JP2008145589A - Image forming apparatus and image processing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve not only monochromatic unevenness, but also multicolor unevenness that an image formed by an electrophotography system has. <P>SOLUTION: An image processing unit 60 of an image forming apparatus 1 generates a monochromatic correction table 640 correcting monochromatic unevenness and a multicolor correction table 650 which corrects multicolor unevenness, and stores them. When image data are input, the image processing unit 60 corrects the input image data based upon the multicolor correction table 650 and monochromatic unevenness table 640. An image forming unit 50 forms an image on a form based upon the thus corrected image data. Consequently, the image having both the monochromatic and multicolor unevenness corrected is formed on the form. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus and an image processing apparatus.

  It is known that an image formed by an electrophotographic method is inferior in color uniformity as compared with, for example, an image by an ink jet recording method. That is, in an image formed by an electrophotographic method, color differences and shading are likely to occur in an area that should have a uniform density with the same color. This phenomenon is called color unevenness, and there are single color unevenness and multi-order color unevenness. The single color is the color of the toner itself used for development, and is, for example, Y (yellow), M (magenta), C (cyan), or K (black). This monochromatic unevenness occurs due to wear on the surface of the photoreceptor, and typically appears as a thin streak-like grayscale image extending in the sub-scanning direction.

  On the other hand, the multi-order color is a color expressed by a plurality of single colors, for example, green expressed by overlapping cyan and yellow. When the color to be superimposed is two colors, it is called a secondary color, and when the color to be superimposed is three colors, it is called a tertiary color. The cause of the unevenness of the multi-order color is that when a toner image of another color is transferred onto the toner image transferred from the photosensitive member to the intermediate transfer member, it is transferred first. The transferred toner image may be transferred to the surface of the photoreceptor on which another color toner image is placed, or the amount of toner transferred may be different when the contact state of the transfer roller or the intermediate transfer belt is not uniform. It has been known. In particular, such a phenomenon that the toner returns to the photosensitive member as in the former is called “retransfer”. This multi-order color unevenness typically appears as an image in which the color and density gradually change over a relatively wide area.

As a method of eliminating the unevenness of the single color, a method of correcting by adjusting the charge amount and the development amount based on the position information of the photoreceptor (see Patent Document 1), and a method of correcting by changing the exposure amount in the main scanning direction Alternatively (see Patent Document 2), a method of preparing a pixel value conversion table for each minute area of an image and converting the pixel value using this table (see Patent Document 3) has been proposed.
Japanese Patent Application Laid-Open No. 08-030145 JP 09-197316 A Japanese Patent Laid-Open No. 06-003911

  However, the methods proposed in Patent Documents 1 to 3 have little effect of correcting the multi-order color unevenness as described above. The present invention has been made in view of such a background, and an object thereof is to provide a technique for improving unevenness of not only a single color but also a multi-order color.

  In order to solve the above problems, the present invention irradiates a photoconductor with light corresponding to each image of a plurality of single colors to form an electrostatic latent image corresponding to each single color on the photoconductor, and In each of the plurality of single colors, the latent image is developed with toner corresponding to the single color to form a plurality of toner images, and the plurality of formed toner images are superimposed and transferred to a recording medium. A first test image representing a first test image including a test pattern including a plurality of regions having the same density in the first direction of the recording medium and different densities in a second direction orthogonal to the first direction. Storage means for storing test image data and second test image data representing a second test image including the test pattern for a multi-order color composed of at least two of the plurality of single colors; Medium of A first reading unit configured to read the formed image and generate read image data; and a first test image formed on the predetermined medium based on the first test image data stored in the storage unit. 1 test image forming means, read image data of the first test image generated by the reading means reading the first test image, and first test image data stored in the storage means Based on the calculated gradation characteristics, a gradation characteristic at each position with the first direction as a reference axis is calculated, and a correction that is a predetermined input gradation value and a correction value of the input gradation value A first correction table generating unit that generates a first correction table that represents a correspondence relationship with a gradation value for each position, and a predetermined medium based on second test image data stored in the storage unit In The second test image forming means for forming the second test image, and the read image data of the second test image generated by the reading means reading the second test image constitute the multi-order color. Based on color separation means for separating into a plurality of single color read image data, the second test image data stored in the storage means, and the plurality of single color read image data generated by the reading means Then, the gradation characteristics at each position with the first direction as a reference axis are calculated, and based on the calculated gradation characteristics, a predetermined input gradation value and a correction level that is a correction value of the input gradation value are calculated. Second correction table generation means for generating a second correction table that represents the correspondence relationship with the tone value for each position, and the input image data in the first correction table and the second correction table. Based on There is provided an image forming apparatus comprising: a correcting unit that corrects the image; and an image forming unit that forms an image on the recording medium based on the image data corrected by the correcting unit.

  The present invention also irradiates a photoconductor with light corresponding to each image of a plurality of single colors to form an electrostatic latent image corresponding to each single color on the photoconductor, In an image forming apparatus that develops with a toner corresponding to a single color to form a plurality of toner images, and superimposes the formed toner images on a recording medium and transfers the toner images to a recording medium. First test image data representing a first test image including a test pattern composed of a plurality of regions having the same density in the first direction and different densities in a second direction orthogonal to the first direction; Storage means storing second test image data representing a second test image including the test pattern for a multi-order color composed of at least two of the plurality of single colors, and formed on a predetermined medium Images Reading means for reading and generating read image data, and first test image forming means for forming the first test image on the predetermined medium based on the first test image data stored in the storage means And the first test image read image data generated by the reading means reading the first test image and the first test image data stored in the storage means. The gradation characteristics at each position with the direction of the reference axis as the reference axis are calculated, and based on the calculated gradation characteristics, correspondence between a predetermined input gradation value and a correction gradation value that is a correction value of the input gradation value First correction table generation means for generating a first correction table representing the relationship for each position, and second test image data stored in the storage means are corrected based on the first correction table. Second test image forming means for forming the second test image on a predetermined medium based on the corrected second test image data; and a second test image generated by reading the second test image by the reading means. Color separation means for separating the read image data of the second test image into a plurality of single-color read image data constituting the multi-order color, and the first test image data and the second test image data stored in the storage means Based on the first test image data, the read image data of the first test image generated by the reading unit, and the read image data of the plurality of single colors, at each position with the first direction as a reference axis. A tone characteristic is calculated, and based on the calculated gradation characteristic, a second relationship that represents a correspondence relationship between a predetermined input tone value and a correction tone value that is a correction value of the input tone value for each position. A second correction table generating unit that generates a correction table; a correction unit that corrects input image data based on the second correction table and then corrects based on the first correction table; An image forming apparatus comprising: an image forming unit that forms an image on the recording medium based on the image data corrected by the correcting unit.

In a preferred aspect of the present invention, there is provided a high frequency removing means for removing a high frequency component higher than a predetermined spatial frequency from the read image data of the second test image generated by the reading means reading the second test image. The color separation means may separate the read image data of the second test image that has undergone removal of the high-frequency component by the high-frequency removal means into the plurality of single-color read image data.
In another preferable aspect of the present invention, when the difference between the input gradation value and the correction gradation value is smaller than a threshold value in the first correction table, the second test image is not formed. You may provide the alerting | reporting means to alert | report that it may be sufficient.
The second correction table creating means calculates a total average value of density characteristics respectively represented by the read image data of the first test image and the read image data of a plurality of single colors for each of the input gradation values. The second correction table may be generated based on the obtained target gradation value.
The predetermined medium may be at least one of the photosensitive member, an intermediate transfer member to which the toner image is transferred, or the storage medium.

  The present invention also provides a test pattern comprising a plurality of regions having the same density in the first direction of the recording medium and different densities in the second direction orthogonal to the first direction for each of the plurality of single colors. A second test image representing the second test image including the first test image data representing the first test image including, and the test pattern for a multi-color composed of at least two of the plurality of single colors. Storage means storing image data, and a first test image generated by reading the first test image formed on a predetermined medium based on the first test image data stored in the storage means Based on the read image data of the test image and the first test image data stored in the storage unit, the gradation characteristics at each position with the first direction as a reference axis are calculated and calculated. A first correction table that generates a first correction table that represents a correspondence relationship between a predetermined input gradation value and a correction gradation value that is a correction value of the input gradation value for each position based on the tone characteristics Generation image and read image data of the second test image generated by reading the second test image formed on a predetermined medium based on the second test image data stored in the storage unit Are separated into a plurality of single color read image data constituting the multi-color, the second test image data stored in the storage means, and the plurality of single color read image data. Based on the calculated gradation characteristics, a gradation characteristic at each position with the first direction as a reference axis is calculated, and a correction that is a predetermined input gradation value and a correction value of the input gradation value Previous correspondence with gradation value Second correction table generating means for generating a second correction table for each position, and correction for outputting the input image data after correcting the input image data based on the first correction table and the second correction table. And an image processing apparatus.

  Furthermore, the present invention provides a test pattern composed of a plurality of regions having the same density in the first direction of the recording medium and different densities in the second direction orthogonal to the first direction for each of the plurality of single colors. A second test image representing the second test image including the first test image data representing the first test image including, and the test pattern for a multi-color composed of at least two of the plurality of single colors. Storage means storing image data, and a first test image generated by reading the first test image formed on a predetermined medium based on the first test image data stored in the storage means Based on the read image data of the test image and the first test image data stored in the storage unit, the gradation characteristics at each position with the first direction as a reference axis are calculated and calculated. First correction for generating a first correction table for each position indicating a correspondence relationship between a predetermined input gradation value and a correction gradation value which is a correction value of the input gradation value based on the gradation characteristics A table generating means; a first correcting means for correcting the second test image data stored in the storage means based on the first correction table; and the second test corrected by the correcting means. The read image data of the second test image generated by reading the second test image formed on the predetermined medium based on the image data is converted into a plurality of single-color read image data constituting the multi-color. Color separation means for separating the first test image data, the second test image data stored in the storage means, the read image data of the generated first test image, and the previous Based on a plurality of single-color read image data, a gradation characteristic at each position with the first direction as a reference axis is calculated, and a predetermined input gradation value and the input are calculated based on the calculated gradation characteristic. Second correction table generating means for generating a second correction table for each position corresponding to a correction gradation value which is a correction value of the gradation value; and input image data as the second correction table. There is provided an image processing apparatus comprising: a second correction unit that performs correction based on a correction table and then outputs a correction based on the first correction table.

Next, the best mode for carrying out the present invention will be described.
(1) Outline of Embodiment In this embodiment, input image data is corrected based on a multi-order color correction table and then corrected based on a single color correction table. The multi-order color correction table is a table (second correction table) for correcting multi-order color unevenness caused by retransfer as described above. The monochromatic correction table is a table (first correction table) for correcting monochromatic unevenness caused by the above-described wear of the device. Thus, by correcting image data using both the multi-order color correction table (second correction table) and the single color correction table (first correction table), an image formed based on the image data is formed. Both the single color unevenness and the multi-color unevenness are improved.
In the following description, the main scanning direction is the direction that coincides with the scanning direction of the exposure light during image formation, and the sub-scanning direction is the rotation direction of the photoconductor used for image formation (the direction of movement of the photoconductor surface). ). These main scanning direction and sub-scanning direction are orthogonal to each other.

(2) Details of Embodiment (2-1) Configuration FIG. 1 is a diagram illustrating an overall configuration of an image forming apparatus 1 according to the present embodiment. As shown in FIG. 1, the image forming apparatus 1 includes a control unit 10, a UI unit 20, a communication unit 30, an image reading unit 40, an image forming unit 50, and an image processing unit 60. The image processing unit 60 is housed inside the housing of the image forming apparatus 1. However, in the drawing, the image processing unit 60 is illustrated outside the housing of the image forming apparatus 1 for easy understanding of the configuration of the image processing unit 60. ing. The control unit 10 includes a CPU (Central Processing Unit) and a memory, and the CPU controls each unit of the image forming apparatus 1 by executing various programs stored in the memory. The UI unit 20 includes a touch panel and operation buttons, displays an image corresponding to an image signal supplied from the control unit 10, and accepts an instruction input from a user. The communication unit 30 is an interface for exchanging information with an external device connected via a network. The communication unit 30 receives image data and an instruction regarding image formation from an external device, and supplies the received information to the control unit 10 and the image processing unit 60.

  The image reading unit 40 is a so-called scanner, optically reads an image of a set paper, and generates read image data representing the read image. More specifically, the image reading unit 40 irradiates the sheet with light from the light source, and guides the reflected light to the imaging lens using a reflection mirror. Then, the reflected light guided to the imaging lens is imaged on the CCD sensor. When light is imaged by the imaging lens, the CCD sensor outputs analog signals of R (red), G (green), and B (blue) colors corresponding to the amount of light. The analog signal output from the CCD sensor is converted into a digital signal by an A / D converter and then subjected to various signal processing. In this way, read image data of each color of R, G, and B representing the paper image is generated.

The image forming unit 50 forms an image on a sheet based on the supplied image data. The image forming unit 50 includes an image forming unit 51, an intermediate transfer belt 52, a secondary transfer unit 53, a paper feeding unit 54, a paper transport belt 55, and a fixing unit 56.
The image forming unit 51 is individually provided for each of Y (yellow), M (magenta), C (cyan), and K (black), and in the rotation direction of the intermediate transfer belt 52 (the direction of arrow B in the drawing). The image forming units 51Y, 51M, 51C, and 51K are arranged in this order from the upstream side. Each image forming unit 51 includes a photosensitive drum, a charging unit, an exposure unit, a developing unit, and a primary transfer unit. The photosensitive drum is rotated at a predetermined speed in the direction of arrow A in the figure by a driving unit (not shown). The charging unit uniformly charges the peripheral surface of the photosensitive drum. The exposure unit irradiates the circumferential surface of the photosensitive drum charged by the charging unit with laser light corresponding to the image data of each color, and electrostatic latent images corresponding to the image data of the respective colors on the circumferential surface of the photosensitive drum. Form an image. The developing unit develops the electrostatic latent image generated by the exposure unit with each color toner, thereby forming each color toner image. The primary transfer unit superimposes and transfers the toner images of the respective colors formed on the peripheral surface of the photosensitive drum onto the intermediate transfer belt 52. The intermediate transfer belt 52 is rotated in the direction of arrow B in the figure by the transport roll.

  Here, FIG. 2 is a diagram illustrating a state in which the toner images of the respective colors are transferred onto the intermediate transfer belt 52. The toner is transferred to the intermediate transfer belt 52 in the order of Y, M, C, and K. That is, when a plurality of toner images are transferred onto the intermediate transfer belt 52, another toner image formed by the downstream image forming unit 51 is formed on the toner image formed by the upstream image forming unit 51. A color toner image is further superimposed. For example, when forming an R toner image with a halftone dot area ratio (hereinafter referred to as “Cin: Input Coverage”) = 60%, first, a Y toner image with Cin = 60% is formed on the intermediate transfer belt 52. Transcribed. Subsequently, the M toner image of Cin = 60% is transferred so as to overlap the Y toner image. In this way, an R toner image with Cin = 60% is formed on the intermediate transfer belt 52. The R toner image is conveyed to the intermediate transfer belt 52 and thereby contacts the peripheral surfaces of the photosensitive drums C and K installed on the downstream side of the photosensitive drum M. At this time, retransfer occurs in which the M toner superimposed lastly transfers to the peripheral surfaces of the photoconductive drums C and K. If the contact state is not uniform, multi-color unevenness occurs. That is, this retransfer occurs when the toner image superimposed last comes into contact with another photosensitive drum. Therefore, the same phenomenon occurs in process black (hereinafter referred to as “PB”), which is a color obtained by superimposing three colors of Y, M, and C at the same ratio, and C toner when forming B and G toner images. Will occur.

  In FIG. 1, a paper supply unit 54 stores a plurality of sheets as recording media, and sends out the stored sheets one by one. The paper transport belt 55 transports the paper fed from the paper feed unit 54 to the paper discharge port via the secondary transfer unit 53 and the fixing unit 56. When the toner image is conveyed by the intermediate transfer belt 52 and the sheet is conveyed by the sheet conveying belt 55, the secondary transfer unit 53 uses the potential difference to transfer the toner image to the sheet. When the sheet having the toner image transferred thereon is conveyed, the fixing unit 56 applies heat and pressure to fix the toner image on the sheet. Then, the sheet on which the toner image is fixed by the fixing unit 56 is discharged from the discharge port.

  The image processing unit 60 corrects input image data based on the single color correction table 640 and the multi-order color correction table 650, and outputs the corrected image data to the image forming unit 50. The image data input to the image processing unit 60 may be image data generated by the image reading unit 40 or image data received by the communication unit 30 from an external device. The image processing unit 60 includes a test image data generation unit 61, a selector 62, a switch 63, a single color correction unit 64, and a multi-order color correction unit 65. The test image data generation unit 61, the single color correction unit 64, and the multi-order color correction unit 65 are realized by a calculation unit such as a CPU or an ASIC (Application Specific Integrated Circuit) (not shown) or a storage unit such as various memories. The test image data generating unit 61 stores in advance monochromatic test image data 610 representing a monochromatic test image and multi-order color test image data 611 representing a multi-order color test image.

Here, FIG. 3A is a diagram showing a monochromatic test image, and FIG. 3B is a diagram showing a multi-order color test image. In this embodiment, the number of pixels in the main scanning direction (arrow X direction in the figure) of these test images is 7000, the range of gradation values for each color can be 0 to 255, and the density value (Cin) is 0% to 100. The following explanation is given assuming the case of%. Note that the gradation value and the density value are substantially the same, except for the expression format.
A single-color test image has a plurality of Y, M, C, and K having the same density in the main scanning direction of the image and different densities in the sub-scanning direction (arrow Y direction in the figure) orthogonal to the main scanning direction. Contains a test pattern consisting of areas. This monochromatic test image is formed with a K test pattern, a C test pattern, a Y test pattern, and an M test pattern in order from the top, and each test pattern has a total of 10 regions with different densities by 10%. Have For example, the area N1 is an area having a density value (Cin) = 10%, the area N2 is an area having a density value (Cin) = 20%, and the area N10 is an area having a density value (Cin) = 100%. .

  The multi-color test image is formed with the same test pattern as the above-described single-color test image except for the color of the test pattern. The multi-color test image is formed with a PB test pattern, an R test pattern, a G test pattern, and a B test pattern in order from the top. Each color forming the multi-order color test image is a multi-order color including at least two of Y, M, and C. For example, as described above, PB is a color obtained by superimposing three colors Y, M, and C at the same ratio, and R is a color obtained by superimposing two colors Y and M at the same ratio. G is a color obtained by superimposing two colors Y and C at the same ratio, and B is a color obtained by superimposing two colors C and M at the same ratio.

  In FIG. 1, the selector 62 supplies the test image data supplied from the test image data generation unit 61 or the image data supplied from the single color correction unit 64 to the image forming unit 50. The operation modes of the image forming apparatus 1 include a normal operation mode for forming an image based on arbitrary image data and a test mode for correcting a gradation value based on each test image described above. When the user operates the UI unit 20 to specify the normal operation mode, the selector 62 supplies the image data supplied from the single color correction unit 64 to the image forming unit 50. On the other hand, when the user operates the UI unit 20 to specify a test mode, the selector 62 receives test image data (monochromatic test image data 610 and multi-order color test image data 611) supplied from the test image data generation unit 61. Is supplied to the image forming unit 50.

  When the user operates the UI unit 20 and designates the test mode, the switching unit 63 switches the single color correction unit 64 or the multi-order color correction unit 65 according to the content of the image data supplied from the image reading unit 40. The image data is supplied. For example, when read image data of a single color test image generated by reading a single color test image by the image reading unit 40 is supplied, the switch 63 supplies the read image data to the single color correction unit 64. On the other hand, when the read image data of the multi-order color test image generated by reading the multi-order color test image by the image reading unit 40 is supplied, the switch 63 converts the read image data into the multi-order color correction unit 65. To supply.

In the test mode, the monochromatic correction unit 64 generates a monochromatic correction table 640 for correcting monochromatic unevenness based on the read image data of the monochromatic test image supplied from the switch 63. On the other hand, in the normal operation mode, the input image data is corrected based on the single color correction table 640.
In the test mode, the multi-order color correction unit 65 generates a multi-order color correction table 650 for correcting multi-order color unevenness based on the read image data of the multi-order color test image supplied from the switch 63. To do. On the other hand, in the normal operation mode, the input image data is corrected based on the multi-order color correction table 650. Next, a method for generating these correction tables will be described in the order of the single color correction table 640 and the multi-order color correction table 650.

(2-2) Generation Method of Monochromatic Correction Table 640 When a user performs a predetermined operation from the UI unit 20 and designates a test mode, the control unit 10 switches the operation mode to the test mode. In the test mode, the test image data generation unit 61 outputs monochromatic test image data 610. The monochromatic test image data 610 is supplied to the image forming unit 50 by the selector 62. The image forming unit 50 forms a monochrome test image on a sheet based on the supplied monochrome test image data 610. When a sheet on which a monochromatic test image is formed is discharged from the image forming apparatus 1, the operator of the image forming apparatus 1 sets the sheet in the image reading unit 40 and performs a predetermined operation from the UI unit 20. Instructs to read the image. When an image reading instruction is input to the UI unit 20, the image reading unit 40 reads a single color test image of the set paper, and generates read image data of the R, G, and B color single color test images. The read image data of the monochrome test image is supplied to the monochrome correction unit 64 by the switch 63.

The single color correction unit 64 includes a correction amount calculation unit 64a and a single color data conversion unit 64b.
First, the correction amount calculation unit 64a converts the read image data of the supplied single-color test image of each color of R, G, and B into image data of each color of Y, M, C, and K. The correspondence between the R, G, and B data values and the Y, M, C, and K data values is obtained in advance by experiment or calculation, and the correction amount calculation unit 64a stores them. The correction amount calculation unit 64a may perform the conversion based on the stored contents. Next, the correction amount calculation unit 64a inputs the input gradation value for each pixel position with the main scanning direction as the reference axis for the read image data of the single color test image converted into each color of Y, M, C, and K. A tone characteristic representing the relationship between the output tone value and the output tone value is obtained. The input gradation value is a gradation value at each pixel position constituting the test image data stored in the test image data generation unit 61. The output gradation value is the output gradation value obtained by the image reading unit 40 using a single-color test image. It is a gradation value at each pixel position constituting the read image data obtained by reading. These gradation values all take values in the range of 0 to 255.

FIG. 4 is a diagram illustrating the gradation characteristics at each pixel position. In the figure, “pixel” represents a pixel position in the main scanning direction. For example, when the resolution is 600 dpi (dot per inch), the number of pixels connected in the main scanning direction is about 7000. In this case, pixel = 0 represents the position of the pixel at the origin in the main scanning direction (for example, the left end portion of the image), and pixel = 6999 represents the position of the pixel at the end point in the main scanning direction (for example, the right end portion of the image). Yes.
The broken line C in the figure represents the gradation characteristic when the input gradation value and the output gradation value are the same value. In addition, solid lines C ₀ , C _1, C ₂ ... C ₆₉₉₉ in the figure represent the relationship between the input gradation value and the output gradation value obtained as described above, that is, the gradation characteristics for each pixel position. ing. When the broken line C and the solid lines C ₀ , C ₁ , C ₂ ... C ₆₉₉₉ are compared, the output gradation value and the input gradation value at each pixel position are often not the same value. For example, in the gradation characteristic at the pixel position pixel = 2, the output gradation value tends to be larger than the input gradation value.

By canceling the tendency of the gradation characteristic at each pixel position and adjusting the input gradation value and the output gradation value to be substantially the same value, the single color unevenness is corrected. Therefore, the correction amount calculation unit 64a obtains a gradation conversion characteristic for converting the input gradation value into the corrected gradation value for each pixel position. The solid lines C ₀ ′, C ₁ ′, C ₂ ′,..., C ₆₉₉₉ ′ in FIG. 4 indicate the gradation conversion characteristics at the respective pixel positions. As shown in the figure, for example, in the gradation characteristics indicated by solid lines C ₀ , C ₁ , C ₂ ... C ₆₉₉₉ , the pixel position of the pixel position where the output gradation value tends to be larger than the input gradation value. The correction gradation value is set so that the value becomes smaller by the tendency. On the other hand, the corrected gradation value at the pixel position where the output gradation value tends to be smaller than the input gradation value is set so that the value is increased by the tendency.

  The correction amount calculation unit 64a generates a single color correction table 640 representing the gradation conversion characteristics for each pixel position in a table format for each color of Y, M, C, and K. FIG. 5 is a diagram illustrating an example of the contents of the single color correction table 640. In the figure, the values are thinned out for the sake of simplicity, but this single color correction table 640 includes input gradation values from 0 to 255 and correction gradation values that are correction values of the input gradation values. Is associated with each pixel position from pixel = 0 to 6999. For example, when the input gradation value is “111” at the pixel position of pixel = 438, the corresponding correction gradation value is “117”. The single color correction table 640 generated in this way is stored in the single color data conversion unit 64b.

(2-3) Generation Method of Multi-Order Color Correction Table 650 When the single-color correction table 640 is generated as described above, the test image data generation unit 61 in FIG. And the output multi-order color test image data 611 is supplied to the single color data converter 64b. The single color data conversion unit 64b acquires the pixel position in the main scanning direction and the gradation value of each pixel position from the supplied multi-order color test image data 611. Then, the single color data conversion unit 64b converts the gradation value of the multi-order color test image data 611 as a correction gradation value corresponding to the input gradation value as the input gradation value in the single color correction table 640. That is, the multi-order color test image data 611 output from the test image data generation unit 61 is corrected based on the single color correction table 640.

  Next, the test image data generation unit 61 supplies the multi-color test image data 611 corrected by the single color data conversion unit 64b to the selector 62. The multi-order color test image data 611 is supplied to the image forming unit 50 by the selector 62. The image forming unit 50 forms a multi-color test image on a sheet based on the supplied multi-color test image data 611. As described above, this multi-order color test image is formed based on the multi-order color test image data 611 corrected in advance by the single-color data conversion unit 64b, and thus, for example, a thin stripe-like single color extending in the sub-scanning direction. The non-uniformity is almost improved. Therefore, the multi-order color correction unit 65 generates a high-precision multi-order color correction table 650 based on the multi-order color test image data 611. When the sheet on which the multi-color test image is formed is discharged from the image forming apparatus 1, the operator of the image forming apparatus 1 sets the sheet in the image reading unit 40 and performs a predetermined operation from the UI unit 20. To instruct reading of the image. When an image reading instruction is input to the UI unit 20, the image reading unit 40 reads the multi-order color test image of the set paper, and reads the image data of the multi-order color test image for each of R, G, and B colors. Is generated. The read image data of the multi-order color test image is supplied to the multi-order color correction unit 65 by the switch 63.

The multi-order color correcting unit 65 includes a high frequency removing unit 65a, a color separation processing unit 65b, a target setting unit 65c, a correction amount calculating unit 65d, and a multi-order color data converting unit 65e.
The high frequency removing unit 65a removes high frequency components higher than a predetermined spatial frequency from the read image data of the multi-order color test image supplied from the switch 63 using, for example, an averaging filter having a width of 20 mm. In some cases, the single color data conversion unit 64b may not be able to correct the color unevenness, but the noise component that causes the color unevenness can be removed by this high frequency component removal processing. The high frequency removing unit 65a supplies the read image data that has undergone the high frequency component removal processing to the color separation processing unit 65b.

The color separation processing unit 65b converts the read image data of each of R, G, and B colors supplied from the high frequency removal unit 65a into read image data of each of the Y, M, and C colors constituting the multi-color, and performs color separation. I do. This color separation is performed in accordance with, for example, a color separation rule set before the image forming apparatus 1 is shipped. Hereinafter, the density characteristics of the read image data of C color-separated by the color separation processing unit 65b will be described in detail.
FIG. 6 is a diagram illustrating an example of density characteristics of various types of read image data. In the figure, the horizontal axis indicates each position (mm) from the origin with the main scanning direction of each test image as the reference axis, and the vertical axis indicates the density (Cin:%) of each read image data. A broken line C0 in the figure represents an output gradation value at each position in the read image data obtained by reading the area N6 (Cin = 60%) of the test pattern C of the single-color test image. This output gradation value is a value obtained by the correction amount calculation unit 64a of the monochrome correction unit 64 described above.
On the other hand, the polygonal line CP in the figure indicates the density characteristic represented by the read image data of C obtained by the image reading unit 40 reading the region N6 of the test pattern PB of the multi-order color test image. Similarly, the polygonal line CG in the figure indicates the region N6 of the test pattern G of the multi-order color test image by the image reading unit 40, and the polygonal line CB indicates the region N6 of the test pattern B of the multi-order color test image by the image reading unit 40. The density characteristics represented by the read image data of C respectively obtained by reading

  As shown in the figure, the density values represented by the polygonal lines C0, CP, CG, and CB are supposed to be Cin = 60% originally, but vary depending on the position in the main scanning direction. Of these density values, the density value represented by the polygonal line C0 should be corrected to approximately 60% by the monochrome correction unit 64 described above. On the other hand, changes in density values represented by broken lines CP, CG, and CB indicate that multi-order color unevenness occurs in the multi-order color test image. In other words, even if correction is performed by the single color correction unit 64 based on the C single color read image data, it means that color unevenness occurs in the multi-order color image due to the above-described retransfer or the like. Yes.

  Therefore, in multi-order color correction, a target gradation value obtained by averaging the density characteristics represented by each read image data is set, and a correction gradation value is obtained based on the target gradation value. Based on the read image data of the single color test image described above and the read image data of the multi-color test image converted into each color Y, M, and C by the color separation processing unit 65b, the target setting unit 65c A target tone value is determined for each value. FIG. 7 is a diagram in which the density characteristics of the read image data of C0, CP, CG, and CB shown in FIG. 6 and the average value of these density characteristics are superimposed. This average value can be obtained by a calculation formula of (CA1 + CA2 + CA3 + CA4) / 4, where, for example, the average value of the density values at each pixel position in C0, CP, CG, CB is CA1 to CA4, respectively. The target setting unit 65c obtains an average value of each color of Y, M, and C in units of 10% density such as 10%, 20%, 30%,... 100%, and the obtained average value is a target for each color. The gradation value.

ＤＲ＝補正階調値
ＤＩ＝入力階調値
ＤＭ＝目標階調値
ＤＯ＝出力階調値
例えば、ＤＩ＝５０、ＤＭ＝５２、ＤＯ＝５３の場合、上記数１で算出されるＤＲ（補正階調値）は４９となる。このようにして、画素位置毎に補正階調値を算出することにより、図の実線ｃ_０’ｃ_１’、ｃ_２’・・ｃ_６９９９’にて示す各画素位置の階調変換特性が求められる。
補正量演算部６５ｄは、この各画素位置の階調変換特性に基づいて、各入力階調値とその入力階調値における補正階調値との対応関係を画素位置毎に表す、Ｙ、Ｍ、Ｃ各色の多次色補正テーブル６５０を生成する。この多次色補正テーブル６５０は、上述した単色補正テーブル６４０と同様に、０〜２５５までの各入力階調値とその入力階調値における補正階調値との対応関係が、０〜６９９９までの画素位置毎に対応付けられている。生成された多次色補正テーブル６５０は、多次色データ変換部６５ｅに記憶される。なお、Ｋの画像については多次色のムラが発生しにくいため、Ｋの多次色補正テーブル６５０は、上述したＫの単色補正テーブル６４０と同一のものである。また、Ｙ及びＭの読み取り画像データの濃度特性については、Ｃの読み取り画像データとほぼ同様の傾向を示すため、その説明を省略する。 The correction amount calculation unit 65d has a target gradation characteristic (hereinafter referred to as a target gradation characteristic) for each pixel position with the main scanning direction as a reference axis for the read image data of Y, M, and C colors, The actually measured gradation characteristics read at the pixel position are respectively obtained. In FIG. 8, a broken line c represents a target gradation characteristic at each pixel position, and solid lines c ₀ , c ₁ , c ₂ ... C ₆₉₉₉ represent an actually measured gradation characteristic. Solid lines c ₀ , c ₁ , c ₂ ... C ₆₉₉₉ illustrate the average of the gradation characteristics obtained from the read image data of CP, CG, and CB. The correction amount calculation unit 65d obtains, for each pixel position, a correction gradation value for converting the actually measured gradation characteristic shown in FIG. 8 into the target gradation characteristic in the same manner as the generation of the single color correction table 640 described above. . Equation 1 below is an expression for obtaining the corrected gradation value.

DR = correction gradation value DI = input gradation value DM = target gradation value DO = output gradation value For example, when DI = 50, DM = 52, and DO = 53, DR calculated by the above equation 1 (correction) (Gradation value) is 49. In this manner, by calculating the corrected grayscale value for each pixel position, the solid line c ₀ 'c _1' of FIG obtains gradation conversion characteristic of each pixel position indicated by c _{2 '··} c _6999' It is done.
Based on the gradation conversion characteristics at each pixel position, the correction amount calculation unit 65d represents the correspondence between each input gradation value and the corrected gradation value at the input gradation value for each pixel position. , C, a multi-order color correction table 650 for each color is generated. In the multi-order color correction table 650, as in the above-described single color correction table 640, the correspondence relationship between each input gradation value from 0 to 255 and the correction gradation value in the input gradation value is from 0 to 6999. Are associated with each pixel position. The generated multi-order color correction table 650 is stored in the multi-order color data conversion unit 65e. Note that since the multi-order color unevenness hardly occurs in the K image, the K multi-order color correction table 650 is the same as the K single-color correction table 640 described above. Further, the density characteristics of the read image data of Y and M show a tendency similar to that of the read image data of C, and thus description thereof is omitted.

(2-4) Correction Processing Next, processing for correcting color unevenness of input image data using the single color correction table 640 and the multi-order color correction table 650 will be described.
In FIG. 1, when image data is input from the image reading unit 40 or the communication unit 30 in a state where the normal operation mode is designated by the user operating the UI unit 20, the image processing unit 60 is input. First, the image data is supplied to the multi-order color data converter 65e. The multi-order color data conversion unit 65e acquires the pixel position in the main scanning direction and the gradation value of each pixel position from the supplied image data, and based on the multi-order color correction table 650, the level of the image data. The tone value is converted into a corrected tone value. That is, the image data input to the image processing unit 60 is corrected based on the multi-order color correction table 650. Subsequently, the image data corrected by the multi-color data conversion unit 65e is supplied to the single color data conversion unit 64b. The monochrome data conversion unit 64b acquires the pixel position in the main scanning direction and the gradation value of each pixel position from the supplied image data, and based on the monochrome correction table 640, the gradation value of the image data is corrected. Convert to key value. That is, the image data corrected by the multi-order color data conversion unit 65e is further corrected based on the single color correction table 640. The selector 62 supplies the image data corrected by the single color correction table 640 to the image forming unit 50. The image forming unit 50 forms an image on a sheet based on the supplied image data. Thus, since the image data supplied to the image forming unit 50 is corrected based on the multi-order color correction table 650 and then corrected based on the single color correction table 640, the image formed on the paper is Both the single color unevenness and the multi-order color unevenness are improved.

(2-5) Correction Table Update Processing Next, a method for updating the single color correction table 640 and the multi-order color correction table 650 will be described. The color unevenness that occurs in an image is worn over the devices of the image forming apparatus 1, and the location of the color unevenness and the degree of color unevenness change over time. For this reason, it is desirable to periodically update the correction table for correcting the color unevenness of the image.
When the user operates the UI unit 20 to instruct the update of the correction table, the image processing unit 60 causes the test image data generation unit 61 to output the monochromatic test image data 610, and the monochromatic correction table 640 is stored in the same manner as described above. Generate. At this time, when the difference between the input gradation ground and the corrected gradation value is equal to or greater than the threshold in the single color correction table 640, the image processing unit 60 stores the multi-color test image data 611 in the test image data generation unit 61. The multi-order color correction table 650 is generated in the same manner as described above. Thereby, both the correction tables of the single color correction table 640 and the multi-order color correction table 650 are updated. On the other hand, when the difference between the input gradation ground and the corrected gradation value is smaller than the threshold value in the single color correction table 640, the message indicating that the image processing unit 60 does not have to form a multi-color test image. Is displayed on the UI unit 20 to notify the user. As a result, only the monochrome correction table 640 is updated. Since the multi-color unevenness is caused by retransfer, it is less likely to change over time than the single-color unevenness. Therefore, when the degree of correction of the single color correction table 640 is small, there is no particular problem even if the multi-order color correction table 650 is not updated, and thus such update processing is performed. By updating the correction table as described above, highly accurate color unevenness correction is always performed.

(3) Modifications The following modifications can be applied to the above embodiment.
In the above embodiment, the single-color test image and the multi-color test image include a test pattern composed of a plurality of regions having the same density in the main scanning direction of the image and different densities in the sub-scanning direction orthogonal to the main scanning direction. It was. On the other hand, as shown in FIG. 9, these test images have the same density in the sub-scanning direction (arrow Y direction in the figure) and the density in the main scanning direction (arrow X direction in the figure). You may include the test pattern which consists of a several different area | region. By generating the single color correction table 640 and the multi-order color correction table 650 using this test image, color unevenness in the sub-scanning direction is improved.

When generating a correction table in the above embodiment, first, a single color correction table 640 is generated, and then a test image that has undergone single color correction using the single color correction table 640 is read, and a multiplicity is calculated based on the read result. A next color correction table 650 is generated. When performing correction, first, multi-order color correction is performed using the multi-order color correction table 650, and then single color correction is performed using the single color correction table 640.
Even if the table generation order and the correction order are reversed between the single color and the multi-order color, since there is an effect of correcting the single-color unevenness and the multi-order color unevenness, such a configuration may be adopted. In short, since the table generation order and the correction order may be either single-color unevenness or multi-order color unevenness, the present invention can be understood as follows. That is, the photosensitive member is irradiated with light corresponding to each image of a plurality of single colors to form an electrostatic latent image corresponding to each single color on the photosensitive member, and each of the electrostatic latent images corresponds to the single color. In an image forming apparatus for developing with toner to form a plurality of toner images and transferring the formed toner images to a recording medium in a superimposed manner, a first direction of the recording medium for each of the plurality of single colors First test image data representing a first test image including a test pattern including a plurality of regions having the same density and different densities in a second direction orthogonal to the first direction, and the plurality of single colors Storage means storing second test image data representing a second test image including the test pattern for a multi-order color composed of at least two colors, and reading an image formed on a predetermined medium Reading means for generating read image data, and first test image forming means for forming the first test image on the predetermined medium based on the first test image data stored in the storage means , Based on the read image data of the first test image generated by the reading means reading the first test image and the first test image data stored in the storage means. Calculate the tone characteristics at each position with the direction as the reference axis, and based on the calculated tone characteristics, the correspondence between the predetermined input tone value and the corrected tone value that is the correction value of the input tone value First correction table generating means for generating a first correction table for each position, and the second test image on a predetermined medium based on second test image data stored in the storage means Forming Second test image forming means, and read image data of the second test image generated by reading the second test image by the reading means, a plurality of single-color read image data constituting the multi-order color The first direction is determined based on the color separation means for separating the image data, the second test image data stored in the storage means, and the plurality of monochrome read image data generated by the reading means. A gradation characteristic at each position as a reference axis is calculated, and a correspondence relationship between a predetermined input gradation value and a correction gradation value that is a correction value of the input gradation value is calculated based on the calculated gradation characteristic. Second correction table generating means for generating a second correction table representing each position; correction means for correcting the input image data based on the first correction table and the second correction table; Said An image forming apparatus comprising: an image forming unit that forms an image on the recording medium based on the image data corrected by the correcting unit.

  In the embodiment described above, the image reading unit 40 reads a test image formed on a medium called paper and generates read image data. However, the medium on which the test image is formed may be the photosensitive drum or the intermediate transfer belt 52. Thus, the monochrome correction table 640 and the multi-color correction table 650 can be generated without printing the paper on which the single-color test image and the multi-color test image are formed each time the correction table is generated.

  In the above embodiment, the image processing unit 60 does not need to form a multi-color test image when the difference between the input gradation value and the correction gradation value in the single color correction table 640 is smaller than the threshold value. Is displayed on the UI unit 20 and only the single color correction table 640 is updated. On the other hand, when the user operates the UI unit 20 to instruct the update of the correction table, the UI unit 20 updates only the single color correction table 640 or both the single color correction table 640 and the multi-order color correction table 650. Any input of update may be accepted. Thereby, the user can select one of the update processes according to the accuracy of correction and the time required for the update.

In the above embodiment, tone characteristics and tone conversion characteristics are obtained for each pixel. However, tone characteristics and tone conversion characteristics may be obtained for each region composed of a plurality of pixels. “Each position” in the present invention is a concept including the position of each pixel and the position of an area composed of a plurality of pixels.
Note that the image processing unit 60 of the present invention is not limited to the one built in the image forming apparatus 1, but is realized as an image treatment apparatus by, for example, the image forming apparatus 1 and a host device connected to a network. Also good.

1 is a diagram illustrating an overall configuration of an image forming apparatus 1. FIG. 6 is a diagram illustrating a state where toner images of respective colors are transferred onto an intermediate transfer belt 52. It is a figure which shows a monochromatic test image and a multi-order color test image. It is a figure which shows the gradation characteristic and gradation conversion characteristic which are obtained from a monochromatic test image. It is a figure which shows an example of the content of the single color correction table. It is a figure which shows an example of the density | concentration characteristic which various read image data represents. It is a figure which shows the average value of the density | concentration characteristic which each read image data represents. It is a figure which shows the gradation characteristic and gradation conversion characteristic which are obtained from a multi-order color test image. It is a figure which shows the test image concerning a modification.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus 10 ... Control part 20 ... UI part 30 ... Communication part 40 ... Image reading part 50 ... Image forming part 51 ... Image forming unit 52 ... Intermediate transfer belt 53 ... Secondary transfer , 54... Paper feeding section, 55... Paper conveying belt, 56... Fixing section, 60... Image processing section, 61 .. test image data generating section, 610. ... selector, 63 ... switch, 64 ... monochromatic correction unit, 64a, 65d ... correction amount calculation unit, 64b ... monochromatic data conversion unit, 640 ... monochromatic correction table, 65 ... multiple color correction unit, 65a ... high frequency removal 65b: Color separation processing unit, 65c: Target setting unit, 65e: Multi-order color data conversion unit, 650: Multi-order color correction table.

Claims (8)

The photosensitive member is irradiated with light corresponding to each image of a plurality of single colors to form an electrostatic latent image corresponding to each single color on the photosensitive member, and each of the electrostatic latent images is formed with toner corresponding to the single color. In an image forming apparatus that develops and forms a plurality of toner images, and superimposes and transfers the formed toner images to a recording medium.
Each of the plurality of single colors includes a first test pattern including a plurality of regions having the same density in the first direction of the recording medium and different densities in a second direction orthogonal to the first direction. First test image data representing a test image, and second test image data representing a second test image including the test pattern for a multi-order color composed of at least two of the plurality of single colors. Memorized storage means;
Reading means for reading an image formed on a predetermined medium and generating read image data;
First test image forming means for forming the first test image on the predetermined medium based on first test image data stored in the storage means;
Based on the read image data of the first test image generated by the reading unit reading the first test image, and the first test image data stored in the storage unit, the first direction Based on the calculated tone characteristics, the correspondence between a predetermined input tone value and a corrected tone value that is a correction value of the input tone value is calculated. First correction table generation means for generating a first correction table that represents each position;
Second test image forming means for forming the second test image on a predetermined medium based on second test image data stored in the storage means;
Color separation means for separating the read image data of the second test image generated by the reading means by reading the second test image into a plurality of single-color read image data constituting the multi-order color;
On the basis of the second test image data stored in the storage unit and the plurality of single-color read image data generated by the reading unit, a floor at each position with the first direction as a reference axis. A second correction that represents a correspondence relationship between a predetermined input gradation value and a correction gradation value that is a correction value of the input gradation value for each position based on the calculated gradation characteristic; Second correction table generating means for generating a table;
Correction means for correcting the input image data based on the first correction table and the second correction table;
An image forming apparatus comprising: an image forming unit that forms an image on the recording medium based on the image data corrected by the correcting unit. The photosensitive member is irradiated with light corresponding to each image of a plurality of single colors to form an electrostatic latent image corresponding to each single color on the photosensitive member, and each of the electrostatic latent images is formed with toner corresponding to the single color. In an image forming apparatus that develops and forms a plurality of toner images, and superimposes and transfers the formed toner images to a recording medium.
Each of the plurality of single colors includes a first test pattern including a plurality of regions having the same density in the first direction of the recording medium and different densities in a second direction orthogonal to the first direction. First test image data representing a test image, and second test image data representing a second test image including the test pattern for a multi-order color composed of at least two of the plurality of single colors. Memorized storage means;
Reading means for reading an image formed on a predetermined medium and generating read image data;
First test image forming means for forming the first test image on the predetermined medium based on first test image data stored in the storage means;
Based on the read image data of the first test image generated by the reading unit reading the first test image, and the first test image data stored in the storage unit, the first direction Based on the calculated tone characteristics, the correspondence between a predetermined input tone value and a corrected tone value that is a correction value of the input tone value is calculated. First correction table generation means for generating a first correction table that represents each position;
The second test image data stored in the storage means is corrected based on the first correction table, and the second test image is applied to a predetermined medium based on the corrected second test image data. Second test image forming means to be formed;
Color separation means for separating the read image data of the second test image generated by the reading means by reading the second test image into a plurality of single-color read image data constituting the multi-order color;
The first test image data and the second test image data stored in the storage unit, the read image data of the first test image generated by the reading unit, and the read image data of a plurality of single colors Based on the above, a gradation characteristic at each position with the first direction as a reference axis is calculated, and based on the calculated gradation characteristic, a predetermined input gradation value and a correction value of the input gradation value are calculated. A second correction table generating means for generating a second correction table representing a correspondence relationship with a certain correction gradation value for each position;
Correction means for correcting the input image data based on the first correction table after correcting the input image data based on the second correction table;
An image forming apparatus comprising: an image forming unit that forms an image on the recording medium based on the image data corrected by the correcting unit. A high-frequency removing unit that removes a high-frequency component higher than a predetermined spatial frequency from the read image data of the second test image generated by the reading unit reading the second test image;
The color separation means separates the read image data of the second test image that has undergone removal of high-frequency components by the high-frequency removal means into the plurality of single-color read image data. The image forming apparatus described in 1. Informing means for informing that the second test image need not be formed when the difference between the input gradation value and the corrected gradation value is smaller than a threshold value in the first correction table. The image forming apparatus according to claim 1, further comprising an image forming apparatus. The second correction table creating means calculates a total average value of density characteristics respectively represented by the read image data of the first test image and the read image data of a plurality of single colors for each of the input gradation values. 3. The image forming apparatus according to claim 2, wherein the second correction table is generated based on the calculated target gradation value. The image forming apparatus according to claim 1, wherein the predetermined medium is at least one of the photosensitive member, an intermediate transfer member to which the toner image is transferred, and the storage medium. For each of a plurality of single colors, a first test image including a test pattern including a plurality of regions having the same density in the first direction of the recording medium and different densities in a second direction orthogonal to the first direction. And first test image data representing a second test image including the test pattern for a multi-order color composed of at least two of the plurality of single colors. Storage means;
Read image data of a first test image generated by reading the first test image formed on a predetermined medium based on the first test image data stored in the storage unit, and the storage Based on the first test image data stored in the means, a gradation characteristic at each position with the first direction as a reference axis is calculated, and a predetermined input floor is calculated based on the calculated gradation characteristic. First correction table generation means for generating a first correction table that represents a correspondence relationship between a tone value and a correction gradation value that is a correction value of the input gradation value for each position;
Read image data of a second test image generated by reading the second test image formed on a predetermined medium based on the second test image data stored in the storage unit, Color separation means for separating into a plurality of single-color read image data constituting the next color;
Based on the second test image data stored in the storage unit and the plurality of single-color read image data, a gradation characteristic at each position with the first direction as a reference axis is calculated and calculated A second correction table that generates a second correction table that represents a correspondence relationship between a predetermined input gradation value and a correction gradation value that is a correction value of the input gradation value for each position based on the gradation characteristics Correction table generating means;
An image processing apparatus comprising: correction means for correcting and outputting input image data based on the first correction table and the second correction table in the previous period. For each of a plurality of single colors, a first test image including a test pattern including a plurality of regions having the same density in the first direction of the recording medium and different densities in a second direction orthogonal to the first direction. And first test image data representing a second test image including the test pattern for a multi-order color composed of at least two of the plurality of single colors. Storage means;
Read image data of a first test image generated by reading the first test image formed on a predetermined medium based on the first test image data stored in the storage unit, and the storage Based on the first test image data stored in the means, a gradation characteristic at each position with the first direction as a reference axis is calculated, and a predetermined input floor is calculated based on the calculated gradation characteristic. First correction table generation means for generating a first correction table that represents a correspondence relationship between a tone value and a correction gradation value that is a correction value of the input gradation value for each position;
First correction means for correcting second test image data stored in the storage means based on the first correction table;
Read image data of a second test image generated by reading the second test image formed on a predetermined medium based on the second test image data corrected by the correction unit, Color separation means for separating into a plurality of single-color read image data constituting the next color;
Based on the first test image data and the second test image data stored in the storage means, and the generated read image data of the first test image and the plurality of single color read image data. Then, the gradation characteristics at each position with the first direction as a reference axis are calculated, and based on the calculated gradation characteristics, a predetermined input gradation value and a correction level that is a correction value of the input gradation value are calculated. A second correction table generating means for generating a second correction table for each position corresponding to the adjustment value;
And second correction means for correcting the input image data based on the second correction table and then outputting the corrected image data based on the first correction table. Processing equipment.

Images