JP2007189406A - Color adjustment method, color image forming method, and color image forming system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a color adjustment method, a color image forming method using the color adjustment method; and color image forming system for improving repeatability of gray tone generated from a first color image output device and reproduced by the second color image output device, and for improving color tone repeatability of red low tone portion. <P>SOLUTION: A combination of CMY tone values is sought for reproducing gray color system value which can be obtained by printing using L*a*b*→CMY tone value LUT (S52), and a combination of MY tone values for reproducing R color system value is sought which can be obtained by printing using L*a*b*→CMY tone value LUT (S53). The M or Y tone value of the combination of CMY tone values sought in a predetermined tone value range is corrected based on the sought combination of MY tone values (S54), and correction characteristics for correcting the tone value is formed by using the combination of corrected CMY tone values (S55). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a color adjustment method, a color image forming method, and a color for setting a color tone output by a first color image output device as a target of color matching and outputting a target color tone by a second color image output device. In particular, color adjustment is performed by correcting gradation values of a plurality of basic colors including at least C (cyan), M (magenta), and Y (yellow) using correction characteristics for each color. About what to do.

  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 calibration is performed at the stage of the original film, so that the Y (yellow) plate, the M (magenta) plate, the C (cyan) plate, and the BK (black) plate are obtained. Make a proof (color proof) using each separated color separation net original film, and before making the actual printing plate, there is no mistake in the original film layout, color mistakes, or text errors Inspected for the presence of the printed matter, etc., so that the finished product was confirmed in advance.

  In this case, once film output or printing plate output is performed only for calibration confirmation, and printing calibration or calibration with other calibration materials, there is a 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. . DDCP uses digital image data processed on a computer to record on a plate-making film using an image setter, etc., or to perform a final printing operation by directly creating a printing plate using CTP, or on a cylinder of a printing machine using CTC. Create a color proof that reproduces the output target indicated by the digital image processed on the computer before recording the image directly on the printing plate wound on the paper, and check the pattern, color tone, text, etc. Is what you do.

  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 printer for calibration that reproduces a halftone image by exposing dots to develop dots of three basic colors Y, M, and C, thereby creating a color proof. In a color printer for calibration that outputs such a dot type color proof, the color of each color material of CMYK is close to the color of the printing ink, so correction of differences in dot thickness (dot gain curve correction) is performed for each color of CMYK. By performing based on the measurement result of the halftone dot area ratio, it was possible to match the color to the printing press to some extent.

  However, since correction is performed for each single color of CMYK, reproduction of gradation for each single color is good, but the gray color output by superimposing the three CMY colors may not match the gray of the printed material. For example, compared to the gray of printed matter, it may appear reddish or greenish and the overall color tone may not match.

  Therefore, each level for correcting each of CMY from the measurement result of the printed gray color and the device profile indicating the output characteristics of the color of the calibration color printer so that the tone of gray is adjusted when output by the calibration color printer. A tone correction curve (correction characteristic) is obtained, and CMY correction is performed using the tone correction curve to match the color tone (for example, see Patent Document 1).

JP 2003-78775 A

  However, although the gray tone of the CMY three colors matches by performing the correction using the tone correction curve as described in Patent Document 1, the average skin tone may not match. The average skin color is the color output by the low gradation part (highlight part) of R (red) composed of MY. For example, although it depends on the characteristics of the printer, it is red due to the balance between M and Y. It may be deficient or reddish.

  The present invention has been made in view of the above circumstances, and an object thereof is to improve the reproducibility of the gray tone output by the first color image output device by the second color image output device. Another object of the present invention is to provide a color adjustment method capable of improving the reproducibility of the color tone of the low gradation part of red, a color image forming method and a color image forming system using the color adjustment method.

  In order to achieve the above object, the invention according to claim 1 is a gradation value indicating a step of density of each of a plurality of basic colors including at least C (cyan), M (magenta) and Y (yellow). A color adjustment method for performing color adjustment so that the color tone output from the first color image output device is output from the second color image output device based on the above, and a plurality of C, M, and Y tone values A table in which the combination of the color values and the color system values of each color output by a plurality of combinations of the C, M, and Y gradation values in the second color image output device are stored in advance, C, M, and Y gradations output by the second color image output device corresponding to gray color system values composed of C, M, and Y output by the first color image output device Find a combination of values by referring to the table And M and Y output from the second color image output device corresponding to the R (red) color system value composed of M and Y output from the first color image output device. Obtaining a combination of gradation values with reference to the table, and obtaining the M or Y gradation value of the obtained combination of C, M, and Y gradation values; A correction characteristic for each of C, M, and Y is created using the step of correcting a range of predetermined gradation values based on the combination of C, M, and Y using the corrected combination of C, M, and Y gradation values. And performing the color adjustment by correcting the respective gradation values of C, M, and Y using the respective correction characteristics.

  According to a second aspect of the present invention, in the step of storing the table in advance, the first reference table in which the color system values respectively corresponding to the plurality of combinations of the C, M, and Y gradation values are associated with each other. And a step of creating a second reference table associating a combination of gradation values respectively corresponding to the color system values of the plurality of color system values based on the first reference table A combination of C, M, and Y tone values corresponding to the values of the gray color system is obtained by referring to the second reference table, and the R (red) color system The combination of the M and Y gradation values corresponding to the values is obtained with reference to the second reference table.

  In the invention according to claim 3, the correction of the M or Y tone value is performed by obtaining a ratio of the M and Y tone values from the obtained combination of the M and Y tone values. The other gradation value corresponding to one of the gradation values of M or Y in the combination of gradation values of C, M, and Y is corrected based on the ratio.

  The invention according to claim 4 further includes a step of storing a weight for the gray or R in advance for the range of the predetermined gradation value, and the correction of the M or Y gradation value is performed by the obtained M The ratio of the gradation values of M and Y is obtained from the combination of the gradation values of Y and Y, and corresponds to one of the gradation values of M or Y of the obtained combination of the gradation values of C, M and Y. The other tone value is corrected based on the corresponding other tone value, the tone value obtained from the one tone value according to the ratio, and the weight stored in advance.

  Further, the invention described in claim 5 is configured to include a gradation value indicating a stage of density of each of a plurality of basic colors including at least C (cyan), M (magenta), and Y (yellow). The color tone of the image output from the first color image output device based on the image data is set as a color matching target, and the color tone of the image output from the second color image output device based on the image data is set as the target. A color image forming method for forming a color image by performing color adjustment so as to obtain a color to be obtained, wherein a plurality of combinations of C, M, and Y gradation values and the second color image output apparatus Storing in advance a table in which the color system values of each color outputted by a plurality of combinations of M, Y and Y gradation values are associated, and C, M outputted by the first color image output device And gray composed of Y Determining a combination of C, M, and Y gradation values to be output by the second color image output device corresponding to the color system values of the first color image with reference to the table, and outputting the first color image A combination of M and Y gradation values output by the second color image output apparatus corresponding to the R (red) color system value composed of M and Y output by the apparatus is stored in the table. A predetermined gradation value based on the obtained combination of the obtained M and Y gradation values, and the M or Y gradation value of the obtained combination of the obtained C, M, and Y gradation values; A correction characteristic for each of C, M, and Y using a combination of the corrected C, M, and Y gradation values, and each of the generated ranges. Using the correction characteristics, the image data C, M and Each the steps of correcting the tone value of is characterized by comprising the steps of forming a color image based on the corrected image data.

  According to a sixth aspect of the present invention, in the step of storing the table in advance, the first reference table in which the color system values respectively corresponding to the plurality of combinations of the C, M, and Y gradation values are associated with each other. And a step of creating a second reference table associating a combination of gradation values respectively corresponding to the color system values of the plurality of color system values based on the first reference table A combination of C, M, and Y tone values corresponding to the values of the gray color system is obtained by referring to the second reference table, and the R (red) color system The combination of the M and Y gradation values corresponding to the values is obtained with reference to the second reference table.

  In the invention according to claim 7, the correction of the M or Y tone value is performed by obtaining a ratio of the M and Y tone values from the obtained combination of the M and Y tone values. The other gradation value corresponding to one of the gradation values of M or Y in the combination of gradation values of C, M, and Y is corrected based on the ratio.

  The invention according to claim 8 further includes the step of preliminarily storing a weight for the gray or R for the range of the predetermined gradation value, and the correction of the M or Y gradation value is performed by the obtained M The ratio of the gradation values of M and Y is obtained from the combination of the gradation values of Y and Y, and corresponds to one of the gradation values of M or Y of the obtained combination of the gradation values of C, M and Y. The other tone value is corrected based on the corresponding other tone value, the tone value obtained from the one tone value according to the ratio, and the weight stored in advance.

  The invention according to claim 9 includes a gradation value indicating a stage of density of each of a plurality of basic colors including at least C (cyan), M (magenta), and Y (yellow). A second color image output device configured to output the image based on the image data, with the color tone of the image output from the first color image output device based on the image data as a target of color matching; A color image forming system for forming a color image by performing color adjustment so that the color tone of an image output by a color image output device becomes the target color, and a plurality of gradation values of C, M, and Y Storage means for storing in advance a table in which the combination of the color values and the values of the color system of each color output by the plurality of combinations of the C, M, and Y gradation values in the second color image output apparatus are associated with each other The first A combination of C, M, and Y gradation values output by the second color image output device corresponding to the gray color system values composed of C, M, and Y output by the color image output device. The second color image output device corresponding to the value of the R (red) color system composed of M and Y obtained by referring to the table and output from the first color image output device. A combination of M and Y gradation values to be output is obtained with reference to the table, and the obtained M and Y gradation values of the obtained combination of C, M, and Y gradation values are obtained. A correction characteristic for each of C, M, and Y is corrected using a combination of the corrected C, M, and Y gradation values. Correction characteristic creating means for creating the created The tone value correcting means for correcting the C, M, and Y tone values of the image data using the correction characteristics, and the color image is formed based on the corrected image data. And a control means for controlling the two color image output devices.

  According to a tenth aspect of the present invention, there is provided a plurality of reference data created based on a first reference table that associates color system values corresponding to a plurality of combinations of the C, M, and Y gradation values. At least a second reference table that associates a combination of gradation values corresponding to the color system values of the color system values is stored, and the correction characteristic creating means corresponds to the values of the gray color system A combination of C, M, and Y gradation values to be obtained is obtained with reference to the second reference table, and a combination of M and Y gradation values corresponding to the R (red) color system value is obtained. , By referring to the second reference table.

  Further, in the invention described in claim 11, the correction characteristic creating means obtains a ratio of M and Y gradation values from the obtained combination of M and Y gradation values, and obtains the obtained C, M and Y. The other gradation value corresponding to one of the gradation values of M or Y in the combination of the gradation values is corrected based on the ratio.

  According to a twelfth aspect of the present invention, the correction characteristic creating means stores a weight for the gray or R in advance for the range of the predetermined gradation value, and from the obtained combination of the M and Y gradation values. A ratio of gradation values of M and Y is obtained, and the other gradation value corresponding to one of the gradation values of M or Y in the combination of the obtained gradation values of C, M, and Y is determined as the correspondence. Correction is performed based on the other gradation value to be performed, the gradation value obtained from the one gradation value in accordance with the ratio, and the weight stored in advance.

  According to the color adjustment method or the image output method according to the present invention, a combination of C, M, and Y gradation values obtained so as to reproduce the values of the gray color system output by the first color image output device Based on the combination of MY gradation values obtained so as to reproduce R (red), the M or Y gradation value of the obtained combination of C, M, and Y gradation values is set to a predetermined gradation. Since correction is made for the range of values, the reproducibility of gray tone can be improved, and the reproducibility of R can be improved within a predetermined range of gradation values. Therefore, for example, by correcting the low gradation part of R, the reproducibility of the skin color can be improved.

  First, before explaining the present invention, the colors and color system values used in the following explanation will be explained. The four basic colors are C for cyan (blue green), M for magenta (red purple), Y for yellow (yellow), and K for black (black) (hereinafter “C, M, Y, K”). , “YMCK”, “CMYK”, etc. In some cases, the display for the three colors “C, M, Y” is the same.), L * a * b * color system The value 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, and the hue and saturation are expressed by the a * b * plane. L * is a value of a color characteristic orthogonal to the a * b * plane and representing lightness. In addition, the values of the L * a * b * color system are x (λ), y (defined by the CIE (Commission Internationale de l'Eclairage)) as equivalent to the sensitivity of the human eye. λ), z (λ) (in the CIE 1931, bar (-) is attached above x, y, z) The value of the XYZ color system obtained by integrating the amount of light with the spectral characteristics. It is based on. This XYZ is called a color tristimulus value and represents a color in a three-dimensional space of the X, Y, and Z axes. X is the amount of red light, Y is the amount of green light, and Z is It corresponds to the amount of blue-violet light.

  Hereinafter, in describing the color adjustment method and color image forming method of the present invention, an embodiment applied to a color image forming system that operates as a color image output device will be described as an example, and will be specifically described with reference to the drawings. To do.

[Outline of output]
First, an outline of image output in the present embodiment will be described. The color image forming system of the present embodiment uses image data (referred to as so-called vector graphics, each object is a point coordinate and a line or surface equation parameter connecting it, and a fill color (YMCK each color level). The gradation value is a value that indicates stepwise with white as 0 and solid as 255. Also, a halftone dot area ratio (halftone%) that indicates the color as white and 0 as solid. It may be expressed as a), special effects, character data that indicates the shape of the character, vector data that is a collection of drawing information such as its size, and so-called bitmap graphics. A raster in which a plurality of pixels arranged at a predetermined interval (resolution) constitute one line, and further, the lines are arranged in the vertical direction at a predetermined interval, and each pixel is indicated by drawing information indicated by a gradation value. The color proof is output by the proof color printer (second color image output device) based on the data), and at this time, for example, the color tone to be printed (output) by the printing press (first color image output device) is targeted. The color proof output from the color printer for calibration is adjusted so that the target color tone is obtained.

[Control configuration of color image forming system]
Next, a control configuration of a color image forming system that creates a color proof based on image data as described above will be described with reference to FIG. FIG. 1 shows a functional block diagram of a color image forming system. As shown in FIG. 1, the color image forming system according to the present embodiment includes a control device 1 and a calibration color printer 2.

  The calibration color printer 2, for example, sensitizes a cyan coloring layer (C layer) of a photosensitive material with green (G) light based on image data of each color of YMCK, and a magenta coloring layer of the photosensitive material with red (R) light. (M layer) is exposed, the yellow coloring layer (Y layer) of the photosensitive material is exposed to blue (B) light, development processing is performed, and basic colors C, M, and Y are revealed and output, and color Form an image.

  The control device 1 includes a control unit 10, a storage unit 20, an input unit 40, and an image data receiving unit 30.

  The storage unit 20 is configured by a storage device such as a hard disk drive or an image memory, and includes a target color table 21, a gradation correction table storage unit 22, and an LUT storage unit 23.

  The target color table 21 stores color system values that are targets for color matching. FIG. 2 shows the configuration of the target color table 21. For example, as shown in FIG. 2 (a), CMY printed on printing paper using a C, M, Y ink on a printing press is 0 gradation white, 255 gradation black, 0 gradation to 255 gradation. A plurality of gradations, such as 26 gradations, 51 gradations, 77 gradations, 102 gradations, 128 gradations, 153 gradations, 179 gradations, 204 gradations, and 230 gradations, which are division points such as 10 The values of the L * a * b * color system of the gray level and the 51st, 77th, 102th, and 128th floors of the MY2 color (C = 0) as shown in FIG. Multi-tone red (R) L * a * b * color system values and 0 gradation white, 255 gradation black printed using K ink as shown in FIG. 2 (c) , Gradations to be divided points from 0 gradation to 255 gradations, 26 gradations, 51 gradations, 77 gradations, 102 gradations, 128 gradations, 153 floors , 179 gradations, 204 gradations, and stores the respective (not shown in the drawing) the value of the gray of the L * a * b * color system of a plurality of stages of 230 gradations.

  The gradation correction table storage unit 22 uses the CMYK gradation values indicated by the image data as input values so that the gray color tone, skin tone color tone, and K single color brightness output from the printing press are output by the calibration color printer. A gradation correction table indicating correction characteristics for correcting the gradation values of CMYK and CMYK is stored. As shown in FIG. 3, the gradation correction table storage unit 22 includes a C gradation correction table 221 for correcting the C gradation value, an M gradation correction table 222 for correcting the M gradation value, A Y gradation correction table 223 for correcting gradation values and a K gradation correction table 224 for correcting K gradation values are stored.

  As shown in FIG. 4, the LUT storage unit 23 includes a measurement table 231, a CMY tone value → L * a * b * LUT 232 (first reference table), and an L * a * b * → CMY tone value LUT 233 (first table). 2 reference table). The measurement table 231 takes 5 steps of 0, 64, 128, 191 and 255 between the minimum values 0 to 255 of C, M, and Y in the calibration color printer 2, and C × M × Y: 5 × A color chart as shown in FIG. 8 in which color patches are arranged for a combination of 5 × 5 = 125 points is output, and the measurement result of each color patch and 0 gradation, 26 gradations, 51 gradations, 77 gradations are output. , 102 *, 128 *, 153 *, 179 *, 204 *, 230 *, and 255 * gray patch measurement result L * a * b * table Color system values are stored as the measurement table 231. FIG. 5 shows the configuration of the measurement table 231. For example, as shown in FIG. 5A, the L * a * b * color system value of the color patch measurement result (not shown), and as shown in FIG. 5B, the L * of the gray patch measurement result. The value of the a * b * color system (not shown in the figure) is stored. The CMY gradation value → L * a * b * LUT 232 and the L * a * b * → CMY gradation value LUT 233 indicate color output characteristics in the color printer for calibration.

  The input unit 40 is for inputting numerical values stored in the target color table 21, the measurement table 231, and the like, for example. Also, for example, an interface for connecting to a measuring instrument, or a reading apparatus for detachably mounting an FD (Floppy (registered trademark) Disk) to which an area ratio, a color measurement result, and the like are input. Also good.

  The image data receiving means 30 is composed of a transmission / reception interface circuit or the like, and receives the above-described gradation image data transmitted from an external terminal (not shown). Further, it may be a reading device that mounts a CD-ROM (Compact Disk Read-Only Memory) or the like to which gradation image data or the like is input so as to be put in and out.

  The control unit 10 is configured by an arithmetic control device such as a CPU, and controls each unit by executing a computer program stored in a program storage unit (not shown) such as a ROM or a hard disk drive. In addition, the control unit 10 executes functions as the gradation value correction unit 11, the image recording control unit 14, the gradation correction table creation unit 12, and the LUT creation unit 13 according to the computer program.

  The gradation value correcting unit 11 corrects the gradation value indicated in the image data received by the image data receiving unit 30 based on each gradation correction table stored in the gradation correction table storage unit 22, and the gradation value is corrected. The processed image data is output.

  The image recording control means 14 has a function as a control means for controlling the calibration color printer 2 so as to output an image based on the corrected image data.

  The gradation correction table creation unit 12 has a function as a correction characteristic creation unit, and is stored in the target color table 21 and the L * a * b * → CMY gradation value LUT 233 stored in the LUT storage unit 23. Each gradation correction table for CMY using a plurality of levels of gray color system values composed of three CMY colors and a plurality of levels of red color system values composed of MY2 colors printed by a printing press 221 to 223 are obtained. Further, the values of the L * a * b * color system of black and multiple levels of gray using K ink, which are stored in the target color table 21, and the calibration color printer 2 which is stored in the measurement table 231. The gray level correction table 224 for K is obtained using the values of the gray L * a * b * color system including the black output in step S2.

  Based on the L * a * b * color system values that are the color patch measurement results stored in the measurement table 231, the LUT creation unit 13 determines the CMY tone value → L * a * b * LUT 232, L *. a * b * → CMY gradation value LUT 233 is created.

[Color image forming method]
Next, the procedure of each process in the color image forming system of this embodiment to which the color image forming method of the present invention is applied will be described with reference to flowcharts.

  FIG. 6 is a flowchart showing an example of a procedure for forming a color image by performing color adjustment so as to match the output colors of the printing machine, which is the target of color matching, particularly gray and flesh color. Hereinafter, for example, step S11 in FIG. 6 is omitted, and S11 is displayed as S11. The other steps are the same.

  First, the LUT creation unit 13 creates a CMY tone value → L * a * b * LUT 232 and an L * a * b * → CMY tone value LUT 233 and stores them in the LUT storage unit 23 (S11). This L * a * b * → CMY gradation value LUT 233 is used to obtain a combination of CMY gradation values from the values of the L * a * b * color system. The L * a * b * color system value indicated by R (red) is used to obtain a combination of CMY tone values output from the calibration color printer 2.

  Details of the procedure for creating the CMY gradation value → L * a * b * LUT 232 and L * a * b * → CMY gradation value LUT 233 will be described below with reference to the flowchart shown in FIG.

  First, 5 steps of 0, 64, 128, 191, 255 are taken between the minimum values 0 to 255 of C, M, and Y, and C × M × Y: 5 × 5 × 5 = 125 points A color chart as shown in FIG. 8 in which color patches are arranged is output by a calibration color printer, and each patch of 5 × 5 × 5 = 125 points is measured in order to obtain the value of the L * a * b * color system. Ask. The color measurement result is stored in the measurement table 231 of the LUT storage unit 23 via the input unit 40 as shown in FIG. 5A (S41).

  Then, using this color measurement result, first, the LUT creation means 13 creates a CMY gradation value → L * a * b * LUT (S42). For example, the CMY gradation value → L * a * b * LUT is as shown in FIG. 9, and the value of the L * a * b * color system is the CMY LUT input point (9 × 9 × 9). 3D input / 3D output. Therefore, L * a for points between 9 × 9 × 9 grid points is first interpolated from the values of the L * a * b * color system of each patch of 5 × 5 × 5 = 125 points. * B * Calculate the value of the color system. As shown in FIG. 10, if black circles ● are lattice points (sample points) and Δ and x are points to be interpolated, respectively, there are two points before and after, as indicated by Δ, Different interpolation formulas are used when there are 1 point and 3 points before and after the mark.

Here, when the color system of the points to be interpolated is Lm * am * bm * and the color system of each sample point is Li * ai * bi * (i = 1 to 4), the former (Δ mark). In the case of the following interpolation formula,
Lm * =-(1/16) L1 * + (9/16) L2 * + (9/16) L3 *-(1/16) L4 *
am * =-(1/16) a1 * + (9/16) a2 * + (9/16) a3 *-(1/16) a4 *
bm * =-(1/16) b1 * + (9/16) b2 * + (9/16) b3 *-(1/16) b4 *
Is interpolated.

In the latter case (x mark), the following interpolation formula is used:
Lm * = (5/16) L1 * + (15/16) L2 *-(5/16) L3 *-(1/16) L4 *
am * = (5/16) a1 * + (15/16) a2 *-(5/16) a3 *-(1/16) a4 *
bm * = (5/16) b1 * + (15/16) b2 *-(95/16) b3 *-(1/16) b4 *
Is interpolated.

  FIG. 11 shows an example of the order of interpolation processing for CMY three dimensions. CMY5 × 5 × 5 is interpolated to 9 × 9 × 9 by performing interpolation processing in the order of numbers 1, 2, and 3 (corresponding to Roman numerals in FIG. 11 respectively) shown in FIG. As a result, although only 5 × 5 × 5 = 125 patches are actually measured, the value of the L * a * b * color system is expanded to 9 × 9 × 9 = 729 points for CMY combinations. The CMY gradation value → L * a * b * LUT 232 is obtained by associating the combination of these CMY with the value of the L * a * b * color system.

  Next, the LUT creation unit 13 creates L * a * b * → CMY tone value LUT 233 based on CMY tone value → L * a * b * LUT 232 (S43). L * a * b * → CMY gradation value LUT is a three-dimensional input / three-dimensional output LUT as shown in FIG. 12, for example, by interpolating points between 33 × 33 × 33 lattice points. Convert.

  A method for obtaining the three-dimensional input / three-dimensional output LUT in FIG. 12 will be described. For simplicity, the basic color will be described as two colors C and M. Note that C, M, and Y all take values from 0 to 255.

  First, L * a * b * → CMY LUT is calculated using the above-mentioned CMY → L * a * b * LUT C × M × Y: 9 × 9 × 9 three-dimensional data. FIG. 13 is a plot of L * on the vertical axis and a * on the horizontal axis for a two-dimensional 9 × 9 combination of M and C in CMY (Y = 0). Although it is actually three-dimensional, it is shown in two dimensions for simplicity.

  Target points [L * (0 to 100) a * (− 127 to 128) b * (− 127 to 128)] 33 × 33 × 33 = 35937 target LUTs to be obtained for this CMY distribution L * a * b * of point] is given as the target value T ′. When the target value T ′ is in the region surrounded by the lattice points a ′ to d ′ as shown in FIG. 13, the combination of MC (target value T) in the MC coordinate system is as shown in FIG. Presumed to be in the region surrounded by d. Then, where the target value T is in the region formed by the grid points a to d is obtained by performing a convergence calculation process while associating the color system of FIG. 13 with the coordinate system of FIG. Convergence calculation processing is performed in this way, although the conversion from the coordinate system of FIG. 14 to the color system of FIG. 13 is known, the reverse conversion is very complicated and a good conversion formula is still known. It is because it is not done.

  Next, convergence calculation processing is further performed, and the region So formed by the lattice points a to d in FIG. 15 is equally divided into four regions S1 to S4. The five division points e to i are calculated by weighted average using surrounding grid points that have already been obtained. Then, the values obtained by converting the values corresponding to the division points e to i into the L * a * b * color system are plotted in the color system of FIG. 16, and the plotted division points e ′ to i ′ are used. Which region among the four formed regions S1 ′ to S4 ′ has the target value T ′ is obtained. When it is in the region S2 'as shown in FIG. 16, it is estimated that the target value T is in S2 corresponding to the region S2' as shown in FIG.

  Next, the estimated region S2 is equally divided into S5 to S8. The five division points j to n are calculated by weighted averaging using the surrounding grid points or division points that have already been obtained. Then, values obtained by converting values corresponding to the division points j to n into the L * a * b * color system are plotted in the color system of FIG. 16, and the plotted division points j ′ to n ′ are plotted. Which region among the four formed regions S5 ′ to S8 ′ has the target value T ′ is determined. When it is in the region S8 'as shown in FIG. 16, it is estimated that the target value T is in the region S8 corresponding to the region S8' as shown in FIG.

  Next, the estimated area S8 is equally divided into four areas S9 to S12. The five division points o to s are calculated by weighted average using the surrounding grid points or division points that have already been obtained. Then, values obtained by converting the values corresponding to the division points o to s into the L * a * b * color system are plotted in the color system of FIG. 16, and the plotted division points o ′ to s ′ are used. Which region of the four formed regions S9 ′ to S12 ′ has the target value T ′ is determined. When it is in the region S10 'as shown in FIG. 16, it is estimated that the target value T is in the region S10 corresponding to the region S10' as shown in FIG.

  By repeating the division of the region as described above, the lattice gradually becomes smaller and finally converges. Then, the target value T is obtained by averaging the four grid points or division points forming the converged region, and therefore, a combination of basic colors indicating the output color to be obtained can be obtained.

  In the present embodiment, the method using the convergence calculation as described above is described. However, an interpolation method described in the specification of Japanese Patent No. 2895086 by the present applicant may be used.

  When the target value T ′ is outside the color reproduction range formed by the vertices W ′, C ′, M ′, and B ′ of the L * a * b * color system as shown in FIG. It is necessary to move the value T ′ to the color reproduction range. In this case, the target value T ′ is moved in the achromatic color direction, the coordinates of the intersection point with the boundary of the color reproduction range in the achromatic color direction are set as the target value as shown in FIG. 18, and the target value T ′ corresponds to T ′ as shown in FIG. A target value T to be calculated is calculated.

  Note that the target value T ′ does not necessarily need to be moved to the boundary, and may be moved within the color reproduction range. In addition, for the sake of explanation, an example is shown for two dimensions of C × M, but in actuality, three dimensions of C × M × Y are performed, and each of 33 × 33 × 33 points of L * a * b * is performed. It is necessary to calculate the values of C, M, and Y one by one using the LUT input point as the target value T ′.

  L * a * b * → CMY gradation value LUT233 is obtained by associating the combination with the CMY pair corresponding to the L * a * b * color system value obtained as described above.

  Next, the gradation correction table creation means 12 creates gradation correction tables 221 to 223 for each of C, M, and Y, and stores them in the gradation correction table storage unit 22 (S12). Details of the procedure for creating the C, M, and Y gradation correction tables will be described below with reference to the flowchart shown in FIG.

  First, 0 gradation, 26 gradation, 51 gradation, 77 gradation, 102 gradation, 128 gradation, 153 gradation by CMY printed on a printing paper using C, M, Y ink on a printing press. A plurality of gray patches of 179 gradations, 204 gradations, 230 gradations, and 255 gradations are output and measured to determine the value of the L * a * b * color system. Also, a red patch of a plurality of levels of 51 gradations, 77 gradations, 102 gradations, and 128 gradations of MY2 colors is output and measured to obtain the value of the L * a * b * color system. These color measurement results are stored in the target color table 21 via the input unit 40 as shown in FIGS. 2A and 2B, respectively (S51).

  Next, the gradation correction table creating means 12 sets the combination of CMY gradation values corresponding to the CMY gray color system values printed by the printing machine stored in the target color table 21 to L * a * b. * → CMY gradation value LUT 233 is used to determine (S52). The combination of CMY gradation values obtained here is a combination of CMY gradation values for reproducing the color tone of CMY gray printed by the printing machine with a color printer for calibration. A combination of CMY gradation values can be obtained as follows using L * a * b * → CMY gradation value LUT233.

For example, if the L * a * b * color system values are L * = 57.0, a * = 5.3, and b * = 3.6, then L * a * b *: 33 × 33 × 33 → CMY LUT L * a * b *: The distance between the input point of 33 × 33 × 33 and each input point of L * a * b * is
Since L *: 57.0 / 100 × 32 = 18.2, the distance DL1 to the first point L1 and L1 of L * and the distance DL2 to the second point L2 and L2 of L * are L1 = 18, DL1 = 0.2, L2 = 19, DL2 = 0.8
Since a * :( 5.3 + 127) /255×32=16.6, the distance DL1 to the first points a1 and a1 of a * and the distance Da2 to the second points a2 and a2 of a * Are a1 = 16, Da1 = 0.6, a2 = 17, Da2 = 0.4
Since b * :( 3.6 + 127) /255×32=16.4, the distance DL1 to the first points b1 and b1 of b * and the distance Db2 to the second points b2 and b2 of b * B1 = 16, Db1 = 0.4, b2 = 17, Db2 = 0.6
It becomes.

L * a * b *: 33 × 33 × 33 → About L * 2 points (L1, L2) × a * 2 points (a1, a2) × b * 2 points (b1, b2) = 8 points from the CMY LUT CMY values of
CL1a1b1, CL1a1b2, CL1a2b1, CL1a2b2,
CL2a1b1, CL2a1b2, CL2a2b1, CL2a2b2,
ML1a1b1, ML1a1b2, ML1a2b1, ML1a2b2,
ML2a1b1, ML2a1b2, ML2a2b1, ML2a2b2,
YL1a1b1, YL1a1b2, YL1a2b1, YL1a2b2,
YL2a1b1, YL2a1b2, YL2a2b1, YL2a2b2,
Then, CMY values for L * = 57.0, a * = 5.3, b * = 3.6 are obtained by the following equation:
C = DL2 × Da2 × Db2 × CL1a1b1
+ DL2 × Da2 × Db1 × CL1a1b2
+ DL2 × Da1 × Db2 × CL1a2b1
+ DL2 × Da1 × Db1 × CL1a2b2
+ DL1 × Da2 × Db2 × CL2a1b1
+ DL1 × Da2 × Db1 × CL2a1b2
+ DL1 × Da1 × Db2 × CL2a2b1
+ DL1 × Da1 × Db1 × CL2a2b2
M = DL2 × Da2 × Db2 × ML1a1b1
+ DL2 × Da2 × Db1 × ML1a1b2
+ DL2 × Da1 × Db2 × ML1a2b1
+ DL2 × Da1 × Db1 × ML1a2b2
+ DL1 × Da2 × Db2 × ML2a1b1
+ DL1 × Da2 × Db1 × ML2a1b2
+ DL1 × Da1 × Db2 × ML2a2b1
+ DL1 × Da1 × Db1 × ML2a2b2
Y = DL2 * Da2 * Db2 * YL1a1b1
+ DL2 × Da2 × Db1 × YL1a1b2
+ DL2 × Da1 × Db2 × YL1a2b1
+ DL2 × Da1 × Db1 × YL1a2b2
+ DL1 × Da2 × Db2 × YL2a1b1
+ DL1 × Da2 × Db1 × YL2a1b2
+ DL1 × Da1 × Db2 × YL2a2b1
+ DL1 × Da1 × Db1 × YL2a2b2
It becomes.

  As described above, combinations of CMY gradation values for the values of the L * a * b * color system of each CMY gray are obtained. For white and black, C = M = Y = 0 and C = M = Y = 255 on the input side and the output side, respectively. For example, the calculation result is shown in FIG. FIG. 21 shows combinations of CMY tone values indicating white, black, and CMY gray on the input side, and the input side by the printing press for each combination of CMY tone values on the input side. The combination of CMY gradation values for reproducing the gray tone of the combination of the CMY gradation values by the calibration color printer is shown. Further, in this embodiment, by interpolating the gradation values on the input side so as to be further divided, the combination of the CMY gradation values on the input side and the CMY gradation values on the output side as shown in FIG. Find a combination. The CMY tone values on the output side with respect to the division points of the tone values on the input side are 5 × 5 × 5 = 125 points of L as shown in the description of CMY tone value → L * a * b * LUT 232 creation described above. It can be obtained in the same manner by interpolation by calculating a value of 9 * 9 * 9 L * a * b * color system from the value of * a * b * color system.

  Next, the gradation correction table creating means 12 sets the combination of MY gradation values corresponding to the values of the red color system printed by the printing machine stored in the target color table 21 to L as in S52. * A * b * → CMY gradation value This is obtained using the LUT 233 (S53). The combination of the MY gradation values obtained here is a combination of the MY gradation values for reproducing the red color tone printed by the printing machine with the calibration color printer (here, the C component is slight). Ignored and written as MY (however, C is also shown in FIGS. 23 and 24).

  For example, the calculation result is shown in FIG. As shown in FIG. 23, a combination of red MY gradation values is shown on the input side, and an MY gradation on the input side by the printing press for each combination of MY gradation values on the output side. A combination of MY gradation values for reproducing a red color tone of a value combination by a color printer for calibration is shown. Further, as shown in FIG. 23, Y / M ratio Y / M is obtained for each combination of MY gradation values. This ratio Y / M is the ratio of Y and M for reproducing the red color tone. Further, a weight (W) is assigned to each MY tone value combination as shown in FIG. This weight (W) is used for correction described later. For example, if the weight (W) is 0.5, the reproduction of gray and red is equivalent. If the weight (W) is smaller than 0.5, the gray reproducibility is emphasized. If the weight (W) is greater than 0.5, the red reproducibility is emphasized. To do. The weight (W) is set in advance, and may be programmed in advance or input from the input means 40, for example.

  Further, as in the case of gray, the input-side gradation value is further divided to obtain a combination of the input-side MY gradation value and the output-side MY gradation value as shown in FIG. Further, the ratio Y / M and the weight (W) are obtained.

  Then, the combination of the CMY gradation values obtained in S52 is corrected based on the combination of the MY gradation values obtained in S53 (S54).

  In this embodiment, of the combinations of the CMY gradation values on the input side and the CMY gradation values on the output side shown in FIG. The Y gradation value is corrected. The reason why the correction range is from 51 to 128 gradations is that the MY gradation value indicating a general skin color is almost in such a range, and in particular, the correction range is from 51 to 128 gradations. For example, the correction range can be determined depending on the output characteristics and application of the printer, for example, correcting 128 gradations or less, or correcting 77 gradations to 102 gradations. Therefore, the R (red) low gradation part (highlight part) composed of MY in the present invention means 128 gradations or less.

  Here, the correction on the output side shown in FIG. 22 shows the ratio Y / M of M and Y of the combination of the CMY gradation values shown in FIG. 22 so as to improve the reproducibility of the red color tone. The Y gradation value is corrected so as to approach the ratio Y / M shown in FIG.

For example, the case where the input side C = M = Y = 77 in FIG. 22 will be described as an example. On the input side C = M = Y = 77, the tone value of M on the output side is 88.4, and the tone value of Y is 80.9. First, the ratio Y / M for reproducing the red color tone when the gradation value of M is 88.4 is obtained. Since the M gradation value 88.4 is between the M gradation values 84.5 and 98.3 in FIG. 24, the ratio Y / M of the M gradation value 88.4 is the M gradation value. The similarity is obtained from the values 84.5 and 98.3 and the respective ratios Y / M1.10 and 1.07.
Ratio Y / M = 1.10- (1.10-1.07) × (88.4-84.5) / (98.3-84.5) = 1.09
It becomes.

Further, the M gradation value is multiplied by the obtained ratio to 88.4 to obtain the Y gradation value Yr for reproducing the red color tone when the M gradation value is 88.4.
Yr = 88.4 × 1.09 = 96.4
The Y tone value 80.9 on the output side 77 of the CMY tone value on the input side shown in FIG. 22 is corrected using Yr. If correction is performed by replacing the Y gradation value 80.9 with Yr96.4, the red color tone can be reproduced. However, in this example, correction is performed using Yr, the Y gradation value on the output side, and the weight (W) so as to ensure the reproducibility of gray. According to FIG. 24, the weight (W) at 77 of the MY gradation value is 0.6.
Yf = W * Yr + (1.0-W) * Y = 0.6 * 96.4 + (1-0.6) * 80.9 = 90.2
It becomes. Correction is performed by replacing the Y tone value of 77 on the output side of the CMY tone value on the input side shown in FIG. 22 with this Yf90.2. Similarly, the Y-side gradation value shown in FIG. 22 is corrected by obtaining Yf for gradations 51 to 128. The correction result is shown in FIG.

  Further, tone correction tables 221 to 223 for each color in which the input side and the output side are associated with each other for CMY configured as shown in FIGS. 26A to 26C are created from the correction results shown in FIG. S55).

  As described above, the reproducibility of the red color tone is improved by correcting the Y tone value on the output side. Further, the correction on the output side may correct the M gradation value so as to approach the ratio Y / M of M and Y of the combination of the MY gradation values for reproducing the red color tone.

  Further, the gradation correction table creating means 12 creates a gradation correction table 224 for K and stores it in the gradation correction table storage unit 22 (S13). Details of the procedure for creating the K gradation correction table will be described below with reference to the flowchart shown in FIG.

  First, K printed on printing paper using a K ink on a printing press is 0 gradation, 26 gradation, 51 gradation, 77 gradation, 102 gradation, 128 gradation, 153 gradation, 179 gradation, 179 gradation, 204. Each patch of gray in a plurality of levels of gradation, 230 gradations, and 255 gradations is output and measured to obtain a value of the L * a * b * color system. The color measurement result is stored in the target color table 21 via the input unit 40 as shown in FIG. 2C (S31).

  Next, in the calibration color printer 2, K is 0 gradation, 26 gradation, 51 gradation, 77 gradation, 102 gradation, 128 gradation, 153 gradation, 179 gradation, 204 gradation, 230 gradation. Each patch of gray in a plurality of stages of 255 gradations is output and measured to obtain a value of the L * a * b * color system. The color measurement result is stored in the measurement table 231 via the input unit 40 as shown in FIG. 5B (S32).

  Then, the gradation correction table creating means 12 calculates L * values for 0 to 255 of K of the printing press from the L * values (lightness data) of the gray patch by the printing press and the gray patch by the calibration color printer 2. The K gradation value of the proof color printer 2 to be reproduced is obtained. Although not shown, the K gray gradation value is shown on the input side, and the gray brightness of the K gradation value on the input side by the printer is calibrated with respect to the K gradation value on the input side on the output side. The K gradation correction table 234 indicating the K gradation values to be reproduced by the color printer is created and stored in the gradation correction table storage unit 22 (S33).

When the image data is received by the image data receiving unit 30 (S14), the gradation value correcting unit 11 converts the YMCK gradation values of the image data into the gradation levels of the respective colors stored in the gradation correction table storage unit 22. Correction is performed using the tone correction tables 221 to 224 (S15). The correction is performed by using the YMCK tone values of the image data as input values, obtaining output values using the tone correction tables 221 to 224 of the respective colors, and replacing them with the output values.
The image recording control means 14 controls the calibration color printer 2 to output an image based on the corrected image data (S16).

  Then, the calibration color printer 2 outputs an image based on the corrected image data. At this time, since the image data is corrected by the gradation correction table so as to improve the reproducibility of the red color composed of CMY three-color gray and MY, the image output from the calibration color printer 2 is the gray of the printed matter. And red (skin color) can be improved in reproducibility.

1 is a functional block diagram showing a configuration of a color image forming system according to the present invention. It is a figure which shows the structure of the target color table of this Embodiment. It is a figure which shows the structure of the gradation correction table memory | storage part of this Embodiment. It is a figure which shows the structure of the LUT memory | storage part of this Embodiment. It is a figure which shows the structure of the measurement table of this Embodiment. 4 is a flowchart illustrating an example of a procedure for forming a color image by performing color adjustment so as to match an output color of a printing machine that is a target of color matching. It is a flowchart which shows the procedure of preparation of CMY gradation value-> L * a * b * LUT and L * a * b *-> CMY gradation value LUT. FIG. 6 is a diagram illustrating an example of a color patch image for measuring CMY color values in the present embodiment. It is explanatory drawing of LUT which converts the color value of CMY into the value L * a * b * of a color system in this Embodiment. FIG. 6 is a diagram illustrating a distribution of sample points and points to be interpolated on a locus based on CMY color values and color system values in the present embodiment. FIG. 5 is a diagram illustrating an order of interpolation processing when converting a combination of CMY colors into color system values in the present embodiment. FIG. 6 is an explanatory diagram of an LUT for converting a color system value L * a * b * into a CMY color value in the present embodiment. FIG. 5 is a coordinate diagram showing a target value T ′ in coordinates of C and M color systems in the present embodiment. It is a coordinate diagram which shows the target value T in the coordinate of the combination of the color of C and M in this Embodiment. It is a coordinate diagram of the convergence calculation process for estimating the target value T in the coordinate of the combination of the color of C and M in this Embodiment. FIG. 6 is a coordinate diagram of a convergence calculation process for estimating a target value T ′ in coordinates of C and M color systems in the present embodiment. It is a figure which shows the target value T 'in the coordinate of the C, M color system when the target value T' is outside the color reproduction range in the present embodiment. In the present embodiment, the target value T ′ is outside the color reproduction range, and is a coordinate diagram showing the target value T ′ in the coordinates of the C and M color systems, and the target value T ′ is within the color reproduction range. It is a coordinate diagram which shows having moved. It is a figure which shows the target value T in the coordinate of the combination of the C and M color at the time of moving the target value T 'which exists out of a color reproduction range in the color reproduction range in this Embodiment. It is a flowchart which shows the procedure of preparation of the C, M, and Y gradation correction table of this Embodiment. It is a figure which shows an example of the calculation result which shows the combination of the CMY gradation value for reproducing the gray color tone of the combination of the CMY gradation value of the input side by a printing machine with a calibration color printer. It is a figure which shows the calculation result obtained by further interpolating the calculation result shown in FIG. It is a figure which shows an example of the calculation result which shows the combination of the CMY gradation value for reproducing the red color tone of the combination of the CMY gradation value of the input side by a printing machine with a calibration color printer. It is a figure which shows the calculation result obtained by further interpolating the calculation result shown in FIG. It is a figure which shows the result which correct | amended the calculation result shown in FIG. 22 based on the calculation result shown in FIG. It is a figure which shows an example of a structure of the gradation correction table of this Embodiment. It is a flowchart which shows the procedure of preparation of the K gradation correction table of this Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Control apparatus 10 Control part 11 Tone value correction means 12 Tone correction table creation means 13 LUT creation means 14 Image recording control means 20 Storage part 21 Target color table 22 Tone correction table storage part 23 LUT storage part 30 Image data reception Means 40 Input unit 2 Color printer for calibration

Claims (12)

The color tone output from the first color image output device based on the gradation value indicating the density level of each of a plurality of basic colors including at least C (cyan), M (magenta), and Y (yellow). A color adjustment method for performing color adjustment so as to be output by a second color image output device,
A plurality of combinations of C, M, and Y gradation values, and a color system value of each color that is output by the plurality of combinations of C, M, and Y gradation values in the second color image output device; Pre-store a table associated with
C, M, and Y gradations output by the second color image output device corresponding to gray color system values composed of C, M, and Y output by the first color image output device Obtaining a combination of values by referring to the table;
M and Y gradation values output by the second color image output device corresponding to the R (red) color system value composed of M and Y output by the first color image output device. Obtaining a combination of the above with reference to the table;
Correcting a predetermined gradation value range based on the obtained combination of M and Y gradation values, based on the obtained combination of M and Y gradation values, of the obtained C, M, and Y gradation value combinations; ,
Creating correction characteristics for each of C, M, and Y using the corrected combination of C, M, and Y tone values, and each of the C, M, and Y tone values The color adjustment method is characterized in that the color adjustment is performed by correcting each color using the respective correction characteristics. The step of storing the table in advance includes
Creating a first reference table in which color system values respectively corresponding to a plurality of combinations of the C, M, and Y gradation values are associated;
Creating a second reference table based on the first reference table and associating a combination of gradation values respectively corresponding to the color system values of the plurality of color system values;
A combination of C, M, and Y gradation values corresponding to the gray color system values is obtained by referring to the second reference table,
2. The color adjustment method according to claim 1, wherein a combination of M and Y gradation values corresponding to the R (red) color system value is obtained by referring to the second reference table. The correction of the M or Y gradation value is as follows.
A ratio of the M and Y gradation values is obtained from the obtained combination of the M and Y gradation values, and either the M or Y gradation of the obtained combination of the C, M and Y gradation values is obtained. The color adjustment method according to claim 1, wherein the other gradation value corresponding to the value is corrected based on the ratio. Storing the weighting for the gray or R for the predetermined range of gradation values in advance;
The correction of the M or Y gradation value is as follows.
A ratio of the M and Y gradation values is obtained from the obtained combination of the M and Y gradation values, and either the M or Y gradation of the obtained combination of the C, M and Y gradation values is obtained. The other gradation value corresponding to the value is corrected based on the other gradation value corresponding to the value, the gradation value obtained from the one gradation value according to the ratio and the weight stored in advance. The color adjustment method according to claim 2. The first color image based on image data including gradation values indicating the density levels of each of a plurality of basic colors including at least C (cyan), M (magenta), and Y (yellow) The color tone of the image output from the output device is set as a color matching target, and the color adjustment is performed based on the image data so that the color tone of the image output from the second color image output device becomes the target color. A color image forming method for forming a color image,
A plurality of combinations of C, M, and Y gradation values, and a color system value of each color that is output by the plurality of combinations of C, M, and Y gradation values in the second color image output device; Pre-store a table associated with
C, M, and Y gradations output by the second color image output device corresponding to gray color system values composed of C, M, and Y output by the first color image output device Obtaining a combination of values by referring to the table;
M and Y gradation values output by the second color image output device corresponding to the R (red) color system value composed of M and Y output by the first color image output device. Obtaining a combination of the above with reference to the table;
Correcting a predetermined gradation value range based on the obtained combination of M and Y gradation values, based on the obtained combination of M and Y gradation values, of the obtained C, M, and Y gradation value combinations; ,
Creating correction characteristics for each of C, M, and Y using the corrected combination of C, M, and Y tone values;
Correcting each gradation value of C, M and Y of the image data using each of the created correction characteristics;
Forming a color image on the basis of the corrected image data. The step of storing the table in advance includes
Creating a first reference table in which color system values respectively corresponding to a plurality of combinations of the C, M, and Y gradation values are associated;
Creating a second reference table based on the first reference table and associating a combination of gradation values respectively corresponding to the color system values of the plurality of color system values;
A combination of C, M, and Y gradation values corresponding to the gray color system values is obtained by referring to the second reference table,
6. The color image forming method according to claim 5, wherein a combination of M and Y gradation values corresponding to the R (red) color system value is obtained with reference to the second reference table. The correction of the M or Y gradation value is as follows.
A ratio of the M and Y gradation values is obtained from the obtained combination of the M and Y gradation values, and either the M or Y gradation of the obtained combination of the C, M and Y gradation values is obtained. The color image forming method according to claim 5, wherein the other gradation value corresponding to the value is corrected based on the ratio. Storing the weighting for the gray or R for the predetermined range of gradation values in advance;
The correction of the M or Y gradation value is as follows.
A ratio of the M and Y gradation values is obtained from the obtained combination of the M and Y gradation values, and either the M or Y gradation of the obtained combination of the C, M and Y gradation values is obtained. 6. The other gradation value corresponding to the value is corrected based on the gradation value obtained from the corresponding other gradation value and the one gradation value according to the ratio and a weight stored in advance. The color image forming method according to claim 6. The first color image based on image data including gradation values indicating the density levels of each of a plurality of basic colors including at least C (cyan), M (magenta), and Y (yellow) A second color image output device that outputs the image based on the image data, with the color tone of the image output by the output device as a target for color matching, and the image output by the second color image output device; A color image forming system that forms a color image by performing color adjustment so that a color tone becomes the target color,
A plurality of combinations of C, M, and Y gradation values, and a color system value of each color that is output by the plurality of combinations of C, M, and Y gradation values in the second color image output device; Storage means for storing in advance a table associated with
C, M, and Y gradations output by the second color image output device corresponding to gray color system values composed of C, M, and Y output by the first color image output device A combination of values is obtained by referring to the table, and the second color corresponding to the value of the R (red) color system constituted by M and Y output from the first color image output device A combination of M and Y gradation values output by the image output apparatus is obtained with reference to the table, and the M or Y gradation value of the obtained combination of C, M and Y gradation values is obtained. A predetermined gradation value range is corrected based on the combination of M and Y gradation values, and each of C, M, and Y is corrected using the corrected combination of C, M, and Y gradation values. Correction characteristic creating means for creating a correction characteristic for,
Gradation value correcting means for correcting the gradation values of C, M, and Y of the image data using the created correction characteristics;
And a control means for controlling the second color image output device so as to form a color image based on the corrected image data. The storage means
A color system of a plurality of color system values created based on a first reference table in which color system values respectively corresponding to a plurality of combinations of the C, M, and Y gradation values are associated. Storing at least a second reference table in which a combination of gradation values corresponding to each value is associated;
The correction characteristic creating means includes
A combination of C, M, and Y gradation values corresponding to the gray color system value is obtained by referring to the second reference table, and corresponds to the R (red) color system value. The color image forming system according to claim 9, wherein a combination of M and Y gradation values is obtained with reference to the second reference table. The correction characteristic creating means includes
A ratio of the M and Y gradation values is obtained from the obtained combination of the M and Y gradation values, and either the M or Y gradation of the obtained combination of the C, M and Y gradation values is obtained. The color image forming system according to claim 9 or 10, wherein the other gradation value corresponding to the value is corrected based on the ratio. The correction characteristic creating means includes
Pre-stores weights for the gray or R for the predetermined range of gradation values;
A ratio of the M and Y gradation values is obtained from the obtained combination of the M and Y gradation values, and either the M or Y gradation of the obtained combination of the C, M and Y gradation values is obtained. 10. The other gradation value corresponding to the value is corrected based on the gradation value obtained according to the ratio from the corresponding other gradation value and the one gradation value and a weight stored in advance. The color image forming system according to claim 10.

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