JP2014072823A - Control device, image formation device, control method, and control program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reproduce a multiple color with accuracy over a long time period even when printing on paper of a different type from one preliminarily stored without limiting a type of paper.SOLUTION: After an image indicated by image information is searched for a colorimetry adaptive area suitable for colorimetry, an algorithm representing a relation between an output color preliminarily stored for each of Y, C, M, K toner images and a setting value of an image processing parameter is calculated. On the basis of a difference between a measurement color that is a result of colorimetry of the colorimetry adaptive area of a multiple color toner image formed on the basis of the image information and a reference color that is an original color, an area ratio in the colorimetry adaptive area of the Y, C, M, K toner images in the multiple colors toner image, a colorimetry value of a recording sheet that is preliminarily stored and the colorimetry result of the recording sheet used for the colorimetry, and a current setting value of the image processing parameter, a correction amount for the image processing parameter for further reducing the difference is determined. Then, the image processing parameter is corrected on the basis of the correction amount.

Description

  The present invention relates to an image forming apparatus such as a copying machine, a facsimile, and a printer, and a control device, a control method, and a control program used therefor.

  In an image forming apparatus that forms a toner image by an electrophotographic method, if the environment such as temperature and humidity changes or if a continuous printing operation is performed over a long period of time, the toner adhesion amount per unit area with respect to the toner image is increased. It may change and change the image density.

In a color image forming apparatus that forms a color image, if the toner adhesion amount fluctuates for each of a plurality of primary colors, the color tone of a multi-order color (for example, L ^* value and a ^* value in the L ^* a ^* b ^* color system). And b ^* value) are disturbed.

  Specifically, colors reproduced by the color image forming apparatus are roughly classified into primary colors and multi-order colors. The primary color is a color expressed by only one type of toner. For example, in a configuration using four types of toners of yellow (Y), magenta (M), cyan (C), and black (K), it is expressed by only one of Y, M, C, and K toners. The color to be performed is the primary color.

  In contrast, a multi-order color is a color expressed using two or more types of toner. Multi-order colors are reproduced by superimposing a plurality of primary color toner images. However, if the amount of toner attached to each primary color toner image fluctuates, the color tone of the multi-order color toner image is determined by the superposition of these primary color toner images. Will be disturbed.

  Therefore, Patent Documents 1 and 2 propose image forming apparatuses that periodically perform the following processing for each primary color of Y, M, C, and K. That is, a tone reproduction curve TRC (Tone Reproduction Curve) indicating the relationship between the input density value and the output density value of the primary color image data is stored in the data storage unit, and the input density value is stored in the tone reproduction curve. By correcting and outputting in accordance with the TRC, it is possible to form a primary color toner image that well reproduces the original color tone.

  However, if the image forming performance changes due to environmental fluctuations, etc., the primary color reproduction accuracy will be reduced. Therefore, at a regular timing, a test print is performed to form a test toner image of a specific multi-order color on a recording sheet, and the color of the test toner image on the test print paper is measured with a spectrometer and the original color. The difference is calculated.

  Then, based on the difference and the current gradation reproduction curve TRC, a correction amount necessary for matching the color measurement result with the original color is obtained. Then, the gradation reproduction polarity TRC is corrected based on the correction amount. By periodically performing such processing for Y, M, C, and K, it is possible to form a multi-color toner image having a stable color tone over a long period of time.

  However, in such a configuration, since the test print paper that outputs the test toner image is discharged separately from the print paper that outputs the image based on the user's command, the user is forced to sort the two. There is a problem that such sorting work is very time-consuming.

  Therefore, the present inventors have proposed the following image forming apparatus (Patent Document 3). The image forming apparatus disclosed in Patent Document 3 first includes a colorimetric adaptation region suitable for colorimetry from an image indicated by image information acquired by data reception from an external device or image reading based on a user command. An area search process for searching for is performed. In addition, among all the regions of the multi-color toner image actually formed based on the image information, a plurality of colorimetric adaptive regions specified by the region search process are respectively measured by a spectrometer to obtain a plurality of colorimetric results. . The data storage means stores tone reproduction curves TRC for Y, M, C, and K, respectively, as control parameters.

  Based on the gradation reproduction curve TRC and a result obtained by obtaining a difference from the original color for each of a plurality of color measurement results, a curve correction amount for further reducing the color difference is determined. Then, the gradation reproduction curve TRC is corrected based on the determined curve correction amount. Such processing is performed for Y, M, C, and K, respectively. In such a configuration, the test print paper is output by appropriately correcting the gradation reproduction curve TRC based on the result of colorimetric measurement of the colorimetric adaptation region of the print paper image output based on the user's command. Therefore, it is possible to accurately reproduce multi-order colors. Therefore, it is possible to form a multi-color toner image having a stable color tone for a long period of time without forcing the user to sort test prints.

  However, the image forming apparatus disclosed in Patent Document 3 has room for improvement as described below. That is, in order to determine the curve correction amount for further reducing the color difference based on the gradation reproduction curve TRC and the result of obtaining the difference from the original color for each of the plurality of color measurement results, For a plurality of multi-order color toner images, it is necessary to store a quantitative relationship between the TRC correction amount and the color change as a model in advance.

  In order to construct this model, it is necessary to actually measure a color by actually printing a test color patch on paper as offline processing. However, when the type of paper actually used by the user for printing is different from the paper used for model construction, the quantitative relationship between the TRC correction amount and the color change also differs from the model stored in advance.

  For example, yellow printed on white paper and yellow printed on reddish paper are perceived as different colors by human eyes even if the Y density in the digital data is the same. Therefore, since it is necessary to construct a model for each paper type, not only a great amount of labor is required, but there is a problem that the accuracy of TRC correction cannot be guaranteed for paper for which no model is prepared. Arise.

  Up to now, the problems that occur in the image forming apparatus that corrects the gradation reproduction curve TRC as a control parameter have been described. However, control parameters that are different from the gradation reproduction curve, such as a developing bias and a latent image writing intensity, are corrected. The same problem may occur in an image forming apparatus that stabilizes color reproducibility.

  The present invention has been made in view of the above background, and the multi-colors are long even when printed on a paper of a different type from that stored in advance without limiting the type of paper used by the user. An object of the present invention is to provide an image forming apparatus that can be accurately reproduced over a period of time, and a control device, a control method, and a control program used therefor.

  In order to achieve such an object, a control apparatus according to the present invention includes an image forming unit that forms a primary color toner image based on image information, and an image information processing unit that processes image information input to the image forming unit. And a transfer unit that obtains a multi-color toner image based on the primary color toner image, and a control device for the image forming apparatus, which is suitable for colorimetry from an image indicated by the image information. Area search means for searching for a color adaptation area; (1) an output color stored in advance for each of a plurality of multi-order color toner images and a set value of an image processing parameter for processing an image by the image information processing means; Information representing the relationship; (2) the difference between the measured color obtained by measuring the colorimetric adaptation region and the reference color; and (3) the colorimetric adaptation region of the primary color toner image in the multi-color toner image. (4) Store in advance The image processing for reducing the difference based on the colorimetric value of the recording sheet and the colorimetric result of the recording sheet used for colorimetry, and (5) the current setting value of the image processing parameter A correction amount determining unit that determines a correction amount of the parameter; and a parameter correcting unit that corrects the image processing parameter based on the correction amount.

  According to the present invention, a multi-order color can be accurately reproduced over a long period of time even when printing on a different type of paper stored in advance without limiting the type of paper used by the user. it can.

1 is a schematic configuration diagram illustrating a main part of a printer according to an embodiment of the present invention. FIG. 3 is an enlarged configuration diagram illustrating an image forming unit of a printer. It is a block diagram which shows the electrical connection of the various apparatuses in a printer. FIG. 2 is a block diagram illustrating a main body control unit of the printer and its surrounding configuration. It is a flowchart which shows the processing flow of the color reproduction accuracy improvement process implemented by the main body control part. It is a schematic diagram which shows an example of the image represented by the image information provided from a user. It is a schematic diagram which shows the colorimetry adaptive area searched from the image represented by the image information provided by the user. The relationship between the gradation reproduction curves τ (t) and τ (t + 1) at the times t and t + 1, the difference δ (t), and the gradation reproduction curve τ (t + n) after time n when L = 32 is shown. FIG.

  Hereinafter, the configuration according to the present invention will be described in detail based on the embodiment shown in FIGS.

(Control device overview)
The control apparatus according to the present embodiment includes an image forming unit (such as the image forming unit 103) that forms a primary color toner image based on image information, and an image information processing that processes image information input to the image forming unit. Means (print controller 410, etc.) and transfer means (primary transfer roller 106, intermediate transfer belt 105, secondary transfer roller 108, etc.) for acquiring a multi-color toner image based on the primary color toner image. A control device (main body control unit 406) of the image forming apparatus (printer 100), and region search means (region search unit 406d) for searching for a colorimetric adaptation region suitable for colorimetry from an image indicated by image information; (1) Information indicating the relationship between the output color stored in advance for each of a plurality of multi-color toner images and the setting value of the image processing parameter for processing the image by the image information processing means Algorithm), (2) the difference between the measured color obtained by measuring the colorimetric adaptation region and the reference color, and (3) the area ratio of the primary color toner image in the colorimetric adaptation region in the multi-color toner image, (4) The difference is made smaller based on the colorimetric value of the recording sheet stored in advance and the colorimetric result of the recording sheet used for colorimetry, and (5) the current setting value of the image processing parameter. Correction amount determining means (measurement value acquisition unit 406a, algorithm calculation unit 406c, RGB / L ^* a ^* b ^* conversion unit 406f, paper color acquisition unit 406g, correction amount determination unit 406b) ) And parameter correction means (parameter setting unit 406e) for correcting the image processing parameter based on the correction amount.

  That is, instead of forming a test image for measuring multi-order colors and performing color measurement, the output image is measured based on a user command. Specifically, a colorimetric adaptive region suitable for colorimetry is searched from an image output based on a user command by the region search means, and colorimetry is performed on the colorimetric adaptive region, Further, the color of the paper used for printing is measured.

  Then, the correction amount determination means offline the plurality of multi-color toner images in order to determine the image processing parameter correction amount for reducing the difference from the original color for each of the plurality of color measurement results. The measured model representing the quantitative relationship between the image processing parameter correction amount and the color change, and the color information of the paper used for the measurement are stored in advance.

  Further, the correction amount determination means obtains the difference between the model stored in advance and the sheet color information, and the original color for each of the plurality of color measurement results, and as a result, the color information of the sheet used in printing, the color measurement adaptation area The correction amount of the image processing parameter for further reducing the difference is determined based on the area ratio of the primary color toner images and the current setting value of the image processing parameter.

  The image processing parameter is corrected based on the correction amount determined by the parameter correction unit. A color reproduction accuracy improving process for improving the color reproduction accuracy of the multi-color toner image is performed by using the corrected image processing parameter.

  In this way, based on the result of measuring the colorimetric adaptive region of the image formed based on the user's command without forming a test toner image for measuring the actually output multi-color, An appropriate correction amount of the image processing parameter is determined. Thereafter, the image processing parameter is corrected based on the determined correction amount.

(Configuration of image forming apparatus)
Hereinafter, an embodiment of an image forming apparatus to which the present invention is applied will be described. First, a basic configuration of the image forming apparatus according to the present embodiment will be described. The image forming apparatus according to the present embodiment is a color production printer that realizes color on-demand printing that outputs a large amount of color documents such as bills at high speed.

  Such a color production printer is used when, for example, invoices and receipts for tens of millions of telephone charges are issued in about one week. Continuous printing is performed in such a situation (several hundreds of high-speed prints per minute are continuously operated in units of tens of hours).

  FIG. 1 is a schematic configuration diagram showing a main part of a color production printer. In FIG. 1, only an image forming process part (process engine part) using an electrophotographic process for exposure, charging, development, transfer, and fixing in the entire color production printer 100 (hereinafter simply referred to as the printer 100). Is shown. In addition to the components shown in FIG. 1, the printer 100 includes a paper feeding device that supplies the recording paper 115 as a recording material, a manual tray for manually feeding the recording paper 115, and an image-formed recording. A paper discharge tray or the like (none of which is shown) for discharging the paper 115 is provided.

  The printer 100 is provided with an endless belt-like intermediate transfer belt 105 that is an intermediate transfer member. The intermediate transfer belt 105 is endlessly moved in the counterclockwise direction in the figure by the rotational driving of the support roller 112 having a function as a drive roller while being stretched around the four support rollers 112, 113, 114, and 119.

  Four image forming units 103Y, 103C, M, and K for each color of yellow (Y), cyan (C), magenta (M), and black (K) are disposed on the stretched portion of the intermediate transfer belt 105. ing. The image forming units 103Y, 103C, 103M, and 103K have substantially the same configuration except that the toner colors used are different. Note that the subscripts Y, C, M, and K added to the end of the reference numerals indicate members and devices for Y, C, M, and K.

  The image forming units 103Y, 103C, 103M, and 103K include drum-shaped photoreceptors 101Y, 101C, 101M, and 103K, developing devices 102Y, 102C, 103M, and K, a charging device that uniformly charges the photoreceptor. . In the loop of the intermediate transfer belt 10, primary transfer rollers 106 Y, C, M, and K are disposed at positions facing the photoconductors 101 Y, C, M, and K via the belt so that the belt is exposed to light. The body 101Y, C, M, K is pressed. As a result, primary transfer nips for Y, C, M, and K in which the photoconductors 101Y, C, M, and K abut on the intermediate transfer belt 105 are formed.

  Above the intermediate transfer belt 105, toner bottles 104Y, 104C, M, and K for storing Y, C, M, and K toners to be supplied into the developing devices 102Y, 102C, 102M, and 102K are disposed. .

  The charging devices of the image forming units 103Y, 103C, 103M, and 103K uniformly charge the surfaces of the photoreceptors 101Y, 101C, 101M, and 101K as latent image carriers to the same polarity as the charging polarity of the toner. In the figure, as an example of the charging device, a charging brush roller to which a charging bias is applied is shown in contact with or close to the photosensitive members 101Y, 101C, 101M, 101K, but other devices such as a scorotron charger are also shown. You may use the charging device of the structure.

  A latent image writing unit 200 is provided below the image forming units 103Y, 103C, M, and K. The latent image writing unit 200 drives a semiconductor laser (not shown) based on image information sent from an external personal computer or the like and emits Y, M, C, K writing light Lb. The writing light Lb is deflected in the main scanning direction by a polygon mirror (not shown), and the photosensitive members 101Y, 101C, 101M, and 101K as latent image carriers are optically scanned. As a result, electrostatic latent images for Y, C, M, and K are written on the surfaces of the uniformly charged photoreceptors 101Y, C, M, and K. The light source is not limited to a semiconductor laser, and may be an LED (light emitting diode), for example.

(Configuration of image forming unit)
Hereinafter, the configuration of the image forming units 103Y, 103C, 103M, and 103K will be described with reference to FIG. The four image forming units 103Y, 103C, 103M, and 103K have substantially the same configuration except that the color of the toner to be used is different, and FIG. 2 shows only one of the four. ing. The suffix (Y, C, M, K) at the end of the code is omitted without limiting which color unit. In the following description, the suffixes (Y, C, M, K) at the end of the reference numerals are omitted.

  The image forming unit 103 includes a charging device 301 for charging the photosensitive member 101, a developing device 102, a photosensitive member cleaning device 311, and the like around the photosensitive member 101. In the loop of the intermediate transfer belt 105, a primary transfer roller 106 is disposed at a position facing the photoconductor 101 through the belt. Instead of the primary transfer roller 106, a conductive brush shape or a non-contact corona charger may be employed.

  The charging device 301 is of a contact charging type employing a charging roller, and uniformly charges the surface of the photoconductor 101 by applying a voltage in contact with the photoconductor 101. As the charging device 301, a non-contact charging type using a non-contact scorotron charger or the like can be used.

  The developing device 102 contains a developer (not shown) containing a magnetic carrier and a nonmagnetic toner. As the developer, a one-component developer may be used. The developing device 102 can be broadly divided into a stirring unit 303 and a developing unit 304 provided in the developing case. In the agitation unit 303, a two-component developer (hereinafter simply referred to as “developer”) is conveyed while being agitated and supplied onto a developing sleeve 305 as a developer carrier.

  The stirring unit 303 is provided with two parallel screws 306. Between these two screws 306, a partition plate 309 is provided for partitioning so that both ends communicate with each other. Further, a toner density sensor 418 for detecting the toner density of the developer in the developing device 102 is attached to the developing case 308 that houses the developing sleeve 305, the two screws 306, and the like. On the other hand, in the developing unit 304, the toner in the developer attached to the developing sleeve 305 is transferred to the photoreceptor 101.

  The developing unit 304 is provided with a developing sleeve 305 that faces the photoreceptor 101 through the opening of the developing case, and a magnet (not shown) is fixedly disposed in the developing sleeve 305. A doctor blade 307 is provided so that the tip approaches the developing sleeve 305. In the present embodiment, the distance at the closest portion between the doctor blade 307 and the developing sleeve 305 is set to 0.9 [mm]. In the developing device 102, the developer is conveyed and circulated while being stirred by two screws 306, and is supplied to the developing sleeve 305. The developer supplied to the developing sleeve 305 is drawn up and held by a magnet. The developer pumped up by the developing sleeve 305 is conveyed as the developing sleeve 305 rotates, and is regulated to an appropriate amount by the doctor blade 307. The regulated developer is returned to the stirring unit 303.

  The developer thus transported to the developing area facing the photoconductor 101 is brought into a spiked state by a magnet and forms a magnetic brush. In the developing region, a developing electric field for moving the toner in the developer to the electrostatic latent image portion on the photoreceptor 101 is formed by the developing bias applied to the developing sleeve 305. As a result, the toner in the developer is transferred to the electrostatic latent image portion on the photosensitive member 101, and the electrostatic latent image on the photosensitive member 101 is visualized to form a toner image. The developer that has passed through the developing region is transported to a portion where the magnetic force of the magnet is weak, thereby leaving the developing sleeve 305 and being returned to the stirring unit 303. When the toner concentration in the stirring unit 303 becomes light by repeating such operations, the toner concentration sensor 418 detects this, and toner is supplied to the stirring unit 303 based on the detection result.

  The photoconductor cleaning device 311 includes a cleaning blade 312 made of polyurethane rubber, for example, which is disposed so that the tip of the cleaning blade 312 can be pressed against the photoconductor 101. In this embodiment, in order to improve the cleaning performance, a conductive fur brush 310 that contacts the photoconductor 101 is also used. A bias is applied to the fur brush 310 from a metal electric field roller (not shown), and the tip of a scraper (not shown) is pressed against the electric field roller. The toner removed from the photoconductor 101 by the cleaning blade 312 and the fur brush 310 is accommodated in the photoconductor cleaning device 311 and collected by a waste toner collecting device (not shown).

  In the image forming unit 103, the surface of the rotationally driven photoconductor 101 is uniformly charged by the charging device 301. Then, based on image information from the print controller 410 (see FIG. 3), the latent image writing unit 200 performs optical scanning with the writing light Lb to write an electrostatic latent image on the surface of the photoconductor 101. The electrostatic latent image is developed by the developing device 102 to become a primary color toner image having a primary color of Y, M, C, or K. This primary color toner image is primarily transferred from the surface of the photoreceptor 101 to the front surface of the intermediate transfer belt 105 in the primary transfer nip. The transfer residual toner adhering to the surface of the photoconductor 101 after passing through the primary transfer nip is removed by the photoconductor cleaning device 311.

  In FIG. 1 described above, the image forming units 103Y, 103C, 103M, and 103K form Y, C, M, and K toner images on the surfaces of the photoconductors 101Y, 101C, M, and K by the process described above. To do. These Y, C, M, and K toner images are primarily transferred while being superimposed on the front surface of the intermediate transfer belt 105 at the primary transfer nip for Y, M, C, and K. As a result, a four-color superimposed toner image is formed on the front surface of the intermediate transfer belt 105.

  Outside the loop of the intermediate transfer belt 105, a secondary transfer roller 108 that is in contact with a place where the intermediate transfer belt 105 is wound around the support roller 112 and forms a secondary transfer nip is formed. It is arranged. A secondary transfer bias having a polarity opposite to the charging polarity of the toner is applied to the secondary transfer roller 108. A pair of registration rollers is disposed below the secondary transfer nip, which feeds the recording paper 115 toward the secondary transfer nip at a timing synchronized with the four-color superimposed toner image of the intermediate transfer belt 105. . A four-color superimposed toner image on the intermediate transfer belt 105 is secondarily transferred onto the recording paper by the action of the secondary transfer bias and the nip pressure on the recording paper that has entered the secondary transfer nip. The four-color superimposed toner image is combined with the white color of the recording paper 115 to become a full-color toner image. A scorotron charger or the like may be used instead of the secondary transfer roller 108.

  Above the secondary transfer roller 108 in the figure, a fixing device 111 is provided for fixing the full color toner image transferred onto the recording paper 115 to the recording paper 115. The fixing device 111 has a configuration in which a pressure roller 118 is pressed against a heating roller 117. The fixing device 111 is a color measuring unit that performs color measurement using a full-color toner image formed on the recording paper P after passing through the fixing nip formed by the contact between the heating roller 117 and the pressure roller 118 as a test target. The spectrometer 109 is provided. Examples of the spectrometer 109 include those disclosed in Japanese Patent Application Laid-Open No. 2005-315883.

  A belt cleaning device 110 is disposed outside the belt loop. The belt cleaning device 110 is in contact with a portion where the intermediate transfer belt 105 is wound around the support roller 113 in the circumferential direction. Then, the toner adhering to the intermediate transfer belt 105 after passing through the secondary transfer nip is removed.

(Function block of image forming apparatus)
FIG. 3 is a block diagram showing the electrical connection of each unit in the printer 100. The printer 100 includes a main body control unit 406 that functions as a control device. The main body control unit 406 controls image forming operations using an electrophotographic process by driving and controlling the respective units. A main body control unit 406 includes a ROM (Read Only Memory) 405 that stores in advance fixed data such as a computer program via a bus line 409 in a CPU (Central Processing Unit) 402 that executes various calculations and drive control of each unit. A RAM (Random Access Memory) 403 that functions as a work area for storing various data in a rewritable manner is connected. The main body control unit 406 also includes an A / D conversion circuit 401 that converts information from the spectrometer 109, the toner concentration sensor 418, and the temperature / humidity sensor 417, which are color measuring means, into digital data. The circuit 401 is connected to the CPU 402 via the bus line 409.

  Connected to the main body control unit 406 is a print controller 410 that processes image data sent from a PC (Personal Computer) 411, a scanner 412, a FAX (Facsimile) 413, etc., and converts it into exposure data. The main body control unit 406 is connected to a drive circuit 414 that drives a motor and a clutch 415. Further, the main body control unit 406 generates a high voltage that generates a voltage necessary for image formation in the image forming unit (the image forming unit 103, the primary transfer device 106, the latent image writing unit 200, the secondary transfer roller 108, and the like). A device 416 is also connected.

  A parameter setting unit 404 is also connected to the main body control unit 406. The parameter setting unit 404 uses the laser intensity of the latent image writing unit 200 and the charging device 301 based on the result calculated by the CPU 402 based on information measured by the spectrometer 109 or the like in order to obtain a stable image density. Image processing parameters such as a charging applied voltage and a developing bias of the developing device 102 are changed.

  When printing is performed by the printer 100 according to information from the PC 411, print information including image data is transmitted from the PC 411 using a printer driver installed in the PC 411. A print controller 410 corresponding to image processing means receives print information including image data transmitted from the PC 411, processes the image data, converts it into exposure data, and outputs a print command to the main body control unit 406.

  Receiving the print command, the CPU 402 of the main body control unit 406 executes image formation control processing using an electrophotographic process by following the computer program stored in the ROM 405. More specifically, the CPU 402 of the main body control unit 406 drives the motor and the clutch 415 via the drive circuit 414, the support roller 112 is driven to rotate, and the intermediate transfer belt 105 is driven to rotate. At the same time, the CPU 402 of the main body control unit 406 performs an image forming unit (image forming unit 103, primary transfer device) using an electrophotographic process via the drive circuit 414, the high voltage generator 416, and the parameter setting unit 404. 106, the latent image writing unit 200, the secondary transfer roller 108, etc.).

  The main body control unit 406 drives the motor and the clutch 415 via the drive circuit 414 in accordance with the timing when the four-color superimposed toner image formed on the intermediate transfer belt 105 enters the secondary transfer nip as described above. Then, the recording paper 115 is supplied by controlling a paper feeding device (not shown). The recording paper 115 supplied from the paper feeding device is fed between the intermediate transfer belt 105 and the secondary transfer roller 108, and the secondary transfer roller 108 causes the composite toner image on the intermediate transfer belt 105 to be transferred onto the recording paper 115. Secondary transfer is performed. Thereafter, the recording paper 115 is conveyed to the fixing device 111 while being attracted to the secondary transfer roller 108, and heat and pressure are applied by the fixing device 111 to perform a toner image fixing process. The recording paper 115 that has passed through the fixing device 111 is discharged and stacked on a paper discharge tray (not shown). The transfer residual toner remaining on the intermediate transfer belt 105 after the secondary transfer is removed by the belt cleaning device 110.

(Configuration of main unit control unit)
Next, a characteristic configuration of the printer according to the present embodiment will be described. FIG. 4 is a block diagram showing the main body control unit 406 and the surrounding configuration (functional configuration related to parameter control processing). In the figure, a main body control unit 406 includes a measured value acquisition unit 406a, a correction amount determination unit 406b, an algorithm calculation unit 406c, an area search unit 406d, a parameter setting unit 406e, and RGB / L ^* a ^* b ^*. A conversion unit 406f and a paper color acquisition unit 406g are provided. Each of these units is not configured by hardware, but by a program stored in the data storage unit of the main body control unit 406.

  The print controller 410 also includes a 3D lookup table (hereinafter abbreviated as 3D-LUT) 410a, undercolor removal (hereinafter abbreviated as UCR) / gray component replacement (hereinafter abbreviated as GCR) 410b, and gradation reproduction curve. It has a storage unit 410c (hereinafter abbreviated as TRC) and a halftone processing unit 410d.

(Processing flow)
FIG. 5 is a flowchart showing a processing flow of color reproduction accuracy improvement processing (parameter control processing) performed by the main body control unit 406. In the color reproduction accuracy improving process, when a print job is started (step 101; YES), an area search process is performed (step S102). This area search process is a process for searching a colorimetric adaptive area suitable for multi-color measurement from the image based on the image information of the image to be output, and the area search unit 406d (see FIG. 4). ). Prior to this area search process, image information of an image to be output is acquired by the print controller 410 (see FIG. 4).

  Image information sent from the outside has pixel values representing the brightness of monochromatic components of R (red), G (green), and B (blue), respectively, for a plurality of pixels arranged in a matrix that form an image. However, the print controller 410 has the image information having pixel values representing the brightness of the single color components of C (cyan), M (magenta), Y (yellow), and K (black). Convert. Then, the converted image information is transferred to the area search unit 406d of the main body control unit 406.

  The area search unit 406d searches which area of the entire area of the image indicated by the image information is the colorimetric adaptive area that is a colorimetric target. After the search, when the recording paper on which the image is formed is sent into the fixing device 111 (see FIG. 1), the spectrometer 109 (see FIG. 3) performs colorimetry in the colorimetric adaptation region. The color measurement result is acquired by the measurement value acquisition unit 406a (see FIG. 4) of the main body control unit 406.

  The search for the colorimetric adaptation region is performed as follows. That is, a pixel at a predetermined position in the pixel matrix represented by the image information is set as a target pixel, and a region having a predetermined size centered on the target pixel is extracted as a partial region.

  For example, in the first extraction, for example, the pixel in the 21st column and the 21st row from the upper left in the pixel matrix having a resolution of 200 dpi is the pixel of interest, and a pixel of about 41 mm × 41 pixels having a size of about 5 mm square. An area is extracted as a partial area (corresponding to a square of 61 pixels on one side at 300 dpi). And the flatness which shows the flatness of the light and dark as the whole partial area is calculated, referring the pixel value (C, M, Y, K) of each pixel in the extracted partial area. As the flatness, those obtained by various calculation methods can be used.

  As a first example of flatness, one obtained by the following calculation method can be cited. That is, first, the variance of each pixel is obtained for C, M, Y, and K, respectively. Next, a value obtained by adding a negative sign to the sum of the variances is obtained as the flatness in the partial region.

  As a second example of flatness, a determinant of a variance-covariance matrix can be given. Specifically, for C, M, Y, and K, the variance and covariance at each pixel in the partial area are obtained. Next, a 4 × 4 variance-covariance matrix is constructed in which variance is arranged in the diagonal component and covariance is arranged in the non-diagonal component, and the determinant thereof is calculated. Then, a value obtained by adding a negative sign to the value of the determinant may be obtained as the flatness. This is because the spread of the distribution in the CMYK space can be evaluated by using the determinant of the variance-covariance matrix. Compared to the flatness of the first example described above, the color spread between different components can be evaluated.

  Further, as a third example of flatness, one using the frequency characteristics of color can be cited. Specifically, the Fourier transform is performed using each pixel value in the partial region, and the sum of the squares of the absolute values of the Fourier coefficients of the specific frequency is obtained. A flatness is obtained by adding a negative sign to this sum. A plurality of frequencies can be used for the specific frequency.

  In the flatness of the first example, there is a case in which a flat region cannot be identified for an image subjected to halftone processing due to the influence of the pattern of halftone processing. On the other hand, in the flatness of the third example, the flatness excluding the influence of halftone processing can be calculated by using the sum of squares of the absolute values of the Fourier coefficients of the specific frequency. The flatness is not limited to the first to third examples described so far, and a known flatness calculation technique can be used.

  When the flatness of the extracted partial areas is obtained, it is next determined whether or not all partial areas have been extracted (whether or not extraction of partial areas has been completed for all areas of the image). If it is determined that there is a partial area that has not yet been extracted, the position of the target pixel is shifted by one pixel in the right direction, and an area of about 5 mm square of 41 pixels × 41 pixels centered on it is obtained. Extract as a partial area. Similarly, the flatness of the color of the extracted partial area is calculated. Thereafter, when extracting the third, fourth, fifth,..., Nth partial area, the position of the target pixel is shifted by one pixel to the right. After shifting the position of the pixel of interest in the column direction from the right end of the matrix to the 21st position, the position of the pixel of interest in the column direction is returned from the left end of the matrix to the right to the 21st position. At the same time, the position in the row direction is shifted downward by one pixel. Thereafter, the process of shifting the position of the target pixel to the right by one pixel is repeated. As described above, the position of the target pixel is sequentially shifted like raster scanning to cover the entire area of the image.

  Instead of shifting the target pixel by one pixel, each partial area may be extracted so that the edges of the extracted partial areas do not overlap each other. For example, after extracting a partial region having a size of 41 pixels × 41 pixels centered on the pixel of interest in the 21st column and the 21st row, 41 pixels × centering on the pixel of interest in the 62nd column and the 62nd row A partial region having a size of 41 pixels is extracted.

  When extracting partial areas from all areas of the image and calculating flatness, the best flatness is identified from all the partial areas, and the flatness is superior to the specified standard flatness. It is determined whether or not. If it is excellent, the partial area is set as a colorimetric adaptation area suitable for colorimetry.

  By such area search processing, for example, in the case of an image as shown in FIG. 6 (an example of arbitrary digital image data), 27 colorimetric adaptive areas indicated by A1 to 27 in FIG. Explored.

  Further, in the present embodiment, one or two or more areas (non-printing areas) in which the CMYK density is 0, that is, nothing is printed, are selected from the partial areas and added to the colorimetric adaptation area. As described above, the pixel of interest is sequentially scanned as described above, and search is performed until a predetermined number of regions each having a CMYK density of 0 are found. For example, when only one area in which nothing is printed is found, in the case of an image as shown in FIG. 6, the area indicated by symbol B in FIG. 7 is searched.

The paper color acquisition unit 406g (see FIG. 4) acquires the L ^* a ^* b ^* measurement color in the colorimetry adaptive region in which the CMYK density is 0 from the color measurement results acquired by the measurement value acquisition unit 406a. To do. If there are a plurality of colorimetric adaptation areas where the CMYK densities are all 0, the average of those is obtained as the L ^* a ^* b ^* measurement color.

  When the region search process is completed, the algorithm calculation unit 406c (see FIG. 4) performs the algorithm calculation process to calculate an algorithm for obtaining an appropriate correction amount for the image processing parameter (step S104). The image processing parameter to be corrected is the value of the gradation reproduction curve TRC for each density of Y, M, C, and K. The algorithm calculation unit 406c stores in advance in the ROM 405 model values of output colors for mixed colors composed of Y, M, C, and K having various area ratios. Based on the output model values, the area ratio of the Y, M, and C toner images in the colorimetry adaptive region, and the difference between the color measurement result of the colorimetric adaptive region of the actually output image and the original color An algorithm for obtaining an appropriate correction amount can be calculated.

  When the algorithm calculation process is completed, the correction amount determination unit 406b (see FIG. 4) performs the correction amount determination process (step S105), and determines the correction amounts of the image processing parameters in Y, M, C, and K. This determination is made based on the algorithm calculated by the algorithm calculation process.

  Based on the correction amounts of various image processing parameters determined in such correction amount determination processing, the parameter setting unit 406e (see FIG. 4) performs image processing parameter correction processing to correct various image processing parameters. (Step S106). Thereafter, when the print to be output still remains (step S107; NO), the processes from step S102 are performed again.

(Algorithm calculation processing)
The algorithm calculation process will be described in more detail. It is assumed that the density (area ratio) of each primary color of CMYK is quantized from 0 to L-1 (where 0 is blank and L-1 is solid). The TRC (tone reproduction curve) is a function τ _c , τ _m , τ _y , τ _k that can be determined independently for each primary color of CMYK.

τ _c , τ _m , τ _y , τ _k : {0, 1,..., L−1} → {0, 1,.
τ _c (0) = τ _m (0) = τ _y (0) = τ _k (0) = 0,
τ _c (L−1) = τ _m (L−1) = τ _y (L−1) = τ _k (L−1) = L−1

The TRC outputs for inputs 0 (blank) and L-1 (solid) are fixed at 0 and L-1, respectively. The gradation reproduction curve TRC for each primary color of CMYK at time t is _denoted by τ _c ^(t) , τ _m ^(t) , τ _y ^(t) , τ _k ^(t) . Differences δ _c ^(t) , δ _m ^(t) , δ _y ^(t) , and δ _k ^(t) between times t and t + 1 are determined by “TRC control” as follows.

δ _c ^(t) , δ _m ^(t) , δ _y ^(t) , δ _k ^(t) : {0, 1,..., L−1} → {0, 1,. }
δ _c ^(t) (0) = δ _m ^(t) (0) = δ _y ^(t) (0) = δ _k ^(t) (0) = 0,
δ _c ^(t) (L−1) = δ _m ^(t) (L−1) = δ _y ^(t) (L−1) = δ _k ^(t) (L−1) = 0

Then, the TRC during time t + 1 is determined as follows.
τ _c ^{(t + 1)} (x) = τ _c ^(t) (x) + τ _c ^(t) (x), τ _m ^{(t + 1)} (x) = τ _m ^(t) (x) + τ _m ^(t) (x),
τ _y ^{(t + 1)} (x) = τ _y ^(t) (x) + τ _y ^(t) (x), τ _k ^{(t + 1)} (x) = τ _k ^(t) (x) + τ _k ^(t) (x)
x = 0, 1,..., L−1

  FIG. 8 is a diagram showing a gradation reproduction curve and its correction amount. The gradation reproduction curves τ (t) and τ (t + 1) and the difference δ (t) at times t and t + 1 when L = 32. , And the relationship of the gradation reproduction curve τ (t + n) after time n.

The algorithm calculation unit 406c stores in advance in the ROM 405 (see FIG. 3) output color model values for mixed colors composed of Y, M, C, and K having various densities (area ratios). This model value is previously measured offline. First, for each primary color of CMYK, the density (0 to L−1) is divided into Q equal parts (Q is a divisor of L), and sampled to the Q + 1 level as shown in the following expression 1.

Then, the XYZ tristimulus values are measured and stored for the color synthesized by the combination of (Q + 1) ⁴ . For example, if L = 16 and Q = 4, each primary color is quantized to 5 levels {0, 3, 7, 11, 15}, and XYZ tristimulus values are obtained for 5 ⁴ = 625 composite colors. Measured and stored in ROM 405 as a database.

  Further, assuming that the XYZ tristimulus values when CMYK are all 0 are (Xw, Yw, Zw), this corresponds to the XYZ tristimulus values of the paper used at the time of measurement.

N samples sampled from the output image (on paper) determined from the digital data (CMYK) of the user image after UCR / GCR processing, based on characteristics such as the flatness of the color change, by the area search processing in step S102 And a color T represented by the following expression.
T = {(x _i , y _i , c _i , m _i , y _i , k _i ): i = 1, 2,..., N}
Here, (x _i , y _i ) is the CMYK density in the digital data corresponding to the i th sampling position, (c _i , m _i , y _i , k _i ).

Further, the RGB / L ^* a ^* b ^* conversion unit 406f refers to the sampling position recorded in T from the original image data (RGB), and the reference color R = {(L _i , a _i , b _i ): i = 1, 2,..., N} is calculated. Here, (L _i , a _i , b _i ) is an L ^* a ^* b ^* reference color obtained by converting RGB values at the i-th sampling position (x _i , y _i ).

  The paper output of the user image is measured by acquiring the colorimetric data in the colorimetric adaptation area in step S103, and the measurement color acquired by referring to the sampling position recorded in T is expressed by the following equation.

M (t) = {(L _i ^(t) , a _i ^(t) , b _i ^(t) ): i = 1, 2,..., N}
Here, (L _i ^(t) , a _i ^(t) , b _i ^(t) ) is the L ^* a ^* b ^* measurement color at the i-th sampling position (x _i , y _i ) at time t. is there.

Here, a value obtained by converting the L ^* a ^* b ^* measurement color of the paper used for printing acquired by the paper color acquisition unit 406g (see FIG. 4) into XYZ tristimulus values (Xb, Yb, Zb). And (Xb, Yb, Zb) is the XYZ tristimulus value of the paper used in the actual printing operation, and is different from the XYZ tristimulus value (Xw, Yw, Zw) of the paper used when measured offline. Good. For example, (Xb, Yb, Zb) can be acquired from the measured color in the region indicated by the symbol B in FIG.

  The algorithm calculation unit 406c (see FIG. 4) stores the model value of the output color for the mixed color composed of Y, M, C, and K having various area ratios stored in the ROM 405, and Y, An algorithm for obtaining an appropriate correction amount and an area ratio T between the M and C toner images, a difference between the color measurement result area M (t) of the actually output image, M (t), and the original color R Calculate.

The estimated value of L ^* a ^* b ^* measurement color at the i-th sampling position (x _i , y _i ) at time t + 1 is expressed as the following formula 2.

This estimated value is obtained by measuring L ^* a ^* b ^* measured color (L _i ^(t) , a _i ^(t) , b _i ^(t) ) at the i-th sampling position (x _i , y _i ) at time t, L ^* a ^* b ^* Jacobian matrix that collects partial differential coefficients for CMYK concentrations (c _i , m _i , y _i , k _i ) of each component, and TRC difference δ _c ^{(t )} , Δ _m ^(t) , δ _y ^(t) , and δ _k ^(t) can be expressed as in the following Expression 3.

Then, a Jacobian matrix at the i-th sampling position as shown in the following equation 4 is calculated.

Further, if q _c is an integer satisfying the relationship of the following equation 5, (∂L / ∂c) is Y, M, C of various concentrations (area ratios) measured offline in advance. , K output color model values for mixed colors, XYZ tristimulus values (Xw, Yw, Zw) of paper used when measured offline, XYZ of paper used in actual printing work Using the tristimulus values (Xb, Yb, Zb), it can be calculated as in the following Equation 6.

Here, the following Expression 7 is an XYZ tristimulus value in which the CMYK density is a color as shown in Expression 8 below, and is calculated by interpolation with reference to a database of XYZ stimulation values. The other 11 elements of the Jacobian matrix can be calculated similarly.

The above calculation method can be derived as follows. Now, while the density of each Q level of CMYK is the following formula 9,

It is assumed that a spectral reflectance model function such as the following Equation 10 is prepared.

These model functions are calculated off-line. The subscripts c, m, y, and k represent primary colors, and each model function P _x ^(q) (λ; u _x ) represents a process setting u _x (charging DC bias potential, exposure laser) for a single color x. This represents a standard value of reflectance at a wavelength (λ) of density (qL) / Q−1 at the time of (power, developing bias potential). Also, P _x ⁽⁰⁾ (λ; u _x ) is defined as the spectral reflectance of white paper.
P _c ⁽⁰⁾ (λ; u _c ) ≡P _w (λ), P _m ⁽⁰⁾ (λ; u _m ) ≡P _w (λ), P _y ⁽⁰⁾ (λ; u _y ) ≡P _w (Λ), P _k ⁽⁰⁾ (λ; u _k ) ≡P _w (λ)

For CMYK color mixture (c, m, y, k), integers q _c , q _m , q _y , q _k are integers that satisfy the condition of the following expression 11.

Spectral reflectances when the process settings of the four stations are u = (u _c , u _m , u _y , u _k ) are used for the Cellular Spectral Neugebauer model and CMYK four primary colors, offline model measurement. By multiplying the spectral reflectance Pw (λ) of the printed paper and the spectral reflectance Pb (λ) of the paper used in the actual printing operation, the following equation 12 can be obtained.

When the TRC output changes as (c, m, y, k) → (c + δc, m + δm, y + δy, k + δk), the partial differentiation of the XYZ tristimulus values with respect to c is expressed by the following equation (13).

Here, Equation 14 is a color matching function of X, Y, and Z, I (λ) is the reflectance at the wavelength λ of the standard light source, k is a normalization constant, and is expressed by the following Equation 15.

Therefore, the following equation 16 is obtained.

In an actual online situation, P _m ^(q _m ⁾ (λ; u _m ) and P _m ^(q _m ⁺¹⁾ (λ; u _m ) are determined by the process control operating in the image forming engine by the process parameters. By adjusting u _m , it may be considered that the state is stable in a state close to a predetermined reference value. ^{_{Therefore, P m (q m) (}} λ; u m), P m (q m +1) (λ; u m) is the reference value independent on ^{_{u m P m (q m)}} (λ), P m ^It can be approximated by replacing it with ^(q _m ⁺¹⁾ (λ). The same applies to Y and K, as shown in Equation 17 below.

Here, R (λ; c, m, y, k) is a model value of the reflectance at the wavelength λ of the density (c, m, y, k). From Expression 17 and Expression 13, it is expressed by Expression 18.

In Expression 18, the X, Y, and Z color matching functions x (λ), y (λ), and z (λ) are represented by the Dirac δ function and the X, Y, and Z color matching function values that are maximized. When approximated as shown in Equation 19 by the values λx (≈600 nm), λy (≈550 nm), and λz (≈450 nm),
The following equation 20 is obtained.

  The above is the details of the algorithm calculation in step S104.

(Correction amount determination process)
Next, details of the calculation in determining the correction amount in step S105 will be described. The correction amount δ (t) needs to satisfy the following conditions (1) and (2).
(1) The estimated value of L ^* a ^* b ^* measurement color at the i-th sampling position (x _i , y _i ) at time t + 1 is expressed as the following equation (21).
The square error of the reference value (L _i , a _i , b _i ) of L ^* a ^* b ^{* at} the i-th sampling position (x _i , y _i ) is small.

  (2) The TRC at time t + 1 becomes a smooth function with no inflection point.

In order to satisfy these two conditions, the TRC differences δ _c ^(t) (c), δ _m ^(t) (m), δ _y ^(t) (y), δ _k ^{( t)} (k), c, m, y, k = 0, 1,..., L−1 δ _c ^(t) (0) = δ _m ^(t) (0) = δ _y ^(t) (0 ) = Δ _k ^(t) (0) = 0 δ _c ^(t) (L−1) = δ _m ^(t) (L−1) = δ _y ^(t) (L−1) = δ _k ^(t) Calculate (L-1) = 0. As this method, δ _c ^(t) (c), δ _m ^(t) (m), δ _y ^(t) (y), δ _k ^(t) ( k), c, m, y, k = 0, 1,..., L−1 are obtained.

The first term is an estimated value (Equation 23) of L ^* a ^* b ^* measurement color at the i-th sampling position (x _i , y _i ) at time t + 1,
It represents the square error of the reference value (L _i , a _i , b _i ) of L ^* a ^* b ^{* at} the i-th sampling position (x _i , y _i ), and c _i , m _i , y _i , k _i ( i = 1, 2,..., N) is any one of 0 to L-1.

The second term includes a certain positive constant coefficient α and 2 of δ _c ^(t) (c), δ _m ^(t) (m), δ _y ^(t) (y), and δ _k ^(t) (k). This is the product of an expression representing the sum of squares of the magnitude of the second derivative, and the TRC function δ _c ^(t) (c), δ _m ^(t) (m), δ _y ^(t) (y), δ _k ^(t) The smoother the change in (k), the smaller. The second term can maintain the smoothness of the tone reproduction curve (TRC) such that there is no inflection point. Since the evaluation function of Expression 22 is a quadratic form for the variable of Δ (t), it can be solved by a standard optimization calculation method.

As a modification of the evaluation function of the formula (22), the following evaluation function may be used.

The third term is a positive constant coefficient β and the magnitude of δ _c ^(t) (c), δ _m ^(t) (m), δ _y ^(t) (y), δ _k ^(t) (k). This is the product of an expression representing the sum of squares, and becomes smaller as the change in the TRC function is smaller. By this third term, it is possible to suppress a rapid fluctuation of the gradation reproduction curve (TRC). Since the evaluation function as shown in Equation 24 is also a quadratic form for the variable of Δ (t), it can be solved by a standard optimization calculation method. The above is the details of the correction amount calculation in step S105.

(Parameter correction processing)
In the parameter correction in step S106, the TRC is updated as follows based on the correction amount determined in step S105 and the value of the gradation reproduction curve TRC.
τ _c ^{(t + 1)} (x) = τ _c ^(t) (x) + δ _c ^(t) (x),
τ _m ^{(t + 1)} (x) = τ _m ^(t) (x) + δ _m ^(t) (x),
τ _y ^{(t + 1)} (x) = τ _y ^(t) (x) + δ _y ^(t) (x),
τ _k ^{(t + 1)} (x) = τ _k ^(t) (x) + δ _k ^(t) (x)
x = 0, 1,..., L−1

As described above, in the printer according to the present embodiment, the main body control unit 406 serving as a control device selects a colorimetric adaptation region suitable for measuring multi-order colors from the image indicated by the image information. An area search process for searching is performed. A plurality of mathematical models (algorithms) representing the relationship between the output color stored in advance for each toner image that can be formed by the image forming means and the setting value of the image processing parameter of the print controller 410 are stored in advance. A measurement color (L _i ^(t)) which is a color measurement result obtained by measuring the color measurement adaptive region of the multi-color toner image formed based on the color measurement value and image information of the recording sheet by the spectrometer 109 as the color measurement means. , A _i ^(t) , b _i ^(t) ) and the reference color (L _i , a _i , b _i ) which is the original color, the color measurement result of the recording sheet used for color measurement, and the color measurement Based on the area ratio of each color toner image in the adaptive area and the current setting value of the image processing parameter, the correction amount of the image processing parameter (δ _c ^(t) (c), δ _m ^{(t) (m), δ} y (t) y), determines [delta] _k a ^{_{(t) (k)),}} carrying out the color reproduction accuracy processing to improve the correction to the color reproduction accuracy of the multi-color toner image an image processing parameter based on the correction amount .

  Thus, the multi-order color can be accurately reproduced over a long period of time, even when printing on a different type of paper stored in advance, without limiting the type of paper used by the user.

  In the printer according to this embodiment, the image processing parameter is a gradation reproduction curve (TRC) of a plurality of different primary color toner images. Then, the correction amount determination unit 406c determines the correction amount of the image processing parameter so as to maintain smoothness without an inflection point in the gradation reproduction curves of a plurality of different primary color toner images. Alternatively, the correction amount of the image processing parameter is determined so as to suppress rapid fluctuations in the gradation reproduction curves of a plurality of different primary color toner images.

  The above-described embodiment is a preferred embodiment of the present invention, but is not limited thereto, and various modifications can be made without departing from the gist of the present invention.

100 printer (color production printer, image forming device)
101Y, C, M, K photoconductor (image carrier)
102Y, C, M, K Developing device 103Y, C, M, K Image forming unit (image forming means)
104Y, C, M, K Toner bottle 105 Intermediate transfer belt 106Y, C, M, K Primary transfer roller 108 Secondary transfer roller 109 Spectrometer 110 Belt cleaning device 111 Fixing device 112, 113, 114, 119 Support roller 115 Recording Paper (recording sheet)
117 Heating roller 118 Pressure roller 200 Latent image writing unit 301 Charging device 303 Stirring unit 304 Developing unit 305 Developing sleeve 306 Screw 307 Doctor blade 308 Developing case 309 Partition plate 310 Fur brush 311 Photoconductor cleaning device 312 Cleaning blade 401 A / D conversion circuit 402 CPU
403 RAM
404 Parameter setting unit 405 ROM
406 Main body control unit 406a Measurement value acquisition unit 406b Correction amount determination unit 406c Algorithm calculation unit 406d Area search unit 406e Parameter setting unit 406f RGB / L ^* a ^* b ^* conversion unit 406g Paper color acquisition unit 410 Print controller 410a 3D-LUT
410b UCR / GCR
410c TRC
410d Halftone processing unit 411 PC
412 Scanner 413 FAX
414 Drive circuit 415 Motor clutch 416 High pressure generator 417 Temperature / humidity sensor 418 Toner concentration sensor Lb Writing light

JP 2002-33935 A JP 2004-229294 A JP 2012-70360 A

Claims (8)

An image forming means for forming a primary color toner image based on image information;
Image information processing means for processing image information input to the image forming means;
A transfer unit that acquires a multi-color toner image based on the primary color toner image;
Area search means for searching a colorimetric adaptation area suitable for colorimetry from the image indicated by the image information;
(1) Information representing the relationship between the output color stored in advance for each of the plurality of multi-color toner images and the set value of the image processing parameter for processing the image by the image information processing means;
(2) a difference between a measured color obtained by measuring the colorimetric adaptation region and a reference color;
(3) an area ratio of the primary color toner image in the multi-color toner image in the color measurement adaptive region;
(4) The colorimetric value of the recording sheet stored in advance and the colorimetric result of the recording sheet used for colorimetry,
(5) a current setting value of the image processing parameter;
A correction amount determining means for determining a correction amount of the image processing parameter for reducing the difference based on
Parameter correction means for correcting the image processing parameter based on the correction amount;
A control device comprising:   The control apparatus according to claim 1, wherein the image processing parameter is a gradation reproduction curve of a plurality of different primary color toner images.   The correction amount determining means determines the correction amount of the image processing parameter so as to maintain smoothness without an inflection point in gradation reproduction curves of a plurality of different primary color toner images. The control device according to claim 1 or 2.   The correction amount determining means determines the correction amount of the image processing parameter so as to suppress a rapid variation with an inflection point in a gradation reproduction curve of a plurality of different primary color toner images. The control device according to claim 1 or 2.   5. The control device according to claim 1, wherein the area search unit adds a non-printing area to the color measurement adaptive area among the images indicated by the image information. The imaging means;
The image information processing means;
The transfer means;
Colorimetric means for colorimetrically measuring a multi-color toner image formed based on the image information;
An image forming apparatus comprising: the control device according to claim 1. An image forming means for forming a primary color toner image based on image information;
Image information processing means for processing image information input to the image forming means;
A transfer unit that acquires a multi-color toner image based on the primary color toner image, and a control method for an image forming apparatus,
An area search step for searching a colorimetric adaptation area suitable for colorimetry from the image indicated by the image information;
(1) Information representing the relationship between the output color stored in advance for each of the plurality of multi-color toner images and the set value of the image processing parameter for processing the image by the image information processing means;
(2) a difference between a measured color obtained by measuring the colorimetric adaptation region and a reference color;
(3) an area ratio of the primary color toner image in the multi-color toner image in the color measurement adaptive region;
(4) The colorimetric value of the recording sheet stored in advance and the colorimetric result of the recording sheet used for colorimetry,
(5) a current setting value of the image processing parameter;
A correction amount determining step for determining a correction amount of the image processing parameter for reducing the difference based on
A parameter correction step of correcting the image processing parameter based on the correction amount;
The control method characterized by performing. An image forming means for forming a primary color toner image based on image information;
Image information processing means for processing image information input to the image forming means;
An image forming apparatus comprising: a transfer unit that acquires a multi-color toner image based on the primary color toner image;
An area search process for searching for a colorimetric adaptation area suitable for colorimetry from the image indicated by the image information;
(1) Information representing the relationship between the output color stored in advance for each of the plurality of multi-color toner images and the set value of the image processing parameter for processing the image by the image information processing means;
(2) a difference between a measured color obtained by measuring the colorimetric adaptation region and a reference color;
(3) an area ratio of the primary color toner image in the multi-color toner image in the color measurement adaptive region;
(4) The colorimetric value of the recording sheet stored in advance and the colorimetric result of the recording sheet used for colorimetry,
(5) a current setting value of the image processing parameter;
A correction amount determination process for determining a correction amount of the image processing parameter for reducing the difference based on
Parameter correction processing for correcting the image processing parameter based on the correction amount;
A control program characterized by causing