JP2005288775A - Color estimation method, color adjustment method, and color image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a color estimation method by which color estimation can be highly accurately executed by using values of the color characteristics after measuring the values of the color characteristics of one/multiple-color by C, M, Y, and K inks when color obtained by overprint is estimated with calculation by using values of the color characteristics of each single color, and further, color is estimated by repeatedly executing calculation using values of the color characteristics of the other single colors. <P>SOLUTION: The spectral density of color obtained by overprinting a plurality of color materials on a recording medium is estimated by using each spectral density of colors obtained by printing each of a plurality of the color materials on the recording medium on the basis of the overprint order after receiving input of the overprint order for a plurality of the color materials, the spectral density of color obtained by overprinting two or three color materials in the color materials of yellow, magenta, cyan, and black stored in a color characteristic table, and the spectral density of a ground color of the recording medium. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a color estimation method for estimating a color obtained by printing a plurality of color materials on each other, a color adjustment method using the estimation method, and a color image forming apparatus to which the color adjustment method is applied.

  In recent years, with the spread of DTP (Desk Top Publishing) and the like, the work of image editing and page imposition on computer software has become common, and full digital editing has become rare.

  In these processes, aiming for further efficiency, image setter output that directly outputs image data that has undergone page editing on film, CTP (Computer to Plate) output that directly records images on a printing plate, and printing A CTC (Computer to Cylinder) for directly recording an image on a printing plate wound on a cylinder of the machine is performed.

  Moreover, in the calibration process in such a printing process, (1) confirmation of internal errors in the work site, that is, internal school, (2) external school to be submitted to the orderer and designer for confirmation of finishing, (3) printing Proofs are created and used in three main applications: a print sample provided to the captain of the machine as a sample of the final print.

  As described above, when color printing is made, color correction is performed at the stage of the original film to obtain a C (cyan) plate, an M (magenta) plate, a Y (yellow) plate, and a BK (black) plate. Produce a proof (color proof) using each color separation net original film, and make the original printing plate, the color of the original film is correct, the color is correct, and there is no character error. The printed matter was checked in advance.

  In this case, film output or printing plate output is performed only for calibration confirmation, and printing calibration or calibration with other calibration materials has the problem that waste of film and printing plate and unnecessary work increase. .

  Therefore, in particular, in a process of creating and editing a full digital image by such a computer, a system for directly outputting a color image called DDCP (Direct Digital Color Proof) or DCP (Digital Color Proof) is required. .

  Such DDCP records digital image data processed on a computer on a plate-making film with an image setter or the like, performs a final printing operation for directly producing a printing plate with CTP, or a printing machine with CTC. Create a color proof that reproduces the output object indicated by the digital image processed on the computer before recording the image directly on the printing plate wound on the cylinder, and the design, color, text, etc. This is to confirm.

  Further, as a means for creating a color proof, on the basis of halftone dot image data of each color separation halftone document, light composed of a combination of a plurality of lights having different wavelengths such as R, G, B, etc. There is a color proof creation device that reproduces a halftone image by exposing dots to develop dots of three basic colors Y, M, and C to create a color proof. It also reproduces the primary colors of printing presses (single color (ink material)), multi-colors (colors with superimposed ink) obtained by overprinting inks, and ground colors of printing paper (recording media). As described above, there is a type of DDCP that performs color adjustment by changing the output intensity of the three basic colors for each of the primary color, the multi-order color, and white (for example, Patent Document 1).

However, in order to perform the color adjustment described above, primary colors and multi-colors are output by a printing machine, and the color values of the colors and the ground color of the printing paper (for example, L * a * b * color specification). However, when special color inks are overprinted, special colors need to be measured each time because they differ in color, which requires a great deal of time and labor.

  Therefore, a method for estimating the color system value of the color obtained by repeatedly printing the ink containing the pigment using the values of the color characteristics of the lower color and the upper color, for example, the lower side and Color estimation method (Japanese Patent Application No. 2003-055365) for estimating from the spectral density of the target color and the upper color, and the L * a * b * color system values and L of the lower color and the upper color The applicant has proposed a color estimation method (for example, Japanese Patent Application No. 2003-292890) in which estimation is performed based on a density based on spectral characteristics different from the spectral characteristics used for obtaining the values of the * a * b * color system.

Japanese Unexamined Patent Publication No. 2003-149996 (paragraphs [0119]-[0168], FIGS. 3 to 5)

  However, the above-described color estimation method is an estimation method in the case where a special color is overprinted on 1 / multiple colors using, for example, C, M, Y, and K inks. For example, any of C, M, Y, and K inks is used. This is not a method for replacing these with special colors or for printing a plurality of inks in the desired order of printing. In such a case, even if the color characteristic values for the 1 / multi-order colors with C, M, Y, and K inks have already been obtained, for example, the multi-order colors are used as the values of the color characteristics of each single color. All calculations were repeated and estimated. However, in such estimation by repeated calculation, since estimation is further repeated by calculation using the spectral density obtained by calculation, there is a case where a deviation occurs between the obtained color and the actual color.

  The present invention has been made in view of the above circumstances, and the object of the present invention is to estimate the color obtained by overprinting using the values of the color characteristics of each single color, and to calculate the color of another single color. When estimating the color by repeating the calculation using the characteristic value, the value of the color characteristic of the 1 / multi-order color by C, M, Y, K ink is measured, and the value of the color characteristic is used. It is to provide a color estimation method capable of accurately estimating colors, a color adjustment method for reproducing colors estimated by the estimation method, and a color image forming apparatus to which the color adjustment method is applied. .

  In order to achieve the above object, the invention described in claim 1 is a color estimation method for estimating a color obtained by printing a plurality of color materials including a pigment on a recording medium, and at least yellow ( Y), magenta (M), cyan (C), and black (K) 2 or 3 of the color materials are printed on a recording medium and printed, and the measurement result of the spectral density of the color obtained is shown. The color obtained by storing the color characteristic table in advance and receiving the input of the order of printing of the plurality of color materials, and printing each of the plurality of color materials on a recording medium based on the order of printing overlay The spectral density of each color, the spectral density of the color obtained by printing two or three of the yellow, magenta, cyan, and black color materials stored in the color characteristic table and printing them, and The spectral density of the ground color of the recording medium There are, is characterized in that it comprises an estimation step for estimating the spectral density of the resulting color and print overprinting said plurality of color materials on a recording medium.

  In the invention according to claim 2, the estimation is performed by calculating a spectral density of a combination of the color materials obtained each time the plurality of color materials are sequentially printed on the recording medium in the order of the print overlap. Each is obtained by calculation using the spectral density of the color material and the spectral density of the ground color of the recording medium, and the calculation is repeated to estimate the spectral density of the color obtained by printing the plurality of color materials overprinted. Each time the printing is repeated and before the calculation, the color characteristic table is referred to and two or three of the yellow, magenta, cyan and black color materials corresponding to the color material combination are referred to. If there is a spectral density of a color obtained by printing one over another, the corresponding spectral density is adopted without performing the calculation.

  According to a third aspect of the present invention, in the calculation, the spectral density which is lower in the printing overlap order is adjusted by a numerical value indicating the transparency of the color material which is upper in the printing overlap order, and the spectral which is on the upper side is adjusted. It is characterized in that the density is adjusted by a numerical value indicating a state where the density is put on another color material on the upper side.

  According to a fourth aspect of the present invention, the calculation further uses the calculation result and a value proportional to a product of the spectral density on the lower side and the spectral density on the upper side.

  The invention described in claim 5 further includes the step of converting the estimated spectral density into a color system value.

  According to a sixth aspect of the present invention, the color of a halftone dot line portion obtained by printing each halftone dot image of a plurality of color materials including a pigment on a recording medium is reproduced as a target color. A color adjustment method for performing color adjustment by changing output intensities of a plurality of basic colors, wherein the correspondence relationship between the output intensities of the plurality of basic colors and the values of the L * a * b * color system A reference table to be stored in advance and at least two or three of yellow (Y), magenta (M), cyan (C) and black (K) color materials are printed on the recording medium and printed. The color characteristic table showing the measurement result of the spectral density of the color obtained in advance, and the input of the order of overprinting of the plurality of colorants, and the plurality of colorants based on the order of overprinting Of each of the colors obtained by printing each on the recording medium The spectral density of the color obtained by printing two or three of the yellow, magenta, cyan and black color materials stored in the color characteristic table, and the ground of the recording medium. An estimation stage for estimating the spectral density of the color of the halftone image using the spectral density of the color, and a color conversion stage for converting the estimated spectral density into a value of the L * a * b * color system, A color channel table for obtaining a combination of output intensities of the plurality of basic colors for reproducing the target color based on the value of the L * a * b * color system obtained by the color conversion and the reference table A generation step of generating the halftone image, and based on the color channel table, the color intensity is adjusted by changing the output intensity of the plurality of basic colors to reproduce the color of the halftone image line portion.

  According to a seventh aspect of the present invention, the estimation is performed by calculating a spectral density of a combination of the color materials obtained each time the plurality of color materials are sequentially printed on the recording medium in the order of the print overlap. Each is obtained by calculation using the spectral density of the coloring material and the spectral density of the ground color of the recording medium, and the calculation is repeated to estimate the spectral density of the color of the halftone line portion, and the printing is repeated. Before each calculation, the color characteristic table is referred to and two or three of the yellow, magenta, cyan, and black color materials corresponding to the color material combination are printed and printed. If there is a spectral density of the obtained color, the corresponding spectral density is adopted without performing the calculation.

  According to an eighth aspect of the present invention, in the calculation, the spectral density which is lower in the printing overlap order is adjusted by a numerical value indicating the transparency of the color material which is upper in the printing overlap order, and the spectral which is on the upper side is adjusted. It is characterized in that the density is adjusted by a numerical value indicating a state where the density is put on another color material on the upper side.

  The invention according to claim 9 is characterized in that the calculation further uses a value proportional to a product of the calculation result and the spectral density on the lower side and the spectral density on the upper side.

  The invention according to claim 10 is characterized in that a plurality of basic colors are obtained by setting the color of a halftone dot line portion obtained by printing each halftone image of a plurality of color materials including a pigment on a recording medium as a target color. A color image forming apparatus that forms a color image while changing and reproducing a color output intensity, and a correspondence relationship between the output intensity of the plurality of basic colors and the value of the L * a * b * color system And at least two or three of yellow (Y), magenta (M), cyan (C) and black (K) color materials are printed on the recording medium and printed. In response to an input of a color characteristic table showing the measurement result of the spectral density of the color and the printing order of the plurality of coloring materials, each of the plurality of coloring materials is printed on a recording medium based on the printing order. Spectral density of each color obtained by the above, the color characteristic table The spectral density of the color obtained by printing two or three of the yellow, magenta, cyan and black color materials stored in the printer and the spectral density of the ground color of the recording medium. And calculating means for obtaining the spectral density of the color of the halftone image line portion, color converting means for converting the obtained spectral density into a value of the L * a * b * color system, and the color converting means. Generating means for generating a color channel table by obtaining a combination of output intensities of the plurality of basic colors for reproducing the target color based on the values of the L * a * b * color system and the reference table; And control means for controlling the output intensity of the plurality of basic colors based on the color channel table when forming the color image.

  According to the color estimation method according to claim 1, the spectral density of each of the colors obtained by printing each of the plurality of color materials on the recording medium and the spectral density of the ground color of the recording medium based on the order of overprinting. In addition to the estimation performed, the measurement result of the spectral density of the color obtained by printing two or three of Y, M, C, and K color materials measured and stored in advance is used. A color obtained by printing a plurality of color materials on a recording medium with high accuracy can be estimated.

  According to the color estimation method of claim 2, using the spectral density of the ground color of the recording medium and the spectral density of each color obtained by printing each of the plurality of color materials on the recording medium, When calculating the spectral density of the combination of color materials obtained each time printing is performed sequentially in the order of printing, if the color material combination is in the color characteristic table, the spectral density measured by the color characteristic table is used, so accuracy A color obtained by printing a plurality of color materials on a recording medium can be estimated.

  According to the color estimation method of claim 3, the lower spectral density is adjusted by a value indicating the transparency of the upper color material, and the upper spectral density is a numerical value indicating a state of being put on another color material. By adjusting, it is possible to estimate with high accuracy the color obtained by overprinting and printing.

  According to the color estimation method of claim 4, the color density of the lower color material itself or the color density of the color material itself on the upper side is printed at a wavelength indicating a relatively high density. By further correcting the spectral density of the obtained color, it is possible to estimate the color obtained by overprinting with high accuracy.

  According to the color estimation method of the fifth aspect, the color system value can be obtained from the estimated spectral density obtained.

  According to the color adjustment method of claim 6, the spectral density of each of the colors obtained by printing each of the plurality of color materials on the recording medium and the spectral density of the ground color of the recording medium based on the order of overprinting. In addition to the estimation performed, the measurement result of the spectral density of the color obtained by printing two or three of Y, M, C, and K color materials measured and stored in advance is used. It is possible to accurately estimate the color of the halftone image line portion and perform color adjustment using a plurality of basic colors so as to reproduce the estimated color as a target.

  According to the color adjustment method of claim 7, using the spectral density of the ground color of the recording medium and the spectral density of each color obtained by printing each of the plurality of color materials on the recording medium, When calculating the spectral density of the combination of color materials obtained each time printing is performed sequentially in the order of printing, if the color material combination is in the color characteristic table, the spectral density measured by the color characteristic table is used, so accuracy The color of the halftone dot line can be estimated well, and color adjustment can be performed using a plurality of basic colors so as to reproduce the estimated color as a target.

  According to the color adjustment method described in claim 8, the spectral density on the lower side is adjusted with a value indicating the transparency of the upper color material, and the spectral density on the upper side is a numerical value indicating a state where the spectral density is on another color material. By adjusting, it is possible to estimate the color of the halftone image line portion with high accuracy, and to perform color adjustment using a plurality of basic colors so as to reproduce the estimated color as a target.

  According to the color adjustment method of the ninth aspect of the present invention, it is obtained by overprinting and printing at a wavelength at which the spectral density of the lower colorant itself or the spectral density of the upper colorant itself is relatively high. By further correcting the spectral density of the generated color, it is possible to estimate the color of the halftone image portion with high accuracy, and perform color adjustment using a plurality of basic colors so as to reproduce the estimated color as a target. be able to.

  According to the color image forming apparatus of claim 10, based on the printing order, the spectral density of each of the colors obtained by printing each of the plurality of color materials on the recording medium and the spectral of the ground color of the recording medium. In addition to the density and estimation to be performed, the measurement result of the spectral density of the color obtained by printing two or three of the Y, M, C, and K color materials measured and stored in advance is used. Therefore, it is possible to accurately estimate the color of the halftone image line portion, and to perform color adjustment using a plurality of basic colors so as to reproduce the estimated color as a target.

  The present invention relates to a color obtained by printing a plurality of inks on a printing paper as a recording medium, and printing the measured inks on the basis of values of color characteristics obtained by measuring the printed inks. Is estimated. In particular, it works suitably when the ink contains a pigment.

  In addition, a description will be given of a method using a transmission density (hereinafter referred to as a spectral density) for each wavelength λ of light as a color characteristic value used in the color estimation method.

Here, the spectral density is, for example, the reflectance R is measured by changing the wavelength every 10 nm between 380 nm and 730 nm, and from the reflectance R,
-0.5 × LOG10 (R)
It is converted into a density by the formula of

  The value of the L * a * b * color system is one of the values of the color system representing the color, and represents the color in the three-dimensional space of the L * axis, a * axis, and b * axis. The hue and saturation are represented by the a * b * plane, and L * is a value of a color characteristic that is orthogonal to the a * b * plane and represents the lightness. The values of the L * a * b * color system are x-bar, y-bar defined by the CIE (Commission Internationale de l'Eclairage) as equivalent to the sensitivity of the human eye. , Z-bar spectral characteristics (predetermined spectral characteristics) based on the values of the XYZ color system obtained by integrating the amount of light.

  In the following description of the present invention, an embodiment applied to a color proof producing apparatus (color image forming apparatus) is shown as an example, and will be specifically described with reference to the drawings.

(Control configuration of color proofing device)
First, the color proof creating apparatus according to the present embodiment uses a color of a halftone dot line portion obtained by printing each halftone dot image of a plurality of inks on a printing machine as a target color, and the target color is a color. In some cases, a plurality of basic colors (Y (yellow), M (magenta), C (cyan)) in the proof creation apparatus are described in the order of “C, M, Y”, “YMC”, “CMY”. .)) Is output while changing the output intensity and is suitable for applying the color adjustment method using the color estimation method of the present invention.

  FIG. 1 shows a functional block diagram of the color proof producing apparatus. As shown in FIG. 1, the color proof creating apparatus according to the present embodiment includes a control unit 1, a color calculation unit 2, a color channel creation unit 3, and an image recording unit 4. Further, details of each part will be described below.

  The color calculation unit 2 includes a color calculation unit 21, a color characteristic table 22, a coefficient table 23 (numerical value table), a color table 24, and an input unit 25.

  The color characteristic table 22 is a primary color, a secondary color, a tertiary color, a quaternary color (hereinafter, referred to as “color”) printed on a printing paper using, for example, C, M, Y, and K (black) inks. In some cases, the colors may be collectively referred to as CMYK1 / 2/3/4 quaternary colors, and in some cases, 2/3/4 quaternary colors may be described as multi-order colors.) Spectral density is stored in advance. The color characteristic table 22 may store in advance the spectral density obtained by measuring the spot color.

  Here, CMYK1 / 2/3/4 quaternary colors will be described. A primary color is a color in CMYK, a secondary color is a color that combines two of CMYK, a tertiary color is a color that combines three of CMYK, and a quaternary color Colors that combine four of CMYK. Primary colors are C, M, Y, K. Secondary colors are R (M + Y), G (C + Y), B (C + M), K + C, K + M, K + Y. The tertiary colors are C + M + Y, KR (K + M + Y), KG (K + C + Y), KB (K + C + M), and the quaternary colors are C + M + Y + K, for a total of 15 colors.

  Further, FIG. 2 shows the configuration of the color characteristic table 22. As shown in FIG. 2, each of the above-mentioned colors and the background color of the printing paper are composed of spectral densities. However, notation of each numerical value was omitted. Moreover, R (red) and G (green) are shown as examples of the special colors.

  The coefficient table 23 is storage means for storing the transparency coefficient a, the trapping rate coefficient b, and the correction coefficient c for each ink in a configuration as shown in FIG. 3, for example. The transparency coefficient a is a numerical value indicating the transparency of the ink, and is a coefficient for correcting the spectral density of the lower color when a spot color is overprinted. Moreover, the trapping rate coefficient b is a numerical value indicating whether it is easy or difficult to get on other ink, in other words, a state where it is on the other ink, and when it is on the upper side, the spectral density of the color of that ink is corrected. Is a coefficient for The correction coefficient c is a coefficient used for a correction term included in an expression used for color estimation described later.

  If the ink is completely transparent, the transparency coefficient a is “1”. If the ink is completely opaque, the transparency coefficient a is “0”. Therefore, the transparency coefficient a is a constant between 0 and 1. is there. Further, the trapping rate coefficient b is a constant between 0 and 1 because if the value for the printing paper is 1, generally the amount of the ink is reduced compared to the printing paper. It depends on the ink.

  The input means 25 is, for example, for specifying an ink used for printing (C, M, Y, K, and a special color) and an ink printing order and inputting a color proof creation instruction. Further, the color characteristic table 22 is used to input the above-described colors and their spectral densities, and the coefficient table 23 is used to input each coefficient. In addition, for example, it is an interface for connecting to a measuring instrument, a reading device for mounting a FD (Floppy (Registered Trademark) Disk) or the like into which spectral density measurement results and coefficients are input so as to be able to be put in and out. May be.

  Further, the color characteristic table 22 and the coefficient table 23 may be incorporated from the beginning in storage means such as an HDD (Hard Disk Drive) provided in the color proof creating apparatus, for example.

  The color calculation means 21 functions as an extraction means for extracting each coefficient from the coefficient table 23, and the color of the halftone dot line portion obtained by overprinting from each spectral density stored in the color characteristic table 22. The function as the calculation means of the present invention for obtaining the spectral density, or the acquisition means for searching the color characteristic table 22 for the spectral density of the color obtained each time the ink is printed in the process of calculating the spectral density, and acquiring it if there is. Function, function as color conversion means for converting spectral density into L * a * b * color system value, and function for storing the obtained L * a * b * color system value in the color table 24 Is provided. A detailed calculation method will be described later.

  The color table 24 stores the ground color of the printing paper and the value of the L * a * b * color system of the color of the halftone image portion obtained by the color calculation means 21 (details will be described later).

  The color channel creation unit 3 includes a color channel calculation unit 31, a reference table 32, and a color channel table 33.

  The reference table 32 defines L * a * b * → CMY, which defines the correlation with the combination of the output intensity of each basic color corresponding to the value of the L * a * b * color system as output characteristics in the image recording unit 4. The LUT is stored. This L * a * b * → CMY LUT indicates the output intensity of C, M, and Y of the image recording unit 4 (described later) as described in the specification of Japanese Patent Application No. 2003-066429 by the present applicant. A color chart in which a plurality of color images in which the respective outputs are combined with equal division between the minimum value 0 and the maximum value is arranged is output, and the L * a * b * color system values of the plurality of color images A CMY → L * a * b * LUT is created from the combination of the output intensity of C, M, and Y and the value of the L * a * b * color system at that time, and the CMY → L * Output intensity of C, M, and Y for each combination obtained by equally dividing L * (0 to 100), a *, (-127 to 128), and b * (-127 to 128) using an a * b * LUT Can be obtained by performing a convergence calculation process.

  The color channel calculation means 31 is based on the L * a * b * color system value stored in the color table 24 and the L * a * b * → CMY LUT stored in the reference table 32. It has the function as a production | generation means of this invention which produces | generates. For example, as described in the specification of Japanese Patent Application No. 2003-066429 by the present applicant, L * a * b * → CMY LUT input point L * a * b * is stored in the color table 24. L * a * b * color system value L * a * b * L * 2 point (L1, L2), a * 2 point (a1, a2), b * 2 point (b1) , B2) from the output intensity of C, M, Y for 8 points and the distance from each input point of L * a * b * each value of L * a * b * color system A combination of C, M, and Y output intensities with respect to the stored L * a * b * color system values can be obtained.

  Further, in the present embodiment, it has been described that L * a * b * → CMY LUT is stored as the reference table 32. However, as the reference table 32, L * a * b corresponding to combinations of output intensities of basic colors. * CMY → L * a * b * LUT defining the correlation with the value of the color system may be stored. In that case, when obtaining a combination of CMY output intensities for outputting L * a * b * color system values, CMY → L * a * b * LUT to L * a * b * → CMY What is necessary is just to obtain | require LUT. Therefore, the “reference table” of the present invention includes an output intensity of a plurality of basic colors such as L * a * b * → CMY LUT and CMY → L * a * b * LUT, and L * a * b * color system. It is sufficient if it shows the correspondence between the values of.

  The color channel table 33 stores a combination of the background color of the printing paper and the output intensity of CMY in the image recording unit 4 constituting the color of the halftone image line unit. Although details will be described later, for example, the output intensity combination of Y indicates the minimum value 0 to the maximum value 140, and the output intensity of M and C indicates the minimum value 0 to the maximum value 160.

  The image recording unit 4 sensitizes the magenta coloring layer (M layer) of the photosensitive material with red (R) light, and sensitizes the cyan coloring layer (C layer) of the photosensitive material with green (G) light. The yellow color developing layer (Y layer) of the photosensitive material is exposed to light, and development processing is performed to reveal and output basic colors Y, M, and C, thereby forming a color image. The photosensitivity by the red (R) light, the green (G) light, and the blue (B) light is performed by simultaneously irradiating light of these colors for each pixel in a dot-sequential manner.

  The control unit 1 has a function of controlling each unit and also has a function as a control unit of the present invention, and the image storage unit 4 is based on halftone image data separated for each ink from the image data. A combination of output intensities constituting colors to be output by each pixel is obtained with reference to the color channel table 33, and the image recording unit 4 changes the output intensities of the basic colors Y, M, and C and outputs them. As described above, the Y, M, and C output intensity data obtained from the color channel table 33 are converted into B, R, and G exposure output intensity data, and the light intensity of each color of the image recording unit 4 is changed. Control. In order to realize such functions, a CPU (not shown), a program for performing overall control, a program for changing the output intensity of Y, M, and C, and various data necessary for executing each program are stored. A system memory (not shown) that constitutes a work area for storing and executing each program is configured.

  In this way, the color proof creating apparatus reproduces colors created by printing each halftone dot image of a plurality of inks on a printing machine by changing the output intensity of the basic colors Y, M, and C. Create a color proof.

(Color estimation method and color adjustment method using the color correction method)
Next, the color estimation method of the present invention and the color adjustment method using the color correction method will be described. In order to make the explanation easy to understand, the color estimation method will be explained while explaining the procedure of processing performed by the color proof creating apparatus.

  A processing procedure in the color proof creation apparatus of the present embodiment to which the color adjustment method including the color estimation method described above is applied will be described with reference to the flowchart shown in FIG. Here, the transparency coefficient a, the trapping rate coefficient b, and the correction coefficient c are stored in the coefficient table 23 in advance. In addition, the CMYK1 / 2/3/4 color and the ground color spectral density of the printing paper printed on the printing paper using the C, M, Y, and K inks were printed on the printing paper, and the spot color was printed on the printing paper. The color is measured in advance and stored in the color characteristic table 22. Further, each step is omitted as S21 in FIG. The other steps are the same.

(S21)
As shown in FIG. 4, first, an instruction for creating a color proof input by the operator using the input means 25, for example, a plurality of inks used for printing and the order of overprinting are input, and the ink and the order of overprinting are input. An instruction to create a color proof when printing with is accepted. For example, the following description will be given by taking as an example the case where C, R, and K inks are used and the printing overlap order is instructed as K → C → R. In addition, the spectral density of the spot color is stored in the color characteristic table 22 in advance, but the spot color used when the operator inputs an instruction to create a color proof using the input unit 25 is applied to the printing paper. You may make it input the measurement result of the spectral density of the printed color.

(S22)
In response to the input of the instruction, the color calculation means 21 obtains the color of the halftone dot line portion obtained by printing the designated ink on top of each other. In this case, since the C, R, and K inks are printed in the order of K → C → R, the color of the halftone dot line portion is 7 of K, C, K + C, R, K + R, C + R, and (K + C) + R. Color. The seven colors and the ground color of the printing paper are shown in FIG. 5, and the correspondence between each color and ink (denoted by ● marks) is shown. Further, the ink printing order is the order from the left ink in FIG. 5, that is, the order of K → C → R.

(S23)
Next, the color calculation unit 21 calculates the spectral density of the ground color of the printing paper and the color of the above-described halftone image line portion by calculation. First, the spectral density of the ground color of the printing paper is the spectral density stored in the color characteristic table 22. Then, as shown in FIG. 6, the spectral density of the color of each halftone line portion is determined by the spectral density of the ground color of the printing paper, the primary color of the designated ink printed on the printing paper, and the color characteristics. It is determined using the CMYK 2/3 tertiary colors in Table 22. FIG. 6 is a flowchart showing the procedure of the color estimation method of the present invention. In addition, since the color estimation of the present invention is obtained using the CMYK 2/3 tertiary color of the color characteristic table 22, it is effective when the plurality of inks input in S21 include at least two of the CMYK inks. It works.

  First, the case of primary color (single color) will be described by taking C as an example. According to FIG. 6, the spectral density of the color obtained by printing the first-printed ink on the printing paper is acquired from the color characteristic table 22 (S11). In this case, the C spectral density of the color characteristic table 22 is acquired. Subsequently, it is determined whether there is ink to be overprinted next (S12). Here, since it is about C single color, the process proceeds to S17, and the acquired spectral density of C is set as the spectral density of C. The same applies to K and R.

  Next, the case of a secondary color will be described by taking K + C and K + R as examples. First, K + C acquires the K spectral density of the color characteristic table 22 as the spectral density of the color obtained by printing the first-printed ink on the printing paper (S11). Subsequently, it is determined whether or not there is ink to be overprinted next (S12). Since C is overprinted, the process proceeds to S13. Here, the color calculation means 21 searches the color characteristic table 22 and determines whether there is a color obtained by printing C over K. Since there is KC in the color characteristic table 22 (S13, Y), the spectral density of KC in the color characteristic table 22 is acquired as the spectral density obtained by printing K and C on the printing paper. Further, it is determined whether or not there is ink to be printed next (S12). Here, since it is about two colors of K + C, the process proceeds to S17, and the acquired spectral density of KC is set as the spectral density of K + C.

  On the other hand, K + R acquires the K spectral density of the color characteristic table 22 as the spectral density of the color obtained by printing the first-printed ink on the printing paper (S11). Subsequently, it is determined whether or not there is ink to be overprinted next (S12). Since R is overprinted, the process proceeds to S13. Here, the color calculation means 21 searches the color characteristic table 22 and determines whether or not there is a color obtained by printing R over K. Since there are no overprinted colors in the color characteristic table 22 (S13, N), the spectral density of the color obtained by printing the upper ink R on the printing paper is obtained from the color characteristic table 22 (S14). . In this case, the spectral density of the special color 1 (R) in the color characteristic table 22 is acquired. Then, using the spectral densities of K and R acquired from the color characteristic table 22, the spectral density of the color obtained by printing K and R on the printing paper is obtained (S15).

  Here, the spectral density of the color (hereinafter referred to as color 1) obtained by printing the lower ink (first color material) (hereinafter referred to as ink 1) on the printing paper is represented by SD1 (λ). To do. In this case, SD1 (λ) is the spectral density of the color obtained by printing K on the printing paper, that is, the spectral density of K in the color characteristic table 22. The spectral density of the color (hereinafter referred to as color 2) obtained by printing the upper ink (second color material) (hereinafter referred to as ink 2) on the printing paper is defined as SD2 (λ). In this case, SD2 (λ) is the spectral density of the color obtained by printing R on the printing paper, that is, the spectral density of spot color 1 (R) in the color characteristic table 22. The spectral density of the ground color of the printing paper (hereinafter referred to as color W1) is SDW1 (λ). Furthermore, a trapping rate coefficient b set for ink 2 or R, a transparency coefficient a set for ink 2 or R, and a correction coefficient c are acquired.

Then, a color obtained by printing ink 2 on ink 1 and printing ink 2 (hereinafter referred to as color M12), in this case, a color obtained by printing K and R on printing paper is estimated. Here, assuming that the spectral density of the color M12 is SDM12 (λ), SDM12 (λ) is
SDM12 (λ) = a × (SD1 (λ) −SDW1 (λ)) + b × (SD2 (λ) −SDW1 (λ)) + SDW1 (λ) −c × a × (SD1 (λ) −SDW1 (λ) ) × b × (SD2 (λ) −SDW1 (λ))
Asking.

  In the first term, SD1 (λ) is adjusted by a. a × (SD1 (λ) −SDW1 (λ)) indicates the spectral density of the ink 1 itself obtained through the ink 2. That is, by subtracting SDW1 (λ) from SD1 (λ), the spectral density of ink 1 itself without the spectral density SDW1 (λ) of the printing paper can be obtained, and the transparency of ink 2 is defined as the transparency coefficient a. By applying, the spectral density of ink 1 obtained through ink 2 is obtained. As described above, the transparency coefficient a is “1” if the ink 2 is completely transparent, and the transparency coefficient a is “0” if the ink 2 is completely opaque.

  In the second term, SD2 (λ) is adjusted by b. b × (SD2 (λ) −SDW1 (λ)) indicates the spectral density of the ink 2 itself when it is superimposed on the ink 1. That is, by subtracting SDW1 (λ) from SD2 (λ), the spectral density of ink 2 itself without the spectral density SDW1 (λ) of the printing paper can be obtained, and the trapping rate coefficient set for ink 2 can be obtained. By multiplying as b, the spectral density of the ink 2 itself when overlaid on the ink 1 is obtained. Moreover, as described above, the trapping rate coefficient b is a constant between 0 and 1.

  The third term is added with the spectral density SDW1 (λ) because the spectral density SDW1 (λ) of the printing paper is excluded in the above item 2.

  The fourth term c * a * (SD1 ([lambda])-SDW1 ([lambda])) * b * (SD2 ([lambda])-SDW1 ([lambda])) is a correction term for calculating a correction value, and the spectrum of ink 1 itself. Since the spectral density obtained by the sum of the above three terms is larger than the measured value at a wavelength at which the density or the spectral density of the ink 2 itself is relatively high, the spectral density of the ink 1 itself or the ink 2 itself The product of a × (SD1 (λ) −SDW1 (λ)) and b × (SD2 (λ) −SDW1 (λ)) so that the value to be reduced when the spectral density is relatively high is corrected. Multiplied by the correction coefficient c. In other words, the value is proportional to the product of SD1 (λ) and SD2 (λ).

  The coefficient values a, b, and c set for each ink used here are the spectral density SD measured for a plurality of overprinted colors, and the spectral density measured by measuring the plurality of overprinted colors. What is necessary is just to obtain | require beforehand so that the difference of the spectral density by estimation may become the minimum.

  Further, it is determined whether or not there is ink to be printed next (S12). Here, since it is about two colors of K + R, the process proceeds to S17, and the spectral density obtained by calculation is set as the spectral density of K + R. The same applies to C + R.

  Next, the case of the tertiary color K + C + R will be described. First, K + C + R acquires the spectral density of K in the color characteristic table 22 as the spectral density of the color obtained by printing the first-printed ink on the printing paper (S11). Subsequently, it is determined whether or not there is ink to be overprinted next (S12). Since C is overprinted, the process proceeds to S13. Here, the color calculation means 21 searches the color characteristic table 22 and determines whether there is a color obtained by printing C over K. Since there is KC in the color characteristic table 22 (S13, Y), the spectral density of KC in the color characteristic table 22 is acquired as the spectral density obtained by printing K and C on the printing paper. Further, it is determined whether or not there is ink to be printed next (S12). Since R is overprinted, the process proceeds to S13. Here, the color calculation means 21 searches the color characteristic table 22 and determines whether or not there is a color obtained by further printing R over K and C. Since there are no overprinted colors in the color characteristic table 22 (S13, N), the spectral density of the color obtained by printing the upper ink R on the printing paper is obtained from the color characteristic table 22 (S14). . In this case, the spectral density of the special color 1 (R) in the color characteristic table 22 is acquired. Then, using the spectral densities of KC and R acquired from the color characteristic table 22, the spectral density of the color obtained by printing K, C, and R on the printing paper is obtained (S15). According to the above equation for calculating the spectral density SDM12 (λ), in this case, K + C is ink 1, the spectral density of KC acquired from the color characteristic table 22 is SD1 (λ), R is ink 2, and the color characteristic table The spectral density of spot color 1 (R) acquired from 22 is calculated as SD2 (λ).

  Further, it is determined whether or not there is ink to be printed next (S12). Here, since it is about three colors of K + C + R, the process proceeds to S17, and the spectral density obtained by calculation is set as the spectral density of K + C + R.

  As described above, according to the color estimation procedure shown in the flowchart of FIG. 6, the spectral density of the ground color of the printing paper and the spectral density of each of the colors obtained by printing each of the plurality of inks on the printing paper. Are used to calculate the spectral density of ink combinations (for example, K, K + C, K + C + R in the above example) that are obtained each time printing is performed sequentially in the order of printing. In some cases, the spectral density obtained by measuring the color characteristic table (for example, K + C in the above example) is used to estimate the color obtained by printing a plurality of color materials on the recording medium (for example, In the above example, the spectral density of K + C + R was obtained using the spectral density measured for K + C and the spectral density of R), so each ink was printed on the printing paper with the spectral density of the color obtained by overprinting. If the spectral density of the resulting color was calculated using the estimated can be accurately performed color estimation compared to.

(S24)
Furthermore, from each spectral density of color M12 obtained by printing ink 2 on ink 1 obtained by estimation from each spectral density SDM12 (λ), XYZ color system, L * a * b * color system, etc. The value of the color system is obtained as follows. The process of obtaining the color system value from the spectral density is generally known, so only an outline will be described.

First, X, Y, and Z values of the XYZ color system are obtained. First, the spectral reflectance RM12 (λ) of each wavelength from the spectral density SDM12 (λ).
RM12 (λ) = 10 ^ (− 2 × SDM12 (λ))
(However, the notation a ^ b indicates a to the bth power.)
X is obtained by adding the value obtained by multiplying RM12 (λ) by x (λ) for all wavelengths (380 nm to 730 nm), and Y is obtained by multiplying RM12 (λ) by y (λ). The value is obtained by adding the values for all wavelengths (380 to 730 nm), and Z is obtained by adding the value obtained by multiplying RM12 (λ) by z (λ) for all wavelengths (380 to 730 nm). These x (λ), y (λ), and z (λ) are defined as CIE1931 XYZ color system color matching functions x (λ) defined by CIE (Commission Internationale de l'Eclairage (International Lighting Commission)), y (λ), z (λ) (in CIE 1931, a bar (-) is attached above x, y, z) and the value of the D50 standard light source. is there.

Then, the L * value, a * value, and b * value of the L * a * b * color system value are obtained from the obtained X, Y, and Z values of the XYZ color system. First,
Xd = X / X0, Yd = Y / Y0, and Zd = Z / Z0. However, X0, Y0, and Z0 are values obtained by adding x (λ), y (λ), and z (λ) for all wavelengths (380 nm to 730 nm), respectively. And
X2 = Xd ^ (1/3); Xd> 0.008856 = Xd × 7.787 + 16/116; otherwise Y2 = Yd ^ (1/3); Yd> 0.008856 = Yd × 7.787 + 16/116; otherwise Z2 = Zd ^ (1/3); if Zd> 0.008856 = Zd × 7.787 + 16/116; otherwise, X2, Y2, Z2 are determined.
L * = Y2 × 116-16
a * = 500 × (X2−Y2)
b * = 200 × (Y2-Z2)
Then, the L * a * b * color system value indicated by the L * value, a * value, and b * value is obtained. Then, the L * a * b * color system value is stored in the color table 24. With the configuration shown in FIG. 7, the background color of the printing paper (indicated as W (white) in the drawing), K, C, K + C, R, K + R, C + R, and (K + C) + R L * a * b * Stores the value of the color system.

(S25)
Next, the color channel calculation means 31 calculates the ground color of the printing paper from the L * a * b * color system value stored in the color table 24 and the L * a * b * → CMY LUT in the reference table 32. A combination of output intensities of a plurality of basic colors is obtained for K, C, K + C, R, K + R, C + R, and (K + C) + R, and stored in the color channel table 33 in the configuration shown in FIG.

(S26)
Then, the control unit 1 refers to the color channel table 33 and controls the image recording unit 4 to change the output intensities of a plurality of basic colors based on the image data, and the image recording unit 4 forms an image according to the control. I do. As described with reference to FIG. 6, when the spectral density of the combination of color materials obtained each time printing is sequentially performed in the order of printing overlap, the color is estimated accurately using the measured values. The color channel table is created using the result, and the output intensity of a plurality of basic colors is changed based on the color channel table, so that the color of the target halftone line portion can be accurately reproduced. .

  Further, the above color estimation or color channel table generation is performed using an information processing device such as a PC (Personal Computer), and the color estimation result or the color channel table is transmitted to a color proof via a medium such as a floppy disk. It is also possible for the creation device to acquire and use it for forming a color image.

  Further, in an image output system comprising an information processing device such as a PC and a color proof creating device, the information processing device such as a PC has the above-described color estimation or color channel table generation function, and the color estimation result or color channel table is provided. It is also possible for the color proof making apparatus to acquire the image via the interface and use it for forming a color image.

  Next, a specific example is shown in which the color obtained by performing the overprinting of ink using the color estimation method of the present invention is estimated. In this example, an example in which special color 2 (R) is overprinted on K (black) and C (cyan) is shown as an example.

  First, FIG. 9 shows the measurement result of the spectral reflectance R, that is, the spectral reflectance RW1 (λ) of the ground color of the printing paper, the spectral reflectance R1 (λ) of K + C, and the spectral reflectance R2 (2) of the spot color 2 (R). λ). In addition, for comparison of the spectral density described later between the color obtained by estimation and the color obtained by actually overprinting, the result of actually printing K, C, and spot color 2 (R) on the printing paper and measuring them. Is also shown as spectral reflectance RT12 (λ). In addition, in FIG. 9, the result measured about the wavelength of 10 nm increments between 380 nm and 730 nm was shown.

Next, from the spectral reflectance R, the spectral density SD is changed to SD = −0.5 × LOG10 (R).
From the above equation, the spectral density SDW1 (λ) of the ground color of the printing paper, the spectral density SD1 (λ) of K + C, and the spectral density SD2 (λ) of spot color 2 (R) are obtained, and further, K + C, spot color 2 (R). The spectral density SDM12 (λ) of the color obtained by printing
SDM12 (λ) = a × (SD1 (λ) −SDW1 (λ)) + b × (SD2 (λ) −SDW1 (λ)) + SDW1 (λ) −c × a × (SD1 (λ) −SDW1 (λ) ) × b × (SD2 (λ) −SDW1 (λ))
The calculation is performed for each wavelength by the following formula. At this time, the transparency coefficient a is the transparency coefficient 0.9 of the spot color 2 (R) from FIG. 3, the trapping rate coefficient b is the trapping ratio coefficient 0.9 of the spot color 2 (R) from FIG. Is 0.75 from FIG. Further, a spectral density SD1 ′ (λ) of K + C obtained by calculation from the spectral reflectance of K and the spectral reflectance of C is obtained, and the spectral density SDM of the color obtained by repeatedly printing the spot color 2 (R) in the same manner. '12 (λ) is obtained.

  The spectral density SDM12 (λ) is shown in FIG. FIG. 10 also shows the spectral density SDT12 (λ) obtained from the spectral reflectance RT12 (λ) for comparison between the color obtained by estimation and the color actually obtained by overprinting. Further, FIG. 10 also shows the spectral density SDM′12 (λ).

  Since the process of obtaining the color system value from the spectral density is generally known, only the outline is described by taking the case of the spectral density SDM12 (λ) as an example.

First, X, Y, and Z of the XYZ color system are obtained. First, the spectral reflectance RM12 (λ) of each wavelength from the spectral density SDM12 (λ).
RM12 (λ) = 10 ^ (− 2 × SDM12 (λ))
(However, the notation a ^ b indicates a to the bth power.)
X is obtained by adding the value obtained by multiplying RM12 (λ) by x (λ) for all wavelengths (380 nm to 730 nm), and Y is obtained by multiplying RM12 (λ) by y (λ). The value is obtained by adding the values for all wavelengths (380 to 730 nm), and Z is obtained by adding the value obtained by multiplying RM12 (λ) by z (λ) for all wavelengths (380 to 730 nm). These x (λ), y (λ), and z (λ) are defined as CIE1931 XYZ color system color matching functions x (λ) defined by CIE (Commission Internationale de l'Eclairage (International Lighting Commission)), y (λ), z (λ) (in CIE 1931, a bar (-) is attached above x, y, z) and the value of the D50 standard light source. is there. In this way, X, Y, Z are
(X, Y, Z) = (1.08, 0.99, 0.88)
It is obtained.

Further, L * a * b * color system value L * value, a * value, and b * value are obtained from X, Y, and Z. First, Xd, Yd, and Zd are obtained. And
X2 = Xd ^ (1/3); Xd> 0.008856 = Xd × 7.787 + 16/116; otherwise Y2 = Yd ^ (1/3); Yd> 0.008856 = Yd × 7.787 + 16/116; otherwise Z2 = Zd ^ (1/3); if Zd> 0.008856 = Zd × 7.787 + 16/116; otherwise, X2, Y2, Z2 are determined.
L * = Y2 × 116-16
a * = 500 × (X2−Y2)
b * = 200 × (Y2-Z2)
It can be asked.

From the spectral density SDM12 (λ) shown in FIG. 10 and the SDT 12 (λ) actually measured as described above, the L * value, a * value, and b * value are converted into LM *, aM *, and bM *, respectively. And LT *, aT *, and bT *
(LM *, aM *, bM *) = (8.9, 4.7, −1.2),
(LT *, aT *, bT *) = (9.5, 3.2, 2.0)
Is obtained. The color difference ΔE is
ΔE = ((LM * −LT *) ^ 2+ (aM * −aT *) ^ 2+ (bM * −bT *) ^ 2) ^ (1/2) = 3.5
It can be seen that the color is sufficiently small and the color is estimated accurately.

On the other hand, when the values LM ′ *, aM ′ *, and bM ′ * of the L * a * b * color system are similarly obtained from the spectral density SDM′12 (λ),
(LM ′ *, aM ′ *, bM ′ *) = (10.8, 4.1, −2.2)
Similarly, when the color difference from the L * a * b * color system value obtained from SDT12 (λ) is obtained,
ΔE = 4.5
Thus, it can be seen that using the spectral density obtained by printing and measuring K + C results in a smaller color difference and more accurate color estimation. Therefore, it can be seen that the estimation method of the present invention works effectively.

  In the present embodiment, the values of the L * a * b * color system of ink 1, ink 2, and printing paper as proposed by the applicant in Japanese Patent Application No. 2003-29289, and the L * a * b * The density is measured by a spectral characteristic different from the spectral characteristic of the color system value, and at least one of the XYZ color system values of the overprinted color is the value of the L * a * b * color system. In addition, when determining by using the density due to different spectral characteristics, if the value of the L * a * b * color system of the color obtained by overprinting and the density due to different spectral characteristics are determined by measurement, It is possible to carry out using measured values.

It is a functional block diagram which shows the structure of the color proof production apparatus which concerns on this invention. It is explanatory drawing which shows an example of a structure of the color characteristic table of this Embodiment. It is explanatory drawing which shows an example of a structure of the coefficient table of this Embodiment. It is a flowchart which shows the process sequence in the color proof production apparatus to which the color estimation method of this invention is applied. It is a figure which shows the correspondence of each color and ink which are printed. It is a flowchart which shows the procedure of the color estimation method of this invention. It is explanatory drawing which shows an example of a structure of the color table of this Embodiment. It is explanatory drawing which shows an example of a structure of the color channel table of this Embodiment. It is a figure which shows the measurement result of spectral reflectance RW ((lambda)) of the ground color of printing paper, spectral reflectance R1 ((lambda)) of K + C, and spectral reflectance R2 ((lambda)) of a special color (red). Spectral density SDM12 (λ) obtained by using K + C spectral density SD1 (λ) and spot color (red) spectral density SD2 (λ), spectral density SDT12 (λ) based on actual measurement, and spectral density obtained by measuring K FIG. 6 is a diagram showing a spectral density SDM′12 (λ) obtained by using a spectral density SD1 ′ (λ) of K + C and a spectral density SD2 (λ) of a special color (red) obtained from the spectral density obtained by measuring C and C. .

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Control part 2 Color calculation part 21 Color calculation means 22 Color characteristic table 23 Coefficient table 24 Color table 25 Input means 3 Color channel creation part 31 Color channel calculation means 32 Reference table 33 Color channel table 4 Image recording part

Claims (10)

A color estimation method for estimating a color obtained by printing a plurality of color materials including a pigment on a recording medium.
Measurement of spectral density of a color obtained by printing two or three of at least yellow (Y), magenta (M), cyan (C) and black (K) color materials on a recording medium. Pre-store a color characteristic table showing the results;
The spectral characteristics of the colors obtained by printing each of the plurality of color materials on a recording medium based on the order of printing overlap upon receiving the input of the order of printing of the plurality of color materials, the color characteristic table The spectral density of the color obtained by printing two or three of the yellow, magenta, cyan and black color materials stored in the printer and the spectral density of the ground color of the recording medium. And a estimating step of estimating a spectral density of a color obtained by printing the plurality of color materials on a recording medium.   The estimation is based on the spectral density of the combination of color materials obtained each time the plurality of color materials are sequentially printed on the recording medium in the order of printing, the spectral density of the color material combination and the recording medium. And calculating the spectral density of the color obtained by repeatedly printing the plurality of color materials and printing, and each time the printing is repeated and Before the calculation, the color characteristic table is referred to, and two or three of the yellow, magenta, cyan and black color materials corresponding to the color material combination are printed and printed. The color estimation method according to claim 1, wherein if there is a spectral density of a color, the corresponding spectral density is adopted without performing the calculation.   The calculation is performed by adjusting the spectral density that is lower in the printing overlap order with a numerical value indicating the transparency of the color material that is upper in the printing overlap order, and the spectral density that is on the upper side in addition to the color material that is on the upper side. The color estimation method according to claim 2, wherein the color estimation method is performed by adjusting a numerical value indicating a state of being on the color material.   4. The color estimation method according to claim 3, wherein the calculation further uses a value proportional to a product of the calculation result and the spectral density on the lower side and the spectral density on the upper side.   The color estimation method according to claim 1, further comprising a step of converting the estimated spectral density into a color system value. Change the output intensity of multiple basic colors to reproduce the color of the halftone image area obtained by printing each halftone image of multiple color materials containing pigment on a recording medium. A color adjustment method for performing color adjustment,
Preliminarily storing a reference table indicating a correspondence relationship between the output intensity of the plurality of basic colors and the value of the L * a * b * color system;
Measurement of spectral density of a color obtained by printing two or three of at least yellow (Y), magenta (M), cyan (C) and black (K) color materials on a recording medium. Pre-store a color characteristic table showing the results;
The spectral characteristics of the colors obtained by printing each of the plurality of color materials on a recording medium based on the order of printing overlap upon receiving the input of the order of printing of the plurality of color materials, the color characteristic table The spectral density of the color obtained by printing two or three of the yellow, magenta, cyan and black color materials stored in the printer and the spectral density of the ground color of the recording medium. Using the estimation step of estimating the spectral density of the color of the halftone dot line part,
A color conversion step of converting the estimated spectral density into a value of the L * a * b * color system;
A color channel table for obtaining a combination of output intensities of the plurality of basic colors for reproducing the target color based on the value of the L * a * b * color system obtained by the color conversion and the reference table And a generation stage for generating
A color adjustment method, wherein color adjustment is performed by changing output intensities of the plurality of basic colors based on the color channel table to reproduce colors of the halftone image line portion.   The estimation is based on the spectral density of the combination of color materials obtained each time the plurality of color materials are sequentially printed on the recording medium in the order of printing, and the spectral density of each color material combination and the recording medium. The spectral density of the background color of the image is obtained by calculation, and the calculation is repeated to estimate the spectral density of the color of the halftone image line portion, and the color before each calculation is repeated before the calculation. With reference to the characteristic table, if there is a spectral density of a color obtained by printing two or three of the yellow, magenta, cyan and black color materials corresponding to the color material combination, The color adjustment method according to claim 6, wherein the corresponding spectral density is adopted without performing the calculation.   The calculation is performed by adjusting the spectral density that is lower in the printing overlap order with a numerical value indicating the transparency of the color material that is upper in the printing overlap order, and the spectral density that is on the upper side in addition to the color material that is on the upper side. The color adjustment method according to claim 7, wherein the color adjustment method is performed by adjusting a numerical value indicating a state of being on the color material.   The color adjustment method according to claim 8, wherein the calculation further uses a value proportional to a product of the calculation result and the spectral density on the lower side and the spectral density on the upper side. Reproduced by changing the output intensity of multiple basic colors with the color of the halftone dot line obtained by printing each halftone image of multiple color materials including pigments printed on the recording medium. A color image forming apparatus for forming a color image while
A reference table indicating a correspondence relationship between output intensity of the plurality of basic colors and values of the L * a * b * color system;
Measurement of spectral density of a color obtained by printing two or three of at least yellow (Y), magenta (M), cyan (C) and black (K) color materials on a recording medium. A color property table showing the results;
The spectral characteristics of the colors obtained by printing each of the plurality of color materials on a recording medium based on the order of printing overlap upon receiving the input of the order of printing of the plurality of color materials, the color characteristic table The spectral density of the color obtained by printing two or three of the yellow, magenta, cyan and black color materials stored in the printer and the spectral density of the ground color of the recording medium. Computing means for obtaining the spectral density of the color of the halftone image line portion using,
Color conversion means for converting the obtained spectral density into a value of the L * a * b * color system;
A color channel for obtaining a combination of output intensities of the plurality of basic colors for reproducing the target color based on the L * a * b * color system value obtained by the color conversion means and the reference table Generating means for generating a table;
A color image forming apparatus, comprising: a control unit configured to control the output intensity of the plurality of basic colors based on the color channel table when forming the color image.

Images