JP2005151506A - 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, capable of estimating over-printing colors by calculating the spectral density corresponding to the values of a white background and a color table of CMYK 1/2/3/4-th order colors read from a device profile of a printer, and performing over-printing with the spectral density of a specific color. <P>SOLUTION: Spectral density base data 32 are produced by using a spectral density meter 7 to measure the spectral density of a background color of print paper, basic colors, characteristics and a background color of paper with the characteristics printed thereon. A spectral density calculating means 311 calculates the spectral density, corresponding to L*a*b* values of the background color and the CMYK1/2/3/4-th order colors stored in a color table 34 of a printer 6 from the spectral density of the background color and the basic colors stored in the spectral density basic data 32. On the basis of the spectral density, characteristics and the spectral density of the paper with the characteristics printed thereon, a spectral density estimating means 312 calculates the estimate value of the spectral density of the over-printing color resulting from printing the characteristics over the CMYK1/2/3/4-th order colors. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a color estimation method for estimating an overprinting color that is printed by overprinting a plurality of color materials such as inks including pigments, and to reproduce and output the overprinted color with a calibration color printer using the color estimation method. The present invention relates to a color adjustment method for performing color adjustment, and a color image forming apparatus capable of executing the color estimation method and the color adjustment method.

  In recent years, as represented by DTP (Desk Top Publishing) and the like, digitization of editing and printing has been advanced. For example, full digital processes such as taking in an image into a computer using a scanner and performing image editing and page imposition on software are also widely used.

  Also, image setter output that directly outputs image data that has been edited on the film, CTP (Computer To Plate) output that directly records the image on the printing plate, and image recording directly on the printing plate that is wound around the cylinder of the printing press Techniques such as CTC (Computer To Cylinder) output have been developed to increase the efficiency of the process.

  However, when such a method is used, in order to perform the calibration work, it is necessary to actually perform film output and printing plate output, which causes a problem that waste of film and printing plate and extra work increase. .

  Under these circumstances, when creating and editing full-digital images, a system called DDCP (Direct Digital Color Proof) or DCP (Digital Color Proof), which can directly output color images, is used. There are great expectations.

  DDCP performs digital processing before performing the process of recording digital image data on a plate-making film with an imagesetter, the final process of creating a printing plate directly with CTP, and the process of recording an image directly with a CTC on a printing plate. In this method, a color proof is directly output from the processed image data to reproduce an output target. According to this DCCP, before creating a final printing plate, a color separation network original document that has been separated into a C (cyan) plate, an M (magenta) plate, a Y (yellow) plate, and a K (black) plate. It is possible to create a proof (color proof) from the film and confirm the finished product in advance.

  As an apparatus for creating a color proof, for example, a silver salt color photosensor is used while controlling a plurality of laser beams having different wavelengths such as R, G, and B based on halftone dot image data separated into basic colors. Generally, a material that reproduces a halftone image with dots of the basic colors C, M, and Y by exposing the material is used. In such a proofreading color printer, by adjusting and outputting the output intensity of each of the three basic colors, the primary color (single color ink) output from the printing press or the multi-order obtained by repeatedly printing inks. There is known one configured to reproduce a color, and further white (ground color of printing paper). At this time, the characteristic values of the respective colors are obtained by actually outputting the primary color, the multi-order color, and white by a printing machine and measuring the color. That is, if the ink used in the printing press is C, M, Y, or K, measurement was performed for 16 types of 1/2/3/4 color and white. When spot color ink is used, the spot colors are overlaid on the 16 colors and output, and measurements are made for a total of 32 colors.

  However, there are thousands of special colors, and they are usually used in different ways depending on the printed matter, and even for the same special colors, the colors may differ depending on the lot or manufacturer. Unless each of the inks is output and measured in the above-described 16 colors, the color cannot be reproduced accurately, and much time and labor have been expended for this purpose.

  In order to deal with such a problem, when the spot color is overprinted on each of the 16 colors based on the characteristics of the 1/2/3/4 color and the white color and the characteristics of the spot color alone. A method for estimating the color has been proposed. As an example of such a color estimation method, there is a method of estimating the overprinting color by measuring the spectral densities of the above 16 colors and spot colors with respect to a plurality of light of a predetermined wavelength and simply adding the measurement results. . In this method, when the ink contains a dye, an estimated value that is sufficiently close to the measured value is obtained. However, when the ink contains a pigment, the accuracy of the estimation decreases due to factors such as light scattering by the pigment. End up. In addition, when adding the spectral densities, it is possible to correct the spectral density of the lower ink using the transparency coefficient of the upper ink, or to correct using the trapping rate coefficient indicating the so-called ink paste. However, there is a case where accuracy is deteriorated particularly in a wavelength region where the color has a relatively high density and accurate color estimation cannot be performed.

  Therefore, instead of simply adding the spectral density, the value obtained by subtracting the spectral density of the printing paper from the spectral density obtained by printing and measuring the lower ink on the printing paper, and the upper ink (special color) By using a value that is proportional to the product of the spectral density obtained by printing on the printing paper and subtracting the spectral density of the printing paper, the accuracy of estimating the overprinted color is improved. (For example, Japanese Patent Application No. 2003-055365, paragraphs [0039]-[0047], FIG. 5 by the present applicant).

  On the other hand, for color adjustment of the entire CMYK image as well as the halftone line portion, a device profile (color) representing the relationship between the CMYK value and the L * a * b * color system value for the printing press and the proof color printer. Also called table). The device profile of the printing machine includes the L * a * b * color system of the CMYK1 / 2/3/4 color halftone dot line (solid part). Can be used for color adjustment, but since the spectral density value is not included only in the L * a * b * color system, the special colors are overprinted on the CMYK1 / 2/3/4 color. In this case, the color estimation cannot be performed with high accuracy.

  The present invention has been made in view of the circumstances as described above. Overprinting colors with special color inks based on the color system values of the basic colors CMYK1 / 2/3/4 color read from the device profile of the printing press. Color estimation method capable of estimating the color with high accuracy, a color adjustment method for performing color adjustment for reproducing and outputting the overprinted color with a calibration color printer using the color estimation method, and the color estimation It is an object of the present invention to provide a color image forming apparatus capable of executing the method and the color adjustment method.

  In order to achieve the above object, the invention according to claim 1 is characterized in that the output intensity of the ground material of the printing paper and the color materials of the basic colors C (cyan), M (magenta), Y (yellow), and K (black). The CMYK1 / 2/3/4 quaternary color and the special color are printed on the printing paper by using a color table storing a predetermined color system value of the CMYK1 / 2/3/4 quaternary color composed of A color estimation method for estimating a spectral density of an overprinted color obtained by overlapping, a first acquisition step of acquiring a spectral density of a ground color of the printing paper and a spectral density of each basic color, and the spot color A second acquisition step of acquiring the spectral density of the base color of the paper on which the spot color is printed, and the spectral density of the base color and the basic colors acquired in the first acquisition step. And the background color stored in the color table and the CMYK1 / 2 / / Calculation step for calculating the spectral density corresponding to the value of the predetermined color system of the quaternary color, the spectral density calculated in the calculation step, and the spectral of the spot color acquired in the second acquisition step And an estimation step of calculating an estimated value of the spectral density of the overprinting color using the density and the spectral density of the ground color of the paper on which the spot color is printed.

  In order to achieve the above object, the invention described in claim 2 is the color estimation method according to claim 1, wherein the estimation step includes the CMYK1 / 2/3 / calculated in the calculation step. The ground color of the paper on which the spot color is printed from the first value based on the value obtained by subtracting the spectral density of the ground color from the spectral density of the quaternary color and the spectral density of the spot color acquired in the second acquisition step. A second value based on a value obtained by subtracting the spectral density of the first color, and adding the first value, the second value, and the spectral density value of the ground color calculated in the calculating step The estimated value is calculated using the obtained value.

  In order to achieve the above object, the invention according to claim 3 is the color estimation method according to claim 2, wherein the transparency of the color material of the special color that is overprinted from above in the overprinting is obtained. A third acquisition step, wherein the estimating step subtracts the spectral density of the ground color from the spectral density of the CMYK1 / 2/3/4 color calculated in the calculating step. The first value is calculated by multiplying the transparency obtained in the obtaining step.

  In order to achieve the above object, the invention according to claim 4 is the color estimation method according to claim 2, wherein the trapping rate of the color material of the special color that is overprinted from above in the overprinting is obtained. A fourth obtaining step of obtaining, wherein the estimating step subtracts the spectral density of the ground color of the paper on which the spot color is printed from the spectral density of the spot color obtained in the second obtaining step; The second value is calculated by multiplying the trapping rate acquired in the fourth acquisition step.

  In order to achieve the above object, a fifth aspect of the present invention is the color estimation method according to the second aspect, wherein the estimation step includes the first value, the second value, and the The estimated value is obtained by subtracting a value proportional to the product of the first value and the second value from the value obtained by adding the spectral density value of the ground color calculated in the calculating step. It is characterized by calculating.

  In order to achieve the above object, the invention described in claim 6 is the color estimation method according to any one of claims 1 to 5, wherein the predetermined color system is L *. It is a * b * color system.

  In order to achieve the above object, the invention described in claim 7 is based on the background colors of printing paper and the basic colors C (cyan), M (magenta), Y (yellow), and K (black). A color table for storing predetermined color system values of CMYK1 / 2/3/4 quaternary colors composed of combinations of output intensities of color materials, and a white background and halftone image line portion for exposure output by a calibration color printer Using the exposure amount-color system table that stores the correspondence between the output intensities of a plurality of basic colors and the values of the predetermined color system, the halftone dot image separated into each basic color and special color is A color adjustment method for performing color adjustment for reproducing and outputting an image obtained by being overprinted on the printing paper by a printing machine using the color printer for calibration, wherein the spectral density of the ground color and each basic color is determined. A first acquisition step of acquiring, and a spectral density of the spot color; A second acquisition step of acquiring a ground color spectral density of the paper on which the special color is printed, and the color based on the ground color and the spectral density of each basic color acquired in the first acquisition step. A calculation step of calculating a spectral density corresponding to the value of the predetermined color system for the ground color and the CMYK1 / 2/3/4 quaternary color halftone image line portion stored in the table; and calculating in this calculation step Using the spectral density thus obtained, the spectral density of the spot color acquired in the second acquisition step, and the spectral density of the paper on which the spot color is printed, an estimated value of the spectral density of the overprinting color is calculated. Using the estimation step, a conversion step of converting the estimated value of the spectral density of the overprint color calculated in the estimation step into a value of the predetermined color system, and the exposure amount-color system table, Obtained in the conversion step An exposure amount acquisition step for obtaining a combination of exposure amounts of the respective basic colors of the calibration color printer corresponding to the values of the predetermined color system of the printed overprint color, and acquired in the exposure amount acquisition step A table creation step of creating a color channel table using a combination of exposure amounts of the basic colors corresponding to the overprinted colors, and based on the color channel table, a halftone dot line is drawn by the proof color printer. The exposure amount of the basic color for outputting the color of the part is adjusted.

  In order to achieve the above object, the invention described in claim 8 is based on the background color of the printing paper and the basic colors C (cyan), M (magenta), Y (yellow), and K (black). The CMYK1 / 2/3/4 quaternary color and the special color are obtained by using a color table storing a predetermined color system value of the CMYK1 / 2/3/4 quaternary color composed of a combination of output intensities of color materials. A color image forming apparatus for estimating an overprinting color obtained by overprinting on a printing paper and reproducing the overprinting color with a calibration color printer, wherein the spectral density of the ground color of the printing paper, and Accepting means for receiving input of the spectral density of each basic color, the spectral density of the spot color, and the spectral density of the ground color of the paper on which the spot color is printed, the ground color of the printing paper stored in the color table, and The predetermined color specification of the CMYK1 / 2/3/4 quaternary color Spectral density calculation means for calculating the spectral density corresponding to the value of the base color and the spectral density of each basic color received by the receiving means, and the spectral density calculated by the spectral density calculation means And a spectral density estimating unit that calculates an estimated value of the spectral density of the overprinting color using the spectral density of the spot color received by the receiving unit and the spectral density of the ground color of the paper on which the spot color is printed. And.

  In order to achieve the above object, a ninth aspect of the present invention is the color image forming apparatus according to the eighth aspect, wherein the calibration color printer exposes and outputs a white background and a halftone image line portion. An exposure amount-color system table storing the correspondence between the output intensity of the plurality of basic colors and the value of the predetermined color system, and the spectral density of the overprinted color calculated by the spectral density estimating means A conversion unit that converts the estimated value into a value of the predetermined color system, and a value of the predetermined color system of the overprint color obtained by the conversion unit using the exposure amount-color system table Exposure amount acquisition means for acquiring a combination of exposure amounts of the respective basic colors of the calibration color printer, and exposure amounts of the respective basic colors corresponding to the overprint colors acquired by the exposure amount acquisition means. Using a combination of A table creating means for creating a color table, and adjusting an exposure amount of the basic color for outputting a color of a halftone image line portion by the calibration color printer based on the color channel table. Features.

  According to the first, seventh, eighth, and ninth aspects of the present invention, the white background read from the device profile (color table) of the printing press and the basic colors CMYK1 / 2/3/4 of the primary color. It is possible to estimate the spectral density of the spot color and the spectral density of the overprint by calculating the spectral density value corresponding to the value of the color system.

  According to the second aspect of the present invention, the overprinting color including the special color can be specifically estimated from the first value, the second value, and the spectral density of the ground color of the printing paper. According to the third aspect of the present invention, the first value indicating the spectral density of the lower color is calculated in consideration of the transparency of the color material of the special color that is overprinted from above, so that the estimation accuracy is improved. Is done. Similarly, according to the fourth aspect of the present invention, since the second value indicating the spectral density of the upper color is calculated in consideration of the trapping rate of the color material of the special color that is overprinted from above, the accuracy of the estimation is calculated. Is improved. Further, according to the present invention, the value proportional to the product of the first value and the second value is obtained from the sum of the first value, the second value, and the spectral density of the ground color. Since the estimated value of the spectral density of the overprinting color is calculated by subtraction, the estimation accuracy can be improved by using an appropriate value as the proportionality constant.

  Hereinafter, preferred embodiments of a color estimation method, a color adjustment method, and a color image forming apparatus according to the present invention will be described with reference to the drawings. The present invention estimates the spectral density of overprinting colors including spot colors using basic spectral density data, coefficient table, color table, and exposure amount-color system table (all of which will be described later). Color CMYK1 / 2/3/4 The color system value of the halftone dot line portion of the quaternary color can be read from the device profile of the printing press, enabling highly accurate color estimation and color adjustment. Is.

[Definition of terms]
First, terms used in the specification are defined. First, “CMYK1 / 2/3/4 color” means a color that is output by combining the basic colors C, M, Y, and K. The basic color is a primary color, and any two arbitrary colors. A combination of three basic colors is called a secondary color, a combination of any three basic colors is called a tertiary color, and a combination of four basic colors is called a quaternary color.

  Further, the L * a * b * color system is used as the “predetermined color system”. The L * a * b * color system values L *, a *, and b * are determined by the CIE (Commission Internationale de l'Eclairage) as equivalent to the sensitivity of the human eye. This is a general one based on the value of the XYZ color system obtained by integrating the amount of light with the spectral characteristics of x-bar, y-bar, and z-bar.

〔Constitution〕
FIG. 1 shows the configuration of an image output system which is an example of a usage form of a color image forming apparatus capable of executing the color estimation method and the color adjustment method of the present invention. As shown in the figure, the image output system includes image editing terminals 1A to 1C that are upstream terminals for image editing of printed matter, RIP (Raster Image Processor) 2, and various types for outputting a color proof of printed matter. The color image forming apparatus 3 capable of performing the image conversion process and the proofreading color printer 4 for outputting the color proof are configured. The image editing terminals 1A to 1C, the RIP 2, and the color image forming apparatus 3 are communicably connected via a network N such as a LAN or the Internet.

  The image output system is further provided with a CTP output device 5 capable of directly imaging and outputting data transmitted from the RIP 2 on a printing plate. The printing plate F output by the CTP output device 5 is mounted on the printing machine 6 to perform a printing process, whereby a printed matter F is output. Further, the printing machine 6 can also output a color chart (also using the symbol F).

  Further, a spectral densitometer 7 for measuring the spectral density of the color of the output product (color chart F) output by the printing machine 6 is provided. In particular, the spectral densitometer 7 measures the monochromatic solid density of the basic colors CMYK included in the color chart F output by the printing machine 6, the spectral density measurement of the ground color of the printing paper, and the special density monochromatic spectral density measurement. , And the spot color is used to measure the spectral density of the ground color of the printed paper.

[Image editing terminal configuration]
Each of the image editing terminals 1A to 1C includes a computer terminal in which application software for dividing and editing image data of a printed matter into a plurality of color plate information using a DTP technique is installed. The computer main body, a keyboard, and a monitor In addition to the above, an image input device such as an image scanner is provided (not shown). Such an image editing terminal is usually provided with a plurality of units (in this embodiment, three units 1A to 1C are provided, but of course, only one unit or an arbitrary number of units may be used). Image data edited by the image editing terminals 1A to 1C is transmitted to the RIP 2 through the network N.

[RIP configuration]
The RIP 2 functions as a processor that receives image data, which is the basis of electronic plate making of printed matter edited using the image editing terminals 1A to 1C, through the network N, and converts it into a bitmap while scanning characters and image data. It is composed of a server or the like, and generates halftone dot image data of basic colors C (cyan), M (magenta), Y (yellow), and K (black) in a raster image format. Further, when generating image data of an image output by the proofreading color printer 4, CMYK image data before halftoning can be generated.

[Configuration of color image forming apparatus]
The color image forming apparatus 3 is an information processing apparatus in which a predetermined operation program is incorporated, and includes a computer main body, a keyboard, a monitor, and the like as usual. The color image forming apparatus 3 obtains image data separated into CMYK by the RIP 2 via the network N, and outputs the CMYK for the printing machine 6 and the calibration color printer 4 for output by the calibration color printer 4. Conversion of CMYK values, that is, color conversion, is performed by a device profile (a color table described later) representing the relationship between the value of L * a * b * and the color system value, or a device link profile created from two device profiles. The halftone image is created after the color conversion. Further, a color adjustment table (color channel table) for halftone image line portion calculation is calculated by the color estimation method and color adjustment method of the present invention, which will be described later, and is transmitted to the calibration color printer together with the halftone image to adjust the color. Is configured to run.

  Hereinafter, the color image forming apparatus 3 will be described in detail with reference to FIGS. Here, FIG. 2 is a functional block diagram for explaining the functional configuration of the color image forming apparatus 3, FIG. 3 is a functional block diagram for explaining processing executed by an arithmetic control unit described later, and FIG. 4 is a color image. The block diagram of the hardware constitutions of the forming apparatus 3 is shown, respectively.

(Functional configuration of color image forming apparatus)
As shown in FIG. 2, the color image forming apparatus 3 includes an arithmetic control unit 31, the spectral density of the ground color of the printing paper, and each basic color C, M, Y, K output to the printing paper by the printing machine 6. Spectral density basic data 32 storing the spectral density of a single color, a coefficient table 33 storing various coefficients described later, a color table 34 storing output characteristics of the printing machine 6, and output characteristics of the calibration color printer 4 An exposure amount-color system table 35 for storing the color, a color channel table 36 for storing the correspondence between each color of the white background and halftone line portion of the printing machine 6 and the exposure amount of the calibration color printer 4, and a spectral densitometer 7 performs input processing of spectral density measurement results according to 7, color conversion of CMYK image data and halftone image creation processing, and outputs the created data to the calibration color printer 4 It is configured to include an output processing unit 38 of the order.

  The arithmetic control unit 31 performs various arithmetic processes and control of each part of the apparatus. In particular, the arithmetic control unit 31 performs a process for creating the color table 34 and the exposure amount-color system table 35, a process for creating the color channel table 36, and the like. The details of the function of the arithmetic processing unit 31 will be described later with reference to FIG.

  The spectral density basic data 32 is a spectral densitometer based on the spectral density of the ground color of the printing paper obtained by measuring the printing paper used in the printing machine 6 with the spectral densitometer 7 and each basic color output on the printing paper. 7 is information in a table format for storing spectral densities of C single color, M single color, Y single color, and K single color obtained by measuring in Step 7. Specific examples of the spectral density basic data 32 are shown in the tables of FIGS. 7 and 8 and the graph of FIG. In addition, you may comprise including the spectral density obtained by measuring the various special colors output to the said printing paper with the spectral densitometer 7. FIG.

  In the coefficient table 33, the transparency (acquired in the third acquisition step) and the trapping rate (acquired in the fourth acquisition step) measured in advance for the special color ink used in the printing press 6 are stored. Data is stored. Further, a correction coefficient described later used in the color estimation process of the present embodiment is also obtained and stored in advance.

  The color table 34 is a device profile of the printing machine 6 and includes a lookup table (abbreviated as LUT) that defines the color output characteristics of the printing machine 6. The LUT of the color table 34 includes L * a * b * values measured for the CMYK1 / 2/3/4 quaternary colors output by the printer 6 and L measured for the ground color of the printing paper. * A * b * values are stored in a table format.

  Similarly, the exposure amount-color system table 35 stores an LUT that defines color output characteristics for the white background and the halftone image line portion of the calibration color printer 4. In the LUT of the exposure amount-color system table 35, the exposure amount (output intensity) of each basic color of the calibration color printer 4 corresponding to various L * a * b * values is defined. This LUT is a color in which a plurality of color images (color patches) in which the output intensity of each basic color of the calibration color printer 4 is equally divided between the minimum value 0 and the maximum value and the output intensity is combined are arranged. By outputting chart C and measuring the L * a * b * value of each color patch, the correspondence between the output intensity combination of each basic color and the L * a * b * value of the output color is obtained. (For example, Japanese Patent Application No. 2003-064629 by the present applicant).

  The color channel table 36 is a CMYK1 / 2/3/4 color, a spot color single color, a print color that is obtained by printing a spot color on the CMYK1 / 2/3/4 color, and a print color. It is an LUT for storing combinations of output intensities of basic colors of the calibration color printer 4 corresponding to the ground colors of the paper. Note that the output intensity of the basic color of the calibration color printer corresponding to the overprinted color obtained by overprinting the special colors on the CMYK1 / 2/3/4 quaternary colors is based on the estimated value by the color estimation method of the present embodiment. Defined in

  The input processing unit 37 constitutes the “accepting unit” of the present invention, and is an input interface that performs input processing of measured values by the spectral densitometer 7 of the color chart F output from the printing machine 6. The measurement value may be input directly, for example, by connecting the spectral densitometer 7 and the color image forming apparatus 3 by wire or wirelessly, or the user may manually input the measurement value. . Further, a means for recording the measured value on a predetermined recording medium may be provided in the spectral densitometer 7 and input via this storage medium.

  The output processing unit 38 performs color conversion of CMYK image data and halftone processing, and transmits the generated halftone image data to the proofreading color printer 4 together with the color channel table 36. Thereby, the exposure amount of each basic color of the calibration color printer 4 is changed to adjust the output color.

(Detailed configuration of the arithmetic processing unit)
Next, details of the configuration of the arithmetic processing unit 31 of the color image forming apparatus 3 will be described. As shown in FIG. 3, the arithmetic processing unit 31 includes a spectral density calculation unit 311, a spectral density estimation unit 312, a conversion unit 313, an exposure amount acquisition unit 314, and a table creation unit 315. . Each of these means is constituted by a later-described CPU that operates according to a predetermined program.

  The spectral density calculation means 311 is based on the ground color of the printing paper stored in the color table 34 of the printing machine 6 based on the ground color received by the input processor 37 and the spectral density of each of the basic colors C, M, Y, and K. In addition, a process of calculating the spectral density corresponding to the value of the L * a * b * color system of the CMYK1 / 2/3/4 color is performed.

  The spectral density estimation unit 312 receives the spectral density corresponding to the ground color of the printing paper calculated by the spectral density calculation unit 311 and the spectral density corresponding to the CMYK1 / 2/3/4 color and the input processing unit 37. Using the spectral density of the spot color, a process of calculating an estimated value of the spectral density of the overprinted color that is output by overprinting the CMYK1 / 2/3/4 color and the spot color is performed.

  The conversion unit 313 performs processing for converting the spectral density of the estimated value of the overprinting color calculated by the spectral density estimation unit 312 into an L * a * b * value using the relationships shown in the following equations. In the following equation, the transmission density is represented by D and the reflectance is represented by R.

[Formula 1: Relationship between transmission density and reflectance]
D = −0.5 log ₁₀ (R)
R = 10 ^ (-2D)

[Formula 2: Relationship between spectral reflectance and value of XYZ color system]
X / X0 = {Σx (λ) R (λ)} / {Σx (λ)}
Y / Y0 = {Σy (λ) R (λ)} / {Σy (λ)}
Z / Z0 = {Σz (λ) R (λ)} / {Σz (λ)}
Here, each Σ is a sum for the wavelength λ, for example, λ = 380, 390, 400,..., 720, 730 nm (that is, every 10 nm in the range of 380 to 730 nm). Note that x (λ), y (λ), and z (λ) are D50 standards for x-bar, y-bar, and z-bar defined by the CIE (Commission Internationale de l'Eclairage). The spectral characteristic of the light source is multiplied for each wavelength.

[Formula 3: Relationship between XYZ color system values and L * a * b * color system values]
L * = Yd × 116-16
a * = 500 × (Xd−Yd)
b * = 200 × (Yd−Zd)
here,
Xd = (X / X0) ^ (1/3) (X / X0> 0.008856)
= (X / X0) x 7.787 + 16/116 (otherwise)
Yd = (Y / Y0) ^ (1/3) (Y / Y0> 0.008856)
= (Y / Y0) × 7.787 + 16/116 (otherwise)
Zd = (Z / Z0) ^ (1/3) (Z / Z0> 0.008856)
= (Z / Z0) x 7.787 + 16/116 (otherwise)
Conversely,
Yd = (L * + 16) / 116
Xd = a * / 500 + Yd
Zd = Yd−b * / 200
here,
X / X0 = Xd ^ 3 (Xd> = 0.026893)
= (Xd-16 / 116) /7.787 (otherwise)
Y / Y0 = Yd ^ 3 (Yd> = 0.026893)
= (Yd-16 / 116) /7.787 (otherwise)
Z / Z0 = Zd ^ 3 (Zd> = 0.026893)
= (Zd-16 / 116) /7.787 (otherwise)

  The exposure amount acquisition unit 314 refers to the exposure amount-color system table 35 of the color printer 4 for calibration and corresponds to the L * a * b * value of the estimated value of the overprinting color obtained by the conversion unit 313. A process of acquiring a combination of exposure amounts (output intensity) of the basic colors C, M, and Y of the calibration color printer 4 is performed.

  The table creation means 315 creates the color channel table 36 based on the exposure amount combination of the basic color of the proofreading color printer 4 acquired by the exposure amount acquisition means 314.

  Note that specific processing contents by the respective units 311 to 315 constituting the arithmetic processing unit 31 will be described in detail in the description of the color estimation processing and the color adjustment processing.

(Hardware configuration of color image forming apparatus)
Next, the hardware configuration of the color image forming apparatus 3 having the functional configuration as described above will be described with reference to the block diagram of FIG.

  The color image forming apparatus 3 includes a CPU 301 that executes arithmetic processing and control processing according to a predetermined program, a RAM 302 as a main memory that develops programs executed by the CPU 301 and various data, a program such as a BIOS, and the like. ROM 303 to be stored, hard disk drive (HDD) 304 for storing operating programs such as OS and various data, application software, and the like, and reading / writing for reading data recorded on the information recording medium and writing data And an input / output interface (input / output IF) 307 that controls input / output of various data. The input device 305 includes an operation interface (operation IF) 306 that inputs and processes operation signals from operation means such as a keyboard and a mouse. . In particular, the input / output IF 307 performs input processing of measurement results from the spectral densitometer 7 (see FIG. 2). In addition, a display interface for sending image data to the monitor is also provided.

  The color image forming apparatus 3 realizes the functions according to the present invention by copying a program stored in the ROM 303 or the HDD 304 to the RAM 302 and executing the program by the CPU 301. The program is recorded in advance on an information recording medium such as a floppy (registered trademark) disk, a CD-ROM, a DVD-ROM, and the like, and is installed using the reading / writing device 305, so that the color image forming apparatus 3 is to be operated. Note that this program may be used by downloading from a server on a network such as the Internet or a LAN.

  The CPU 301 is an arithmetic control device that performs overall control of the color image forming apparatus 3, control of each unit, and arithmetic processing, and constitutes an arithmetic control unit 31 together with various programs developed in the RAM 302.

  The HDD 304 stores programs as a spectral density calculation unit 311, a spectral density estimation unit 312, a conversion unit 313, an exposure amount acquisition unit 314, and a table creation unit 315 that constitute the calculation control unit 31. In addition, a storage area as a buffer for temporarily storing halftone dot image data from RIP2 and adjusting processing timing, a coefficient table 33, a color table 34, an exposure amount-color system table 35, and a color channel table A storage area for storing 36 is set, and a storage area for storing various arithmetic expressions such as Expressions 1 to 3 is set. The various data may be stored in the ROM 303.

  As the reading / writing device 305, a floppy (registered trademark) disk drive (FDD) for reading / writing to a floppy (registered trademark) disk and a reading / writing to a CD-ROM (and / or DVD-ROM) are available. A device according to the application, system configuration, or the like, such as a CD (DVD) -ROM drive for writing, can be used. Also, the above-mentioned various data to be stored in the HDD 304 (or the ROM 303) is stored in an information storage medium, and this information storage medium is set in the reading / writing device 305 when performing color estimation processing or color adjustment processing. The data may be read and used as appropriate.

  The input / output IF 307 functions as the input processing unit 37 and the output processing unit 38 in FIG. 2, and performs input processing of CMYK image data sent from the RIP 2.

[Configuration of color printer for calibration]
Next, the proofreading color printer 4 that outputs the color proof C as the proofreading material of the printed matter F output by the printing machine 6 will be described. Since the calibration color printer 4 used here has a known configuration, only a brief description will be given.

  The calibration color printer 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. ) Exposure processing is performed by exposing the yellow coloring layer (Y layer) of the photosensitive material with light, and development processing is performed on this to form a color image. The exposure process using R, G, and B light is performed for each pixel in a dot-sequential manner. The exposure amount is adjusted based on the color channel table 36. In general, a silver salt photosensitive material is used as the photosensitive material.

  The calibration color printer 4 generates a color proof C based on the halftone image data separated into the basic colors C, M, Y, K (and special colors) transmitted from the output processing unit 38 of the color image forming apparatus 3. Output.

[Color estimation processing and color adjustment processing by color image forming apparatus]
Color estimation processing and color adjustment processing executed by the color image forming apparatus 3 having the above configuration will be described with reference to flowcharts. FIG. 5 is a flowchart showing an outline of the color estimation process and the color adjustment process. FIG. 6 is a flowchart showing the flow of the color estimation process. Hereinafter, the outline of the processing by the color image forming apparatus 3 will be described first, and then each step of the processing will be described in detail. A specific example of the process described below will be described later as an example.

[Outline of processing]
With reference to FIG. 5, the outline of the processing by the color image forming apparatus 3 will be described. The coefficient table 33, the color table 34 of the printing machine 6, and the exposure amount-color system table 35 of the calibration color printer 4 are created in advance (S1), and the spectral (transmission) density of the ground color of the printing paper, the printing machine. The spectral density basic data 32 is created by measuring the spectral density of each basic color output in step 6, the spectral density of various special colors, and the spectral density of the ground color of the paper on which the special color is printed with the spectral densitometer 7. (S2). When the input processing unit 37 of the color image forming apparatus 3 receives the image data from the RIP 2 (S3), the spectral density calculation means 311 of the calculation control unit 31 uses the ground color and each basic color stored in the spectral density basic data 32. The spectral density corresponding to the L * a * b * values of the ground color and CMYK1 / 2/3/4 color of the printing paper stored in the color table 34 of the printing press 6 is calculated based on S4). Next, the spectral density estimation unit 312 calculates the spectral density calculated by the spectral density calculation unit 311, the spectral density of the spot color stored in the spectral density basic data 32, and the spectral density of the ground color of the paper on which the spot color is printed. Are used to calculate the estimated value of the spectral density of the overprinted color obtained by overprinting the spot colors on the CMYK1 / 2/3/4 color (S5). Subsequently, the conversion unit 313 converts the estimated value of the spectral density of the overprinting color calculated by the spectral density estimation unit 312 and the spectral density of the single-color single color into values of the L * a * b * color system (S6). ). Further, the exposure amount acquisition unit 314 refers to the exposure amount-color system table 35 of the calibration color printer 4 and the L * a * b * value of the overprinting color obtained by the conversion unit 313 and the single color of the special color. Correspond to the L * a * b * value, the white L * a * b * value of the printed material read from the color table 34, and the L * a * b * value of the CMYK1 / 2/3/4 color. A combination of exposure amounts of each basic color of the proofreading color printer 4 is acquired (S7). Next, the table creating means 315 creates the color channel table 36 of the proofreading color printer 4 based on the combination of exposure amounts of the respective basic colors (S8). Then, the output processing unit 38 performs color conversion on each of the CMYK image data and creates a halftone image, and transmits this halftone image together with the color channel table 36 to the calibration color printer 4 (S9). The calibration color printer 4 outputs a color proof while adjusting the exposure amount of the basic color based on the color channel table 36 (S10).

  Here, the processing from S1 to S5 shows an example of the color estimation method of the present invention, and S1 to S10 show an example of the color adjustment method of the present invention.

[Details of each processing step]
Next, the processing content of each step constituting the above processing will be described in detail.

(S1: Various table creation processing)
First, a coefficient table 33, a color table 34 of the printing machine 6, and an exposure amount-color system table 35 of the calibration color printer 4 are created. An example of the process of creating the coefficient table 33 is shown in the description of step S5. Known creation processing of the color table 34 and the exposure amount-color system table 35 has been described above.

(S2: Creation processing of spectral density basic data)
The spectral density basic data 32 stores the ground color of the printing paper and the spectral density of each basic color of the printing machine 6 (referred to as basic spectral transmission density). For this purpose, the printing paper used in the printing machine 6 is measured by the spectral densitometer 7 to obtain the spectral density of the ground color of the printing paper. Further, a color chart F including patches of the basic colors C, M, Y, and K is output on the printing paper, and the patches of the basic colors are respectively measured by the spectral densitometer 7 to obtain C, M, Y, K. The monochromatic spectral density of is determined. These spectral densities are collected in a table format and stored as spectral density basic data 32 (first acquisition step).

  Here, the basic spectral transmission density of the ground color of the printing paper is SW (λ), the basic spectral transmission density of C is SC (λ), the basic spectral transmission density of M is SM (λ), and the basic spectral transmission density of Y is The basic spectral transmission density of SY (λ) and K is expressed as SK (λ). “W” indicates the ground color (white background) of the printing paper. “(Λ)” indicates that the basic spectral transmission density is defined as a function of the wavelength λ.

  Further, by outputting a color chart F including a spot color patch on the printing paper, and measuring the spot color patch and the white background of the printing paper with the spectral densitometer 7, the single color spectral density of the spot color and the spot color are determined. The spectral density of the ground color of the printed paper is obtained (second acquisition step). FIG. 10 shows the measurement result of the spectral density in the case of the red spot color. In this embodiment, the same paper as the printed matter of CMYK is used as the paper on which the special color is printed. Therefore, FIG. 10 does not show the measurement result of the ground color of the paper on which the special color is printed.

  Here, the spectral density basic data 32 may be stored in the spectral density basic data 32, or the spectral density basic data 32 including only the ground color of each printing paper and each basic color is formed. The spectral density data and the spectral density data of the ground color of the paper on which the special color is printed may be stored separately. That is, since the same data is always used for the ground color and each basic color of the printing paper, it is preferable to store the data independently as the spectral density basic data 32. On the other hand, for spot colors, it is common to use spot colors specified from among thousands of types depending on the printed material to be reproduced, so spectral density data for all spot colors is acquired and stored from the beginning. It is difficult to keep. Therefore, for spot colors that are used relatively frequently, data is compiled in advance to create spectral density basic data for spot colors, and for spot colors that are not included, the spectral density is measured before color proof output. It is preferable that the measurement data is added to the spectral density basic data for the spot color. Even in this case, it is only necessary to measure the spectral density of the single color of the special color to be used and the spectral density of the ground color of the printing paper on which the special color is printed, and the spot color can be obtained by printing over the ground color or the basic color. It is not necessary to measure all 16 overprint colors.

(S4: Calculation processing of spectral density of ground color and CMYK1 / 2/3/4 color)
Refer to the flowchart shown in FIG. 6 (calculation step). First, using the color table 34 of the printing machine 6, L * a * b * values corresponding to all 16 colors of the ground color of the printing paper and the CMYK1 / 2/3/4 quaternary colors are fetched (S41). The color table 34 created in S1 of the flowchart of FIG. 5 is, for example, an L * a * b * value corresponding to C × M × Y × K = 9 × 9 × 9 × 9, that is, 0% to L * a * b * values corresponding to 9 levels of output intensity of 0 to 8 levels are defined by dividing 100% into 8 equal parts. Therefore, L * a * b * values corresponding to combinations of C, M, Y, and K output intensities when solid colors are output as follows for each color of CMYK1 / 2/3/4 are captured. FIG. 11 shows L * a * b * values for each color of white background and CMYK1 / 2/3/4 color captured from the color table 34.

W: L * a * b * value at (0, 0, 0, 0) C: L * a * b * value at (8, 0, 0, 0) M: at (0, 8, 0, 0) L * a * b * value Y: L * a * b * value at (0, 0, 8, 0) R: L * a * b * value at (0, 8, 8, 0) G: (8, L * a * b * value B at 0,8,0): L * a * b * value at (8,8,0,0) CMY: L * a * b at (8,8,8,0) * Value K: L * a * b * value at (0,0,0,8) KC: L * a * b * value at (8,0,0,8) KM: (0,8,0,8) ) L * a * b * value KY in (0, 0, 8, 8) L * a * b * value KR in (0, 8, 8, 8) L * a * b * value KG in (0, 8, 8, 8): ( L * a * b * value KB in (8,0,8,8): (8,8,0,8) Kick L * a * b * value KCMY: L * a * b * values in the (8,8,8,8)

  Next, the basic spectral transmission densities SW (λ), SC (λ), SM (λ), SY (λ), and SK (λ) stored in the spectral density basic data 32 created in S2 are used, and in S41. The spectral transmission density corresponding to each L * a * b * value fetched from the color table 34 is calculated. Specifically, first, the following formulas representing spectral transmission densities including undetermined coefficients a, b, c, d, and e are created for all 16 colors of W to KCMY (S42).

W: SW (λ) + a × SC (λ) + b × SM (λ) + c × SY (λ)
C: SW (λ) + a × SC (λ)
M: SW (λ) + b × SM (λ)
Y: SW (λ) + c × SY (λ)
R: SW (λ) + b × SM (λ) + c × SY (λ)
−e × b × SM (λ) × c × SY (λ)
G: SW (λ) + a × SC (λ) + c × SY (λ)
−e × a × SC (λ) × c × SY (λ)
B: SW (λ) + a × SC (λ) + b × SM (λ)
−e × a × SC (λ) × b × SM (λ)
CMY: SW (λ) + a × SC (λ) + b × SM (λ) + c × SY (λ)
−e × a × SC (λ) × b × SM (λ)
−e × (a × SC (λ) + b × SM (λ)
−e × a × SC (λ) × b × SM (λ)) × c × SY (λ)
K: SW (λ) + d × SK (λ)
KC: SW (λ) + a × SC (λ) + d × SK (λ)
−e × a × SC (λ) × d × SK (λ)
KM: SW (λ) + b × SM (λ) + d × SK (λ)
−e × b × SM (λ) × d × SK (λ)
KY: SW (λ) + c × SY (λ) + d × SK (λ)
−e × c × SY (λ) × d × SK (λ)
KR: SW (λ) + b × SM (λ) + c × SY (λ) + d × SK (λ)
−e × d × SK (λ) × b × SM (λ)
−e × (d × SK (λ) + b × SM (λ)
−e × d × SK (λ) × b × SM (λ)) × c × SY (λ)
KG: SW (λ) + a × SC (λ) + c × SY (λ) + d × SK (λ)
−e × d × SK (λ) × a × SC (λ)
−e × (d × SK (λ) + a × SC (λ)
−e × d × SK (λ) × a × SC (λ)) × c × SY (λ)
KB: SW (λ) + a × SC (λ) + b × SM (λ) + d × SK (λ)
−e × d × SK (λ) × a × SC (λ)
−e × (d × SK (λ) + a × SC (λ)
−e × d × SK (λ) × a × SC (λ)) × b × SM (λ)
KCMY: SW (λ) + a × SC (λ) + b × SM (λ)
+ C × SY (λ) + d × SK (λ)
−e × d × SK (λ) × a × SC (λ)
−e × (d × SK (λ) + a × SC (λ)
−e × d × SK (λ) × a × SC (λ)) × b × SM (λ)
−e × (d × SK (λ) + a × SC (λ) + b × SM (λ)
−e × (d × SK (λ) + a × SC (λ)
−e × d × SK (λ) × a × SC (λ))
× b × SM (λ)) × c × SY (λ)

  For each of these equations, coefficients a to e are determined by performing the following processing, and the spectral transmission density of each color is calculated. First, the coefficient e is a coefficient for correcting the tendency that the calculation result of the high density portion becomes too high in the calculation of the ink printing overlap, and 0.75 is always used. Next, the transmission density value indicated by the equation is calculated while changing the other undetermined coefficients (S43), and this transmission density is converted to the L * a * b * value by the above-mentioned [Equation 1] to [Equation 3]. Conversion is performed (S44). Then, among the plurality of L * a * b * values obtained in this way, L * a * b * that optimally approximates the L * a * b * value of the color according to the equation fetched in S41. A value is specified (S45). The undetermined coefficient for deriving the specified L * a * b * value is adopted as a coefficient for defining the equation of the spectral transmission density of the color (S46). In the equation for KCMY, three undecided coefficients a, b, and c are obtained by this method using the value of d obtained by the equation for K.

For example, with respect to the white background W, the coefficients a, b, c are obtained by changing the coefficients a, b, c from 0 to 1 to 0.00, 0.01, 0.02,..., 0.99, 1.00, respectively. Of the L * a * b * values of × 101 × 101, closest to the L * a * b * value at (C, M, Y, K) = (0, 0, 0, 0) captured in S41 A formula SW (λ) that specifies the L * a * b * value and optimally approximates the spectral transmission density of the white background W using the coefficients a ₀ , b ₀ , and c ₀ that lead to the L * a * b * value. + A ₀ × SC (λ) + b ₀ × SM (λ) + c ₀ × SY (λ) is defined. FIG. 12 shows the result obtained for M (magenta) as a spectral transmission density approximate to the L * a * b * value of FIG.

(S5: CMYK1 / 2/3/4 color and special color estimation process of overprinting color)
Using the spectral transmission density data obtained in S4, the spectral transmission density of the overprinted color that is output by overprinting the spot color on the CMYK1 / 2/3/4 color is estimated (estimation step). Hereinafter, the spectral transmission density of the CMYK1 / 2/3/4 color that is the lower color in the overprinting is D1 (λ), and the spectral transmission density of the special color that is the upper color (obtained in S2 of the flowchart of FIG. 5). ) Is D2 (λ), and the spectral transmission density of the paper on which the spot color is printed is DW2 (λ). Note that D1 (λ) is the spectral transmission density represented by the equation defined in S4. Further, the transparency of the spot color stored in the coefficient table 33 acquired in S1 is represented as a, and the trapping rate is represented as b. The correction coefficient stored in the coefficient table 33 is c. At this time, the spectral transmission density DM (λ) of the overprinted color is defined by the following equation.

[Formula 4]
DM (λ) = a × (D1 (λ) −DW (λ))
+ B × (D2 (λ) −DW2 (λ)) + DW (λ)
−c × a × (D1 (λ) −DW (λ)) × b × (D2 (λ) −DW2 (λ))

  The first term a × (D1 (λ) −DW (λ)) corresponds to the “first value” in the present invention, and the spectrum of the lower ink itself obtained through the upper special color ink. The concentration is shown. First, by subtracting DW (λ) from D1 (λ), the spectral density of the lower ink itself without the spectral density DW (λ) of the printing paper is obtained. Furthermore, the spectral density of the lower ink itself obtained through the upper ink can be obtained by multiplying the transparency a of the upper ink as a coefficient. Here, the transparency coefficient a is a constant between 0 and 1, and is “1” if the upper ink is completely transparent, and “0” if it is completely opaque.

  The second term b × (D2 (λ) −DW2 (λ)) corresponds to the “second value” in the present invention, and the spectral density of the spot color ink itself that is the upper side when superimposed on another ink. Indicates. First, by subtracting DW2 (λ) from D2 (λ), the spectral density of the spot color ink itself on the upper side excluding the spectral density DW2 (λ) of the printing paper is obtained, and printing is further performed on the printing paper. By multiplying the difference between the so-called ink paste when printing on the other ink and the other ink as the trapping rate coefficient b, the spectral density of the upper ink itself when overlaid on the other ink is obtained. Note that this ink paste generally falls when printing on other inks compared to when printing on printing paper, and the trapping rate coefficient b is between 0 and 1. Is a constant.

  The third term is a term for adding the spectral density DW (λ) corresponding to the fact that the spectral densities DW (λ) and DW2 (λ) of the printing paper are excluded in the first and second terms, respectively. It has become.

  The fourth term c × a × (D1 (λ) −DW (λ)) × b × (D2 (λ) −DW2 (λ)) is a correction term for calculating a correction value. Corresponds to a value proportional to the product of the value of 1 and the second value. If the overprinting color is estimated using only the first to third items, the estimated spectral density is larger than the actual measured value in the wavelength region where the spectral density of the lower or upper ink is relatively high, and the approximation accuracy is improved. It will decline. Therefore, a value obtained by multiplying a product of a × (D1 (λ) −DW (λ)) and b × (D2 (λ) −DW2 (λ)) by a predetermined correction coefficient c is subtracted from the first to third terms. Thus, the correction amount is increased when the spectral density of the lower or upper ink itself is relatively high. In other words, this correction term is a value proportional to the product of (D1 (λ) −DW (λ)) and (D2 (λ) −DW2 (λ)).

  Here, 0.8 was used for the transparency coefficient a, 0.9 for the trapping rate coefficient b, and 0.75 for the correction coefficient c. By changing the transparency coefficient a and the trapping ratio coefficient b according to the type of the special color ink, it is possible to cope with the difference in the reproduction of the printing overlap depending on the type of the ink. The table of FIG. 13 and the graph of FIG. 14 show the results of color estimation for overprinting colors obtained by overprinting the red special color on magenta (M).

(S6: Conversion processing of estimated spectral density value to L * a * b * value)
Using the relationship shown in [Expression 1] to [Expression 3], the estimated value DM (λ) of the overprinting color spectral density is converted into an L * a * b * value (conversion step).

(S7: Exposure amount acquisition process)
The exposure amount-color system table 35 of the calibration color printer 4 stores the exposure amounts of C, M, and Y by the calibration color printer 4 corresponding to the combination of L * a * b * values. The L * a * b * value of the overprinted color obtained in S6, the L * a * b * value obtained for the special color, and the L * a * b for the white background and CMYK1 / 2/3/4 color * Values are input to the exposure amount-color system table 35, respectively, and the interpolation calculation processing shown in the specification of Japanese Patent Application No. 2003-066429 is performed, so that all the colors in the halftone line portion are correspondingly calibrated. A combination of exposure amounts of each basic color of the color printer 4 is acquired (exposure amount acquisition step).

(S8: Color channel table creation process)
Color channel table of exposure amount values for a total of 32 colors of white background, CMYK1 / 2/3/4 color, special color, special color and overprint colors of each CMYK1 / 2/3/4 color obtained in S7 Write to 36.

  Since S3, S9, and S10 in the flowchart of FIG. 5 are general processing as color adjustment processing at the time of color proof output, detailed description is omitted.

  According to the present embodiment described above, the values of the L * a * b * color system of the white background and the basic colors CMYK1 / 2/3/4 are read from the color table 34 (device profile) of the printing machine 6. It is possible to estimate the spectral density of the spot color and the spectral density of the overprinting color based on the calculation result. Furthermore, it is possible to adjust the color of the halftone dot line portion of the proof color printer 4 using this estimation result.

  In the present embodiment, the case where a measuring device capable of measuring the spectral density is used is described. However, the spectral density measurement cannot be performed, and the value of the L * a * b * color system or the XYZ color system is used. When using a measuring device that can measure only the system value and the concentration value, a plurality of concentration values are obtained by a method as described in Japanese Patent Application No. 2003-292890 by the present applicant, It is possible to estimate the color using the density value instead of the spectral density.

  The embodiments and examples described in detail above are merely exemplary configurations for implementing the color estimation method, the color adjustment method, and the color image forming apparatus according to the present invention, and the disclosure of the present invention is thereby described. The range should not be construed as limiting. Further, within the scope of the disclosure of the present invention, the configuration can be appropriately modified, changed, and added.

1 is a block diagram showing a system configuration for outputting a color proof of a printed matter using a color image forming apparatus according to the present invention. 1 is a functional block diagram illustrating an example of an embodiment of a color image forming apparatus according to the present invention. It is a functional block diagram for explaining an example of processing by an arithmetic control unit of the color image forming apparatus according to the present invention. 1 is a block diagram illustrating an example of a hardware configuration of a color image forming apparatus according to the present invention. 5 is a flowchart showing an outline of an example of color estimation processing and color adjustment processing executed by the color image forming apparatus according to the present invention. 6 is a flowchart illustrating a specific example of part of color estimation processing and color adjustment processing executed by the color image forming apparatus according to the present invention. It is a figure which shows the value of the basic spectral transmission density used for description of the Example of the color estimation method which concerns on this invention. It is a figure which shows the value of the basic spectral transmission density used for description of the Example of the color estimation method which concerns on this invention. It is a figure which shows the graph of the basic spectral transmission density used for description of the Example of the color estimation method which concerns on this invention. It is a figure which shows the measurement result of the spectral density of the special color (red) used for description of the Example of the color estimation method which concerns on this invention. It is a figure which shows the value of the L * a * b * color system of CMYK1 / 2/3/4 order color taken from the color table used for description of the Example of the color estimation method based on this invention. It is a figure which shows the calculation result of the transmission density of the magenta M used for description of the Example of the color estimation method based on this invention. It is a figure which shows the estimated value of the spectral density of overprinting color M + spot color (red) used for description of the Example of the color estimation method which concerns on this invention. It is a graph which shows the estimated value of the spectral density of overprinting color M + spot color (red) used for description of the Example of the color estimation method based on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 3 Color image forming apparatus 31 Operation control part 311 Spectral density calculation means 312 Spectral density estimation means 313 Conversion means 314 Exposure amount acquisition means 315 Table preparation means 32 Spectral density basic data 33 Coefficient table 34 Color table 35 (Proofreading) Exposure amount-color system table 36 color channel table 37 input processing unit 38 output processing unit 4 color printer for calibration 6 printing machine 7 spectral densitometer

Claims (9)

A predetermined table of CMYK1 / 2/3/4 quaternary colors composed of combinations of output intensities of color materials of printing paper ground color and basic colors C (cyan), M (magenta), Y (yellow), and K (black) A color estimation method for estimating a spectral density of an overprinted color obtained by overprinting the CMYK1 / 2/3/4 color and a special color on the printing paper using a color table storing color system values. There,
A first obtaining step of obtaining a spectral density of a ground color of the printing paper and a spectral density of each basic color;
A second acquisition step of acquiring the spectral density of the spot color and the spectral density of the ground color of the paper on which the spot color is printed;
Based on the ground color obtained in the first obtaining step and the spectral density of each basic color, the ground color stored in the color table and the predetermined color of the CMYK1 / 2/3/4 color are stored. A calculation step for calculating a spectral density corresponding to the value of the color system;
Using the spectral density calculated in this calculating step, the spectral density of the spot color acquired in the second acquiring step, and the spectral density of the ground color of the paper on which the spot color is printed, An estimation step for calculating an estimated value of the spectral density;
A color estimation method comprising:   The estimating step includes a first value based on a value obtained by subtracting the spectral density of the ground color from the spectral density of the CMYK1 / 2/3/4 color calculated in the calculating step, and the second acquiring step. And calculating a second value based on a value obtained by subtracting the spectral density of the ground color of the paper on which the spot color is printed from the spectral density of the spot color acquired in step S1, and calculating the first value, the second value, and the second value. The color estimation method according to claim 1, wherein the estimated value is calculated using a value obtained by adding the spectral density value of the ground color calculated in the calculating step. A third acquisition step of acquiring the transparency of the color material of the special color that is overprinted from above in the overprinting;
In the estimating step, the transparency acquired in the third acquiring step is calculated by subtracting the spectral density of the ground color from the spectral density of the CMYK1 / 2/3/4 color calculated in the calculating step. The color estimation method according to claim 2, wherein the first value is calculated by multiplication. A fourth obtaining step of obtaining a trapping rate of the color material of the special color that is overprinted from above in the overprinting;
In the estimation step, the trapping acquired in the fourth acquisition step is obtained by subtracting the spectral density of the ground color of the paper on which the spot color is printed from the spectral density of the spot color acquired in the second acquisition step. The color estimation method according to claim 2, wherein the second value is calculated by multiplying by a rate.   In the estimating step, the first value and the second value are obtained from a value obtained by adding the spectral density value of the ground color calculated in the calculating step. The color estimation method according to claim 2, wherein the estimated value is calculated by subtracting a value proportional to a product of the value of 2.   The color estimation method according to claim 1, wherein the predetermined color system is an L * a * b * color system. CMYK1 / 2/3/4 quaternary color consisting of the combination of the ground color of the printing paper and the output intensities of the basic colors C (cyan), M (magenta), Y (yellow), and K (black). Correspondence between a color table for storing values of a predetermined color system, output intensities of a plurality of basic colors for exposing and outputting white background and halftone image lines by a calibration color printer, and values of the predetermined color system Using the exposure amount-color system table storing the relationship, an image obtained by printing a halftone image separated into each basic color and special color on the printing paper by the printing machine is used for the calibration. A color adjustment method for performing color adjustment for reproduction output by a color printer,
A first acquisition step of acquiring a spectral density of the ground color and each basic color;
A second acquisition step of acquiring the spectral density of the spot color and the spectral density of the ground color of the paper on which the spot color is printed;
Based on the ground color acquired in the first acquisition step and the spectral density of each basic color, the ground color and the halftone dot line of the CMYK1 / 2/3/4 color stored in the color table. A calculating step for calculating a spectral density corresponding to a value of the predetermined color system for the unit;
Using the spectral density calculated in this calculation step, the spectral density of the spot color acquired in the second acquisition step, and the spectral density of the paper on which the spot color is printed, the spectral density of the overprinted color An estimation step for calculating an estimate of
A conversion step for converting the estimated value of the spectral density of the overprint color calculated in this estimation step into a value of the predetermined color system;
Using the exposure amount-color system table, a combination of exposure amounts of each basic color of the proofreading color printer corresponding to the predetermined color system value of the overprint color obtained in the conversion step An exposure amount obtaining step for obtaining
A table creation step of creating a color channel table using a combination of exposure amounts of the basic colors corresponding to the overprint colors acquired in the exposure amount acquisition step;
Including
A color adjustment method, comprising: adjusting an exposure amount of the basic color for outputting a color of a halftone image line portion by the calibration color printer based on the color channel table. CMYK1 / 2/3/4 quaternary color consisting of the combination of the ground color of the printing paper and the output intensities of the basic colors C (cyan), M (magenta), Y (yellow), and K (black). By using a color table that stores values of a predetermined color system, an overprint color obtained by overprinting the CMYK1 / 2/3/4 color and the special color on the printing paper is estimated, and a calibration color A color image forming apparatus for reproducing the overprinted color with a printer,
Receiving means for receiving input of the spectral density of the ground color of the printing paper, the spectral density of each basic color, the spectral density of the spot color, and the spectral density of the ground color of the paper on which the spot color is printed;
The ground color received by the accepting means for the spectral density corresponding to the ground color of the printing paper stored in the color table and the value of the predetermined color system of the CMYK1 / 2/3/4 color. And spectral density calculation means for calculating based on the spectral density of each basic color,
Using the spectral density calculated by the spectral density calculating unit, the spectral density of the spot color received by the receiving unit, and the spectral density of the ground color of the paper on which the spot color is printed, Spectral density estimating means for calculating an estimated value of spectral density;
A color image forming apparatus comprising: An exposure amount-color system table storing a correspondence relationship between the output intensity of a plurality of basic colors and values of the predetermined color system for exposing and outputting a white background and a halftone image line portion by the calibration color printer;
Conversion means for converting an estimated value of the spectral density of the overprint color calculated by the spectral density estimation means into a value of the predetermined color system;
A combination of exposure amounts of each basic color of the proofreading color printer corresponding to the value of the predetermined color system of the overprinted color obtained by the conversion unit using the exposure amount-color system table. Exposure amount acquisition means for acquiring
Table creating means for creating a color channel table using a combination of exposure amounts of the respective basic colors corresponding to the overprinting colors obtained by the exposure amount obtaining means;
9. The color according to claim 8, further comprising: adjusting an exposure amount of the basic color for outputting a color of a halftone image line portion by the calibration color printer based on the color channel table. Image forming apparatus.

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