JP2017200728A - Image processing method, image processing device, image forming device, image forming system, and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image processing method capable of enhancing a reduction effect of a streak-like image failure as compared with a conventional method.SOLUTION: There is provided an image processing method in which calculation processing for calculating correction information based on a result of the measurement of color information on a correction chart output before and after the correction is executed a plurality of times for each of a plurality of colors used for image formation, and image data is corrected based on the calculated correction information, the correction information being associated with a correction value for acquiring a target output value for each combination of a plurality of density values and a plurality of positions in a main scanning direction. Of the calculation processing executed a plurality of times, the correction information is destroyed when unevenness in the main scanning direction is larger than a correction result of the correction chart previous time.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an image processing method for correcting image data for image formation, an image processing apparatus, an image forming apparatus, an image forming system, and a program used therefor.

Conventionally, in order to reduce streak-like image defects that occur in the same direction as the feeding direction of a recording material such as a sheet on which an image has been formed by an image forming apparatus, the density of image data input to the image forming apparatus Image processing methods for correcting values are known.
For example, in Patent Document 1, streaks and unevenness are generated by correcting image data (input gradation value) at each pixel position in the main scanning direction with a correction value (correction gradation value) at each pixel position. The following image processing methods for reducing the above are described.

Specifically, correction information (correction table) in which correction values for obtaining target output values are associated with each combination of a plurality of density values and a plurality of positions in the main scanning direction is as follows. Calculated.
A calculation process for calculating the color information (tone value) of the correction chart (test pattern) output before and after correction is performed a plurality of times (twice) for each of a plurality of colors used for image formation. Seeking.
Then, for each pixel, correction is performed using the calculated correction value for the portion of the pixel whose image quality has improved over the previous correction chart or before correction, and the correction information is not used for the other portions. Has been fixed.
By obtaining correction information in this way, Patent Document 1 discloses that image data is corrected using a correction value calculated (calculated) for a pixel that is determined to improve image quality. It is stated that it can be improved reliably.

In recent years, there has been an increasing demand for increasing the effect of reducing streak-like image defects.
However, the conventional image processing method that corrects correction information so that correction is performed using correction values calculated only for pixel portions with improved image quality may not increase the effect of reducing streak-like image defects. It was.

  In order to solve the above-described problem, the invention described in claim 1 associates correction values for obtaining target output values for each combination of a plurality of density values and a plurality of positions in the main scanning direction. A calculation process for calculating the correction information based on the measurement result of the color information of the correction chart output before and after correction is performed a plurality of times for each color used for image formation, and the image data is corrected based on the calculated correction information. In the image processing method, the correction information of a time in which the unevenness in the main scanning direction is larger than the correction result of the previous correction chart among the calculation processes performed a plurality of times is discarded. .

  According to the present invention, it is possible to provide an image processing method capable of enhancing the effect of reducing streak-like image defects as compared with the prior art.

1 is a schematic configuration diagram of an image forming system according to an embodiment. The flowchart when performing re-correction. The figure which showed an example of the chart for a correction | amendment. The graph which shows an example of the relationship between the density value of a scanner (gamma) image, and the reading luminance value of a scanner (gamma) pattern. The graph which shows an example of the relationship between the read luminance value before re-correction of each of a plurality of positions in the main scanning direction of the test pattern and the read luminance value when correction is performed with the calculated second correction value. The flowchart of a correction result confirmation process. An example of a correction confirmation chart. Explanatory drawing of an example of a correction confirmation application. Explanatory drawing of the main scanning direction profile in each sub-scanning position. Explanatory drawing about an example of the main scanning direction profile before and behind re-correction when correction information is correctly calculated. Explanatory drawing about an example of the main scanning direction profile before and after re-correction when correction information cannot be calculated correctly. Explanatory drawing about the measurement position of profile creation. Explanatory drawing about the profile fluctuation | variation at the time of performing correction repeatedly. It is explanatory drawing about the comparison of correction precision.

Hereinafter, as an image forming system capable of performing an image processing method to which the present invention is applied, an image forming system equipped with an electrophotographic multifunction device (hereinafter referred to as a multifunction device 500) compatible with high-speed printing that can be used in the field of production printers. One embodiment of the system 800 will be described.
FIG. 1 is a schematic configuration diagram of an image forming system 800 according to the present embodiment.
Here, in the following description, an image forming system in which correction values of image data to be formed by the multi-function device 500 are set by a correction application provided in the personal computer 600 based on correction chart information measured by the colorimeter 700. A description will be given by taking 800 as an example. However, the image forming system of the present embodiment is not limited to the image forming system having such a configuration. For example, the scanner unit 300 of the multi-function device 500 is used as a device for measuring a correction chart, and a correction application provided in the control unit of the multi-function device 500 is used to correct image data input from a host device such as a personal computer or the scanner unit 300. It may be configured to set a value.

A multifunction peripheral 500 shown in FIG. 1 is a tandem indirect transfer type color multifunction peripheral. The multi-function device 500 includes a printer unit 100, a paper feed table 200 on which the printer unit 100 is placed, a scanner unit 300 mounted on the printer unit 100, and an automatic document mounted on the scanner unit 300. It is comprised by the conveying apparatus (henceforth ADF) 400 grade | etc.,.
The personal computer 600 includes a desktop personal computer main body 601, a slice pad integrated keyboard 602 as an input device, and a liquid crystal monitor 603, and an application for correcting image data input to the multi-function device 500 is installed. .
A flat head scanner type color measuring device 700 comprising a color measuring device main body 701 and an upper cover 702 as a line color measuring device is connected to a personal computer 600 with a USB cable or the like, and the personal computer 600 is combined with a wired LAN or a USB cable or the like. Connected to the machine 500.
Here, as the personal computer 600 and the color measuring device 700, off-the-shelf products distributed in the market can be used, and thus detailed description of the configuration is omitted.

First, a schematic configuration of the multi-function device 500 will be described with reference to FIG.
The printer unit 100 of the multifunction peripheral 500 shown in FIG. 1 includes an endless belt-like intermediate transfer belt 21 as an intermediate transfer member. The intermediate transfer belt 21 is wound around a driving roller 22, a driven roller 23, and a secondary transfer counter roller 24, which are a plurality of rollers, in an attitude of an inverted triangle as shown in FIG. It is supported. Then, it is rotated (hereinafter referred to as “rotation”) in the clockwise direction indicated by the arrow in FIG.

  Above the intermediate transfer belt 21, there are four image forming units 1C, M, Y, and K for forming C (cyan), M (magenta), Y (yellow), and K (black) toner images. Arranged along the rotational direction of the intermediate transfer belt 21 to constitute the tandem image forming unit 10. This is an image forming unit that forms a toner image on a latent image carrier to be described later.

Each of the image forming units 1C, M, Y, and K includes a photosensitive drum 2C, M, Y, and K as a latent image carrier, a developing unit 3C, M, Y, and K, and a photosensitive member cleaning device 4C and M, respectively. , Y, K.
The photosensitive drums 2C, M, Y, and K are in contact with the intermediate transfer belt 21 at positions facing the primary transfer rollers 25C, M, Y, and K, respectively, and have primary transfer nips for C, M, Y, and K, respectively. While forming, it is driven to rotate clockwise in FIG.

  The developing units 3C, M, Y, and K develop the electrostatic latent images formed on the photosensitive drums 2C, M, Y, and 2K with toners of C, M, Y, and K colors. Further, the photoreceptor cleaning devices 4C, M, Y, and K clean the transfer residual toner adhering to the photoreceptor drums 2C, M, Y, and K after passing through the primary transfer nip.

  An optical writing unit 15 is disposed above the tandem image forming unit 10 in the printer unit 100. The optical writing unit 15 performs an optical writing process by scanning a laser beam on the surface of the photosensitive drums 2C, M, Y, and K that are rotationally driven counterclockwise in FIG. An electrostatic latent image is formed. Prior to the optical writing process, the surfaces of the photoconductive drums 2C, M, Y, and K are uniformly charged by respective charging chargers (charging devices).

  The transfer unit 20 including the intermediate transfer belt 21 has primary transfer rollers 25C, M, Y, and K inside the loop of the intermediate transfer belt 21. These primary transfer rollers 25C, M, Y, and K press the intermediate transfer belt 21 toward the photosensitive drums 2C, M, Y, and K on the back side of the primary transfer nip for each color of C, M, Y, and K. doing.

  A secondary transfer roller 30 as a secondary transfer member is disposed below the intermediate transfer belt 21. The secondary transfer roller 30 is rotationally driven by a drive motor, and is pressed against and brought into contact with the front surface side of the portion of the intermediate transfer belt 21 that is wound around the secondary transfer counter roller 24. The next transfer nip is formed. The sheet S as a recording material is fed into the secondary transfer nip by a positioning roller pair 95 at a predetermined timing. The four color superimposed toner images on the intermediate transfer belt 21 are collectively transferred onto the sheet S at the secondary transfer nip.

  The scanner unit 300 reads image information of a document placed on the contact glass 301 by the reading sensor 302 and sends the read image information to the control unit of the printer unit 100. This control unit controls a light source such as a laser diode in the optical writing unit 15 of the printer unit 100 on the basis of the image information received from the scanner unit 300, and outputs laser writing light for C, M, Y, and K. Then, the photosensitive drums 2C, M, Y, and K are optically scanned. By this optical scanning, an electrostatic latent image is formed on the surface of the photoreceptor drums 2C, M, Y, and K, and the latent image is developed into toner images of C, M, Y, and K colors through a predetermined development process. Is done.

  The paper feed table 200 separates the paper feed cassettes 202 arranged in multiple stages in the paper bank 201, a paper feed roller 203 that feeds out the sheet S as a recording material from the paper feed cassette 202, and the fed-out sheets S separately. A separation roller 205 that leads to the paper path 204, a transport roller pair 206 that transports the sheet S to the paper feed path 99 of the printer unit 100, and the like are provided.

  In addition to the paper feed table 200, manual paper feed is also possible, and the manual feed tray 98 for manual feed and the recording sheets on the manual feed tray 98 are separated one by one toward the manual feed path 97. A separating roller 96 is also provided. The manual paper feed path 97 joins the paper feed path 99 in the printer unit 100. A registration roller pair 95 is disposed near the end of the paper feed path 99. The registration roller pair 95 sandwiches the sheet S conveyed in the sheet feeding path 99 or the manual sheet feeding path 97 between the rollers and then feeds the sheet S toward the secondary transfer nip at a predetermined timing.

When copying a color image by the multi-function device 500, the original is set by setting the original on the original table 401 of the ADF 400 or by opening the ADF 400 and setting and closing the original on the contact glass 301 of the scanner unit 300. Hold down.
When a start button on an operation panel provided as an operation unit is pressed, if the document is set on the ADF 400, the document is conveyed onto the contact glass 301. Thereafter, the scanner unit 300 starts driving, and the first traveling body 303 and the second traveling body 304 start traveling along the document surface.

  The light emitted from the light source of the first traveling body 303 is reflected by the document surface, and the reflected light is turned back and directed toward the second traveling body 304. The folded light is further folded by the mirror of the second traveling body 304 and then enters the reading sensor 302 through the imaging lens 305. As a result, the document content is read by the reading sensor 302 and the signal processing circuit of the scanner unit 300, temporarily stored as image information, and then sequentially sent to the printer unit 100.

  When the printer unit 100 receives the image information from the scanner unit 300, the printer unit 100 feeds a recording sheet having a size corresponding to the image information to the paper feed path 99. Along with this, the driving roller 22 is rotationally driven by the driving motor to rotate the intermediate transfer belt 21 in the direction indicated by the arrow in FIG. At the same time, after the photosensitive drums 2C, M, Y, and K of the image forming units 1C, M, Y, and K of the tandem image forming unit 10 start to rotate in the directions indicated by the arrows, their respective surfaces are uniformly charged. The

  Based on the image data received from the scanner unit 300, optical writing processing is performed by the optical writing unit 15, and electrostatic latent images are formed on the surfaces of the photosensitive drums 2C, M, Y, and K, respectively. These are developed with toner of each color by the developing units 3C, M, Y, and K. The toner images of C, M, Y, and K colors formed on the surfaces of the photosensitive drums 2C, M, Y, and K by these processes are sequentially overlapped at the primary transfer nip for C, M, Y, and K. In addition, primary transfer is performed on the intermediate transfer belt 21 to form a full-color toner image in which four colors are superimposed.

  In the paper feed table 200, one of the paper feed rollers 203 is selectively rotated so as to feed a sheet S having a size corresponding to the document size, and the sheet S is sent out from one of the three paper feed cassettes 202. It is. The sheet S thus fed is separated one by one by the separation roller 205 and introduced into the paper feed path 204, and then conveyed by a plurality of transport roller pairs 206 to the paper feed path 99 in the printer unit 100. It is done.

  When the manual feed tray 98 is used, the paper feed roller 94 of the manual feed tray 98 rotates to feed the sheet S on the tray, and is fed to the manual feed path 97 while being separated by the separation roller 96. Near the end of road 99. In the vicinity of the end of the paper feed path 99, the sheet S stops by abutting the leading edge against the registration roller pair 95.

  Thereafter, when the registration roller pair 95 rotates at a timing that can be synchronized with the full-color toner image on the intermediate transfer belt 21, the sheet S is fed into the secondary transfer nip, and the full-color toner image on the intermediate transfer belt 21. Close contact with. Then, the toner image is collectively transferred onto the sheet S by the action of the secondary transfer electric field by the nip pressure and the secondary transfer bias voltage. The secondary transfer nip is a secondary transfer portion formed by the secondary transfer roller 30 facing the secondary transfer counter roller 24 and the intermediate transfer belt 21.

  The sheet S on which the full-color toner image is secondarily transferred in the secondary transfer portion is sent into the fixing device 71 by the paper transport belt 70. Then, the toner image is fixed on the surface by the pressurization and the heat treatment by the fixing device 71 being sandwiched in the fixing nip between the pressure roller 72 and the fixing belt 73.

The sheet S on which the color image is formed in this way is sent out by the discharge roller pair 74 and stacked on the discharge tray 75 outside the apparatus.
Here, when an image is also formed on the other surface of the sheet S, the sheet S is discharged from the fixing device 71 and then sent to the sheet reversing device 77 by the path switching by the switching claw 76. Then, after being turned upside down, it is returned again to the registration roller pair 95 and sent to the secondary transfer nip to transfer the full color toner image to the other surface, and the toner image is again passed through the fixing device 71. Are fixed on the paper discharge tray 75.

  After passing through the secondary transfer nip, the belt cleaning device 26 is in contact with the surface of the intermediate transfer belt 21 before entering the cyan primary transfer nip where the primary transfer process is the most upstream of the four colors. The belt cleaning device 26 cleans transfer residual toner adhering to the surface of the intermediate transfer belt 21.

The primary transfer rollers 25C, M, Y, and K are constituted by an elastic roller including a metal cored bar and a conductive sponge layer fixed on the surface thereof. The primary transfer rollers 25C, M, Y, and K are shifted about 2.5 [mm] from the axis of the photosensitive drums 2C, M, Y, and K to the downstream side in the belt movement direction. It is arranged so as to occupy a different position. In the multi-function device 500 of this embodiment, a primary transfer bias is applied to such primary transfer rollers 25C, M, Y, and K by constant current control.
Here, instead of the primary transfer rollers 25C, M, Y, and K, a transfer charger, a transfer brush, or the like may be used as the primary transfer member.

The secondary transfer roller 30 of the transfer unit 20 is disposed outside the loop of the intermediate transfer belt 21, and the intermediate transfer belt 21 is sandwiched between the secondary transfer counter roller 24 inside the loop. As a result, a secondary transfer nip where the surface of the intermediate transfer belt 21 and the secondary transfer roller 30 abut is formed.
In this example, the secondary transfer roller 30 is grounded, whereas the secondary transfer bias roller output from the secondary transfer bias power source is applied to the secondary transfer counter roller 24. As a result, a secondary transfer electric field that electrostatically moves negative polarity toner from the secondary transfer counter roller 24 side to the secondary transfer roller 30 side between the secondary transfer counter roller 24 and the secondary transfer roller 30. Is formed.

The secondary transfer bias power source includes a DC power source and an AC power source, and has a configuration for outputting a superimposed bias in which an AC voltage is superimposed on a DC voltage.
Here, it is assumed that the secondary transfer counter roller 24 is grounded and a superimposed bias is applied to the secondary transfer roller 30, and a DC voltage having a positive polarity opposite to the toner is used, and the time average of the superimposed bias is used. May be set to a positive polarity opposite to that of the toner.

  Here, in the image forming apparatus such as the multi-function device 500 according to the present embodiment, the input is performed in order to reduce vertical stripes (image defects) such as stripes generated in the same direction as the feeding direction of the recording material such as the sheet S. Various image processing methods for correcting the density value of image data are conventionally known.

For example, in Patent Document 2, in addition to the gradation characteristics of each primary color when a primary color image is output (printed), a multi-color image in which a plurality of basic constituent colors are superimposed is printed. An image processing method is described in which gradation characteristics of each primary color are obtained and a correction table based on them is created.
However, in the image processing method described in Patent Document 2, a test pattern is created for every combination of primary colors to obtain gradation characteristics of each primary color, and a correction table based on these is created. There is a need. For this reason, there is a problem that the number of test patterns to be imaged and the amount of calculation are enormous.
In addition, the luminance profile in the main scanning direction read from the correction chart may be a profile having a density different from the desired density, and may greatly differ from the luminance profile in the main scanning direction at other sub-scanning positions. In such a case, there arises a problem that density uniformity deteriorates by applying correction.

Patent Document 3 describes a configuration in which in-plane unevenness after correction is visually confirmed, whether or not the unevenness has been eliminated, and whether the correction information is to be discarded or not is described.
However, in the image processing method described in Patent Document 3, since it is visually confirmed, unevenness of Y color cannot be determined, and color unevenness to a mixed color (Green, Red) using Y color when there is unevenness. There was a problem that the impact was great.
Similarly to the image processing method of Patent Document 2, the luminance profile in the main scanning direction read from the correction chart becomes a profile having a density different from the desired density, and the luminance in the main scanning direction at other sub-scanning positions. It can also be very different from the profile. In such a case, there arises a problem that density uniformity deteriorates by applying correction.

In the image processing method disclosed in Patent Document 1, as described above, the calculation is performed by outputting the correction chart after correction using the correction information calculated based on the result of measuring the color information of the output correction chart. The processing is obtained by performing a plurality of times for each of a plurality of colors used for image formation.
Then, for each pixel, correction is performed using the calculated correction value for the portion of the pixel whose image quality has improved over the previous correction chart or before correction, and the correction information is not used for the other portions. Has been fixed.
By making corrections in this way, in Patent Document 1, the image data is corrected using the calculated (calculated) correction value for the pixel that is determined to improve the image quality, so that the image quality is reliably improved. It is stated that it can be done.
However, in the image processing method described in Patent Document 2, for the reasons described above, it is not possible to meet the recent demand for increasing the reduction effect of streak-like image defects that is increasing more than before, that is, streak-like images. There is a possibility that the effect of reducing defects cannot be increased.

Therefore, the inventors have been able to reduce the problems caused by the problems of Patent Documents 2 and 3 and solve the problems of the image processing method described in Patent Document 1, that is, the streak-like shape as compared with the prior art. It was investigated whether an image processing method capable of enhancing the effect of reducing image defects could be provided.
Then, after calculating the correction information, when re-correction is performed, the color information at a plurality of locations in the main scanning direction is measured, and the unevenness in the main scanning direction is greater after correction from the profile before and after correction. In this case, an image processing method for discarding the correction information was found.
In this way, among the calculation processes for calculating the correction information performed a plurality of times, the correction information at the time when the unevenness in the main scanning direction is larger than the previous correction result of the correction chart is discarded, so that Also, the effect of reducing streak-like image defects can be enhanced.
Further, after correcting the image, the color information at a plurality of locations in the main scanning direction is measured, and if the unevenness in the main scanning direction is larger after correction from the profiles before and after correction, the correction information is discarded. As a result, it is possible to prevent the deterioration of density uniformity.

Here, the first correction is based on the image processing apparatus of Japanese Patent Application No. 2015-023646 (hereinafter referred to as the prior application) filed by the applicant, as it can solve the problems of Patent Document 2. That is, the image processing method of the image processing apparatus that can correct the density value of the input image data with a simpler configuration described in the prior application is adopted.
The image processing method relating to the correction of the prior application is characterized by the following points.
A correction value for obtaining a target output value is associated with each combination of a plurality of density values of image data corresponding to any one of a plurality of colors and a plurality of positions in the main scanning direction of the image data. The corrected information is stored for each of a plurality of colors.
When the pixel in the input image data indicating the image data includes two or more colors, the correction value corresponding to the combination of the color density value and the position of the pixel in the main scanning direction is determined for each of the two or more colors. In other words, the color density value is corrected using a smaller value.

When two or more colors are printed in an overlapping manner, a value obtained by multiplying a correction value included in a correction table for eliminating an image defect that occurs when printing is performed with only one color by a coefficient (correction coefficient) of 1 or less. By using it, it can correct | amend appropriately. By correcting in this way, there is no need to create a test pattern and calculate the gradation characteristics of each color for every combination of colors, as in Patent Document 2, so the input can be made with a simpler configuration. The density value of the image data (original data) to be corrected can be corrected.
Then, after executing the image processing method (correction method) of the prior application, the correction accuracy of the prior application can be improved by performing the image processing method (recorrection) of the image forming system 800 of the present embodiment.

Next, a density value correction method (re-correction method) of input image data in the image forming system 800 of this embodiment will be described.
The method for correcting the density value of image data in the image forming system 800 of the present embodiment is characterized by the following points.
After correcting the image data, when re-correction is performed to improve the correction accuracy, the color information at multiple locations in the main scanning direction is measured before and after the re-correction. If the unevenness in the main scanning direction after recorrection is large, the correction information is discarded.
For this reason, in the following description, a correction method for performing re-correction after correcting image data once will be described.

Hereinafter, each step of the correction method when performing re-correction performed in the image forming system 800 of the present embodiment will be described with reference to FIG.
FIG. 2 is a flowchart when recorrection according to the present embodiment is performed.

1. Outputting the correction chart after correction When the correction is started after the image data is corrected, the following correction chart is first output (printed). The image data of the correction chart used to calculate the first correction information A when the previous correction is applied is output from the multi-function device 500 in a state where the image data is corrected by the first correction information A calculated at the previous correction. (Print) (S101).
Here, the correction information is a target output value for each combination of a plurality of density values of image data corresponding to any one of a plurality of colors and a plurality of positions in the main scanning direction of the image data. The first correction value to be obtained is associated and stored as a correction table. The first correction information A when applying the previous correction specifically indicates a correction table including (including) the first correction value used when applying the previous correction. And stored in the personal computer 600.

As the correction chart, for example, a correction chart (calibration chart) as shown in FIG. 3 can be used.
FIG. 3 is a diagram showing an example of a correction chart used in the present embodiment.
In the description of the correction chart shown in FIG. 3, the test pattern and the scanner γ pattern included in the correction chart will be described focusing on C among C, M, Y, and K. The same applies to the two colors (M, Y, K).

In the example illustrated in FIG. 3, the plurality of test patterns corresponding to C include a plurality of density values (10 [%], 20 [%]) for every 10 [%] of image data (C color plate) corresponding to C. ,..., 90 [%], 100 [%]) and a plurality of test patterns (10 in this example) corresponding to one to one. In other words, in the example shown in FIG. 3, the plurality of test pattern images that are the basis of the plurality of test patterns corresponding to C correspond one-to-one with the plurality of density values for every 10% of the C color plate. doing.
For example, a test pattern image corresponding to a density value of C color plate: 10 [%] has a density value set to 10 [%] over the entire main scanning direction. The same applies to test pattern images corresponding to other density values as described above.

In the example shown in FIG. 3, the density value of the scanner γ image that is the source of the scanner γ pattern corresponding to C increases as the position in the main scanning direction progresses from left to right in FIG. 29 steps). The intervals are, for example, in increments of 3 [%] from the first 0 [%] patch to the 13th patch and from the 14th patch to the 29th patch as it advances from left to right. Can be set to increase (change in 29 steps).
That is, the scanner γ image that is the source of the scanner γ pattern corresponding to C has different density values of the C color plates at a plurality of positions (29 in this example) in the main scanning direction.
However, the arrangement of the patch in the above example is merely an example, and the patch from 0 [%] to 100 [%] may be arranged so as to change in predetermined stages.

2. Recorrection information for performing recorrection by measuring the correction chart after correction is calculated. Next, recorrection information for performing recorrection by measuring the output correction chart after correction is calculated (S102). ).
Here, the recorrection information for performing the recorrection to be calculated is the first correction information A created and applied at the time of the previous correction, and the second correction information calculated from the corrected correction chart. This is the average of B. The average here is the average of the first correction value at the position corresponding to each of the two correction tables and the second correction value calculated from the corrected correction chart.

First, the corrected correction chart output from the multi-function device 500 is placed on the contact glass of the color measuring device main body 701 of the color measuring device 700 shown in FIG. 1, and the upper cover 702 is closed. Operate to measure.
In this measurement, for each of four colors C, M, Y, and K, the 29-stage density value included in the scanner γ image corresponding to each color and the reading luminance of the scanner γ pattern corresponding to each color are measured ( read).

In the application of the personal computer 600, the relationship representing the relationship between the density value of the image data corresponding to each color and the read luminance value of the image obtained by forming the image data corresponding to each color on the sheet S from each measurement result. An expression (second relational expression of the prior application) is calculated.
In the example using the correction chart shown in FIG. 3, the density value of the scanner γ image and the reading luminance value of the scanner γ pattern are expressed by 8-bit values (0 to 255), and the density value of the scanner γ image is high. The higher the value is, the lower the reading luminance value at the corresponding position.
This relationship is illustrated in FIG.
FIG. 4 is a graph showing an example of the relationship between the density value of the scanner γ image corresponding to C and the reading luminance value of the scanner γ pattern corresponding to C.

In the example shown in FIG. 4, the application of the personal computer 600 specifies the read luminance value at the corresponding position in the scanner γ pattern for each of 29 levels of density values included in the scanner γ image corresponding to C. After the specification, the relational expression representing the relationship between the density value of the C color plate and the read luminance value of the image formed with the C color plate on the sheet S is calculated using a least square method or the like. .
Here, for example, the above relational expression can be expressed by a quadratic expression, but is not limited thereto, and may be, for example, a form represented by a primary expression or a form represented by a cubic expression. There may be.

The application of the personal computer 600 uses the above relational expression corresponding to each color for each of the four colors C, M, Y, and K, and uses each of a plurality of positions in the main scanning direction of a plurality of test patterns corresponding to each color. A second correction value for correcting the reading luminance value is calculated.
In the present embodiment, the application of the personal computer 600 reads the reading luminance at each of a plurality of positions in the main scanning direction of the test pattern corresponding to the specific density value according to the slope of the relational expression corresponding to the specific density value. A second correction value for correcting the value is calculated.
For example, taking C as an example, if the slope of the relational expression corresponding to the density value of C color plate: 30 [%] is different from a predetermined reference value, the application of the personal computer 600 is: The following second correction value is calculated. Density value of C color plate: main scan of test pattern corresponding to density value 30 [%] of C color plate so that the slope of the relational expression corresponding to 30 [%] becomes a predetermined reference value. This is a second correction value for correcting the reading luminance value at each of a plurality of positions in the direction.

More specifically, for example, when the gradient of the above relational expression corresponding to the density value of the C color plate: 30 [%] is density: 0 [%], the luminance value is 255 and the density is 100 [%]. It is assumed that −255 indicating a slope of a straight line having a luminance value of 0 at the time is a predetermined reference value.
When the slope of the reference value and the relational expression are different, the application of the personal computer 600 calculates the second correction value as follows. Main scanning of the test pattern corresponding to the density value 30 [%] of the C color plate so that the slope of the relational expression corresponding to the density value 30 [%] of the C color plate becomes the reference value, that is, −255. This is a second correction value for correcting the read luminance value at each of a plurality of positions in the direction.

Here, referring to FIG. 5, the read luminance value before re-correction at each of a plurality of positions in the main scanning direction of the test pattern corresponding to the density value of the C color plate: 30 [%] and the calculated first value are calculated. An example of the relationship with the read luminance value when correction is performed with the second correction value is shown in FIG.
FIG. 5 shows the read luminance value before re-correction at each of a plurality of positions in the main scanning direction of the test pattern and the calculated second correction value corresponding to the density value of the C color plate: 30 [%]. 6 is a graph illustrating an example of a relationship with a read luminance value when correction is performed according to FIG. In this graph, the position in the main scanning direction is shown in pixel units (pix).

In the example shown in FIG. 5, at each position in the main scanning direction of the test pattern, the read luminance value when corrected with the second correction value is the luminance centroid value, that is, the target output, rather than the read luminance value before re-correction. The value is approaching. However, due to various factors that will be described in detail later, as shown in the example of FIG. 5, when the reading luminance value corrected with the second correction value is closer to the target output value than the reading luminance value before re-correction. Is not limited.
For this reason, in this embodiment, as will be described later, the first correction information A created at the previous correction and stored in the personal computer 600 and the second correction information B calculated from the corrected correction chart are used. On average, re-correction information for re-correction is calculated.

Then, the application of the personal computer 600 sets the second correction value for setting the read luminance value after recorrection as a target output value, for example, the centroid value of the read luminance value at each of a plurality of positions in the main scanning direction. Calculation is performed for each of a plurality of positions in the scanning direction. That is, the application of the personal computer 600 calculates a second correction value for correcting the density value of the input image data for each of a plurality of positions in the main scanning direction in order to reduce image defects such as vertical stripes.
More specifically, the application of the personal computer 600 uses the read luminance value after re-correction as a target output value for each of a plurality of test patterns corresponding to each color for each of four colors C, M, Y, and K. A second correction value is calculated for each of a plurality of positions in the main scanning direction.
In this way, the application of the personal computer 600 determines, for each of four colors C, M, Y, and K, a plurality of density values of image data corresponding to each color and a plurality of positions in the main scanning direction of the image data. For each combination, second correction information B in which a second correction value for obtaining a target output value is associated can be created.

In this example, a plurality of density values of this color corresponding to a plurality of test patterns corresponding to one color among C, M, Y, and K are 10 [%], 20 [ %], 30 [%], 40 [%], 50 [%], 60 [%], 70 [%], 80 [%], 90 [%], and 100 [%]. For this reason, the application of the personal computer 600 can calculate correction values corresponding to other density values for each main scanning position by performing interpolation processing such as linear interpolation.
The four pieces of second correction information B corresponding to the four colors C, M, Y, and K generated on the one-to-one basis are images such as vertical stripes generated when printing with one color. It can be considered as information for eliminating the defect.

As described above, the application of the personal computer 600 includes the first correction information A created at the previous correction and stored in the personal computer 600, and the second correction information B calculated from the corrected correction chart. Are averaged to calculate recorrection information for recorrection.
Specifically, the first correction value included in the correction table of the first correction information A stored in the personal computer 600 and the second correction included in the correction table of the second correction information B calculated this time. A correction table for re-correction is created by averaging the values at the corresponding positions.

3. Image Correction Using Recorrection Information Image data of the same correction chart (for example, FIG. 3) output in the above “1” is corrected using the calculated recorrection information (S103).
Specifically, the application of the personal computer 600 performs correction as follows. Using the correction value in the correction information corresponding to the color included in the target pixel, that is, the correction value in the re-correction information corresponding to the combination of the color density value in the target pixel and the position in the main scanning direction, Correct the density value.
Here, in the correction method of the prior application that is performed in the first correction, the flow of processing branches between the case of the secondary color or more and the case of the primary color. However, in the re-correction method of this embodiment, the secondary color Even in the above, the correction method of the previous application is different in that the previous correction information is used as it is.

4). Recorrected correction chart is output A correction chart corrected again using the recorrection information is output (S104).
Here, the reason why the correction chart re-corrected using the re-correction information is output again is necessary to determine whether or not the state after the re-correction is sufficiently corrected.

5. Measure the images before and after re-correction, and create a profile in the main scanning direction. Correction chart after correction (before re-correction) output in "1" and correction chart after re-correction output in "4" Are measured by the colorimeter 700, and a profile in the main scanning direction for each color and each density is created (S105).
Here, the measurement location of each correction chart in the colorimeter 700 will be described later.

6). Compare before and after re-correction to determine whether the color difference is smaller after re-correction From the profile before and after re-correction created in “5” above, compare the unevenness of each color and density, and re-correct However, it is determined whether or not the color difference is small (S106).
What is compared here is, for example, the standard deviation of the color difference in the entire main scanning direction with reference to colorimetric data at the center position in the main scanning direction for each color and density. What is used as the color difference is ΔE that is generally used by using L * a * b * obtained by the colorimeter.

The color information at the reference position is L * 0, a * 0, b * 0, and the color information obtained at other positions is L * n, a * n, b * n (n is the number of measurement points, for example, n = 1 to 15), ΔE at each main scanning position is expressed by the following Expression 1.
ΔEn = ((L * 0−L * n) ² + (a * 0−a * n) ² + (b * 0−b * n) ² ) ^1/2 (Formula 1)
The average value of the color difference ΔE expressed by the equation 1 is expressed by the following equation 2.
ΔEm = 1 / n * Σ (ΔEn) (Formula 2)
The standard deviation is expressed by the following formula 3.
σΔE = (1 / n * Σ (ΔEn−ΔEm)) ^1/2 (Formula 3)

The value of this standard deviation is obtained before and after re-correction and compared.
Assuming that the value of the standard deviation before re-correction is σΔE and the value of the standard deviation after re-correction is σΔE ′, when the value after re-correction is smaller, that is, when the following Expression 4 is satisfied (Yes in S106): Then, the correction information stored in the personal computer 600 is updated (applied) to the calculated re-correction information (S107).
σΔE> σΔE ′ (Formula 4)
On the other hand, when the value after re-correction does not become smaller than the value before re-correction, that is, when it is determined that the following Expression 5 is satisfied (No in S106), the re-correction information created (used) at that time is used. Discard (S108).
σΔE ≦ σΔE ′ (Formula 5)

  Here, what is used for the comparison is not limited to the standard deviation of the color difference, and for example, the sum of the color differences may be used. Further, it is possible to make a comparison using only the lightness L * for the C, M, and K colors instead of the color difference. The Y color cannot be compared with L * because the difference in brightness is small, but it can be compared with b *.

Also, the maximum color difference at each sub-scanning position can be used as a value used for comparison.
In this case, two points having the maximum color difference are calculated from the color information at each measurement point in the main scanning direction at a certain sub-scanning position. This is because if a fixed reference point (for example, the center position of the chart) is provided, the color difference is represented by an absolute value, so that a profile in a state different from the color difference that the user really wants to see may be created.

For example, when the color difference is calculated using color information measured at three points A, B, and C, if A is used as a reference, the AB color difference is 1.5, and the AC color difference is 1.5. The maximum color difference is determined as 1.5.
However, a case where the color difference of BC is 3.0 is considered, and the maximum color difference in that case is 3.0. This is very different from the actual appearance.
Since correct determination processing cannot be performed in such a case, it is important to obtain two points that give the maximum color difference at a certain sub-scanning position. This is obtained by repeatedly calculating the color difference using a combination of all two measured points.

Here, as a great merit of comparison using the colorimeter 700, it is possible to cope with cases where confirmation cannot be made visually (mainly yellow color). Even if it is a non-uniformity level that cannot be visually confirmed or sufficiently satisfied in a single color, it may be noticeable when it becomes a secondary color. This is particularly noticeable with colors using Yellow.
Although the unevenness can be confirmed by outputting the secondary color, it is difficult to determine which color should be corrected in that case. The present embodiment exhibits an excellent effect in this respect.
That is, as described above, by using a colorimeter such as the colorimeter 700 for measuring color information, and using the color difference in the main scanning direction for unevenness determination, the Y color is difficult to visually determine. Even if it exists, it becomes possible to determine appropriately the magnitude of unevenness by the measurement result of the colorimeter.

This measuring method is not limited to the colorimeter 700, and for example, a scanner may be used. In that case, comparison can be made using RGB luminance values. For example, two points having the largest difference in the main scanning direction in the R value, the C value is the G value, and the Y color is the B value. Alternatively, the standard deviation in the main scanning direction is used. In addition, as described above, the scanner unit 300 of the multi-function device 500 is used, and the correction value of the image data input from the host device such as a personal computer or the scanner unit 300 is set by the correction application provided in the control unit of the multi-function device 500. It may be a configuration.
With this configuration, an image forming apparatus or the like provided with a scanner does not need to newly provide a colorimeter or the like as a measuring unit, and can contribute to cost reduction.

  As another comparison method, a colorimeter is used for measurement, and color density, for example, status A used in the printing industry is used to determine (determine) the difference between the maximum density and the minimum density in the main scanning direction. It is also possible to do. By determining in this way, the size of the unevenness can be determined by a simple method.

7). Judgment whether or not to re-correction In “6” above, the state when the correction information is updated to the re-correction information for that time or the re-correction information for that time is discarded can be sufficiently corrected for the user. If the density uniformity is good and it is determined that further recorrection is not necessary (No in S109), the recorrection flow is terminated.
On the other hand, the state when the correction information is updated to the recorrection information of the time or the recorrection information of the time is discarded is not sufficient for the user, and the uniformity is further improved. When re-correction is applied to (Yes in S109), the process returns to step "2" again.
As a determination criterion here, the determination level can be changed according to the level required by the user. For example, if the maximum color difference ΔE is 2.5 or less, the process can be terminated when the level is reached.

If it is determined in the above “7” that re-correction is to be performed, the corrected correction chart used for the next re-correction has been output, and the corrected correction chart in the main scanning direction is also output. Since it has already been created, in the example shown in FIG. In the above “5”, only the image after re-correction is measured and only the profile in the main scanning direction after correction is created, and the previously created profile in the main scanning direction is used. it can.
However, the flow when performing recorrection according to the present embodiment is not limited to such a configuration, and may be returned to “1” when it is determined that recorrection is to be performed. However, again, the correction chart output after correction and the image before correction are measured to create a profile in the main scanning direction, which increases the workload on the user.

As described above, in the image processing method of the image forming system according to the present embodiment, the correction information in which the correction value for obtaining the target output value is associated with each combination of the plurality of density values and the plurality of positions in the main scanning direction. Find it as follows.
A calculation process for calculating the color information of the correction chart output before and after correction is performed a plurality of times for each color used for image formation, and the image data is corrected based on the calculated correction information. .
Then, the correction information of the times when the unevenness in the main scanning direction is larger than the previous correction result of the correction chart among the calculation processes performed a plurality of times is discarded.

By configuring the recorrection method (image processing method) in this way, the following effects can be achieved.
In an electrophotographic image forming apparatus, every time a correction chart is output due to factors such as photoconductor blur, mechanical vibration during conveyance of the recording material, and shock jitter when the recording material enters the fixing roller. In addition, a density profile different from the desired density may be measured.
In the conventional image processing method that corrects correction information so that correction is performed using correction values calculated only for pixel portions with improved image quality, correction is performed with an inappropriate correction value due to any of the factors described above. Even with a pixel, a density profile close to a desired density may be measured.
When such a profile is measured, an inappropriate correction value is held, and it becomes difficult to converge the correction value of the pixel to an appropriate value. Then, the correction information is set (determined) without converging the correction value of the pixel holding the inappropriate correction value to an appropriate value, and the effect of reducing streak-like image defects cannot be enhanced. .

On the other hand, in the configuration in which the correction information at the time when the unevenness in the main scanning direction is larger than the previous time is discarded, for example, a density profile close to a desired density is measured with pixels corrected with an inappropriate correction value. However, the correction information for the time when the unevenness in the main scanning direction is large is not retained.
Therefore, it is possible to suppress the occurrence of a pixel in which an inappropriate correction value is held due to any of the factors described above, and correction information can be obtained without converging the correction value of a pixel in which an inappropriate correction value is held to an appropriate value. By avoiding setting, it is possible to enhance the effect of reducing streak-like image defects.
Therefore, it is possible to provide an image processing method capable of enhancing the effect of reducing streak-like image defects as compared with the prior art.

  Further, after correcting the image, the color information at a plurality of locations in the main scanning direction is measured, and if the unevenness in the main scanning direction is larger after correction from the profiles before and after correction, the correction information is discarded. As a result, it is possible to prevent the deterioration of density uniformity.

Next, as an example of a correction result confirmation method (judgment means) after re-correction, which can be performed to further improve the correction accuracy in the image forming system of the present embodiment, the user can confirm the desired result. A correction result confirmation process after outputting a chart and measuring will be described.
Here, the correction result confirmation processing described below will be described as being executed and provided by the correction confirmation application of the personal computer 600.
First, the flow of the correction result confirmation process will be described with reference to FIG.
FIG. 6 is a flowchart of the correction result confirmation process.

1. Selection of Check Chart The user selects a correction check chart to be output and measured as a correction check chart using the correction check application of the personal computer 600 (S201).
Here, as the correction confirmation chart, for example, the density 0 [%], 10 [%],..., 100 [%] on the entire surface of A3 for only a specific color desired by the user as shown in FIG. The correction confirmation chart in which patches extending throughout the main scanning direction are arranged.
FIG. 7 is an example of a correction confirmation chart.

  The correction check chart illustrated in FIG. 7 has the same density and color of the arranged test pattern (patch) as the correction chart used when generating correction information. In this correction check chart, the area of each patch in the sub-scanning direction is large, and the range in which density unevenness can be detected is wide. Accordingly, for example, colorimetric data at a plurality of sub-scanning positions can be obtained at the same main scanning position, so that the result can be confirmed with high accuracy. In this case, an average value at each sub-scanning position is used as data of the main scanning position of the patch.

2. Next, the correction check chart before and after re-correction is output, measured by the colorimeter 700, and the measurement data is input to the correction check application of the personal computer 600 (S202).

3. Determination of whether correction conditions are satisfied Next, it is determined which density uniformity before and after re-correction is better (S203).
As described above, as described above, before and after re-correction, the standard deviation of the color difference is obtained and compared, and if the standard deviation after re-correction is smaller than the standard deviation before re-correction, the next step ( The process proceeds to S204) (Yes in S203). On the other hand, before and after re-correction, the standard deviation of the color difference is obtained and compared, and if the standard deviation after re-correction is not smaller than the standard deviation before re-correction (No in S203), the re-correction information for that time Is discarded (S205).

4). Determination of whether or not the achievement condition is satisfied Here, it is determined whether or not the achievement condition set in advance can be satisfied (S204).
First, as the achievement condition, for example, the maximum color difference ΔE in the main scanning direction can be selected to be 1.5 or less, 2.0 or less, or 2.5 or less, and the achievement condition to be used is set. .
Of course, as other achievement conditions, L * and b *, the standard deviation of the color difference ΔE in the main scanning direction, the sum, and the like may be selected.
If the set achievement condition is satisfied (Yes in S204), “correction complete” is displayed on the result display dialog (liquid crystal monitor 603 of the personal computer 600) of the correction confirmation application (S206), and the process ends.
On the other hand, if the set achievement condition is not satisfied (No in S204), “Needs further correction” is displayed in the application result display dialog (S207), and the process is terminated.

  The flow of an example of the correction result confirmation method described above has been described for the case where the correction confirmation application of the personal computer 600 is used (used). However, the present invention is not limited to such a configuration, and of course, the user makes his / her own judgment. It is also possible.

Here, the appearance (interface screen) of the correction confirmation application used when confirming the correction result and an example of the operation will be described with reference to FIG.
FIG. 8 is an external view explanatory diagram of an example of the correction confirmation application.
On the screen of the liquid crystal monitor 603 of the personal computer 600, an input / output interface screen 630 of the correction confirmation application as shown in FIG. 8 is displayed.
In the interface screen 630, the correction confirmation chart selection unit 631 and the achievement condition input unit 634 are arranged in the order from the top in the upper left part in FIG. 8, and in the upper right part in FIG. The data input unit 632 and the re-corrected data input unit 633 are arranged in this order.
In the lower part of the interface screen 630, a result determination execution button 635 and a result display dialog 636 are arranged in this order from the top in the substantially horizontal center.

The correction confirmation chart selection unit 631 has a drop-down list format, and selects the color and the like of the correction confirmation chart.
The achievement condition input unit 634 is also in the form of a drop-down list and selects an achievement condition.
The pre-re-correction data input unit 632 is an input button / display unit that executes output of the correction confirmation chart before re-correction, executes input (measurement), and displays after input is executed. , “Measurement”, and the reduced schematic diagram of the measured correction confirmation chart before re-correction.
The post-recorrection data input unit 633 is an input button / display unit that executes output of a correction confirmation chart after re-correction, executes input (measurement), and displays after input is executed. , “Measurement”, and a reduced schematic diagram of the measured correction confirmation chart after re-correction.

The result determination execution button 635 is selected and input by the correction confirmation chart selection unit 631 and the achievement condition input unit 634, and before and after recorrection using the data input unit 632 before recorrection and the data input unit 633 after recorrection. When pressed (clicked) after the correction check chart is measured, the correction result check process described above is executed.
The result display dialog 636 displays either “correction completed” or “needs further correction”, which is the correction confirmation result of the correction result confirmation process described above.
As described above, the image processing method of the present embodiment outputs a correction confirmation chart for confirming the effect when the obtained correction information is applied, and performs recorrection to determine whether further correction is necessary. A correction result confirmation method using a correction confirmation application of the personal computer 600 after being performed is provided.
As a result, the correction result after re-correction (correction) or the like can be confirmed, and the correction accuracy can be further improved.

Next, it will be described whether the density uniformity after recorrection is deteriorated by recorrection depending on the case.
The information used for calculating the correction information in the present embodiment described above is unevenness in the main scanning direction at a certain sub-scanning position. However, in an electrophotographic image forming apparatus, the density differs from a desired density due to photoconductor blur, mechanical vibration during conveyance of the sheet material, shock jitter caused by paper entering the fixing roller, and the like. Lines may occur.
It has been confirmed through experiments that if the area is measured as information for creating correction information, it cannot be corrected to the correct target density, and the uniformity deteriorates.

Here, a specific example when the uniformity deteriorates will be described with reference to FIG.
FIG. 9 is an explanatory diagram of a main scanning direction profile at each sub-scanning position.
The middle profile shown in FIG. 9 is different in shape from the other two profiles. If correction information is created by measuring such an area, correct correction information cannot be obtained.
For example, horizontal bands due to the photoreceptor period often occur in electrophotography. This may occur at a correction target position on the correction chart because the generation position on the sheet S changes.

Such a region usually occurs as a thin line, and for example, when a uniform image is output to the entire region in the A3 plane, it can be clearly seen.
However, each patch (patch extending in the main scanning direction) of the correction chart shown in FIG. 3 used in this embodiment is thin and cannot be judged well visually. It is difficult to exclude it as a data exclusion.
In addition, when trying to create a correction chart that takes this influence into account, the number of charts required for correction at one time is greatly increased because the photosensitive member and roller cycle of a production printer, which generally forms images at high speed, is large. End up. For this reason, it is necessary to output and measure many sheets, which increases the load on the user.

Next, the profile before and after correction when correction information is correctly calculated using data obtained by repeating recorrection (correction) and measuring a plurality of correction charts will be described with reference to FIG.
FIG. 10 is an explanatory diagram illustrating an example of a main scanning direction profile before and after re-correction when correction information is correctly calculated.
FIG. 10 shows the color difference at each position when one of the two points giving the maximum color difference with respect to the main scanning direction is used as a reference, and after the fourth correction, that is, the third time. After re-correction, the maximum color difference is sufficiently smaller than the first time. In such a case, the correction information is applied as it is because the correction (re-correction) at that time is successful.

On the other hand, a profile example before and after correction when correction information cannot be calculated correctly, that is, when a line having a density different from a desired density is present in the correction information generation area will be described with reference to FIG.
FIG. 11 is an explanatory diagram illustrating an example of a main scanning direction profile before and after re-correction when correction information cannot be calculated correctly.
FIG. 11 shows the color difference at each position when one of the two points giving the maximum color difference with respect to the main scanning direction is the same as in FIG. 10, and after the fifth correction, That is, after the fourth recorrection, the maximum color difference is larger than the previous time (the third recorrection).
In such a case, since correction (recorrection) is not successful, the correction information created at that time is discarded.

Next, a measurement example of data necessary for creating a profile used for determining whether correction information created when re-correction is correct will be described with reference to the drawings.
FIG. 12 is an explanatory diagram of a measurement position for profile creation.

When creating a profile to be used for determining whether correction information is correct, as shown in FIG. 12, for example, a region of density 70 [%] in the correction chart before and after correction and the correction confirmation chart are arranged in the main scanning direction. 17 points are measured at intervals of 15 mm.
Here, in the example shown in FIG. 12, a part of the correction chart is enlarged, and at least seven measurement points are necessary, but there is no problem even if the number is increased.
In the image forming system 800 of the present embodiment, as described above, each point is measured by the flat head scanner type colorimeter 700 to obtain L * a * b *. However, the measurement means is not limited to this. For example, L * a * b * may be obtained by measuring each point with a hand-held colorimeter generally used for colorimetry.
Using the data obtained in this way, profiles of each color and density are created and compared by the method described above.

Next, a profile in the main scanning direction when correction (recorrection) is repeatedly performed will be described with reference to the drawings.
FIG. 13 is an explanatory diagram of profile fluctuations when repeated correction is performed.

In the correction method (re-correction method) of the present embodiment, since the area used for creating the correction table is narrow, it is necessary to perform correction a plurality of times when more accurate correction is required.
This is because the above-described electrophotographic image forming apparatus creates correction information from data obtained from a plurality of locations rather than creating correction information for the entire area from information at a certain point due to the influence of various density fluctuations. This is because the uniformity after correction is improved.

Here, the correction accuracy improves by increasing the number of corrections (the number of re-corrections), but if you use a region that differs greatly from other profiles for creating correction information, it will be worsened. The same as described above.
It has been confirmed that once an average value containing such data is used, the final accuracy when it is repeatedly corrected is worse than when an average value not included is used.
In addition, more corrections are required to restore the original accuracy, increasing the load on the user. Therefore, it is important to exclude data that deteriorates uniformity.

Next, when the correction is performed a plurality of times, the correction between the conventional method in which the average value of the correction value obtained last time and the newly obtained correction value is the current correction value, and the method of the present embodiment described above are corrected. A difference in accuracy, that is, an example of the effect of the correction method of the present embodiment will be described with reference to the drawings.
FIG. 14 is an explanatory diagram for comparison of correction accuracy, and compares the maximum ΔE in the main scanning direction after the correction is performed six times in total.

In this example, the corrected correction chart (correction LUT) measured at the second and fourth correction times happens to have horizontal stripes.
As a result, ΔE deteriorated in the conventional method in which the average value of the correction value obtained last time and the newly obtained correction value indicated by a broken line in FIG. 14 is the current correction value.
On the other hand, in the method of the present embodiment indicated by a broken line in FIG. 14, the result obtained from the correction chart after correction with horizontal stripes, that is, the correction information obtained from the correction chart after correction with horizontal stripes is obtained. Is not reflected (correction information is discarded), and ΔE is not deteriorated.

More specifically, when the measurement values are used as they are in the conventional case, the final color difference is 2.2 in the method of the present embodiment and 3.1 in the conventional method, and ΔE is deteriorated in the conventional method. did.
Since it is noticeable that the maximum color difference is 3.0 or more in the main scanning direction, further correction (recorrection) is necessary. By making the determination, the correction accuracy can be improved efficiently.
In the use of the production printer field such as the image forming system 800 of the present embodiment, this difference is very large because there are many users who require accuracy with a maximum color difference of 3.0 or less.
For this reason, it is possible to efficiently improve the correction accuracy by configuring the process of repeating the re-correction (correction) when the maximum color difference in the main scanning direction is smaller than 3.0. .

  Although the present embodiment has been described with reference to the drawings, the specific configuration is not limited to the configuration of the image forming system 800 including the correction method (recorrection method) of the present embodiment described above. The design may be changed without departing from the scope of the invention.

What was demonstrated above is an example, and there exists an effect peculiar for every following aspect.
(Aspect A)
For each combination of a plurality of density values and a plurality of positions in the main scanning direction, correction information in which correction values for obtaining a target output value are associated is measured, and color information of a correction chart output before and after correction is measured. Image processing for calculating the first correction information A, the second correction information B and the like based on the result a plurality of times for each color used for image formation, and correcting the image data based on the calculated correction information A method is characterized in that, among the calculation processes performed a plurality of times, the correction information of the times when the unevenness in the main scanning direction is larger than the previous correction result of the correction chart is discarded.

According to this, as described in the present embodiment, the following effects can be achieved.
In an electrophotographic image forming apparatus, every time a correction chart is output due to factors such as photoconductor blur, mechanical vibration during conveyance of the recording material, and shock jitter when the recording material enters the fixing roller. In addition, a density profile different from the desired density may be measured.
In the conventional image processing method that corrects correction information so that correction is performed using correction values calculated only for pixel portions with improved image quality, correction is performed with an inappropriate correction value due to any of the factors described above. Even with a pixel, a density profile close to a desired density may be measured.
When such a profile is measured, an inappropriate correction value is held, and it becomes difficult to converge the correction value of the pixel to an appropriate value. Then, the correction information is set (determined) without converging the correction value of the pixel holding the inappropriate correction value to an appropriate value, and the effect of reducing streak-like image defects cannot be enhanced. .

On the other hand, in the configuration in which the correction information at the time when the unevenness in the main scanning direction is larger than the previous time is discarded, for example, a density profile close to a desired density is measured with pixels corrected with an inappropriate correction value. However, the correction information for the time when the unevenness in the main scanning direction is large is not retained.
Therefore, it is possible to suppress the occurrence of a pixel in which an inappropriate correction value is held due to any of the factors described above, and correction information can be obtained without converging the correction value of a pixel in which an inappropriate correction value is held to an appropriate value. By avoiding setting, it is possible to enhance the effect of reducing streak-like image defects.
Therefore, it is possible to provide an image processing method capable of enhancing the effect of reducing streak-like image defects as compared with the prior art.

(Aspect B)
In (Aspect A), the correction confirmation chart for confirming the effect when the obtained correction information is applied is output, and the personal computer 600 after the re-correction for determining whether further correction is necessary is performed. It is characterized by comprising determination means such as a correction result confirmation method using a correction confirmation application.
According to this, as described in the present embodiment, it is possible to check the correction result after performing re-correction (correction) or the like, and it is possible to further improve the correction accuracy.

(Aspect C)
In (Aspect A) or (Aspect B), a colorimeter such as a colorimeter 700 is used for measuring the color information, and a color difference in the main scanning direction is used for determining unevenness.
According to this, as described in the present embodiment, it is possible to appropriately determine the size of the unevenness based on the measurement result of the colorimeter even for the Y color that is difficult to visually determine.

(Aspect D)
In any one of (Aspect A) to (Aspect C), the process is terminated when the maximum color difference in the main scanning direction becomes smaller than 3.0.
According to this, as described in the present embodiment, the correction accuracy can be increased efficiently.

(Aspect E)
In (Aspect A) or (Aspect B), a colorimeter is used for measuring the color information, and the difference between the maximum density and the minimum density in the main scanning direction is used for unevenness determination.
According to this, as described in the present embodiment, the unevenness determination can be performed by a simple method.

(Aspect F)
In (Aspect A) or (Aspect B), a scanner such as the scanner unit 300 is used to measure the color information, and the difference between the maximum and minimum RGB luminance values in the main scanning direction is used for unevenness determination. It is characterized by.
According to this, as described in the present embodiment, in an image forming apparatus equipped with a scanner, it is not necessary to newly provide a colorimeter or the like as a measuring unit, which can contribute to cost reduction.

(Aspect G)
For each combination of a plurality of density values and a plurality of positions in the main scanning direction, correction information in which correction values for obtaining a target output value are associated is measured, and color information of a correction chart output before and after correction is measured. A calculation process calculated based on the result is performed a plurality of times for each color used for image formation, and a personal computer 600 to which a colorimeter 700 using an image processing method that corrects image data based on the calculated correction information is connected. An image processing apparatus is characterized in that any one of (Aspect A) to (Aspect F) is used as the image processing method.

  According to this, as described in the present embodiment, it is possible to provide an image processing apparatus that can achieve the same effects as the image processing method of any one of (Aspect A) to (Aspect F).

(Aspect H)
For each combination of a plurality of density values and a plurality of positions in the main scanning direction, correction information in which correction values for obtaining target output values are associated with each other, based on the result of measuring the color information of the output correction chart An image processing method that performs the calculation processing calculated for each color used for image formation a plurality of times and uses the image processing method for correcting the image data based on the calculated correction information, or an image processing apparatus that uses the image processing method is provided. The image processing apparatus according to any one of (Aspect A) to (Aspect F) is used as the image processing method, or the image processing apparatus according to (Aspect G) is used as the image processing apparatus. It is characterized by providing.

  According to this, as described in the present embodiment, the same effects as those of the image processing method of any one of (Aspect A) to (Aspect F) or the image processing apparatus of (Aspect G) can be achieved. An image forming apparatus can be provided.

(Aspect I)
For each combination of a plurality of density values and a plurality of positions in the main scanning direction, correction information in which correction values for obtaining a target output value are associated is measured, and color information of a correction chart output before and after correction is measured. A calculation process that is calculated based on the result is performed a plurality of times for each color used for image formation, and an image processing apparatus that uses an image processing method that corrects image data based on the calculated correction information and an image are formed on the recording material An image forming system such as an image forming system 800 including an image forming apparatus, wherein the image processing apparatus includes the image processing apparatus of (Aspect G).

  According to this, as described in the present embodiment, it is possible to provide an image forming system that can achieve the same effect as the image processing apparatus of (Aspect G).

(Aspect J)
For each combination of a plurality of density values and a plurality of positions in the main scanning direction, correction information in which correction values for obtaining a target output value are associated is measured, and color information of a correction chart output before and after correction is measured. An image processing method, an image forming apparatus, and an image forming system that perform calculation processing based on a result a plurality of times for each color used for image formation and correct image data based on the calculated correction information. Any one of (Aspect A) to (Aspect F) is executed as the image processing method.

  According to this, as described in the present embodiment, it is possible to provide a program that can achieve the same effects as the image processing method of any one of (Aspect A) to (Aspect F).

DESCRIPTION OF SYMBOLS 100 Printer part 300 Scanner part 500 Multifunction machine 600 Personal computer 601 Personal computer main body 602 Keyboard 603 Liquid crystal monitor 630 Interface screen 700 Colorimeter 800 Image forming system

JP 2006-343680 A Japanese Patent No. 4661376 Japanese Patent Laying-Open No. 2005-015881

Claims (10)

Correction information in which a correction value for obtaining a target output value is associated with each combination of a plurality of density values and a plurality of positions in the main scanning direction,
A calculation process for calculating the color information of the correction chart output before and after correction is performed a plurality of times for each color used for image formation,
An image processing method for correcting image data based on calculated correction information,
An image processing method for discarding correction information of a time in which unevenness in the main scanning direction is larger than a correction result of the previous correction chart among the calculation processes performed a plurality of times. The image processing method according to claim 1,
An image processing method comprising: a determination unit that outputs a correction confirmation chart for confirming an effect when the obtained correction information is applied and determines whether further correction is necessary. The image processing method according to claim 1 or 2,
An image processing method, wherein a colorimeter is used for measuring the color information, and a color difference in the main scanning direction is used for unevenness determination. The image processing method according to any one of claims 1 to 3,
An image processing method, comprising: terminating a process when a maximum color difference in a main scanning direction is smaller than 3.0. The image processing method according to claim 1 or 2,
An image processing method, wherein a colorimeter is used for measuring the color information, and a difference between the maximum density and the minimum density in the main scanning direction is used for unevenness determination. The image processing method according to claim 1 or 2,
An image processing method, wherein a scanner is used for measuring the color information, and a maximum and minimum difference in RGB luminance values in the main scanning direction is used for unevenness determination. Correction information in which a correction value for obtaining a target output value is associated with each combination of a plurality of density values and a plurality of positions in the main scanning direction,
A calculation process for calculating the color information of the correction chart output before and after correction is performed a plurality of times for each color used for image formation,
An image processing apparatus using an image processing method for correcting image data based on calculated correction information,
An image processing apparatus using the image processing method according to claim 1 as the image processing method. Correction information in which a correction value for obtaining a target output value is associated with each combination of a plurality of density values and a plurality of positions in the main scanning direction,
A calculation process for calculating the color information of the correction chart output before and after correction is performed a plurality of times for each color used for image formation,
An image forming apparatus using an image processing method for correcting image data based on calculated correction information, or comprising an image processing apparatus using the image processing method,
An image forming apparatus using the image processing method according to any one of claims 1 to 6 as the image processing method, or comprising the image processing device according to claim 7 as the image processing device. . Correction information in which a correction value for obtaining a target output value is associated with each combination of a plurality of density values and a plurality of positions in the main scanning direction,
A calculation process for calculating the color information of the correction chart output before and after correction is performed a plurality of times for each color used for image formation,
An image forming system comprising: an image processing apparatus that uses an image processing method that corrects image data based on calculated correction information; and an image forming apparatus that forms an image on a recording material,
An image forming system comprising the image processing apparatus according to claim 7 as the image processing apparatus. Correction information in which a correction value for obtaining a target output value is associated with each combination of a plurality of density values and a plurality of positions in the main scanning direction,
A calculation process for calculating the color information of the correction chart output before and after correction is performed a plurality of times for each color used for image formation,
A program that causes an image processing method for correcting image data based on calculated correction information to be executed by any of an image processing apparatus, an image forming apparatus, and an image forming system,
A program that causes the image processing method according to any one of claims 1 to 6 to be executed as the image processing method.