Information processing system and program

Abstract

To enable a conversion of an RGB value when a patch image is read into a Lab value with high accuracy in a calibration of printing using a color material of a special color other than a CMYK color which is a basic color.SOLUTION: A conversion data storage part 32 stores, for each combination of a plurality of colors, a plurality of pieces of conversion data generated by using a calibration chart including a patch image of a multi-order color composed of a combination of a plurality of basic colors and a patch image of a multi-order color composed of the combination of a plurality of colors in which any one of the plurality of basic colors is replaced with a special color. A color conversion part 33 selects conversion data corresponding to the patch image from among a plurality of pieces of conversion data according to combination information indicating which combination of the plurality of colors the patch image corresponds to, and converts an RGB value when the patch image is read into a Lab value. A multi-dimensional LUT generation part 34 generates a multi-dimensional LUT for executing calibration using the converted Lab value.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates to an information processing system and a program. [Background technology]

[0002] Patent Document 1 discloses a color separation image correction device for correcting color separation image signals input as electrical signals to reproduce a target color using cyan C, magenta M, yellow Y, high saturation colorants, and black K, which determines a combination of colorants to be used in image output by combining K and at least an area reproduced by a combination of two other colors, thereby estimating the printer characteristics using a small number of measurement points in a printer with a large number of colorants including spot colors and systematically determining a combination of colorants corresponding to the target color.

[0003] Patent document 2 discloses an image forming device that enables highly accurate color measurement using a scanner by creating a scanner profile from a first color value in a device-dependent color space obtained by reading a printed copy of chart image data with a scanner, a K value of the chart image data, and a second color value in a device-independent color space obtained by measuring the color of the printed copy with a colorimeter. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-032284 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-228579 Summary of the Invention [Problem to be solved by the invention]

[0005] Calibration is performed to correct color shifts in a printing device due to the operating environment or aging and to improve color reproducibility. This calibration involves printing a calibration chart composed of multiple patch images using a printing device, measuring the color values ​​of the multiple patch images using a colorimeter, and obtaining color values ​​in the Lab color space (hereinafter referred to as Lab values). Based on the obtained Lab values ​​of the multiple patch images, a multidimensional LUT (Look Up Table) is created to perform multidimensional conversion in the CMYK color space so that the color values ​​of each patch image are the expected color values. The printing device then uses the created multidimensional LUT to perform printing, thereby improving the color reproducibility of the printed image.

[0006] However, a colorimeter is required to measure the color values ​​of multiple patch images in a calibration chart as Lab values, and measuring the color values ​​of each of the multiple patch images using a colorimeter is time-consuming. Therefore, the color values ​​of the multiple patch images are read using an image reading device such as an inline sensor or scanner that is provided in a general image forming apparatus. However, because the color values ​​read by the image reading device are RGB values, conversion data for converting the read RGB values ​​to Lab values ​​must be prepared in advance.

[0007] Therefore, Lab data obtained by measuring the color of each patch image in a chart image having multiple multi-color or single-color patch images formed by combining multiple colors from among CMYK colors using a colorimeter, and RGB data read by an image reading device are obtained, and conversion data for converting the RGB values ​​into Lab values ​​is created.

[0008] However, in recent years, in order to expand the color gamut of images printed by printing devices, printing has begun to be performed using not only color materials of the basic colors of CMYK, but also color materials of special colors such as fluorescent pink (hereinafter referred to as P) and fluorescent green (hereinafter referred to as G). However, if the RGB values ​​obtained by reading each patch image of a chart image having a plurality of patch images of multi-colors including such special colors using an image reading device are converted to Lab values ​​using conversion data generated based on a chart image composed of patch images consisting only of combinations of the basic colors of CMYK, high-precision conversion cannot be achieved. Even if conversion data is created based on a chart image composed of patch images of multi-colors combining basic colors and special colors, high-precision conversion cannot be achieved compared to conversion using conversion data generated based on patch images of multi-colors combining only basic colors. This is because even if CMY colors excluding K from the basic colors of CMYK are combined with two special colors, a five-dimensional color combination results. Therefore, if the color values ​​of this five-dimensional patch image of multi-colors are converted to three-dimensional color values ​​such as RGB, patch images with different actual Lab values ​​but the same RGB values ​​will exist. Furthermore, if patch images that satisfy all five-dimensional color combinations are generated, the number of patch images will become enormous, and reading the color values ​​of the patch images will require a huge amount of effort, making it unrealistic.

[0009] The object of the present disclosure is to provide an information processing system and program that can convert RGB values ​​to Lab values ​​with high accuracy when calibrating printing using color materials of special colors other than the basic CMYK colors, compared to converting RGB values ​​to Lab values ​​using conversion data generated based on patch images of multi-colors that combine only the basic colors. [Means for solving the problem]

[0010] An information processing system according to a first aspect of the present disclosure includes a processor and a memory, the memory stores, for each combination of multiple colors, a plurality of conversion data for converting RGB values ​​into Lab values, the conversion data being generated using a calibration chart including a patch image of multiple colors formed by a combination of multiple basic colors and a patch image of multiple colors formed by a combination of multiple colors in which any one of the multiple basic colors is replaced with a special color other than the basic color; The processor: selecting, from among the plurality of conversion data stored in the memory, conversion data corresponding to the patch image, based on RGB values ​​obtained by reading the patch image in the calibration chart using an image reading device, in accordance with combination information indicating which combination of multiple colors the patch image corresponds to; Converts the read RGB values ​​to Lab values ​​using the selected conversion data, A multidimensional LUT is generated to perform calibration using the converted Lab values.

[0011] An information processing system of a second aspect of the present disclosure is the information processing system of the first aspect, wherein the patch image of multi-order colors formed by a combination of the plurality of basic colors is a patch image of tertiary colors or less formed by a combination of CMY colors; The multi-color patch image consisting of a combination of multiple colors in which any one of the plurality of basic colors is replaced with a special color is a patch image of tertiary or lower colors consisting of a combination of three colors in which any one of the CMY colors is replaced with a special color other than CMYK colors.

[0012] An information processing system of a third aspect of the present disclosure is the information processing system of the second aspect, wherein the plurality of conversion data includes conversion data generated based on the color values ​​of monochrome patch images of each of the CMYK basic colors and special colors.

[0013] An information processing system of a fourth aspect of the present disclosure is the information processing system of the first aspect, wherein the combination information includes page information indicating the page of the calibration chart of the patch image, position information indicating the position on the page, and colorant concentration information when the patch image is output.

[0014] An information processing system of a fifth aspect of the present disclosure is the information processing system of the first aspect, wherein when the processor generates a multidimensional LUT using Lab values ​​converted by selected conversion data, it generates tertiary or lower color combinations of basic colors and special colors based on the Lab values.

[0015] An information processing system of a sixth aspect of the present disclosure is the information processing system of the fifth aspect, wherein when the processor generates a multidimensional LUT using Lab values ​​converted by selected conversion data, the K color portion of the basic colors is generated based on the Lab values ​​of a monochrome patch image.

[0016] The program according to the seventh aspect of the present disclosure includes: a step of storing, for each combination of multiple colors, a plurality of conversion data for converting RGB values ​​into Lab values, the conversion data being generated using a calibration chart including a patch image of a multi-order color formed by a combination of multiple basic colors and a patch image of a multi-order color formed by a combination of multiple colors in which any one of the multiple basic colors is replaced with a special color other than the basic colors; a step of selecting, from among a plurality of stored conversion data, conversion data corresponding to a patch image, based on RGB values ​​obtained by reading the patch image in the calibration chart using an image reading device, in accordance with combination information indicating to which combination of multiple colors the patch image corresponds; converting the read RGB values ​​to Lab values ​​using the selected conversion data; and generating a multidimensional LUT for performing calibration using the converted Lab values. [Effects of the Invention]

[0017] According to the information processing system of the first aspect of the present disclosure, when calibrating printing using color materials of special colors other than the basic colors CMYK, it is possible to convert RGB values ​​to Lab values ​​with higher accuracy than when RGB values ​​are converted to Lab values ​​using conversion data generated based on patch images of multi-colors that combine only the basic colors.

[0018] According to the information processing system of the second aspect of the present disclosure, it is possible to limit the combination of each patch image in the calibration chart to tertiary colors or less.

[0019] According to the information processing system of the third aspect of the present disclosure, the accuracy of an image formed using a single color material can be managed separately from the accuracy of an image formed using multi-color color materials.

[0020] According to the information processing system of the fourth aspect of the present disclosure, when the color values ​​of each patch image of the calibration chart are read by an image reading device, it is possible to automatically identify the conversion data to be selected.

[0021] According to the information processing system of the fifth aspect of the present disclosure, it is possible to generate a multidimensional LUT even when Lab values ​​for patch images of all combinations of basic colors and special colors do not exist.

[0022] According to the information processing system of the sixth aspect of the present disclosure, it is possible to generate a multidimensional LUT even when there are no Lab values ​​for a patch image of a multi-order color that is a combination of K color from among the basic colors and a special color.

[0023] According to the program of the seventh aspect of the present disclosure, when calibrating printing using color materials of special colors other than the basic CMYK colors, it is possible to convert RGB values ​​to Lab values ​​with higher accuracy than when RGB values ​​are converted to Lab values ​​using conversion data generated based on patch images of multi-colors that combine only the basic colors. [Brief explanation of the drawings]

[0024] [Figure 1] 1 is a diagram illustrating a system configuration of an image forming system according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a cross-sectional view showing the structure of an image forming apparatus 20, which is a target apparatus for performing calibration. [Figure 3] 1 is a diagram illustrating a hardware configuration of a terminal device 10 in an image forming system according to an embodiment of the present disclosure. [Figure 4] 1 is a block diagram showing a functional configuration of a terminal device 10 in an image forming system according to an embodiment of the present disclosure. [Figure 5] 10 is a diagram showing a state in which calibration is performed using a colorimeter 40 in the terminal device 10. FIG. [Figure 6] 10A and 10B are diagrams for explaining preparations to be made in advance when performing calibration without using the colorimeter 40. FIG. [Figure 7] 10 is a diagram for explaining the flow of processing when actually performing calibration in the case where calibration is performed without using the colorimeter 40. FIG. [Figure 8] FIG. 10 is a diagram for explaining preparations to be made before calibration is performed on the image forming apparatus 20 that uses a special color (PG). [Figure 9] FIG. 10 is a diagram for explaining the flow of processing when actually performing calibration in the case where calibration is performed on the image forming apparatus 20 that uses a special color (PG). [Figure 10] FIG. 10 is a diagram showing an example of patch images in which the toner coverage is different but the read RGB values ​​are the same. [Figure 11] 10 is a flowchart illustrating a processing flow during advance preparation for calibration to generate conversion data in the terminal device 10 according to an embodiment of the present disclosure. [Figure 12] FIG. 10 is a diagram showing an example of the configuration of patch images of a calibration chart in the case of CMYK+P colors. [Figure 13] FIG. 10 is a diagram showing an example of a calibration chart including patch images of CMYK+P colors. [Figure 14] FIG. 10 is a diagram illustrating an example of combination information of patch images. [Figure 15] FIG. 10 is a diagram illustrating an example of combination information of patch images. [Figure 16] FIG. 10 is a diagram showing another example of combination information of patch images. [Figure 17] 10 is a diagram showing how a plurality of pieces of conversion data generated by a conversion data generation unit 31 are stored in a conversion data storage unit 32. FIG. [Figure 18] 10 is a flowchart illustrating a processing flow when calibration is performed in the terminal device 10 according to an embodiment of the present disclosure. [Figure 19] 10A and 10B are diagrams illustrating examples of correspondence between color combinations of patch images and conversion data in the case of CMYK+P colors. [Figure 20] 10A and 10B are diagrams showing how patch images of each color combination are converted into Lab values ​​using CMY conversion data 41, MPC conversion data 42, YPM conversion data 43, CYP conversion data 44, and monochrome conversion data 45. [Figure 21] FIG. 10 is a diagram showing an example of a multidimensional LUT generated in the case of CMYK+P colors. [Figure 22] 10A and 10B are diagrams illustrating an example of correspondence between combinations of patch images and conversion data in the case of CMYK+P+G colors. [Figure 23] FIG. 10 is a diagram showing an example of a multidimensional LUT generated in the case of CMYK+P+G colors. DETAILED DESCRIPTION OF THE INVENTION

[0025] Next, embodiments of the present disclosure will be described in detail with reference to the drawings.

[0026] FIG. 1 is a diagram showing a system configuration of an image forming system according to an embodiment of the present disclosure.

[0027] 1, the image forming system of this embodiment is composed of an image forming apparatus 20, an image forming apparatus 60, and a terminal device 10, all interconnected via a network 30, and a colorimeter 40 connected to the terminal device 10. The image forming apparatus 20 is, for example, a so-called production printer used for commercial printing, and has the ability to perform high-quality, high-speed printing. The image forming apparatus 60 is a so-called multifunction device that has multiple functions, such as printing, scanning, copying, and facsimile functions.

[0028] The color of an image printed by image forming apparatus 20 changes due to various factors such as the environmental conditions in which image forming apparatus 20 is installed, aging of image forming apparatus 20, and variations between individual devices. Therefore, calibration is performed to correct the color reproduction of the image printed by image forming apparatus 20 so that the color values ​​of the printed image match target color values.

[0029] When performing this calibration, first, a calibration chart 50 composed of a plurality of patch images is printed by the image forming device 20. Then, the color values ​​of each patch image on the printed calibration chart 50 are measured by the colorimeter 40, and the color values ​​are input to the terminal device 10. The terminal device 10 then creates a multidimensional LUT (Look Up Table) such that the color values ​​of the measured patch images become target color values, and installs the created multidimensional LUT into the image forming device 20. The image forming device 20 then corrects the specified CMYK values ​​using the installed multidimensional LUT and executes printing processing using the corrected CMYK values, so that the color values ​​of the printed image approach the target color values.

[0030] Here, the color values ​​measured by the colorimeter 40 are generally in accordance with the L standard defined by the International Commission on Illumination (CIE). * a * b * In the following explanation, the color space is expressed as L * a * b* The values ​​in the color space will be simply expressed as Lab values ​​in the following explanation.

[0031] Next, the structure of an image forming apparatus 20, which is the target apparatus for performing calibration, is shown in FIG.

[0032] As shown in Figure 2, the image forming device 20 has six image forming units 21. These six image forming units 21 are configured to form images on a recording medium using toners of the basic colors yellow (Y), magenta (M), cyan (C), and black (K), respectively, and toners of two special colors, fluorescent pink (P) and fluorescent green (G).

[0033] The image forming unit 21 is composed of a photosensitive drum, a charging device that uniformly charges the surface of the photosensitive drum, a developing device that develops the electrostatic latent image formed on the photosensitive drum, and a cleaning device. The photosensitive drum is a cylindrical image carrier that holds a toner image (developer image), and is uniformly charged by the charging device, and an electrostatic latent image is formed on the photosensitive drum by laser light irradiated by an optical scanning device 24. The electrostatic latent image formed on the photosensitive drum is developed with toner by the developing device and transferred to the intermediate transfer belt 22. After the toner image transfer process, residual toner and paper dust remaining on the photosensitive drum are removed by a cleaning device.

[0034] The image forming units 21 are provided adjacent to an intermediate transfer belt 22. The intermediate transfer belt 22 rotates in the direction of arrow A in FIG. 2. Primary transfer rolls 23 are disposed opposite the photosensitive drums across the intermediate transfer belt 22. The primary transfer rolls 23 are provided to transfer the toner images of each color formed on the photosensitive drums onto the intermediate transfer belt 22.

[0035] A transport path 29 for transporting the recording medium is formed below the intermediate transfer belt 22. The transport path 29 is provided with a plurality of transport rolls that transport the recording medium from the inlet 25 to the outlet 28. The transport path 29 also includes a secondary transfer device 26 that performs a second transfer of a toner image, which has been primarily transferred from the photosensitive drum to the intermediate transfer belt 22, onto the recording medium transported along the transport path 29. A fixing device 27 is provided downstream of the secondary transfer device 26 in the recording medium transport direction. The fixing device 27 is a device for fixing an image formed by the plurality of image forming units 21 onto the recording medium by heating it, and fixes the image on the recording medium onto which the toner image has been transferred onto the recording medium by heat and pressure. The recording medium with the image fixed by the fixing device 27 is discharged from the outlet 28.

[0036] As described above, the image forming device 20 is configured to print using a special color toner called PG in addition to the normal color toners called CMYK, and therefore the terminal device 10 needs to perform calibration so that the color values ​​of the image printed using the normal color toners and the special color toners match the target values.

[0037] Next, the hardware configuration of the terminal device 10 in the image forming system of this embodiment is shown in FIG.

[0038] 3, the terminal device 10 has a CPU 11, a memory 12, a storage device 13 such as a hard disk drive, a communication interface (abbreviated as IF) 14 for transmitting and receiving data to and from external devices via a network 30, and a user interface (abbreviated as UI) device 15 including a touch panel or liquid crystal display and a keyboard. These components are connected to each other via a control bus 16.

[0039] The CPU 11 is a processor that controls the operation of the terminal device 10 by executing predetermined processes based on a control program stored in the memory 12 or the storage device 13. In the present embodiment, the CPU 11 is described as reading and executing the control program stored in the memory 12 or the storage device 13, but this is not limiting. The control program may be provided in a form recorded on a computer-readable recording medium. For example, the program may be provided in a form recorded on an optical disc such as a CD (Compact Disc)-ROM or a DVD (Digital Versatile Disc)-ROM, or in a form recorded on a semiconductor memory such as a USB (Universal Serial Bus) memory or a memory card. The control program may also be acquired from an external device via a communication line connected to the communication interface 14. The control program may be provided as standalone application software, or may be incorporated into the software of each device of the terminal device 10 as a function of the device.

[0040] FIG. 4 is a block diagram showing the functional configuration of the terminal device 10 realized by executing the above control program.

[0041] As shown in Fig. 4, the terminal device 10 of this embodiment includes a conversion data generation unit 31, a conversion data storage unit 32, a color conversion unit 33, and a multidimensional LUT generation unit 34. Fig. 4 shows only the portion of the functional configuration of the terminal device 10 that is related to the execution of calibration. Fig. 4 also shows a case where calibration is performed using a calibration chart 50 consisting of a combination of CMYK colors.

[0042] Before explaining the calibration when printing using special color toners in addition to normal colors using the terminal device 10 of this embodiment, we will first explain the calibration when printing using normal CMYK color toners.

[0043] FIG. 5 shows how calibration is performed using the colorimeter 40 in the terminal device 10.

[0044] 5, if color measurement is performed using the colorimeter 40 every time calibration is performed, a calibration chart 50 may be printed by the image forming apparatus 20 and the color may be measured using the colorimeter 40. In this case, the multidimensional LUT generation unit 34 generates a multidimensional LUT using Lab data consisting of color values ​​of each patch image of the calibration chart 50 measured by the colorimeter 40. Then, the calibration of the image forming apparatus 20 is completed by installing the multidimensional LUT generated by the multidimensional LUT generation unit 34 in the image forming apparatus 20.

[0045] However, measuring the color values ​​of the multiple patch images in the calibration chart 50 as Lab values ​​requires a colorimeter 40, and measuring the color values ​​of each of the multiple patch images one by one using the colorimeter 40 is time-consuming. As the number of patch images increases, the time and effort required to measure the color values ​​of each patch image using the colorimeter 40 becomes enormous. Furthermore, if the image forming apparatus 20 is calibrated periodically, this enormous effort is incurred each time calibration is performed. Therefore, the color values ​​of the multiple patch images are typically read using an image reading device, such as an inline sensor or scanner, included in a typical image forming apparatus 60. Obtaining the color values ​​of each patch image using the image reading device eliminates the need for the labor required to scan the entire calibration chart 50. However, because the color values ​​read by the image reading device are RGB values, conversion data must be prepared in advance to convert the read RGB values ​​into Lab values.

[0046] Next, a process for performing calibration without using the colorimeter 40 will be described with reference to FIGS.

[0047] Fig. 6 is a diagram for explaining preparations to be made before performing calibration without using the colorimeter 40. Fig. 7 is a diagram for explaining the flow of processing when actually performing calibration without using the colorimeter 40.

[0048] 6, in advance preparation for calibration without using the colorimeter 40, first, Lab data obtained by measuring the color of a calibration chart 50 with the colorimeter 40 and RGB data obtained by reading the same calibration chart 50 with an image reading device of an image forming apparatus 60 are input to the conversion data generation unit 31. Then, the conversion data generation unit 31 generates conversion data for predicting the Lab data from the input RGB data using a method such as weighted linear regression, and stores the conversion data in the conversion data storage unit 32.

[0049] 7, when the actual calibration is performed, a calibration chart 50 is printed by the image forming apparatus 20, and the printed calibration chart 50 is read by the image reading device of the image forming apparatus 60 to obtain RGB data. Then, the color conversion unit 33 converts the obtained RGB data into Lab data using conversion data previously stored in the conversion data storage unit 32. Then, the multidimensional LUT generation unit 34 generates a multidimensional LUT using the Lab data converted by the color conversion unit 33, and installs the multidimensional LUT in the image forming apparatus 20.

[0050] By performing such processing, it becomes possible to perform calibration without using the colorimeter 40 when actually performing calibration as shown in FIG. 7, by simply using the colorimeter 40 in the preliminary preparation stage.

[0051] However, if such calibration without using a colorimeter is applied in the same way to an image forming device 20 that prints using special color toners in addition to the normal CMYK color toners, there arises the problem that it is not possible to perform high-precision calibration, and that it takes an enormous amount of effort to generate conversion data in advance.

[0052] Specifically, a case where two colors PG are added as special colors to the normal colors CMYK will be described. The preparations for performing calibration on the image forming apparatus 20 that uses the special colors (PG) will be described with reference to Fig. 8. Also, the process flow during actual calibration when performing calibration on the image forming apparatus 20 that uses the special colors (PG) will be described with reference to Fig. 9.

[0053] 8, in advance preparations for performing calibration on the image forming apparatus 20 that uses the special color (PG), Lab data obtained by measuring the color of a calibration chart 51 made up of patch images of three-dimensional colors that combine the normal colors CMYK and the special color PG using a colorimeter 40, and RGB data obtained by reading the same calibration chart 51 using an image reading device of the image forming apparatus 60 are input to the conversion data generation unit 31. Then, the conversion data generation unit 31 generates conversion data for predicting the Lab data from the input RGB data using a method such as weighted linear regression, and stores the conversion data in the conversion data storage unit 32.

[0054] 9, when actually performing calibration, a calibration chart 51 configured with patch images of three-dimensional colors combining normal colors CMYK and special colors PG is printed by the image forming device 20, and the printed calibration chart 51 is read by the image reading device of the image forming device 60 to obtain RGB data. Then, the color conversion unit 33 converts the obtained RGB data into Lab data using conversion data stored in advance in the conversion data storage unit 32. The multidimensional LUT generation unit 34 then generates a multidimensional LUT using the Lab data converted by the color conversion unit 33 and installs it in the image forming device 20.

[0055] 8 and 9, it is not possible to perform calibration with high accuracy if the processing shown in these figures is applied in the same way as when only the normal colors CMYK are used. The reason why the accuracy of calibration deteriorates when the processing for only CMYK colors is simply applied to the case of CMYK+PG colors is explained below.

[0056] For example, combining the three CMY colors (excluding the achromatic color K) with the two special colors PG results in a five-color combination. In other words, calibration chart 51 creates patch images with five colors. If calibration chart 51 containing these patch images with five colors is scanned by the image scanning device of image forming apparatus 60 and converted into RGB data, as shown in FIG. 10, patch images will exist with different toner coverages—that is, patch images with different actual Lab values ​​but identical scanned RGB values—as shown in FIG. 10. In FIG. 10, patch image 81 has a toner coverage of P=25% and M=70%, while patch image 82 has a toner coverage of C=2%, M=75%, and Y=50%. However, it can be seen that the RGB values ​​of both patch images 81 and 82 are the same: R=80, G=30, and B=70. This phenomenon occurs because a five-dimensional color combination is converted into three-dimensional RGB values. When RGB values ​​are expressed in 8 bits, they are expressed by values ​​from 0 to 255.

[0057] Here, the toner coverage is the amount of toner used per unit area on the recording medium, for example, the toner weight (g / m 2 ), but in the following explanation, it is expressed as a percentage of the amount of toner of each color used when printing, assuming that the maximum amount of each color toner used per unit area, for example, per pixel, is 100%.

[0058] As mentioned above, the conversion accuracy of the conversion data generated based on the RGB values ​​obtained in this way will be worse than the conversion accuracy of the conversion data generated when only the three colors of CMY are used.

[0059] Furthermore, for the three colors CMY, for example, even if each color is expressed in five gradations (0, 25, 50, 75, and 100%) and all gradations are combined, only 5 x 5 x 5 = 125 patch images are required. However, if patch images are generated using a combination of five colors (CMY plus PG), each color is expressed in five gradations (0, 25, 50, 75, and 100%) and all gradations are combined, a massive number of patch images (5 x 5 x 5 x 5 x 5 = 3125) are required. Creating a calibration chart that includes such a large number of patch images would require a huge number of calibration charts, and measuring each patch image with a colorimeter would require a huge amount of effort. Furthermore, creating conversion data to convert RGB values ​​to Lab values ​​would require a huge amount of effort and time, making it unrealistic.

[0060] However, if the RGB values ​​read from a patch image that combines the basic colors of CMYK as well as the special color PG are converted into Lab values ​​using conversion data generated based on a multi-color patch image that combines only the basic colors of CMYK, the prediction accuracy of the Lab values ​​will deteriorate and high-precision calibration will not be possible.

[0061] Therefore, in the terminal device 10 of this embodiment, by performing the calibration as shown below, when calibrating printing using toner of a special color other than the basic colors CMYK, the RGB values ​​of the read patch image are converted to Lab values ​​with high accuracy, compared to when RGB values ​​are converted to Lab values ​​using conversion data generated based on a patch image of multi-colors that combines only the basic colors, thereby achieving high-precision calibration.

[0062] In this embodiment, the conversion data storage unit 32 stores, for each combination of multiple colors, multiple conversion data for converting RGB values ​​into Lab values, which are generated using a calibration chart including a patch image of a multi-color consisting of a combination of multiple basic colors and a patch image of a multi-color consisting of a combination of multiple colors in which any one of the multiple basic colors CMY is replaced with a special color PG other than the basic colors.

[0063] The color conversion unit 33 then selects conversion data corresponding to a patch image from among the plurality of conversion data stored in the conversion data storage unit 32, based on the RGB values ​​obtained when the patch image in the calibration chart is read by the image reading device, in accordance with combination information indicating which combination of multiple colors the patch image corresponds to. The color conversion unit 33 then converts the read RGB values ​​into Lab values ​​using the selected conversion data. The multidimensional LUT generation unit 34 then generates a multidimensional LUT for performing calibration using the converted Lab values.

[0064] Here, the multi-color patch image made up of a combination of multiple basic colors is specifically a patch image of tertiary or lower colors made up of a combination of CMY colors, and the multi-color patch image made up of a combination of multiple colors in which one of the multiple basic colors is replaced with a special color is a patch image of tertiary or lower colors made up of a combination of three colors in which one of the CMY colors is replaced with a special color other than CMYK colors.

[0065] The plurality of conversion data includes conversion data generated based on the color values ​​of patch images of single colors of the CMYK basic colors and special colors.

[0066] In addition, the combination information indicating which combination of multiple colors the patch image corresponds to can include page information indicating the page of the calibration chart for the patch image, position information indicating the position on that page, and toner coverage information, which is color material concentration information when the patch image is output.

[0067] When generating a multidimensional LUT using Lab values ​​converted by the conversion data selected by the color conversion unit 33, the multidimensional LUT generation unit 34 generates the tertiary or lower combinations of basic colors and special colors based on the Lab values.

[0068] When generating a multidimensional LUT using the Lab values ​​converted by the conversion data selected by the color conversion unit 33, the multidimensional LUT generation unit 34 generates the K color portion of the basic colors based on the Lab values ​​of a monochrome patch image.

[0069] Next, the operation of the terminal device 10 of this embodiment when performing calibration for printing using a special color in addition to the CMYK basic colors will be described in detail with reference to the drawings. Note that, for simplicity, the following description will focus on the case where calibration is performed for printing using P color as a special color in addition to the CMYK basic colors.

[0070] First, the flow of processing in advance preparation for calibration for generating conversion data in the terminal device 10 of this embodiment will be described with reference to the flowchart of FIG.

[0071] In step S101, the terminal device 10 instructs the image forming device 20 to print a calibration chart including patch images of multi-colors of CMYK+special color (P). Specifically, the terminal device 10 instructs the image forming device 20 to print a calibration chart consisting of patch images of primary to tertiary colors in which any one of the colors of CMY is replaced with the special color P.

[0072] An example of the configuration of patch images in a calibration chart for CMYK+P colors is shown in Fig. 12. In Fig. 12, the gradation of each color will be explained using a case where the toner coverage is 0, 25, 50, 75, and 100%. The method for calculating the number of patch images to be generated in this case will be explained separately for the following cases (1) to (5).

[0073] (1) Patch images of secondary and tertiary colors using CMY basic colors In this case, there are five gradations for the three colors CMY, so all combinations result in 5 x 5 x 5 = 125 patch images. However, we subtract the single CMY colors (other than 0%), that is, 3 colors x 4 gradations = 12 patch images, and one patch image where all CMY is 0%. In other words, the number of patch images that meet the conditions is 125 - 12 - 1 = 112.

[0074] (2) Secondary and tertiary color patch images using MC+P colors In this case, there are five gradations for the three MCP colors, so all combinations result in 5 x 5 x 5 = 125 patch images. However, the 16 patch images for the secondary MC colors overlap with the case (1) above. Also, subtract the single MCP colors (other than 0%), that is, 3 colors x 4 gradations = 12 patch images, and the one patch image where the MCP is all 0%. In other words, the number of patch images that meet the conditions is 125 - 16 - 12 - 1 = 96.

[0075] (3) Secondary and tertiary color patch images using YM+P colors In this case, there are five gradations for the three colors YMP, so all combinations result in 5 x 5 x 5 = 125 patch images. However, the patch images (16) for the secondary colors of YM overlap with case (1) above. Also, the patch images (16) for the secondary colors of MP overlap with case (2) above. Furthermore, we subtract the single-color YMP (other than 0%) patch images, that is, 3 colors x 4 gradations = 12 patch images, and the one patch image where YMP is all 0%. In other words, the number of patch images that meet the conditions is 125 - 16 - 16 - 12 - 1 = 80.

[0076] (4) Secondary and tertiary color patch images using CY+P colors In this case, there are five gradations for the three CYP colors, so all combinations result in 5 x 5 x 5 = 125 patch images. However, the CY secondary color patch images (16) overlap with case (1) above. Also, the CP secondary color patch images (16) overlap with case (2) above. Furthermore, the YP secondary color patch images (16) overlap with case (3) above. Then, subtract the CYP single color (other than 0%), that is, 3 colors x 4 gradations = 12 patch images, and the one patch image where all CYP are 0%. In other words, the number of patch images that meet the conditions is 125 - 16 - 16 - 16 - 12 - 1 = 64.

[0077] (5) CMYK+P monochrome patch image In this case, there are four gradations (25, 50, 75, 100%) for the five CMYKP colors, and one patch image with all CMYKP at 0% is included. Therefore, the number of patch images that meet the conditions is 5 x 4 + 1 = 21.

[0078] 12 is 112 + 96 + 80 + 64 + 21 = 373. In other words, it can be seen that the total number of patch images can be significantly reduced compared to the total number of patch images for all combinations of five gradations for each of the five colors of CMYK+P, which is 5 × 5 × 5 × 5 × 5 = 3125.

[0079] FIG. 13 shows an example of a calibration chart including patch images of CMYK+P colors configured in this way.

[0080] In the calibration chart shown in Fig. 13, each patch image is composed of a single color, a secondary color, and a tertiary color. For example, Fig. 13 shows that a certain patch image is composed of tertiary colors of M=75%, P=50%, and C=25%.

[0081] Next, in step S102, the conversion data generation unit 31 acquires the RGB data obtained by reading the calibration chart printed by the image forming device 20 using the image reading device of the image forming device 60, and acquires the RGB values ​​of each patch image.

[0082] Next, in step S103, the conversion data generation unit 31 acquires Lab data obtained by measuring the calibration chart printed by the image forming device 20 with the colorimeter 40, and acquires the Lab values ​​of each patch image.

[0083] Then, in step S104, the conversion data generation unit 31 generates conversion data for converting the RGB values ​​of the patch image that combines only CMY into Lab values ​​based on the RGB values ​​and Lab values ​​of the patch image that is composed of secondary and tertiary colors of CMY.

[0084] Then, in step S105, the conversion data generation unit 31 generates conversion data for converting the RGB values ​​of the patch image composed of secondary colors and tertiary colors that combine CMY and the special color into Lab values ​​based on the RGB values ​​and Lab values ​​of the patch image.

[0085] Finally, in step S106, the conversion data generation unit 31 generates conversion data for converting the RGB values ​​of the single-color patch images of CMY and special colors into Lab values ​​based on the RGB values ​​and Lab values ​​of the single-color patch images of CMY and special colors.

[0086] When the calibration chart is generated, combination information indicating which combination of multiple colors each patch image corresponds to is generated and recorded. By matching the acquired RGB data with this combination information, the conversion data generation unit 31 and the color conversion unit 33 determine which combination of multiple colors each patch image corresponds to and what the toner coverage value of each color is, and then generate color conversion data or select color conversion data to use from multiple color conversion data generated in advance.

[0087] An example of this patch image combination information is shown in FIGS.

[0088] In Fig. 14, it can be seen that the CMYK+P color calibration chart is divided into areas 1 to 5. Fig. 15 shows a table indicating which color combinations make up each of the patch images in areas 1 to 5, which conversion data should be selected from multiple conversion data when converting RGB values ​​to Lab values, and as which conversion data the generated conversion data should be stored. For example, it can be seen that when converting the RGB values ​​of a patch image in area 1 to Lab values, MPC conversion data should be selected, and when converting the RGB values ​​of a patch image in area 2 to Lab values, YPM conversion data should be selected.

[0089] An example of the patch image combination information is shown in FIG.

[0090] Fig. 16 shows a case where toner coverage information is included in the patch combination information. As an example, Fig. 16 shows a table for specifying the toner coverage values ​​of each CMYKP color and the corresponding conversion data type, in order from the patch image in the upper left.

[0091] Based on the combination information as described above, the conversion data generation unit 31 generates conversion data used to convert the RGB values ​​of each patch image into Lab values ​​according to the position of that patch image in the RGB data, and stores the conversion data in the conversion data storage unit 32. Fig. 17 shows how the multiple conversion data generated by the conversion data generation unit 31 are stored in the conversion data storage unit 32.

[0092] FIG. 17 shows how five conversion data, namely, CMY conversion data 41, MPC conversion data 42, YPM conversion data 43, CYP conversion data 44, and monochrome conversion data 45, are stored in the conversion data storage unit 32.

[0093] When actual calibration is performed, the color conversion unit 33 selects, based on the combination information described above, from among the plurality of conversion data, conversion data to be used when converting the RGB values ​​of each patch image into Lab values, depending on the position of the patch image in the RGB data.

[0094] Next, the flow of processing when calibration is performed in the terminal device 10 of this embodiment will be described with reference to the flowchart of FIG.

[0095] First, in step S201, the terminal device 10 instructs the image forming device 20 to be calibrated to print a calibration chart including patch images of multi-colors of CMYK+special color (P) as shown in FIG.

[0096] Next, in step S202, the color conversion unit 33 acquires RGB data obtained by reading the calibration chart printed by the image forming device 20 using the image reading device of the image forming device 60, and acquires the RGB values ​​of each patch image. Then, in step S203, the color conversion unit 33 acquires combination information of each patch image of the calibration chart as shown in FIGS. 14 to 16.

[0097] Then, in step S204, when converting the RGB values ​​of each patch image into Lab values, the color conversion unit 33 selects color conversion data according to the acquired combination information and sequentially executes the process of converting the RGB values ​​into Lab values.

[0098] For example, an example of the correspondence between the color combinations of patch images and the conversion data in the case of CMYK+P colors is shown in Fig. 19. Also, Fig. 20 shows how patch images with each color combination are converted into Lab values ​​using CMY conversion data 41, MPC conversion data 42, YPM conversion data 43, CYP conversion data 44, and monochrome conversion data 45, respectively.

[0099] For example, in the table shown in Fig. 19, it can be seen that the conversion data to be used when converting the RGB values ​​of a patch image of tertiary colors (CMYK) or secondary colors (CM, CY, YM) of CMY colors into Lab values ​​is CMY conversion data. Therefore, for a patch image of a combination of CMY, as shown in Fig. 20, the color conversion unit 33 selects CMY conversion data 41 to convert the RGB values ​​into Lab values.

[0100] 19, it can be seen that the conversion data to be used when converting the RGB values ​​of a patch image of a tertiary color (MCP) or secondary color (CP, MP) of an MCP color into Lab values ​​is MPC conversion data. Therefore, as shown in FIG. 20, for a patch image based on an MCP combination, the color conversion unit 33 selects MPC conversion data 42 to convert the RGB values ​​into Lab values.

[0101] Finally, in step S205, the multidimensional LUT generator 34 generates and outputs multidimensional LUT data for performing calibration based on the converted Lab values. By installing this multidimensional LUT in the image forming device 20, calibration is performed so that the colors of the image printed by the image forming device 20 approach the target colors.

[0102] An example of a multidimensional LUT generated by the multidimensional LUT generating unit 34 in this manner is shown in FIG.

[0103] 21, it can be seen that CMYKP output values ​​correspond to CMYKP input values. Note that Fig. 21 shows a table in which nine combinations of values, namely, 0, 32, 64, 96, 128, 160, 192, 224, and 255, out of the 256 levels of values ​​from 0 to 255 for each color, are input. Note that when generating a multidimensional LUT, a one-dimensional LUT is applied to the combination of K color and P color, which is unlikely to actually be used.

[0104] In the above, for simplicity of explanation, the case where five color toners, CMYK+P, are used is described, but the same is applicable to the case where six color toners, CMYK+P+G, are used.

[0105] For example, FIG. 22 shows an example of correspondence between patch image combinations and conversion data in the case of CMYK+P+G colors.

[0106] 22, it can be seen that in addition to CMY conversion data, MPC conversion data, YPM conversion data, CYP conversion data, and monochrome conversion data, MGC conversion data, YGM conversion data, and CYG conversion data are used. Note that since the P color and G color are unlikely to be used simultaneously, conversion data is not required when the two special colors PG are used simultaneously.

[0107] An example of a multidimensional LUT generated in the case of CMYK+P+G colors is shown in Fig. 23. Referring to Fig. 23, it can be seen that CMYKPG output values ​​correspond to CMYKPG input values.

[0108] In each of the above embodiments, the term "processor" refers to a processor in a broad sense, and includes general-purpose processors (e.g., CPU: Central Processing Unit, etc.) and dedicated processors (e.g., GPU: Graphics Processing Unit, ASIC: Application Specific Integrated Circuit, FPGA: Field Programmable Gate Array, programmable logic device, etc.).

[0109] Furthermore, the operations of the processor in each of the above embodiments may be performed not only by a single processor but also by multiple processors located at physically separate locations working together. Furthermore, the order of the operations of the processor is not limited to the order described in each of the above embodiments and may be changed as appropriate.

[0110] In this embodiment, the term "system" includes both a system made up of multiple devices and a system made up of a single device.

[0111] [Note] Preferred embodiments of the present disclosure will be described below.

[0112] (((1))) a processor and a memory, the memory stores, for each combination of multiple colors, a plurality of conversion data for converting RGB values ​​into Lab values, the conversion data being generated using a calibration chart including a patch image of multiple colors formed by a combination of multiple basic colors and a patch image of multiple colors formed by a combination of multiple colors in which any one of the multiple basic colors is replaced with a special color other than the basic color; The processor: selecting, from among the plurality of conversion data stored in the memory, conversion data corresponding to the patch image, based on RGB values ​​obtained by reading the patch image in the calibration chart using an image reading device, in accordance with combination information indicating which combination of multiple colors the patch image corresponds to; Converts the read RGB values ​​to Lab values ​​using the selected conversion data, Generate a multidimensional LUT to perform calibration using the converted Lab values; Information processing system.

[0113] (((2))) the patch image of multi-color consisting of a combination of a plurality of basic colors is a patch image of tertiary or lower colors consisting of a combination of CMY colors, the multi-color patch image consisting of a combination of multiple colors in which any one of the plurality of basic colors is replaced with a special color is a patch image of tertiary or lower colors consisting of a combination of three colors in which any one of CMY colors is replaced with a special color other than CMYK colors; The information processing system according to (((1))).

[0114] (((3))) The plurality of conversion data include conversion data generated based on color values ​​of patch images of single colors of the CMYK basic colors and special colors. The information processing system according to (((2))).

[0115] (((4))) the combination information includes page information indicating a page of a calibration chart for the patch image, position information indicating a position on the page, and color material density information when the patch image is output. An information processing system according to any one of (((1))) to (((3))).

[0116] (((5))) When generating a multidimensional LUT using the Lab values ​​converted by the selected conversion data, the processor generates tertiary or lower color combinations among combinations of basic colors and special colors based on the Lab values. The information processing system according to (((1))).

[0117] (((6))) When generating a multidimensional LUT using the Lab values ​​converted by the selected conversion data, the processor generates the K color portion of the basic colors based on the Lab values ​​of a single-color patch image. The information processing system according to (((5))).

[0118] (((7))) a step of storing, for each combination of multiple colors, a plurality of conversion data for converting RGB values ​​into Lab values, the conversion data being generated using a calibration chart including a patch image of a multi-order color formed by a combination of multiple basic colors and a patch image of a multi-order color formed by a combination of multiple colors in which any one of the multiple basic colors is replaced with a special color other than the basic colors; a step of selecting, from among a plurality of stored conversion data, conversion data corresponding to a patch image, based on RGB values ​​obtained by reading the patch image in the calibration chart using an image reading device, in accordance with combination information indicating to which combination of multiple colors the patch image corresponds; converting the read RGB values ​​to Lab values ​​using the selected conversion data; generating a multidimensional LUT for performing calibration using the converted Lab values; A program that causes a computer to execute the following.

[0119] The effects of the configuration described above will be described below.

[0120] According to the information processing system (((1))), when calibrating printing using color materials of special colors other than the basic CMYK colors, it is possible to convert RGB values ​​to Lab values ​​with higher accuracy than when RGB values ​​are converted to Lab values ​​using conversion data generated based on patch images of multi-colors that combine only the basic colors.

[0121] According to the information processing system of (((2))), it is possible to limit the combination of each patch image in the calibration chart to tertiary colors or less.

[0122] According to the information processing system (((3))), the accuracy of an image formed using a single color material can be managed separately from the accuracy of an image formed using multi-color color materials.

[0123] According to the information processing system (((4))), when the color values ​​of each patch image of the calibration chart are read by an image reading device, it becomes possible to automatically specify the conversion data to be selected.

[0124] According to the information processing system of (((5))), it is possible to generate a multidimensional LUT even when Lab values ​​for patch images of all combinations of basic colors and special colors do not exist.

[0125] According to the information processing system (((6))), it is possible to generate a multidimensional LUT even when there are no Lab values ​​for a patch image of multi-colors that is a combination of K color and a special color among the basic colors.

[0126] According to the program (((7))), when calibrating printing using color materials of special colors other than the basic CMYK colors, it is possible to convert RGB values ​​to Lab values ​​with higher accuracy than when RGB values ​​are converted to Lab values ​​using conversion data generated based on patch images of multi-colors that combine only the basic colors. [Explanation of symbols]

[0127] 10 Terminal Equipment 11 CPU 12 Memory 13 Storage device 14 Communication Interface 15 User Interface Device 16 Control Bus 20 Image forming device 21 Image forming unit 22 Intermediate transfer belt 23 Primary transfer roll 24 Optical scanning device 25 Loading entrance 26 Secondary transfer device 27 Fixing device 28 Outlet 29 Transport Path 30 Network 31 Conversion data generation unit 32 Conversion data storage section 33 Color conversion unit 34 Multidimensional LUT generator 40 Colorimeter 41 CMY conversion data 42 MPC conversion data 43 YPM conversion data 44 CYP Conversion Data 45 Monochrome conversion data 50, 51 Calibration chart 60 Image forming device 81, 82 patch images

Claims

1. a processor and a memory, the memory stores, for each combination of a plurality of colors, a plurality of conversion data for converting RGB values ​​into Lab values, the conversion data being generated using a calibration chart including a patch image of a multi-order color formed by a combination of a plurality of basic colors and a patch image of a multi-order color formed by a combination of a plurality of colors in which any one of the plurality of basic colors is replaced with a special color other than the basic color; The processor: selecting, from among the plurality of conversion data stored in the memory, conversion data corresponding to the patch image, based on RGB values ​​obtained by reading the patch image in the calibration chart using an image reading device, in accordance with combination information indicating to which combination of multiple colors the patch image corresponds; Converting the read RGB values ​​into Lab values ​​using the selected conversion data; generating a multidimensional LUT for performing calibration using the converted Lab values; Information processing system.

2. the patch image of multi-color consisting of a combination of a plurality of basic colors is a patch image of tertiary or lower colors consisting of a combination of CMY colors, the patch image of multi-order colors consisting of a combination of a plurality of colors in which any one of the plurality of basic colors is replaced with a special color is a patch image of tertiary or lower colors consisting of a combination of three colors in which any one of the CMY colors is replaced with a special color other than the CMYK colors; The information processing system according to claim 1 .

3. The plurality of conversion data include conversion data generated based on color values ​​of patch images of single colors of the CMYK basic colors and special colors. The information processing system according to claim 2 .

4. the combination information includes page information indicating a page of a calibration chart for the patch image, position information indicating a position on the page, and color material density information when the patch image is output. The information processing system according to claim 1 .

5. When generating a multidimensional LUT using the Lab values ​​converted by the selected conversion data, the processor generates tertiary or lower combinations of basic colors and special colors based on the Lab values. The information processing system according to claim 1 .

6. When generating a multidimensional LUT using the Lab values ​​converted by the selected conversion data, the processor generates the K color portion of the basic colors based on the Lab values ​​of a single-color patch image. The information processing system according to claim 5 .

7. a step of storing, for each combination of multiple colors, a plurality of conversion data for converting RGB values ​​into Lab values, the conversion data being generated using a calibration chart including a patch image of a multi-nary color formed by a combination of multiple basic colors and a patch image of a multi-nary color formed by a combination of multiple colors in which any one of the multiple basic colors is replaced with a special color other than the basic colors; a step of selecting, from among a plurality of stored conversion data, conversion data corresponding to a patch image, based on RGB values ​​obtained by reading the patch image in the calibration chart using an image reading device, in accordance with combination information indicating to which combination of multiple colors the patch image corresponds; converting the read RGB values ​​to Lab values ​​using the selected conversion data; generating a multidimensional LUT for performing calibration using the converted Lab values; A program that causes a computer to execute the following.

Images