JP2006340221A - Color adjustment method, color image forming method, and color image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a color adjustment method, a color image forming method, and a color image forming apparatus capable of easily obtaining a correction characteristic for gradation correction and colors whose color tones are respectively different from a target color and executing highly accurate color adjustment in a CMY gray when a gradation value of gradation image data is corrected and color is adjusted by configuring colors of a dot image line part configuring a dot image by a pixel in the target color and pixels in colors having different color tones from the target color. <P>SOLUTION: Values of a first color pixel (pixel a) and a second color pixel (pixel b) in a color system configuring colors of the dot image line part are obtained by using values of solid and neutral colors in the color system obtained by printing the dot image and values of colors of a recording medium in the color system, and an area ratio table, a color chart is outputted, and the correction characteristic is corrected to adjust the color tone of the CMY gray. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a color adjustment method for performing color adjustment by configuring the color of a halftone image line portion of a halftone image by a pixel of a target color and a pixel of a color different from the target color, The present invention relates to a color image forming method using a color adjustment method and a color image forming apparatus.

  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. .

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

  Further, as a means for creating a color proof, on the basis of halftone dot image data of each color separation halftone document, light composed of a combination of a plurality of lights having different wavelengths such as R, G, B, etc. There is a color 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. Among them, the primary color (single color), which is the color of the halftone dot line portion constituting the halftone dot image obtained by printing each color plate of a plurality of inks on a printing press, and the multi-color (multiple inks) There is a type of DDCP that performs color adjustment by changing the output intensity of the three basic colors so that each color is reproduced, with the background color of the print paper and the background color of the printing paper as the target of the output color (for example, Patent Document 1).

  However, when the color proof is output based on the halftone image data by the above-described DDCP, there may occur a phenomenon that the color tone is slightly shifted in the halftone region, although the color tone matches in the solid region. For example, in the cyan portion, when the halftone dot of the halftone area constituting the halftone area becomes small, it may appear yellowish.

  As a countermeasure against this, a so-called color management system that performs color adjustment using device link profiles obtained from the respective device profiles indicating characteristics of output colors of the DDCP and the printing press so as to adjust the color tone of the output image ( It is conceivable to use a technique called CMS). However, in color adjustment using a color management system, for example, a halftone dot of a color that does not originally exist may be mixed in the printed matter, resulting in a problem that the plate inspection property is impaired. Also, since the color management system cannot be used for halftone image data (halftone image data), the color of the halftone image can be adjusted when outputting based on the halftone image data. There was also a problem that it was not possible.

  Therefore, the color of the halftone dot line portion constituting the halftone dot image output based on the halftone dot image data by DDCP has a color tone between the target output color pixel output by the printing press and the target output color. The present applicant has proposed a method (for example, Japanese Patent Application No. 2003-312527) that comprises and outputs with pixels of different colors. This makes it possible to perform color adjustment in the halftone area, and further, according to this method, color adjustment can be performed even when a halftone image is output based on halftone image data.

Japanese Patent Laid-Open No. 2003-149796

  However, it is possible to adjust the solid output color as described in Patent Document 1, but the solid output color constituting the color of the halftone area of one halftone region There was no means for easily obtaining the color of different colors.

  In addition, although some color adjustment was possible, errors such as color tone and density differ depending on the gradation value, and for example, a situation occurs in which the color tone in the high gradation region is good but not in the low gradation region. In some cases, a multi-order color obtained by superimposing a plurality of inks, particularly CMY gray, may be reddish or greenish, and it is difficult to match the color tone. As a result, it may be difficult to perform highly accurate color adjustment.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to correct the gradation value of gradation image data and to change the color of a halftone image line portion constituting a halftone image. When color adjustment is performed by configuring a pixel of a target color and a pixel of a different color tone from the target color, the correction characteristics for performing gradation correction and the target color have a color tone Provided are a color adjustment method capable of easily obtaining different colors and performing highly accurate color adjustment in CMY gray, a color image forming method using the color adjustment method, and a color image forming apparatus. There is to do.

  In order to achieve the above object, the invention described in claim 1 is obtained by printing on a recording medium using a plurality of color plates including at least C (cyan), M (magenta) and Y (yellow) color plates. Correcting the gradation value of gradation image data composed of drawing information including gradation values indicating gradation levels of each color of the plurality of color plates, and adjusting the gradation value of the halftone image An area of each color of a halftone image line portion constituting a halftone dot image based on halftone dot image data obtained by converting halftone image data whose value has been corrected into the first color pixel and the aforementioned color A color adjustment method comprising and reproducing at least one second color pixel having a color tone different from that of a first color, and forming a halftone image showing an intermediate color of each color of the halftone image portion When each color area of the halftone image line portion is composed of the first color and the second color A step of storing in advance an area ratio table indicating the area ratio of each of the first color and the second color of the color and the color of the recording medium, and the halftone image line unit obtained by the printing Obtaining a value of a solid color system of each color, a value of an intermediate color system of each color of the halftone image portion, and a value of a color system of the color of the recording medium, and the obtained colors The halftone image using the intermediate color value, the obtained solid color value of each color, and the obtained color value of the recording medium color and the area ratio table. A value of the color system of the first color and a value of the color system of the second color of each color of the line part are obtained, and the pixel of the first color is obtained for each color of the plurality of color plates , Correcting the gradation value of the intermediate color of each color composed of the pixels of the second color to a gradation value that becomes the density of the intermediate color of each acquired color Obtaining a first correction characteristic, and correcting the plurality of colors indicated by the combination of the gradation values of each color of the plurality of color plates with the obtained first correction characteristic, and obtaining the obtained first correction characteristic; A value of the color system obtained by configuring with a color pixel and the second color pixel, and C, M, and Y of the intermediate colors of the colors of the halftone image portion obtained by printing Based on the value of the gray color system that is configured, the first correction characteristic for each of CMY is corrected among the obtained first correction characteristics so as to reproduce the value of the gray color system. And a step of using the corrected first correction characteristic for correcting a gradation value of the gradation image data.

  According to a second aspect of the present invention, in the step of obtaining the first correction characteristic, a gradation value of an intermediate color of each of the acquired colors is used as an input value, and the first color pixel and the second color of the second color are determined. A step of correcting the first correction characteristic by including, as an output value, a gradation value in which the density of the intermediate color of each color constituted by the pixels becomes the density of the acquired intermediate color as an output value. Generating a first reference table in which color system values respectively corresponding to combinations of the gradation values for the plurality of colors are associated, and a plurality of tables based on the first reference table Creating a second reference table in which each color system value is associated with a combination of gradation values corresponding to the color indicated by the color system value; Corresponds to the gray color system value using a reference table C, M, and Y gradation value combinations are obtained, and the C, M, and Y gradation values when the gray is printed are used as input values. A first correction characteristic for each CMY is obtained based on the second correction characteristic for each CMY associated with each gradation value as an output value, and the second correction characteristic for each CMY obtained. And a step of correcting the above.

  According to a third aspect of the present invention, each color of the halftone line portion is a color obtained by superimposing a primary color of one plate color among the plurality of color plates and a color of at least two plates. Determining the color system value of the first color and the color system value of the second color include determining the primary color and the multi-color. The step of obtaining the primary color comprises obtaining a value of the color system of the first color of each color of the halftone image line unit as a value of the color system of the obtained solid color, The value of the color system of the second color for each primary color of the stipple line portion is the value of the color system of the intermediate color of the acquired colors for each primary color, and the value of the color system of each primary color. The acquired solid color system value of each color, and the acquired color value of the recording medium color system and the area ratio table for each primary color The step of obtaining the multi-order color includes the step of correcting the area ratio of the area ratio table based on the obtained first correction characteristic, and each of the halftone image line portions. The value of the color system of the second color for the multi-order color, the value of the color system of the intermediate color of the acquired colors for the multi-color, the value of the solid color system of the acquired colors And a step of obtaining using the obtained color system value of the color of the recording medium and the corrected area ratio table for each of the multi-order colors.

  According to a fourth aspect of the present invention, the value of the color system of the second color for the multi-order color is the second color that has already been obtained in order from the lowest order with the smallest number of superimposed colors. It is characterized in that it is obtained using the values of the color system.

  According to a fifth aspect of the present invention, the value of the color system of the second color is the value for each color of the halftone dot line portion constituting a halftone dot image showing an intermediate color of each color of the halftone dot line portion. The value of the color system of one color, the value of the color system of the second color, and the value of the color system of the recording medium and the area shown in the area ratio table corresponding to each color The total value obtained by adding the products with the ratio is a value when the acquired color value of the intermediate color of each of the colors is obtained.

  Further, in the invention according to claim 6, the area ratio table indicates the area ratio for a plurality of intermediate colors of each color of the halftone image line portion, and the value of the color system of the acquired intermediate colors is: The color values of the second color system are obtained by calculating an error between the total value and the value of the color system of the acquired intermediate colors. It is characterized in that the intermediate color is required to have the smallest error.

  The invention described in claim 7 is characterized in that the value of the color system for each color used when obtaining the value of the color system of the second color is a value of the XYZ color system.

  In the invention according to claim 8, the pixel of the first color is arranged at a center portion of each color area of the halftone image line portion constituting the halftone image, and the pixel of the second color is It is arranged at the peripheral part of each color area of the halftone image line part constituting the halftone image.

  According to a ninth aspect of the invention, the color tone of a halftone image obtained by printing on a recording medium using a plurality of color plates including at least C (cyan), M (magenta) and Y (yellow) color plates. Correcting the gradation value of gradation image data composed of drawing information including gradation values indicating the gradation level of each color of the plurality of color plates, and correcting the gradation value of the gradation value. Each color area of a halftone image line portion constituting a halftone image based on halftone image data obtained by converting halftone image data into halftone dots is defined as a first color pixel and a first color for each color. A color image forming method comprising a pixel of at least one second color having a different color tone, and forming a color image so as to reproduce by changing the output intensity of a plurality of basic colors according to the color of each pixel Between the output intensity of the plurality of basic colors and the value of the color system A step of storing a third reference table indicating the correspondence relationship in advance, and a region of each color of the halftone dot line portion constituting a halftone dot image indicating an intermediate color of each color of the halftone dot line portion as the first color and the second color And storing the area ratio table indicating the area ratio of the first color and the second color of each color and the area ratio of the color of the recording medium in advance, and obtained by the printing Obtaining a solid color system value of each color of the halftone image line portion, an intermediate color system value of each color of the halftone image line portion, and a color system value of the color of the recording medium A color system value of the intermediate color of each acquired color, a value of the solid color system of each acquired color, and a value of the color system of the acquired color of the recording medium and the area ratio table Using the value of the color system of the first color and the color system of the second color And for each color of the plurality of color plates, a gradation value in which the density of the intermediate color of each color constituted by the pixel of the first color and the pixel of the second color becomes the density of the acquired intermediate color of each color Determining a first correction characteristic to be corrected, a value of the color system of the acquired recording medium, a value of the obtained first color system, and a color system of the second color A color channel table is generated by determining a combination of output intensities of the plurality of basic colors corresponding to the color of the recording medium, the first color, and the second color based on the value of the color and the third reference table And correcting the plurality of colors indicated by the combination of the gradation values of each color of the plurality of color plates with the obtained first correction characteristic, and obtaining the first color pixel obtained and the first color A color system value obtained by constituting with two color pixels, and the printing The gray color system value is reproduced based on the gray color system value composed of C, M and Y among the intermediate colors of the obtained halftone image line portion. Correcting the first correction characteristic for each of CMY of the obtained first correction characteristics, and using the corrected first correction characteristic for correcting the gradation value of the gradation image data; Forming a color image by changing the output intensity of a plurality of basic colors according to the color of each pixel based on the generated color channel table.

  According to a tenth aspect of the present invention, the plurality of basic colors are three colors of cyan (C), magenta (M), and yellow (Y), and the reference table includes the cyan (C), magenta The color system values for each combination in which the output intensities of (M) and yellow (Y) are changed in stages are shown.

  According to an eleventh aspect of the present invention, in the step of obtaining the first correction characteristic, a gradation value of an intermediate color of each acquired color is used as an input value, and the first color pixel and the second color of the second color are determined. The step of correcting the first correction characteristic includes the step of associating, as an output value, a gradation value at which the density of the intermediate color of each color constituted by the pixels becomes the density of the acquired intermediate color as an output value. Creating a first reference table in which color system values corresponding to the combinations of gradation values for the plurality of colors are associated with each other, and a plurality of color specifications based on the first reference table Creating a second reference table in which a combination of gradation values corresponding to a color indicated by the color system value is associated with each color system value of the system value; and the second reference Using a table, it corresponds to the value of the gray color system. A combination of C, M, and Y gradation values is obtained, and each of the gradation values of C, M, and Y when the gray is printed is used as an input value, and each of the obtained combinations of C, M, and Y is obtained. And calculating the second correction characteristic for each of the CMYs associated with the gradation values of the first and second gradation values as output values, and the first correction characteristic for each of the CMYs based on the obtained second correction characteristic for each of the CMYs. And a step of correcting.

  According to a twelfth aspect of the present invention, each color of the halftone image line portion is a color obtained by superimposing a primary color of one plate color among the plurality of color plates and a color of at least two plates. Determining the color system value of the first color and the color system value of the second color include determining the primary color and the multi-color. The step of obtaining the primary color comprises obtaining a value of the color system of the first color of each color of the halftone image line unit as a value of the color system of the obtained solid color, The value of the color system of the second color for each primary color of the stipple line portion is the value of the color system of the intermediate color of the acquired colors for each primary color, and the value of the color system of each primary color. The acquired solid color system value of each color, the acquired color value of the recording medium color system, and the area ratio table for each primary color The step of obtaining the multi-order color includes the step of correcting the area ratio of the area ratio table based on the obtained first correction characteristic; and The value of the color system of the second color for each multi-order color, the value of the color system of the intermediate color of each acquired color for each multi-color, the value of the solid color system of each acquired color And using the acquired value of the color system of the color of the recording medium and the corrected area ratio table for each of the multi-order colors.

  According to a thirteenth aspect of the present invention, the value of the color system of the second color for the multi-order color is the second color that has already been obtained in order from the lowest order with the smallest number of superimposed colors. It is characterized in that it is obtained using the values of the color system.

  According to a fourteenth aspect of the present invention, the value of the color system of the second color is the second value for each color of a halftone dot line portion constituting a halftone dot image showing an intermediate color of each color of the halftone dot line portion. The value of the color system of one color, the value of the color system of the second color, and the value of the color system of the recording medium and the area shown in the area ratio table corresponding to each color The total value obtained by adding the products with the ratio is a value when the acquired color value of the intermediate color of each of the colors is obtained.

  In the invention according to claim 15, the area ratio table indicates the area ratio for a plurality of intermediate colors of each color of the halftone image portion, and the value of the color system of the acquired intermediate colors is: The color values of the second color system are obtained by calculating an error between the total value and the value of the color system of the acquired intermediate colors. It is characterized in that the intermediate color is required to have the smallest error.

  The invention described in claim 16 is characterized in that the value of the color system for each color used when obtaining the value of the color system of the second color is a value of the XYZ color system.

  According to a seventeenth aspect of the present invention, the pixel of the first color is arranged at the center of each color area of the halftone image line portion constituting the halftone image, and the pixel of the second color is It is arranged at the peripheral part of each color area of the halftone image line part constituting the halftone image.

  The invention according to claim 18 is the color tone of a halftone image obtained by printing on a recording medium using a plurality of color plates including at least C (cyan), M (magenta) and Y (yellow) color plates. Correcting the gradation value of gradation image data composed of drawing information including gradation values indicating the gradation level of each color of the plurality of color plates, and correcting the gradation value of the gradation value. Each color area of a halftone image line portion constituting a halftone image based on halftone image data obtained by converting halftone image data into halftone dots is defined as a first color pixel and a first color for each color. A color image forming apparatus configured with at least one second color pixel having a different color tone, and forming a color image so as to reproduce by changing the output intensity of a plurality of basic colors according to the color of each pixel The output intensity of the plurality of basic colors and the value of the color system A third reference table indicating the correspondence between the first and second colors, and a region of each color of the halftone image line portion constituting a halftone image indicating an intermediate color of each color of the halftone image line portion is configured by the first color and the second color An area ratio table showing the area ratios of the first color and the second color of each color and the color of the recording medium, and each color of the halftone image portion obtained by the printing A solid color system value, an intermediate color system value of each color of the halftone image portion, and a color system value of the color of the recording medium are received, and the acquired intermediate color system of each color Value of the obtained solid color system of each color, and the obtained color value of the color system of the recording medium and the area ratio table, A color system value of the first color and a color system value of the second color are obtained, and each color of the plurality of color plates Next, a color for obtaining a first correction characteristic for correcting the density of the intermediate color of each color composed of the pixels of the first color and the pixel of the second color to a gradation value that is the density of the intermediate color of each acquired color An adjustment value calculating means; the obtained color system value of the color of the recording medium; the obtained first color system value; the second color system value; and the reference table Generating means for determining a combination of output intensities of the plurality of basic colors corresponding to the color of the recording medium, the first color, and the second color, and generating a color channel table; and the plurality of color plates A plurality of colors indicated by the combination of the gradation values of each color are corrected with the obtained first correction characteristic, and are constituted by the obtained first color pixel and the second color pixel. Value of the color system obtained by printing and each color of the halftone image line portion obtained by printing Based on the values of the gray color system composed of C, M, and Y of the intermediate colors, CMY among the obtained first correction characteristics so as to reproduce the values of the color system of gray. Correction characteristic correcting means for correcting a first correction characteristic for each, gradation value correcting means for correcting a gradation value of the gradation image data using the corrected first correction characteristic, and the generation And a control means for controlling the output intensity of a plurality of basic colors to change in accordance with the color of each pixel based on the color channel table.

  According to the color adjustment method of claim 1, the gradation value of the gradation image data is corrected, and each color of the halftone image line portion is a color having a color tone different from that of the solid color pixel. Correction characteristics for performing tone correction when color adjustment is performed with a pixel and a solid color that is different from the tone of a solid color can be easily obtained, and CMY gray can be reproduced with high accuracy. it can.

  According to the color image forming method of the ninth aspect, the gradation value of the gradation image data is corrected, and each color of the halftone image line portion is a target color pixel and a target color. A correction characteristic for performing tone correction in the case of performing color adjustment with pixels having different color tones and a target color easily obtain a color having a different tone, and CMY gray with high accuracy Further, the target color of the halftone image line portion based on the gradation image data (halftone image data) whose gradation value is corrected, and a color whose tone is different from the obtained target color A color image is formed by obtaining a combination of the output intensity of a plurality of basic colors corresponding to the color from the reference table indicating the correspondence between the output intensity of the plurality of basic colors and the value of the color system. It can be performed with high accuracy.

  According to the color image forming apparatus of claim 18, the gradation value of the gradation image data is corrected, and each color of the halftone image line portion is a target color pixel and a target color. A correction characteristic for performing tone correction in the case of performing color adjustment with pixels having different color tones and a target color easily obtain a color having a different tone, and CMY gray with high accuracy Further, the target color of the halftone image line portion based on the gradation image data (halftone image data) whose gradation value is corrected, and a color whose tone is different from the obtained target color A color image is formed by obtaining a combination of the output intensity of a plurality of basic colors corresponding to the color from the reference table indicating the correspondence between the output intensity of the plurality of basic colors and the value of the color system. It can be performed with high accuracy.

  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.

Further, the L * value, a * value, and b * value of the L * a * b * color system value are obtained from the X value, Y value, and Z value of the XYZ color system value as follows. be able to. First,
Xd = X / X0, Yd = Y / Y0, and Zd = Z / Z0. However, X0, Y0, and Z0 are values obtained by adding x (λ), y (λ), and z (λ) for all wavelengths (380 nm to 730 nm), respectively. And
X2 = Xd ^ (1/3); Xd> 0.008856 = Xd × 7.787 + 16/116; otherwise Y2 = Yd ^ (1/3); Yd> 0.008856 = Yd × 7.787 + 16/116; otherwise Z2 = Zd ^ (1/3); if Zd> 0.008856 = Zd × 7.787 + 16/116; otherwise, X2, Y2, Z2 are determined.
L * = Y2 × 116-16
a * = 500 × (X2−Y2)
b * = 200 × (Y2-Z2)
Then, the L * a * b * color system value indicated by the L * value, a * value, and b * value is obtained. Further, the X value, the Y value, and the Z value of the values of the XYZ color system can be obtained by calculating backward from the values of the L * a * b * color system.

  Further, the above Xd, Yd, and Zd are values indicating the respective densities of C (cyan), M (magenta), Y (yellow), and K (black) in the description of the present embodiment. Use. Xd is used for C, Yd for M and K, and Zd for Y.

  Hereinafter, in describing the color adjustment method and the color image forming method of the present invention, an embodiment applied to a calibration color printer (color image forming apparatus) will be described as an example, and will be specifically described with reference to the drawings.

[Outline of output]
First, an outline of the output of the calibration color printer of this embodiment will be described. The color printer for calibration uses gradation image data (so-called vector graphics, each object is represented by the coordinates of the points and the parameters of the line and surface equations, and the fill color (the gradation value of each color of YMCK). The gradation value is a value indicating stepwise by setting white as 0 and solid as 255. Further, the halftone dot area ratio (referred to as halftone dot) indicating the color as white and 0 as solid. May be represented by a certain)), special effects, vector data represented by a set of drawing information such as character font information indicating the shape of the character and its size, or so-called bitmap graphics, and a predetermined interval in the horizontal direction. (Raster data indicated by drawing information in which a plurality of pixels arranged at (resolution) constitute one line, and the lines are further arranged in the vertical direction at predetermined intervals, and each pixel is indicated by a gradation value) , M, C, and K are divided into halftone dot image data, and a color proof is created from the halftone dot image data based on the halftone dot image data. The halftone dots are composed of the pixels in the area of, and the halftone dots are arranged by changing the so-called screen angle for each color so that the arrangement directions of the halftone dots are different for each color, in other words, the size of each halftone dot. Is changed in a predetermined area based on the gradation value to express light and shade.

In addition, the tone values of each color of YMCK shown in the tone image data are corrected before the halftone dot conversion, and the halftone dot image is composed of a halftone dot line portion composed of YMCK halftone dots. Each color of the halftone dot line portion is a color obtained by superimposing one or more colors of YMCK (a primary color, a secondary color, a tertiary color, and a quaternary color. Each color region is, for example, a plurality of inks (C, M, Y, and K) in a printing machine (hereinafter, simply referred to as a printing machine) that is a target of color matching. ) Of each color (first color) corresponding to the target output color obtained by overprinting each of the plates (hereinafter also referred to as pixel a), the target output color, Is composed of pixels of different colors (second colors) (hereinafter sometimes referred to as pixels b). It has been made to, thereby enabling the color adjustment by using a correction and a second color of the tone value.
The colors of each pixel are changed to the three basic colors (Y, M, C, hereinafter referred to as “C, M, Y”, “YMC”, “CMY”) used for image formation by the calibration color printer. The output intensity is changed (details will be described later). Further, in this example, the target color is described as the color of the halftone image line portion that constitutes the halftone image obtained by overprinting using four color plates. This can be applied when one or four of the four-color plates are used.

  The target output color is, for example, a color printed on a printing paper (recording medium) using C, M, Y, and K inks on a printing machine, for example, a primary color, a secondary color, and a tertiary color. Color, quaternary color (hereinafter sometimes collectively referred to as CMYK1 / 2/3/4 quaternary color, and 2/3/4 quaternary color corresponds to the multi-order color of the present invention). A primary color is a color in CMYK, a secondary color is a color that combines two of CMYK, a tertiary color is a color that combines three of CMYK, and a quaternary color A combination of four of CMYK. Primary colors are C, M, Y, K. Secondary colors are R (M + Y) (red), G (C + Y) (green), and B (C + M). (Blue), K + C, K + M, K + Y, the tertiary colors are C + M + Y, KR (K + M + Y), KG (K + C + Y), KB (K + C + M), and the quaternary colors are C + M + Y + K, for a total of 15 colors. In FIG. 1, the correspondence relationship of the ink used in each case is indicated by the mark ● for the CMYK1 / 2/3/4 color and the ground color (W) of the printing paper. Further, it is assumed that the inks are printed in order from the left ink in FIG. 1, that is, in order of K → C → M → Y.

  Here, the color and each pixel constituting the color of the dot image line portion will be described with reference to FIG. In the following description, a case where the pixels b are arranged in the peripheral portion and the pixels a are arranged in the central portion to form each color region of the halftone image portion (details of the arrangement method will be described later) will be described as an example.

  First, a case where the halftone image line portion is composed of one halftone dot will be described with reference to the schematic diagram of FIG. For example, when one halftone dot is represented using a 15 pixel × 15 pixel region, the halftone dot has a halftone dot size of 15 pixels according to the halftone dot% as shown in FIG. It is shown in a region of x15 pixels. Here, when the color corresponding to the pixel a of C is indicated as Ca and the color corresponding to the pixel b is indicated as Cb (a or b is similarly added to other colors, the color corresponding to the pixel a or The color corresponding to the pixel b is shown.) As shown in FIG. 2A, the color of the peripheral pixel of the region C is Cb, and the color of the central pixel is Ca, Cb. The color of the outer pixel is composed of W.

  Next, with reference to FIG. 2B, a case where the halftone dot image line portion is composed of two halftone dots will be described by taking C and M printing as an example. Since the display of the frame of each pixel becomes complicated, the schematic diagram is omitted. Since the screen angles of C and M are different from each other in the screen angle between C and M, as shown in FIG. 2B, the halftone dots are shifted in position and overlapped. Is different. Further, as shown in FIG. 2 (b), the color of each pixel constituting each color of the halftone image line portion is Bb in the peripheral region of the region B of the overlapping portion of C and M, and the pixel in the central portion. The peripheral pixel of the C region excluding the overlapping portion with Ba and M is Cb, the central pixel is Ca, the peripheral pixel of the M region excluding the overlapping portion with Ca and C is Mb, and the central pixel is Ma and W are the outer pixels.

  Next, referring to the schematic diagram of FIG. 2C, description will be given of the case where the halftone image line portion is composed of three halftone dots, taking CMY overprinting as an example. As shown in FIG. 2C, the halftone dots of C, M, and Y are shifted in position and overlapped as in the case of the secondary color described above, and the colors of the pixels constituting the color of the halftone dot line portion are as shown in FIG. In addition, the peripheral pixel of the CMY region of the overlapping portion of C, M, and Y is CMYb, the central pixel is CMYa, and each pixel is represented by Bb, Ba, Rb, as shown in FIG. It is composed of Ra, Gb, Ga, Ca, Cb, Ma, Mb, Ya, Yb and W.

  Further, the arrangement of the pixel b is not limited to the arrangement at the peripheral edge, and it is also possible to use a pixel b ′ having a different color tone in addition to the pixel b.

[Control configuration of calibration color printer]
Next, as described above, the gradation image data is separated for each color plate of Y, M, C, and K to form halftone image data, and a color proof is created from the halftone image based on the halftone image data. A control configuration of the calibration color printer will be described with reference to FIG. FIG. 3 shows a functional block diagram of the calibration color printer. As shown in FIG. 3, the calibration color printer according to the present embodiment includes a control unit 1, a storage unit 2, an image recording unit 3, an input unit 4, and an image data receiving unit 5.

  The image recording unit 3 sensitizes the cyan coloring layer (C layer) of the photosensitive material with green (G) light, and sensitizes the magenta coloring layer (M layer) of the photosensitive material with red (R) light. The yellow color developing layer (Y layer) of the photosensitive material is exposed to light, and development processing is performed. The basic colors C, M, and Y are revealed and output to form a color image. The photosensitivity by the green (G) light, the red (R) light, and the blue (B) light is performed by irradiating light of these colors simultaneously for each pixel in a dot sequence. Further, by changing the intensity of green (G) light, red (R) light, and blue (B) light, the output intensity of C, M, and Y can be changed. The output intensities of C, M, and Y are made to correspond to the intensities of green (G) light, red (R) light, and blue (B) light so that output is performed at the output intensity of C, M, and Y based on 22. A table (not shown) is preliminarily built in and is exposed with each light intensity corresponding to the output intensity of C, M, and Y.

  The image recording density of the image recorded on the photosensitive material is preferably 600 dpi or more (especially 1000 dpi or more, more preferably 1200 dpi or more) in both the main scanning direction and the sub-scanning direction from the viewpoint of gradation reproducibility by a halftone image, etc. Further, from the viewpoints of saturation of gradation reproducibility by a halftone image, image recording speed, apparatus cost, etc., it is preferably 10,000 dpi or less (particularly 5000 dpi or less) in both the main scanning direction and the sub-scanning direction. The image recording density in the main scanning direction and the sub-scanning direction is indicated by a unit of dpi indicating how many pixels to be image-recorded are within a length of 1 inch in the main scanning direction or the sub-scanning direction.

  Further, it is preferable that one halftone dot is recorded from 100 or more (especially 200 or more) pixels because the reproduction is close to a halftone of actual printing. Further, it is preferable that one halftone dot is recorded from pixels of 5000 or less (particularly 2000 or less) because the image data can be easily handled and the image data can be processed at high speed.

  The number of recording pixels per second for each color of exposure light is preferably 3 million pixels / second or more (particularly 10 million pixels / second or more). Thereby, both high-speed image recording and high-definition image recording can be achieved. The number of recording pixels per second for each color of exposure light is preferably 4 billion pixels or less (particularly 500 million pixels or less). As a result, the driving circuit is stabilized, the image recording is stabilized, the exposure output intensity and the exposure position are stabilized, and the adjustment is easy at low cost.

  The storage unit 2 includes a storage device such as a hard disk drive or an image memory, and includes an image data storage unit 21, an image data table 26, a color channel table 22, a CMY output intensity-L * a * b * table 23, and an output color table. 27, a target color table 24, an area ratio table 25, a gradation correction table storage unit 28, and an LUT storage unit 29.

  The image data storage unit 21 stores halftone dot image data that has been divided into halftone dots for each of the C, M, Y, and K color plates by the halftone dot forming means 11 described later. The halftone dot image data expresses the shading of the image by forming halftone dots with pixels in each predetermined region (for example, 15 pixels × 15 pixels) and changing the size of the halftone dots. For example, if the halftone image is composed of n pixels, “1” is output for each of the n pixels for each color plate of YMCK, and “0” is not output. ".

  As shown in FIG. 9, the image data table 26 includes a combination of “1” output by each color plate of YMCK, “0” not output, and pixel types to be described later, for each of n pixels of halftone dot image data. The discrimination result of the discrimination means 12 is indicated as “1” for pixel b and “0” for not pixel b.

  The color channel table 22 stores the CMYK1 / 2/3/4 color and the W and CMY output intensities associated with the pixel a and the pixel b in association with each other. The color channel table 22 is used to determine a combination of CMY output intensities for each pixel when the image recording unit 3 performs output. FIG. 4 shows an example of the configuration of the color channel table 22. FIG. 4 shows an example of a combination of the above-described CMYK1 / 2/3/4 color and white background (displayed as W (white) in the figure). The output intensity of Y is changed from a minimum value 0 to a maximum value 140. The output intensities of M and C are shown from the minimum value 0 to the maximum value 180 (the value of the pixel b is omitted).

  The CMY output intensity-L * a * b * table 23 indicates output characteristics in the image recording unit 3, and for example, the values of L * a * b * color system corresponding to combinations of CMY output intensities. CMY output intensity defining a correlation → L * a * b * LUT. FIG. 5 shows an example of the CMY output intensity-L * a * b * table 23. FIG. 5 shows 8 × 10 × 10 = 800 combinations of each stage in which Y is divided into 7 steps and divided into 8 steps and M and C are divided into 9 steps, and L * corresponding to the combinations. It shows the value of the a * b * color system.

  The CMY output intensity-L * a * b * table 23, which will be described in detail later, is used to obtain a combination of output intensity of each basic color from the values of the L * a * b * color system. In this case, the combination of the output intensity of each basic color corresponding to the value of the L * a * b * color system is defined from the CMY output intensity → L * a * b * LUT. b * → CMY output intensity LUT is obtained by using a convergence calculation process as described in, for example, the specification of Japanese Patent Application Laid-Open No. 2004-274546 by the present applicant. Therefore, the “third reference table” of the present invention may be L * a * b * → CMY output intensity LUT or CMY output intensity → L * a * b * LUT, that is, output intensity of a plurality of basic colors. And a correspondence relationship between L * a * b * color system values.

  As shown in FIG. 10, the output color table 27 is an L * a * b * color specification for the color of the pixel a, W, and the color of the pixel b of the above-mentioned CMYK1 / 2/3/4 color. Stores the system value. In FIG. 10, the values of the L * a * b * color system for each pixel b of the above-described CMYK1 / 2/3/4 color are omitted.

  The target color table 24 stores color system values that are targets of color matching using the pixels a and b. Specifically, a solid color of CMYK1 / 2/3/4, which is printed on the printing paper using the ink of each color of C, M, Y, K with a printing press, and CMYK1 / 2/3/4. Values of the L * a * b * color system of intermediate colors of the next colors are stored in advance. Here, solid means that the halftone dot area ratio (sometimes called halftone) of each halftone dot of the colors constituting each color of CMYK1 / 2/3/4 is 100%, and 255 if the tone value. An intermediate color of CMYK1 / 2/3/4 quaternary colors, which is of a gradation, is 100 except that the halftone dot of each halftone dot of the colors constituting the CMYK1 / 2/3/4 quaternary colors is 0%. It is equal to less than%. FIG. 6 shows an example of the configuration of the target color table 24. For each color of the CMYK1 / 2/3/4 color, 26 gradations, 51 gradations obtained by dividing the 0 gradation to the 255 gradation into 10 equal parts,・ ・ ・, 204 gradation, 230 gradation (10%, 20%,..., 80%, 90% if halftone) values of L * a * b * color system of intermediate colors in multiple stages In addition, the value of the L * a * b * color system for W is shown for 0 gradation of each color, and the value of the L * a * b * color system for solid is shown for 255 gradations of each color.

  The area ratio table 25 stores the area ratios of the colors constituting the intermediate colors for each of the CMYK1 / 2/3/4 quaternary colors (a method for calculating the area ratio will be described later). FIG. 7 shows the 26th floor in which the halftone dots of the color plates constituting each color are 10% increments (10%, 20%... 80%, 90%) for each color of CMYK1 / 2/3/4. This shows the area ratio of colors constituting intermediate colors of tone, 51 gradation,..., 204 gradation, and 230 gradation. As shown in FIG. 2A, the primary color is composed of W, Ca, and Cb, for example, if it is C, and the multi-color is, for example, B (secondary color), As shown in FIG. 2B, since the halftone dots of C and M are shifted and overlapped, they are composed of W, Ca, Cb, Ma, Mb, Ba, and Bb. Then, the area ratio of each color is indicated by the ratio of the color to the entire area. For example, Ba in the intermediate color of B stores (area of Ba / total area) (specific area ratio) The calculation method will be described later.)

  The gradation correction table storage unit 28 is configured as shown in FIG. 17, and the gradation image is output so that each density of CMYK output by the printing machine at the gradation value indicated by the gradation image data is output by the calibration color printer. Using the gradation value indicated by the data as an input value, the gradation correction table (1) indicating the first correction characteristics for correcting the gradation values of CMYK and the color tone of CMY gray output from the printing press are used for calibration. A gradation correction table (2) indicating a second correction characteristic for correcting each gradation value of CMY is stored by using the gradation value indicated by the gradation image data as an input value so as to be output by a color printer. To do.

  The configuration of the LUT storage unit 29 is shown in FIG. 18, but the measurement table 291 for storing the measurement results of the color patches constituting the color chart, the CMY tone value at K = 0 of the calibration color printer → L * a * b * LUT292 (first reference table), L * a * b * → CMY gradation value LUT293 (second reference table) of the color printer for calibration are stored (details will be described later).

  The control unit 1 is configured by an arithmetic control device such as a CPU, and controls each part of the device by executing a computer program stored in a program storage unit (not shown) such as a ROM or a hard disk drive. In accordance with the computer program, the control unit 1 includes a gradation value correction unit 16, a halftone dot conversion unit 11, a pixel type determination unit 12, an image recording control unit 13, a color channel calculation unit 14, a color calculation unit 15, and a gradation correction. It operates as a table creation means 17, an area ratio table correction means 18, and an LUT creation means 19. The color calculation means 15, the gradation correction table creation means 17, the area ratio table correction means 18 and the LUT creation means 19 constitute the color adjustment value calculation means of the present invention.

  The gradation value correction means 16 uses the gradation value indicated by the drawing information of the gradation image data received by the image data reception means 5 based on the gradation correction table stored in the gradation correction table storage unit 28 as an input value. to correct.

  The halftone dot forming means 11 performs halftone dot conversion of gradation image data by AM screening (Amplitude Modulation Screening) using halftone dot reference data, and is an area composed of a predetermined number of pixels (for example, 15 pixels × 15 pixels). Each color plate that expresses the shading of an image by forming a halftone dot by indicating “1” when outputting the pixels in that area for each), and “0” when not outputting, and changing the size of the halftone dots. To halftone dot image data. Further, the converted halftone image data is stored in the image data storage unit 21.

  The pixel type discriminating unit 12 discriminates between the pixel a or W (white) and the pixel b for each pixel constituting the halftone image data in order to configure each color of the halftone image line portion by the pixel a and the pixel b. Do.

  Here, an example will be described in which the peripheral portion as illustrated in FIGS. 2A to 2C is configured to include the pixel b and the central portion includes the pixel a. In this case, a 3 × 3 digital filter shown in FIG. 8 is used. Each halftone dot image data of each color is scanned using a digital filter, and the pixel located at the center 121 of the digital filter is discriminated as follows. For the halftone dot image data of each color plane, when the data of the pixel 121 located in the center is “0” that is not output, it is determined that the pixel is not the pixel b, and the data of the pixel 121 located in the center is output “ In the case of “1”, it is determined that the pixel 121 located in the center is the pixel “b” if “0” in which two or more of the eight peripheral pixels 122 do not output is less than two. Is not a pixel a, that is, a pixel b. Then, when it is determined that the pixel b is at least one of the color plates, the pixel is the pixel b, and when it is not determined that the pixel b is any of the color plates, the pixel is the pixel b. It is determined that it is not b. As a result of such discrimination, the pixel at the peripheral edge of each color of the halftone dot line portion as shown in FIGS. 2A to 2C can be set as the pixel b, and the center portion can be set as the pixel a.

  Further, if the above-mentioned 3 × 3 digital filter is used, the pixels b are configured in almost one row at the peripheral portion. For example, the pixels b are configured in two rows at the peripheral portion using a 5 × 5 digital filter. It is also possible to change the configuration of the pixel b by changing the conditions of surrounding pixels used for determination.

  In addition, according to the method using the digital filter, the peripheral area of the solid area may be the pixel b, but it is a few pixels of the peripheral area and has almost no influence on the color tone. There is no problem even if b is included.

  The image recording control means 13 is a control means according to the present invention, and is obtained from n halftone dot image data separated for each color plate of C, M, Y, and K and the discrimination result by the pixel type discrimination means 12. With reference to the color channel table 22 for each pixel, a combination of CMY output intensities is obtained, and the image recording unit 3 is controlled to output with the combination of the output intensities. In response to this, the image recording unit 3 exposes each pixel with the intensity of green (G) light, red (R) light, and blue (B) light corresponding to the combination of the output intensity of CMY.

  Specifically, the combination of CMY output intensities is determined from the halftone image data to determine whether the color to be output is W or a CMYK1 / 2/3/4 color, and whether or not it is a pixel b. From the determination result, the combination of the corresponding CMY output intensities is obtained from the color channel table 22 as follows.

  In the image data table 26 of FIG. 9, for each of n pixels from pixel 1 to pixel n, the combination of “1” output by each color plate of YMCK, “0” not output, and the pixel type determination means 12 The discrimination result is “1” for pixel b and “0” for not pixel b, but pixel 1 is W and not pixel b because KCMY is “0”, so CMY output The intensity combination is set to a value corresponding to W (white) of the pixel a in the color channel table 22 shown in FIG. 4, and since the pixel 2 is W and not the pixel b because KCMY is “0”, the output intensity of CMY 4 is a value corresponding to W (white) of the pixel a in the color channel table 22 shown in FIG. 4, and since the pixel 3 is “1” CMY is “0” and the pixel b, the output of CMY Illustration of strength combinations The value corresponding to K of the pixel b in the color channel table 22 shown in FIG. 5 is a combination of CMY output intensities since the pixel k is “1”, KY is “0”, and the pixel b. 4 is a value corresponding to B (CM) of the pixel b of the color channel table 22 shown in FIG. 4, and since the pixel k + 1 has M of “1”, KCY of “0” and is not the pixel b, the output intensity of CMY The combination is a value corresponding to M of the pixel a in the color channel table 22 shown in FIG. 4..., And the pixel n is W and is not the pixel b because KCMY is “0”. Is a value corresponding to W (white) of the pixel a in the color channel table 22 shown in FIG.

  The color calculation means 15 stores the L * a * b * color system value of the color of the pixel a for each of the CMYK1 / 2/3/4 quaternary colors and the corresponding CMYK1 / 2 / The function as the first color calculation means for storing in the output color table 27 as the value of the solid color system of the 3/4 color, and the value of the L * a * b * color system of the color of the pixel b CMYK1 / 2/3/4 color solid color system values stored in the target color table 24, CMYK1 / 2/3/4 color intermediate color L * a * b * color system And the value of the L * a * b * color system of W are calculated based on the area ratio table 24 (details will be described later) and stored in the output color table 27. It has a function as color calculation means.

  The color channel calculation means 14 receives the CMY values corresponding to the L * a * b * color system values of the color of the pixel a and the pixel b for the CMYK1 / 2/3/4 color stored in the output color table 27. A combination of output intensity is obtained based on the CMY output intensity-L * a * b * table 23, and a color channel indicating a combination of CMY output intensity for each color is generated. Therefore, it has a function as a production | generation means of this invention.

  For example, as described in the specification of Japanese Patent Application Laid-Open No. 2004-274546 by the present applicant, L * a * b * → CMY output intensity LUT is obtained from CMY output intensity → L * a * b * LUT. Then, for the value of the L * a * b * color system for obtaining a combination of CMY output intensities, the value of the L * a * b * color system from the input point of L * a * b * → CMY output intensity LUT C, M, and Y output intensities at 8 points in combination of neighboring L * 2 points (L1, L2), a * 2 points (a1, a2), b * 2 points (b1, b2), and L * The L * a * b * value of the a * b * color system value and the distance from each input point of each value, C, M, and Y of the stored L * a * b * color system value A combination of output intensities can be determined.

  The gradation correction table creating means 17 has a function as a gradation correction characteristic creating means, and outputs using the color of each pixel b of the CMYK primary colors obtained by the color computing means 15 and stored in the output color table 27. In this case, the CMYK primary color density values of the CMYK primary colors and the CMYK primary color L * a * b * color system values stored in the target color table 24 are used to determine the intermediate color levels of the CMYK primary colors. From the density values, CMY gray (CMYK tertiary color CMY) printed by the printing machine stored in the CMYK tone correction table (1) and the color measurement results of the color chart (described later) and the target color table 24. Each tone correction curve (2) for CMY is obtained using the values of the color system (described later in detail).

  Although the details will be described later, the gradation correction curve (2) acts to correct the gradation correction table (1), so the gradation correction table creating means 17 uses the gradation correction table (1). It has a function as correction characteristic correction means for correcting with the gradation correction curve (2).

  The area ratio table correction unit 18 has a function as an area ratio correction unit, and for each color of CMYK1 / 2/3/4 colors stored in the area ratio table 25 based on the gradation correction table 28. The area ratio of the colors constituting the intermediate color is corrected (details will be described later).

  Based on the measurement results stored in the measurement table 291, the LUT creation unit 19 creates CMY tone values → L * a * b * LUT 292, L * a * b * → CMY tone values LUT 293 (details will be described later). ).

  The input unit 4 is for inputting, for example, numerical values stored in the CMY output intensity-L * a * b * table 23, the target color table 24, and the area ratio table. 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 5 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.

[Color image forming method]
Next, each processing procedure in the proofreading color printer to which the color image forming method of the present invention is applied will be described with reference to flowcharts.

  FIG. 11 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. Hereinafter, for example, step S11 in FIG. 11 is omitted, and S11 is displayed as S11. The other steps are the same.

  First, the CMY output intensity-L * a * b * table 23 shown in FIG. 5 is stored in advance (S11). The CMY output intensity-L * a * b * table 23 shown in FIG. 5 is composed of combinations of stages, with Y divided into 7 parts and divided into 8 stages, and M and C divided into 9 parts. 8 × 10 × 10 = 800 types of patches, each of which is composed of L * a * b * color system values corresponding to the combinations obtained by outputting and measuring with the image recording unit 3 It is.

  Further, an area ratio table 25 as shown in FIG. 7 is stored in advance (S12). The area ratio table shows gradation values (26 gradations, 51 gradations,..., 204 gradations) for each color of CMYK1 / 2/3/4 quaternary colors by dividing the 0 gradation to the 255 gradation into 10 equal parts. , 230 gradations), the area ratio of the colors constituting each color in the intermediate colors is stored. Moreover, the area ratio which comprises the area ratio table 25 can be calculated | required as follows. For example, gradation values (26 gradations, 51 gradations,..., 204 gradations) that divide the colors constituting the CMYK1 / 2/3/4 colors into 10 equal parts from 0 gradation to 255 gradations. , 230 gradations), for example, in the case of B, a 26 gradation patch is a pixel of C26 gradation, M26 gradation, Y0 gradation, K0 gradation, and 51 pixels. The gradation patch is a pixel of C51 gradation, M51 gradation, Y0 gradation, K0 gradation, and the 230 gradation patch is an image composed of pixels of C230 gradation, M230 gradation, Y0 gradation, K0 gradation. Data) is made the same as the halftone doting performed by the halftone doting means 11 of the proof color printer, and further the same discrimination as the pixel type discrimination means 12 is performed. It is calculated as follows. For the primary color, the ratio of the number of pixels to the number of pixels in the area constituting one halftone dot from the number of W pixels in the area constituting one halftone dot, the number of pixels a, and the number of pixels b is the area. It can be easily obtained as a ratio. However, the screen color of each color plate is different in the secondary color or higher, so that each halftone dot is shifted and overlapped. Therefore, the area ratio differs depending on the selected position in an area that forms one halftone dot. Therefore, it is desirable to use a patch having a size that is larger than an area that reduces the error in consideration of the shift of halftone dots. For example, an image data table as shown in FIG. 9 is created for each patch. Then, the color constituting the patch can be determined by counting the number of pixels of each color in the patch and obtaining the ratio to the number of pixels constituting the patch. For example, in the case of a B patch, the colors constituting the B patch are seven colors of Ca, Cb, Ma, Mb, Ba, Bb, and W as shown in FIG. A ratio to the number of pixels constituting the patch is obtained as an area ratio. Hereinafter, the area ratio of each color will be indicated by adding f in front of each color. For example, taking B as an example, each area ratio is displayed as fCa, fCb, fMa, fMb, fBa, fBb, and fW.

  These tables are received and created by the control unit 1 via the input unit 4, or written in a computer program stored in the program storage unit of the control unit 1, and the control unit 1 is based on the computer program. May be created.

  Next, the solid color L * of CMYK1 / 2/3/4 color printed on the printing paper using the ink of each color of C, M, Y, K on the printing machine which is the target of color matching from the input unit 4 Value of a * b * color system, L * a * b * color system value of printing paper color, and L * a * b * table of intermediate colors of CMYK1 / 2/3/4 color In response to the input of the color system value, the control unit 1 writes it in the target color table 24 (see FIG. 6) of the storage unit 2 (S13). For example, the value of the L * a * b * color system to be input is the halftone dot of the color plate constituting each color of CMYK1 / 2/3/4 color in increments of 10% (0%, 10%, 20% .. Gradation value that divides 10 levels from 0 gradation to 255 gradation (90%, 100%) (0 gradation, 26 gradations, 51 gradations, ..., 204 gradations, 230 gradations) A color chart including intermediate colors (255 gradations), printing paper color, and solid patches is printed on printing paper and measured.

  Then, the color calculation means 15 stores the C, M, Y, K, C, and K quaternary colors printed on the printing paper using the C, M, Y, and K inks on the printing paper with the W stored in the target color table 24. From the values of the L * a * b * color system of the solid colors and the intermediate colors of the CMYK1 / 2/3/4 colors and the area ratio stored in the area ratio table 25, the CMYK1 / 2/3/4 order The values of the L * a * b * color system of the color of the pixel a and the pixel b for each color are obtained, and the gradation correction table creating unit 17 obtains the CMYK primary color pixels a and C obtained by the color computing unit 15. The density value of each color obtained from the L * a * b * color system value of the color of the pixel b and the area ratio stored in the area ratio table 25, and the CMYK primary colors stored in the target color table 24 From the density value obtained from the L * a * b * color system value of the intermediate color, to each color of CMYK There create a tone correction table (1) of (S14). Here, it demonstrates in detail using the flowchart shown in FIG. FIG. 12 is a flowchart showing a procedure for obtaining the L * a * b * color system values of the pixel a and the pixel b and the gradation correction table (1).

  First, the color calculation means 15 uses the color system values of the solid colors of CMYK1 / 2/3/4 that are printed on the printing paper using the inks of C, M, Y, and K on the printing paper. Is the color system value of the color of each pixel a for each color of CMYK1 / 2/3/4, and the color system value of the color of the pixel a and the L * a * b * of W The color system values are stored in the output color table 27 (S21).

  First, the color of the pixel b for each color of the CMYK primary colors, the L * a * b * color system values of the intermediate colors of the CMYK primary colors stored in the target color table 24, and the output color table 27. The L * a * b * color system value of W and the L * a * b * color system value of the color of the pixel a of the CMYK primary color and the CMYK primary color in the intermediate color of the area ratio table 25 Are obtained using the area ratio of the colors constituting each of the colors and stored in the output color table 27 (S22). In the following calculation, an XYZ color system value is used as a color system value. Because the value of the XYZ color system is a linear value with respect to the amount of light, the color composed of a plurality of colors should be indicated by the sum of the product of the value of the XYZ color system and the area ratio of that color. Because you can. The value of the XYZ color system can be obtained from the value of the L * a * b * color system as described at the beginning of [Best Mode for Carrying Out the Invention]. The value of the L * a * b * color system can be obtained from the value of.

For example, a description will be given taking C shown in FIG. Here, the target X value of the C intermediate color is XC, the Y value is YC, and the Z value is ZC. Further, as shown in FIG. 2A, the intermediate color of C is composed of W pixels, Ca pixels, and Cb pixels, so that the X value of W is XW, the Y value is YW, the Z value is ZW, The X value of the color Ca of the C pixel a is XCa, the Y value is YCa, the Z value is ZCa, the X value of the color Cb of the pixel b is XCb, the Y value is YCb, and the Z value is ZCb. If the area ratio of W is fW, the area ratio of the C pixel a is fCa, and the area ratio of the C pixel b is fCb, the X value XC, the Y value YC, and the Z value ZC of the C intermediate color are Since the product of the value of the XYZ color system and the area ratio of the color to be configured can be indicated by a total value added,
XC = fW × XW + fCa × XCa + fCb × XCb,
YC = fW × YW + fCa × YCa + fCb × YCb,
ZC = fW × ZW + fCa × ZCa + fCb × ZCb
It can be expressed as.

  The XYZ values other than Cb in the above formula are obtained from the values of the L * a * b * color system of the C intermediate color stored in the target color table 24 as the XC, YC, and ZC as the target of the C intermediate color. XCa, YCa, and ZCa are obtained from the values of the L * a * b * color system of the color of the C pixel a stored in the output color table 27, and each area ratio is stored in the area ratio table 25. Yes. Therefore, the X value XCb, the Y value YCb, and the Z value ZCb of the color of the pixel b can be obtained so that the total value of the values of the color system on the right side of the above equation becomes the value of the color system on the left side. .

  For example, the X value XCb, the Y value YCb, and the Z value ZCb of the color of the pixel b in each intermediate color are obtained using the above formula, and the average value of each result is determined as the X value of the color of the pixel b for C. The value XCb, the Y value YCb, and the Z value ZCb may be determined. Further, the value of the L * a * b * color system of the basic color intensity at a finer level than that of the CMY output intensity-L * a * b * table 23 shown in FIG. More preferably it is performed. Further, since the obtained XYZ color system values are obtained as combinations of CMY output intensities based on the CMY output intensity-L * a * b * table 23, they are converted to L * a * b * color system values. deep. Similarly, for M, Y, and K, the L * a * b * color system value of the color of the pixel b is obtained and stored in the output color table 27.

  Next, a gradation correction table (1) is created for CMYK (S23). Specifically, the color system value of the color of the pixel b for each of the CMYK primary colors obtained in S22, the L * a * b * color system value of W stored in the output color table 27, and the CMYK1 Each XYZ value is obtained from the L * a * b * color system value of the color of the pixel a of the next color, and the area of the color constituting each color of the CMYK primary color in the intermediate color of the XYZ value and the area ratio table 25 By substituting the ratio into the right side of the equation used to determine the pixel b, an XYZ value of the intermediate color of each color output by the calibration color printer is obtained, and further, from the XYZ value, a value indicating the density [invention] As described at the beginning of the description, Xd is obtained for C, Yd is obtained for M and K, and Zd is obtained for Y, while being stored in the target color table 24. Intermediate colors of each of the CMYK primary colors Similarly, from the values of the L * a * b * color system, Xd for C, Yd for M and K, and Zd for Y are obtained as density values, and both density values are compared. As a result, a correction characteristic in which the gradation value as an input value and the gradation value output from the printing press with the gradation value are output as a calibration value by associating the gradation value as an output value is created. The tone correction table (1) is as follows.

  For example, C will be described as an example. FIG. 14 is a diagram in which a curve indicating Xd of the intermediate color C output from the printing press and a curve indicating Xd of the intermediate color C output from the calibration color printer are shown together with a plurality of gradation values. Each curve was obtained by interpolating from each value for a plurality of intermediate levels of 13 gradations, 26 gradations, 38 gradations, 51 gradations,..., 217 gradations, 230 gradations, and 242 gradations. Is. Then, for example, the gradation value 20 in C output from the calibration color printer, which is Xd of the intermediate color C output from the printing press at 13 gradations, is obtained, and similarly, 26 gradations, 38 gradations, 51 gradations are obtained. ..., 217 gradations, 230 gradations, and 242 gradations are obtained. FIG. 15 shows the correction characteristic of the C output value corresponding to the C input value of each gradation value as a gradation correction table, and FIG. 16 shows the gradation display as a gradation correction curve. M and K are similarly created using Yd, and Y is similarly created using Zd.

  Further, although it has been described that the XYZ values of the intermediate colors of the colors output by the calibration color printer are calculated, the intermediate color patch is actually output with the calculated color of the pixel b (the color of the pixel b is output). Therefore, the tone correction table (1) may be created by measuring the output result and comparing the output result of the intermediate color patch of the printing press.

  Therefore, the area ratio table correcting means 18 constitutes an intermediate color in the halftone image line portion obtained by outputting each CMYK halftone dot with the corrected gradation value from the area ratio stored in the area ratio table 25. The area ratio of each color is corrected (S24). CMYK of the gradation image data constituting the plurality of patches having 26 gradations, 51 gradations,..., 204 gradations, 230 gradations of the colors constituting each color of CMYK1 / 2/3/4. Each tone value may be corrected by each tone correction table (1) and obtained from the number of pixels of each color constituting each patch as described above, or from the stored area ratio, the tone correction table ( Each area ratio may be obtained by interpolation so as to satisfy the correction relationship shown in 1).

  Next, the color of the pixel b for each color of the CMYK secondary colors is stored in the output color table 27 and the L * a * b * color system values of the intermediate colors of the CMYK secondary colors stored in the target color table 24. The stored L * a * b * color system value of W, the L * a * b * color system value of the CMYK ½ color pixel a, and the CMYK primary color obtained in S22 S24 of the color constituting the L * a * b * color system value of the pixel b (the value of the XYZ color system may be used as it is) and the CMYK secondary colors in the intermediate color of the area ratio table 25 Is obtained using the area ratio corrected in the above and stored in the output color table 27 (S25).

For example, a description will be given by taking B shown in FIG. Here, the X value of the target color of the intermediate color of B is XB, the Y value is YB, and the Z value is ZB. Further, as shown in FIG. 2B, the intermediate color of B is composed of W pixels, Ca pixels, Cb pixels, Ma pixels, Mb pixels, Ba pixels, and Bb pixels. XW is XW, Y value is YW, Z value is ZW, X value of color Ca of C pixel a is XCa, Y value is YCa, Z value is ZCa, X value of color Cb of pixel b is XCb, Y value is YCb, Z value is ZCb, X value of Ma color of pixel a is XMa, Y value is YMa, Z value is ZMa, X value of color Mb of pixel b is XMb, Y value is YMb, Z The value is ZMb, the X value of the color Ba of the B pixel a is XBa, the Y value is YBa, the Z value is ZBa, the X value of the color Bb of the pixel b is XBb, the Y value is YBb, the Z value is ZBb, and S24 The area ratio of W in the intermediate color corrected in step fW ', the area ratio of C pixel a is fCa', the area ratio of C pixel b is fCb ', If the area ratio of a is fMa ′, the area ratio of M pixel b is fMb ′, the area ratio of B pixel a is fBa ′, and the area ratio of B pixel b is fBb ′, the X value of the intermediate color of B XB, Y value YB, Z value ZB
XB = fW ′ × XW + fCa ′ × XCa + fCb ′ × XCb + fMa ′ × XMa + fMb ′ × XMb + fBa ′ × XBa + fBb ′ × XBb,
YB = fW ′ × YW + fCa ′ × YCa + fCb ′ × YCb + fMa ′ × YMa + fMb ′ × YMb + fBa ′ × YBa + fBb ′ × YBb,
ZB = fW ′ × ZW + fCa ′ × ZCa + fCb ′ × ZCb + fMa ′ × ZMa + fMb ′ × ZMb + fBa ′ × ZBa + fBb ′ × ZBb,
It can be expressed as.

  The XYZ values other than Bb in the above formula are the L * a * b * color system values stored in the target color table 24 and the L * a values stored in the output color table 27 as in the case of the primary color. Each area ratio obtained and corrected from the value of the * b * color system is stored in the area ratio table 25. Therefore, as in the case of the primary color, the X value of the color of the pixel b is XBb, the Y value is YBb, the Z value is ZBb, and the value of the L * a * b * color system is obtained from the above formula. it can. Similarly, for R, G, KC, KM, and KY, the L * a * b * color system value of the color of the pixel b is obtained.

  Further, the color of the pixel b for each color of the CMYK tertiary colors is stored in the output value table 27 and the L * a * b * color system values of the intermediate colors of the CMYK tertiary colors stored in the target color table 24. L * a * b * color system value of W, L * a * b * color system value of CMYK1 / 2/3 color pixel a, and S22 and S25 S24 of the color constituting each color of the CMYK tertiary color in the intermediate color of the area ratio table 25 and the L * a * b * color system value (may be an XYZ color system value) of the pixel b of the CMYK 1 / 2-order color It is obtained using the area ratio corrected in (S26). Although detailed arithmetic expressions are omitted, as in S25, the L * a * b * color system value of the intermediate color of the tertiary color, the L * a * b * color system value of W, and the tertiary color Of the L * a * b * color system of the color of the pixel b of the tertiary color from the values of the color systems of the respective colors of the pixels a and b constituting the pixel and the corrected area ratio of those colors Find the value.

  Next, the color of the pixel b for the CMYK quaternary color is stored in the output value table 27 and the L * a * b * color system value of the intermediate color of the CMYK quaternary color stored in the target color table 24. The value of the L * a * b * color system of W, the value of the L * a * b * color system of the pixel a of the CMYK1 / 2/3/4 color, and the values obtained in S22, S25 and S26 Correction of L * a * b * color system value (may be an XYZ color system value) of the pixel b of the CMYK1 / 2/3 tertiary color and the color constituting the intermediate color of the CMYK quaternary color of the area ratio table 25 It calculates | requires using the determined area ratio (S27). Although detailed arithmetic expressions are omitted, as in S25, the L * a * b * color system value of the quaternary color, the L * a * b * color system value of W, and the quaternary color The value of the L * a * b * color system of the color of the pixel b of the quaternary color is obtained from the color system value of each color of the pixel a and the pixel b constituting the image and the area ratio of those colors. .

  Returning to the flowchart of FIG. 11, the color channel calculation means 14 then selects the W * L * a * b * color system values stored in the output color table 27 and CMYK1 / 2/3/4 color pixels. From the L * a * b * color system value of the color a and the L * a * b * color system value of the pixel b of the CMYK1 / 2/3/4 color, the CMY output intensity -L * a A combination of CMY output intensities is obtained based on the * b * table 23, and the color channel table 22 is generated (S15). As described above, for example, as described in the specification of Japanese Patent Application Laid-Open No. 2004-274546 by the present applicant, L * a * b * → CMY LUT is obtained from CMY → L * a * b * LUT. Then, for the value of the L * a * b * color system for obtaining the combination of CMY output intensities, from the input point of L * a * b * → CMY LUT, the value near the value of the L * a * b * color system C *, M *, and Y * output intensities for L * 2 points (L1, L2), a * 2 points (a1, a2), b * 2 points (b1, b2) combined, and L * a * The output intensity of C, M, and Y with respect to the stored L * a * b * color system value from the distance from each input point of the L * a * b * value of the b * color system value Can be obtained.

  Here, CMY gray level correction tables (2) for adjusting the color tone of CMY gray are obtained. For this purpose, first, a plurality of patches in which each gradation value of CMY is changed at K = 0 by using the gradation correction table (1) obtained so far and the generated color channel table 22 in the calibration color printer. A color chart including CMY is output, and the colorimetric result of the color chart and the color system values of CMY gray (CMYK tertiary color CMY) printed by the printing machine stored in the target color table 24 are used. A gradation correction table (2) is obtained for (S16). Details of the procedure for creating the gradation correction table (2) in S16 will be described below with reference to the flowchart shown in FIG.

  First, the minimum values 0 to 255 of C, M, and Y are each divided into four, and five levels of 0, 64, 128, 191, and 255 are taken. C × M × Y: 5 × 5 × 5 = 125 points A color chart as shown in FIG. 20 in which color patches are arranged for the combination is output by a calibration color printer, and each patch of 5 × 5 × 5 = 125 points is measured in order, and the L * a * b * color system is displayed. Find the value. The color measurement result is stored in the measurement table 291 of the LUT storage unit 29 via the input unit 4 (S41).

  However, the above color chart is a color printer for calibration, and is output using the gradation correction table (1) obtained in S14 and the color channel table 22 generated in S15. That is, the image data receiving means 5 receives gradation image data representing a color chart, and the gradation correction means 16 corrects each CMY gradation value using the gradation correction table (1), thereby generating halftone dots. A halftone image data representing a color chart is formed into halftone dots 11 to create halftone dot image data for each color plate. Then, the image type determining unit 12 determines whether each pixel constituting the halftone dot image data of each color is a pixel b, and creates an image data table 26 based on the determination result and the halftone dot image data. To do. Further, the image recording control unit 13 outputs the color (W or CMYK1 / 2/3/4 color) to be output from each pixel shown in the image data table 26 and the image type determination unit 12. Based on the determination result, a combination of CMY output intensities is obtained by referring to the color channel table 22, and the image recording unit 3 is controlled to output the combination of the output intensities. The image recording unit 3 forms an image according to the control. Is output.

  Then, using this color measurement result, first, the LUT creation means 19 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. 19, and the three-dimensional input / three-dimensional value in which the value of the L * a * b * color system enters the CMY LUT input point. It is an output, and for each point between 9 × 9 × 9 grid points, 5 × 5 × 5 = 125 patches are interpolated into 9 × 9 × 9 patches. As shown in FIG. 21, when black circles ● are lattice points (sample points) and Δ marks and X marks are points to be interpolated, there are two cases where there are two points before and after, as indicated by Δ marks. 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. 22 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 (each corresponding to Roman numerals in FIG. 22) shown in FIG. Further, after interpolation of CMY5 × 5 × 5 to 9 × 9 × 9 is performed for all five levels, for each point of CMY9 × 9 × 9, calculation for interpolating 5 points of K to 9 points is performed. This is performed in the same manner as 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 is obtained by associating the combination of these CMY with the value of the L * a * b * color system.

  Next, the LUT creation means 19 creates an L * a * b * → CMY tone value LUT based on the CMY tone value → L * a * b * LUT (S43). L * a * b * → CMY gradation value LUT is a three-dimensional input / three-dimensional output LUT, as shown in FIG. 23, and interpolates and converts points between 33 × 33 × 33 lattice points. .

  A method for obtaining the three-dimensional input / three-dimensional output LUT in FIG. 23 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. 24 is a plot of L * on the vertical axis and a * on the horizontal axis for a two-dimensional 9 × 9 combination (Y = 0) of M and C in CMY. 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 area surrounded by the lattice points a ′ to d ′ as shown in FIG. 24, the combination of MCs (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. 24 with the coordinate system of FIG. Convergence calculation processing is performed in this way, although the conversion from the coordinate system of FIG. 25 to the color system of FIG. 24 is known, the reverse conversion is very complicated and a good conversion formula is still known. It is because it is not done.

  Next, the region So formed by the lattice points a to d in FIG. 26 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, values obtained by converting values corresponding to the division points e to i into the L * a * b * color system are plotted in the color system of FIG. 27, 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. 27, 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 the values corresponding to the division points j to n into the L * a * b * color system are plotted in the color system of FIG. 27, 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. 27, 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. 27, and the plotted division points o 'to s' are plotted. 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. 27, 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.

  By the way, when the target value T ′ is outside the color reproduction range formed by the vertices W ′, C ′, M ′, 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, and the coordinates of the intersection with the boundary of the color reproduction range in the achromatic color direction are set as the target value as shown in FIG. 29, 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 ′.

  The L * a * b * → CMY gradation value LUT 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 creating means 17 stores CMY gradation values corresponding to CMY gray (CMYK tertiary color CMY) color system values printed by the printing press stored in the target color table 24. The combination, that is, the combination of CMY gray values for reproducing the color tone of CMY gray printed on the printing press with the color printer for calibration is obtained using L * a * b * → CMY gradation value LUT, A gradation correction table (2) for each is created (S44).

For example, if the L * a * b * color system values are L * = 57,0, a * = 5.3, b * = 3.6, 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. Here, CMY gray is an intermediate color based on a combination of CMY tone values in the CMYK tertiary colors, and the CMY gray CMY combinations stored in the target color table 24 have the same CMY tone value, and the 26th floor. Tone, 51 gradation,..., 204 gradation, 230 gradation, and for each of CMY, this gradation value (26 gradation, 51 gradation,..., 204 gradation, 230 floor) Tone) as an input value, and the corresponding obtained gradation value as an output value, so that the 0th gradation and the 255th gradation are corrected as the 0th gradation and the 255th gradation, respectively, so that the white background is white and the solid is solid. The characteristics are created as a gradation correction table (2). Further, although the configuration of the gradation correction table (2) is not particularly shown, it has the same configuration as the gradation correction table (1) shown in FIG.

  Then, returning to the flowchart of FIG. 11, image formation is performed based on the gradation image data (S17). FIG. 13 is a flowchart showing an example of an image forming procedure performed by the calibration color printer. The image data receiving means 5 receives the gradation image data (S31). Next, the gradation value correction means 16 uses the CMYK gradation values of the drawing information shown in the gradation image data, CMY uses the respective gradation correction tables (1) and (2), and K indicates the level. Correction is performed using the tone correction table (1) (S32).

  Here, in the correction using the CMY gradation correction tables (1) and (2), the correction is first performed using the gradation correction table (1), and further corrected using the gradation correction table (2). The gradation correction table (1) and the gradation correction table (2) may be combined and corrected using the correction table as one correction table.

  Further, the halftone dot forming means 11 halftones the gradation image data whose gradation value is corrected, and creates halftone dot image data for each color plate (S33). Then, the image type discriminating means 12 discriminates whether or not each pixel constituting the halftone dot image data of each color plane is the pixel b (S34), and the image data table is based on the discrimination result and the halftone dot image data. 26 is created (S35).

  The image recording control unit 13 then outputs the color (W or CMYK1 / 2/3/4 color) to be output from each pixel shown in the image data table 26 and the image type determination unit 12. Based on the determination result, a combination of CMY output intensities is obtained with reference to the color channel table 22, and the image recording unit 3 is controlled so as to output with the combination of the output intensities (S36). The image recording unit 3 forms an image according to the control (S37).

  As described above, halftone dot image data obtained by correcting the gradation value of each color of the drawing information indicated in the gradation image data using the gradation correction table and converting the corrected gradation image data into halftone dots. The color of the halftone image line portion based on the color, the pixel color of the color matching the target output color, and the pixel (pixel b) having a color tone different from the target output color In addition, since the tone correction table and the target output color can be easily obtained a color different from the tone, and the tone correction table is adapted to reproduce the color tone of CMY gray. Highly accurate color adjustment can be performed for CMY gray.

  The color calculation, color channel table generation, or gradation correction table creation described above is performed using an information processing apparatus such as a PC (Personal Computer), and the color calculation result, color channel table, or gradation correction table is obtained. Can be obtained by a calibration color printer via a medium such as a floppy (registered trademark) disk and used for forming a color image.

  In addition, in an image output system including an information processing apparatus such as a PC and a color printer for calibration, the information processing apparatus such as a PC includes the above-described color calculation function, color channel table generation function, or gradation correction table creation function. The color calculation result or the color channel table can be acquired by a calibration color printer via an interface and used for forming a color image.

It is a figure which shows the correspondence of each color and ink which are printed. It is a schematic diagram for demonstrating the color of each pixel which comprises the color of a halftone image line part. FIG. 2 is a functional block diagram illustrating a configuration of a calibration color printer according to the present invention. It is explanatory drawing which shows an example of a structure of the color channel table of this Embodiment. It is explanatory drawing which shows an example of a structure of the CMY output intensity-L * a * b * table of this Embodiment. It is explanatory drawing which shows an example of a structure of the target color table of this Embodiment. It is explanatory drawing which shows an example of a structure of the area ratio table of this Embodiment. It is explanatory drawing for demonstrating an example of the digital filter used for pixel classification discrimination. It is explanatory drawing which shows an example of the image data table which shows the presence or absence of the output of YMCK about each pixel which comprises halftone dot image data, and whether it is the pixel b. It is explanatory drawing which shows an example of a structure of the output color 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 calculating | requiring the value of the L * a * b * colorimetric system of the pixel a and the pixel b, and a gradation correction table. 6 is a flowchart illustrating an example of an image forming procedure performed by a calibration color printer. 5 is a graph in which a curve indicating Xd of C intermediate color output from the printing press and a curve indicating Xd of C intermediate color output from the calibration color printer are shown together for a plurality of gradation values. It is explanatory drawing which shows an example of a structure of the gradation correction table of this Embodiment. It is a graph which shows an example of the gradation correction curve 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 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 an example of a color patch image for measuring CMY color values in the present 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 color of C and M 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 gradation correction table (2) of this Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Control part 11 Halftone forming means 12 Pixel type discrimination means 13 Image recording control means 14 Color channel calculation means 15 Color calculation means 16 Tone value correction means 17 Tone correction table creation means 18 Area ratio table correction means 19 LUT creation means 2 Storage Unit 21 Image Data Storage Unit 22 Color Channel Table 23 CMY Output Intensity-L * a * b * Table 24 Target Color Table 25 Area Ratio Table 26 Image Data Table 27 Output Color Table 28 Gradation Correction Table Storage Unit 29 LUT Storage Section 3 Image recording section 4 Input section 5 Image data receiving means

Claims (18)

The tone of a halftone image obtained by printing on a recording medium using a plurality of color plates including at least C (cyan), M (magenta), and Y (yellow) color plates is determined for each color of the plurality of color plates. It is obtained by correcting the gradation value of gradation image data composed of drawing information including gradation values indicating density levels, and converting the gradation image data with the gradation value corrected into halftone dots. A region of each color of a halftone image line portion constituting a halftone dot image based on halftone dot image data is represented by at least one second color pixel having a color tone different from that of the first color pixel and the first color for each color. A color adjustment method configured to reproduce with color pixels,
The first color and the first color of each color when the area of each color of the halftone dot line portion constituting the halftone dot image indicating the halftone image of each color of the halftone dot line portion is constituted by the first color and the second color. Storing in advance an area ratio table indicating the area ratio of each of the two colors and the color of the recording medium;
The solid color system value of each color of the halftone line portion obtained by the printing, the intermediate color system value of each color of the halftone line portion, and the color system of the color of the recording medium Obtaining the value of
Using the obtained color system value of the intermediate color of each color, the obtained solid color system value of each color, and the obtained color system color value of the recording medium and the area ratio table The color system value of the first color and the color system value of the second color of each color of the halftone image line portion are obtained, and the first color color value of each of the plurality of color plates is obtained. Obtaining a first correction characteristic for correcting to a gradation value in which the density of the intermediate color of each color constituted by the pixel of the second color and the pixel of the second color becomes the density of the intermediate color of each acquired color;
The plurality of colors indicated by the combination of the gradation values of the colors of the plurality of color plates are corrected with the obtained first correction characteristic, and the obtained first color pixel and the second color are corrected. A color system value obtained by configuring with pixels, and a gray color system value composed of C, M, and Y among the intermediate colors of the halftone image line portion obtained by printing And correcting the first correction characteristic for each of CMY among the obtained first correction characteristics so as to reproduce the value of the color system of gray, based on
And a step of using the corrected first correction characteristic for correcting a gradation value of the gradation image data. The step of obtaining the first correction characteristic includes:
The acquired gradation value of the intermediate color of each color is used as an input value, and the density of the intermediate color of each color constituted by the pixels of the first color and the second color is the density of the intermediate color of each acquired color. Associating a tone value as an output value to provide a first correction characteristic;
The step of correcting the first correction characteristic includes:
Creating a first reference table in which color system values respectively corresponding to combinations of the gradation values for the plurality of colors are associated;
A second one in which a combination of gradation values corresponding to a color indicated by the color system value is associated with each color system value of the plurality of color system values based on the first reference table; Creating a reference table for
Using the second reference table, a combination of C, M, and Y gradation values corresponding to the value of the gray color system is obtained, and the C, M, and Y levels when the gray is printed are obtained. Obtaining a second correction characteristic for each of CMY in which each of the tone values is an input value and each of the obtained combinations of C, M, and Y tone values is associated as an output value;
The color adjustment method according to claim 1, further comprising: correcting the first correction characteristic for each of CMY based on the obtained second correction characteristic for each of CMY. Each color of the halftone dot line portion includes a primary color of one plate color of the plurality of color plates, and a multi-order color of a color in which at least two plate colors are superimposed,
Obtaining the color system value of the first color and the color system value of the second color comprises obtaining the primary color and the multi-color.
Determining the primary color comprises:
Obtaining a value of the color system of the first color of each color of the halftone line portion as a value of the color system of the obtained solid color;
The value of the color system of the second color for each primary color of the halftone image line portion is the value of the color system of the intermediate color of the acquired colors for each primary color, the value of each primary color Using the obtained solid color system value of each color and the obtained color value of the recording medium color and the area ratio table for each primary color. Including
The step of obtaining the multi-order color includes:
Correcting the area ratio of the area ratio table based on the determined first correction characteristic;
The value of the color system of the second color for each multicolor of the halftone image line portion is the value of the color system of the intermediate color of the acquired colors for each multicolor and the value of each color of the acquired colors And determining using the solid color system value, the color system value of the acquired color of the recording medium, and the corrected area ratio table for each multi-order color. The color adjustment method according to claim 1 or 2.   The value of the color system of the second color with respect to the multi-order color is obtained using the value of the color system of the second color that has already been obtained in order from the lowest order in which the number of superimposed colors is small. The color adjustment method according to claim 3.   The value of the color system of the second color is the value of the color system of the first color for each color of the halftone image line part constituting the halftone image showing the intermediate color of each color of the halftone image line part, The total value obtained by adding the color system value of the second color and the product of the color system value of the color of the recording medium and the area ratio shown in the area ratio table corresponding to each color. 5. The color adjustment method according to claim 1, wherein the color adjustment value is a value when the acquired color value is an intermediate color system of each color. The area ratio table indicates the area ratio for a plurality of intermediate colors of each color of the halftone dot line portion,
The acquired color value of the intermediate color of each color is for the intermediate color of the plurality of stages,
The value of the color system of the second color is obtained so that an error between the total value and the value of the color system of the acquired intermediate colors is obtained so that the error is minimized for the intermediate colors of the plurality of stages. 6. The color adjusting method according to claim 5, wherein the color adjusting method is performed.   The color adjustment method according to any one of claims 1 to 6, wherein a color system value for each color used when obtaining a color system value of the second color is a value of an XYZ color system. . The first color pixel is disposed in the center of each color region of the halftone image line portion constituting the halftone image,
8. The color adjustment method according to claim 1, wherein the second color pixels are arranged in a peripheral portion of each color region of a halftone image line portion constituting the halftone image. The tone of a halftone image obtained by printing on a recording medium using a plurality of color plates including at least C (cyan), M (magenta), and Y (yellow) color plates is determined for each color of the plurality of color plates. It is obtained by correcting the gradation value of gradation image data composed of drawing information including gradation values indicating density levels, and converting the gradation image data with the gradation value corrected into halftone dots. A region of each color of a halftone image line portion constituting a halftone dot image based on halftone dot image data is represented by at least one second color pixel having a color tone different from that of the first color pixel and the first color for each color. A color image forming method for forming a color image so as to reproduce by changing the output intensity of a plurality of basic colors according to the color of each pixel.
Storing in advance a third reference table indicating the correspondence between the output intensity of the plurality of basic colors and the value of the color system;
The first color and the first color of each color when the area of each color of the halftone dot line portion constituting the halftone dot image indicating the halftone image of each color of the halftone dot line portion is constituted by the first color and the second color. Storing in advance an area ratio table indicating the area ratio of each of the two colors and the color of the recording medium;
The solid color system value of each color of the halftone line portion obtained by the printing, the intermediate color system value of each color of the halftone line portion, and the color system of the color of the recording medium Obtaining the value of
Using the obtained color system value of the intermediate color of each color, the obtained solid color system value of each color, and the obtained color system color value of the recording medium and the area ratio table The color system value of the first color and the color system value of the second color of each color of the halftone image line portion are obtained, and the first color color value of each of the plurality of color plates is obtained. Obtaining a first correction characteristic for correcting to a gradation value in which the density of the intermediate color of each color constituted by the pixel of the second color and the pixel of the second color becomes the density of the intermediate color of each acquired color;
The acquired color value of the color of the recording medium, the calculated value of the first color system, the value of the second color system and the third reference table, Obtaining a combination of output intensities of the plurality of basic colors corresponding to the color of the recording medium, the first color, and the second color, and generating a color channel table;
The plurality of colors indicated by the combination of the gradation values of the colors of the plurality of color plates are corrected with the obtained first correction characteristic, and the obtained first color pixel and the second color are corrected. A color system value obtained by configuring with pixels, and a gray color system value composed of C, M, and Y among the intermediate colors of the halftone image line portion obtained by printing And correcting the first correction characteristic for each of CMY among the obtained first correction characteristics so as to reproduce the value of the color system of gray, based on
Using the corrected first correction characteristic for correcting a gradation value of the gradation image data;
Forming a color image by changing the output intensity of a plurality of basic colors according to the color of each pixel based on the generated color channel table. The plurality of basic colors are three colors of cyan (C), magenta (M), and yellow (Y),
10. The reference table shows color system values for each combination in which the output intensities of cyan (C), magenta (M), and yellow (Y) are changed stepwise. 2. A color image forming method according to 1. The step of obtaining the first correction characteristic includes:
The acquired gradation value of the intermediate color of each color is used as an input value, and the density of the intermediate color of each color constituted by the pixels of the first color and the second color is the density of the intermediate color of each acquired color. Associating a tone value as an output value to provide a first correction characteristic;
The step of correcting the first correction characteristic includes:
Creating a first reference table in which color system values respectively corresponding to combinations of the gradation values for the plurality of colors are associated;
A second one in which a combination of gradation values corresponding to a color indicated by the color system value is associated with each color system value of the plurality of color system values based on the first reference table; Creating a reference table for
Using the second reference table, a combination of C, M, and Y gradation values corresponding to the value of the gray color system is obtained, and the C, M, and Y levels when the gray is printed are obtained. Obtaining a second correction characteristic for each of CMY in which each of the tone values is an input value and each of the obtained combinations of C, M, and Y tone values is associated as an output value;
The color image forming method according to claim 9, further comprising: correcting the first correction characteristic for each of CMY based on the obtained second correction characteristic for each of CMY. Each color of the halftone dot line portion includes a primary color of one plate color of the plurality of color plates, and a multi-order color of a color in which at least two plate colors are superimposed,
Obtaining the color system value of the first color and the color system value of the second color comprises obtaining the primary color and the multi-color.
Determining the primary color comprises:
Obtaining a value of the color system of the first color of each color of the halftone line portion as a value of the color system of the obtained solid color;
The value of the color system of the second color for each primary color of the halftone image line portion is the value of the color system of the intermediate color of the acquired colors for each primary color, the value of each primary color Using the obtained solid color system value of each color and the obtained color value of the recording medium color and the area ratio table for each primary color. Including
The step of obtaining the multi-order color includes:
Correcting the area ratio of the area ratio table based on the determined first correction characteristic;
The value of the color system of the second color for each multicolor of the halftone image line portion is the value of the color system of the intermediate color of the acquired colors for each multicolor and the value of each color of the acquired colors And determining using the solid color system value, the color system value of the acquired color of the recording medium, and the corrected area ratio table for each multi-order color. The color image forming method according to claim 9.   The value of the color system of the second color with respect to the multi-order color is obtained using the value of the color system of the second color that has already been obtained in order from the lowest order in which the number of superimposed colors is small. The color image forming method according to claim 12.   The value of the color system of the second color is the value of the color system of the first color for each color of the halftone image line part constituting the halftone image showing the intermediate color of each color of the halftone image line part, The total value obtained by adding the color system value of the second color and the product of the color system value of the color of the recording medium and the area ratio shown in the area ratio table corresponding to each color. 14. The color image forming method according to claim 9, wherein the value is a value when the acquired color value of an intermediate color of each of the colors is obtained. The area ratio table indicates the area ratio for a plurality of intermediate colors of each color of the halftone dot line portion,
The acquired color value of the intermediate color of each color is for the intermediate color of the plurality of stages,
The value of the color system of the second color is obtained so that an error between the total value and the value of the color system of the acquired intermediate colors is obtained so that the error is minimized for the intermediate colors of the plurality of stages. The color image forming method according to claim 14.   The color image formation according to any one of claims 9 to 15, wherein a color system value for each color used when obtaining a color system value of the second color is a value of an XYZ color system. Method. The first color pixel is disposed in the center of each color region of the halftone image line portion constituting the halftone image,
17. The color image forming method according to claim 9, wherein the second color pixels are arranged in a peripheral portion of each color region of a halftone image line portion constituting the halftone image. The tone of a halftone image obtained by printing on a recording medium using a plurality of color plates including at least C (cyan), M (magenta), and Y (yellow) color plates is determined for each color of the plurality of color plates. It is obtained by correcting the gradation value of gradation image data composed of drawing information including gradation values indicating density levels, and converting the gradation image data with the gradation value corrected into halftone dots. A region of each color of a halftone image line portion constituting a halftone dot image based on halftone dot image data is represented by at least one second color pixel having a color tone different from that of the first color pixel and the first color for each color. A color image forming apparatus configured to form a color image so as to be reproduced by changing the output intensity of a plurality of basic colors according to the color of each pixel.
A third reference table showing a correspondence relationship between the output intensity of the plurality of basic colors and the value of the color system;
The first color and the first color of each color when the area of each color of the halftone dot line portion constituting the halftone dot image indicating the halftone image of each color of the halftone dot line portion is constituted by the first color and the second color. An area ratio table showing the area ratio of each of the two colors and the color of the recording medium;
The solid color system value of each color of the halftone line portion obtained by the printing, the intermediate color system value of each color of the halftone line portion, and the color system of the color of the recording medium Value of the intermediate color of each acquired color, the value of the solid color system of each acquired color, and the value of the color system of the acquired recording medium and the area ratio And a color system value of the first color and a color system value of the second color of each color of the halftone image line portion using a table, and each color of the plurality of color plates A color for obtaining a first correction characteristic for correcting the density of the intermediate color of each color composed of the first color pixel and the second color pixel to a gradation value that is the density of the acquired intermediate color of each color Adjustment value calculation means;
Based on the obtained color system value of the color of the recording medium, the calculated value of the first color system, the value of the color system of the second color and the reference table, Generating means for obtaining a combination of output intensities of the plurality of basic colors corresponding to the color, the first color, and the second color, and generating a color channel table;
The plurality of colors indicated by the combination of the gradation values of the colors of the plurality of color plates are corrected with the obtained first correction characteristic, and the obtained first color pixel and the second color are corrected. A color system value obtained by configuring with pixels, and a gray color system value composed of C, M, and Y among the intermediate colors of the halftone image line portion obtained by printing Correction characteristic correction means for correcting the first correction characteristic for each of CMY among the obtained first correction characteristics so as to reproduce the values of the gray color system, based on
Gradation value correcting means for correcting a gradation value of the gradation image data using the corrected first correction characteristic;
A color image forming apparatus, comprising: a control unit configured to control the output intensity of a plurality of basic colors according to the color of each pixel based on the generated color channel table.

Images