JP2007121645A - Calibration method in image formation and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a calibration method for performing calibration without being influenced by a difference between the kinds of media, and an image forming apparatus achieving the same. <P>SOLUTION: In calibration for recording material that an image is formed on the medium, a patch image having predetermined recording density is formed on one side of the medium, and a plurality of patch images having different recording density are formed at a position corresponding to the patch image having the predetermined recording density on the other side of the medium. The plurality of patch images having the different recording density and formed on the other side of the medium are read and compared with read density stored in advance so as to generate a calibration value. The patch image having the predetermined recording density is the one having the recording density in accordance with the kind of the medium or the one having the recording density exceeding predetermined density that the kind of the medium does not influence the read. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a calibration method and an image forming apparatus in image formation. More particularly, the present invention relates to a calibration technique for a digital color multi-function peripheral having a function of scanning or copying a paper document and a function of printing electronic data created on a host computer.

  As an example of the image forming apparatus, there is a digital color multifunction peripheral having a document reading device (also referred to as a scanner), an image data processing device (also referred to as a controller), and a color printing unit (also referred to as a print engine).

  This digital color multifunction peripheral generally has a copying function of processing image data captured by a scanner with a controller and printing with a print engine.

  It also has a network scan function for transmitting image data captured by the scanner to other digital color multifunction peripherals or various servers, client PCs, etc. connected via a network.

  Furthermore, it has a network print function. That is, document data created by application software on the host computer is converted into a PDL (Page Description Language) file by printer driver software to generate a print job. Send the print job to the controller via the local interface or network. Bitmaps are developed by RIP (Raster Image Processing) on the controller and printed by the print engine.

  There are various types of print engines. Here, an electrophotographic print engine will be described below as an example.

  In an electrophotographic print engine, an image signal is irradiated onto a photosensitive drum by exposure means such as laser light. Toner is electrostatically developed on the latent image formed on the photosensitive drum, and the toner image is electrostatically transferred to a print medium. An image is formed on the print medium by fusing and fixing by a fixing means. In these print engines, color variations of a printed image may occur due to changes in the usage environment such as temperature and humidity, changes in the apparatus over time, and member performance deterioration due to durability. For this reason, a calibration technique has been proposed in order to suppress the color variation caused by these and obtain a stable output.

  There are many calibration techniques depending on the type of print engine and the measurement method. The basic idea is to print a measurement sample under conditions that produce the output characteristics of the print engine, measure the measurement sample by some measurement means, and then use the correction table based on the measurement result and preset target data. It has become the idea of creating. In the case of a normal color printer, this correction table is created for each color such as cyan, magenta, yellow, and black, and has a configuration for the purpose of matching the density of each color. When printing from a scanned image or a print job from a host computer, data correction is performed by the correction table at the time of RIP or in the subsequent process so that it is reflected in printing from the final print engine. work.

  However, in general, there are various types of media used for printing, and there are many types of paper ranging from thickness to a difference in texture. There are differences in the electrostatic properties of the media itself, differences in surface characteristics (characteristics such as roughness), differences in heat capacity, etc. depending on the type of these print media. There will be a big difference. For this reason, a calibration technique has been proposed in which a measurement page including a color patch is printed for each type of media to be printed, and a correction table is created from the measurement result of the measurement page.

  On the other hand, the purpose of performing calibration is to guarantee the color accuracy of the final printed image due to the difference in the type of media. However, with only calibration that guarantees the density for each color as in the prior art, the final color accuracy cannot be guaranteed because it is affected by the color mixture and the color of the media itself. Therefore, in order to realize high-precision color reproduction accuracy, it is necessary to use both calibration and a color profile for each medium. That is, calibration that does not depend on the difference between media and the color profile for each media are performed independently and combined.

  As the color profile, an ICC (International Color Consortium) profile is generally known. This is composed of a multi-dimensional matrix table that can obtain an optimum color reproduction in a state where an ideal amount of toner is placed on the medium.

Here, when performing calibration for each print medium, it is necessary to first print a measurement page including a color patch on the print medium and measure the color patch of the measurement page as described above. In general, a method of measuring the density of a color patch using a scanner or a densitometer is used. As a method for measuring the density, a method of projecting light from a standard light source under a standardized condition with respect to the color patch and measuring a reflected light amount (measured reflected light) is used.
JP 2002-268318 A

  The problem of the prior art of such calibration will be described with reference to FIG.

  FIG. 14 is a cross-sectional view of a color patch printing unit for each medium, taking as an example the case where two types of paper having different thicknesses are used as print media. In FIG. 14, the paper A113 shown in FIG. 14A is a thin paper, and the paper B113 ′ shown in FIG. 14B is a thick paper thicker than the paper A113, and toner A112 and toner B112 for forming a color patch are placed on each paper. ing. FIG. 14 shows a case where the amount of toner A112 on the surface of the paper A113 in (a) is equal to the amount of toner B112 on the surface of the paper B113 'in (b). Here, when the density is measured, the incident light 10 from the incident light source is projected onto the toner A 112 or the toner B 112, and the density is calculated by measuring the light quantity of the measurement reflected light A111 or B111 'reflected.

  However, a measurement error occurs when the amount of reflected light is measured by the conventional method as described above. Some proportion of the incident light 10 passes through the toner layer of the toner A 112 or B 112, a part of the light is reflected by the paper surface of the paper A 113 or B 113 ′, and a part of the light also enters the paper. To disperse. Part of the dispersed light passes through the paper and reaches the surface opposite the paper surface (the paper back surface). Accordingly, a difference in the amount of reflected light on the surfaces of the sheets A113 and B113 'and the amount of light entering the sheet due to the difference in thickness of the sheets such as the sheets A113 and B113'. For this reason, the toner transmitted light 115 and 115 ′ are different, and the amounts of the measured reflected light A 111 and the measured reflected light B 111 ′ are different.

  Returning to the purpose of calibration, the purpose of measuring the density of the color patch on the measurement page is to estimate the amount of toner on the print medium. Therefore, when the amounts of the toner A 112 and the toner B 112 are equal, it is expected that the measured density value will be the same. According to this example, the same value is obtained as the measured density value. It is understood that cannot be done.

  The same phenomenon can occur not only in the thickness of the paper, but also in the surface type (roughness and other characteristics), the material, the color of the paper itself, and these combined factors. It is easily anticipated and has actually been confirmed to be such a phenomenon.

  As described above, in the prior art, when the type of paper is different, the toner amount cannot be accurately measured from the toner density. For this reason, it has been difficult to realize high-precision calibration that requires image development by setting development / transfer process conditions based on accurate toner amount information.

  In the above description of the conventional example, the color image formation has been described. However, the problem is common to monochrome image formation or monochromatic / multicolor image formation.

  The present invention has been invented in view of the difficulties of the conventional techniques as described above, and provides a calibration method for performing calibration that is not affected by the difference in the type of media, and an image forming apparatus that realizes the calibration method. .

  In order to solve this problem, a calibration method of the present invention is a calibration method for a recording material for forming an image on a medium, and forms a patch image having a predetermined recording density on one surface of the medium. One image forming step, a second image forming step of forming a plurality of patch images of different recording densities at positions corresponding to the patch images of the predetermined recording density on the other side of the medium; And a calibration value creating step of creating a calibration value by reading a plurality of patch images formed with different recording densities and comparing them with a stored reading density stored in advance.

  Here, the patch image having the predetermined recording density is a patch image having a recording density corresponding to the type of the medium, and a plurality of patch images having different recording densities are provided on one surface of another medium of the same type as the medium type. A third image forming step of forming a patch image having a predetermined recording density at a position corresponding to the plurality of patch images having different recording densities on the other surface of the other medium. The first image forming step reads the patch image of the predetermined recording density formed on the other surface, and the patch image of the one surface at the position corresponding to the patch image of the other surface having the predetermined reading density. And a patch image selection step of selecting as a patch image having a recording density corresponding to the type of the medium to be formed. In the case of color image formation, in the third image forming step, a plurality of patch images having different types of color materials to be used, amounts of color materials, and halftone screen methods are formed. When there is no patch image for the reading density, the type of color material to be used, the amount of color material, and the halftone screen method are used alone or in combination to set the patch image formed in the first image forming step. . The patch image registration step of registering the patch image of the one surface selected in the patch image selection step in association with the type of the medium is further included. The patch image having a predetermined recording density is a patch image having a recording density exceeding a predetermined density at which the type of media does not affect reading. The media type includes media basis weight, media color value, media material, and media surface type.

  The image forming apparatus of the present invention is an image processing apparatus having a function of calibrating a recording material for forming an image on a medium, and forms a patch image having a predetermined recording density on one surface of the medium. A first image forming unit; a second image forming unit that forms a plurality of patch images with different recording densities at positions on the other side of the medium corresponding to the patch images with the predetermined recording density; and the other side. And a calibration value creating means for creating a calibration value by reading a plurality of patch images having different recording densities and comparing them with a read density stored in advance.

  Here, the image forming apparatus further includes a storage unit that stores a patch image having a predetermined recording density in association with the type of the medium, and the first image forming unit stores the predetermined recording stored in the storage unit in association with the type of the medium. Third image forming means for reading a patch image having a density, forming the patch image on one surface of the medium, and forming a plurality of patch images having different recording densities on one surface of another medium of the same type as the medium A fourth image forming means for forming a patch image having a predetermined recording density at a position corresponding to the plurality of patch images having different recording densities on the other surface of the other medium, and formed on the other surface. The first image forming means forms the patch image on the one surface at a position corresponding to the patch image on the other surface having a predetermined reading density. Further comprising a patch image selecting means for selecting as a patch image recording density in accordance with the type of A. In the case of color image formation, the third image forming unit forms a plurality of patch images with different types of color materials to be used, amounts of color materials, and halftone screen methods, and the patch image selection unit When there is no patch image for the reading density, the type of color material to be used, the amount of color material, and the halftone screen method are used alone or in combination to set the patch image formed by the first image forming means. . The image processing apparatus further includes patch image registration means for registering the patch image of the one surface selected by the patch image selection means in the storage means in association with the type of the medium. Further, the storage means includes a plurality of patch images having different recording densities formed on one surface of the other medium, a patch image having a predetermined recording density formed on the other surface of the other medium, and the predetermined reading. The concentration is further stored. In addition, the image forming apparatus further includes a storage unit that stores a patch image having a recording density exceeding a predetermined density that does not affect reading, and the first image forming unit includes a recording density exceeding the predetermined density stored in the storage unit. Are read out and formed on one side of the medium. The media type includes media basis weight, media color value, media material, and media surface type.

  The control program of the present invention is a control program for an image processing apparatus having a function of calibrating a recording material for forming an image on a medium, and a patch image having a predetermined recording density is applied to one surface of the medium. A first image forming step for forming, a second image forming step for forming a plurality of patch images of different recording densities at positions corresponding to the patch images of the predetermined recording density on the other surface of the medium, and the other And a calibration value creating step of creating a calibration value by reading a plurality of patch images having different recording densities formed on the surface and comparing them with a read density stored in advance.

  Here, in the first image forming step, a patch image having a predetermined recording density corresponding to the type of the medium is formed on one surface of the medium, and the one surface of the other medium of the same type as the medium type is formed. A third image forming step for forming a plurality of patch images having different recording densities; and a patch image having a predetermined recording density at a position corresponding to the plurality of patch images having different recording densities on the other surface of the other medium. A fourth image forming step to be formed, and a patch image of the one surface at a position corresponding to the patch image of the other surface having a predetermined reading density by reading a patch image of a predetermined recording density formed on the other surface A patch image selecting step of selecting a patch image having a recording density corresponding to the type of the medium formed in the first image forming step. In the case of color image formation, in the third image forming step, a plurality of patch images having different types of color materials to be used, amounts of color materials, and halftone screen methods are formed. When there is no patch image for the reading density, the type of the color material to be used, the amount of the color material, and the halftone screen method are combined singly or in combination to set the patch image formed in the first image forming step. . In the first image forming step, a patch image having a recording density exceeding a predetermined density that does not affect reading is formed on one surface of the medium.

  Furthermore, a storage medium for storing the control program in a computer-readable form is provided.

  According to the present invention, it is possible to provide a calibration method for performing calibration that is not affected by the difference in the type of media, and an image forming apparatus that realizes the calibration method.

  In particular, regarding the measurement of the color patch on the calibration value determination measurement page, the color patch is printed on the back surface of the measurement page under appropriate conditions. Thus, there is an effect that it is possible to measure the surface color patches necessary for calibration with high accuracy without being affected by the difference in the types of paper.

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

  In this embodiment, when an image is formed by normal printing, the image is corrected with reference to the calibration table and output. Therefore, a digital color image forming apparatus that obtains a constant calibration table regardless of the type of media (for example, paper) used for calibration will be described. In particular, the present invention relates to image formation of color patches for creating a calibration table.

  At the time of calibration, a measurement page including the front and back color patches for each type of media used for calibration is printed. The printed measurement page is read by a measuring device such as a scanner, and the calculated toner density results for each color are compared with a preset target toner density. A calibration table for each color material that is not affected by the type of media is created from the difference (difference) between the two.

<Concept of creating measurement page for calibration value determination in this embodiment>
The basic idea of the present invention will be described with reference to a cross-sectional view of a calibration value determining measurement page used in the electrophotographic image forming apparatus of the present embodiment shown in FIG.

  In FIG. 1, a sheet A13 shown in (a) is a thin sheet, and a sheet B13 'shown in (b) is a thick sheet thicker than the sheet A13. Toner A12 and toner B12 for color patches are placed on the surface of each sheet. Here, the toner amount of the toner A12 for the thin paper sheet A13 in FIG. 1A and the toner amount of the toner B12 for the thick paper sheet B13 'thicker than the paper sheet A13 in FIG.

  When measuring the toner density, the incident light 10 from the incident light source is projected onto the image forming toner A12 or the toner B12, and the density is calculated by measuring the light quantity of the measurement reflected light A11 or the measurement reflected light B11. At this time, as indicated by thin arrows in FIG. 1, a certain proportion of incident light passes through the toner layer, is reflected on the paper surface, and enters and disperses into the paper.

  In FIG. 1, the back toner A 14 and the back toner B 14 are placed at positions corresponding to the back side of the paper with respect to the toner A 12 or the toner B 12 that is the image formation on the front side. The back toner A14 of the thin paper A13 has a larger amount than the back toner B14 ′ of the thick paper B13 ′, and the action of these back toners adjusts the re-reflection amount of the scattered light entering the paper. , The same toner transmitted light 15 is obtained.

  FIG. 2 shows the measured reflected light A11 or B11 when the re-reflected light 21 or 23 by the action of the back toner A14 or the back toner B14 ′ is added to the light quantity of the reflected light 20 or 22 when no back toner exists. A state diagram is shown.

  In FIG. 2, the measurement reflected light A <b> 11 in FIG. 2A is obtained by adding the re-reflected light 21 due to the effect of the back toner A <b> 14 to the reflected light 20 in the absence of the back toner A <b> 14. The measured reflected light B11 in (b) is obtained by adding the re-reflected light 13 due to the effect of the back surface toner B14 'to the reflected light 22 when the back surface toner B14' is not present.

  When the amounts of the color patch toner A12 and the toner B12 on the front surface are the same, the image formation on the back surface is adjusted so that the light amounts of the reflected light for measurement A11 and the reflected light for measurement B11 are also equal. That is, an image is formed by adjusting the toner amounts of the back surface toner amount A14 and the back surface toner amount B14 'to the toner amounts optimally set for each color material in advance according to the type of paper (media).

  As described above, the amount of backside toner, that is, the amount of toner for image formation on the backside is set to an optimal value in advance for each color according to the type of paper (media). Then, when printing the front color patch on the calibration value determination measurement page, the back side toner is adjusted by applying the optimal back side toner amount preset for each color to the media used. An image is formed as a patch. As a result, the toner amount of the surface color patch necessary for calibration can be measured with high accuracy without being affected by the difference in the type of media.

<Example of Configuration of Image Forming Apparatus of Present Embodiment>
FIG. 3 is a block diagram illustrating a main configuration example of the digital color image forming apparatus 300 of the present embodiment.

  The image forming apparatus 300 includes an arithmetic control CPU 301 that performs overall control, and a storage unit 302 that includes a ROM, various PROMs, a flash memory, a RAM, a hard disk, a memory stick, a floppy (registered trademark) disk, and the like. In addition, the image forming apparatus includes a printing unit 303 that forms an image by printing output, and an image reading unit (image scanner) 304 that reads a printed image. In addition, a media identification unit 305 for identifying the type of media (paper), and a communication unit 306 for performing communication via a LAN, the Internet, or other communication media are provided. In addition, other I / F units 307 for interfacing with other peripheral units (display unit, key input unit, etc.), a bus 308 including data and control connected to each unit around the CPU 301, etc. .

  The storage unit 302 includes a control storage unit 310 that stores a control program for controlling the apparatus, communication control, input / output processing, and the like. The control storage unit 310 further includes a program unit 320 that performs various controls described in the present embodiment, and in this example, the normal print control unit 320-1, the calibration control unit 320-2, and the back color patch are particularly provided. And a determination control unit 320-3. It should be noted that the program unit 320 does not show anything not characteristic of the present embodiment, such as an OS.

  The storage unit 302 further includes a DBA 311 that stores a database (table) for correcting a color to be used for image formation during normal printing. Further, it has a database DBB 312 for storing information for calibration. Furthermore, it has database DBC313 which memorize | stores the information for determining a back surface color patch.

  The DBA 311 includes a color material-specific calibration table (correction table) 326 that stores calibration values created in the present embodiment. The present embodiment relates to the creation of a highly accurate calibration table 326. For actual printing, there are characteristics at the time of shipment of the image forming apparatus (for example, γ correction, etc.), media-specific correction (color profile described in the conventional example) for correcting by media type, and the like. Although not shown in FIG.

  The DBB 312 has calibration back surface color patch information 323 for each medium and each color material that stores information on the back surface color patch having a predetermined recording density for determining a calibration value corresponding to the type of media and the color material. Corresponding to the color material, there is a back color patch information 324 for calibration for each color material for storing information of the front color patch having a plurality of recording densities for determining the calibration value. Furthermore, it has color material-specific reference color patch density information 325 for storing reference density information for determining a calibration value in comparison with the measured density from the surface color patch.

  In the first embodiment below, the back color patch information 323 for calibration is a fixed value stored in advance in association with each medium / color material. On the other hand, in the second embodiment, the back color patch information 323 for calibration is a variable value created by the back color patch determination procedure.

  The DBC 313 includes color material-specific back surface color patch determination reference density information 327 for storing a reference value of the measured density for determining the back surface color patch for each color material. In addition, it has surface color patch information 321 for determining the back color patch by color material for storing one surface color patch of a predetermined recording density for determining the back color patch by color material. In addition, back surface color patch information 322 for determining back surface color patches for each color material for storing back surface color patches having a plurality of recording densities for determining back surface color patches for each color material is included. Here, the front surface color patch information 321 for determining the back surface color patch may store a predetermined recording density regardless of the color material by setting the back surface color patch determining reference density information 327 for each color material. If there is a recording density preferable for determining the back surface color patch by the color material, it is stored for each color material as in this example.

  These databases are configured to be stored in a nonvolatile storage unit, and in particular, the calibration table 326 and the back color patch information for calibration 323 in the second embodiment are stored in a rewritable storage unit.

<Operation Example of Image Forming Apparatus of this Embodiment>
(Operation example during normal printing)
Control of image formation by normal printing is controlled by the normal printing control unit 320-1 of the program unit 320 shown in FIG.

  Specifically, the normal printing control unit 320-1 has a density shift for each color material to be subjected to image formation shown in the DBA 311 in addition to the characteristics (for example, γ correction) at the time of shipment of the image forming apparatus. Correction is performed with reference to the recorded calibration table 326. Further, the amount of toner is controlled by performing media-specific correction (color profile described in the conventional example) for correcting media by type.

  Hereinafter, calibration and selection of the back surface color patch will be described in detail using each embodiment. In addition, this invention is not limited by this embodiment.

<Embodiment 1: Example of creating calibration table 326>
In the present embodiment, an example in which calibration, that is, a calibration table 326 for each color material is created regardless of the type of media (paper) to be used will be described in detail.

  A schematic operation by the calibration control unit 320-2 (FIG. 3) of the present embodiment is as follows. First, the type of media is recognized, and a back color patch having a predetermined print density corresponding to the type of media is printed. Next, the calibration value determination measurement page 400 (FIG. 4) is printed as a surface color patch having a plurality of print densities. Next, each density of the patch on the printed calibration value determination measurement page is measured, the difference from the reference color patch density information 325 is registered in the calibration table 326 for each color material, and the process is terminated.

  FIG. 4 is an example of a measurement page 400 for determining a calibration value formed on a medium to be calibrated. In FIG. 4, each of columns A to D is classified by color material, and rows 1 to 5 are classified by density.

  As shown in FIG. 4, the present embodiment is characterized in that an image of a back color patch 402 is formed. That is, referring to the back color patch information 323 for calibration by medium / color material in FIG. 3, the back color patch 402 having a predetermined density that is predetermined with the same color material as the front color patch corresponding to each color material, Printing is performed as shown in FIG.

  Taking the A column as an example, the back color patch forms the same image on all the A columns with the same color material as the front surface and the same type of color patches (type of halftone screen, density, number of lines, etc.). That is, if attention is paid to a certain color material, the density of the front color patch differs for each patch on the selected medium, and the back color patch forms the same color material as the front color patch and all forms the same density image. . Such a patch is applied to each color material to create a calibration value determination measurement page 400.

  The surface color patch 402 of the calibration value determination measurement page 400 created in this way is read, and the read density is compared with the reference value of the reference color patch density information 325. The result is registered in the calibration table 326.

(Example of processing procedure of Embodiment 1)
Hereinafter, the flow of calibration control according to the present embodiment will be described in detail with reference to FIGS. 3 and 4 according to the steps of the flowchart of the processing shown in FIG. The order of front surface color patch image formation (S52) and back surface color patch image formation (S53) does not matter.

S51: Identification of Media (Paper) The media identification unit 305 identifies the media (paper) 400 to be calibrated. Identification of the media type at the time of calibration may be performed using an automatic identification device, or a result separately identified by a calibration operator may be input. The feature for identifying the type of paper to be calibrated is described as thin paper or thick paper in the description of FIG. However, for paper attributes such as media basis weight (mass per unit area), paper color characteristics (color value), media material differences, paper surface type (roughness and other characteristics), etc. Is also applicable. That is, high-precision measurement of the front surface color patch is possible by forming an image of the back surface toner (back surface color patch).

S52: Surface color patch image formation The image formation of the surface color patch 401 is performed by using the “calibration surface color patch information 324” for each color material in the DBB 312 which is fixedly stored by the apparatus for each color. On the other hand, the printing unit 303 performs a density gradient. Here, in the example shown in FIG. 4, the front color patch 401 is cyan in the A column, magenta in the B column, yellow in the C column, and black in the D column. That is, the surface color patch 401 is image-formed as a patch in which each column A to D is classified by color material, and each row 1 to 5 is a patch having a density gradient for each color material.

S53: Back side color patch image formation In forming the back side color patch 402, if the apparatus has a double-sided printing function, the back side color patch image may be formed on the back side by the double-sided printing function. If there is no, after the image formation of the front surface color patch is completed, the paper 400 is manually reversed and the back surface color patch is applied to the opposite surface (back surface). The back surface color patch 402 performs the same type of back color patch that is predetermined for each color in the same color as the front surface color patch in accordance with the “calibration back surface color patch information 323” in the printing paper attribute database of FIG.

  The back color patch 402 is formed by, for example, forming the same image with the same cyan colorant as the front color patch and the image ratio of 20% for the rows 1 to 5 in the A column, which are stored in advance corresponding to the paper attributes. Made. Similarly, the other back surface color patches are the same image formation with a magenta image ratio of 15% for the B row, an image ratio of 25% for yellow for the C row, and a 10% image ratio for black for the D row. Made.

  As shown in FIG. 4, the position of the back surface color patch 402 is printed at the position of the back surface facing the front surface color patch so as to overlap the front surface color patch. The shape may be an independent shape that is the same shape as the surface color patch, an independent shape that is larger than the surface color patch, or a shape that is continuous on the back surface with respect to the color patches of the same color material in each row.

  In addition, the image formation of the back color patch set in advance according to the type of media to be calibrated for each color can be performed by changing the type of color material to be used, the amount of color material, and the type of halftone screen individually or in combination. It is possible to set in combination.

S54: Reading Measurement Page The surface color patch 401 of the calibration measurement page 400 printed on both sides by the processing of the previous steps S52 and S53 is read by the image reading unit 304 shown in FIG. Here, the measurement page 400 for calibration may be read by an image scanner provided in the apparatus or a densitometer.

S55: Density calculation The density of each patch is calculated from the data of each color read by the image scanner or the like in the process of step S54.

S56: Obtaining the difference (deviation) The density difference (deviation) is obtained by comparing the density calculation result for each patch of each color material with the density in the “reference color patch density information 325” serving as the reference value.

S57: Registration in Calibration Table The density difference (deviation) obtained from the comparison result is registered in the calibration table 326, and the calibration is completed.

  As described above in detail with reference to the first embodiment, according to the present invention, during calibration, a color patch to be calibrated is image-formed on the surface of the medium as a surface color patch. At the same time, an image is formed on the back surface color patch corresponding to the type of media so as to overlap the front surface color patch at the position of the back surface facing the image formed surface color patch. Accordingly, it is possible to provide a digital color image forming apparatus with little difference in reflected light to be measured with respect to the type of media used for calibration.

  That is, the optimum amount of backside toner is set in advance for the type of paper, and when printing a measurement page for calibration, the optimum amount of backside toner is applied to the paper used. Acts like As a result, the toner amount of the surface color patch necessary for calibration can be measured with high accuracy without being affected by the difference in the type of paper.

  In this embodiment, the paper type is described as thin paper or thick paper. However, for the attributes such as the color characteristics of the paper itself, the difference in material, and the difference in surface characteristics, the surface color patch by the back toner is similarly high. Accuracy measurement is possible.

<Embodiment 2: Creation Example 1 of Back Color Patch Information 323 for Calibration>
The present embodiment is an embodiment in which the amount of toner in the back color patch of the calibration value determination measurement page of the first embodiment is set as an optimal value in advance according to the type of each medium and the type of color material.

  The general operation of the back surface color patch determination control unit 320-3 (FIG. 3) of the present embodiment is as follows. First, the type of media is recognized. Next, a back toner condition measurement page 600 (FIG. 6) having patches with constant density on the front surface and a plurality of patches with different densities on the back surface is printed. Next, the density of the front surface patch corresponding to each back surface patch on the printed back surface toner condition measurement page 600 is measured and compared with the reference density information 327 (FIG. 3) for determining the back surface color patch by color material. The back surface color patch having the same density value is registered as calibration back surface color patch information 323 for each medium / color material, and the process is terminated. The surface of the back toner condition measurement page 600 is a patch having a constant density, but it may not be printed on the surface.

  FIG. 6 is an example of the layout of a measurement page that determines the image forming conditions of the back color patch. This is an example in which an image is formed by printing in order to determine the optimum value of the image formation condition of the back surface toner for each sheet, and is an example in which the back surface toner condition measurement page 600 that is a back surface color patch measurement page is viewed from the front surface direction.

  On the back surface toner condition measurement page 600 in FIG. 6, 20 surface color patches 601 are arranged based on the back surface color patch determination surface color patch information 321 and an image is formed. Twenty back color patches 602 are also arranged and image-formed corresponding to the position of the front color patch 601 based on the back color patch information 322 for determining the back color patch.

  In FIG. 6, the back surface color patch 602 indicated by a broken line is not visible from the front surface, but the back surface color patch 602 is image-formed at the position of the back surface facing the front surface color patch 601 so as to overlap the front surface color patch. The back color patch 602 has a smaller area than the front color patch 601 and has less influence from the area where the peripheral image is not formed.

  FIG. 7 shows an example of the back surface color patch 602 in each column row stored in the back surface color patch determining back surface color patch information 322.

  The back surface color patch 602 is the same color material as the front surface color patch for each column, and the A column is cyan, the B column is magenta, the C column is yellow, and the D column is black. In each row, the image ratio, that is, the amount of toner on the paper, is 30% for the first row, 25% for the second row, 20% for the third row, 15% for the fourth row, The line is 10%, and based on this, the back color patch 602 of the back toner condition measurement page 600 of FIG. 6 is printed.

(Example of processing procedure of Embodiment 2)
FIG. 8 is a diagram showing a system flow for selecting the image forming condition of the back color patch for each medium (paper) used for calibration. FIG. 8 is a flowchart showing a back toner condition measurement page 600, a back color patch image formation condition database 322, and a printing paper attribute database 323 centering on the digital color image forming apparatus 300.

  First, the digital color image forming apparatus 300 prints a back toner condition measurement page 600 having a patch having a constant density on the front surface and a plurality of patches having different densities on the back surface (S1). Next, the density of the front surface patch corresponding to each back surface patch of the printed back surface toner condition measurement page 600 is measured (S2). Next, reference density information 327 for determining the color patch for each color material is referred to (S3). The back surface color patch having the closest density value is found and the corresponding patch information is acquired from the table of FIG. 7 (S4), and is registered as back surface color patch information 323 for calibration for each medium / color material (S5). finish.

  FIG. 9 is a flowchart illustrating the processing flow of the second embodiment. Hereinafter, the processing of this embodiment will be described with reference to FIGS. 3, 6, and 8 along the steps of the flowchart shown in FIG.

S901: Identification of Media (Paper) The media identification unit 305 identifies the paper 600 on which the image of the back toner condition measurement page is formed. The media type may be identified by using an automatic identification device, or may be input by the operator after separately identifying it.

S902: Image formation of front surface color patch The front surface color patch 601 for image formation on the back surface toner condition measurement page 600 for the sheet identified by the media identifying unit 305 is determined for the rear surface color patch for each color material in the DBC 313 shown in FIG. The image is formed with reference to the front surface color patch information 321. As shown in FIG. 6, the surface color patch 601 in this embodiment is classified into rows and columns to form images, and the columns are A column cyan, B column magenta, C column yellow, D column. The black toner is an image forming material, that is, a color material. There are 1 to 5 rows for each color column of columns A to D, and each row is an image of the same halftone screen type and the same halftone screen density. Therefore, when converted into the toner amount, the same amount is recorded.

S903: Back color patch image formation The back color patch 602 is arranged with respect to the front color patch 601 corresponding to columns A to D and 1 to 5 rows in FIG. That is, as in each row of each column of the image forming condition table of the back color patch shown in FIG. 7 as an example, the color material of each color patch is A column to D column, and the halftone screen density (image ratio) is set in each row. It arrange | positions so that it may differ in each line of 1-5 lines. That is, the back surface color patch 602 is formed with reference to the back surface color patch information 322 for determining the back surface color patch for each color material in the DBC 311 shown in FIG.

  That is, at the back surface position corresponding to the front surface color patch 601, the back surface color patch 602 with a plurality of types of image formation (toner amount) is arranged if the image ratio is different from 1 to 5 rows for each column (each color). Print. In this manner, the back toner condition measurement page 600 for determining the back side image forming conditions is created.

S904: Reading the Back Toner Condition Measurement Page The surface of the back toner condition measurement page 600 printed by the processes of steps S902 and S903 is read by the image reading unit (optical reading device) 304. Here, the back side toner condition measurement page 600 may be read by an image scanner provided in the apparatus or a densitometer.

S905: Selection of optimal back surface color patch From the result read in step S904, the predetermined back surface color patch determining reference density information 327 in each of the patch rows 1 to 5 for each column of each of the color materials A to D is obtained. The color patch position of the measured density closest to the density is selected for each color material.

S906: Selection of back surface color patch image forming condition Referring to the table of FIG. 7, the back surface color patch optimal for the corresponding color material of the corresponding media is set to the image ratio of the back surface color patch at the color patch position selected in step S905. The image forming conditions are selected. For example, it is assumed that the color patch selected as the optimum value closest to a preset value is represented by columns and rows, and is A column 4 rows, B column 3 rows, C column 3 rows, and D column 2 rows. In this case, the image forming conditions of the back toner suitable for the paper are 15% for cyan, 20% for magenta, 20% for yellow, and 25% for black.

S907: Recording of Back Color Patch Image Formation Conditions The results obtained by the above processing are recorded and stored in the back color patch information 323 for calibration in the DBB 312 of FIG. The back patch information determination process for calibration for the paper type is terminated.

  With the above processing, even when the back color patch corresponding to the type of media is not registered in the back color patch information for calibration 323, the back color patch for calibration for a new medium can be determined and registered.

  In the second embodiment, the characteristics for identifying the media type for determining the image forming condition of the back color patch in the image formation of the measurement page when performing calibration have been described as thin paper and thick paper. However, it can also be applied to attributes such as media basis weight (mass per unit area), media color characteristics (color values), media material differences, media types (surface roughness, etc.) differences. Is possible. That is, high-precision measurement of the front surface color patch with the back surface toner can be similarly performed.

  When color patch image formation is set according to the type of media, the type of color material to be used, the amount of color material, and the type of halftone screen can be set individually or in combination. it can.

  As described above in detail in the second embodiment, the image forming condition of the back surface color patch for determining the image forming condition of the back surface color patch can easily set the image forming condition of the back surface toner optimum for the type of media. It becomes possible. For this reason, it is possible to obtain an effect that the user can output an optimum calibration page even for a type of media that is not prepared in advance at the time of device shipment.

  That is, the back surface color patch corresponding to the paper is determined and registered in the back surface patch information 323 for calibration for each medium / color material. If the first embodiment is executed using the registration information, a calibration table that does not depend on the medium can be created.

<Embodiment 3: Creation Example 2 of Back Color Patch Information 323 for Calibration>
In the present embodiment, the amount of toner in the back color patch of the calibration value determination measurement page of the first embodiment is set to a more accurate value in advance according to the type of each medium and the type of color material. It is a form.

  The back color patch determination control unit of the present embodiment will be described as the back color patch determination control unit 320-3 of FIG. Further, the back surface color patch information 321 for determining the back surface color patch and the back surface color patch information 322 for determining the back surface color patch are also used as they are because they are functionally similar but have the same internal structure.

  A feature of the present embodiment is an example in which one sheet is used for each color material for each medium, and a back color patch for the color material is determined. In this embodiment, the black toner will be described in detail, but the same applies to other color materials.

  FIG. 10 is a diagram showing a layout when the back toner condition measurement page 1000 for determining the image forming condition of the back toner with high accuracy is viewed from the front surface direction. On the back surface toner condition measurement page 1000 in FIG. 10, fifteen front color patches 1001 are arranged and an image is formed. Fifteen back surface color patches 1002 are also arranged corresponding to the position of the front surface color patch 601 to form an image.

  In FIG. 10, the back surface color patch 1002 indicated by the broken line is not visible from the front surface, but the back surface color patch is printed at the position of the back surface facing the front surface color patch 1001 so as to overlap the front surface color patch. A larger area with a larger area than the back surface color patch 1002 and the front surface color patch 1001 has less influence from the surrounding area where no image is formed.

  FIG. 11 is an image forming condition table for the back surface color patch 1002 stored in the back surface color patch information 322 for determining the back surface color patch.

  As shown in FIG. 11, each back patch forms an image with a toner of a corresponding color material (here, black) so as to have different halftone screen types and different halftone screen densities (image ratios).

  For example, the column direction in FIG. 11 is set to include SCR1, SCR2, and error diffusion halftone screen types. Here, for example, SCR1 is set to have a different halftone screen type such as a 175 lpi dot screen and SCR2 is a 133 lpi dot screen. The back side color patch of the back side toner condition measurement page 1000 so that the direction of the line is different from the density of the halftone screen from the first line to the fifth line, that is, the density image ratio is 30%, 25%, 20%, 15%, 10%. 1002 is set.

(Example of processing procedure of Embodiment 3)
FIG. 12 is a flowchart showing the flow of processing when the image forming conditions for the backside toner are calculated with high accuracy. Hereinafter, with reference to FIG. 3, FIG. 10, and FIG. 11, the processing of this embodiment will be described along the steps of the flowchart shown in FIG.

S1201: Identification of Media (Paper) The media identification unit 305 identifies the media (paper) 600 on which the image of the back toner condition measurement page is formed.

S1202: Image formation of front surface color patch The front surface color patch 1001 for image formation on the back surface toner condition measurement page 1000 for the medium (paper) identified by the media identifying unit 305 is the back surface for each color material in the DBC 311 shown in FIG. Image formation is performed with reference to the color patch determination surface color patch information 321. As shown in FIG. 10, the back surface toner condition measurement page 1000 according to the third exemplary embodiment has a front surface color patch 1001 of BK-A, BK-B, BK-C in the column direction, and 1 to 5 in the row direction, which is 15 in total. As individual patches, they are arranged in a matrix consisting of columns and rows.

S1203: Image formation of back surface color patch The back surface color patch 1002 is a toner of a corresponding color material (here, black), as shown in the image forming condition table of the back surface color patch in FIG. Images are formed to have different halftone screen densities (image ratios).

S1204: Reading the back toner condition measurement page The surface of the back toner condition measurement page 1000 output by the processes of steps S1002 and S1203 is read by the image reading unit (optical reading device) 304. Here, the back side toner condition measurement page 1000 may be read by an image scanner provided in the apparatus or a densitometer.

S1205: Selection of surface color patch The signal levels at the respective positions in the columns BK-A to BK-C and rows 1 to 5 of each patch are calculated from the image data read in step S1204. Among the calculated signal levels, a plurality of back surface color patches before and after the signal level of reference color information 327 for determining the back surface color patch set in advance shown in FIG. Choose from.

S1206: Interpolation Calculation From the plurality of front surface color patches selected in step S1205, an optimum value is calculated by interpolation calculation from each image forming condition of the back surface color patch with reference to the table of FIG. For example, assuming that the signal level set in advance is 220, the surface color patch having a nearby signal level is assumed to be A column 3 rows (signal level 210) and B column 3 rows (signal level 230). In this case, the calculation is performed so that the number of lines as the type of the halftone screen is an intermediate level between SCR1 and SCR2. That is, since SCR1 is a 175 lpi halftone screen and SCR2 is a 133 lpi halftone screen, 150 lpi is calculated and a value of 20% of the image ratio is calculated.

S1207: Recording of Back Color Patch Image Forming Conditions The result obtained by the above processing is used as back color patch image forming conditions for the selected color material of the corresponding paper as back color patch information 323 for calibration in DBB 312 of FIG. Record and save.

S1208: Judgment of completion of all color materials Until the recording of the back color patch image forming conditions for each color material is completed, the above processing is repeated for each color material, and the recording of the back color patch image forming conditions for all the color materials is performed. When is finished, the process is terminated.

  As described in detail above, a measurement page in which the front color patch and the back color patch are image-formed on one sheet for each color material is created in accordance with the type of the selected medium. Select the front and back color patches closest to the value held in advance by the device from the scanned results, and perform interpolation calculation from the halftone type and image ratio value of the corresponding back color patch and the value held by the device in advance. Thus, the type of halftone and the image ratio are calculated. Accordingly, it is possible to determine the optimum image forming condition of the back surface color patch with higher accuracy for the corresponding medium.

<Embodiment 4: Example of creating back side patch with white toner>
The fourth embodiment is an embodiment in which white toner is used as the back toner when creating the calibration table.

  FIG. 13 is a cross-sectional view of a measurement page for determining a calibration value of an electrophotographic image forming apparatus when white toner is used as the back toner.

  In FIG. 13, a sheet A103 shown in (a) is a thin sheet, and a sheet B103 ′ shown in (b) is a thick sheet thicker than the sheet A103, and toner A102 and toner B102 for forming a color patch are placed on each sheet. Yes. In the present embodiment, the toner A102 for the thin paper A103 in FIG. 13A and the toner B102 for the thick paper B103 thicker than the paper A103 in FIG. When measuring the toner density, the incident light 10 from the incident light source is projected onto the toner A102 or the toner B102, and the density is calculated by measuring the light quantity of the measured reflected light A101 or the measured reflected light B101. At this time, as indicated by a thin arrow, a certain proportion of incident light passes through the toner layer, is reflected on the paper surface, and enters and disperses into the paper.

  In the fourth embodiment, as described above, the back surface white toner 104 of the same amount is mounted on the back surface position corresponding to the front surface color patch of the paper with respect to the toner A 102 or the toner B 102. Is a feature. The white toner on the back surface secures a sufficient amount of toner so as to avoid the influence of transmitted light depending on the type of paper so that the same condition can be used regardless of the type of paper. By the action of this backside white toner, the amount of re-reflected incident light scattered into the paper is adjusted to be the same regardless of the type of paper, so the amount of toner on the front color patch required for calibration can be reduced. It becomes possible to measure with high accuracy.

  The advantage of using white toner is that the paper used as a printing medium is generally white, and the color reproducibility obtained with a white medium is the best in the color reproduction principle by the subtractive color mixing method. is there.

  As described above in detail, the surface color patch can be measured with high accuracy regardless of the type of paper by printing a certain amount of backside white toner on the measurement page for calibration.

  Note that the present invention may be applied to a system or an integrated apparatus constituted by a plurality of devices (for example, a host computer, an interface device, a printer, etc.) or an apparatus constituted by a single device.

  Needless to say, the object of the present invention can also be achieved by the following configuration. First, a storage medium (or recording medium) that records a program code of software that implements the functions of the above-described embodiments is supplied to a system or apparatus. Then, the computer (or CPU or MPU) of the system or apparatus reads and executes the program code stored in the storage medium. In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiment, and the storage medium storing the program code constitutes the present invention. The functions of the above-described embodiments are not only realized by executing the program code read by the computer. This includes the case where the operating system (OS) running on the computer performs part or all of the actual processing based on the instruction of the program code, and the functions of the above-described embodiments are realized by the processing. Needless to say.

  Further, the program code read from the storage medium is written in a memory provided in a function expansion card inserted into the computer or a function expansion unit connected to the computer. Thereafter, the CPU of the function expansion card or function expansion unit performs part or all of the actual processing based on the instruction of the program code, and the function of the above-described embodiment is realized by the processing. Needless to say.

  When the present invention is applied to the storage medium, the storage medium stores program codes corresponding to the flowcharts described above.

FIG. 3 is a cross-sectional view of a calibration value determination measurement page of the electrophotographic image forming apparatus according to the first embodiment. FIG. 6 is a state diagram of measurement reflected light when re-reflected light due to the action of the back surface toner of Embodiment 1 is added. 1 is a block diagram illustrating a configuration example of a digital color image forming apparatus according to an embodiment. FIG. 6 is a layout diagram when an example of a calibration value determination measurement page according to the first embodiment is viewed from a surface direction. 3 is a flowchart illustrating an example of a calibration processing procedure according to the first exemplary embodiment. FIG. 6 is a layout diagram when an example of a back surface toner condition measurement page of Embodiment 2 is viewed from the front surface direction. 6 is a diagram illustrating an example of an image forming condition table for a back surface color patch according to Embodiment 2. FIG. FIG. 6 is a substance flow diagram when determining image forming conditions for a back toner according to a second exemplary embodiment. FIG. 10 is a flowchart illustrating an example of a processing procedure for determining an image forming condition for a back toner according to a second exemplary embodiment. FIG. 10 is a layout diagram when an example of a back surface toner condition measurement page of Embodiment 3 is viewed from the front surface direction. FIG. 10 is a diagram illustrating an example of an image forming condition table for a back surface color patch according to a third embodiment. FIG. 10 is a flowchart illustrating an example of a processing procedure for determining an image forming condition for a back toner according to a third exemplary embodiment. FIG. 10 is a cross-sectional view of a measurement page for calibration value determination using backside white toner according to a fourth embodiment. It is a figure which shows sectional drawing of the color patch printing part of a medium at the time of making two types of paper from which thickness differs as a prior art into print media.

Claims (20)

A method for calibrating a recording material for forming an image on a medium,
A first image forming step of forming a patch image having a predetermined recording density on one surface of the medium;
A second image forming step of forming a plurality of patch images of different recording densities at positions corresponding to the patch images of the predetermined recording density on the other surface of the medium;
A calibration value generating step of reading a plurality of patch images having different recording densities formed on the other surface and comparing the read patch density with a pre-stored read density. Method.   The calibration method according to claim 1, wherein the patch image having a predetermined recording density is a patch image having a recording density corresponding to a type of media. A third image forming step of forming a plurality of patch images having different recording densities on one surface of another medium of the same type as the medium type;
A fourth image forming step of forming a patch image having a predetermined recording density at a position corresponding to the plurality of patch images having different recording densities on the other surface of the other medium;
The patch image of the predetermined recording density formed on the other surface is read, and the patch image on the one surface at the position corresponding to the patch image on the other surface having the predetermined reading density is obtained in the first image forming step. The calibration method according to claim 2, further comprising a patch image selection step of selecting a patch image having a recording density corresponding to a type of the medium to be formed. In the case of color image formation, in the third image forming step, a plurality of patch images having different types of color materials to be used, amounts of color materials, and halftone screen methods are formed,
In the patch image selection step, when there is no patch image having a predetermined reading density, the type of the color material to be used, the amount of the color material, and the halftone screen method are used alone or in combination, and the first image forming step The calibration method according to claim 3, wherein a patch image to be formed is set.   5. The calibration according to claim 3, further comprising a patch image registration step of registering the patch image of the one surface selected in the patch image selection step in association with the type of the medium. Method.   The calibration method according to claim 1, wherein the patch image having the predetermined recording density is a patch image having a recording density exceeding a predetermined density that does not affect reading.   The calibration method according to claim 1, wherein the media type includes media basis weight, media color value, media material, and media surface type. An image processing apparatus having a function of calibrating a recording material for forming an image on a medium,
First image forming means for forming a patch image of a predetermined recording density on one surface of the medium;
Second image forming means for forming a plurality of patch images having different recording densities at positions corresponding to the patch images having the predetermined recording density on the other surface of the medium;
An image having calibration value creation means for reading a plurality of patch images of different recording densities formed on the other surface and comparing the read density stored in advance with a calibration value. Forming equipment. Storage means for storing a patch image having a predetermined recording density in association with the type of the medium;
9. The first image forming unit reads out a patch image having a predetermined recording density stored in the storage unit corresponding to the type of the medium, and forms the patch image on one surface of the medium. The image forming apparatus described. A third image forming unit for forming a plurality of patch images having different recording densities on one surface of another medium of the same type as the medium;
A fourth image forming means for forming a patch image having a predetermined recording density at a position corresponding to the plurality of patch images having different recording densities on the other surface of the other medium;
The first image forming unit reads a patch image having a predetermined recording density formed on the other surface, and the patch image on the one surface at a position corresponding to the patch image on the other surface having a predetermined reading density. The image forming apparatus according to claim 9, further comprising a patch image selecting unit that selects a patch image having a recording density according to a type of the medium to be formed. In the case of color image formation, the third image forming means forms a plurality of patch images having different types of color materials to be used, amounts of color materials, and halftone screen methods,
When there is no patch image having a predetermined reading density, the patch image selection unit is configured to combine the type of color material to be used, the amount of color material, and the halftone screen method, either alone or in combination. The image forming apparatus according to claim 10, wherein a patch image to be formed is set.   12. The patch image registration unit according to claim 10, further comprising a patch image registration unit that registers the patch image of the one surface selected by the patch image selection unit in the storage unit in association with the type of the medium. The image forming apparatus described.   The storage means includes a plurality of patch images having different recording densities formed on one surface of the other medium, a patch image having a predetermined recording density formed on the other surface of the other medium, and the predetermined reading density. The image forming apparatus according to claim 10, further storing an image. Storage means for storing a patch image having a recording density exceeding a predetermined density where the type of media does not affect reading;
9. The image formation according to claim 8, wherein the first image forming unit reads a patch image having a recording density exceeding a predetermined density stored in the storage unit, and forms the patch image on one surface of the medium. apparatus.   15. The image forming apparatus according to claim 8, wherein the media type includes a media basis weight, a media color value, a media material, and a media surface type. A control program for an image processing apparatus having a function of calibrating a recording material for forming an image on a medium,
A first image forming step of forming a patch image having a predetermined recording density on one surface of the medium;
A second image forming step of forming a plurality of patch images having different recording densities at positions corresponding to the patch images having the predetermined recording density on the other surface of the medium;
A calibration value creating step of reading a plurality of patch images having different recording densities formed on the other surface and comparing them with a read density stored in advance to create a calibration value; program. In the first image forming step, a patch image having a predetermined recording density corresponding to the type of the medium is formed on one surface of the medium,
A third image forming step of forming a plurality of patch images having different recording densities on one surface of another medium of the same type as the medium;
A fourth image forming step of forming a patch image having a predetermined recording density at a position corresponding to the plurality of patch images having different recording densities on the other surface of the other medium;
The patch image of the predetermined recording density formed on the other surface is read, and the patch image of the one surface at a position corresponding to the patch image of the other surface having the predetermined reading density is obtained in the first image forming step. The control program according to claim 16, further comprising a patch image selection step of selecting a patch image having a recording density corresponding to a type of the medium to be formed. In the case of color image formation, in the third image forming step, a plurality of patch images having different types of color materials to be used, amounts of color materials, and halftone screen methods are formed,
In the patch image selection step, when there is no patch image having a predetermined reading density, the type of the color material to be used, the amount of the color material, and the halftone screen method are combined alone or in combination to form the first image forming step. 18. The control program according to claim 17, wherein a patch image to be formed is set.   17. The control program according to claim 16, wherein in the first image forming step, a patch image having a recording density exceeding a predetermined density that does not affect reading is formed on one surface of the medium.   A storage medium for storing the control program according to any one of claims 16 to 19 in a computer-readable form.

Images