JP2013115762A - Image forming apparatus and method for creating correction data of density unevenness in main scanning direction - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of suppressing the number of output sheets of a measurement chart, and calculating a correction value of density unevenness generated in the main scanning direction while reducing influence of density unevenness generated in a sub scanning direction, and to provide a method for creating correction data of density unevenness in a main scanning direction.SOLUTION: A density distribution profile of a measurement chart corrects influence of density unevenness in a sub scanning direction at a certain position in a main scanning direction in order to obtain a correction value, and finds correction values at positions other than the certain position from the obtained correction value. Thus, a density distribution profile in which the influence of the density unevenness in the sub scanning direction is corrected can be obtained. A correction value of density unevenness in the main scanning direction is found on the basis of the density distribution profile.

Description

  The present invention relates to an image forming apparatus that detects density unevenness in the main scanning direction and a method for creating density unevenness correction data in the main scanning direction.

  When a printing apparatus performs print output, unevenness (density unevenness) occurs in the printed matter even if a certain gradation of color is output on the data due to various factors such as device characteristics and changes over time. . In a printing apparatus that generates a two-dimensional image by repeatedly forming an image in the main scanning direction while gradually moving the position in the sub-scanning direction, density unevenness that occurs in the main scanning direction (hereinafter referred to as density unevenness in the main scanning direction). ) Is reproducible, and tends to cause vertical stripe density unevenness.

  Therefore, in order to correct the density unevenness in the main scanning direction, a measurement chart in which a plurality of uniform density belt images extending in the main scanning direction are juxtaposed in the sub scanning direction for different densities is output, and the measurement result of the density distribution Thus, correction data is calculated so that the density of the image formed on the paper is uniform, and the image signal value is corrected using the correction data.

  However, the density at which an image is formed is affected not only by density unevenness that occurs in the main scanning direction but also by density unevenness that occurs in the sub-scanning direction (hereinafter referred to as density unevenness in the sub-scanning direction). For this reason, if the correction value for the density unevenness in the main scanning direction is calculated from the measurement result of the measurement chart that is affected by the density unevenness in the sub-scanning direction, an inappropriate correction value may be calculated. In view of this, a method for correcting the density unevenness in consideration of the density unevenness in the sub-scanning direction has been proposed.

  For example, a test image for one page having a constant density in the main scanning direction and the sub-scanning direction is created by changing the density step by step for each page, and detecting the density distribution thereof. There has been proposed a method for creating correction data for correcting density unevenness in the scanning direction without being affected by density unevenness in the sub-scanning direction (see Patent Document 1). Also, patches of the same color and same density gradation value are generated at two positions separated by a predetermined distance in the sub-scanning direction, the density of each patch generated at the two positions is measured, and sub-scanning is performed from the measured values. There has been proposed a method of creating correction data of image signal values so as to reduce directional density unevenness (see Patent Document 2).

JP 2009-192896 A JP 2007-264364 A

  Since the method disclosed in Patent Document 1 must output a number of measurement charts equal to the number of gradations for measuring density, the number of measurement charts increases to perform density detection for a large number of gradation values. End up.

  Further, the method disclosed in Patent Document 2 detects density only at a specific main scanning direction position, and density detection is not performed at positions other than the specific main scanning direction position. The influence of density unevenness in the sub-scanning direction that occurs at positions other than the main scanning direction position cannot be corrected.

  The present invention is to solve the above-described problem, and calculates correction data for density unevenness in the main scanning direction in which the influence of density unevenness in the sub-scanning direction is reduced while suppressing the number of output measurement charts. An object of the present invention is to provide an image forming apparatus and a method for creating density unevenness correction data in the main scanning direction.

  The gist of the present invention for achieving the object lies in the inventions of the following items.

[1] An image forming unit that forms an image based on image data, a correction data generating unit that generates density unevenness correction data in the main scanning direction for correcting density unevenness in the main scanning direction of the image forming unit,
A correction unit that corrects image data to be output to the image forming unit based on main scanning direction density unevenness correction data created by the correction data generation unit;
With
The correction data generation unit
The density distribution data obtained by measuring the density distribution of the measurement chart of density unevenness in the main scanning direction formed by the image forming unit is acquired, and the density of a predetermined test image formed by the image forming unit The first density data that is generated based on the measurement result and from which the influence of density unevenness in the sub-scanning direction at the specific main scanning direction position is eliminated, and the influence of density unevenness in the sub-scanning direction at the specific main scanning direction position is eliminated. Second density data that has not been obtained,
Correction data for density unevenness in the sub-scanning direction at the specific main scanning direction position is obtained from the first density data and the second density data,
Estimating correction data for density unevenness in the sub-scanning direction at each main scanning direction position other than the specific main scanning direction position based on the correction data;
Correcting the density value at each position in the main scanning direction of the density distribution data with the correction data corresponding to the position in the main scanning direction to obtain second density distribution data from which the influence of density unevenness in the sub-scanning direction is eliminated; The image forming apparatus, wherein the main scanning direction density unevenness correction data is obtained from the second density distribution data.

  In the invention according to any one of [1] and [5] below, the density distribution data obtained by measuring the density distribution in the main scanning direction density unevenness measurement chart is used as the influence of the density unevenness generated in the sub-scanning direction. The second density distribution data that has not been received is corrected, and density correction data in the main scanning direction for correcting the influence of density unevenness occurring in the main scanning direction is created from the corrected second density distribution data. When correcting the density distribution data obtained by the measurement to the second density distribution data not affected by the density unevenness generated in the sub-scanning direction, the influence of the density unevenness generated in the sub-scanning direction at the specific main scanning direction position Then, a correction value for correcting the density unevenness in the sub-scanning direction at a position other than the position in the other main scanning direction is determined from the calculated correction value. As a result, it is possible to create correction data that corrects the influence of density unevenness that occurs in the main scanning direction without being affected by density unevenness that occurs in the sub-scanning direction.

[2] The correction data generation unit uses the same correction data as the density unevenness correction data in the sub-scanning direction at the specific main scanning direction position as correction data for each main scanning direction position other than the specific main scanning direction position. The image forming apparatus according to [1], wherein the estimation is performed.

  In the invention according to any one of [2] and [6] below, when correcting the density distribution data obtained by measurement to the second density distribution data not affected by density unevenness generated in the sub-scanning direction, Then, correction data for correcting the influence of density unevenness occurring in the sub-scanning direction at the specific main scanning direction position is calculated, and the same correction data as the correction data is obtained at each main scanning direction position other than the specific main scanning direction position. Estimated as correction data.

[3] The density distribution data obtained by measuring the density distribution of the measurement chart is composed of density distribution data in the main scanning direction relating to each of a plurality of gradation values,
The correction data generation unit includes the specific main in the density distribution data related to the density value in the specific main scanning direction and the density distribution data related to the second gray level in the density distribution data related to the first gray level. Find the ratio between the difference between the density value in the scanning direction position and the density unevenness correction data in the sub-scanning direction at the specific main scanning direction position,
The correction data for density unevenness in the sub-scanning direction at an arbitrary main scanning direction position is used as the density value at the arbitrary main scanning direction position in the density distribution data related to the first gradation value and the second floor. The image forming apparatus according to [1], wherein the estimation is based on a difference between the density value at the arbitrary main scanning direction position in the density distribution data relating to the tone value and the ratio.

  In the invention according to any one of [3] and [7] below, when the density distribution data obtained by measurement is corrected to the second density distribution data not affected by density unevenness generated in the sub-scanning direction. Correction data for correcting the influence of density unevenness occurring in the sub-scanning direction at the specific main scanning direction position is calculated, and the density at the specific main scanning direction position in the density distribution data related to the first gradation value; A ratio between the density difference between the density at the specific main scanning direction position in the density distribution data related to the second tone value different from the first tone value and the correction data calculated earlier is obtained. Then, the correction data at the main scanning direction position other than the specific main scanning direction position, the density value at that position in the density distribution data related to the first gradation value, and the density distribution data related to the second gradation. The correction data in the main scanning direction position other than the specific main scanning direction position is determined so that the ratio of the density difference with the density value at that position is the same as the previously obtained ratio.

[4] The first gradation value is the gradation value having the highest density in the measurement chart, and the second gradation value is the gradation value having the lowest density in the measurement chart. The image forming apparatus according to [3], which is characterized.

[5] Density distribution data obtained by measuring the density distribution of the measurement chart for density unevenness in the main scanning direction formed by the predetermined image forming unit is acquired, and the predetermined image formed by the image forming unit is obtained. First density data that is generated based on the density measurement result of the test image and in which the influence of density unevenness in the sub-scanning direction at the specific main scanning direction position is eliminated, and density unevenness in the sub-scanning direction at the specific main scanning direction position The second concentration data in which the influence of is not excluded,
Correction data for density unevenness in the sub-scanning direction at the specific main scanning direction position is obtained from the first density data and the second density data,
Estimating correction data for density unevenness in the sub-scanning direction at each main scanning direction position other than the specific main scanning direction position based on the correction data;
Correcting the density value at each position in the main scanning direction of the density distribution data with the correction data corresponding to the position in the main scanning direction to obtain second density distribution data from which the influence of density unevenness in the sub-scanning direction is eliminated; The main scanning direction density unevenness correction data generation method, wherein the main scanning direction density unevenness correction data is obtained from the second density distribution data.

[6] The correction data that is the same as the density unevenness correction data in the sub-scanning direction at the specific main scanning direction position is estimated as correction data for each main scanning direction position other than the specific main scanning direction position. The method for creating density unevenness correction data in the main scanning direction according to [5].

[7] The density distribution data obtained by measuring the density distribution of the measurement chart is composed of density distribution data in the main scanning direction related to each of a plurality of gradation values.
A density value at the specific main scanning direction position in the density distribution data according to the first gradation value, and a density value at the specific main scanning direction position in the density distribution data according to the second gradation value; And the ratio of the density non-uniformity correction data in the sub-scanning direction at the specific main scanning direction position,
The correction data for density unevenness in the sub-scanning direction at an arbitrary main scanning direction position is used as the density value at the arbitrary main scanning direction position in the density distribution data related to the first gradation value and the second floor. The density unevenness in the main scanning direction according to [5], wherein the density unevenness is estimated based on a difference between the density value at the arbitrary main scanning direction position in the density distribution data relating to the tone value and the ratio. Correction data creation method.

[8] The first gradation value is the gradation value having the highest density in the measurement chart, and the second gradation value is the gradation value having the lowest density in the measurement chart. The method for creating density unevenness correction data in the main scanning direction as described in [7].

  According to the image forming apparatus and the main scanning direction density unevenness correction data creation method according to the present invention, the correction value of the density unevenness generated in the main scanning direction is generated in the sub-scanning direction while suppressing the number of output charts for measurement. Calculation can be performed while reducing the influence of density unevenness.

It is explanatory drawing which shows the image forming apparatus which concerns on embodiment of this invention, and the chart for a measurement. 1 is a block diagram illustrating a schematic configuration of an image forming apparatus according to an embodiment of the present invention. It is explanatory drawing which shows the density distribution profile obtained by measuring the test image which concerns on embodiment of this invention, and a test image. It is explanatory drawing which shows the density distribution profile which is not influenced by the sub-scanning direction density | concentration nonuniformity, and the density distribution profile affected. FIG. 10 is an explanatory diagram showing a state in which a density distribution profile not affected by density unevenness in the sub-scanning direction and a line indicating the average density of each gradation are added to the affected density distribution profile. It is a flowchart which shows the flow which correct | amends the density distribution profile obtained by measuring a test image so that the influence of sub-scanning direction density nonuniformity may be reduced. It is explanatory drawing which shows the specific example which determines the correction amount in another main scanning direction position from the correction amount of the density unevenness in the sub-scanning direction at the specific main scanning direction position. It is explanatory drawing which shows two examples between the gradations used as the reference | standard of a ratio. It is explanatory drawing which shows the 2nd calculation method.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows an image forming apparatus 10 according to an embodiment of the present invention and a measurement chart 50 used for density adjustment of the image forming apparatus 10.

  The measurement chart 50 is a density sample sheet for measurement for examining the density difference between the density output on the data by the image forming apparatus 10 and the actual image formed.

  The image forming apparatus 10 is a copy job that optically reads a document and prints a duplicate image on a recording sheet, a scan job that saves the image data of the read document as a file, or transmits it to an external device, from a PC This is a so-called multi-function machine having a function of executing a job such as a print job for printing an image relating to the transmitted data on a recording sheet and outputting the image. In the present invention, the image forming apparatus 10 measures the density of the measurement chart 50, calculates a density difference (density unevenness) between the actually measured value obtained thereby and the density output on the data, and the density unevenness is calculated. Among these, a correction value for correcting density unevenness in the main scanning direction is obtained. Note that the direction in which the recording paper moves along the paper passage path during image formation is defined as the sub-scanning direction, and the direction orthogonal to the sub-scanning direction is defined as the main scanning direction.

  FIG. 2 shows a schematic configuration of the image forming apparatus 10. The image forming apparatus 10 includes a CPU (Central Processing Unit) 11 that controls the operation of the image forming apparatus 10, a ROM (Read Only Memory) 12 connected to the CPU 11, a RAM (Random Access Memory) 13, and a nonvolatile memory. Memory 14, hard disk device 15, display unit 16, operation unit 17, network I / F unit 19, scanner unit 20, image processing unit 21, printer unit 22, facsimile communication unit 23, density The sensor unit 18 is provided.

  The CPU 11 is based on an OS (Operating System) program, on which middleware and application programs are executed. Various programs are stored in the ROM 12, and each function of the image forming apparatus 10 such as job execution is realized by the CPU 11 executing processes according to these programs. The RAM 13 is used as a work memory for temporarily storing various data when the CPU 11 executes a program, an image memory for storing image data, and the like. In the present invention, the CPU 11 obtains a correction value for correcting density unevenness in the main scanning direction, and corrects an image signal value output at the time of image formation based on the obtained correction value.

  The nonvolatile memory 14 is a rewritable memory (flash memory) that can retain memory even when the power is turned off. The nonvolatile memory 14 stores device-specific information and various setting information. The hard disk device 15 is a large-capacity nonvolatile storage device, and stores an OS program, various application programs, print data and image data, an information history related to a job, and the like.

  The display unit 16 is composed of a liquid crystal display (LCD) and the like, and fulfills a function of displaying contents related to various operations and settings. The operation unit 17 has a function of accepting various operations such as job input from the user and setting change. The operation unit 17 includes a touch panel that is provided on the screen of the display unit 16 and detects a pressed coordinate position, and includes a numeric keypad, a character input key, a start key, and the like outside the screen.

  The network I / F unit 19 communicates with other external devices connected through a network such as a LAN.

  The scanner unit 20 performs a function of optically reading a document and acquiring image data. The scanner unit 20 sequentially moves, for example, a light source that irradiates light on a document, a line image sensor that receives the reflected light for one line in the width direction, and a reading position in line units in the length direction of the document. An optical path composed of a lens, a mirror, and the like for guiding the reflected light from the document to the line image sensor to form an image, a conversion unit for converting the analog image signal output from the line image sensor into digital image data, etc. It is prepared for.

  The image processing unit 21 performs rasterization processing for converting print data into image data, image data compression and expansion processing, in addition to processing such as image enlargement / reduction and rotation.

  The printer unit 22 has a function of forming an image corresponding to the image data on a recording sheet. Here, it has a recording paper transport device, a photosensitive drum, a charging device, a laser unit, a developing device, a transfer separation device, a cleaning device, a fixing device, etc., and forms an image by an electrophotographic process. It is configured as a so-called laser printer. When image formation output (printing) is performed, the image formation target (recording paper) is moved in the sub-scanning direction while repeating image formation for one line in the main scanning direction, so that it is two-dimensionally printed on the recording paper. Images are formed.

  The facsimile communication unit 23 controls operations related to facsimile transmission and reception.

  The density sensor unit 18 measures the density distribution of the measurement chart 50 output from the printer unit 22. Here, light emitted from red, green, and blue LED (Light Emitting Diode) light sources is read by a sensor, and the voltage of the sensor (photodiode) is converted into a Lab color system. This data is calibrated based on the correlation with the colorimeter. In the embodiment of the present invention, when the density of the measurement chart 50 is measured, for example, the user sets the measurement chart 50 in the image forming apparatus 10 in the same manner as when the scanner unit 20 scans an image, and the scan is performed. By doing.

  The image forming apparatus 10 forms and outputs the measurement chart 50 (FIG. 1 (1)), measures the density distribution of the output measurement chart 50 (FIG. 1 (2)), and measures the measured density and measurement. When the density unevenness generated on the measurement chart 50 is detected from the difference from the density output on the data when the chart 50 is output, when the image formation (printing) output is performed thereafter, the density unevenness is detected. Among them, the correction data for correcting the image signal value is calculated so as to reduce the influence of the density unevenness in the main scanning direction (FIG. 1 (3)). When calculating the correction data, the image forming apparatus 10 creates corrected density distribution data excluding the influence of density unevenness in the sub-scanning direction from the measured density distribution data (density distribution profile). Correction data for density unevenness in the main scanning direction is calculated from the density distribution data.

  FIG. 3 shows a test image 30 represented by image data for forming an image of the measurement chart 50 and the density distribution of the measurement chart 50 formed by the printer unit 22 based on the image data. An example of the concentration distribution profile 40 showing the obtained concentration distribution as a graph is shown.

  The test image 30 is an image in which a plurality of monochromatic bands extending in the main scanning direction and having different densities are arranged adjacent to each other in the density order in the sub-scanning direction. For the color of the band, the color with the darkest density is black, the color with the lightest density is white, and the band between them is a color that gradually increases so that the density difference is equal. The band has a length substantially equal to the width in which the printer unit 22 can form an image in the main scanning direction, and the width of the band in the sub-scanning direction is appropriately set within a range where the density can be measured. In the present embodiment, color bands of nine levels of density from white to black are arranged in the order of density in the sub-scanning direction (see FIG. 3).

  The density distribution profile 40 is a graph showing the density distribution of each band at the position in the main scanning direction of the measurement chart 50 formed on the recording paper based on the image data of the test image 30. Since the test image 30 in FIG. 3 has nine bands, the density distribution profile 40 also shows the density for each position in the main scanning direction for each of the nine bands. Since the density of each band on the image data is uniform, if the density is reproduced as it is on the recording paper, the line indicating the density of each band in the main scanning direction in the density distribution profile 40 is a straight line. However, when density unevenness in the main scanning direction and density unevenness in the sub-scanning direction occur when an image is formed, the density fluctuates as in the density distribution profile 40 shown in FIG.

  4 and 5 show a density distribution profile 40 in a state where the influence of density unevenness in the sub-scanning direction is not reduced, and a density distribution profile 40A when the influence of density unevenness in the sub-scanning direction is removed from the density distribution profile 40. Show. In the drawing (FIGS. 4 and 5), the density distribution profile 40A and the density distribution profile 40 are arranged side by side (the density distribution profile 40A on the left and the density distribution profile 40 on the right) (on the same scale). In FIG. 5, in two density distribution profiles, a straight line (gray solid line) indicating the average density of the density distribution of each band is further drawn. Since the density unevenness in the sub-scanning direction does not always have an effect in the main scanning direction, it is easy to confirm the influence of the density unevenness in the sub-scanning direction by showing the average density distribution of each band. When the density distribution profile 40A and the density distribution profile 40 are compared in FIG. 5, there is a part where the average density differs on the measurement chart 50, although it is a line indicating the density distribution of the same band. It can be confirmed that the density unevenness in the sub-scanning direction has occurred at the portion where the band to be imaged is formed. In the part of the broken line ellipse 43 in the figure, the difference in average density between the density distribution profile 40A and the density distribution profile 40 is noticeable.

  FIG. 6 shows the flow of processing until the image forming apparatus 10 corrects the density distribution profile 40 measured from the measurement chart 50 to the density distribution profile 40A that is not affected by the density unevenness in the sub-scanning direction. .

  The following processing is processing that is performed for each of the entire bands on the measurement chart 50. Here, the description will be given focusing on predetermined bands. First, density measurement information from which the influence of density unevenness in the sub-scanning direction is removed is acquired by a known technique (Patent Document 2) at a specific main scanning direction position when the image forming apparatus 10 performs image formation (step S601). This density measurement information refers to the effect of density unevenness in the sub-scanning direction on the density of the band of interest at a specific main scanning direction position on the measurement chart 50 formed on the recording paper based on the image data of the test image 30. The density in the removed state was examined in advance.

  Next, the measurement chart 50 is printed out, and the density distribution in the main scanning direction of the band of interest on the output measurement chart 50 is measured (step S602). From this measurement result, a density distribution profile (see density distribution profile 40 in FIGS. 3, 4 and 5) is created. The density distribution profile created here shows the density distribution in a state affected by the density unevenness in the sub-scanning direction and the density unevenness in the main scanning direction.

  The difference between the density value indicated by the density measurement information obtained in step S601 and the density value at the specific main scanning direction position of the density distribution profile obtained in step S602 is used as a correction value for correcting the influence of density unevenness in the sub-scanning direction. Obtained (step S603).

  The density difference between the density value (tone value) of the lightest density band and the density value (tone value) of the darkest density band at the specific main scanning direction position on the density distribution profile is obtained in step S603. A ratio with the correction value (movement amount) is obtained (step S604).

  In each main scanning direction position other than the specific main scanning direction position, the density difference between the density value of the lightest band and the density value of the darkest band at the position in the main scanning direction is obtained in step S605. From the ratio, a correction value for correcting the influence of density unevenness in the sub-scanning direction at the position in the main scanning direction is calculated (step S605). The calculation formula is ((correction value at specific position / maximum / minimum density difference at specific position) × maximum / minimum density difference at arbitrary position). By this method, correction values at all positions other than the specific position are obtained.

  Finally, the correction values obtained in steps S603 and S605 are corrected to reduce the influence of density unevenness in the sub-scanning direction on the density values of all the main scanning direction positions of the band of interest (step S606), and the process ends. .

  When this process is performed for all bands, a density distribution profile in which the influence of density unevenness in the sub-scanning direction is corrected is obtained. The image forming apparatus 10 creates correction data for correcting density unevenness in the main scanning direction from the corrected density distribution profile. This correction data is created from the difference between the density value of each band of the corrected density distribution profile and the density value of each band of the test image 30. In the subsequent image formation output, the image forming apparatus 10 uses this correction data to correct the density value represented by the image signal value so as to reduce the influence of density unevenness in the main scanning direction.

  Here, two specific examples of step S604 and step S605 in FIG. 6 (a method for calculating a correction value at a position other than the position in the specific main scanning direction) are shown.

<First calculation method>
FIG. 7 shows density lines F (see FIG. 7, density distribution profile 40 in the figure) at a specific main scanning direction position 41 on the density distribution profile 40 and at a second main scanning direction position 42 other than the specific main scanning direction position 41. FIG. 9 shows how to obtain a correction value for reducing the influence of density unevenness in the sub-scanning direction from the density value at each position in the main scanning direction (density line indicating the density of the third band from the top). In FIG. 7, the same density distribution profiles 40 are arranged one above the other. In the upper part (A) of FIG. 7, correction values for density unevenness in the sub-scanning direction at the specific main scanning direction position 41 of the density line F are obtained. In FIG. 7B, a correction value for density unevenness in the sub-scanning direction at the position of the density line F in the second main scanning direction is obtained.

  In FIG. 7A, the influence of density unevenness in the sub-scanning direction at the specific main scanning direction position 41 of the density line F is corrected, and correction from density 0.5 to density 0.6 is performed (correction value). = 0.1). In the density distribution profile 40, the density difference between the density value of the darkest band and the density value of the thinnest band at the specific main scanning direction position 41 is 2.0. In FIG. 7B, using the ratio (0.1: 2.0) of the correction value (movement amount by correction) 0.1 and the density difference 2.0 at the specific main scanning direction position 41, A correction value X for correcting the influence of density unevenness in the sub-scanning direction at the second main scanning direction position 42 of the line F is calculated.

  In FIG. 7B, the density difference (referred to as density difference Y) between the density value of the darkest band and the density value of the thinnest band at the second main scanning direction position 42 is 2.2. The correction value X is set so that the ratio between the correction value X and the density difference Y (Y = 2.2) at the second main scanning direction position 42 is the same as the ratio at the specific main scanning direction position 41 obtained earlier. decide. ({0.1: 2.0} = {X: 2.2}), so that X = 0.11 (see FIG. 7B).

  FIG. 8 shows a modification of the first calculation method. In FIG. 8, the same density distribution profiles 40 as in FIG. 7 are arranged side by side. 8A on the upper side shows the same calculation method as FIG. 7, and FIG. 8B on the lower side shows a modification. In the density distribution profile 40 of FIG. 8A, the density difference Ya between the density value of the darkest band and the density value of the thinnest band at the specific main scanning direction position 41 as in FIG. The ratio with the value Xa is adopted as a reference (ratio reference A) for calculating correction values at other main scanning direction positions. However, in the density distribution profile 40 of FIG. 8B, the density difference Yb between the density value of the band with the highest density at the specific main scanning direction position 41 and the blank paper portion (density 0), and the correction value Xb in the density line F Is used as a reference (ratio reference B) for calculating correction values at other positions in the main scanning direction. When using the first calculation method, the image forming apparatus 10 employs either the ratio criterion A or the ratio criterion B.

<Second calculation method>
FIG. 9 shows an example in which correction values at other main scanning direction positions other than the specific main scanning direction position 41 are determined by a method different from that in FIG. In FIG. 9, the correction value Xc at the specific main scanning direction position 41 of the density line F is directly adopted as the correction value at the other main scanning direction position of the density line F. That is, in the second calculation method, the correction value at the specific main scanning direction position 41 of the predetermined density line is applied as it is to all main scanning direction positions on the same density line. The second calculation method requires less processing amount in the image forming apparatus 10 than the first calculation method.

  Thus, in the present invention, the influence of density unevenness in the sub-scanning direction of the density distribution profile 40 (graph) obtained by measuring the measurement chart 50 is corrected (corrected from the density distribution profile 40 to the density distribution profile 40A). ). Then, correction data for correcting density unevenness in the main scanning direction is calculated from the corrected density distribution profile 40A. The density distribution profile 40A is correction data for appropriately correcting the density unevenness in the main scanning direction when it is assumed that the density unevenness in the sub scanning direction is corrected and no density unevenness in the sub scanning direction is generated. The correction data is used to correct the influence of density unevenness in the main scanning direction during subsequent image formation.

  The embodiment of the present invention has been described with reference to the drawings. However, the specific configuration is not limited to that shown in the embodiment, and there are changes and additions within the scope of the present invention. Are also included in the present invention.

  In the embodiment of the present invention, the correction by the density distribution profile has been described by taking the correction in the direction of increasing the density as an example, but the correction may be performed in the direction of decreasing the density.

  In the embodiment of the present invention, the concentration distribution is measured by scanning the measurement chart 50 with the scanner unit 20. However, the concentration distribution of the measurement chart 50 may be measured by the concentration sensor unit 18 of the internal device. . Further, the density distribution measurement of the measurement chart 50 may be performed by a density measuring device provided outside the image forming apparatus 10. In this case, the measurement chart 50 output by the image forming apparatus 10 is measured by the external density measuring apparatus, and the result is transmitted to the image forming apparatus 10. The image forming apparatus 10 receives this measurement result, and performs correction for reducing the influence of density unevenness in the sub-scanning direction on the measurement result.

DESCRIPTION OF SYMBOLS 10 ... Image forming apparatus 11 ... CPU
12 ... ROM
13 ... RAM
DESCRIPTION OF SYMBOLS 14 ... Non-volatile memory 15 ... Hard disk device 16 ... Display part 17 ... Operation part 18 ... Density sensor part 19 ... Network I / F part 20 ... Scanner part 21 ... Image processing part 22 ... Printer part 23 ... Facsimile communication part 30 ... Test image 40 ... Density distribution profile 40A ... Density distribution profile without density unevenness in the sub-scanning direction 41 ... Specific main scanning direction position 42 ... Second main scanning direction position 43 ... Broken line ellipse 50 ... Measurement chart X (Xa, Xb, Xc) ) ... Correction value Y (Ya, Yb) ... Density difference F ... Density line

Claims (8)

An image forming unit that forms an image based on image data; a correction data generating unit that generates density unevenness correction data in the main scanning direction for correcting density unevenness in the main scanning direction of the image forming unit;
A correction unit that corrects image data to be output to the image forming unit based on main scanning direction density unevenness correction data created by the correction data generation unit;
With
The correction data generation unit
The density distribution data obtained by measuring the density distribution of the measurement chart of density unevenness in the main scanning direction formed by the image forming unit is acquired, and the density of a predetermined test image formed by the image forming unit The first density data that is generated based on the measurement result and from which the influence of density unevenness in the sub-scanning direction at the specific main scanning direction position is eliminated, and the influence of density unevenness in the sub-scanning direction at the specific main scanning direction position is eliminated. Second density data that has not been obtained,
Correction data for density unevenness in the sub-scanning direction at the specific main scanning direction position is obtained from the first density data and the second density data,
Estimating correction data for density unevenness in the sub-scanning direction at each main scanning direction position other than the specific main scanning direction position based on the correction data;
Correcting the density value at each position in the main scanning direction of the density distribution data with the correction data corresponding to the position in the main scanning direction to obtain second density distribution data from which the influence of density unevenness in the sub-scanning direction is eliminated; The image forming apparatus, wherein the main scanning direction density unevenness correction data is obtained from the second density distribution data. The correction data generation unit estimates the same correction data as density unevenness correction data in the sub-scanning direction at the specific main scanning direction position as correction data for each main scanning direction position other than the specific main scanning direction position. The image forming apparatus according to claim 1. The density distribution data obtained by measuring the density distribution of the measurement chart is composed of density distribution data in the main scanning direction according to each of a plurality of gradation values,
The correction data generation unit includes the specific main in the density distribution data related to the density value in the specific main scanning direction and the density distribution data related to the second gray level in the density distribution data related to the first gray level. Find the ratio between the difference between the density value in the scanning direction position and the density unevenness correction data in the sub-scanning direction at the specific main scanning direction position,
The correction data for density unevenness in the sub-scanning direction at an arbitrary main scanning direction position is used as the density value at the arbitrary main scanning direction position in the density distribution data related to the first gradation value and the second floor. The image forming apparatus according to claim 1, wherein the estimation is based on a difference between the density value at the arbitrary main scanning direction position in the density distribution data relating to a tone value and the ratio. The first gradation value is a gradation value having the highest density in the measurement chart, and the second gradation value is a gradation value having the lowest density in the measurement chart. The image forming apparatus according to claim 3. The density distribution data obtained by measuring the density distribution of the measurement chart of the density unevenness in the main scanning direction formed by the predetermined image forming unit is acquired, and the predetermined test image formed by the image forming unit is acquired. The first density data, which is generated based on the density measurement result, from which the influence of density unevenness in the sub-scanning direction at the specific main scanning direction position is eliminated, and the influence of density unevenness in the sub-scanning direction at the specific main scanning direction position The second concentration data which is not excluded,
Correction data for density unevenness in the sub-scanning direction at the specific main scanning direction position is obtained from the first density data and the second density data,
Estimating correction data for density unevenness in the sub-scanning direction at each main scanning direction position other than the specific main scanning direction position based on the correction data;
Correcting the density value at each position in the main scanning direction of the density distribution data with the correction data corresponding to the position in the main scanning direction to obtain second density distribution data from which the influence of density unevenness in the sub-scanning direction is eliminated; The main scanning direction density unevenness correction data generation method, wherein the main scanning direction density unevenness correction data is obtained from the second density distribution data. The correction data identical to the density unevenness correction data in the sub-scanning direction at the specific main scanning direction position is estimated as the correction data for each main scanning direction position other than the specific main scanning direction position. 5. A method of creating density unevenness correction data in the main scanning direction according to 5. The density distribution data obtained by measuring the density distribution of the measurement chart is composed of density distribution data in the main scanning direction relating to each of a plurality of gradation values,
A density value at the specific main scanning direction position in the density distribution data according to the first gradation value, and a density value at the specific main scanning direction position in the density distribution data according to the second gradation value; And the ratio of the density non-uniformity correction data in the sub-scanning direction at the specific main scanning direction position,
The correction data for density unevenness in the sub-scanning direction at an arbitrary main scanning direction position is used as the density value at the arbitrary main scanning direction position in the density distribution data related to the first gradation value and the second floor. The density unevenness in the main scanning direction according to claim 5, wherein the density unevenness is estimated based on a difference between the density value at the arbitrary main scanning direction position in the density distribution data relating to the tone value and the ratio. Correction data creation method. The first gradation value is a gradation value having the highest density in the measurement chart, and the second gradation value is a gradation value having the lowest density in the measurement chart. The method for creating density unevenness correction data in the main scanning direction according to claim 7.