correction information. Extract. As a result, second shading correction information for correcting the read density unevenness of each pixel of the imaging unit 32 with respect to a predetermined color and a predetermined density is calculated. Then, using the first shading correction information and the second shading correction information, image information obtained by forming an image to be read on the imaging unit 32 is corrected.

Specifically, the image information obtained by reading the white reference plate 40 and the image information obtained by reading the light without entering the imaging unit 32 (or the image obtained by reading a predetermined dark reference plate). Information), sensitivity correction (shading correction) of each pixel with respect to the achromatic color is performed.

Further, in order to perform reading without being affected by the fine density distribution of the printed matter, the distribution of the reading light is smoothed by blurring the image formed on the imaging unit 32 by the diffusing member 34 to obtain a predetermined color in advance. Read the printed matter with the specified density. For example, FIG. 4A shows an example of a reading result obtained by reading a yellow printed matter having a predetermined density blurred by the diffusion member 34 and forming an image on the imaging unit 32.

The second shading correction information is calculated by extracting a predetermined spatial frequency from the image information obtained by reading the printed matter using a filter (for example, a high-pass filter or a band-pass filter). Thereby, more accurate correction information can be acquired. FIG. 4B shows the result of applying the low-pass filter to the reading result of FIG. 4A, and FIG. 4C shows the result of applying the band-pass filter by further applying the high-pass filter to FIG. 4B. Further, FIG. 4C shows a range where the color density is uneven. When the second shading correction information is generated and corrected from the result of applying the bandpass filter, color density unevenness can be suppressed as shown in FIG. 4D.

Subsequently, detailed processing performed by the reading control device 42 of the image forming apparatus 10 according to the present embodiment configured as described above will be described. FIG. 5 is a flowchart illustrating an example of a flow of processing performed by the reading control device 42 of the image forming apparatus 10 according to the present embodiment. Note that the process of FIG. 5 is performed when shading correction information is calculated. The shading correction may be performed, for example, in the production process of the image forming apparatus 10 or when the image forming apparatus 10 is installed. Alternatively, it may be performed when instructed by the user, or may be performed every predetermined time. The following steps 100 to 108 correspond to the first calculation unit, and steps 110 to 116 correspond to the second calculation unit.

In step 100, the CPU 42A controls the white reference plate driving unit 46, moves the white reference plate 40 onto the reading optical path of the imaging unit 32, and proceeds to step 102.

In step 102, the CPU 42A turns on the light source 38, reads the white reference plate 40 by the imaging unit 32, and proceeds to step 104. That is, image information obtained by imaging the white reference plate 40 in the bright state on the imaging unit 32 is acquired.

In step 104, the CPU 42 A turns off the light source 38 and performs reading by the imaging unit 32 with the white reference plate 40 moving on the reading optical path of the imaging unit 32, and the process proceeds to step 106. That is, the white reference plate 40 blocks the reading optical path to prevent stray light from the outside, and the light source 38 is turned off to acquire image information obtained by the imaging unit 32 in a dark state where almost no light is incident.

In step 106, the CPU 42 A controls the white reference plate driving unit 46 to retreat the white reference plate 40 from the reading optical path of the imaging unit 32 and proceeds to step 108.

In step 108, the CPU 42A generates first shading correction information based on the two reading results of the reading result of the white reference plate 40 and the reading result in the dark state, and proceeds to step 110.

In step 110, the CPU 42 A controls the diffusing member driving unit 44, moves the diffusing member 34 onto the reading optical path of the imaging unit 32, and proceeds to step 112. Thereby, the image formed on the imaging unit 32 is blurred and the density distribution is also blurred, so that the distribution of the reading light can be smoothed.

In step 112, the CPU 42 A turns on the light source 38, reads the correction printed matter (printed matter printed with a predetermined color and a predetermined density) by the imaging unit 32, and proceeds to step 114. The correction printed matter may be set at the reading position on the reading optical path of the imaging unit 32 by the operator, or set on the paper feed tray 50 of the image forming apparatus 10 to instruct conveyance.

In step 114, the CPU 42A corrects the image information obtained by reading the correction printed matter having a predetermined color and a predetermined density with the first shading correction information, and proceeds to step 116. When there is a difference in density unevenness distribution depending on the conveyance direction of the correction printed matter using a line sensor, in order to reduce the fine density unevenness distribution of the correction printed matter, the direction in which the density unevenness distribution is small is imaged. The reading may be performed in accordance with the pixel arrangement direction of the unit 32. Specifically, when printing with a single-pass inkjet head, the conveyance direction of the paper is smaller than the direction perpendicular to the conveyance direction, so the conveyance direction of the printed matter for correction is the pixel alignment direction of the imaging unit 32. It may be rotated and read so as to match.

In step 116, the CPU 42A extracts a predetermined spatial frequency from the image information corrected by the first shading correction information, generates second shading correction information, and proceeds to step 118. For example, the second shading correction information is generated by extracting a predetermined spatial frequency from the image information corrected in step 114 using a high-pass filter or a band-pass filter. In other words, since the image obtained by reading the correction printed matter as described above reads the printed matter having a substantially uniform density and corrects it with the first shading correction information, ideally, the entire printed portion of the image information is substantially uniform. Expected to be a density reading. However, if there is uneven reading in the imaging unit 32, the read image becomes an image including an image corresponding to uneven read pixels with respect to the ink of the printed matter. Therefore, the ratio of the read values of the individual pixels of the imaging unit 32 with respect to the average value of the read image of the printed portion having a substantially uniform density is obtained, and this is used as a correction coefficient, and this reciprocal is used as the second shading correction information. By multiplying the read image, the read image can suppress uneven density.

In step 118, the CPU 42A stores the first shading correction information and the second shading correction information in a memory or the like, sets the correction information, and ends the series of processes.

Using the correction information set in this way, the reading control device 42 corrects the image information obtained by reading by the imaging unit 32, so that the imaging unit 32 can be adapted to the actual color material and illumination characteristics. It is possible to correct variations caused by the spectral characteristics of each pixel.

Further, when the processing of FIG. 5 is performed for each of the colors R, G, and B, it is possible to realize more uniform image reading.

In the above processing, the example in which the second shading correction information is generated for a predetermined color and a predetermined density has been described. However, the present invention is not limited to this. For example, by performing the above-described processing for each color and each density to generate the second shading correction information, it is possible to correct the color density unevenness in each color and each density. In addition, it is possible to generate correction prints for several densities to generate second shading correction information without generating correction prints for each density, and generate second shading correction information by interpolation for other densities. It may be generated. Specifically, a correction printed matter having a uniform density is created for several densities, and the ratio of the read values of the individual pixels of the imaging unit 32 is obtained for each density. For the density that is not actually read, the ratio (correction coefficient) of the read value of each pixel of the imaging unit 32 is interpolated or extrapolated from the read results of one or more densities before and after the density. It may be estimated. As a result, correction coefficients are obtained for 0 to 255 for all read values, for example, 8-bit read values, for all pixels. Therefore, when various printed materials are read, an image in which color density unevenness is corrected can be obtained by multiplying the read value of each pixel by the reciprocal of this correction coefficient in accordance with the read value.

Further, the correction printed matter is not limited to one color per sheet, and one correction printed matter in which a plurality of colors and a plurality of density reference prints are applied to one printed matter, Second shading correction information for a plurality of colors and a plurality of densities for each color may be generated.

In addition, as for the printed matter for correction, for the output corresponding to red of the color image pickup unit 32, a printed matter having a reference density is created with cyan ink. For the output corresponding to green, a printed matter with a reference density is created with magenta ink. For the output corresponding to blue, a printed matter for correcting the reference density is created with yellow ink.

Subsequently, in addition to the method of diffusing light and blurring the image formed on the imaging unit 32, and the method of shifting the focus by moving at least one of the imaging lens 36 and the imaging unit 32, the image is formed on the imaging unit 32. A method for smoothing the distribution of reading light to be read will be described.

As a first example of a method other than the above, Keller illumination is configured by inserting an optical system 60 as shown in FIG. 6 while the imaging unit 32 is in focus. In this case, instead of the diffusing member driving unit 44, a driving unit 68 for moving and retracting the optical system 60 on the reading optical path of the imaging unit 32 is provided. In the example of FIG. 6, as an optical system 60 as a blurring portion, a state in which reflecting mirrors 62 A, 62 B, 62 C and 62 D that bend an optical path and a condenser lens 64 are inserted between the imaging lens 36 and the imaging unit 32 is shown. .

As a second example, Keller illumination is configured by retracting the imaging unit 32 with the imaging unit 32 in focus and inserting a condenser lens 64 as shown in FIG. In this case, in place of the diffusing member driving unit 44, the condenser lens 64 is moved and retracted on the reading optical path of the imaging unit 32, and a driving unit 68 for moving the imaging unit 32 is provided. In the example of FIG. 7, a state in which the imaging unit 32 is retracted and the condenser lens 64 is inserted between the imaging lens 36 and the imaging unit 32 as a blurring unit is shown.

Also, as a third example, Keller illumination is configured by inserting an optical system 61 including a fly array lens 66 and a collimator lens 67 as shown in FIG. 8 in a state where the imaging unit 32 is in focus. In this case, instead of the diffusing member driving unit 44, a driving unit 68 for moving and retracting the optical system 61 including the fly array lens 66 and the collimator lens 67 on the reading optical path of the imaging unit 32 is provided. In the example of FIG. 8, as the optical system 61 as the blurring unit, the reflecting

mirrors

62A, 62B, 62C, and 62D that bend the optical path, the fly array lens 66, the collimator lens 67, and the condenser lens 64 are formed with the imaging lens 36 and the imaging unit 32. The state of being inserted between is shown.

As a fourth example, the imaging unit 32 is retracted while the imaging unit 32 is in focus, and a fly array lens 66, a collimator lens 67, and a condenser lens 64 are inserted as shown in FIG. Configure lighting. In this case, instead of the diffusion member driving unit 44, the fly array lens 66, the collimator lens 67, and the condenser lens 64 are moved and retracted on the reading optical path of the imaging unit 32, and the imaging unit 32 is moved. A driving unit 68 is provided. In the example of FIG. 9, a state where the imaging unit 32 is moved backward as a blurring unit and the fly array lens 66, the collimator lens 67, and the condenser lens 64 are inserted between the imaging lens 36 and the imaging unit 32 is shown.

The methods of the first and second examples constitute a Keller illumination system in which the surface to be read is regarded as a light emitting surface and the imaging unit 32 is regarded as an illumination target. The imaging lens 36 corresponds to a collector lens of the Keller illumination system, and the condenser lens 64 of the first and second examples corresponds to a condenser lens of the Keller illumination system. In this case, the focal position of the imaging lens 36 is arranged so that the reading target surface and the entrance pupil of the condenser lens 64 are conjugated (position where the imaging unit 32 is in focus). The focal position of the condenser lens 64 is arranged so that the exit pupil of the imaging lens 36 and the imaging unit 32 are conjugated. With such an arrangement, the distance from the imaging lens 36 to the imaging unit 32 needs to be longer than the distance between the imaging lens 36 and the imaging unit 32 when the imaging unit 32 is in focus. Therefore, in the first example, reflecting

mirrors

62A, 62B, 62C, 62D and reflecting prisms are inserted before and after the condenser lens 64, and the optical path is bent so that the required optical path length is obtained. In the second example, the imaging unit 32 is moved backward so as to have a required optical path length. In this way, when the Keller illumination system is configured, when the surface to be read is regarded as a surface light source, light reflected or transmitted from each point on the surface to be read is captured by the imaging unit by the function of the lens of the Keller illumination system. 32 is reached. On the contrary, the light reflected or transmitted from each point (all points) on the surface to be read reaches one pixel of the imaging unit 32. Accordingly, even if there is a difference in density at each point on the surface to be read and there is unevenness in the reflected or transmitted light, it affects all the pixels of the imaging unit 32. It reaches all the pixels of the imaging unit 32. This is because the condenser lens 64 is given a projection characteristic of y = f · sin (θ). Actually, a light amount difference of a gradual change occurs between the central pixel and the end pixel of the lens of the Keller illumination system due to the difference in the transmittance of the lens. This is a feature of the present embodiment, which is “the spatial frequency of the image. In contrast, by extracting unevenness in the reading density from the read image using a high-pass filter or a band-pass filter, the influence is eliminated.

Further, in the third example and the fourth example, a fly array lens 66 and a collimator lens 67 are added between the imaging lens 36 and the condenser lens 64 in the first example and the second example, respectively. In this case, the collimator lens 67 is brought into the focal position of the imaging lens 36, and collimator light is incident on the fly array lens 66. Further, the optical system 61 including the fly array lens 66 and the collimator lens 67 of the third example so that the exit surface of the fly array lens 66 and the imaging unit 32 are conjugated, and the fly array lens 66 and the collimator lens of the fourth example. 67 and a condenser lens 64 are arranged. As described above, even when the fly array lens 66 and the collimator lens 67 are used, the optical characteristics of the Keller illumination systems of the first and second examples are provided, but the light reaching the imaging unit 32 is uniform. Improves. This is because Keller illumination makes the in-plane luminance distribution non-uniformity of the light source uniform in principle, and when a fly array lens 66 and a collimator lens 67 are added, the surface to be read is further viewed as a surface light source. In this case, a large number of secondary light sources are created from the surface light source by the fly array lens 66. This is because the nonuniformity of the luminance distribution in the angular direction of the light source is also corrected, and the uniformity is further enhanced as compared with the Keller illumination. When the position of the imaging lens 36 is moved to the reading target side so that the light emitted from the imaging lens becomes collimated light and enters the fly array lens 66, the collimator lens 67 becomes unnecessary.

In any of the above methods, even if the image to be read is blurred on the imaging unit 32 and there is a fine density distribution of the printed matter, this is averaged and becomes inconspicuous.

This effect is superior to the above embodiment in the first to fourth examples. On the other hand, the method using the diffusing member 34 and the lens diffusing plate of the above embodiment has a slightly weak effect. Alternatively, when the effect is strengthened, the amount of light reaching the imaging unit 32 is greatly reduced. However, as a cost for the realization, the method using the diffusing member 34 and the lens diffusing plate as in the above embodiment is significantly cheaper than the first to fourth examples. This is also because it is not necessary to change the optical distance between the imaging lens 36 and the imaging unit 32. Further, the method using the diffusing member 34 and the lens diffusing plate as in the above-described embodiment is somewhat weak in this effect, but this can be compensated by noise removal processing of the read image information. In the present embodiment, this is realized by using a filter that passes the vicinity of the spatial frequency of the density unevenness in question from the image information. A filter such as a bandpass filter may be applied to the first to fourth examples. Further, a high pass filter may be applied depending on the target density unevenness.

In the above-described embodiment, the example in which the reading control device 42 of the image forming apparatus 10 performs the process of FIG. 5 has been described, but the present invention is not limited to this. For example, the production process at the time of manufacturing the imaging unit 32 may include the configuration of the in-line sensor 90 illustrated in FIG. 2, and the measurement device at the time of inspection may perform the processing in FIG. 5. As a result, the inspection result of the imaging unit 32 can be shipped with the shading correction information added.

In the above embodiment, the shading correction of the inline sensor 90 provided in the image forming apparatus 10 has been described as an example, but the present invention is not limited to this. For example, the present invention may be applied to an image display device that displays an image by the imaging unit 32, and the display image may be corrected using the first shading correction information and the second shading correction information obtained by the processing in FIG.

Further, each process shown in the flowchart described in the above embodiment is merely an example. Therefore, unnecessary steps may be deleted, new steps may be added, or the processing order may be changed within a range that does not depart from the spirit.

In addition, various processors other than the CPU may execute the process of FIG. 5 executed by the CPU (42A) executing software (program) in each of the above embodiments. As a processor in this case, in order to execute specific processing such as PLD (Programmable Logic Device) and ASIC (Application Specific Integrated Circuit) whose circuit configuration can be changed after manufacturing FPGA (field-programmable gate array) or the like. A dedicated electric circuit, which is a processor having a circuit configuration designed exclusively, is exemplified. 5 may be executed by one of these various processors, or a combination of two or more processors of the same type or different types (for example, a plurality of FPGAs and a combination of a CPU and an FPGA). You may perform by combination etc.). More specifically, the hardware structure of these various processors is an electric circuit in which circuit elements such as semiconductor elements are combined.

In the above embodiments, the various programs stored in the reading control device 42 have been described as being prestored (installed) in the ROM 42B. However, the present invention is not limited to this. The program is provided in a form recorded in a non-transitory recording medium such as a CD-ROM (Compact Disk Read Only Memory), a DVD-ROM (Digital Versatile Disk Read Only Memory), and a USB (Universal Serial Bus) memory. Also good. Further, the program may be downloaded from an external device via a network.

In addition, the configurations, operations, and the like of the image forming apparatus 10 and the inline sensor 90 described in the above embodiment are merely examples, and can be changed according to the situation without departing from the gist of the present invention.

This application claims the priority of Japanese Application No. 2018-076911 filed on Apr. 12, 2018, the entire text of which is incorporated herein by reference.

Claims

A plurality of pixels coated with a filter film are formed, and a predetermined bright reference plate is formed as an image of the reading target in an imaging unit that converts the image of the reading target formed on the plurality of pixels into image information. The first calculation unit calculates first shading correction information for correcting light / dark image unevenness using the image information obtained in this manner and the image information obtained from the imaging unit in a predetermined dark reference state. ,
A predetermined spatial frequency is extracted from a correction result obtained by correcting image information obtained by blurring an image of a printed matter having a predetermined color and a predetermined density and forming the image on the imaging unit with the first shading correction information. Accordingly, the second calculation unit calculates second shading correction information for correcting the reading density unevenness of each pixel of the imaging unit with respect to the predetermined color and the predetermined density,
An image reading unevenness correction method in which a correction unit corrects image information obtained by forming an image to be read on the imaging unit using the first shading correction information and the second shading correction information.
In order to blur the image of a printed matter having a predetermined color and a predetermined density to form an image on the imaging unit, the imaging unit is formed between the imaging lens that forms the image to be read on the imaging unit and the imaging unit. The image reading unevenness correcting method according to claim 1, wherein a blurring portion that blurs an image formed on the imaging portion is inserted.
3. The method for correcting unevenness in image reading according to claim 2, wherein the blur portion is a diffusing member or a lens diffusing plate.
The blur part includes a reflecting mirror that adjusts the length of the optical path, and a condenser lens, and each of the blurring parts is arranged to be the length of the optical path constituting the Keller illumination system using the imaging lens as a collector lens, The image reading unevenness correction method according to claim 2, wherein an image formed on the imaging unit is blurred.
The blurring unit includes a condenser lens, adjusts the length of an optical path, and configures a Keller illumination system using the imaging lens as a collector lens, thereby blurring an image formed on the imaging unit. The method for correcting unevenness in image reading as described.
The blur part includes a reflector that adjusts the length of the optical path, a fly array lens, a collimator lens, and a condenser lens, and has a length of an optical path that constitutes a Keller illumination system using the imaging lens as a collector lens. The method for correcting unevenness in image reading according to claim 2, wherein by arranging each of them, an image formed on the imaging unit is blurred.
The blur part includes a fly array lens and a condenser lens, adjusts the length of the optical path, and configures a Keller illumination system using the imaging lens as a collimator lens, thereby blurring an image formed on the imaging part. The image reading unevenness correcting method according to claim 2.
The second shading correction information is calculated for each of a plurality of predetermined colors and a plurality of predetermined densities of printed matter, and is calculated by interpolation for densities other than the plurality of types of densities. 8. The image reading unevenness correcting method according to any one of 1 to 7.
The image reading unevenness correction method according to any one of claims 1 to 8, wherein the extraction of the predetermined spatial frequency is performed using a high-pass filter or a band-pass filter.
An imaging unit that has a plurality of pixels coated with a filter film, and converts an image of a reading target formed on the plurality of pixels into image information;
Using the image information obtained by forming an image of a predetermined bright reference plate on the imaging unit and the image information obtained from the imaging unit in a predetermined dark reference state to correct light and dark image unevenness A first calculation unit for calculating first shading correction information;
A blur imaging unit that blurs an image to be read and forms the image on the imaging unit;
Correction obtained by correcting image information obtained by forming an image formed on the image pickup unit in a state where the image formed by the blur image forming unit is blurred with a predetermined color and a predetermined density with the first shading correction information From the result, by extracting a predetermined spatial frequency, second shading correction information for correcting the read density unevenness of each pixel of the imaging unit for the predetermined color and the predetermined density is calculated. 2 calculation units;
A correction unit that corrects image information obtained by forming an image to be read on the imaging unit based on the calculation results of the first calculation unit and the second calculation unit;
An image reading apparatus comprising:
The blur imaging unit inserts a blur unit that blurs an image formed on the imaging unit between an imaging lens that forms the image to be read on the imaging unit and the imaging unit, The image reading apparatus according to claim 10, wherein an image to be read is blurred and formed on the imaging unit.
12. The image reading apparatus according to claim 11, wherein the blur part is a diffusing member or a lens diffusing plate.
The blur part includes a reflecting mirror that adjusts the length of the optical path, and a condenser lens, and each of the blurring parts is arranged to be the length of the optical path constituting the Keller illumination system using the imaging lens as a collector lens, The image reading apparatus according to claim 11, wherein an image formed on the imaging unit is blurred.
The blurring unit includes a condenser lens, adjusts the length of an optical path, and configures a Keller illumination system using the imaging lens as a collector lens, thereby blurring an image formed on the imaging unit. The image reading apparatus described.
The blur part includes a reflector that adjusts the length of the optical path, a fly array lens, a collimator lens, and a condenser lens, and has a length of an optical path that constitutes a Keller illumination system using the imaging lens as a collector lens. The image reading apparatus according to claim 11, wherein an image formed on the imaging unit is blurred by arranging each of them.
The blur part includes a fly array lens and a condenser lens, adjusts the length of the optical path, and configures a Keller illumination system using the imaging lens as a collimator lens, thereby blurring an image formed on the imaging part. The image reading apparatus according to claim 11.
The second calculation unit calculates the second shading correction information for a plurality of predetermined colors and a plurality of types of predetermined density printed matter, and interpolates for densities other than the plurality of types of densities. The image reading apparatus according to any one of claims 10 to 16, wherein the second shading correction information is calculated by:
The image reading apparatus according to any one of claims 10 to 17, wherein the extraction of the predetermined spatial frequency is performed using a high-pass filter or a band-pass filter.
An image forming unit for forming an image on a recording medium;
The image reading device according to any one of claims 10 to 18,
Including
An image forming apparatus that corrects, by the correction unit, image information converted by forming an image formed on a recording medium by the image forming unit on the imaging unit.
An image reading unevenness correction program for causing a computer to function as the first calculation unit and the second calculation unit in the image reading apparatus according to any one of claims 10 to 18.
An image reading unevenness correction program for causing a computer to function as the first calculation unit, the second calculation unit, and the correction unit in the image reading apparatus according to any one of claims 10 to 18.