JP5903926B2 - Image processing apparatus, image processing method, and program - Google Patents

Description

  The present invention relates to an image processing apparatus, an image processing method, a program, and a recording medium for correcting gradation.

  In order to obtain a γ conversion table (tone correction curve) for each single color of CMY, image data of various tone values for each single color is sent to the output device and output, and the density of the output result is measured, whereby the image There is a technique for creating a γ conversion table that obtains a desired density corresponding to data.

  For example, in Patent Document 1, after obtaining a gradation correction parameter to match a single color to a target color, the gradation correction parameter is corrected when the amount of deviation between the mixed color measurement data and the target color exceeds an allowable range. The correction rate of the gradation correction parameter is reduced when the gradation change rate does not fall within a predetermined allowable range so that a sharp gradation change or gradation inversion due to this correction does not occur.

  However, in the above-described conventional technology, a gradation correction table is created so as to match the target characteristics. However, gradation steps, gradation skipping, and color are caused by a sharp gradation change in a local gradation region. There has been a problem that gradation collapse such as a change in taste occurs.

The present invention has been made in view of the above problems,
An object of the present invention is to provide an image processing apparatus, an image processing method, a program, and a recording medium that create a gradation correction table that suppresses both a single-color and mixed-color gradation change due to a sharp gradation change.

The present invention includes a plurality of single-color patches created by a gray level value different using monochromatic colorant, and, on a predetermined medium a plurality of mixed color patches created in different tone values by using a plurality of monochromatic color materials based image forming means for outputting a color measuring means for colorimetric said single-color patch and the mixed-color patch is output, the color measurement result obtained by colorimetry the single-color patch and the mixed color patch, the image tone values of the monochromatic colorant which is output by the forming means, and generating means for generating tone correction table so that each of the target tone value, by referring to the gradation correction table, the image data and a processing unit that converts the input tone value, before Symbol creation means, calorimetric values of mixed color patches created in target gradation value, in the vicinity of mixed color patches created in the target tone value Obtained by linear interpolation of colorimetric values of mixed color patches As within the range of the constant, the most important feature that you create the gradation correction table.

  According to the present invention, it is possible to create a gradation correction table in which gradation deterioration of both single color and mixed color due to a sharp gradation change is suppressed.

1 shows a configuration example of an image processing system of the present invention. 1 shows a configuration of an image processing unit of the present invention. The processing flowchart of a gradation correction table preparation part is shown. A detailed process flowchart of step S303 of FIG. 3 is shown. A detailed process flowchart of step S304 of FIG. 3 is shown. 2 shows a chart output by an image forming apparatus for creating a gradation correction table. An example of the color measurement result of black is shown. Indicates the target color (black) for each gradation value. An example of gray color measurement results is shown. Indicates the target color (gray) for each gradation value. A black tone correction table is shown. The example of the color difference of the target color and colorimetry result in gray is shown. An example of cyan color measurement results is shown. The colorimetric values for each gradation value obtained by linear interpolation of the colorimetric results of FIG. 13 are shown. It is a figure explaining the calculation method of the range where a gray colorimetric value should exist. An example of the latest cyan tone correction table is shown. 1 shows a hardware configuration example of an image processing apparatus when the present invention is implemented by software.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  In the present invention, the gradation correction table for each single color is determined based on both the color measurement result of the mixed color (gray) and the allowable change range of each single color. Further, based on the color measurement result of the mixed color (gray), it is determined to suppress the gradation deterioration of the mixed color. The permissible change range for each single color is determined so as to suppress gradation deterioration of the single color.

  According to the present invention, in the process of creating the gradation correction table, a range in which the colorimetric value of the target gradation should exist in a single color is determined based on the colorimetric values of the neighboring gradations, and the colorimetric value should exist. An allowable change range of the gradation correction table corresponding to the target gradation is determined from the range, and a gradation correction table of each single color is determined based on the allowable change range of each single color and the color measurement result of mixed colors.

  FIG. 1 shows a configuration example of an image processing system of the present invention. In FIG. 1, 101 is a host computer, 102 is an image processing unit, 103 is an image forming apparatus, 104 is a colorimetric device, 105 is a gradation correction table creation unit, and 106 is a controller. The controller 106 includes an image processing unit 102 and a gradation correction table creation unit 105, and executes print processing, gradation correction table creation processing, and the like.

  When a print process is instructed from an application running on the host computer 101, the host computer 101 operates a printer driver (not shown) and transmits image information to be printed to the controller 106. The controller 106 operates the image processing unit 102 to perform image processing described later on the input image information, converts the image information into print output data, and outputs the print output data to the image forming apparatus 103.

  The image forming apparatus 103 is an output apparatus for printing image data. For example, an image forming apparatus such as an electrophotographic or inkjet color printer or a color facsimile can be used.

  On the other hand, when execution of the gradation correction table creation process is instructed from the host computer 101, the controller 106 creates a gradation correction table and updates the gradation correction table.

  FIG. 2 shows a configuration of the image processing unit 102 of the present invention, and converts image information to be printed into print output data. The image information sent from the application is drawing command format data represented by RGB color signals for normal display display. Therefore, the rasterization processing unit 201 interprets the drawing command and develops it into 8-bit bitmap data for each color of RGB. Next, since the color reproduction range and color reproduction characteristics differ greatly between the display and the printer, the color rendering processing unit 202 uses the profile associated with the display or printer to convert the RGB data of the bitmap image into the color of the printer. The data is converted into R′G′B ′ data that has undergone color gamut compression to fit the reproduction range.

  A general image forming apparatus 103 forms an image using inks of four or more colors of C (cyan), M (magenta), Y (yellow), and K (black). Therefore, the color separation processing unit 203 converts the R′G′B ′ data into color data suitable for printer output. For example, when the image forming apparatus 103 uses four colors of CMYK, it can be converted into data of CMYK four colors by performing color separation processing such as UCR and UCA from the R′G′B ′ data.

  Next, the gradation correction processing unit 204 performs gradation conversion on the data values of each color of CMYK with reference to the gradation correction table 206. In this embodiment, it is assumed that a one-dimensional lookup table is defined as the gradation correction table 206. By changing the gradation correction table 206, changes in density characteristics of the image forming apparatus 103 and individual differences are absorbed.

  A halftone processing unit 205 receives 8-bit image data for each C′M′Y′K ′ color subjected to gradation correction processing, and a CMYK image with a small number of bits that can be output by the image forming apparatus 103. Perform conversion to data. With the image processing described above, CMYK image data that can be output by the image forming apparatus 103 can be created.

  FIG. 3 shows a processing flowchart of the gradation correction table creation unit 105. An outline of a method for creating a gradation correction table will be described with reference to FIG. Hereinafter, the gradation value, that is, the image data is represented by an integer value of 0 or more and 255 or less, and the larger the value, the higher the density. Further, a mixed color having the same gradation values of cyan, magenta, and yellow before gradation correction is referred to as gray.

  The gradation correction table creation unit 105 prevents the gradation correction table 206 from operating the chart data stored in advance via the image processing unit 102, that is, the gradation correction processing unit 204 is through. The image is output to the image forming apparatus 103, the image forming apparatus 103 prints the chart on the printing paper, the colorimetric device 104 performs color measurement, and the target color is determined from the color measurement result (step S301).

  Next, the gradation correction table creation unit 105 creates a gray reproduction estimation model function from the color measurement result of the printed chart (step S302).

  Next, the gradation correction table creation unit 105 determines a gradation correction table so that gray and black are sufficiently close to the target color (step S303).

  Next, the gradation correction table creating unit 105 adjusts the grayscale colorimetric values so that they fall within a predetermined range determined from the colorimetric values of the neighboring gradations of the same color as that of the respective colors. The gradation correction table is determined so that the output gradation value with respect to the input gradation value of the tone correction table falls within a predetermined range (step S304).

  FIG. 6 shows a chart output by the image forming apparatus 103 for creating a gradation correction table. The chart shown in FIG. 6 includes a C patch row 601 composed of patches drawn in cyan single colors from C00 to C32. C00 has a cyan gradation value of 0, C01 has a cyan gradation value of 8, C02 has a cyan gradation value of 16, and the cyan gradation value increases by 8, and C31 has a cyan gradation value of 248. , C32 is a print of image data having a cyan gradation value of 255. Here, the gradation value of the color that is not clearly shown for each patch is zero. For example, C01 has a gradation value of 8 for cyan, and 0 for magenta, yellow, and black.

  Similarly, the chart includes an M patch row 602 composed of patches drawn in magenta single colors from M00 to M32, a Y patch row 603 composed of patches drawn in yellow single colors from Y00 to Y32, and K00. It also has a K patch row 604 composed of patches drawn in black only up to K32.

  Further, a T-patch row 605 composed of patches drawn in gray, that is, mixed colors of equal gradation values of cyan, magenta, and yellow from T00 to T32, that is, gray. T01 is an image with cyan, magenta, and yellow tone values of 8, T02 is cyan, magenta, and yellow each with a tone value of 16, and T32 is an image with cyan, magenta, and yellow tone values of 255. Data is printed. For example, T01 is referred to as gray having a gradation value of 8 using the gradation value at this time.

[Details of Step S301]
The processing content of step S301 will be described. First, a target color is determined for a single black color. From the color measurement results of K00 and K32 in the printed chart of FIG. 6, the former is a target color with a gradation value of 0 and the latter is a gradation value of 255, and the gradation value between them is a value obtained by linear interpolation. To do.

Here, as the black target color, only the L * component of the colorimetric value L * a * b * is given, and the a * component and b * component are not given. FIG. 7 shows an example of the color measurement result of black. As shown in FIG. 7, when the L * component of K00 obtained by colorimetry is 95.1 and the L * component of K32 is 16.5, the target color with gradation value 0 is L * = 95. 1. The target color of gradation value 255 is L * = 16.5, and the target color of gradation value 48 is obtained by performing linear interpolation.
L * = 95.1 + (16.5-95.1) ÷ (255-0) × 48 = 80.3
It becomes. The same processing is performed for each gradation to obtain a target color (black) for each gradation value shown in FIG.

  Next, a target color is determined for gray. The L * component of the gray target color is L * of the black target color having the same gradation value. The a * and b * components of the gray target color are both set to −2.5. However, the a * and b * components are adjusted so as to approach the a * and b * values of K0 or T0 as the gradation value approaches 0 when the gradation value is 96 or less. In addition, the L *, a *, and b * components are adjusted so as to approach L *, a *, and b * of T32 as the gradation value 255 is approached when the gradation value is 192 or higher.

  FIG. 9 shows an example of a gray color measurement result. As shown in FIG. 9, when the colorimetric value of T00, which is gray with a gradation value of 0, is (a *, b *) = (0.4, -3.4), the target of gradation value 0 The color is (a *, b *) = (0.4, -3.4), the target color of the gradation value 96 is (a *, b *) = (− 2.5, −2.5), The a * and b * components of the target color during this period are obtained by linear interpolation.

For example, the gradation value 48 is
a * = 0.4 + (− 2.5−0.4) ÷ (96−0) × 48 = −1.1
b * = − 3.4 + (− 2.5 − (− 3.4)) ÷ (96−0) × 48 = −3.0.

  Further, as shown in FIG. 9, the a * and b * components of the target color from the gradation value 192 to the gradation value 255 have a colorimetric value of T32 that is a gray of the gradation value 255 (a *, b). *) = (− 2.3, 7.4), the target color of tone value 255 is (a *, b *) = (− 2.3, 7.4), tone value 192 The target color is determined by applying a quadratic function having a gradation value of 192 and a gradient of 0, where (a *, b *) = (− 2.5, −2.5).

  On the other hand, the L * component of the target color from the gradation value 192 to the gradation value 255 is that the black target color of the gradation value 192 is L * = 35.9 from FIG. When the colorimetric value of T32 which is 255 gray is L * = 21.4, the target value of L * from the gradation value 192 to the gradation value 255 is obtained by these linear interpolations. By obtaining a target color for each gradation, a gray target color for each gradation value shown in FIG. 10 is obtained. Here, the L * component of the gray target color is obtained so as to be linear from the colorimetric results of T00 and T32 in the chart of FIG. 6 independently of the black target color, similarly to the black single color. Also good.

[Details of Step S302]
The processing content of step S302 will be described. A gray reproduction estimation model function is created from the color measurement result of the chart of FIG. 6 printed in step S301 so that the error is reduced.
For example, the estimated model function is expressed as Equation 1.
L * = Fl (Cg [i], Mg [j], Yg [k]) + L_paper
a * = Fa (Cg [i], Mg [j], Yg [k]) + a_paper
b * = Fb (Cg [i], Mg [j], Yg [k]) + b_paper Equation 1

Equation 1 estimates the color represented by the mixed color of cyan, magenta, and yellow of the tone values i, j, and k after tone correction. Here, L_paper, a_paper, and b_paper represent the colorimetric values (L *, a *, b *) of the paper, and Cg [x], Mg [x], and Yg [x] are after gradation correction, respectively. This is the color difference from cyan, magenta, and yellow paper white with a tone value of x.
The color difference dE (p, q) between the color p and the color q is expressed by the following equation (1).

ただし、Ｌ（ｃ）、ａ（ｃ）、ｂ（ｃ）は、それぞれ色ｃのＬ＊、ａ＊、ｂ＊の値を表すこととする。

However, L (c), a (c), and b (c) represent L *, a *, and b * values of the color c, respectively.

  Fl (), Fa (), and Fb () are estimated model functions, for example, linear functions, higher-order polynomials, or functions expressed by a neural network. Means to determine the coefficient of. The argument Cg [x] or the like indicates an estimation model function that means a color difference from each monochrome paper white, but Cg [x] or the like other than that indicates the density or monochrome gradation of each monochrome. It may be an estimation model function meaning the value itself.

[Details of Step S303]
The processing content of step S303 will be described with reference to FIG. For the gray values of gradation values 0, 8, 16,..., 248, 255, which are the gradation values corresponding to T00 to T32, the gray of each gradation is determined using the gray estimation model function created in step S302. The tone values of cyan, magenta, and yellow that are the target colors are calculated. That is, the tone values of cyan, magenta, and yellow in which the values of L *, a *, and b * in Equation 1 are sufficiently close to the target color are searched by iterative calculation, etc. To do.

  Further, from the colorimetric results of the chart of FIG. 6 printed in step S301 for black single colors of gradation values 0, 8, 16,..., 248, 255, which are gradation values corresponding to K00 to K32. Based on the relationship between the obtained black gradation value and the L * component, the black gradation value which is the target color is searched for and used as a black gradation correction table.

Here, as an example, an output tone value corresponding to the input tone value 96 in the black tone correction table is calculated. From FIG. 8, the target color of the gradation value 48 is L * = 80.3. Therefore, the gradation value for obtaining L * = 80.3 is estimated by linear interpolation from the color measurement result of FIG. According to FIG. 7, the colorimetric values close to L * = 80.3 were obtained when L * = 81.8 when the gradation value was 40 and L * = 79.7 when the gradation value was 48. is there. From here, the gradation value to obtain L * = 80.3 is
40+ (80.3-81.8) / (79.7-81.8) × (48-40) = 45.7
It can be seen that it is. By performing the same processing for each gradation, a gradation correction table for converting the black input gradation value into the output gradation value shown in FIG. 11 is obtained (step S401).
Next, the gradation correction processing unit 204 uses the gradation correction table created in step 401, the image forming apparatus 103 prints the chart on the printing paper, and the colorimetric apparatus 104 performs colorimetry on the printed chart. (Step S402).

  For each color of gray and black, the color difference between the target color and the color measurement result is calculated, and the sum of the color differences in all gradation values is calculated. When the step of creating the gradation correction table in step S401 is the first time, or when the sum of the color differences in the predetermined gradation range is smaller than the previous value after the second time, the gradation correction table is created again. Otherwise, it is determined that it is difficult to adjust to the target color any more, and the tone correction created one time before the last round with the smallest sum of color differences in the specified tone range for that color Adopt a table. When the predetermined upper limit number of times is reached, the gradation correction table with the smallest total sum of color differences in the predetermined gradation range is employed.

  FIG. 12 shows an example of a color difference in which the predetermined range in gray is a gradation value of 0 to 192 in increments of 8 gradation values. If the sum of the color differences is 21.9 for the first time and 14.3 for the second time, the gradation correction table is created again. If the total sum of color differences measured 3 times using the tone correction table is 28.6, the sum of color differences is larger than that of the second time. A correction table will be adopted. When the gray and black tone correction tables are determined, step S303 is ended (step S403).

  In step S401 after the second time, based on the difference between the target color and the color measurement result, the gradation value of each single color for obtaining the corrected target value is searched for and used as a gradation correction table. For example, the gray target value of gradation value 48 is (L *, a *, b *) = (80.3, −1.1, −3.0), and T06 is gradation value 48 of gray. When the color measurement result of (L *, a *, b *) = (81.0, -1.6, -3.6), (L *, a *, b) *) = (79.6, −0.6, −2.4) is used as a gray target color with a gradation value of 48, and the gradation values of cyan, magenta, and yellow are searched. This is because the grayscale value where L * is 80.3 was obtained, but the actual measurement was 81.0, so the gray estimation model function has an error of +0.7. This is because it is determined that it is sufficient to obtain a gradation value of 79.6 in order to obtain 80.3.

[Details of Step S304]
Next, the processing content of step S304 is demonstrated using FIG. Gradation characteristics which are the relationship between the gradation value of each single color and the colorimetric value are grasped from the measurement result of the chart shown in FIG. 6 output so that the gradation correction processing unit 204 is through.

  Here, the gradation characteristic is expressed by an integrated color difference from the gradation value 0 which is paper white, and the integrated color difference at the gradation value n is expressed by the following formula 2. Note that the gradation characteristics may be expressed by an integrated color difference from the highest density.

ただし、ｄＥ（ａ，ｂ）は階調値ａとｂの色差を表すこととする。なお、階調値０の積算色差は０とする。

However, dE (a, b) represents the color difference between the gradation values a and b. Note that the integrated color difference of the gradation value 0 is 0.

  By expressing the gradation characteristics with integrated color differences, the degree of gradation change can be expressed on a scale close to human visual characteristics. Further, both the gradation value and the characteristic value (here, the accumulated color difference) can be expressed by one component (when the gradation characteristic is expressed by L * a * b *, the characteristic value is L *, a *, and b *. Three components are required.In the case of a single color, one component may be expressed by expressing it in terms of density, but the difference in the way of feeling with respect to a density difference of 0.1 differs depending on the density range).

A method for calculating the integrated color difference will be described with reference to FIGS. 13 and 14. FIG. 13 is an example of the color measurement result of cyan. From this cyan color measurement result, as shown in FIG. 14, a color measurement value for each gradation value is obtained by linear interpolation. For example, since the L * of the gradation value 0 in FIG. 13 is 95.23 and the L * of the gradation value 8 is 94.63, the colorimetric value L * of the gradation value 1 is
((94.63−95.23) × (1 / (8−0)) + 95.23≈95.16, 95.16. Similarly, a * and b * are also calculated, By calculating the gradation value, L *, a *, and b * at each gradation value shown in FIG. 14 are obtained.

Next, the color difference between the gradation values separated by the gradation value 1 in each gradation value is obtained. For example, the color difference between tone value 0 and tone value 1 is
((95.23-95.16) ^ 2 + (0.41-0.34) ^ 2 + (-3.50 + 3.57) ^ 2) ^ (1/2) ≈0.12
Is 0.12 (^ is a power).

  Next, an integrated color difference obtained by accumulating the color difference from the gradation value 0 is obtained. For example, the integrated color difference between the gradation value 3 and the gradation value 4 is the color difference 0.12 between the gradation value 0 and the gradation value 1, the color difference 0.13 between the gradation value 1 and the gradation value 2, and the gradation value 2 The color difference of gradation value 3 is 0.12, and the sum of the gradation value 3 and gradation value 4 of color difference 0.14 is 0.51 (step S501).

  Next, a range in which the colorimetric values of the respective gradations of black and gray should exist is calculated from the measurement result of the chart shown in FIG. 6 output using the latest gradation correction table. That is, in order to derive a gradation correction table that does not cause a local rapid gradation change, a value that should have a colorimetric value of a target gradation is determined based on an actually measured value of a neighboring gradation.

  A method for calculating a range in which a gray colorimetric value should exist will be described with reference to FIG. FIG. 15 shows the colorimetric values of the gray gradation values according to the latest gradation correction table. For example, the range in which the gray gradation value 8 of T01 should exist is obtained as follows.

First, a colorimetric value of gradation value 8 is obtained by linear interpolation from the colorimetric values of T00 and T02 across T01. For L * component,
(92.29-95.19) × (8-0) ÷ (16-0) + 95.19 = 93.74
From 93.74. Similarly, by calculating the a * and b * components, as shown in FIG.
(L *, a *, b *) = (93.74, 0.11, −3.32)
Get.

It is suitable for reproducing the gentle gradation change that the colorimetric value of the gradation value 8 becomes this value (93.74, 0.11, −3.32). In consideration of a margin for recognizing the gradation step and the color difference within 0.8 from this value, the gradation step is allowed. That is, the first condition for terminating step S304 is that the gray gradation value 8 is within the color difference of 0.8 (a range that should exist) from this value.
As shown in FIG. 15, the actually measured value of the gradation value 8 at this time is (L *, a *, b *) = (93.77, 0.24, −3.50).
Since the color difference (the color difference between the actually measured value of the gradation value 8 and the colorimetric value of the gradation value 8 by linear interpolation) is 0.22, the gray gradation value 8 satisfies the first condition. ing.

  The colorimetric values of gray T01 to T31 and black K01 to K31 are within the range to be present (first condition), and further, the cyan, magenta, and yellow tone correction tables correspond to the input tone values. If the output gradation value is within a predetermined allowable range (second condition) described later, step S304 is terminated, otherwise the process proceeds to step S503 (step S502).

  The second condition that should be satisfied by each of the tone correction tables for cyan, magenta, and yellow will be described with reference to FIG. FIG. 16 is an example of the latest cyan gradation correction table. The gradation correction table values corresponding to the input gradation value 8 and the input gradation value 24 are the output gradation value 9 and the output gradation value 22, respectively. On the other hand, as shown in FIG. 14, the accumulated color differences of the cyan gradation values 9 and 22 when the gradation correction processing unit 204 outputs through are 1.21 and 4.36, respectively.

  That is, when the latest gradation correction table is used, the image data of cyan input gradation values 8 and 24 are converted into output gradation values 9 and 22 by the image processing unit 102, respectively, and the integrated color difference is 1 .21, 4.36 can be expected to be output from the image forming apparatus 103. When image data that changes evenly and continuously is input, it is desirable to output an image with uniformly changing gradation. Therefore, for the image data having the intermediate gradation value 16 between the cyan gradation values 8 and 24 so that the integrated color difference changes evenly, the fact that the integrated color difference is intermediate between the two is for ending step S304. Condition. However, in consideration of an error such as an output device and a margin for recognizing gradation breakage, the gradation breakage can be allowed if the difference is within 0.8 from this value.

The intermediate value of the integrated color difference is
(1.21 + 4.36) ÷ 2≈2.79
2.79 and considering the allowable range, the integrated color difference of the output gradation value corresponding to the input gradation value 16 is 1.99 to 3.59. When the gradation correction processing unit 204 outputs so as to be through, gradation values satisfying this condition are 14 to 19 (allowable range) from FIG. In other words, the output gradation value of the gradation correction table for the cyan input gradation value 16 needs to be in one of the above-described allowable ranges.

  It should be noted that the allowable range of the colorimetric value is preferably given an independent value for each color or gradation value that does not give the human eyes a sense of incongruity, but the same gradation value is the same value or the same color for different colors. The same value may be used regardless of the gradation value. In gray, an L * component, an a * component, a b * component, or a part or all of the color difference may be used instead of a color difference for an allowable range or determination. In the case of a single color, a lightness difference or a density difference may be used instead of a color difference for an allowable range or determination.

  Next, the gradation correction table is changed so that the gradation value that does not fall within the predetermined allowable range falls within the predetermined allowable range. For example, when only T07 and T08 are not within a predetermined allowable range, target values of T07 and T08 are determined by linear interpolation from the colorimetric values of T06 and T09 sandwiching T07 and T08, and the estimated model function is used to The gradation correction table is changed so that the target value is obtained and the gradation correction tables for cyan, magenta, and yellow satisfy the above-described conditions for the integrated color difference of each single color.

  It should be noted that every time it passes through step S505, the allowable range of the color difference and the integrated color difference that allow the gradation collapse that was initially set to 0.8 may be gradually increased. Thereby, it is possible to avoid that the gradation correction table that satisfies the end condition cannot be created forever. In addition, regarding a certain gradation value, it may be impossible to satisfy both the condition that the colorimetric value should be present for gray (first condition) and the second condition for each gradation correction table for each single color. is there. In order to cope with such a case, which condition is prioritized may be determined in advance or may be selected by the operator.

  Further, the gradation correction tables other than T07 and T08 are not changed, and the gradation values once within the predetermined allowable range in step S502 or step S505 may not be changed in step S304 thereafter. In this case, the number of gradation values to be changed does not increase (step S503).

  Next, the gradation correction processing unit 204 outputs the gradation correction table to the image forming apparatus 103, and the image forming apparatus 103 prints the chart shown in FIG. The color of the 3C gray patch array 605 of the chart printed in step S504 is measured (step S504).

  Similar to step S502, a range in which the colorimetric values for each gradation of black and gray should be present is calculated from the measurement result of the chart shown in FIG. 6 output using the latest gradation correction table. The colorimetric values of T31 and black K01 to K31 are within the above existing range, and the output tone values for the input tone values of the cyan, magenta, and yellow tone correction tables corresponding to T01 to T31 are as follows. If it is within the predetermined allowable range, step S304 is ended, and if not, the process proceeds again to step S503 (step S505).

  As described above, in the present invention, the conditions that the gradation correction parameter should satisfy must be determined in advance so as not to cause a single-color gradation failure, and the gradation correction parameter is set so as not to cause a mixed-color gradation deterioration under that condition. By determining, it is possible to simultaneously suppress a single-color gradation failure and a mixed-color (C = M = Y gray) gradation failure.

  In addition, by linearly interpolating the colorimetric values of the neighboring gradation values, the allowable range can be determined regardless of the gradient of the gradation characteristics (color difference 0 is determined as the best state). For example, the gray color value (L *, a *, b *) of the gray scale value 16 and the gray scale value 32 is averaged with respect to the gray having the gray scale value C = M = Y = 24. The color difference between the value 24 and the colorimetric value is determined to be equal to or less than a predetermined value.

  Also, arithmetic processing can be easily performed by using the integrated color difference which is a one-dimensional numerical value instead of the three-dimensional L * a * b *. By giving C = M = Y gray, which is sensitive to human eyes, as a condition, the quality of the tone correction parameter can be improved. Furthermore, when both the single-color gradation failure and the mixed-color gradation failure cannot be suppressed at the same time, a desired gradation correction parameter can be obtained by allowing the user to make a determination.

FIG. 17 shows a hardware configuration example of an image processing apparatus when the present invention is implemented by software. The computer 1 includes a program reading device 1a, a CPU 1b for controlling the whole, a RAM 1c used as a work area for the CPU 1b, a ROM 1d for storing a control program for the CPU 1b, a hard disk 1e, and a NIC 1f for communicating with devices on the network. , A mouse 1g, a keyboard 1h, a display 2 capable of displaying image data and allowing a user to input information directly by touching the screen, an image forming apparatus 3 such as a color printer, and a color measuring device 4. The image processing apparatus can be realized by, for example, a workstation or a personal computer.

  In the case of such a configuration, the functions of the image processing unit and the gradation correction table creating unit shown in FIG. 1 can be provided to the CPU 1b, and when storing the gradation correction table, image data, chart data, etc. , RAM 1c, ROM 1d, DISK 1e, and other storage devices can be used. Note that the processing functions performed by the CPU 1b can be provided in the form of, for example, a software package, specifically, an information recording medium such as a CD-ROM or a magnetic disk. Therefore, in the example shown in FIG. When the recording medium is set, a medium driving device (not shown) for driving the recording medium is provided.

  As described above, the image processing method according to the present invention causes a general-purpose computer system having a display or the like to read a program recorded on an information recording medium such as a CD-ROM, and causes the central processing unit of the general-purpose computer system to perform image processing. It is also possible to implement in an apparatus configuration that executes In this case, a program for executing the image processing of the present invention, that is, a program used in the hardware system is provided in a state of being recorded on a recording medium. The information recording medium on which the program is recorded is not limited to the CD-ROM, and for example, a ROM, RAM, flash memory, or magneto-optical disk may be used. The program recorded on the recording medium is installed in a storage device incorporated in the hardware system, for example, the hard disk 1e, so that the image processing function can be realized by executing the program. Further, the program for realizing the image processing method of the present invention is not only provided in the form of a recording medium, but may be provided from a server by communication via a network, for example.

DESCRIPTION OF SYMBOLS 101 Host computer 102 Image processing part 103 Image forming apparatus 104 Colorimetry apparatus 105 Gradation correction table preparation part 106 Controller 201 Rasterization processing part 202 Color rendering processing part 203 Color separation processing part 204 Gradation correction processing part 205 Halftone processing part 206 Tone correction table

JP 2010-263345 A

Claims (8)

A plurality of single-color patches created by a gray level value different using monochromatic colorant, and an image forming for outputting a plurality of mixed color patches created by a gray level value different by using a plurality of monochromatic color materials on a predetermined medium Means,
Colorimetric means for measuring the output single color patch and the mixed color patch ;
Based on the colorimetry result obtained by colorimetry the single-color patch and the mixed-color patch, as tone values of the monochromatic colorant which is output by said image forming means comprises a respective target tone values Creating means for creating a gradation correction table;
Referring to the gradation correction table, comprising a processing unit that converts the input tone value of the image data, and
Before Symbol creating means, calorimetric values of mixed color patches created in target gradation value, a colorimetric value of the mixed color patch in the vicinity of mixed-color patch created in the target tone values linearly interpolated to predetermined obtained Create the gradation correction table so that it is within the range.
The image processing apparatus according to claim and this. Image formation that outputs a plurality of single color patches created with different gradation values using a single color material and a plurality of mixed color patches created with different gradation values using a plurality of single color materials onto a predetermined medium Means,
Colorimetric means for measuring the output single color patch and the mixed color patch;
Based on the color measurement results obtained by measuring the single color patch and the mixed color patch, each gradation value of the single color material output by the image forming unit becomes a target gradation value. Creating means for creating a gradation correction table;
Processing means for converting the input gradation value of the image data with reference to the gradation correction table,
The creating means includes a colorimetric value of a single color patch created with a target tone value, and a plurality of single color patches in the vicinity of the single color patch created with the target tone value, and a color difference from paper white or the highest density , The gradation correction table is created so that it falls within a predetermined range determined from the accumulated color difference obtained by accumulating the color difference from paper white or the highest density.
An image processing apparatus. The mixed color patch created with the target gradation value is a patch whose difference from each target gradation value is a predetermined value or more among the mixed color patches read by the colorimetric means. The image processing apparatus according to 1 or 2 . The colorimetric value is, L * a * b * image processing apparatus according to any one of claims 1 3, characterized in that the value of the color space. A plurality of single-color patches created by a gray level value different using monochromatic colorant, and an image forming for outputting a plurality of mixed color patches created by a gray level value different by using a plurality of monochromatic color materials on a predetermined medium Process,
A colorimetric step of measuring the output single color patch and the mixed color patch ;
Based on the colorimetry result obtained by colorimetry the single-color patch and the mixed-color patch, as tone values of the monochromatic colorant which is output by the image forming step, the respective target tone values A creation process for creating a gradation correction table;
Referring to the gradation correction table, wherein the processing step to convert the input gradation value of the image data, and
Before Symbol creation step, the colorimetric values of the mixed color patch created with attention tone value, a colorimetric value of the mixed color patch in the vicinity of mixed-color patch created in the target tone values linearly interpolated to predetermined obtained Create the gradation correction table so that it is within the range.
An image processing method characterized by and this. A program for causing a computer to realize the image processing method according to claim 5 .   Image formation that outputs a plurality of single color patches created with different gradation values using a single color material and a plurality of mixed color patches created with different gradation values using a plurality of single color materials onto a predetermined medium Process,
  A colorimetric step of measuring the output single color patch and the mixed color patch;
  Based on the colorimetric results obtained by measuring the single color patch and the mixed color patch, each gradation value of the single color material output by the image forming step becomes a target gradation value. A creation process for creating a gradation correction table;
  Referring to the gradation correction table, and converting the input gradation value of the image data,
  The creation step includes a colorimetric value of a single color patch created with a target gradation value, and a plurality of single color patches in the vicinity of the single color patch created with the target gradation value, and a color difference from paper white or the highest density, The gradation correction table is created so that it falls within a predetermined range determined from the accumulated color difference obtained by accumulating the color difference from paper white or the highest density.
  An image processing method.   A program for causing a computer to realize the image processing method according to claim 7.

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