JP2009153063A - Color separation table creation method and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To take into account priorities of evaluation items set by a user when automatically creating a color separation table for a second medium on the basis of a color separation table for a first medium in an image forming apparatus forming images to the plurality of media. <P>SOLUTION: A color separation table LUT 1 manually created for a medium A is acquired (S701), and priorities of evaluation items of a color separation table LUT 2 for a medium B are set in accordance with user instructions (S702). On the basis of the priorities and the LUT 1, the LUT 2 is automatically created so as to observe a maximum input quantity (S703-S707). Thus, a color separation table for enabling optimal image formation desired by a user for the medium B can be speedily created. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a color separation table creation method and an image forming apparatus for creating a color separation table for separating a color image signal into color material amounts.

  In recent years, in an image forming apparatus that visualizes a color image on a recording medium (medium) such as a color printer, the demand for media by a user has increased as the image quality of the formed image has improved. Accordingly, it has become essential to allow high-quality images to be output to any medium, as well as making it possible to use many types of media in one printer.

  In general, in a color print system using a color printer or the like, color separation processing is performed in which color image data to be formed is separated into color materials (ink and toner) corresponding to the color amounts in the apparatus. This color separation processing is performed based on a color separation table created in advance, but the optimum color separation processing varies depending on the type of media. Therefore, it is preferable to prepare a plurality of color separation tables that realize optimal color separation for each of a plurality of types of media.

  In order to optimally use multiple types of media in a conventional image forming apparatus, the optimum color separation table is manually input, such as manually inputting all the colorimetric values required for the color separation table for each medium. I was making it. Therefore, in order to realize support for more types of media, it is necessary to manually create a larger number of color separation tables, and the work is considerably complicated, so that the design period of the image forming apparatus is long. Conversion was inevitable.

In order to further reduce the design period while supporting various types of media, it is necessary to quickly create a color separation table. For example, it is desirable to automatically generate a color separation table for arbitrary media. As a technique for quickly creating a color separation table while reflecting the intention of the designer, a method for creating a color separation table for medium B based on the color separation table for medium A has been proposed (for example, a patent). Reference 1). According to this technique, the color separation table for medium A is copied to create the color separation table for medium B.
JP 2003-334934 A

  However, as described above, the technology for automatically creating the color separation table for the medium B based on the color separation table for the medium A has the following problems.

  That is, when an image is formed on the medium B using the copy of the color separation table of the medium A as it is, the color shift occurs due to the difference in the coloring characteristics due to the structure of the medium and the combination of the medium and the ink. End up. Further, a pseudo contour is generated on the medium B due to the ink application amount correction, and the gradation reproducibility is also deteriorated.

  Further, since the color separation table is created without considering the spectral reflectance particularly in the medium B, for example, when the light source is changed, the color constant cannot be maintained. Furthermore, since the maximum color gamut changes depending on the media, the color gamut cannot be used to the maximum extent possible.

  Further, as the evaluation items of the created color separation table, a plurality of items such as color gamut, gradation, graininess, and gloss can be considered. Of course, it is ideal to optimize the evaluation values for all these items, but in reality it is practical to set priorities for these evaluation items. In the conventional system, the priorities of these evaluation items are determined at the time of design and are fixed. Therefore, it has been impossible to create a color separation table so that evaluation values desired by the user are given priority and the evaluation value is increased.

  SUMMARY An advantage of some aspects of the invention is to provide a color separation table creating method and an image forming apparatus having the following features. In other words, when the color separation table for the second medium is automatically created based on the color separation table for the first medium, the priority order of the evaluation items can be set. Further, the number of patches is reduced by correcting the color gamut of the created color separation table by color prediction based on the colorimetric results of the patches formed on the second medium.

  As a technique for achieving the above object, the color separation table creation method of the present invention includes the following steps.

  In other words, a first table obtaining step for obtaining a first color separation table for the first medium, and restriction information on the amount of coloring material applied to each of the first medium and the second medium are obtained. A step of obtaining the amount of placement restriction, a priority order setting step of setting priorities for a plurality of evaluation items of the second color separation table for the second medium, the first color separation table, and the maximum placement A second table generating step for generating the second color separation table based on the quantity information and the priority order of the evaluation items.

  The color gamut of the second color separation table may be corrected by color prediction based on a color measurement result of a patch formed on the second medium.

  According to the present invention, a color separation table creating method and an image forming apparatus having the following features are provided. That is, when the color separation table for the second medium is automatically created based on the color separation table for the first medium, the priority order of the evaluation items can be set. Furthermore, the number of patches can be reduced by correcting the color gamut of the created color separation table by color prediction based on the color measurement result of the patch formed on the second medium.

  Therefore, it is possible to quickly create a color separation table that enables optimum image formation desired by the user on the second medium.

  Hereinafter, the present invention will be described in detail based on preferred embodiments with reference to the accompanying drawings. The configurations shown in the following embodiments are merely examples, and the present invention is not limited to the illustrated configurations.

<First Embodiment>
Output Process FIG. 1 is a diagram showing an image output process of a color printer that performs image formation with a plurality of colors in the present embodiment. In the figure, reference numeral 101 denotes a color matching processing unit for matching the reproduction characteristics of input RGB data with the color of the printer. Reference numeral 102 denotes an ink color separation processing unit for converting the multivalued R′G′B ′ data output from the color matching processing unit 101 into C′M′Y′K ′, which is the color material color of the printer. is there. Reference numeral 103 denotes a halftone processing unit for converting the multi-value C′M′Y′K ′ data output from the ink color separation processing unit 102 into the number of gradations that can be expressed by a printer. Reference numeral 105 denotes an ink color separation table that provides a table that is referred to during the interpolation processing in the ink color separation processing unit 102. An ink color separation table creation unit 104 creates the ink color separation table 105. Hereinafter, the ink color separation table 105 is also simply referred to as “color separation table”.

  FIG. 2 is a diagram showing a system configuration in the present embodiment. In FIG. 1, reference numeral 201 denotes a computer that holds input image data, and includes an input unit (not shown) such as a mouse for inputting a user instruction. Reference numeral 202 denotes a monitor for displaying image data held in the computer 201. Reference numeral 203 denotes a printer for color printing image data held in the computer 201. In the process configuration shown in FIG. 1 described above, the ink color separation table creation unit 104 is provided in the computer 201, but the rest is the configuration of the printer 203. It should be noted that the computer 201 may be provided with all configurations, and the CMYK data output from the halftone processing unit 103 may be input to the printer 203.

  Here, the printing process in the present embodiment will be described with reference to FIGS. 1 and 2. The image data held in the computer 201 is sent to the printer 203 via a cable or a network (not shown) at the time of printing.

  In the printer 203, the color matching processing unit 101 performs color matching processing on the transmitted RGB image data so as to match the color reproduction characteristics of the monitor 202 used by the user. The R′G′B ′ data after the color matching processing is separated into a plurality of ink colors CMYK in the printer 203 by interpolation processing based on the ink color separation table 105 that has already been created by the ink color separation processing unit 102. The The C′M′Y′K ′ multi-valued data after the ink color separation is converted into the number of gradations that can be reproduced by the printer 203 in the halftone processing unit 103 and then printed on a preset medium. . The ink color separation table 105 is generated in advance by the ink color separation table creation unit 104, and the generation method thereof will be described later.

  FIG. 3 is a diagram showing the configuration of the ink color separation table 105. The ink color separation table 105 stores data corresponding to lattice points in a cube in the RGB three-dimensional space as table data corresponding to the input data R′G′B ′. When the input R′G′B ′ data is not on the grid of the ink color separation table 105, the ink color separation processing unit 102 performs an interpolation process using grid point data in the vicinity thereof. There are many interpolation methods such as tetrahedral interpolation and cubic interpolation, but any interpolation method may be used.

  FIG. 4 is a diagram showing a cube on the RGB color space for explaining the method of creating the ink color separation table 105 in the present embodiment. The eight vertices of the cube are respectively represented by W, C, M, Y, and Let R, G, B, Bk. And all 19 which connect WC, M, Y, R, G, B-Bk, MR, RY, YG, GC, CB, B-M, and W-Bk. The book line is shown as a thick solid line. When the number of bits of input data in the ink color separation processing unit 102 is 8, the coordinates of each vertex of W, C, M, Y, R, G, B, and Bk are expressed as follows.

    W = (255, 255, 255): White, that is, a media background color.

    C = (0, 255, 255): Indicates a cyan primary color.

    M = (255, 0, 255): Indicates a magenta primary color.

    Y = (255, 255, 0): Indicates a yellow primary color.

    R = (255, 0, 0): Indicates a red primary color.

    G = (0, 255, 0): Indicates a green primary color.

    B = (0, 0, 255): Indicates a blue primary color.

    Bk = (0, 0, 0): Black, that is, the darkest point of the printer.

  In the ink color separation table creation unit 104, first, WC, M, Y, R, G, B-Bk, MR, RY, YG, GC shown by thick solid lines in FIG. , C-B, B-M, and table data for 19 lines connecting W-Bk are created. Thereafter, all the table data is created by performing an internal interpolation process for the ink colors corresponding to the internal grid points.

  Although a plurality of types of media can be used in the printer 203 of the present embodiment, an example in which two types of media are used will be described below for ease of explanation. That is, an example is shown in which the printer 203 can use the medium A, which is the first type of media, and the medium B, which is the second type of media, and prepare the respective ink color separation tables 105.

  In order to prepare a different color separation table for each media type, conventionally, all media types have been manually created. In the present embodiment, color separation tables for all media types are not manually created. In this embodiment, after manually creating a color separation table for a certain media type, color separation tables for other media types are automatically created based on the manually created color separation table. That is, after the color separation table for medium A is manually created, the color separation table for medium B is automatically created based on this.

● Color separation table creation process (Media A)
Hereinafter, the process for creating the color separation table for the medium A in the present embodiment will be described. FIG. 5 is a flowchart showing a process for manually creating a color separation table corresponding to the medium A in the color print system according to the present embodiment. This process is performed by the ink color separation table creation unit 104.

  First, in step S501, the W-Bk line, WC, M, Y, R, G, B line, C, M, Y, R, G, B-Bk line, and CG, GY, Y -Manually create color separation tables for R, RM, MB, and BC lines. Thereby, the optimum UCR (Under Color Removal) amount and BG (Black Generation) amount can be set for each hue. Therefore, it is possible to set a table in which the influence of the granularity due to black is suppressed as much as possible while maximizing the color reproduction range of the printer 203.

  Next, in step S502, based on the color separation table of the frame line created in step S501, internal interpolation processing for obtaining table data therein is performed.

  Then, the loop processing from step S503 to S505 is performed. The loop corrects the color separation table after the internal interpolation so that it is smooth and does not cause an excessive driving amount.

  In step S <b> 503, the driving amount correction is performed so that the table data of the color separation table, that is, the ink driving amount for each color does not exceed the driving amount limit of the medium A. This driving amount correction is performed by multiplying a driving amount correction rate by a driving amount over-occurrence portion in the color separation table. Here, the driving amount correction rate is defined by the number of loops. In this way, by performing the driving amount correction for the color separation table every time the loop is performed, the portion where the driving amount is over is corrected little by little, and a color separation table is finally obtained that does not cause the driving amount to be over. .

  Here, in the internal interpolation process in step S502 described above, the color space formed by the cube is divided into six tetrahedrons and subjected to the interpolation process for each area. Therefore, a pseudo contour is generated at the boundary of the area. End up. Therefore, in the present embodiment, in step S504, smoothing processing is performed in order to suppress the occurrence of pseudo contours.

  In step S505, in order to ensure that the ink placement amount strictly adheres to the placement amount restriction over the entire color separation table smoothed in step S504, the maximum placement amount is set for the entire table. Check if there is a part that exceeds. If there is no portion that exceeds, the process is terminated assuming that the color separation table is completed, but if there is a portion that exceeds, the process returns to step S503 to correct the driving amount.

  In this way, by correcting the portion of the color separation table that is overprinting amount little by little and performing the implantation amount correction while performing smoothing processing, the overprinting amount of the color separation table is exceeded. The generation of the pseudo contour can be suppressed while correcting the portion.

● Color separation table creation process (Media B)
Hereinafter, a process for creating a color separation table for the medium B in the present embodiment will be described. FIG. 6 is a flowchart showing a process for automatically creating a color separation table corresponding to the medium B based on the already created color separation table for the medium A. This process is performed by the ink color separation table creating unit 104. Is called.

  First, in step S601, the maximum placement amount restriction information U2 of the medium B, which is a new medium, is determined by forming a predetermined patch on the medium B and measuring the color. At this time, the predetermined maximum placement amount restriction information U1 for the medium A is also acquired. In step S602, a color separation table that strictly observes the maximum driving amount is automatically generated. Details of this automatic generation processing will be described later with reference to FIGS. In step S603, the color separation table of media B automatically generated in step S602 is further optimized by color prediction.

  FIG. 7 is a flowchart showing an automatic generation process of a color separation table that strictly observes the maximum printing amount limit of the medium B in step S602 of FIG. In this processing, the color separation table LUT2 of the medium B is automatically generated based on the color separation table LUT1 of the medium A that has been manually created in advance.

  First, in step S701, a manually created color separation table LUT1 of medium A, which is an original color separation table, is acquired. It is assumed that LUT1 has also been optimized.

  In step S702, the priority order of the evaluation items is set using a user interface described later. In step S703, the frame lines of the color separation table LUT2 of the medium B are automatically generated according to the priority order of the evaluation items. . Details of the automatic frame line generation processing will be described later.

  In step S704, based on the frame line created in step S703, internal interpolation processing for obtaining table data inside the frame line is performed. At the end of this internal interpolation processing, data for all grid points in the color space of LUT2 is ready.

  In step S705, driving amount correction processing is performed. That is, in the same way as when creating the LUT 1 for the medium A described above, the portion of the LUT 2 that exceeds the maximum placement limit indicated by U2 is corrected. Then, after smoothing in step S706, the driving amount overcheck is passed in step S707, thereby completing the LUT 2 that strictly observes the maximum driving amount restriction information U2.

  FIG. 8 is a flowchart showing the automatic generation process of the LUT2 frame line according to the priority order of the evaluation items in step S703 of FIG.

  First, in step S803, various parameters such as the priority order of evaluation items in the formed image and the nonlinear correction coefficient for nonlinear interpolation are acquired. In step S804, ink colors that can be used by the printer 203 are classified. Here, an example will be shown in which ink colors are classified into three types: main color, light color, and adjacent color. That is, description will be made assuming that the main color is CMYK ink, the light color is light cyan (Lc), light magenta (Lm), dark gray (Lk1), light gray (Lk2), and the adjacent color is RGB ink.

  In step S805, the frame line of LUT2 is set based on LUT1. With this frame line, W-Bk, WC, M, Y, R, G, B-Bk, MR, RY, Y-G, GC, CB, B-M It is a total of 19 lines to connect. Specifically, Bk and other color switching point information by under color removal (UCR) and separation ratio information of each color material color are acquired from the LUT 1 for each frame line.

  Subsequent processing is sequentially performed for each of the 19 frame lines. As the processing order, first, lines connecting the W and Bk points and the color points (C, M, Y, R, G, and B) are used. Process first, then process the line connecting the color points.

  Hereinafter, each point of C, M, Y, R, G, B, Bk, and W on the color space will be described as a main color point, that is, a primary point.

  In step S806, the color separation value of the primary point in the frame line set in step S805 is calculated so as to protect the maximum driving amount restriction information U2 of the medium B. In step S807, the color separation value of the frame line is linearly interpolated. For example, with respect to the primary point C in the LUT 2, the maximum placement amount is set to 180% in the LUT 1 for the medium A, and the maximum placement amount in the medium B calculated in step S806 is 200%. In this case, the C point of LUT1 is increased by 20% to 200%, and accordingly, the frame line set in step S805 (in this case, any of Bk-C, WC, CB, CG) C) is linearly increased by 20%, and this is used as the value of the frame line of LUT2.

  In step S808, the non-linear correction coefficient strength of each color is determined in accordance with the priority order of each evaluation item set in step S803. The non-linear correction coefficient strength is used at the time of non-linear correction for each ink color of main colors (C, M, Y, K), light colors (Lc, Lm, Lk1, Lk2), and adjacent colors (R, G, B). Each of which is E1, E2, E3. For example, when “granularity priority” is set as the evaluation item, the nonlinear correction coefficient strength is set to E1 = 1, E2 = 3, and E3 = 1 in order to effectively use light ink. For example, when “color gamut priority” is set as the evaluation item, the nonlinear correction coefficient strength is set to E1 = 3, E2 = 1, and E3 = 2 in order to effectively use the main color ink.

  In step S809, the main color is corrected using the non-linear correction coefficient strength E1. In step S810, the light color is corrected using the non-linear correction coefficient strength E2. In step S811, the adjacent color is corrected using the nonlinear correction coefficient strength E3. For the correction of the ink color data using the nonlinear intensity coefficient E, a known correction method using a parameter that enables nonlinear correction can be applied.

  In step S812, it is determined whether or not the total amount of ink for each grid point on the frame line being processed has reached the value indicated by the maximum hit amount restriction information U2. There are various possible determination methods. For example, in consideration of an intensity update method in step S813 to be described later, the maximum value of the ink amount based on the current correction result does not exceed the value indicated by the maximum hit amount restriction information U2. What is necessary is just to determine whether it becomes the value of.

  If each value on the frame line has not reached the value indicated by the maximum driving amount restriction information U2, that is, there is still room for correction, the nonlinear correction coefficient strengths E1, E2, and E3 are updated to increase in step S813. Then, the corrections in steps S809 to S811 are performed again. As a method for updating the nonlinear correction coefficient strength in step S813, for example, one is added to each coefficient strength, but the present invention is not limited to this example. By such a determination loop in step S812, all the values on the frame line are controlled as close as possible to the value indicated by the maximum driving amount restriction information U2, and the set maximum driving amount is maximized. As such, LUT2 can be created.

  In step S814, it is determined whether or not the processing has been completed for all 19 frame lines in the LUT 2. If the processing has not been completed, the process returns to step S805 to process the next frame line.

  FIG. 9 is a diagram showing an example of the contents of the LUT 2 created so as to strictly observe the maximum driving amount restriction information U2 of the medium B as shown in FIG. In the figure, 900 is an example of the Y → Bk line in the LUT 1 for the medium A, and the Y, Lk1, Lk2, and K ink amounts and the total ink applied amount 901 for each grid on the line are shown. Yes.

  Reference numeral 910 denotes an example in which LUT2 is created with priority given to graininess based on the Y → Bk line of LUT1, and Y, Lk1, Lk2, and K ink amounts and their total ink application amount 911 are shown. According to 910, it can be seen that by setting the non-linear correction coefficient strength E2 of the light color ink high, the light color inks Lk1 and Lk2 are used more effectively than in the case of 900. Further, according to the total ink application amount 911, it can be seen that the maximum ink application amount based on the ink application amount restriction information U2 of the medium B is significantly different from the total ink application amount 901 of the medium A shown in 900.

  Reference numeral 920 denotes an example in which LUT2 is created as a color gamut priority based on the Y → Bk line of LUT1, and the ink amounts of Y, Lk1, Lk2, K, R, and G, and the total ink applied amount 921 thereof. It is shown. In this case, the non-linear correction coefficient strength E1 of the main color ink is set high, the non-linear correction coefficient strength E2 of the light color ink is set low, and the non-linear correction coefficient strength E3 of the adjacent color ink is set to an intermediate value thereof. Therefore, according to 920, it can be seen that the adjacent color inks R and G as well as the main color ink Y are effectively used while suppressing the use of the light color inks Lk1 and Lk2. Also in 920, the total ink applied amount 921 is significantly different from the total ink applied amount 901 of the medium A shown in 900.

  The automatic creation process of the color separation table (LUT2) of the medium B based on the maximum driving amount base in step S602 in FIG. 6 has been described above. Next, the LUT2 optimization process based on the color prediction base in step S603 will be described.

  FIG. 11 is a flowchart showing the color gamut optimization processing for the automatically created LUT 2 in step S603 of FIG. The color gamut optimization processing according to the present embodiment is characterized in that color prediction using CMY three colors is performed by Neugrbauer processing.

  First, in step S111, the four color gradation patches and the color mixture patches formed on the medium B are measured. The color measurement result of each patch here is used for color prediction by Neugebauer processing described later. In step S112, the reflectance [T] in the Neugebauer equation shown below is obtained based on the colorimetric data of the patch. In the following formula, [T] is the reflectance of eight basic colors, and by calculating this, the RGB reflectance for an arbitrary combination of CMY can be obtained from the following formula.

  Next, in step S113, an ideal color gamut for LUT2 is calculated based on the Neugebauer equation. Details of the ideal color gamut will be described later. In step S114, the color gamut (actual color gamut) of LUT2 is calculated based on the Neugebauer equation.

  In step S115, the actual color gamut of LUT2 is compared with the ideal color gamut, and LUT2 is corrected by UCR processing based on the difference. As a result, an LUT 2 'obtained by performing color gamut correction on the LUT 2 is obtained. As will be described later, since this color gamut correction process loops, it is assumed that a predetermined amount of correction is performed at a time.

  In step S116, the actual color gamut of the LUT 2 ′ after correction is calculated based on the Neugebauer equation (the color gamut of LUT2 ′ is also described as being calculated by Neugebauer). In step S117, the actual color gamut of the LUT2 ′ is calculated. Compare the actual color gamut with the ideal color gamut. If the difference ΔE between the actual color gamut and the ideal color gamut of the LUT 2 ′ is equal to or smaller than a predetermined threshold N (for example, N = 1), the process ends. If ΔE is larger than N, the process returns to step S115. The correction of LUT2, that is, the creation of LUT2 ′ is repeated.

  In this way, when optimizing the LUT2, by calculating the ideal color gamut and the actual color gamut of the LUT2 by color prediction based on the colorimetric result of the predetermined patch, all patches necessary for the color gamut calculation are obtained. There is no need to form and measure colors. Therefore, the number of patches actually formed can be reduced.

  FIG. 12 shows an example of the ideal color gamut described above. For example, when an ink system of nine colors C, M, Y, K, R, G, B, Lk1, and Lk2 is taken as an example, as shown in the upper part of FIG. 12, the colors for three colors K, Lk1, and Lk2 Arbitrary K, Lk1, and Lk2 can be converted into K by performing the prediction. Thereby, as shown in the lower part of FIG. 12, eight kinds of four-color prediction results of CMYK, RGBK, CMBK, CYGK, MYRK, RGYK, RBMK, GBCK can be obtained, and an ideal color gamut can be calculated.

  FIG. 13 is a diagram illustrating an example in which K, Lk1, and Lk2 on the Y → Bk line are converted to K. According to the figure, it can be seen that K, Lk1, and Lk2 before conversion shown in the upper part are converted only to K ink as shown in the lower part.

User Interface FIG. 10 is a diagram showing an example of a user interface for setting priority order, which is displayed on the monitor 202 in order to make it possible to set the priority order of evaluation items for a formed image in step S702 described above. In the figure, reference numeral 100 denotes an input unit of the LUT 1 of the medium A as the original medium. Reference numeral 101 denotes an evaluation item priority order input unit for inputting numbers such as “1”, “2”,... In the figure, an example is shown in which priorities can be set for “color gamut”, “graininess”, and “glossiness” as evaluation items. However, the evaluation items in the present invention are not limited to this example. . For example, it may be possible to set priorities for other items such as gradation. Reference numeral 102 denotes an output destination setting unit of the LUT 2 of the medium B as a new medium. Reference numeral 103 denotes a button for instructing execution of automatic generation of the LUT 2 according to the evaluation item priority order set in 101. Note that the priority order of the evaluation items set here is held in a memory in the computer 201.

  FIG. 14 is a diagram showing an example of a user interface for inputting the color measurement results of various patches for the above-described LUT2 color gamut optimization.

  In the figure, reference numeral 140 denotes an input unit of the LUT 2 of the medium B as a new medium. Reference numeral 141 denotes an input unit for the color measurement result of a single color gradation patch of four colors (in this case, CMYK). As a specific input method, for example, four colorimetric results may be sequentially described by separating them with commas. Reference numeral 142 denotes an input unit for color measurement results of eight types of four-color mixed patches. Here, the eight types of four-color mixed patches correspond to combinations referred to for calculating the ideal color gamut according to FIG. 12 described above. As a specific input method, for example, an input box may be displayed by clicking each input unit. Reference numeral 143 denotes an input unit for the color measurement result of the light and dark color mixture patch, for example, the color measurement result of the color mixture patch of K, Lk1, and Lk2. Reference numeral 144 denotes a button for instructing execution of LUT2 optimization processing based on the input colorimetric results of various patches.

  As described above, according to the present embodiment, when the second color separation table for the new second medium is automatically created by using the first color separation table for the existing first medium, a plurality of colors are created. Priorities according to user instructions can be set for these evaluation items. As a result, the second color separation table can be created in an optimum state.

  Further, when the automatically created color separation table is optimized, the number of patches actually formed can be reduced by calculating the color gamut of the color separation table by color prediction based on the patch colorimetry result.

  Therefore, it is possible to quickly create a color separation table that enables optimum image formation desired by the user on the second medium.

  In the present embodiment, the Lab space is used as the color space. However, other color spaces may be used.

  Moreover, although the example which performs the color prediction process accompanying color separation table preparation in the computer 201 was shown, you may perform this by hardware, such as a color prediction engine.

<Other embodiments>
The present invention can take the form of, for example, a system, apparatus, method, program, or storage medium (recording medium). Specifically, the present invention may be applied to a system composed of a plurality of devices (for example, a host computer, an interface device, an imaging device, a web application, etc.), or may be applied to a device composed of a single device. good.

  The present invention also provides a software program that implements the functions of the above-described embodiments directly or remotely to a system or apparatus, and the system or apparatus computer reads out and executes the supplied program code. Achieved. The program in this case is a computer-readable program corresponding to the flowchart shown in the drawing in the embodiment.

  Accordingly, since the functions of the present invention are implemented by computer, the program code installed in the computer also implements the present invention. In other words, the present invention includes a computer program itself for realizing the functional processing of the present invention.

  In that case, as long as it has the function of a program, it may be in the form of object code, a program executed by an interpreter, script data supplied to the OS, or the like.

  Recording media for supplying the program include the following media. For example, floppy disk, hard disk, optical disk, magneto-optical disk, MO, CD-ROM, CD-R, CD-RW, magnetic tape, nonvolatile memory card, ROM, DVD (DVD-ROM, DVD- R).

  As a program supply method, the following method is also possible. That is, the browser of the client computer is connected to a homepage on the Internet, and the computer program itself (or a compressed file including an automatic installation function) of the present invention is downloaded to a recording medium such as a hard disk. It can also be realized by dividing the program code constituting the program of the present invention into a plurality of files and downloading each file from a different homepage. That is, a WWW server that allows a plurality of users to download a program file for realizing the functional processing of the present invention on a computer is also included in the present invention.

  In addition, the program of the present invention is encrypted, stored in a storage medium such as a CD-ROM, distributed to users, and key information for decryption is downloaded from a homepage via the Internet to users who have cleared predetermined conditions. It is also possible to make it. That is, the user can execute the encrypted program by using the key information and install it on the computer.

  Further, the functions of the above-described embodiments are realized by the computer executing the read program. Furthermore, based on the instructions of the program, an OS or the like running on the computer performs part or all of the actual processing, and the functions of the above-described embodiments can also be realized by the processing.

  Further, the program read from the recording medium is written in a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer, and then executed, so that the program of the above-described embodiment can be obtained. Function is realized. That is, based on the instructions of the program, the CPU provided in the function expansion board or function expansion unit can perform part or all of the actual processing.

It is a figure which shows the image output process in the color printer of one Embodiment which concerns on this invention. It is a figure which shows the system configuration | structure in this embodiment. It is a figure which shows the structure of the ink color separation table in this embodiment. It is a figure which shows the cube on RGB color space as a color separation table in this embodiment. It is a flowchart which shows the manual preparation process of the color separation table in this embodiment. It is a flowchart which shows the automatic creation process of the color separation table in this embodiment. It is a flowchart which shows the automatic generation process of the frame line of the color separation table which strictly observes the maximum driving amount in this embodiment. It is a flowchart which shows the automatic generation process of the frame line of the color separation table according to the priority of the evaluation item in this embodiment. It is a figure which shows the example of the content of LUT2 produced so that the maximum implantation amount may be strictly observed in this embodiment. It is a figure which shows the UI example for the priority order setting of the evaluation item in this embodiment. It is a flowchart which shows the color gamut optimization process of the color separation table in this embodiment. It is a figure explaining the ideal color gamut referred in the case of color gamut optimization in this embodiment. It is a figure which shows the example which converts K, Lk1, and Lk2 into K in the case of the ideal color gamut calculation in this embodiment. It is a figure which shows the example of UI for the patch colorimetry result input referred in the case of color gamut optimization in this embodiment.

Claims (12)

Obtaining a first color separation table for obtaining a first color separation table for a first medium;
A step of obtaining a driving amount restriction for obtaining restriction information of a driving amount of a coloring material for each of the first medium and the second medium;
A priority setting step for setting a priority for a plurality of evaluation items of the second color separation table for the second medium;
A second color separation table generating step for generating the second color separation table based on the first color separation table, the restriction information of the driving amount, and the priority order of the evaluation items;
A method for creating a color separation table.   The color separation table creation method according to claim 1, wherein in the priority order setting step, priorities of the plurality of evaluation items are set based on a user instruction. In the generation step of the second color separation table,
Generating a frame line corresponding to a frame line on a color space in the second color separation table based on the priority of the evaluation items;
An internal interpolation step of calculating data of all grid points in the second color separation table by an internal interpolation process based on the data of the frame line;
For the second color separation table, a driving amount correction step for correcting data so that the driving amount of the coloring material does not exceed the limit defined by the limitation information of the driving amount;
A smoothing step of smoothing the data of the second color separation table corrected in the driving amount correction step;
The color separation table creation method according to claim 1, wherein: In the frame line generation step,
A main color point color separation step for calculating a color separation value at the main color point of the second color separation table;
A frame line calculation step of calculating data of the frame line by linear interpolation based on a color separation value at the main color point;
A coefficient intensity setting step for setting a nonlinear correction coefficient intensity for each color material based on the priority order of the evaluation items;
A frame line correction step for correcting the data of the frame line based on the nonlinear correction coefficient strength for each color material;
The color separation table creation method according to claim 3, wherein:   5. The method according to claim 1, further comprising a correction step of correcting a color gamut of the second color separation table by color prediction based on a color measurement result of a patch formed on the second medium. The color separation table creation method according to any one of the above items. In the correction step,
A colorimetric step of measuring the color of the patch formed on the second medium;
An ideal color gamut calculation step of calculating an ideal color gamut for the second medium by color prediction based on the color measurement result;
An actual color gamut calculation step of calculating a color gamut of the second color separation table;
A color gamut correction step of correcting the color gamut of the second color separation table based on the ideal color gamut;
The color separation table creation method according to claim 5, wherein:   7. The color separation table creation method according to claim 6, wherein color prediction is performed by Neugebauer processing in the ideal color gamut calculation step.   The color separation table creation method according to any one of claims 1 to 7, wherein the first color separation table is manually created in advance.   9. The color separation table creation method according to claim 1, wherein the plurality of evaluation items include at least one of color gamut, graininess, and glossiness.   An image is formed on the second medium by using a plurality of color materials using the second color separation table created by the color separation table creation method according to claim 1. An image forming apparatus.   A computer-readable program that controls a computer to execute the color separation table creating method according to any one of claims 1 to 9 by reading and executing the computer.   A computer-readable recording medium on which the program according to claim 11 is recorded.

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