JP5644345B2 - Color conversion apparatus, image forming apparatus, and color conversion program - Google Patents

Description

  The present invention relates to a color conversion apparatus, an image forming apparatus, and a color conversion program.

  In Patent Document 1, CMYK image data is converted into XYZ colorimetric values so that the color of a target point on a printed matter that is a target matches the color of the target point on a proof created by a printer. A method for correcting a print profile to be converted into data is described. In this correction method, the color at the point of interest on the proof output from the printer is measured using the print profile corresponding to the desired input data value, and the point corresponding to the point of interest on the color printed matter The color corresponding to the difference between each colorimetric value is added to the colorimetric value specified for the nearest grid point used for the interpolation process surrounding the desired input data value and printed. Modify the profile.

JP 2000-203094 A

  An object of the present invention is to provide gradation in color conversion using a color conversion coefficient group for performing printing based on the color reproduction characteristics of the first device with the second device, as compared with the case without the present configuration. In view of this, the color reproduction accuracy of the color conversion coefficient group is improved.

According to the first aspect of the present invention, there is provided a first color reproduction characteristic acquisition unit that acquires a color reproduction characteristic of a first device, and a color value that depends on the first device as a color value that depends on the second device. The color reproduction characteristics obtained by simulating the color reproduction characteristics of the first device acquired by the first color reproduction characteristic acquisition means based on the color conversion coefficient group for conversion into the second device. A second color reproduction characteristic acquisition unit that acquires the simulated color reproduction characteristic, and a continuity index that is an index relating to gradation continuity in the simulated color reproduction characteristic acquired by the second color reproduction characteristic acquisition unit Continuity index acquisition means for acquiring the color reproduction characteristics of the first device acquired by the first color reproduction characteristic acquisition means and the simulated color reproduction acquired by the second color reproduction characteristic acquisition means Difference information with the characteristics and the continuity index acquisition means. -Out obtained based on said continuity index, the weighting factor indicating the degree to which the continuity index to correct the color reproduction characteristics of the first device from the difference information when it exceeds a predetermined threshold Recreating means for modifying the color reproduction characteristics of the first device by reducing the color reproduction characteristics and recreating the color conversion coefficient group using the corrected color reproduction characteristics of the first device ; This is a characteristic color conversion device.
According to a second aspect of the present invention, the first color reproduction characteristic acquisition unit and the third color reproduction characteristic acquisition unit that acquires the color reproduction characteristic of the second device are respectively connected to the device as the color reproduction characteristic. A correspondence relationship between the input color value of the first device and the color value in the device-independent color space representing the output color from the device according to the input color value, 2. The color conversion coefficient group is re-created based on difference information regarding color values in the device-independent color space between the reproduction characteristics and the simulated color reproduction characteristics and the continuity index. The color conversion device described in 1.
According to a third aspect of the present invention, the re-creation unit is configured to use the continuity index for the simulated color reproduction characteristic acquired by the second color reproduction characteristic acquisition unit based on the re-created new color conversion coefficient group. Weighting factor setting means for setting the weighting factor by gradually reducing the weighting factor until the continuity index acquired by the acquiring unit satisfies a predetermined continuity condition; and the weight The color reproduction characteristic of the first device is corrected using the weighting factor set by the coefficient setting means, and the color conversion coefficient group is regenerated using the corrected color reproduction characteristic of the first device. The color conversion apparatus according to claim 1, further comprising a coefficient group re-creation unit that performs generation.
According to a fourth aspect of the present invention, the continuity index obtaining unit uses the new color conversion coefficient group when the coefficient group recreating unit of the recreating unit performs the recreation. The continuity index is obtained by performing a calculation process for calculating the continuity index for the color value that depends on the second device obtained by color conversion of the color value that depends on the device, and the re-creation The means further comprises continuity determination means for determining whether or not the continuity index calculated by the continuity index acquisition means satisfies the continuity condition, and the weighting factor setting means of the recreating means The color conversion apparatus according to claim 3, wherein the setting is performed again when the continuity determination unit determines that the continuity condition is not satisfied.
The invention according to claim 5 further includes a color area designating unit that designates a color area in a color space that depends on the second device, which is a target of the calculation process, and the continuity index obtaining unit includes: The color conversion apparatus according to claim 4 , wherein the calculation process is performed for a color area designated by a color area designation unit.
According to a sixth aspect of the present invention, the continuity determination unit of the re-creation unit is predetermined according to a color area in a color space depending on the second device as the continuity condition, 6. The color conversion apparatus according to claim 4, wherein it is determined whether or not a condition for the continuity index is satisfied.
According to a seventh aspect of the present invention, the continuity index acquisition unit performs color conversion on a color value that depends on the first device, using the re-created new color conversion coefficient group as the continuity index. A second derivative value of the color value dependent on the second device obtained in relation to the color value dependent on the first device is obtained, and the weighting factor setting unit of the recreating unit is configured to obtain the continuity index. 7. The setting according to claim 3, wherein the setting is performed so that the second-order differential value acquired by the acquisition unit is equal to or less than a predetermined threshold as the continuity condition. A color conversion device.
The invention according to claim 8 is characterized in that the continuity index acquisition unit acquires the secondary differential value for each color component in a color space depending on the second device, and sets the weighting factor of the re-creation unit. 8. The color conversion apparatus according to claim 7, wherein the unit performs the setting so that the secondary differential value is equal to or less than a predetermined threshold value for each color component.
According to a ninth aspect of the present invention, there is provided a first color reproduction characteristic acquisition means for acquiring a color reproduction characteristic of a printing press, and a color for converting a color value depending on the printing press into a color value depending on the own apparatus. Coefficient group obtaining means for obtaining a conversion coefficient group, and depending on the own apparatus obtained by color-converting a color value dependent on the printing press using the color conversion coefficient group obtained by the coefficient group obtaining means Image forming means for forming an image of a color sample group composed of color values to be read, reading means for reading the color sample group formed by the image forming means, and data of the color sample group read by the reading means Based on this, a second color reproduction that acquires a simulated color reproduction characteristic that is a color reproduction characteristic obtained by simulating the color reproduction characteristic of the printing press acquired by the first color reproduction characteristic acquisition unit by the apparatus itself. Characteristic acquisition means and said second color re- Continuity index acquisition means for acquiring a continuity index, which is an index related to gradation continuity in the simulated color reproduction characteristics acquired by the characteristic acquisition means, and the printing acquired by the first color reproduction characteristic acquisition means and difference information between the acquired simulated color reproduction characteristics by the color reproduction characteristics of the machine and the second color reproduction characteristic obtaining unit, based-out in said continuity index acquired by the continuity index acquisition means, When the continuity index exceeds a predetermined threshold value, the weight coefficient indicating the degree of correcting the color reproduction characteristic of the printing press from the difference information is reduced to correct the color reproduction characteristic of the printing press, An image forming apparatus comprising: a re-creation unit that re-creates the color conversion coefficient group using the corrected color reproduction characteristics of the printing press .
According to a tenth aspect of the present invention, a computer acquires a color reproduction characteristic of a first device, and converts a color value dependent on the first device into a color value dependent on a second device. And a function of acquiring a simulated color reproduction characteristic which is a color reproduction characteristic obtained by simulating the acquired color reproduction characteristic of the first device based on the acquired color conversion coefficient group. A function of acquiring a continuity index, which is an index relating to continuity of gradation in the simulated color reproduction characteristic, and acquisition of difference information between the acquired color reproduction characteristic of the first device and the simulated color reproduction characteristic -out based on the continuity indicators are, to reduce the weighting factor indicating the degree to which the continuity index to correct the color reproduction characteristics of the first device from the difference information when it exceeds a predetermined threshold To correct the color reproduction characteristics of the first device. A color conversion program, characterized in that the using the color reproduction characteristics of the first device realizing a function to recreate the color conversion coefficient set.

According to the first aspect of the present invention, compared with the case where the present configuration is not provided, color conversion using a color conversion coefficient group for performing printing by the second device using the color reproduction characteristics of the first device. In consideration of the continuity of gradation in the color conversion accuracy, the color reproduction accuracy of the color conversion coefficient group can be improved.
According to the second aspect of the present invention, the color reproduction accuracy of the color conversion coefficient group can be further improved as compared with the case where the present configuration is not provided.
According to the third aspect of the present invention, the color reproduction accuracy is improved based on the weighting factor set so that gradation continuity is maintained during color conversion as compared with the case where the present configuration is not provided. A color conversion coefficient group that maintains the continuity of gradation during color conversion can be created.
According to the fourth aspect of the present invention, even when the weighting coefficient for maintaining the continuity of the gradation is not set in the color conversion, the color reproduction accuracy is improved as compared with the case where the present configuration is not provided. While improving, it is possible to create a color conversion coefficient group that maintains the continuity of gradation in color conversion.
According to the invention of claim 5, it is possible to set a weighting coefficient for recreating the color conversion coefficient group according to the color region.
According to the sixth aspect of the present invention, the color reproduction accuracy is improved based on the weighting factor set so that the continuity of the gradation is maintained during the color conversion as compared with the case where the present configuration is not provided. A weighting coefficient for recreating a color conversion coefficient group that maintains gradation continuity during color conversion can be set according to the color region.
According to the invention of claim 7, it is possible to set the weighting coefficient for recreating the color conversion coefficient group so that the continuity of the gradation is maintained at a predetermined level during the color conversion.
According to the eighth aspect of the present invention, it is possible to create a color conversion coefficient group in consideration of the continuity of gradation according to the color component, compared to the case where the present configuration is not provided.
According to the invention of claim 9, compared with the case where the present configuration is not provided, the gradation of the color conversion using the color conversion coefficient group for performing the printing by the color reproduction characteristic of the printing press by the own apparatus is compared. In consideration of continuity, the color reproduction accuracy of the color conversion coefficient group can be improved.
According to the tenth aspect of the present invention, color conversion using a color conversion coefficient group for performing printing by the second device using the color reproduction characteristics of the first device as compared with the case where the present configuration is not provided. In consideration of the continuity of gradation in the color conversion accuracy, the color reproduction accuracy of the color conversion coefficient group can be improved.

It is the block diagram which showed the function structural example of the color conversion apparatus in embodiment of this invention. FIG. 3 is a block diagram illustrating a functional configuration example of a color reproduction characteristic correction unit according to the first embodiment. It is a figure for demonstrating the method in which the color reproduction characteristic correction part corrects the data of the color reproduction characteristic of a printing machine. It is the figure which showed the example of the parameter | index regarding the continuity of a gradation. 5 is a flowchart illustrating an operation example of the color conversion apparatus according to the first embodiment. It is the flowchart which showed the operation example of the weighting coefficient setting process in 1st Embodiment. FIG. 10 is a block diagram illustrating a functional configuration example of a color reproduction characteristic correction unit according to a second embodiment. 10 is a flowchart illustrating an operation example of the color conversion apparatus according to the second embodiment. 10 is a flowchart illustrating an operation example of a color reproduction characteristic correction process according to the second embodiment. 1 is a block diagram illustrating a hardware configuration of a printer and a computer that can implement an embodiment of the present invention.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
In the color printing industry, a proof that simulates the printing color is output using a simple color printer such as an electrophotographic printer or an ink jet printer in the pre-process for creating printed matter with this printing machine, and color proofing is thereby performed. A so-called color proofing system is used. In general, the color reproduction characteristics of the printing machine and color printer differ, so that the color signal that can be reproduced by the printing machine can be reproduced by the color printer by correcting the color signal input to the color printer. It is necessary to keep. Specifically, the color profile color measurement data output by the printing machine and a print profile composed of a combination of the corresponding CMYK data, the color chart color measurement data output by the color printer, and the corresponding device-dependent data A printer profile composed of a combination of (for example, CMYK and RGB) is created, and CMYK data depending on the print color used for color calibration is converted into a device-independent color space such as an XYZ color space or L * a * b by the print profile. * After conversion to the color space, the printer profile is converted to data depending on the color printer. By outputting the device-dependent data converted in this way with a color printer, it is possible to obtain a color calibration sample that is close to the printing color of the printing machine, and it is possible to simulate the printing color using the color printer. Become.

  By the way, when simulating the printing color by such a color printer, for example, due to factors such as a colorimeter error due to the accuracy of the colorimeter for obtaining the colorimetric data and a change with time of the color printer, the printing is performed. There may be an error in color reproduction between the printing color in the printing result of this machine and the printing color in the printing result of the color printer. For this reason, the color proof system measures the error in color reproduction using the color chart for creating the print profile, and recreates the print profile using the measured difference, so that the error in color reproduction Is reduced.

  However, if the print profile is recreated so as to improve the color reproduction accuracy, color discontinuity may occur in a color region in which gradation deterioration such as a pure color is easily noticeable. For example, if the colorimetric error included in the colorimetric data or the error in printer aging is large, or if the color reproduction characteristics of the printing machine and printer are significantly different, recreating the profile will produce color reproduction accuracy. However, the gradation may be deteriorated.

  Therefore, the color conversion apparatus according to the embodiment of the present invention is a device link profile that converts color data depending on a printing press (an example of a first device) into color data depending on a printer (an example of a second device). When performing the process of re-creating an error in color reproduction by feeding back to the color reproduction characteristic data of the printing press (hereinafter referred to as “feedback process”), this re-creation is performed with continuous gradation of color reproduction characteristics. Based on gender indicators.

<First Embodiment>
The color conversion apparatus 10 according to the first embodiment of the present invention uses a weight coefficient used when correcting a color value of a printing press for recreating a device link profile as a continuous tone before a feedback process. This is set in advance based on an index related to sex, and the feedback processing is performed using the weighting coefficient.

  FIG. 1 is a block diagram illustrating a functional configuration example of a color conversion apparatus 10 according to the present embodiment. As shown in the figure, the color conversion apparatus 10 according to the present embodiment includes a printing press color reproduction characteristic acquisition unit 11, a printer color reproduction characteristic acquisition unit 12, a device link profile creation unit 14, and a device link color conversion unit 15. , An image output unit 16, a colorimetric unit 17, an error determination unit 18, and a color reproduction characteristic correction unit 20.

  The printing press color reproduction characteristic acquisition unit 11 is data representing the relationship between the input color value to the printing press and the color value of the device-independent color space that represents the output color of the printing press according to the input color value. Get color reproduction characteristics. For example, CMYK data is used as the input color value, and L * a * b * data is used as the color value in the device-independent color space. In the present embodiment, a printing press color reproduction characteristic acquisition unit 11 is provided as an example of the first color reproduction characteristic acquisition unit.

  The printer color reproduction characteristic acquisition unit 12 obtains the color reproduction characteristic of the printer, which is data representing the relationship between the input color value to the printer and the color value of the device-independent color space representing the output color of the printer according to the input color value. get. For example, CMYK data is used as the input color value, and L * a * b * data is used as the color value in the device-independent color space. In the present embodiment, a printer color reproduction characteristic acquisition unit 12 is provided as an example of the third color reproduction characteristic acquisition unit.

  The device link profile creation unit 14 is based on the printing machine color reproduction characteristics acquired by the printing machine color reproduction characteristics acquisition unit 11 and the printer color reproduction characteristics acquired by the printer color reproduction characteristics acquisition unit 12. Create a device link profile for simulating color reproduction characteristics with a printer. That is, the device link profile creating unit 14 creates a device link profile for converting color data depending on the printing press into color data depending on the printer. For example, the technology disclosed in Japanese Patent Application Laid-Open No. 2002-152543 may be used to create a device link profile. In this embodiment, a device link profile is used as an example of a color conversion coefficient group.

  The device link color conversion unit 15 performs color conversion for simulating the color reproduction characteristics of the printing press with a printer. That is, the device link color conversion unit 15 uses the device link profile created by the device link profile creation unit 14 to convert the color data of the color image from color data depending on the printing press to color data depending on the printer. . As color data of a color image, for example, color data created by changing each of C, M, Y, and K in the range of 0 to 100 may be used.

  The image output unit 16 causes the printer to output the color data of the color image color-converted by the device link color conversion unit 15.

  The color measurement unit 17 measures the color image output from the printer, and acquires the color value of the device-independent color space as the color measurement value. If the color data of the color image is color data created by changing C, M, Y, and K, the colorimetric unit 17 uses the CMYK data that is the color data as the color value of the device-independent color space. For example, L * a * b * data is acquired. The color measurement unit 17 may perform color measurement according to an operation of the user sliding the colorimeter on the color image, or is provided in the printer, and the color image output from the printer is not manually input. It may be an inline scanner for reading.

  In the present embodiment, as an example of the simulated color reproduction characteristics obtained by simulating the color reproduction characteristics of the first device by the second device, the color data of the color image color-converted by the device link color conversion unit 15 And data representing the relationship between the color values of the device-independent color space acquired by the color measurement unit 17. As an example of the second color reproduction characteristic acquisition unit, a printer color reproduction characteristic acquisition unit 12, a device link profile creation unit 14, a device link color conversion unit 15, an image output unit 16, and a color measurement unit 17 are provided.

  As will be described later with reference to FIG. 3, the error determination unit 18 determines the color value (for example, L * a * b * data) of the device-independent color space in the color reproduction characteristics of the printing press corresponding to the color data of the color image. Calculating an actual measurement error with a color value (for example, L * a * b * data) of a device-independent color space obtained by measuring the color data of the color image output from the printer by the color measurement unit 17; It is determined whether the device link profile creation by the device link profile creation unit 14 is repeated or finished. As a determination method, for example, a method of calculating an average value of color differences as an actual measurement error for color data of a plurality of color images, and determining whether the user recreates a device link profile by looking at the average value or ends the device link profile. Is used. Alternatively, a method may be used in which the device link profile is recreated when the average value of color differences is 3 or more, and the creation is terminated when the average value is less than 3. However, the evaluation value used for the determination is not limited to the average value, and may be a maximum value, RMS (Root Mean Square), 95th percentile, or the like.

When the error determination unit 18 determines that the device link profile is to be re-created, the color reproduction characteristic correction unit 20 determines the level in the color data of the color image color-converted by the device link color conversion unit 15 as described later. Based on the index of tone continuity, the color value (for example, L * a * b * data) of the device-independent color space of the printing press is corrected using a preset weighting factor, and the device link profile is recreated To do.
Then, the device link color conversion unit 15 performs color conversion for simulating the color reproduction characteristics of the printing press with a printer, using the recreated device link profile. In this way, the creation of the device link profile is repeated until the end of the error determination unit 18 is determined. In the present embodiment, a color reproduction characteristic correcting unit 20 is provided as an example of a recreating unit.

  The above functions can be realized only by hardware, but can also be realized by a combination of hardware and software. In the latter case, the functions from the printing press color reproduction characteristic acquisition unit 11 to the color reproduction characteristic correction unit 20 are executed by a CPU (not shown) of the color conversion device, for example, by reading a program stored in a memory (not shown). It is realized by.

  In the present embodiment, color image data color-converted using the device link profile is output by a printer, and the output color image is measured to obtain device-independent color data. . However, the method for simulating the color reproduction characteristics of a printing press with a printer is not limited to this. For example, color image data that has been color-converted using a device link profile is further color-converted to device-independent color data using a model that expresses the color reproduction characteristics of the printer, thereby simulating without performing colorimetry. You may take the method.

Hereinafter, first, the color reproduction characteristic correcting unit 20 will be described in detail.
FIG. 2 is a block diagram illustrating a functional configuration example of the color reproduction characteristic correcting unit 20 according to the first embodiment. As shown in the figure, the color reproduction characteristic correcting unit 20 of the first embodiment includes a continuity index calculating unit 21, a weighting factor setting unit 22, a printing press characteristic correcting unit 23, and a device link profile recreating unit 24. Is provided.

  The continuity index calculating unit 21 calculates in advance an index relating to continuity of gradations (hereinafter referred to as “continuity index”) when the color reproduction characteristics of the printing press are simulated by a printer. That is, the continuity index calculation unit 21 uses, for example, a temporarily set weighting coefficient before performing feedback processing for improving the color reproduction accuracy, so that the data of the color reproduction characteristics of the printing press as described later is used. Modify and recreate the device link profile. Then, a continuity index as shown in FIG. 4 to be described later is calculated for a color value (for example, CMYK data) after color conversion using the obtained device link profile. In the present embodiment, a continuity index calculation unit 21 is provided as an example of a continuity index acquisition unit.

  The weighting factor setting unit 22 determines the weighting factor used when correcting the color value of the printing press for re-creating the device link profile according to the continuity index calculated by the continuity index calculating unit 21. It is set in advance before the feedback process for improving the reproduction accuracy is performed. For example, the weighting coefficient setting unit 22 sets the weighting coefficient to be small when the continuity index indicates poor gradation continuity with reference to a predetermined threshold. Here, poor gradation continuity indicates a state in which a gradation jump in which gradation does not continuously change occurs. A specific method for setting the weighting coefficient will be described later. In the present embodiment, a weighting factor setting unit 22 is provided as an example of a weighting factor setting unit.

  The printing press characteristic correcting unit 23 is a device independent color of the printing press for re-creating a device link profile based on the weighting factor set by the weighting factor setting unit 22 and the actual measurement error calculated by the error determination unit 18. The color value of the space (for example, L * a * b * data) is corrected. This specific correction method will be described later with reference to FIG.

  The device link profile re-creation unit 24 is based on the device color reproduction characteristics corrected by the printing machine characteristic correction unit 23 and the printer color reproduction characteristic data acquired by the printer color reproduction characteristic acquisition unit 12. Recreate the profile. Similar to the device link profile creation unit 14, this recreation may be performed using, for example, the technique disclosed in Japanese Patent Application Laid-Open No. 2002-152543. In the present embodiment, as an example of a coefficient group recreating unit, a printing press characteristic correcting unit 23 and a device link profile recreating unit 24 are provided.

Next, a method for correcting the color reproduction characteristic data of the printing press by the color reproduction characteristic correction unit 20 will be described.
FIG. 3 is a diagram for explaining a method in which the color reproduction characteristic correcting unit 20 corrects data of color reproduction characteristics of the printing press. FIG. 3A shows the relationship between the data used in correcting the color reproduction characteristic data of the printing press, and FIG. 3B shows how to obtain the corrected color reproduction characteristic data of the printing press. The calculation formula is shown. Here, the processing when the (i + 1) -th correction is performed on the L * a * b * data of the printing press used for creating the device link profile will be described (i = 0, 1, 2,...). In the following description, device-dependent color values are described as CMYK data, and device-independent color space color values are described as L * a * b * data.

  As shown in FIG. 3A, first, print L * a * b * data 52 is obtained by color-converting print CMYK data 51 that is a color value depending on the printing press. As the print L * a * b * data 52, if the color reproduction characteristic acquired by the printing press color reproduction characteristic acquisition unit 11 includes the color measurement value itself, the color measurement value may be adopted. If the color reproduction characteristic is an ICC (International Color Consortium) profile, a value corresponding to a colorimetric value obtained by using the profile may be adopted.

The print CMYK data 51 is converted by the device link color conversion unit 15 into printer CMYK data 53 that is a color value depending on the printer, using the device link profile. Then, printer L * a * b * data 54 is obtained by color-converting the printer CMYK data 53. In this embodiment, the printer L * a * b * data 54 is acquired by causing the image output unit 16 to output the printer CMYK data 53 to the printer, and the colorimetric unit 17 to measure the color of the output color image. Is done.
Then, the error determination unit 18 calculates ΔL * a * b * 56 (that is, L *, a *, L * a * b * data 52 and printer L * a * b * data 54). error of each component of b *) is calculated.

  When the error determination unit 18 determines that the device link profile is to be recreated, the color reproduction characteristic correction unit 20 uses this ΔL * a * b * 56 to print the print L * for regenerating the device link profile. Correct the a * b * data. Specifically, data obtained by multiplying the L * a * b * data 55 before the i-th correction by the weighting coefficient α set by the weighting coefficient setting unit 22 and the actual measurement error ΔL * a * b * 56. Is subtracted, the (i + 1) -th corrected L * a * b * data 57 is obtained.

Referring to FIG. 3B, a calculation formula for obtaining corrected L * a * b * data 57 which is L * a * b * data of a printing press corrected for recreating a device link profile Further explanation will be given. Here, the three-dimensional vector of (L *, a *, b *) is expressed as Lab. The printing L * a * b * data 52 that is L * a * b * data in the color reproduction characteristics of the printing press acquired by the printing press color reproduction characteristics acquisition unit 11 is expressed as Lab _Target . Also, L * a * b * data (L * a * b * data 55 before the (i + 1) th correction) obtained at the i-th correction is denoted as Lab _i, and at the i-th correction. The L * a * b * data obtained by the color measurement unit 17 _{measuring the color image} is denoted as Lab _{i-th color measurement} . Then, Lab _{i + 1} which is L * a * b * data (Li * a * b * data 57 after (i + 1) -th correction) after the color reproduction characteristic correction unit 20 performs (i + 1) -th correction is , Given by the equation shown in FIG.

  The weighting coefficient α may be set to the same value for the entire color area. Alternatively, different values may be set for each color region, and the color reproduction accuracy or the gradation degree weight may be controlled for each color region. In addition, since the actual measurement error is large in the area outside the printer color gamut, it is preferable not to modify the L * a * b * data.

Next, the continuity index calculated by the continuity index calculation unit 21 will be described.
FIG. 4 is a diagram showing an example of an index relating to gradation continuity.
FIG. 4A is a diagram illustrating a relationship between an input value and an output value when color conversion is performed using the device link profile for magenta (M) gradation. That is, in FIG. 4A, the input value is changed from (C, M, Y, K) = (0, 0, 0, 0) to (C, M, Y, K) = (0, 100, 0, 0). ) Shows the relationship between the input value and the output value. The upper part of FIG. 4A shows the relationship of the output magenta (M) value to the input magenta (M) value, and the lower part shows the relationship of the output cyan (C) value to the input magenta (M) value. In this example, the target printer and the simulated printer have different magenta color reproduction characteristics. As shown in the lower part of FIG. 4A, the printer matches the magenta color of the printer. On the side, not only magenta but also cyan is mixed by several percent.

  The broken lines in the upper and lower stages of FIG. 4A are the conversion results by the device link profile before re-creation, and the solid lines are by the device link profile after re-creation with the above weighting factor α being 1. It is a conversion result. The same applies to FIG. 4B described below. The broken line corresponds to the conversion result by the device link profile when re-creation is performed with the weighting factor α set to 0.

  When the gradation characteristics before and after re-creation are confirmed with respect to FIG. 4A, the input M value is around 80 for magenta, and the input M value is around 20 and 60 for cyan. It can be seen that a gradation jump in which the gradation has changed greatly has occurred. When such an output value is actually output by a printer, the gradation jump is more noticeable after re-creation. The color reproduction accuracy is better after re-creation, but in a color region where deterioration in gradation is conspicuous such as a pure color, the deterioration in gradation is more conspicuous than the degree of color matching.

  FIG. 4B is a diagram illustrating the relationship between the input value and the output value in FIG. 4A, the secondary differential value of the output value with respect to the input value (difference in the difference value for each input gradation). Similar to FIG. 4A, the upper part of FIG. 4B shows the relationship between the input M value and the second derivative value of the output M value, and the lower part shows the relationship between the input M value and the second derivative value of the output C value. ing. As can be seen from FIG. 4 (B), both the second derivative value of the output M value in the upper stage and the second derivative value of the output C value in the lower stage have a displacement after re-creation than before re-creation. (In particular, the secondary differential value of the output M value near the input M value of 80, the secondary differential value of the output C value near the input M value of 20, 60, etc.) I can read that In particular, the degree of gradation deterioration in the curve in FIG. 4A is quantified by obtaining the second derivative value of the output value.

  The continuity index calculation unit 21 calculates, for example, a second derivative value of the output value shown in FIG. 4B, and uses an average value or RMS value of these absolute values as a continuity that is an index related to gradation continuity. It is a sex indicator. Thus, before the feedback process for improving the color reproduction accuracy is performed, the continuity index calculating unit 21 quantifies the degree of deterioration of the gradation and the continuity obtained by the weight coefficient setting unit 22 is obtained. A weighting factor α is set based on the index.

  Note that the continuity index calculation method is not limited to the method described above for device-dependent color values after color conversion using the device link profile. For example, using the weight coefficient α that has been temporarily set, the color conversion characteristics data of the printing press is corrected and the device link profile is recreated, and the color chart that can determine the continuity of gradation is converted using this device link profile. Then, the continuity index may be calculated by outputting to a printer and visually determining whether the output result is continuous or not. Also, the output result of the printer is read by a scanner or the like, the read data (for example, RGB values) is converted into a device-independent L * a * b * value, and an index relating to continuity with respect to the L * a * b * value May be calculated.

Next, a method for setting the weighting factor α by the weighting factor setting unit 22 will be described.
The weighting coefficient setting unit 22 sets the weighting coefficient α in advance according to the continuity index calculated by the continuity index calculating unit 21 by the calculation method as described above. At this time, the weighting factor setting unit 22 sets the weighting factor α to be small when the continuity index indicates that the continuity of the gradation is poor with reference to a predetermined threshold.

  This will be described by taking as an example the case where the maximum value of the absolute value is used as the continuity index for the secondary differential value of the output value shown in FIG. Before re-creation of the device link profile (when α = 0) (broken line in FIG. 4B), continuity is good, and after re-creation (when α = 1) (solid line in FIG. 4B), continuous. In light of the poor nature, for example, magenta is set to 0.05 and cyan is set to 0.03 as the threshold value of the continuity index, and the weighting factor setting unit 22 sets the maximum absolute value of the difference to this threshold value. When it exceeds, it shall be judged that continuity is bad. In the example of FIG. 4B, after re-creation (when α = 1), the maximum absolute value of the secondary differential value of the output M value and the secondary differential value of the output C value both exceed the threshold value. Therefore, the weighting factor setting unit 22 changes the weighting factor α from a current setting value α = 1 to a small value such as α = 0.5.

When the weighting factor α is reduced, the correction amount when correcting the color value of the printing press is reduced, so that the effect of improving the color reproduction accuracy is reduced, but the tone is improved. In particular, it is desirable to set the weighting coefficient α to be small for a color region such as a pure color where deterioration of gradation is conspicuous.
When the continuity index is equal to or less than a predetermined threshold value, the weight coefficient α may be set larger than the current set value.

Next, the operation of the color conversion apparatus 10 in the present embodiment will be described.
FIG. 5 is a flowchart illustrating an operation example of the color conversion apparatus 10 according to the first embodiment. FIG. 6 is a flowchart showing an operation example of the weighting factor setting process in the first embodiment.
As shown in FIG. 5, in the color conversion apparatus 10, first, the printing press color reproduction characteristic acquisition unit 11 acquires the color reproduction characteristic of the printing press, and the printer color reproduction characteristic acquisition unit 12 acquires the color reproduction characteristic of the printer. (Step 101). Then, before starting the feedback process, the weight coefficient setting unit 22 performs a process for setting the weight coefficient α (step 102).

  With reference to FIG. 6, the weighting coefficient setting process in step 102 will be described. First, the device link profile creation unit 14 selects a device based on the color reproduction characteristics of the printing press acquired by the printing press color reproduction characteristic acquisition unit 11 and the printer color reproduction characteristics acquired by the printer color reproduction characteristic acquisition unit 12. A link profile is created (step 121). Then, the weighting factor setting unit 22 temporarily sets the weighting factor α to α = 1, for example (step 122). Next, the printing press characteristic correcting unit 23 corrects the color reproduction characteristic data of the printing press using the weighting coefficient α, and the device link profile re-creating unit 24 re-creates the device link profile (step 123). Subsequently, using the re-created device link profile, the device link color conversion unit 15 converts the color data depending on the printing press into color data depending on the printer (step 124). Then, the continuity index calculating unit 21 calculates a continuity index for the color data depending on the printer after color conversion (step 125).

  If the calculated continuity index is less than or equal to a predetermined threshold (No in step 126), the weighting factor setting process ends. On the other hand, if the calculated continuity index exceeds a predetermined threshold value (Yes in step 126), the weighting factor setting unit 22 sets the weighting factor α to a value reduced by a predetermined amount ( Step 127), the process returns to Step 123. In this way, the weighting factor α is set so that the continuity index is equal to or less than a predetermined threshold.

  The continuity index calculating unit 21 calculates a continuity index by designating a color area. Specifically, after the weighting factor setting unit 22 temporarily sets α = 1 as the weighting factor of the entire color area in step 122, the continuity index calculating unit 21 specifies the pure color area in step 125, and the continuity index is set. Is calculated. In step 126, correction is determined based on a predetermined threshold value for each color component in the pure color area. When correcting the weighting factor α, in step 127, the weighting factor setting unit 22 sets the weighting factor α corresponding to the pure color region to a value that is reduced by a predetermined amount.

Subsequently, feedback processing for improving color reproduction accuracy is performed using the set weight coefficient α.
Returning to FIG. 5, the device link profile creation unit 14 converts the printer color reproduction characteristics acquired by the printing machine color reproduction characteristic acquisition unit 11 and the printer color reproduction characteristics acquired by the printer color reproduction characteristic acquisition unit 12. Based on this, a device link profile is created (step 103). After that, the device link color conversion unit 15 converts the color data of the color image from the color data depending on the printing machine to the color data depending on the printer by using the created device link profile (step 104). Then, the image output unit 16 outputs the color data of the color image converted into the color data depending on the printer with the printer (step 105). The color measurement unit 17 measures the color data of the output color image and obtains a color measurement value (step 106).

  Then, the error determination unit 18 compares the color value of the device-independent color space obtained from the color reproduction characteristics of the printing press with the colorimetric value obtained in step 106, and calculates the error (step 107). . Then, the error determination unit 18 determines whether to recreate or end the device link profile based on, for example, a determination made by the user looking at the calculated error (step 108). As a result, if it is determined that the device link profile is to be recreated (Yes in step 108), the color reproduction characteristic correcting unit 20 corrects the data of the color reproduction characteristic of the printer for regenerating the device link profile ( Step 109), returning to Step 103, the device link profile is recreated. On the other hand, if it is determined in step 108 that the device link profile is not recreated (No in step 108), the color conversion apparatus 10 ends the operation.

<Second Embodiment>
Below, the color conversion apparatus 10 in the 2nd Embodiment of this invention is demonstrated. However, the same reference numerals are used for the same functions as those in the first embodiment, and detailed descriptions thereof are omitted.
The color conversion apparatus 10 according to the second embodiment calculates a continuity index using the device link profile recreated in the feedback process, and sets the weighting coefficient α based on the calculated continuity index. Is. The functional configuration of the color conversion apparatus 10 of the second embodiment is the same as that of the first embodiment, but the internal configuration of the color reproduction characteristic correction unit 20 is different.

FIG. 7 is a block diagram illustrating a functional configuration example of the color reproduction characteristic correction unit 20 according to the second embodiment. As shown in the drawing, the color reproduction characteristic correction unit 20 of the second embodiment includes a weighting factor setting unit 22, a printing press characteristic correction unit 23, a device link profile re-creation unit 24, and a device link color conversion unit 25. , A color area specifying unit 26, a continuity index calculating unit 27, and a correction determining unit 28.
Among these, the printing press characteristic correction unit 23 and the device link profile re-creation unit 24 are the same as those in the first embodiment, and thus the description thereof is omitted.

  The weighting factor setting unit 22 first temporarily sets the weighting factor α. In this case, for example, the weighting coefficient α for the entire color area may be a constant value. When the correction determination unit 28 determines that the predetermined condition for continuity is not satisfied and the device link profile is to be recreated, the weight coefficient α is reset.

  The device link color conversion unit 25 uses the device link profile created by the device link profile re-creation unit 24 to convert the color data of the color image from color data depending on the printing press to color data depending on the printer.

  The color area designating unit 26 designates a color area in which the continuity index calculating unit 27 calculates the continuity index. As the color area, the entire color area may be designated, or a specific color area such as a pure color may be designated. In the following, a description will be given of a case where a pure color color region in which deterioration in gradation is conspicuous is designated. In the present embodiment, a color area specifying unit 26 is provided as an example of the color area specifying means.

  The continuity index calculation unit 27 calculates a continuity index, which is an index related to gradation continuity, for the color region specified by the color region specification unit 26, as in the continuity index calculation unit 21 of the first embodiment. To do. For example, when the color area designation unit 26 designates pure magenta, the continuity index as shown in the above-described example of FIG. 4 is calculated. In the present embodiment, a continuity index calculation unit 27 is provided as an example of a continuity index acquisition unit.

The correction determination unit 28 determines whether or not the continuity index calculated by the continuity index calculation unit 27 satisfies a predetermined continuity condition. In other words, when the continuity index does not satisfy a predetermined continuity condition, the correction determination unit 28 determines to recreate a device link profile in order to improve gradation continuity. On the other hand, when the continuity index satisfies a predetermined continuity condition, it is determined that the continuity of gradation is good, and the processing of the color reproduction characteristic correcting unit 20 is ended. For example, the correction determination unit 28 sets a threshold for the continuity index, re-creates the device link profile when the continuity index exceeds the threshold, and ends the process of the color reproduction characteristic correction unit 20 when the continuity index is less than the threshold. Judge that.
If the correction determination unit 28 determines that the device link profile is to be recreated, the weighting factor setting unit 22 changes the weighting factor α from the temporary setting value (sets it smaller than the temporary setting value), and the printing described above. The processing by the machine characteristic correction unit 23 to the correction determination unit 28 is repeated. In the present embodiment, a correction determination unit 28 is provided as an example of continuity determination means.

Next, the operation of the color conversion apparatus 10 in the present embodiment will be described.
FIG. 8 is a flowchart illustrating an operation example of the color conversion apparatus 10 according to the second embodiment. FIG. 9 is a flowchart showing an operation example of the color reproduction characteristic correction processing in the second embodiment.
As shown in FIG. 8, in the color conversion apparatus 10, first, the printing press color reproduction characteristic acquisition unit 11 acquires the color reproduction characteristic of the printing press, and the printer color reproduction characteristic acquisition unit 12 acquires the color reproduction characteristic of the printer. (Step 201). The device link profile creation unit 14 is based on the printer color reproduction characteristics acquired by the printing machine color reproduction characteristic acquisition unit 11 and the printer color reproduction characteristics acquired by the printer color reproduction characteristic acquisition unit 12. Is created (step 202). After that, the device link color conversion unit 15 converts the color data of the color image from the color data depending on the printing machine to the color data depending on the printer by using the created device link profile (step 203). Then, the image output unit 16 outputs the color data of the color image converted into the color data depending on the printer (step 204). The color measurement unit 17 measures the color data of the output color image and acquires a color measurement value (step 205).

  Then, the error determination unit 18 compares the color value of the device-independent color space obtained from the color reproduction characteristics of the printing press with the colorimetric value obtained in step 205, and calculates the error (step 206). . Then, the error determination unit 18 determines whether to recreate the device link profile or to end the process based on, for example, a determination made by viewing the error calculated by the user (step 207). As a result, if it is determined that the device link profile is to be recreated (Yes in Step 207), the color reproduction characteristic correcting unit 20 performs the color reproduction characteristic correcting process shown in FIG. 9 (Step 208), and Step 203 is performed. Return to. On the other hand, if it is determined in step 207 that the device link profile is not recreated (No in step 207), the color conversion apparatus 10 ends the operation.

  Next, the color reproduction characteristic correction process in step 208 will be described with reference to FIG. First, the weight coefficient setting unit 22 temporarily sets the weight coefficient α to α = 1, for example (step 221). Then, the printing press characteristic correcting unit 23 corrects the color reproduction characteristic data of the printing press using the weighting coefficient α (step 222), and the device link profile re-creating unit 24 re-creates the device link profile (step 223). ). Subsequently, using the re-created device link profile, the device link color conversion unit 25 converts the color data depending on the printing press into color data depending on the printer (step 224). Here, the color area designating unit 26 designates a color area in which the continuity index calculating unit 27 calculates the continuity index (step 225). In the designated color area, the continuity index calculating unit 27 performs step 224. A continuity index is calculated for the printer-dependent color data obtained in (2).

Subsequently, the correction determination unit 28 determines whether or not the continuity index calculated by the continuity index calculation unit 27 exceeds a predetermined threshold (step 227). If the calculated continuity index is less than or equal to a predetermined threshold value (No in step 227), the correction determination unit 28 determines that the continuity of the gradation is good, and the color reproduction characteristic correction process ends. Returning to step 203 of FIG. On the other hand, if the calculated continuity index exceeds a predetermined threshold (Yes in Step 227), the weighting factor setting unit 22 sets the weighting factor α to a value that is reduced by a predetermined amount (Step S227). 228). In this manner, the setting of the weighting factor α, the correction of the color reproduction characteristics of the printing press, and the recreation of the device link profile are repeated until it is determined in step 227 that the continuity index is equal to or less than a predetermined threshold value. .
This is the end of the description of the operation of the color conversion apparatus 10.

  Note that the correction determination unit 28 may perform determination using a different continuity condition for each color region. That is, the threshold when the correction determination unit 28 determines continuity may be different for each color region. In this case, for example, it is desirable to set the weighting coefficient α to be smaller for a color region such as a pure color where deterioration of gradation is conspicuous, so the threshold for determining continuity is set smaller than other color regions. It is possible to do. Further, the threshold value may be different for each color component.

The color area designated by the color area designating unit 26 is not limited to a pure color gradation such as a primary color or a secondary color, but is, for example, three-dimensional, in which gradation continuously changes in a CMYK color space. It may be a four-dimensional area.
In addition, the color reproduction characteristic correcting unit 20 of the first embodiment may include a color area specifying unit 26. That is, the color area for which the continuity index calculating unit 21 calculates the continuity index is not limited to the entire color space, and may be a specific color area specified by the color area specifying unit 26.

  By the way, in the present embodiment, the hardware for performing color conversion is not particularly limited. However, for example, it may be realized in a computer such as a personal computer or in an image processing unit of the image forming apparatus. You may make it do. Hereinafter, a hardware configuration of the printer 80 as an example of such an image forming apparatus and a hardware configuration of the computer 90 will be described.

FIG. 10 is a block diagram showing a hardware configuration of the printer 80 and the computer 90 that can realize the present embodiment. FIG. 10A shows an outline of the hardware configuration of a printer 80 to which the color conversion apparatus 10 of the present embodiment is applied.
As shown in the figure, the printer 80 includes a main control unit 81 that performs operation control of the entire printer 80, communication with a personal computer (PC), for example, image processing performed on the image data, and a sheet based on the image data. Data is transmitted and received between an image forming unit 82 that forms an image on the image, an image reading unit 83 that reads an image on a sheet for adjusting an image formed on the sheet by the image forming unit 82, and an external device. And a user interface 85 for receiving an operation input from the user and displaying various information for the user.

  The main control unit 81 creates a device link profile for color-converting color data depending on the printing press into color data depending on the self-apparatus according to the above-described procedure, and color data of the color image to be color-converted (for example, CMYK data) and color reproduction characteristics (an example of simulated color reproduction characteristics) that associate color data (for example, L * a * b * data) read by the image reading unit 83 are acquired. Further, the main control unit 81 calculates a continuity index from the color data read by the image reading unit 83, and re-creates a device link profile. In the present embodiment, the main control unit 81 is provided as an example of a coefficient group acquisition unit, a second color reproduction characteristic acquisition unit, a continuity index acquisition unit, and a re-creation unit.

The image forming unit 82 transfers the image on the paper by, for example, an electrophotographic method in which the toner attached to the photoconductor is transferred to a recording medium to form an image, or an ink jet method in which ink is ejected onto the recording medium to form an image. Form. The image forming unit 82 forms a color image (an example of a color sample group) for calculating an actual measurement error, which is obtained by performing color conversion using a device link profile. As the color data to be color-converted, for example, color data created by changing C, M, Y, K in the range of 0 to 100 is used. Further, a color image for reading gradation continuity may be formed. In the present embodiment, an image forming unit 82 is provided as an example of an image forming unit.
The image reading unit 83 is provided downstream of the image forming unit 82 in the paper transport direction. The image reading unit 83 reads and measures a color image formed on the conveyed paper, and acquires, for example, L * a * b * data. In the present embodiment, an image reading unit 83 is provided as an example of a reading unit.
The communication interface 84 acquires the color reproduction characteristics of the printing press from an external device, for example. In the present embodiment, a communication interface 84 is provided as an example of the first color reproduction characteristic acquisition unit.

FIG. 10B shows a hardware configuration of a computer 90 capable of realizing this embodiment.
As shown in the figure, the computer 90 includes a CPU (Central Processing Unit) 91 as a calculation means, a main memory 92 as a storage means, and a magnetic disk device (HDD: Hard Disk Drive) 93. Here, the CPU 91 executes various types of software such as an OS (Operating System) and applications to realize the above-described functions. The main memory 92 is a storage area for storing various software and data used for execution thereof, and the magnetic disk device 93 is a storage area for storing input data for various software, output data from various software, and the like. .
Further, the computer 90 includes a communication interface 94 for performing communication with the outside, a display mechanism 95 including a video memory and a display, and an input device 96 such as a keyboard and a mouse.

  It should be noted that the program for realizing the present embodiment may be provided by being stored in a recording medium such as a CD-ROM, as well as provided by communication means.

DESCRIPTION OF SYMBOLS 10 ... Color conversion apparatus, 11 ... Printing machine color reproduction characteristic acquisition part, 12 ... Printer color reproduction characteristic acquisition part, 14 ... Device link profile creation part, 15 ... Device link color conversion part, 16 ... Image output part, 17 ... Measurement Color part 18 ... Error determination part 20 ... Color reproduction characteristic correction part 21 ... Continuity index calculation part 22 ... Weight coefficient setting part 23 ... Printing press characteristic correction part 24 ... Device link profile re-creation part 25 ... device link color conversion unit, 26 ... color area designation unit, 27 ... continuity index calculation unit, 28 ... correction determination unit

Claims (10)

First color reproduction characteristic acquisition means for acquiring color reproduction characteristics of the first device;
The first device acquired by the first color reproduction characteristic acquisition unit based on a color conversion coefficient group for converting a color value dependent on the first device into a color value dependent on the second device. Second color reproduction characteristic acquisition means for acquiring a simulated color reproduction characteristic which is a color reproduction characteristic obtained by simulating the color reproduction characteristic of the second device;
Continuity index acquisition means for acquiring a continuity index that is an index relating to continuity of gradation in the simulated color reproduction characteristics acquired by the second color reproduction characteristics acquisition means;
Difference information between the color reproduction characteristic of the first device acquired by the first color reproduction characteristic acquisition unit and the simulated color reproduction characteristic acquired by the second color reproduction characteristic acquisition unit, and the continuity -out based on said continuity index acquired by the index acquiring means, the extent to which the continuity index to correct the color reproduction characteristics of the first device from the difference information when it exceeds a predetermined threshold Recreating means for modifying the color reproduction characteristics of the first device by reducing the weighting coefficient to be represented, and recreating the color conversion coefficient group using the corrected color reproduction characteristics of the first device ; A color conversion device comprising: The first color reproduction characteristic acquisition unit and the third color reproduction characteristic acquisition unit that acquires the color reproduction characteristic of the second device respectively include an input color value to the device and the input color value as the color reproduction characteristic. The correspondence relationship with the color value in the device-independent color space representing the output color from the device according to the
The re-creating means is configured to use the color conversion coefficient based on difference information regarding color values in the device-independent color space between the color reproduction characteristics of the first device and the simulated color reproduction properties, and the continuity index. The color conversion apparatus according to claim 1, wherein the group is recreated. The recreating means includes
The continuity index acquired by the continuity index acquisition unit is predetermined for the simulated color reproduction characteristic acquired by the second color reproduction characteristic acquisition unit based on the re-created new color conversion coefficient group. Weighting factor setting means for setting the weighting factor by gradually reducing the weighting factor until the condition of the sex is satisfied,
The color reproduction characteristic of the first device is corrected using the weighting factor set by the weighting factor setting means, and the color conversion coefficient group is corrected using the corrected color reproduction characteristic of the first device. The color conversion apparatus according to claim 1, further comprising a coefficient group re-creating unit that re-creates the image data. The continuity index acquisition means uses a new color conversion coefficient group when the coefficient group re-creation means of the re-creation means performs the re-creation, and changes the color value depending on the first device to a color For the color value dependent on the second device obtained by conversion, the continuity index is obtained by performing a calculation process for calculating the continuity index,
The re-creation unit further includes a continuity determination unit that determines whether the continuity index calculated by the continuity index acquisition unit satisfies the continuity condition,
The color conversion according to claim 3, wherein the weighting factor setting unit of the re-creation unit performs the setting again when the continuity determination unit determines that the continuity condition is not satisfied. apparatus. A color area designating unit for designating a color area in a color space depending on the second device, which is a target of the calculation process;
The color conversion apparatus according to claim 4 , wherein the continuity index acquisition unit performs the calculation process for a color region designated by the color region designation unit. Whether the continuity determination unit of the re-creation unit satisfies a condition for the continuity index that is predetermined according to a color region in a color space that depends on the second device as the continuity condition. The color conversion apparatus according to claim 4, wherein it is determined whether or not. The continuity index acquisition means uses, as the continuity index, the second device obtained by color-converting a color value dependent on the first device using a newly created color conversion coefficient group. Obtaining a second derivative of the color value depending on the color value depending on the first device;
The weight coefficient setting unit of the re-creation unit performs the setting so that the secondary differential value acquired by the continuity index acquisition unit is equal to or less than a predetermined threshold as the continuity condition. The color conversion device according to claim 3, wherein the color conversion device is a color conversion device. The continuity index acquisition means acquires the second derivative values for each color component in a color space which depends on the second device,
The weight coefficient setting unit of the re-creation unit performs the setting so that the secondary differential value is equal to or less than a predetermined threshold value for each color component. Color conversion device. First color reproduction characteristic acquisition means for acquiring color reproduction characteristics of a printing press;
Coefficient group acquisition means for acquiring a color conversion coefficient group for converting the color value depending on the printing press into a color value depending on the device;
Forms an image of a color sample group consisting of color values depending on the printer, obtained by color-converting color values depending on the printing press using the color conversion coefficient group acquired by the coefficient group acquisition means. Image forming means for
Reading means for reading the color sample group formed by the image forming means;
Based on the data of the color sample group read by the reading unit, the color reproduction characteristic obtained by simulating the color reproduction characteristic of the printing press acquired by the first color reproduction characteristic acquisition unit. Second color reproduction characteristic acquisition means for acquiring a simulated color reproduction characteristic,
Continuity index acquisition means for acquiring a continuity index that is an index relating to continuity of gradation in the simulated color reproduction characteristics acquired by the second color reproduction characteristics acquisition means;
Difference information between the color reproduction characteristic of the printing press acquired by the first color reproduction characteristic acquisition unit and the simulated color reproduction characteristic acquired by the second color reproduction characteristic acquisition unit, and the continuity index acquisition based-out in said continuity index obtained by means of the weighting factor indicating the degree to modify the color reproduction characteristics of the printing press from the difference information when the continuity index exceeds a predetermined threshold And re-creating means for re-creating the color conversion coefficient group using the corrected color reproduction characteristics of the printing press after making the correction of the color reproduction characteristics of the printing press smaller. Image forming apparatus. On the computer,
A function of acquiring the color reproduction characteristics of the first device;
Based on the color conversion coefficient group for converting the color value depending on the first device into the color value depending on the second device, the obtained color reproduction characteristic of the first device is expressed by the second device. A function to acquire simulated color reproduction characteristics, which are color reproduction characteristics obtained by simulating
A function of acquiring a continuity index that is an index relating to continuity of gradation in the acquired simulated color reproduction characteristics;
Color reproduction characteristics of the acquired first device and the difference information between the simulated color reproduction characteristics, based-out in the continuity index obtained when the continuity index exceeds a predetermined threshold Further, the color reproduction characteristic of the first device is corrected by reducing the weighting coefficient indicating the degree to which the color reproduction characteristic of the first device is corrected from the difference information, and the corrected color of the first device is corrected. A color conversion program for realizing a function of recreating the color conversion coefficient group using reproduction characteristics .

Images