JP2006229351A - Image forming device and image processing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To absorb a difference between machines of gradation correction in an image formation system, and also, to reduce a gradation difference in the image formation system between machines. <P>SOLUTION: The image forming device is provided with a scanner correction chart 70 of a chromatic color, a scanner 102 for acquiring RGB scan data by reading the chart 70, a control means 15 for correcting the scanner 102 on the basis of the RGB scan data, and a printer 60 for outputting a printer correction pattern 80 of a chromatic color. The control means 15 acquires (RGB)' scan data by reading the printer correction pattern 80 with the scanner 102 after correction, and corrects an output value of a sensor 12 of the printer 60 on the basis of the (RGB)' scan data. Output gradation of the printer 60 can be corrected in a state that effects of an output difference are removed as occurred due to variation in wavelength or the like of a color filter of the scanner 102. Consequently, the gradation correction of the printer 60 can be highly precisely executed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  INDUSTRIAL APPLICABILITY The present invention is an image forming apparatus and image processing suitable for being applied to a color digital copying machine having the function of executing gradation correction of an image forming system based on a gradation correction chart, the same multifunction machine, etc. It is about the method.

  In recent years, color images are formed on the basis of image data relating to red (R), green (G), and blue (B) colors acquired from chromatic color original images, servers, personal computers (hereinafter simply referred to as personal computers). Color copiers, color multifunction peripherals, and the like that receive image data from a printer controller (external device) such as) and form a color image based on this image data have been used. A color scanner having a CCD unit is used in this type of color copying machine and multifunction machine.

  In connection with the tone correction of this type of color scanner, Patent Document 1 discloses an image processing apparatus and method. According to this image processing method, the color chart is read from a known color chart, and the density value of the color chart is held. Further, a pattern having a predetermined value composed of a plurality of color components forming a color image is read, and the density value of the pattern is held. Thereafter, correction information is calculated from the density value of the color chart and the density value of the pattern composed of a plurality of color components forming the color image, and the gradation of the plurality of color components is corrected based on the correction information. The By configuring the image processing method in this way, a color image can be corrected to an appropriate gradation.

  Patent Document 2 discloses an image reading apparatus and an image reading method thereof. According to this image reading apparatus, when correcting the variation between the bodies with respect to the image reading, the reference density measuring unit detects the density of the pattern for density measurement and measures the reference density. The storage means stores the reference density measured by the reference density measuring means. The reading unit reads the same pattern as the density measurement pattern and measures the sample density value. The extraction means extracts a reference density value corresponding to the density measurement pattern from the storage means. The calculating means calculates a correction value based on the reference density value and the sample density value extracted from the storage means. By configuring the image reading apparatus in this way, it is possible to correct variations between machine bodies regarding image reading based on correction values, improving work efficiency, and flexibly for various system combinations. It can be handled.

  Further, Patent Document 3 discloses a digital color multifunction peripheral. According to this color multifunction peripheral, when ensuring color compatibility between multifunction peripherals of different models, the printer outputs an adjustment chart composed of gradation patches of single colors of YMCK. The scanner reads an adjustment chart composed of YMCK single-color gradation patches output from the printer. When the control device grasps each current patch density / lightness characteristic and Lab value and executes gradation correction on the currently set target, it reads a new adjustment chart with a scanner, and each of the adjustment charts A new target is created based on the patch density / lightness characteristics and the Lab value. By configuring a color multifunction peripheral in this way, a new target can be obtained from an adjustment chart output from a different color multifunction peripheral, and color compatibility can be ensured between multifunction peripherals of different models. is there.

JP-A-8-279919 (page 3 FIG. 6) JP 2002-271625 A (3rd page, FIG. 6) Japanese Patent Laying-Open No. 2004-072620 (page 3 in FIG. 1)

  Incidentally, the color copying machine according to the conventional example having a function of executing gradation correction of the image forming system based on the gradation correction chart has the following problems.

  i. In a scanner equipped with a color CCD unit as shown in Patent Documents 1 to 3, there is usually a wavelength variation of several nanometers in a primary color (for example, RGB) color filter as an optical component. Due to this wavelength variation, even when the same chromatic color original is read, the amount of transmitted light differs for each CCD unit, that is, for each machine, and the scanner may output different values.

  ii. Incidentally, a system has been devised in which a gradation correction pattern of a specific chromatic color is output from a printer, and the gradation correction of the printer is executed from a value obtained by reading this output pattern with a scanner. However, when the gradation correction of the printer unit is performed, it is necessary to output a gradation correction pattern from the printer and calculate and generate the gradation correction data of the printer unit by the scanner. In addition, the gradation correction of the scanner itself is separately performed with a gray scale chart which is an achromatic color. For this reason, there is an output difference of the scanner due to wavelength variation of the color filter. As a result, this output difference interferes with the correction of the output gradation of the printer, and the gradation correction of the printer often includes an error.

  iii. In order to solve these problems, a method of outputting a chromatic tone patch pattern from a printer (hereinafter also referred to as an image forming system) and executing the tone correction of the scanner with the tone patch pattern itself may be considered. The reference value of the gradation patch pattern must be measured using a measuring instrument one by one. A method of correcting the gradation of the printer using a density detection sensor instead of the colorimeter is conceivable, but the sensor must be calibrated for each correction.

  iv. In addition, when there are image defects such as white spots and toner spills in the gradation patch pattern itself, the gradation correction of the scanner is deteriorated and its practicality is poor.

  Accordingly, the present invention solves such a problem related to the conventional example, and can absorb the machine-to-machine difference in the gradation correction of the image forming system, and An object of the present invention is to provide an image forming apparatus and an image processing method capable of reducing the gradation difference of the image forming system.

  In order to solve the above-described problems, an image forming apparatus according to the present invention includes a chromatic color chart for image reading system correction, and an image reading unit that reads the chart and acquires first gradation correction data. A control unit for correcting the image reading unit based on the first gradation correction data acquired by the image reading unit, and a sensor for detecting the image density, and a chromatic pattern for correcting the image forming system. Image forming means for forming and outputting the image, and the control means reads the pattern output from the image forming means with the corrected image reading means to obtain the second gradation correction data, and obtains the second gradation correction data. The output value of the sensor of the image forming means is corrected based on the tone correction data.

  According to the image forming apparatus of the present invention, a chromatic color chart for image reading system correction is prepared in advance. In this chart, for example, a chromatic pattern that is “approximate” to the reflection wavelength of the color material used in the image forming means is formed. Here, the chromatic color pattern "approximating" the reflection wavelength of the color material means the relative sensitivity and reflectance of colors that are complementary in the spectral sensitivity of the image reading means and the absorption characteristics of the color material of the image forming means. Of the spectral sensitivity of the image reading means and the absorption characteristics of the color material of the chromatic color chart for correcting the image reading system, the value obtained by integrating the relative sensitivity and reflectance of the complementary colors. It means a case where the wavelength has a difference with the maximum value within ± 20 nm.

  The image reading unit acquires the first gradation correction data by reading a chart on which a pattern having such a wavelength is formed. The control unit corrects the image reading unit based on the first gradation correction data acquired by the image reading unit. On the premise of this, the control means outputs the output of the sensor of the image forming means based on the second gradation correction data obtained by reading the chromatic color output pattern for image forming system correction by the corrected image reading means. The value will be corrected.

  Accordingly, it is possible to correct the output gradation of the image forming unit correctly with the influence of the output difference due to the wavelength variation of the color filter of the image reading unit being removed, and to perform the gradation correction of the image forming unit with high accuracy. Can be executed. As a result, the difference between the machines for gradation correction of the image forming means can be absorbed, so that the gradation difference of the image forming means between machines such as a color copying machine and a color multifunction peripheral can be reduced.

  The image processing method according to the present invention is based on the step of acquiring a first gradation correction data by reading a chromatic color chart for image reading system correction, and the first gradation correction data acquired here. A step of correcting the image reading system, and a step of forming and outputting a chromatic pattern for image forming system correction in an image forming system having a sensor for detecting the image density, and an image forming output here. Reading the read pattern with the corrected image reading system to acquire second gradation correction data, and correcting the output value of the sensor of the image forming system based on the second gradation correction data. It is characterized by having.

  According to the image processing method of the present invention, when tone correction is performed on an image forming system based on a chromatic chart for image reading system correction prepared in advance, due to wavelength variation of a color filter of the image reading system, etc. With the influence of the output difference removed, the output gradation of the image forming system can be corrected correctly, and the gradation correction of the image forming system can be executed with high accuracy. Therefore, since the difference between the machines for gradation correction in the image forming system can be absorbed, the gradation difference in the image forming system between machines such as a color copying machine and a color multifunction peripheral can be reduced.

  The image forming apparatus according to the present invention includes a control unit that corrects the image reading unit based on the first gradation correction data obtained by reading the chromatic color chart for image reading system correction. The means corrects the output value of the sensor of the image forming means based on the second gradation correction data obtained by reading the chromatic color output pattern for image forming system correction by the corrected image reading means. .

  With this configuration, it is possible to correct the output tone of the image forming unit correctly without the influence of the output difference due to the wavelength variation of the color filter of the image reading unit, and to enhance the tone correction of the image forming unit. It can be executed with accuracy. Therefore, since the difference between the machines for gradation correction of the image forming means can be absorbed, the gradation difference of the image forming means between machines such as a color copying machine and a color multifunction peripheral can be reduced.

  According to the image processing method of the present invention, a chromatic color chart for image reading system correction is read, the image reading system is corrected based on the first gradation correction data obtained by the reading, and then the image is read. A chromatic color pattern for image forming system correction is output from the forming system, and the output value of the sensor of the image forming system is calculated based on the second gradation correction data obtained by reading this pattern in the corrected image reading system. It is made to correct.

  With this configuration, it is possible to correct the output tone of the image forming system correctly in a state where the influence of the output difference due to the wavelength variation of the color filter of the image reading system is removed, and to enhance the tone correction of the image forming system. It can be executed with accuracy. Therefore, since the difference between the machines for gradation correction in the image forming system can be absorbed, the gradation difference in the image forming system between machines such as a color copying machine and a color multifunction peripheral can be reduced.

Next, an embodiment of an image forming apparatus and an image processing method according to the present invention will be described with reference to the drawings.
FIG. 1 is a conceptual diagram illustrating a configuration example of a color copying machine 100 to which an image forming apparatus as an embodiment is applied.

  A color copying machine 100 shown in FIG. 1 acquires an image information by reading a document d composed of a chromatic or achromatic character image, a photographic image, and a halftone image, and performs an image processing on the image information. In this apparatus, colors are superimposed based on formation data (hereinafter referred to as YMCK data) to form a color image on a desired paper P. The color copying machine 100 has a printer correction mode. In this printer correction mode, the printer unit 60 is subjected to gradation correction based on a chromatic color chart for scanner gradation correction (hereinafter referred to as a scanner correction chart 70). In this example, a chromatic color gradation pattern that is “approximate” to the reflection wavelength of the color material used in the printer unit 60 is printed on the scanner correction chart 70.

  The color copying machine 100 includes a copying machine main body 101 and a scanner unit 102. The scanner unit 102 is an example of an image reading unit, and reads the original d, the scanner correction chart 70, and the like to acquire first gradation correction data (hereinafter referred to as RGB scan data). A document reading unit 11 including an automatic document feeder (ADF) 201 and a document image scanning exposure device 202 is attached to the upper part of the copying machine main body 101.

  The ADF 201 includes a document placing portion 41, a roller 42 a, a roller 42 b, a roller 43, a reverse roller 44, a reverse portion 45, and a paper discharge tray 46. The document reading unit 11 includes a first platen glass 51, a second platen glass 52, a light source 53, mirrors 54, 55, and 56, an imaging optical unit 57, a CCD unit 58, and an optical drive unit (not shown). ing.

  The document d placed on the document placement unit 41 of the ADF 201 is transported by transporting means such as a roller 42a and a roller 42b. The document image scanning exposure apparatus 202 scans and exposes the image surface of the document d by its optical system. The CCD unit 58 outputs an image signal obtained by reading image information from the document d. The document d includes a scanner correction chart 70, a printer correction pattern 80, and the like. The image signal photoelectrically converted by the CCD unit 58 is subjected to analog processing, A / D conversion, shading correction, image compression processing, and the like in an image processing means (not shown) to obtain digital image data (hereinafter referred to as RGB scan data). Become. Thereafter, the RGB scan data undergoes predetermined image processing to become YMCK data.

  The YMCK data after image processing is sent to the printer unit 60. In this example, the printer unit 60 outputs a chromatic color gradation pattern for printer gradation correction (hereinafter referred to as a printer correction pattern 80) in the printer correction mode.

  The ADF 201 includes automatic double-sided document conveying means. The ADF 201 reads the contents of a large number of documents d fed from the document placement table all at once, and stores the document contents in an image memory or the like (electronic RDH function). This electronic RDH function is conveniently used when copying the contents of a large number of originals with the copy function or when transmitting a large number of originals d with the facsimile function.

  The copying machine main body 101 is called a tandem type color image forming apparatus, and a printer unit 60 constituting an example of an image forming unit includes a plurality of sets of image forming units 10Y, 10M, 10C, and 10K, and an endless type. The intermediate transfer belt 6, a paper feeding / conveying means including a refeeding mechanism (ADU mechanism), and a fixing device 17 for fixing the toner image.

  The image forming unit 10Y that forms a yellow (Y) image includes a photosensitive drum 1Y, a Y-color charging unit 2Y, an exposing unit 3Y, a developing unit 4Y, and an image forming unit disposed around the photosensitive drum 1Y. It has body cleaning means 8Y. The image forming unit 10M that forms a magenta (M) color image includes a photosensitive drum 1M, an M color charging unit 2M, an exposure unit 3M, a developing unit 4M, and an image forming unit cleaning unit 8M.

  The image forming unit 10C that forms a cyan (C) color image includes a photosensitive drum 1C, a C color charging unit 2C, an exposure unit 3C, a developing unit 4C, and an image forming unit cleaning unit 8C. The image forming unit 10K that forms a black (BK) color image includes a photosensitive drum 1K, a BK color charging unit 2K, an exposure unit 3K, a developing unit 4K, and an image forming unit cleaning unit 8K.

  The charging unit 2Y and the exposure unit 3Y, the charging unit 2M and the exposure unit 3M, the charging unit 2C and the exposure unit 3C, and the charging unit 2K and the exposure unit 3K constitute a latent image forming unit. Development by the developing means 4Y, 4M, 4C, and 4K is performed by reversal development in which a developing bias in which an AC voltage is superimposed on a DC voltage having the same polarity (negative polarity in this embodiment) as the polarity of the toner to be used is applied. . The intermediate transfer belt 6 is wound around a plurality of rollers and is rotatably supported.

  Here, an outline of the image forming process will be described below. Each color image formed by the image forming units 10Y, 10M, 10C, and 10K is applied with a primary transfer bias (not shown) having a polarity (positive in this embodiment) opposite to that of the toner member to be used. By the transfer rollers 7Y, 7M, 7C, and 7K, the image is sequentially transferred onto the rotating intermediate transfer belt 6 (primary transfer), and a combined color image (color image: color toner image) is formed. The color image is transferred from the intermediate transfer belt 6 to the paper P.

  The paper P accommodated in the paper cassettes 20A, 20B, and 20C is fed by the feed roller 21 and the paper feed roller 22A provided in the paper cassettes 20A, 20B, and 20C, respectively, and the transport rollers 22B, 22C, 22D, After passing through the registration roller 23 and the like, the sheet is conveyed to the secondary transfer roller 7A, and the color image is collectively transferred to one surface (front surface) on the paper P (secondary transfer).

  The paper P on which the color image has been transferred is fixed by the fixing device 17, is sandwiched between the paper discharge rollers 24, and is placed on a paper discharge tray 25 outside the apparatus. The transfer residual toner remaining on the peripheral surfaces of the photosensitive drums 1Y, 1M, 1C, and 1K after the transfer is cleaned by the image forming body cleaning means 8Y, 8M, 8C, and 8K, and enters the next image forming cycle.

  At the time of double-sided image formation, the paper P formed on one side (front surface) and discharged from the fixing device 17 is branched off from the sheet discharge path by the branching unit 26, and constitutes a sheet feeding and conveying unit. After passing through the circulation sheet passing path 27A, the front and back are reversed by a reversing conveyance path 27B which is a refeed mechanism (ADU mechanism), passes through the refeed conveyance section 27C, and merges at the sheet feeding roller 22D.

  The reversely conveyed sheet P is conveyed again to the secondary transfer roller 7A through the registration roller 23, and a color image (color toner image) is collectively transferred onto the other side (back side) of the sheet P. The paper P on which the color image has been transferred is fixed by the fixing device 17, is sandwiched between the paper discharge rollers 24, and is placed on a paper discharge tray 25 outside the apparatus. On the other hand, after the color image is transferred to the paper P by the secondary transfer roller 7A, the residual toner is removed by the intermediate transfer belt cleaning means 8A from the intermediate transfer belt 6 that has separated the curvature of the paper P.

The time of forming these images, 52.3~63.9kg / m ² (1000 sheets) about thin and 64.0~81.4kg / m ² (1000 sheets) of approximately plain paper or a paper P 83 .0~130.0kg / m ² using a (1000) about a cardboard and 150.0kg / m ² (1000 sheets) about super thick paper, the linear velocity is about 80~350mm / sec, the temperature as environmental conditions Preferably, the setting conditions are about 5 to 35 ° C. and the humidity is about 15 to 85%. The thickness of the paper P (paper thickness) is about 0.05 to 0.15 mm.

  An image density detection sensor (printer γ sensor; hereinafter referred to as an image density sensor) 12 is provided on the upstream side of the cleaning unit 8A and at a position where the image forming surface of the intermediate transfer belt 6 can be seen through. In the mode, the image density of the gradation patch pattern PS formed (drawn) on the intermediate transfer belt 6 is detected. A reflection type optical sensor is used as the image density sensor 12, and the density detection signal S1 is output to the control means 15.

  FIG. 2 is a block diagram illustrating a configuration example of a control system of the color copying machine 100. The color copying machine 100 shown in FIG. The control unit 15 includes a ROM (Read Only Memory) 31, a RAM (Random Access Memory) 32, and a CPU (Central Processing Unit) 33. The ROM 31 stores system program data for controlling the entire copying machine. The RAM 32 is used as a work memory, and for example, temporarily stores control commands and the like. When the power is turned on, the CPU 33 reads the system program data from the ROM 31 to the RAM 32, starts the system, and controls the entire copying machine based on the operation data D3 from the operation setting means 14.

  For example, the control unit 15 corrects the scanner unit 102 based on the RGB scan data acquired by the scanner unit 102 when the printer correction mode is set. The control unit 15 reads the printer correction pattern 80 output from the printer unit 60 by the corrected scanner unit 102 to acquire (RGB) ′ scan data which is second gradation correction data, and performs (RGB) ′ scan. The printer 60 is subjected to gradation correction based on the data.

  In addition, the CPU 33 performs the tone correction of the scanner unit 102 by using the scanner correction chart 70 that approximates the wavelength of the chromatic (primary) color material of the printer unit 60 (printing or the like), while the printer unit 60 executes the tone correction. A printer correction pattern 80 of a specific chromatic color is output, a sensor output correction coefficient of the image density sensor 12 is calculated from (RGB) ′ scan data obtained by reading the printer correction pattern 80 with the scanner unit 102, and the printer unit 60. The gradation is corrected.

  When the printer unit 60 performs gradation correction, the control unit 15 forms a gradation patch pattern PS on the intermediate transfer belt 6 by the printer unit 60, and an image of the gradation patch pattern PS formed on the intermediate transfer belt 6. The density is detected (read), patch image data is acquired, and a correction coefficient at the time of gradation conversion is calculated based on the patch image data and (RGB) ′ scan data.

  An image density sensor 12 is connected to the control means 15, detects the image density of the gradation patch pattern PS formed on the intermediate transfer belt 6, and outputs a density detection signal S 1. The density detection signal S1 includes RGB color signal components (corresponding to RGB colorimetric values). The control means 15 includes an A / D converter (not shown), and the density detection signal S1 is converted from analog to digital. The density detection data (sensor output value) after A / D conversion is output to the CPU 33. The CPU 33 calculates XYZ data based on the sensor output value obtained from the image density sensor 12.

  In this example, the control means 15 includes a nonvolatile memory 39 as an example of a storage device, and stores a reference colorimetric value (reference XYZ value; reference value) obtained by measuring the scanner correction chart 70 in advance. To be made. The reference XYZ values are measured in advance using, for example, a colorimeter that serves as a reference on the manufacturer side before shipment. The reference XYZ values are stored (stored) in the nonvolatile memory 39 of the color copying machine 100 by data transfer input or manual input.

  The scanner unit 102 includes a document reading unit 11, an A / D conversion unit 34, a shading correction unit 35, an image processing unit 36, and an image memory 37. The document reading unit 11, of course, reads image information from the document d, such as the scanner correction chart 70 and the printer correction pattern 80, and converts the analog image signals SR, SG, SB into analog / digital converters (hereinafter referred to as A / D conversion) 34. Output to. The A / D converter 34 performs A / D conversion on the analog image signals SR, SG, and SB and outputs image data (RGB scan data) including digital R, G, and B color signal components. A shading correction unit 35 is connected to the A / D converter 34, and the RGB scan data is subjected to a shading correction process.

  An image memory 37 is connected to the shading correction unit 35 to temporarily store RGB scan data after shading correction and YMCK data after image processing. For the image memory 37, a DRAM or a hard disk is used. An image processing unit 36 is connected to the image memory 37, and RGB scan data related to the scanner correction chart 70 and the printer correction pattern 80 read from the image memory 37 is input, and luminance gradation analysis and the like are performed based on predetermined parameters. Perform image processing.

  Of course, the image processing means 36 filters the RGB scan data or performs γ adjustment processing on the RGB scan data after the filter processing. The RGB scan data after γ adjustment is subjected to color conversion processing to YMCK data. The YMCK data after the color conversion process is subjected to an error diffusion process or the like. The YMCK data after the image processing is temporarily stored in the image memory 37 (electronic RDH function). In the printer correction mode, the CPU 33 transfers a reference XYZ ′ value obtained by reading from the printer correction pattern 80 to the printer unit 60.

  The scanner unit 102 is provided with a scanner gradation conversion device (table) constituted by the image memory 37 or the non-volatile memory 39, and the scanner gradation conversion coefficient is incorporated into the scanner gradation conversion table by the CPU 33 and the conversion is performed. It is reflected in the table values and used when the scanner unit 102 performs gradation correction. For example, in normal document scan processing, gradation conversion is performed when document read data (RGB scan data) obtained from the scanner unit 102 is corrected. By correcting the original reading data with such a scanner gradation correction coefficient, it becomes possible to acquire scanner image information having no machine difference.

  Further, the control means 15 is connected to the image processing means 36. An operation setting unit 14 and a display unit 18 are connected to the control unit 15. For example, the operation setting means 14 is composed of a touch panel, and the display means 18 is composed of a liquid crystal display panel. In this example, a touch panel constituting the operation setting means 14 is combined with a liquid crystal display panel constituting the display means 18 to constitute a GUI (Graphic User Interface) type operation panel 48. The operation panel 48 is operated to set the printer correction mode.

  A printer unit 60 including the image forming units 10Y, 10M, 10C, and 10K shown in FIG. 1 is connected to the control unit 15, and a printer correction pattern 80 is output based on the mode set by the operation panel 48. To work. The control unit 15 outputs an image formation control signal S2 to the printer unit 60, and controls input / output of the printer unit 60 so as to form (draw) the gradation patch pattern PS on the intermediate transfer belt 6.

  The printer unit 60 is provided with a specific image data generation device configured by the image memory 37 or the nonvolatile memory 39, and transmits the image data of the printer correction pattern 80. Further, the printer unit 60 is provided with a printer gradation conversion device configured by the image memory 37 or the nonvolatile memory 39, and stores gradation correction values (correction formulas and correction coefficients) to form a printer gradation conversion table. To be made.

  In addition to the printer unit 60, the communication unit 19 and the paper feeding unit 30 are connected to the control unit 15. The communication means 19 is connected to a communication line such as a LAN, and is used when communicating with an external computer or the like. When the color copying machine 100 is used as a color printer, the communication means 19 is used to receive print data Din from an external computer in the print operation mode. The reference XYZ values of the scanner correction chart 70 may be transferred to the nonvolatile memory 39 using this function.

  The paper feed means 30 controls the paper feed cassettes 20A, 20B, and 20C shown in FIG. 1 based on the paper feed control signal S3 in the print operation mode. For example, the paper feed means 30 drives the feed roller 21 and the paper feed roller 22A provided in the paper feed cassette 20A to feed out the paper P stored in the paper feed cassette 20A and feed it to the printer unit 60. The The paper feed control signal S3 is supplied from the control means 15 to the paper feed means 30. The printer correction pattern 80 described above is formed on the paper P in the printer correction mode and is output to the paper discharge tray 25.

  FIG. 3 is a top view illustrating a configuration example of the scanner correction chart 70. The scanner correction chart 70 shown in FIG. 3 has the same pattern on the left and right in consideration of the density gradient in the main scanning direction. In addition, the high density portion of one pattern is shifted by 1/3 of the drum cycle so as not to be affected by the cycle unevenness of the photosensitive drum. In this example, each row is composed of a gradation patch pattern PS having 10 patterns in total 30 × 2 (left and right patches), 26 actual gradations, and three white and high density portions.

  The chromatic color scanner correction chart itself is created in advance by printing or the like. For example, a Δ mark indicating the head is printed on the scanner correction chart 70, and a repeated image of gradation patch patterns of Y, M, C, and BK colors is printed. The Δ mark is formed because it is difficult to distinguish the upper and lower sides of the chart itself. In this example, a green Δ mark is printed at the upper end of the output. The color of the Δ mark may be the same color, but it is desirable that the color is not confused with the printer correction pattern 80. The single color is the same as the printer correction pattern 80, and the R color is easily mistaken for the M color. Considering these, the color of the Δ mark is determined.

  Further, the wavelength characteristic of the ink member at the time of printing uses a material that “approaches” the reflection wavelength of the primary color of the color material used in the printer unit 60. When such an ink member is used, a chromatic tone patch pattern PS that is “approximate” to the reflection wavelength of the color material used in the printer unit 60 is obtained. In addition, since the scanner correction chart 70 is created in advance by printing or the like in this way, image defects and the like can be excluded in advance.

  The chromatic scanner correction chart 70 is used only for printer gradation correction. This is because, in the scanner gradation correction using the scanner correction chart 70, the color of the gradation patch pattern PS read by the scanner unit 102 needs to be known and constant (fixed) in order to clarify the comparison reference in the image processing. Because there is.

  Therefore, when correcting only normal copy or scanner gradation, the user cannot specify what color pattern to use, so as usual, it is color dependent as a representative (medium) scanner correction chart. Use a neutral grayscale chart. In the gray scale chart, a value obtained by correcting only a mechanical difference in optical reflectance is used.

FIG. 4 is a graph showing an example of spectral sensitivity characteristics of R, G, and B colors in the scanner unit. 4, the vertical axis represents relative sensitivity I “%” (0 to 100), and the horizontal axis represents wavelength λ [nm] The solid line represents the spectral sensitivity characteristics of red (R) color. The R color has a peak wavelength (main wavelength) in the vicinity of 625 nm, and the wavy line has a spectral sensitivity characteristic of green (G), and the G color has a peak wavelength (main wavelength) in the vicinity of 540 nm. ing.
A one-dot chain line is a spectral sensitivity characteristic of blue (Blue: B). B color has a peak wavelength (main wavelength) in the vicinity of 450 nm.

  FIG. 5 is a graph showing an example of absorption (spectral reflection) characteristics of each of the Y, M, and C color materials used in the printer unit 60. In FIG. 5, the vertical axis represents the reflectance ρ (0.0 to 1.0), and the horizontal axis represents the measurement wavelength λ [nm]. The solid line represents the absorption characteristics of the yellow (Yellow: Y) color material. The Y color material has a constant peak reflectance at a measurement wavelength of 525 nm or later. The wavy line is the absorption characteristic of the magenta (Magenta) color. The M color material has a constant peak reflectance after the measurement wavelength of 625 nm. A one-dot chain line is an absorption characteristic of cyan (Cyan) color. The C color material has a peak reflectance around a measurement wavelength of 475 nm.

  FIG. 6 is a graph showing an example of RGB color scanner sensitivity × YMC color material absorption rate wavelength characteristics. In this example, when two colors that can be made achromatic by additive color mixing or subtractive color mixing are complementary colors, the spectral sensitivity of the scanner unit 102 and the absorption characteristics (absorption rate) of the color material of the printer unit 60 are complementary colors. The graph which integrated the relative sensitivity I and reflectance (rho) of the color which has a relationship, ie, B color and Y color, G color and M color, R color and C color is shown.

  Note that the B color and Y color, the G color and M color, and the R color and C color, which are complementary colors, are arranged at positions facing (opposite) on the hue circle. Additive color mixing refers to color mixing that produces different colors when two types of color light are projected on a screen. R, G, and B colors are used for the three additive primary colors. The subtractive color mixing means that a specific color is expressed by transmitting white light to a color filter or other absorbing medium superimposed. Y, M, and C colors are used as the three subtractive primary colors.

  In FIG. 6, the vertical axis represents the relative sensitivity I ′ [%] (0 to 30), which is an integrated value of the spectral sensitivity I in the scanner unit 102 and the colorant reflectance ρ in the printer unit 60. The horizontal axis is the wavelength λ [nm]. The solid line is the (R × C) scanner sensitivity color material absorption rate wavelength characteristic. The (R × C) color has a peak sensitivity absorption wavelength characteristic around a wavelength of 450 nm. The wavy line represents the (G × M) scanner sensitivity color material absorption rate wavelength characteristic. The (G × M) color has a peak sensitivity absorption wavelength characteristic in the vicinity of a wavelength of 550 nm. The alternate long and short dash line is the (B × C) color scanner sensitivity absorption wavelength characteristic. The (B × C) color has a peak sensitivity absorption wavelength characteristic around a wavelength of 620 nm.

  In this example, the spectral sensitivity of the scanner unit 102 and the absorption characteristics of the color material of the printer unit 60 are complementary colors, that is, B and Y colors, G and M colors, R and C colors, respectively. The maximum value (main wavelength) obtained by integrating the relative sensitivity I and the reflectance ρ, the spectral sensitivity of the scanner unit 102, and the color material absorption characteristics of the scanner correction chart 70 are complementary colors, that is, the B color. Compare the relative sensitivity I and reflectance ρ of the Y, G and M colors, R and C colors in the same way, compare the maximum values (main wavelengths), find the differences, and evaluate the correction effect To be made.

  In this evaluation example, in the spectral sensitivity of the scanner unit 102 and the absorption characteristics of the color material of the printer unit 60, the maximum value (main wavelength) of the values obtained by integrating the relative sensitivity I and the reflectance ρ of complementary colors, and the scanner In the spectral sensitivity of the unit 102 and the absorption characteristic of the color material of the scanner correction chart 70, the difference between the complementary value of the relative sensitivity I and the maximum value (main wavelength) of the reflectance ρ is within ± 20 nm. In this case, it is possible to correct the machine difference in scanner spectral sensitivity. The correction accuracy increases as the difference decreases. In this example, when the difference exceeds ± 29 nm, the correction coefficient increases, and the effect of correcting the scanner spectral sensitivity between machines cannot be expected.

7A and 7B are configuration diagrams showing examples of handling the scanner correction chart 70 and the printer correction pattern 80 in the printer correction mode.
The scanner correction chart 70 shown in FIG. 7A is handled so as to be placed on the document placement portion 41 or the platen glass 51 in the printer correction mode. The scanner correction chart 70 is prepared in advance, and is placed on the platen glass 51 where the ADF 201 is lifted, with the Δ mark indicating the head thereof facing up.

  The printer correction pattern 80 shown in FIG. 7B is handled so as to be placed on the document placement portion 41 or the platen glass 51 in the printer correction mode. The printer correction chart 80 is image-formed and output from the printer unit 60. Similarly, on the platen glass 51 where the ADF 201 is lifted, for example, the Δ mark indicating the top of the platen glass 51 is turned up with the printing surface facing down. Placed.

8A and 8B are perspective views showing an example of forming the gradation patch pattern PS in the printer correction mode.
A gradation patch pattern PS is formed on the intermediate transfer belt 6 shown in FIG. 8A in the printer correction mode. The gradation patch pattern PS is formed by the above-described image forming units 10Y, 10M, and 10C in the belt rotation direction (sub-scanning direction), for example, in the order of YMCK colors.

  An image density sensor 12 is provided at a position where the image forming surface of the intermediate transfer belt 6 can be seen, and detects the image density of the gradation patch pattern PS on the intermediate transfer belt 6. As the image density sensor 12, a reflection type optical sensor is used as shown in a wavy circle diagram of FIG. 8B. The reflective optical sensor includes a light emitting element and a light receiving element (not shown). Incident light (measurement light) is emitted from the light emitting element to the gradation patch pattern PS on the intermediate transfer belt 6. The reflected light from the gradation patch pattern PS is received by the light receiving element, and the density detection signal S1 is output.

  FIG. 9 is a graph showing an example of output characteristics of the image density sensor 12. In FIG. 9, the vertical axis represents XYZ data (RGB colorimetric approximation). The XYZ data is obtained by reading the printer correction pattern 80 output from the printer unit 60 with the scanner unit 102 and converting the RGB scan data output from the scanner unit 102 into colorimetric values (XYZ values). The horizontal axis represents a sensor output value (amount of reflected light) in the image density sensor 12 and indicates the ratio of the intensity of incident light to outgoing light. The sensor output value is a density detection signal S1 including an RGB color signal component (corresponding to an RGB colorimetric value). A solid line is a sensor output value-XYZ data conversion curve calculated from a regression coefficient (sensor output correction coefficient), and is a curve for converting the sensor output value of the image density sensor 12 into XYZ data. A sensor output value (amount of reflected light) can be converted into XYZ data (colorimetric value; XYZ value) by establishing an approximate expression from the relationship between the two.

  In this example, the CPU 33 acquires (RGB) ′ scan data (second gradation correction data) obtained by reading by the scanner unit 102 after correction, and the printer unit 60 based on the (RGB) ′ scan data. The output value of the image density sensor 12 is corrected. For example, when the scanner unit 102 obtains XYZ data as a comparison reference, the printer unit 60 forms (draws) a gradation patch pattern PS similar to the printer correction pattern 80 on the intermediate transfer belt 6 and outputs the sensor output. It is made to get a value. A graph as shown in FIG. 9 can be drawn by using the sensor output value and the XYZ data as the comparison reference from the scanner unit 102 described above. The regression coefficient is recalculated from this graph. By this recalculation, a regression coefficient (sensor output correction coefficient) for converting the sensor output value into XYZ data can be newly obtained. Here, based on the newly obtained sensor output correction coefficient, an image can be formed and output with an appropriate toner (image) density.

  Here, the relationship between the RGB values handled by the scanner unit 102 and the XYZ values handled by the colorimeter will be described. The scanner unit 102 can usually acquire RGB scan data (RGB values). XYZ data (XYZ values) can be measured with the colorimeter. That is, the RGB value can be compared with the XYZ value, and the RGB value can be converted into the XYZ value from the relational expression (first gradation correction data). Note that the RGB value and the XYZ value are close to the straight line because the detection wavelength is approximate.

Next, the relationship among the color material (YMCK) of the printer unit 60, the colorimetric values (XYZ) in the colorimeter, and the detected color (RGB) in the scanner unit 102 is specified.
[Color material of printer section] [Colorimetric value] [Detection color of scanner section]
Y color ← → Z value ← → B color M color ← → Y value ← → G color C color ← → X value ← → R color BK color ← → Y value ← → G color

  For example, for the Y color that is the color material of the printer unit 60, the XYZ value in the colorimeter is sensitive to the wavelength in terms of the Z value. Also, because of the complementary color relationship, the B color is sensitive to the wavelength in terms of RGB values with respect to the Y color. Therefore, when correcting the output value of the image density sensor 12, the Y patch gradation (density) is detected by the value of the B color channel of the scanner unit 102. Further, the Z value of the values (XYZ values) obtained by measuring the Y patch gradation with the colorimeter is used.

  For example, when creating the first gradation correction data, the relationship between the value detected by the B color channel of the scanner unit 102 and the Z value of the colorimeter is obtained. When creating the second gradation correction data, the Z value (equivalent) calculated by correcting the value detected by the B color channel of the scanner unit 102 with the first gradation correction data, the sensor output value, Seeking the relationship. Thereby, the output value of the image density sensor 12 can be converted into a Z value (corresponding). Since BK color has no wavelength dependency, any color can be converted. However, normally, a G color channel and a Y value having high human visibility characteristics are used.

  Next, an image processing method according to the present invention will be described. This embodiment is different from the conventional method in that the printer correction mode is executed using a chromatic scanner correction chart 70 instead of the gray scale chart. In the scanner correction chart 70, a chromatic gradation patch pattern PS that is “approximate” to the reflection wavelength of the (primary color) color material of the printer unit 60 is recorded (printed or the like). Further, reference colorimetric data (reference XYZ values) obtained by using the colorimeter to obtain the scanner correction chart 70 in advance is stored in the nonvolatile memory 39 and prepared. This is because the gradation correction of the scanner unit 102 is executed prior to the printer gradation correction.

  That is, it is preferable that the printer correction pattern 80 obtains the XYZ values by measuring the color with a colorimeter. Cost. Therefore, the scanner unit 102 is used as a jig without using a measuring instrument, and XYZ values are obtained, and the gradation correction of the scanner unit 102 is performed with reference XYZ values stored in advance in the nonvolatile memory 39. .

  These will be described separately under the printer correction conditions when the image density sensor is replaced or manufactured (initial) and when the image density sensor is normally used.

[When replacing the image density sensor and manufacturing]
FIG. 10 is a flowchart (main routine) showing an example of image processing according to the printer correction mode at the time of image density sensor replacement and manufacturing. FIG. 11 is a flowchart (subroutine) showing an example of correction processing of the scanner unit 102, and FIG. 12 is a flowchart (subroutine) showing an example of correction processing of the printer unit 60.

  First, in step A1 of the flowchart shown in FIG. 10, the CPU 33 executes printer correction mode setting processing. When the image density sensor 12 is replaced, the printer correction mode is set for the scanner unit 102 and the printer unit 60. The printer correction mode is set by operating the operation setting unit 14 by the user.

  After setting the printer correction mode, the user sets the chromatic scanner correction chart 70 on the document placing portion 41 or the platen glass 51 as shown in FIG. 7A. Next, in step A2, the scanner unit 102 executes reading processing of the scanner correction chart 70 and acquires RGB scan data. The scanner unit 102 transfers the RGB scan data obtained by the reading process to the image memory 37 or the nonvolatile memory 39 and stores it.

  Thereafter, the process proceeds to step A3, and the CPU 33 corrects the scanner unit 102 based on the RGB scan data. For example, in step B1 of the flowchart shown in FIG. 11, the CPU 33 reads the RGB scan data from the image memory 37 or the nonvolatile memory 39 and develops it in the RAM 32, analyzes the reference position on the scanner correction chart 70, and determines the reference position. taking measurement. Next, in step B2, the CPU 33 sets an analysis region (point) in the gradation portion on the scanner correction chart 70, executes RGB detection processing in the analysis region, and obtains an RGB average value of each gradation patch pattern.

  Then, the process proceeds to step B <b> 3, and the CPU 33 reads the reference XYZ values of the scanner correction chart 70 stored in advance in the nonvolatile memory 39. Thereafter, the process proceeds to step B4, and the CPU 33 calculates a relational expression for approximating the RGB average value of each gradation patch pattern obtained in step B2 to the reference XYZ value read from the nonvolatile memory 39 in the previous step B3. For example, an approximate correction equation (Nth order regression equation) is obtained by a calculation method such as a least square method or spline interpolation. This approximate correction formula is a scanner gradation correction coefficient. Since the detection wavelengths of the RGB value and the XYZ value are relatively approximate, this approximate correction formula is close to a straight line.

  Thereafter, in step B5, the CPU 33 incorporates the scanner gradation correction coefficient into the scanner gradation conversion device (table), is reflected in the conversion table numerical value, and is used when the scanner unit 102 performs gradation correction. The scanner gradation conversion table is composed of, for example, the nonvolatile memory 39, and is used and calculated when correcting document reading data (RGB scan data) obtained from the scanner unit 102 in the normal document scanning process. . By correcting the original reading data with such a scanner gradation correction coefficient, it is possible to acquire original reading data having no machine difference.

  Then, the process returns to step A3 shown in FIG. 10, and then the process proceeds to step A4, where the printer unit 60 outputs a chromatic printer correction pattern 80. The printer correction pattern 80 is output in a state where the printer γ correction processing is not performed. At this time, the image forming unit 10Y of the printer unit 60 forms a Y-color gradation patch pattern on the photosensitive drum 1Y, and the image forming unit 10M forms an M-color gradation patch pattern on the photosensitive drum 1M. In the image forming unit 10C, a C-color gradation patch pattern is formed on the photosensitive drum 1C. In the image forming unit 10K, a BK-color gradation patch pattern is formed on the photosensitive drum 1K.

  These YMCK color tone patch patterns are primarily transferred from the photosensitive drums 1Y, 1M, 1C, and 1K to the intermediate transfer belt 6. The YMCK tone patch pattern PS on the intermediate transfer belt 6 is secondarily transferred onto, for example, a sheet fed from the sheet feeding cassette 20A. The YMCK color tone patch pattern PS after the secondary transfer is fixed by the fixing device 17 and discharged. As a result, the printer correction pattern 80 of YMCK color can be output from the printer unit 60.

  In this example, the printer correction pattern 80 is a YMCK single color measurement output image. Considering the density gradient in the main scanning direction, the left and right patterns are the same. The left and right ends are YMC gray. In addition, the high density portion of one pattern is shifted by 1/3 of the drum cycle so as not to be affected by the cycle unevenness of the photosensitive drum. In this example, each column is composed of a gradation patch pattern having 10 patterns in total, 30 × 2 (left and right patches), 26 actual gradations, and three white and high density portions (see FIG. 4). ).

  Since the arrangement of the YMCK colors in the printer correction pattern 80 is constant (specified), the CPU 33 identifies in advance which color and gradation gradation patch pattern PS exists at which position. is made of. Further, as shown in FIG. 7B, the user sets (places) a chromatic printer correction pattern (output result) 80 on the document placing portion 41 or the platen glass 51. At this time, the Δ mark of the output result is aligned on the platen glass 51, and then the start button is pressed.

  Then, returning to step A5 shown in FIG. 10, using the above-mentioned start button as a trigger, the CPU 33 executes the reading process by the scanner unit 102 after correcting the printer correction pattern 80, and reads each gradation patch pattern PS. (RGB) 'scan data is acquired.

  Thereafter, the process proceeds to step A6, where the CPU 33 converts the (RGB) ′ scan data (second gradation correction data) into XYZ data based on the RGB scan data (first gradation correction data) acquired in step A3. Convert. In step A7, the CPU 33 performs gradation correction on the sensor output value of the image density sensor 12 based on the XYZ data. For example, in order to convert the sensor output value into XYZ data in step C1 of the flowchart shown in FIG. 12, the CPU 33 receives and sets XYZ data as a comparison reference from the scanner unit 102.

  Next, a YMCK color tone patch pattern PS is formed (drawn) on the intermediate transfer belt 6 in step C2. For example, in the image forming unit 10Y, a Y-color gradation patch pattern is formed on the photosensitive drum 1Y, and in the image forming unit 10M, an M-color gradation patch pattern is formed on the photosensitive drum 1M, and the image forming unit 10C. The C tone patch pattern is formed on the photosensitive drum 1C. In the image forming unit 10K, a BK-color gradation patch pattern is formed on the photosensitive drum 1K.

  These YMCK color tone patch patterns are primarily transferred from the photosensitive drums 1Y, 1M, 1C, and 1K to the intermediate transfer belt 6. The YCMBK tone patch pattern PS on the intermediate transfer belt 6 reaches the area where the image density sensor 12 is disposed by the intermediate transfer belt 6 being conveyed in the sub-scanning direction.

  In step C 3, the image density sensor 12 detects (reads) the image density of the gradation patch pattern PS formed on the intermediate transfer belt 6, and outputs a density detection signal S 1 to the control unit 15. The control means 15 is provided with an A / D converter (not shown), and the density detection signal S1 is converted from analog to digital to become a sensor output value. The sensor output value after A / D conversion is output to the CPU 33.

  Next, in step C4, the CPU 33 corrects the sensor output value obtained from the image density sensor 12. At this time, the CPU 33 calculates a sensor output correction coefficient (printer γ sensor regression coefficient) based on the XYZ value obtained in advance in step A6 shown in FIG. 10 and the sensor output value obtained from the image density sensor 12. Calculate (calculate). At this time, the CPU 33 calculates a new regression coefficient in the sensor output value (reflected light amount) vs. XYZ data (value) conversion curve as shown in FIG. 9 by the method of least squares, spline interpolation, or the like. The newly obtained regression coefficient approximates the XYZ value measured by the colorimeter. Thereby, the sensor output correction coefficient of the image density sensor 12 is obtained. This sensor output correction coefficient is stored in the printer gradation conversion device.

[Normal use of image density sensor]
FIG. 13 is a flowchart illustrating an example of image processing according to the printer correction mode when the image density sensor is normally used. First, in step E1 of the flowchart shown in FIG. 13, the CPU 33 executes printer correction mode setting processing. When the image density sensor 12 is normally used, the printer correction mode is set for the printer unit 60. The printer correction mode is set by operating the operation setting unit 14 by the user.

  After setting the printer correction mode, a chromatic printer correction pattern 80 is formed on the intermediate transfer belt from the printer unit 60 in step E2. At this time, the image forming unit 10Y of the printer unit 60 forms a Y-color gradation patch pattern on the photosensitive drum 1Y, and the image forming unit 10M forms an M-color gradation patch pattern on the photosensitive drum 1M. In the image forming unit 10C, a C-color gradation patch pattern is formed on the photosensitive drum 1C. In the image forming unit 10K, a BK-color gradation patch pattern PS is formed on the photosensitive drum 1K.

  These YMCK color tone patch patterns PS are primarily transferred from the photosensitive drums 1Y, 1M, 1C, and 1K to the intermediate transfer belt 6. The YMCK color tone patch pattern PS on the intermediate transfer belt 6 is a YMCK single color measurement output image. Further, since the arrangement of the YMCK colors is specified, the CPU 33 can identify in advance which color and gradation gradation patch pattern PS exists at which position.

  In step E 3, the image density sensor 12 detects the image density of the printer correction pattern 80 on the intermediate transfer belt 7 and outputs a density detection signal S 1 to the control means 15. The density detection signal S1 is A / D converted into a sensor output value. In step E4, the sensor output value obtained in step E3 is corrected with the sensor output correction coefficient obtained in step C4 to obtain a colorimetric value (corresponding to an XYZ value).

  Thereafter, in step E5, the CPU 33 executes gradation correction of the printer unit 60 based on the output value of the corrected image density sensor 12. When the image density is adjusted based on the corrected output value of the image density sensor 12, a printer gradation with little machine-to-machine variation can be obtained, and an image of an optimum color can be formed and output.

  As described above, according to the color copying machine and the image processing method as the embodiment, the chromatic color gradation patch pattern that is “approximate” the reflection wavelength of the color material used in the printer unit 60 is formed. A scanner correction chart 70 is prepared, and a reference XYZ value of the scanner correction chart 70 is prepared. Based on this assumption, the CPU 33 executes the tone correction of the scanner unit 102 by the scanner correction chart 70 that approximates the wavelength of the chromatic (primary) color material of the printer unit 60 (printing, etc.) A printer correction pattern 80 of a specific chromatic color is output from the printer unit 60, and the output value of the image density sensor 12 of the printer unit 60 is obtained from (RGB) ′ scan data obtained by reading the printer correction pattern 80 by the scanner unit 102. It is made to correct.

  Therefore, it is possible to correct the output gradation of the printer unit 60 correctly in the state where the influence of the output difference due to the wavelength variation of the color filter of the scanner unit 102 is removed and compared with the case where the gray scale chart is used. it can.

  Further, according to the present invention, as shown in FIGS. 9 to 12, once, the relationship between the output value of the image density sensor 12 and the colorimetric value (XYZ value) (RGB data = second gradation correction). If the data) is set, a gradation patch pattern PS is created by the printer unit 60 as shown in FIG. 13 and read by the image density sensor 12 as shown in FIG. The RGB data after the A / D conversion of the signal S1 is converted into a colorimetric value (XYZ value) based on the RGB scan data, and the output density of the image density sensor 12 is corrected from the value, and then the corrected image density The gradation of the printer unit 60 can be corrected based on the output value of the sensor 12.

  Therefore, during normal use of the image density sensor, the printer gradation correction can be executed by the operation inside the color copying machine, and the printer gradation correction chart can be output and read processing can be omitted. The gradation correction of the printer unit 60 can be performed with quick and accurate XYZ data (colorimetric values).

  When there is a replacement work due to a sensor failure or the like, the relationship between the output value of the image density sensor 12 and the colorimetric value (XYZ value) (RGB data = second gradation correction data) is set again. Then, the above procedure can be restored.

  Here, it will be described that the case where the scanner correction chart 70 is used is superior to the case where the gray scale chart is used. FIG. 14 is a graph showing an example of G color scanner sensitivity × M color material absorption rate wavelength characteristics, and the G color and M which are complementary colors in the spectral sensitivity of the scanner unit 102 and the color material absorption characteristics of the printer unit 60. The graph which integrated the relative sensitivity I of color and reflectance (rho) is shown.

  In FIG. 14, the vertical axis represents relative sensitivity I ′ (= 0 to 80) [%], and the horizontal axis represents wavelength λ [nm]. In this example, a color copying machine having a certain CCD unit is compared with a color copying machine having another CCD unit in which the wavelength variation of the color filter occurs. The solid line represents the (G × M) scanner sensitivity colorant absorption wavelength characteristic in a color copying machine having a certain CCD unit. The spectral sensitivity I of G color in the scanner unit 102 and M color in the printer unit 60. It is an integrated value with the reflectance ρ of the color material. The (G × M) color has a peak sensitivity absorption wavelength characteristic in the vicinity of a wavelength of 545 nm.

  The wavy line is the (G ′ × M) color scanner sensitivity color material absorption wavelength characteristic in the color copying machine having other CCD units, and the G ′ color spectral sensitivity I in the scanner unit 102 and the printer unit 60. Is an integrated value with the reflectance ρ of the M color material. The (G ′ × M) color has a peak sensitivity absorption wavelength characteristic around a wavelength of 550 nm.

  According to the G color scanner sensitivity × M color material absorption wavelength characteristic example shown in FIG. 14, the G ′ color is the peak of the main wavelength with respect to the G color, that is, the (G ′ × M) color is (G × M ) The peak value is lower than the peak sensitivity absorption wavelength characteristic of the color. In addition, the graph shape near the wavelength of 600 nm is different. Comparing the integrated values (totals) of the relative sensitivities I ′, the (G × M) color is 665, but the G ′ color × M color is 652. Incidentally, the relative ratio is 97.05%. As described above, when the integral value of the (G × M) color and the integral value of the (G ′ × M) color are compared, it can be seen that “there is a difference of just over 2%”.

  In this example, in the color copying machine having a certain CCD unit, the relative sensitivity I and the reflectance ρ of the G color and M color which are complementary colors in the spectral sensitivity of the scanner unit 102 and the absorption characteristics of the color material of the scanner correction chart 70. Similarly, the maximum value (main wavelength) of the integrated values, the spectral sensitivity of the scanner unit 102 in the color copying machine having other CCD units, and the absorption characteristics of the color material of the scanner correction chart 70 are complementary colors. The maximum value (main wavelength) of values obtained by similarly integrating the relative sensitivity I and reflectance ρ of the color and the M color are compared to find the difference, and the correction effect on the gray scale chart is evaluated.

  In this evaluation example, relative sensitivity I and reflectance ρ of complementary colors are integrated in the spectral sensitivity of the scanner unit 102 and the color material absorption characteristics of the scanner correction chart 70 in a color copying machine having a certain CCD unit. The maximum value (main wavelength), the spectral sensitivity of the scanner unit 102 in the color copying machine having other CCD units, and the color material absorption characteristics of the scanner correction chart 70, the relative sensitivities I of complementary colors and The difference from the maximum value (main wavelength) obtained by integrating the reflectance ρ is 5 nm. This wavelength difference = 5 nm is an error when the printer unit 60 is corrected by the conventional gray scale chart. Incidentally, when the conventional gray scale chart is used, both of them are evaluated as having no wavelength difference.

  In the method of the present invention, in the spectral sensitivity of the scanner unit 102 and the absorption characteristics of the color material of the printer unit 60, the maximum value (main wavelength) of the values obtained by integrating the values of the G color and M color that are complementary colors, and the scanner unit 102 In the spectral sensitivity and the absorption characteristic of the color material of the scanner correction chart 70, the difference between the maximum value (main wavelength) obtained by integrating the values of the G color and M color that are complementary colors is within ± 20 nm (the difference is Therefore, the difference in scanner spectral sensitivity between machines can be corrected.

  In this way, the gradation correction of the printer unit 60 can be executed with higher accuracy than when using a gray scale chart. Therefore, since the difference between the gradation correction machines of the printer unit 60 can be absorbed, the printer gradation difference between machines such as the color copying machine 100 and the color multifunction peripheral can be reduced.

  The present invention is preferably applied to a color digital copying machine or a multifunction machine having a function of executing gradation correction of a printer unit based on a scanner gradation correction chart.

1 is a conceptual diagram illustrating a configuration example of a color copying machine 100 to which an image forming apparatus as an embodiment is applied. 2 is a block diagram illustrating a configuration example of a control system of the color copying machine 100. FIG. 4 is a top view illustrating a configuration example of a scanner correction chart 70. FIG. It is a graph which shows the example of the spectral sensitivity characteristic of each color of R, G, B in a scanner part. FIG. 6 is a graph showing an example of absorption (spectral reflection) characteristics of Y, M, and C color materials used in the printer unit 60. FIG. 6 is a graph showing an example of RGB color scanner sensitivity × YMC color material absorption rate wavelength characteristics. (A) and (B) are configuration diagrams showing examples of handling the scanner correction chart 70 and the printer correction pattern 80 in the printer correction mode. (A) And (B) is a perspective view which shows the example of formation of the gradation patch pattern PS at the time of printer correction mode. 6 is a graph showing an example of output characteristics of the image density sensor 12. FIG. 6 is a flowchart (main routine) illustrating an example of image processing in a printer correction mode. 4 is a flowchart (subroutine) showing an example of correction processing of the scanner unit 102; 6 is a flowchart (subroutine) showing an example of correction processing of the printer unit 60; 6 is a flowchart illustrating an example of image processing according to a printer correction mode during normal use of an image density sensor. FIG. 6 is a graph showing an example of G color scanner sensitivity × M color material absorption rate wavelength characteristics.

Explanation of symbols

1Y, 1M, 1C, 1K Photosensitive drum (image forming body)
2Y, 2M, 2C, 2K charging means (image forming means)
3Y, 3M, 3C, 3K exposure means (image forming means)
4Y, 4M, 4C, 4K Developing means (image forming means)
6 Intermediate transfer belt (image forming body)
DESCRIPTION OF SYMBOLS 11 Document reading part 14 Operation setting means 15 Control means 17 Fixing means 18 Display means 30 Paper feed means 33 CPU (control means)
36 Image processing means 37 Image memory (storage means)
39 Nonvolatile memory (storage means)
48 Operation panel 60 Printer section (image forming means)
100 color copier (image forming device)
101 Copier body 102 Scanner unit (image reading means)
201 Automatic Document Feeder 202 Document Image Scanning Exposure Device

Claims (10)

A chromatic chart for image reading system correction,
Image reading means for acquiring first gradation correction data by reading the chart;
Control means for correcting the image reading means based on first gradation correction data acquired by the image reading means;
Image forming means having an image density detection sensor and forming and outputting a chromatic pattern for image forming system correction;
The control means includes
Reading the pattern output from the image forming unit by the corrected image reading unit to obtain second gradation correction data;
An image forming apparatus, wherein an output value of a sensor of the image forming unit is corrected based on the second gradation correction data. The image reading system correction chart is formed with a chromatic pattern that “approximates” the reflection wavelength of the color material used in the image forming means,
The wavelength of the pattern is
In the spectral sensitivity of the image reading unit and the absorption characteristics of the color material of the image forming unit, the maximum value of the values obtained by integrating the relative sensitivity and reflectance of colors in complementary colors, the spectral sensitivity of the image reading unit, and the image In the absorption characteristic of the color material of the chromatic color chart for correcting the reading system, a difference from the maximum value of the values obtained by integrating the relative sensitivity and the reflectance of the complementary color is within ± 20 nm. The image forming apparatus according to claim 1.   The image forming apparatus according to claim 1, further comprising a storage device that stores colorimetric data obtained by performing colorimetry on the image reading system correction chart. The control means includes
When correcting the gradation of the image forming unit,
A patch image is formed on the image carrier by the image forming means,
Patch image data is obtained by detecting the image density of the patch image formed on the image carrier,
The image forming apparatus according to claim 1, wherein a sensor output correction coefficient is calculated based on the patch image data and the second gradation correction data. The image forming means forms a chromatic pattern for image forming system correction on the image forming body,
The image density detection sensor detects the pattern image density formed on the image forming body,
The control means corrects a sensor output value obtained from the sensor with the sensor output correction coefficient, and corrects the gradation of the image forming means based on the corrected sensor output value. 5. The image forming apparatus according to 4. Reading a chromatic color chart for image reading system correction to obtain first gradation correction data;
Correcting the image reading system based on the acquired first gradation correction data;
On the other hand, forming and outputting a chromatic pattern for image forming system correction in an image forming system having an image density detection sensor; and
Reading the pattern formed and output by the corrected image reading system to obtain second gradation correction data;
And a step of correcting an output value of the sensor of the image forming system based on the second gradation correction data. The image reading system correction chart is formed with a chromatic pattern that “approaches” the reflection wavelength of the color material used in the image forming system,
The wavelength of the pattern is
In the spectral sensitivity of the image reading unit and the absorption characteristics of the color material of the image forming unit, the maximum value of the values obtained by integrating the relative sensitivity and reflectance of colors in complementary colors, the spectral sensitivity of the image reading unit, and the image In the absorption characteristic of the color material of the chromatic color chart for correcting the reading system, a difference from the maximum value of the values obtained by integrating the relative sensitivity and the reflectance of the complementary color is within ± 20 nm. The image processing method according to claim 6.   The image processing method according to claim 6, wherein colorimetric data obtained by colorimetric measurement of the image reading system correction chart is prepared. When correcting the gradation of the image forming system,
Forming a patch image on the image forming body in the image forming system;
Detecting the image density of the patch image formed on the image forming body to obtain patch image data;
The image processing method according to claim 6, further comprising a step of calculating a sensor output value correction coefficient based on the patch image data and the second gradation correction data. Forming a chromatic pattern for image forming system correction on the image forming body in the image forming system;
Detecting the pattern image density formed on the image forming body with a sensor for detecting image density;

Correcting the sensor output value obtained from the sensor with the sensor output correction coefficient;
The image processing method according to claim 9, further comprising a step of correcting a gradation of the image forming system based on the sensor output value after correction.