Method for creating color conversion data, device for creating color conversion data, and program

Abstract

Improve profile creation techniques. [Solution] The color conversion data creation method includes the steps of: outputting a pre-application color value from the pre-application ink amount; outputting a post-application ink amount by performing an optimization process using a color prediction model that outputs a spectral reflectance which is the basis for calculating color values, taking the ink amount as input, under constraints determined according to the color conversion option, using the pre-application ink amount and the pre-application color value; outputting a post-application color value after the color conversion option has been applied from the post-application ink amount; outputting the color difference between the pre-application color value and the post-application color value for a target grid point; performing a correction to propagate the application of the color conversion option using the color difference to the ink amounts associated with the propagated grid points existing in a predetermined range around the target grid point, and outputting the propagated ink amount; and correcting the profile using the post-application ink amount and the propagated ink amount.

Description

[Technical Field]

[0001] This disclosure relates to a method for creating color conversion data, a device for creating color conversion data, and a program. [Background technology]

[0002] Creating a device link profile by combining source and destination profiles typically uses the original, uncompressed RGB data. However, there are times when the original image data cannot be obtained for various reasons.

[0003] Therefore, in the technology disclosed in Patent Document 1, a device link profile corresponding to a new device is created by the following method. In the technology disclosed in Patent Document 1, multiple first device values ​​at the outermost edge of the color gamut of the first device are extracted from the AtoB table for the first device. For each extracted first device value, at least one first color value that is color-converted from the first device value to a device value within a predetermined range is color-converted using the BtoA table for the first device to obtain a second device value, the second device value is color-converted using the AtoB table to obtain a second color value, and the process of calculating the color difference between the first color value and the second color value is repeated, and a new AtoB table is created by replacing the color value corresponding to the first device value included in the AtoB table with the first color value that has the largest color difference with the second color value. A device link profile is created using the new AtoB table and the BtoA table for the second device. In this way, a device link profile can be created without using the original RGB data that has not been color-gamut compressed. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2013-5128 [Overview of the project] [Problems that the invention aims to solve]

[0005] In the technology described in Patent Document 1, a degradation of gradation may occur in images converted using a device link profile created to replace the color values ​​corresponding to the device values ​​at the outermost edge of the color gamut in the AtoB table for the first device. Therefore, further improvements were needed in the method for creating the device link profile. [Means for solving the problem]

[0006] This disclosure can be implemented in the following forms:

[0007] According to a first embodiment of this disclosure, a method for creating color conversion data is provided. This color conversion data creation method includes: (a) obtaining a profile that defines the correspondence between input values ​​in the input color space of image data and the ink amounts of multiple ink colors as output values ​​in the output color space of a printing device that prints the image data; (b) accepting the specification of a color conversion option; (c) using the profile to convert the input values ​​in the input color space of the image data into the ink amounts in the output color space as pre-application ink amounts; (d) when the three attribute values ​​of the device-independent color space are defined as "color values", outputting pre-application color values, which are the color values ​​of the device-independent color space before the color conversion option is applied, from the pre-application ink amounts; and (e) using the pre-application ink amounts and the pre-application color values, for the ink amounts associated with target grid points, which are grid points representing the input values ​​that are the target of the application of the color conversion option among the grid points representing the input values ​​in the profile. (f) an optimization process is performed using a color prediction model that takes the amount of ink as input and outputs the spectral reflectance which is the basis for calculating the color value, under constraints determined according to the color conversion option, thereby outputting the amount of ink after the color conversion option has been applied; (g) an optimization process is performed using a color prediction model that takes the amount of ink as input and outputs the spectral reflectance which is the basis for calculating the color value, thereby outputting the amount of ink after the color conversion option has been applied; (i) an optimization process is performed using the amount of ink that is associated with the amount of ink that is linked to

[0008] According to a second embodiment of this disclosure, a color conversion data creation device is provided. This color conversion data creation device includes a process for acquiring a profile that defines the correspondence between input values ​​in the input color space of image data and the ink amounts of multiple ink colors as output values ​​in the output color space of a printing device that prints the image data; a process for accepting the specification of a color conversion option; a process for using the profile to convert the input values ​​in the input color space of the image data into the ink amounts in the output color space as pre-application ink amounts; a process for outputting pre-application color values, which are the color values ​​in the device-independent color space before the color conversion option is applied, when the three attribute values ​​of the device-independent color space are defined as "color values"; and a process for using the pre-application ink amount and the pre-application color value to convert the specified color conversion data to the ink amount associated with the target grid point, which is a grid point representing the input value to which the color conversion option is applied, among the grid points representing the input value in the profile. Under constraints determined according to the conversion option, an optimization process is performed using a color prediction model that takes the amount of ink as input and outputs the spectral reflectance which is the basis for calculating the color value, thereby performing the following: outputting the amount of ink after the application option has been applied; outputting the color value after the application option has been applied from the amount of ink after the application option has been applied; outputting the color difference for the target grid point, which is the difference between the pre-application color value and the post-application color value; outputting the amount of ink after propagation correction is performed to propagate the application of the color conversion option using the amount of ink associated with the propagation grid points that exist in a predetermined range around the target grid point among the grid points representing the input value in the profile, and the color difference; and modifying the profile using the amount of ink after the application option and the amount of ink after propagation.

[0009] According to a third embodiment of this disclosure, a computer program is provided. This program has the function of acquiring a profile that defines the correspondence between input values ​​in the input color space of image data and the ink amounts of multiple ink colors as output values ​​in the output color space of a printing device that prints the image data; a function of accepting the specification of a color conversion option; a function of using the profile to convert the input values ​​in the input color space of the image data into the ink amounts in the output color space as pre-application ink amounts; a function of outputting pre-application color values, which are the color values ​​in the device-independent color space before the color conversion option is applied, when the three attribute values ​​of the device-independent color space are defined as "color values"; and a function of using the pre-application ink amount and the pre-application color value to apply the specified color conversion option to the ink amount corresponding to the target grid point, which is a grid point representing the input value that is the target of the application of the color conversion option, among the grid points representing the input value in the profile. Under constraints determined accordingly, the computer is made to perform an optimization process using a color prediction model that takes the amount of ink as input and outputs the spectral reflectance that forms the basis for calculating the color value, thereby enabling the computer to perform the following functions: outputting the amount of ink after the application option has been applied; outputting the color value after the application option has been applied from the amount of ink after the application option has been applied; outputting the color difference for the target grid point, which is the difference between the pre-application color value and the post-application color value; outputting the amount of ink after propagation correction, which is the amount of ink after propagation correction is performed to propagate the application of the color conversion option using the amount of ink associated with the propagation grid points that exist in a predetermined range around the target grid point among the grid points representing the input value in the profile, and the color difference; and modifying the profile using the amount of ink after the application and the amount of ink after propagation. [Brief explanation of the drawing]

[0010] [Figure 1] An explanatory diagram showing the printing system. [Figure 2]An explanatory diagram showing an example of the configuration of an image processing device. [Figure 3] An explanatory diagram showing a color cube, which represents the CMYK color space in the form of a cube. [Figure 4] The first half of the flowchart showing the color conversion process. [Figure 5] The latter half of the flowchart showing the color conversion process. [Figure 6] An explanatory diagram of lattice points on the MC plane. [Figure 7] An explanatory diagram showing an example of the selection screen W1 for specifying color conversion options. [Figure 8] An explanatory diagram of propagation lattice points. [Figure 9] An explanatory diagram showing the amount of ink associated with grid points on the C-axis after the color conversion option has been applied. [Figure 10] A diagram explaining the ripple effect correction. [Figure 11] An explanatory diagram showing the degree of change in color values ​​due to propagation correction. [Figure 12] An explanatory diagram showing the grid points surrounding the propagation grid points. [Modes for carrying out the invention]

[0011] A. Embodiments: Figure 1 is an explanatory diagram showing the printing system 10. The printing system 10 comprises an image processing device 100, an input device 200, a display device 300, and a printing device 400.

[0012] The image processing device 100 is a computer comprising a memory 101, an input / output interface 102, a processor 103, and an internal bus 104. The memory 101, the input / output interface 102, and the processor 103 are connected bidirectionally via the internal bus 104. The memory 101 stores various programs and data used for various processes performed by the image processing device 100. In the illustrated example, the memory 101 stores a program 110, a device link profile 120, a color prediction model 130, and input image data IM. Hereinafter, the device link profile 120 will be referred to as DLP120. DLP120 and the color prediction model 130 will be described later. The input device 200, the display device 300, and the printing device 400 are connected to the input / output interface 102 by wired or wireless communication.

[0013] The input device 200 is, for example, a keyboard or a mouse. The display device 300 is, for example, a liquid crystal display or an organic EL (Electro-Luminescence) display. The display device 300 displays a GUI (Graphical User Interface), which will be described later. The input device 200 and the display device 300 are used to receive user instructions regarding printing, which will be described later.

[0014] The printing apparatus 400 is an inkjet printing apparatus that prints by ejecting ink droplets onto a printing medium. The printing medium is, for example, white paper. The printing apparatus 400 performs printing using six colors of ink. The six colors of ink include, for example, the process colors CMYK and two spot colors. C is cyan, M is magenta, Y is yellow, and K is black. The spot colors are colors other than the CMYK process colors, such as orange, red, green, violet, and blue. Note that Lc (light cyan), which is a cyan ink with a low density, Lm (light magenta), which is a magenta ink with a low density, Lk (light black), which is a black ink with a low density, and LLk (light gray), which is a black ink with a lower density than light black, are process colors, not spot colors. In this embodiment, the printing apparatus 400 uses the inks C, M, Y, K, Orange, and Red. Hereinafter, Orange may be written as Or.

[0015] Figure 2 is an explanatory diagram showing an example of the configuration of the image processing device 100. The image processing device 100 is, The system includes an image acquisition unit 210, a profile specification unit 220, a profile update unit 230, an ink amount acquisition unit 240, a color conversion option specification unit 250, a color prediction model acquisition unit 260, a color value conversion unit 270, a color change amount calculation unit 280, a propagation correction unit 290, an ink amount conversion unit 310, a converted image acquisition unit 320, and a print data generation unit 330. The functions of each of these units are realized when the processor 103 executes a program 110 that is pre-stored in the memory 101.

[0016] The image acquisition unit 210 acquires the input image data IM, which is to be printed.

[0017] The profile specification unit 220 accepts the specification of a profile. The profile specification unit 220 accepts the specification of an input profile and an output profile.

[0018] The input profile is used for color conversion from the input color space used in the input image data IM to a device-independent color space. The input color space is, for example, a CMYK color space or an RGB color space. The device-independent color space is, for example, CIE-L * a * b * color space or a CIE-XYZ color space. Hereinafter, CIE-L * a * b * color space is simply referred to as L * a * b * color space. Through color conversion using the input profile, input values, which are values representing colors in the input color space of each pixel included in the input image data IM, are converted into colorimetric values, which are values representing colors in the device-independent color space of each pixel.

[0019] The output profile is used for color conversion from a device-independent color space to an output color space for the printing apparatus 400. The output color space is, for example, a CMYK color space. In color conversion using the output profile, colorimetric values, which are values representing colors in the device-independent color space of each pixel included in the input image data IM, are converted into output values that represent colors of each pixel in the output color space used by the printing apparatus. In the present embodiment, the output profile is, for example, an output profile compatible with multi-colors formulated by the International Color Consortium (ICC). Through color conversion using the output profile, colorimetric values in the device-independent color space are converted into ink amounts of inks.

[0020] Instead of accepting specification of the input profile and the output profile, the profile specification unit 220 may accept specification of the device link profile 120.

[0021] A device link profile is a profile in which calculation for converting input values into output values is performed in advance, and the calculation result is stored therein. For example, the DLP 120 is created by combining an input profile and an output profile formulated by the ICC.

[0022] Figure 3 is an explanatory diagram showing a color cube, which conceptually represents the CMYK color space in the form of a cube. Here, we explain an example where both the input and output color spaces are CMYK color spaces. This color solid has White (paper white) as its origin and is defined by three coordinate axes: the C axis, M axis, and Y axis, which are mutually orthogonal. Since the CMYK color space is a four-dimensional space, for example, the plane PL1, where the M component is 0, constitutes a hyperplane in four dimensions. Because it is difficult to illustrate such a hyperplane, it is represented as a surface in three dimensions in Figure 3. Note that some grid lines have been omitted from the illustration in Figure 3.

[0023] Multiple grid points are set in the color cube. Each grid point corresponds to an input value in the input color space. More specifically, the grid points indicate coordinate values ​​that represent the component values ​​of each color component when coordinate axes representing each color component are set in the input color space. The coordinates of the grid points represent the input values ​​(C, M, Y, K) in DLP120. Each grid point is associated with the output value in the output color space that corresponds to the input value in DLP120. In this embodiment, the output value of DLP120 represents the ink amount of each ink. The ink amount is represented by the ink's duty cycle. The ink's duty cycle represents the amount of ink per unit area ejected onto the medium. The duty cycle can take a range of 0 to 100%. In the illustrated example, for grid point P1, the input values ​​for each CMYK component are (0,0,0,0) and the output values ​​for each CMYK component are (0,0,0,0), and for grid point P2, the input values ​​for each CMYK component are (0,0,80,0) and the output values ​​for each CMYK component are (2,0,78,0).

[0024] As shown in Figure 2, when the profile specification unit 220 receives the specifications for the input profile and the output profile, the profile update unit 230 creates the DLP 120 by combining the input profile and the output profile. The profile update unit 230 also updates the DLP 120 when the color conversion option described later is applied.

[0025] The ink quantity acquisition unit 240 uses the DLP 120 to convert the input value representing the color of each pixel in the input color space included in the input image data IM into an output value, which is the ink quantity, representing the color of each pixel in the output color space. In this embodiment, the output values ​​are the ink quantities for C, M, Y, K, Orange, and Red.

[0026] The color conversion option specification unit 250 accepts the specification of a color conversion option. In this embodiment, the user can specify the following three color conversion options. If any of the color conversion options are specified, the DLP 120 is updated so that the specified color conversion option becomes active through a process described later.

[0027] (1) Pure color retention: When an input value indicates that it contains only one of the color components C, M, Y, or K, the printing device 400 uses only the ink of the color corresponding to that color component during printing. For example, if the input value contains only the C component, the amount of ink for color components other than the C component in the output value is set to zero. (2) Unnecessary color removal: For color components in the CMYK input values ​​that are zero, the ink corresponding to the zero color component will not be used during printing by the printing device 400. For example, if the input values ​​are (C,M,Y,K)=(0,50,30,0), the ink amounts for the C and K components of the CMYK output will be set to zero. (3) Darkest part retention: If the input value contains multiple color components that each represent their maximum density, the output value is corrected so that the multiple color components in the output color space corresponding to the input value also have their maximum density. For example, if the input value is (C,M,Y,K)=(100,100,100,100) or (R,G,B)=(0,0,0), the output value is set to (C,M,Y,K)=(100,100,100,100). In this way, printing is performed so that the darkest areas specified in the input value become the darkest.

[0028] When the above color conversion options are applied, the intention set in the input value can be reflected in the ink amount when converting the input value, which was intentionally set in the input color space, to the ink amount in the output color space.

[0029] The color prediction model acquisition unit 260 acquires the color prediction model 130, which will be used in the color value conversion unit 270 and the ink amount conversion unit 310, which will be described later.

[0030] The color value conversion unit 270 uses the color prediction model 130 acquired by the color prediction model acquisition unit 260 to convert the ink amount output by the ink amount acquisition unit 240 into a color value.

[0031] As the color prediction model 130, for example, a neural network model as a color prediction model created by the method described in Japanese Patent Publication No. 2021-150782 disclosed by the applicant of this disclosure can be used. This color prediction model is generated by machine learning using the ink amount set used when printing a color chart and the spectral reflectance obtained by measuring the printed color chart as training data. When the ink amount is input, this color prediction model predicts the spectral reflectance of the printed material when printing is performed with the input ink amount and outputs the predicted spectral reflectance. Three attribute values ​​of the device-independent color space can be calculated based on the spectral reflectance. In this specification, the three attribute values ​​of the device-independent color space are defined as "color values". In this embodiment, the device-independent color space is L * a * b * It is a color space, and the three attribute values ​​represent brightness (L). * a, which represents hue and saturation. * , b * That is the case.

[0032] The color value conversion unit 270 inputs the ink amount to the color prediction model 130 and obtains the spectral reflectance. The color value conversion unit 270 converts the spectral reflectance to L * a * b * L in color space * a * b *Convert to a value to obtain the color value.

[0033] The color value conversion unit 270 inputs the ink amount before the color conversion option is applied, output by the ink amount acquisition unit 240, into the color prediction model 130, and obtains the color value before the color conversion option is applied. The color value before the color conversion option is applied is also called the "pre-application color value".

[0034] The color value conversion unit 270 inputs the ink amount after the color conversion option output by the ink amount conversion unit 310 (described later) has been applied to the color prediction model 130, and obtains the color value after the color conversion option has been applied. The color value after the color conversion option has been applied is also called the "applied color value".

[0035] The color change amount calculation unit 280 calculates the color difference, which is the difference between the color value before application and the color value after application.

[0036] The propagation correction unit 290 performs propagation correction on propagation grid points. Among the multiple grid points distributed in the input color space, the grid points whose output values ​​are corrected by the application of the color conversion option are called target grid points. Among the multiple grid points distributed in the input color space, the grid points that exist within a predetermined range around the target grid points are called propagation grid points. Propagation correction refers to correcting the output values ​​associated with propagation grid points according to the applied color conversion option. Propagation correction is a correction that propagates the application of the color conversion option to propagation grid points. By performing propagation correction, the occurrence of tone jumps caused by the application of the color conversion option can be suppressed.

[0037] The ink volume conversion unit 310 uses the color prediction model 130 to convert the pre-application color value output by the color value conversion unit 270 into the post-application ink volume. Details of the processing of the ink volume conversion unit 310 will be described later.

[0038] The converted image acquisition unit 320 uses the DLP 120 to convert the input values ​​representing the color of each pixel in the input color space in the input image data into the amount of ink representing the color of each pixel in the output color space.

[0039] The print data generation unit 330 generates print data to be supplied to the printing device 400. The print data generation unit 330 separates the input image data, which has been color-converted using the DLP 120, and outputs six separation data corresponding to C, M, Y, K, Or, and Red. The print data generation unit 330 performs halftone processing on each separation data to convert the density and size of the halftone dots, and generates print data corresponding to each separation data.

[0040] Figures 4 and 5 are flowcharts showing the flow of the color conversion process. In step S10, the image acquisition unit 210 acquires the input image data IM by, for example, reading the input image data IM from a predetermined area of ​​the memory 101. The acquired input image data IM may be a color chart such as IT8 or ECI CMYK.

[0041] In step S20, the DLP 120 is prepared. The profile specification unit 220 displays an unillustrated GUI for profile specification on the display device 300. The user specifies the DLP 120 via the input device 200. The profile specification unit 220 reads the specified DLP 120 from a predetermined area of ​​memory 101. The profile specification unit 220 may also accept the specification of an input profile and an output profile instead of a DLP. In this case, the profile update unit 230 creates the DLP 120 by combining the input profile and the output profile.

[0042] Figure 6 is an explanatory diagram of grid points on the MC plane. In DLP120, output values ​​(C, M, Y, K, Or, Red) are associated with each grid point. For example, the input value corresponding to a grid point on the C axis is zero for all components except C, but the ink quantity, which is the output value associated with the grid point on the C axis, includes components other than C.

[0043] As shown in Figure 4, in step S30, the color prediction model acquisition unit 260 acquires the color prediction model 130 by reading data representing the color prediction model 130 from a predetermined area of ​​the memory 101. The color prediction model acquisition unit 260 outputs the color prediction model 130 to the color value conversion unit 270 and the ink amount conversion unit 310 (see Figure 2). Note that in Figure 2, the arrow representing the color prediction model 130 output from the color prediction model acquisition unit 260 to the ink amount conversion unit 310 is omitted.

[0044] As shown in Figure 4, in step S40, the color conversion option specification unit 250 accepts the specification of a color conversion option. Figure 7 is an explanatory diagram showing an example of a selection screen W1, which is a GUI for specifying color conversion options. The color conversion option specification unit 250 displays the selection screen W1 on the display device 300. On the selection screen W1, the user can select pure color retention, unwanted color removal, and darkest area retention as color conversion options. The user selects the desired color conversion option using the input device 200.

[0045] As shown in Figure 4, in step S50, the ink amount acquisition unit 240 uses the DLP 120 to convert the input value, which is a value representing the color of each pixel in the input color space included in the input image data IM, into an output value that represents the color of each pixel in the output color space used by the printing device 400. The output value is the ink amount of each ink. In step S50, the ink amount acquired by the ink amount acquisition unit 240 is the ink amount before the color conversion option is applied. The ink amount acquisition unit 240 outputs the acquired ink amount to the color value conversion unit 270 (see Figure 2).

[0046] As shown in Figure 4, in step S60, the color value conversion unit 270 uses the color prediction model 130 to convert the pre-application ink amount output by the ink amount acquisition unit 240 into a pre-application color value. First, the color value conversion unit 270 inputs the pre-application ink amount to the color prediction model 130. When the ink amount is input, the color prediction model 130 outputs the spectral reflectance. The color value conversion unit 270 uses the spectral reflectance output by the color prediction model 130 and the light source spectrum of the CIE standard light source D50 to convert the spectral reflectance into an XYZ value in the XYZ color space using a known calculation formula. The color value conversion unit 270 converts the XYZ value in the XYZ color space into an L * a * b * L in color space * a * b * The color value is converted to a value to obtain the pre-application color value. The color value conversion unit 270 outputs the pre-application color value to the ink amount conversion unit 310 (see Figure 2).

[0047] Furthermore, the color value conversion unit 270 does not need to acquire the pre-application color values ​​for all grid points in step S60. It is sufficient for the color value conversion unit 270 to acquire the pre-application color values ​​for the target grid points, which are the grid points whose output values ​​will be modified by the application of the color conversion option, and for the ripple grid points, which are grid points located within a predetermined range around the target grid points. In this way, the processing load of the color value conversion unit 270 can be reduced.

[0048] Figure 8 is an explanatory diagram of ripple grid points. Figure 8 shows grid points on the MC plane as an example. For example, when pure color preservation of the C and M components is performed, the output values ​​associated with the grid points on the C axis and M axis are modified by applying the pure color preservation color conversion option. In this case, the grid points on the C axis and M axis become the target grid points. Ripple grid points are grid points that exist within a predetermined maximum distance R from the target grid points. For example, let's say the maximum distance R is "3". The unit of distance is the interval between grid points. In this case, ripple grid points are grid points that exist within a distance R from the grid points on the C axis, and grid points that exist within a distance R from the grid points on the M axis. In the example shown in Figure 8, the target grid points and ripple grid points are represented as gray grid points, and the other grid points are represented as black grid points. Note that since no ink is printed on the origin (white paper), the origin is also represented as a black grid point.

[0049] As shown in Figure 4, in step S70, the ink volume conversion unit 310 performs an optimization process using the color prediction model 130 to convert the pre-application color value output by the color value conversion unit 270 into the post-application ink volume, which is the amount of ink after the color conversion option has been applied.

[0050] In this optimization process, the amount of ink input to the color prediction model 130 is varied, and the amount of ink that minimizes the difference between the pre-application color value output by the color value conversion unit 270 and the color value calculated from the spectral reflectance output by the color prediction model 130 is determined. The amount of ink output by the ink amount acquisition unit 240 is used as the initial value for the optimization process.

[0051] If we consider the color prediction model 130, which takes ink amount x as input and outputs spectral reflectance y, as a function y=h(x), then the spectral reflectance obtained when the ink amount x' output by the ink amount acquisition unit 240 is input to the color prediction model 130 can be expressed as y'=h(x'). Under the constraints described later, the difference L=(y-y') between the predicted spectral reflectance after applying the color conversion option and the spectral reflectance output by the ink amount acquisition unit 240 is2 The goal is to determine the ink amount x that minimizes [the specified value]. The ink amount conversion unit 310 is assumed to be capable of calculating color values ​​from spectral reflectance, similar to the color value conversion unit 270. The solution converges when the difference between the pre-application color value output by the color value conversion unit 270 and the color value calculated from spectral reflectance output by the color prediction model 130 falls below a predetermined threshold.

[0052] The ink amount, which is the input value to the color prediction model 130 at the time of convergence, is considered to be the ink amount after the application of the color conversion option. By minimizing the difference between the color value calculated from the spectral reflectance output by the color prediction model 130 and the pre-application color value output by the color value conversion unit 270, the difference in color values ​​before and after the application of the option can be reduced. The ink amount conversion unit 310 outputs the ink amount after the application of the color conversion option to the color value conversion unit 270 and the profile update unit 230 (see Figure 2).

[0053] <Constraints for "Maintaining Pure Color"> If pure color retention is specified, restrictions must be in place to ensure that only the selected pure color inks are used.

[0054] For example, suppose the inks used by the printing device 400 are C, M, Y, K, Or, and Red.

[0055] When applying pure color retention to the C component, the following constraint is imposed on the ink quantity (C, M, Y, K, Or, Red), which is the input to the color prediction model 130: (use, unuse, unuse, unuse, unuse, unuse). "Use" means that the ink can be used, and "unuse" means that the ink cannot be used. This means that the values ​​of the ink quantity (C, M, Y, K, Or, Red) other than the C component should be set to zero.

[0056] When pure color retention is applied to the M component, the constraint condition (unuse, use, unuse, unuse, unuse, unuse) is imposed on the ink quantities (C, M, Y, K, Or, Red) that are input to the color prediction model 130. This means that all values ​​of the ink quantities (C, M, Y, K, Or, Red) except M should be set to zero. The same applies to pure color retention for the Y and K components.

[0057] For example, suppose the inks used by the printing device 400 are C, M, Y, K, Lc, and Lm.

[0058] When pure color retention is applied to the C component, the constraint (use, unuse, unuse, unuse, unuse, unuse) is imposed on the ink quantity (C, M, Y, K, Lc, Lm) which is input to the color prediction model 130. Alternatively, the constraint (use, unuse, unuse, unuse, use, unuse) may be imposed on the ink quantity (C, M, Y, K, Lc, Lm) assuming that Lc is also included in the C component ink.

[0059] When pure color retention is applied to the M component, the constraint (unuse, use, unuse, unuse, unuse, unuse) is imposed on the ink quantity (C, M, Y, K, Lc, Lm) which is input to the color prediction model 130. Alternatively, the constraint (unuse, use, unuse, unuse, unuse, use) may be imposed on the ink quantity (C, M, Y, K, Lc, Lm) assuming that Lm is also included in the M component ink.

[0060] <Constraints for "Unwanted Color Removal"> If unwanted color removal is specified, restrictions must be in place to prevent the use of inks corresponding to color components with zero input values.

[0061] For example, suppose the inks used by the printing device 400 are C, M, Y, K, Or, Red. If the input values ​​are C=0 and K=0, then the constraint condition (unuse, use, use, unuse, use, use) is imposed on the ink quantity (C, M, Y, K, Or, Red) input to the color prediction model 130. This means that the values ​​of the C and K components of the ink quantity (C, M, Y, K, Or, Red) should be set to zero.

[0062] <Constraints for "maintaining the darkest area"> If darkest area preservation is specified, the output value associated with the grid point representing the darkest area must be the highest duty cycle value. For example, suppose the input value for a certain grid point is (C,M,Y,K)=(100,100,100,100). In this case, a constraint is imposed that the ink amount input to the color prediction model 130 is (C,M,Y,K,Or,Red)=(30,30,30,100,0,0). The sum of the values ​​of each element should preferably be around 200. The desirable value for the sum of the values ​​of each element is determined, for example, by the degree to which the printing medium can absorb ink.

[0063] Figure 9 is an explanatory diagram of the ink amounts associated with grid points on the C axis after the color conversion option has been applied. In the illustrated example, pure color retention is applied to the C component. The ink amounts associated with each grid point on the C axis have values ​​other than the C component set to zero. The ink amount after the color conversion option has been applied is determined by the optimization process performed by the ink amount conversion unit 310.

[0064] While methods such as pure color preservation and non-input color removal may reduce two or more color components, calculating the ink volume after applying color conversion options in such cases requires considering multiple constraints. In this embodiment, the ink volume after applying options can be efficiently obtained through optimization processing.

[0065] As shown in Figure 5, in step S80, the color value conversion unit 270 uses the color prediction model 130 to convert the ink amount after applying the color conversion option output by the ink amount conversion unit 310 into the applied color value. First, the color value conversion unit 270 inputs the ink amount after applying the color conversion option to the color prediction model 130. When the ink amount is input, the color prediction model 130 outputs the spectral reflectance. The color value conversion unit 270 uses the spectral reflectance output by the color prediction model 130 and the light source spectrum of the CIE standard light source D50 to convert the spectral reflectance into XYZ values ​​in the XYZ color space using a known calculation formula. The color value conversion unit 270 converts the XYZ values ​​in the XYZ color space into L * a * b * L in color space * a * b * Convert it to a value and obtain the applied color value, which is the color value after the color conversion option has been applied.

[0066] In step S90, the color change amount calculation unit 280 calculates the color difference, which is the difference between the pre-application color value obtained in step S60 and the post-application color value obtained in step S80, using the following formulas (1) to (3). ΔL, Δa, and Δb calculated using the following formulas (1) to (3) represent the color difference. * before ,a * before ,b * before This is the pre-application color value obtained in step S60. * after ,L * after ,L * after This is the applied color value obtained in step S80. ΔL = L * after -L * before ...(1) Δa=a * after -a * before ...(2) Δb = b *after -b * before ...(3) L * before :L before applying color conversion option * L * after :L after applying the color conversion option * a * before a before applying the color conversion option * a * after : after applying the color conversion option a * b * before :b before applying color conversion option * b * after :b after applying the color conversion option *

[0067] In step S100, the propagation correction unit 290 performs propagation correction on propagation grid points that are located within a predetermined range around the target grid point, among the grid points distributed in the input color space. The propagation correction unit 290 obtains the color values ​​after propagation correction for the propagation grid points using ΔL, Δa, and Δb calculated in step S90. First, the propagation correction unit 290 identifies the propagation grid points.

[0068] Figure 10 is an explanatory diagram of propagation correction. As mentioned above, propagation grid points are grid points that are within a range less than a predetermined maximum distance R from the target grid point. For example, if the maximum distance R is "3" and pure color preservation of the C component is performed, then grid points with a distance D from the C axis of "1" or "2" become propagation grid points. Of the grid points on the MC plane, the grid points excluding the grid points on the M axis correspond to propagation grid points.

[0069] Figure 10 illustrates grid points on the MC plane, but grid points located within a predetermined maximum distance R from the target grid point, among the grid points on the CY, KC, MK, YM, and YK planes, are also considered ripple grid points. Note that grid points on any of the color axes are not included in the ripple grid points.

[0070] Furthermore, grid points that are not located on any of the MC, CY, KC, MK, YM, or YK planes, i.e., grid points where the values ​​of C, M, Y, and K are not zero (see Figure 3), and which are located within a predetermined maximum distance R from the target grid point, are also considered ripple grid points. The distance between the target grid point and the ripple grid point can be calculated as follows: If the index of the target grid point is (C1, M1, Y1, K1), and the index of the grid point not located on any of the MC, CY, KC, MK, YM, or YK planes is (C2, M2, Y2, K2), then the distance D between the target grid point and the grid point with index (C2, M2, Y2, K2) is D = SQRT{(C2-C1) 2 +(M2-M1) 2 +(Y2-Y1) 2 +(K2-K1) 2 This is calculated using}. Here, SQRT(val) represents the square root of the value val. Grid points whose distance D from the target grid point is less than the maximum distance M are considered propagation grid points.

[0071] The propagation correction unit 290 calculates the color value after propagation correction for the identified propagation grid points. The color value after propagation correction for the propagation grid points is also called the "post-propagation color value." The color value before propagation correction for the propagation grid points is also called the "pre-propagation color value." The propagation correction unit 290 uses the pre-propagation color value, the maximum distance R, the distance D from the target grid point to the propagation grid point, ΔL, Δa, and Δb to calculate the color value after propagation correction using the following equations (4) to (6). In equations (4) to (6), the subscript i (where i is a positive integer) is a value that identifies the grid point. ΔL, Δa, and Δb are the color differences obtained in step S90. L * after [i]=L* before [i] + 1 / R·(R-D)·ΔL ··· (4) a * after [i] = a * before [i] + 1 / R·(R-D)·Δa ··· (5) b * after [i] = b * before [i] + 1 / R·(R-D)·Δb ··· (6) L * after [i]: L of the i-th diffusion grid point after diffusion correction * L * before [i]: L of the i-th diffusion grid point before diffusion correction * a * after [i]: a of the i-th diffusion grid point after diffusion correction * a * before [i]: a of the i-th diffusion grid point before diffusion correction * b * after [i]: b of the i-th diffusion grid point after diffusion correction * b * before [i]: b of the i-th diffusion grid point before diffusion correction *

[0072] As shown in formulas (4) to (6), the greater the distance from the target grid point, the smaller the coefficient multiplied by the color difference. Figure 11 is an explanatory diagram showing the degree of change in the amount of color value change due to propagation correction. The smaller the distance D, that is, the closer the propagation grid point is to the target grid point, the larger the change Δ before and after propagation correction. The larger the distance D, that is, the farther the propagation grid point is from the target grid point, the smaller the change Δ before and after propagation correction. Since the degree of propagation to the propagation grid point is changed according to the distance D from the target grid point, it is possible to mitigate the degradation of color value gradation in color conversion using the DLP120 updated by the application of the color conversion option and propagation correction.

[0073] As shown in Figure 5, in step S110, the ink volume conversion unit 310 converts the color value after propagation correction to the ink volume after propagation correction by performing an optimization process using the color prediction model 130.

[0074] In this optimization process, the amount of ink input to the color prediction model 130 is varied, and the amount of ink that minimizes the difference between the color value after propagation correction and the color value calculated from the spectral reflectance output by the color prediction model 130 is determined.

[0075] As the initial value for the optimization process, the average amount of ink associated with the grid points surrounding the propagation grid points is used.

[0076] Figure 12 is an explanatory diagram of the grid points surrounding the propagation grid point. The target propagation grid point P21 is enclosed by a dashed ellipse. The average value of each ink amount (C, M, Y, K, Lc, Lm) associated with the grid points P22 to P25 adjacent to the propagation grid point P21 both vertically and horizontally is used as the initial value for the optimization process. The average value is calculated for each ink color.

[0077] The constraint imposed on the ink quantities (C, M, Y, K, Or, Red) input to the color prediction model 130 is that only ink colors associated with the surrounding grid points used to calculate the initial values ​​of the ink quantities input to the color prediction model 130 should be used.

[0078] For example, suppose the ink amounts (C, M, Y, K, Or, Red) associated with grid points P22 to P25 are as follows: Grid point P22:(76,5,0,0,0,0) Grid point P23:(49,0,0,0,0,0) Grid point P24:(49,20,0,0,0,0) Grid point P25:(32,5,0,0,0,0)

[0079] In this case, only C and M ink colors must be used. Therefore, the constraint condition (use, use, unuse, unuse, unuse, unuse) is imposed on the amount of ink (C, M, Y, K, Or, Red).

[0080] The solution converges when the difference between the color value after propagation correction and the color value calculated from the spectral reflectance output by the color prediction model 130 falls below a predetermined threshold. The ink amount, which is the input value to the color prediction model 130 at the time of convergence, is defined as the ink amount after propagation correction. The ink amount after propagation correction is also called the "post-propagation ink amount." The ink amount conversion unit 310 outputs the ink amount after propagation correction to the profile update unit 230 (see Figure 2).

[0081] By optimizing the process while considering the amount of ink associated with adjacent grid points, abrupt changes in color gradation can be mitigated during color conversion using the updated DLP120.

[0082] Depending on the order in which propagation correction is performed on propagation grid points, it is possible that grid points surrounding the target propagation grid point may already be propagation corrected grid points. For this reason, for example, when pure color preservation of the C component is performed, it is preferable that propagation correction is performed first on the grid point group closest to the C axis. When pure color preservation of the C component is performed, propagation correction is first performed on the propagation grid point group where the distance D from the C axis is "1", and then propagation correction is performed on the propagation grid point group where the distance D from the C axis is "2". When propagation correction is performed on propagation grid points where the distance D from the C axis is "1", the initial value of the optimization process can include information on the corrected ink amount of the grid points on the C axis that have been corrected for pure color preservation. Therefore, it is possible to propagate the effects of color value fluctuations caused by pure color preservation to propagation grid points.

[0083] Figure 12 shows an example where the average ink amount of grid points located above, below, to the left, and to the right of the target propagation grid point in the MC plane is used as the initial value for optimization. However, the average ink amount of grid points located above, below, to the left, to the right, diagonally above, and diagonally below the target propagation grid point in the MC plane may also be used as the initial value for the optimization process. In the illustrated example, the grid points surrounding the target propagation grid point in a two-dimensional plane are shown, but in reality, the CMYK color space is a four-dimensional space, so it is desirable to use the average ink amount associated with the grid points surrounding the target propagation grid point in a four-dimensional space as the initial value.

[0084] As shown in Figure 5, in step S120, the DLP120 is updated. The profile update unit 230 updates the ink amount as an output value associated with the corresponding grid point of the DLP120 with the ink amount after applying the color conversion option (see step S70 in Figure 4). In color conversion using the updated DLP120, the application of the color conversion option becomes effective. Furthermore, the profile update unit 230 updates the ink amount as an output value associated with the corresponding grid point of the DLP120 with the ink amount after propagation correction (see step S110 in Figure 5).

[0085] In step S130, the converted image acquisition unit 320 uses the updated DLP 120 to perform a color conversion process that converts the input values ​​in the input color space of the input image data IM to output values ​​in the output color space. Since the updated DLP 120 supports the application of color conversion options, the output values ​​produced by the color conversion process will have the color conversion options applied.

[0086] In step S140, the print data generation unit 330 separates the color-converted input image and outputs six separation data corresponding to C, M, Y, K, Orange, and Red. The print data generation unit 330 performs halftone processing on each separation data to convert the density and size of the halftone dots and generates print data corresponding to each separation data. In step S140, the generated print data is output to the printing device 400 (see Figure 1).

[0087] As described above, in this embodiment, the amount of ink to which the color conversion option is applied is obtained according to the selected color conversion option, and the DLP120 is modified with the amount of ink to which the color conversion option is applied. Furthermore, in color conversion using the DLP120 modified with the color conversion option applied, propagation correction is performed on propagation grid points existing in a predetermined range around the target grid point in order to suppress the occurrence of gradation jumps caused by the application of the color conversion option. By performing propagation correction, the occurrence of gradation jumps caused by the application of the color conversion option can be suppressed.

[0088] Furthermore, during propagation correction, the color value after propagation correction is calculated for the propagation grid point based on the difference in color values ​​before and after the application of the color conversion option, and the distance between the target grid point and the propagation grid point. The amount of ink associated with the propagation grid point is then determined based on the color value after propagation correction. In this way, by performing correction that propagates the application of the color conversion option to the range affected by the color fluctuations caused by the application of the color conversion option, the accuracy of color changes using the modified DLP120 can be improved.

[0089] B. Other embodiments: (B1) A propagation grid point may be subject to propagation correction due to the application of a color conversion option to two or more target grid points to which at least one color conversion option is applied. In this case, the color value after propagation correction can be calculated using equations (4) to (6) above, using the distance D between the target grid point closest to the propagation grid point and the propagation grid point.

[0090] (B2) A propagation grid point may be subject to propagation correction due to the application of a color conversion option to two or more target grid points for the application of at least one color conversion option. In this case, if the distance between each target grid point and the propagation grid point is the same, L is calculated using equations (7) to (9) with respect to the distance D between each target grid point and the propagation grid point. * after [i][j],a * after [i][j],b * after Calculate [i][j]. The subscript j (where j is a positive integer) is a value that identifies the target grid point. ΔL[j], Δa[j], and Δb[j] are the color values ​​applied to the j-th target grid point. L * after [i][j]=L * before [i]+1 / R·(RD)·ΔL[j]···(7) a * after [i][j]=a * before [i]+1 / R·(RD)·Δa[j]···(8) b * after [i][j]=b * before [i]+1 / R·(RD)·Δb[j]···(9)

[0091] If the number of target lattice points is N, then j is L from 1 to N. * after The average of [i][j] is L after propagation correction for the i-th propagation lattice point. * It is said that a after the ripple effect correction * value, b* Similarly, the average value obtained for the i-th propagation grid point is the propagation-corrected a * , b * For example, if there are two target grid points, the color value calculated for the first target grid point is also called the "first value." The color value calculated for the second target grid point is also called the "second value."

[0092] C. Other forms: This disclosure is not limited to the embodiments described above, and can be implemented in various forms without departing from its spirit. For example, this disclosure can also be implemented in the following forms. The technical features in the embodiments described below that correspond to the technical features in each of the forms described below can be replaced or combined as appropriate in order to solve some or all of the problems of this disclosure, or to achieve some or all of the effects of this disclosure. Furthermore, if such technical features are not described as essential in this specification, they can be deleted as appropriate.

[0093] (1) According to a first embodiment of the present disclosure, a method for creating color conversion data is provided. This color conversion data creation method includes: (a) obtaining a profile that defines the correspondence between input values ​​in the input color space of image data and the ink amounts of multiple ink colors as output values ​​in the output color space of a printing device that prints the image data; (b) accepting the specification of a color conversion option; (c) using the profile to convert the input values ​​in the input color space of the image data into the ink amounts in the output color space as pre-application ink amounts; (d) when the three attribute values ​​of the device-independent color space are defined as "color values", outputting pre-application color values, which are the color values ​​of the device-independent color space before the color conversion option is applied, from the pre-application ink amounts; and (e) using the pre-application ink amounts and the pre-application color values, for the ink amounts that correspond to target grid points, which are grid points representing the input values ​​that are the target of the application of the color conversion option among the grid points representing the input values ​​in the profile, the specified (f) an optimization process is performed using a color prediction model that takes the amount of ink as input and outputs the spectral reflectance which is the basis for calculating the color value, under constraints determined according to the color conversion option, thereby outputting the amount of ink after the color conversion option has been applied; (g) an optimization process is performed using a color prediction model that takes the amount of ink as input and outputs the spectral reflectance which is the basis for calculating the color value, thereby outputting the amount of ink after the color conversion option has been applied; (i) an optimization process is performed using the amount of ink that is associated with the amount of ink that is linked to According to the above configuration, by performing a correction in the profile that extends the application of the color conversion option to the range affected by color fluctuations caused by the application of the color conversion option, it is possible to mitigate the degradation of color value gradation in color conversion using the modified profile and improve the accuracy of color conversion.

[0094] (2) In the color conversion data creation method of the above form, the color conversion option is for reflecting the intention set in the input value in the ink amount when converting the input value that was intentionally set in the input color space to the ink amount in the output color space, The output value may include: pure color preservation, which corrects the output value so that only the color component in the output color space corresponding to the single color component is included when the input value contains only one color component; non-input color removal, which corrects the output value so that the value of the color component in the output color space corresponding to the color component not included in the input value is set to zero; and darkest area preservation, which corrects the output value so that the multiple color components in the output color space corresponding to the multiple color components included in the input value are set to their maximum density when the multiple color components in the input value each have a value indicating maximum density.

[0095] (3) In the color conversion data creation method of the above form, the color prediction model is a neural network model generated by machine learning using the spectral reflectance of a printed color chart and the amount of ink used when printing the color chart as training data, and outputs the spectral reflectance when the amount of ink is input. In step (d), the amount of ink before application may be input to the color prediction model to obtain the spectral reflectance before the color conversion option is applied, and the pre-application color value may be calculated based on the spectral reflectance before the color conversion option is applied. According to the above configuration, the pre-application color values ​​can be accurately predicted using a color prediction model, which is a neural network model.

[0096] (4) In the above-described method for creating color conversion data, in step (e), the amount of ink after application may be obtained by performing the optimization process that determines the amount of ink in the output color space that minimizes the difference between the color value calculated from the spectral reflectance output by the color prediction model and the pre-application color value, under the constraints. In processes such as pure color preservation and non-input color removal, two or more color components are reduced by correction. However, calculating the amount of ink after propagation in such cases requires considering multiple constraints. According to the above configuration, the amount of ink after propagation can be efficiently obtained through optimization processing.

[0097] (5) In the method for creating color conversion data in the above form, in step (h), the propagation grid points are located in a predetermined range around at least one color axis in which at least one of the target grid points representing the input value in the profile exists, and the propagation color value is obtained by adding a value obtained by multiplying the color difference by a coefficient that decreases as the distance between the color axis in which at least one of the target grid points exists and the propagation grid point increases, to the pre-application color value corresponding to the ink amount associated with the propagation grid point, and the propagation ink amount is output by performing an optimization process using the color prediction model with respect to the ink amount associated with the propagation grid point using the propagation color value. According to the above configuration, the degree to which the color conversion option is applied is varied at the propagation grid points depending on the distance from the color axis representing the color component whose ink volume is increased or decreased, thereby mitigating the degradation of the color gradation.

[0098] (6) In the color conversion data creation method of the above form, in step (h), if the propagation grid point is subject to the propagation correction by applying the color conversion option to two or more target grid points for the application of at least one of the color conversion options, the propagation color value may be obtained by adding a value obtained by multiplying the color difference for the closest target grid point by a coefficient corresponding to the distance between the target grid point closest to the propagation grid point and the propagation grid point, which decreases as the distance increases, to the pre-application color value corresponding to the ink amount associated with the propagation grid point, and the propagation ink amount may be output by performing an optimization process using the color prediction model with respect to the ink amount associated with the propagation grid point using the propagation color value.

[0099] (7) In the method for creating color conversion data of the above form, in step (h), if the propagation grid point is subject to the propagation correction by applying the color conversion option to two target grid points for which at least one of the color conversion options is applied, and the distance from the propagation grid point to the two target grid points is the same, a first value is calculated by adding to the pre-application color value corresponding to the amount of ink associated with the propagation grid point a coefficient corresponding to the distance between one of the target grid points and the propagation grid point, which decreases as the distance increases, multiplied by the color difference relating to one of the target grid points, A second value may be calculated by adding to the pre-application color value corresponding to the ink amount associated with the propagation grid point a coefficient corresponding to the distance between the other target grid point and the propagation grid point, which decreases as the distance increases, multiplied by the color difference relating to the other target grid point. The propagation color value may be obtained by calculating the average of the first value and the second value. The propagation ink amount may be output by performing an optimization process using the color prediction model with respect to the ink amount associated with the propagation grid point using the propagation color value.

[0100] (8) In the above-described method for creating color conversion data, in step (f), the amount of ink after application may be input to the color prediction model to obtain the spectral reflectance after the color conversion option has been applied, and the applied color value may be calculated based on the spectral reflectance after the color conversion option has been applied.

[0101] (9) According to a second embodiment of the present disclosure, a color conversion data creation device is provided. This color conversion data creation device includes a process for acquiring a profile which defines the correspondence between input values ​​in the input color space of image data and the ink amounts of multiple ink colors as output values ​​in the output color space of a printing device that prints the image data represented by the image data; a process for accepting the specification of a color conversion option; a process for using the profile to convert the input values ​​in the input color space of the image data into the ink amounts in the output color space as pre-application ink amounts; a process for outputting pre-application color values, which are the color values ​​in the device-independent color space before the color conversion option is applied, when the three attribute values ​​of the device-independent color space are defined as "color values"; and a process for using the pre-application ink amount and the pre-application color value to convert the specified color conversion data to the ink amount associated with the target grid point, which is a grid point representing the input value to which the color conversion option is applied, among the grid points representing the input value in the profile. Under constraints determined according to the conversion option, an optimization process is performed using a color prediction model that takes the amount of ink as input and outputs the spectral reflectance which is the basis for calculating the color value, thereby performing the following: outputting the amount of ink after the application option has been applied; outputting the color value after the application option has been applied from the amount of ink after the application option has been applied; outputting the color difference for the target grid point, which is the difference between the pre-application color value and the post-application color value; outputting the amount of ink after propagation correction is performed to propagate the application of the color conversion option using the amount of ink associated with the propagation grid points that exist in a predetermined range around the target grid point among the grid points representing the input value in the profile, and the color difference; and modifying the profile using the amount of ink after the application option and the amount of ink after propagation.

[0102] (10) According to a third embodiment of the present disclosure, a computer program is provided. This program includes a function to acquire a profile that defines the correspondence between input values ​​in an input color space in image data and the ink amounts of multiple ink colors as output values ​​in an output color space of a printing device that prints the image data; a function to accept the specification of a color conversion option; a function to convert the input values ​​in the input color space in the image data into the ink amounts in the output color space as pre-application ink amounts using the profile; a function to output pre-application color values, which are the color values ​​in the device-independent color space before the color conversion option is applied, when the three attribute values ​​of the device-independent color space are defined as "color values"; and a function to apply the specified color conversion option to the ink amounts corresponding to target grid points, which are grid points representing the input values ​​that are subject to the application of the color conversion option, using the pre-application ink amounts and the pre-application color values. Under constraints determined accordingly, the computer is made to perform an optimization process using a color prediction model that takes the amount of ink as input and outputs the spectral reflectance that forms the basis for calculating the color value, thereby enabling the computer to perform the following functions: outputting the amount of ink after the application option has been applied; outputting the color value after the application option has been applied from the amount of ink after the application option has been applied; outputting the color difference for the target grid point, which is the difference between the pre-application color value and the post-application color value; outputting the amount of ink after propagation correction, which is the amount of ink after propagation correction is performed to propagate the application of the color conversion option using the amount of ink associated with the propagation grid points that exist in a predetermined range around the target grid point among the grid points representing the input value in the profile, and the color difference; and modifying the profile using the amount of ink after the application and the amount of ink after propagation.

[0103] This disclosure can also be implemented in various forms other than a color conversion data creation method, a color conversion data creation apparatus, and a computer program. For example, it can be implemented in the form of an image processing method or a non-transitory storage medium on which a computer program is recorded. [Explanation of symbols]

[0104] D...Distance, IM...Input image data, P1, P2...Grid points, PL1...Plane, R...Maximum distance, W1...Selection screen, 10...Printing system, 100...Image processing device, 101...Memory, 102...Input / output interface, 103...Processor, 104...Internal bus, 110...Program, 120...Device Link Profile (DLP), 130...Color prediction model, 200...Input device, 210...Image acquisition unit, 220...Profile specification unit, 230...Profile update unit, 240...Ink amount acquisition unit, 250...Color conversion option specification unit, 260...Color prediction model acquisition unit, 270...Color value conversion unit, 280...Color change amount calculation unit, 290...Propagation correction unit, 300...Display device, 310...Ink amount conversion unit, 320...Post-conversion image acquisition unit, 330...Print data generation unit, 400...Printing device

Claims

1. A method for creating color conversion data, (a) A step of obtaining a profile in which the correspondence between the input values ​​of the input color space in the image data and the ink amounts of multiple ink colors as output values ​​of the output color space in a printing device that prints the image data represented by the image data is defined, (b) A process for receiving the specification of color conversion options, (c) A step of using the profile to convert the input value of the input color space in the image data into the amount of ink in the output color space as the amount of ink before application, (d) When the three attribute values ​​of the device-independent color space are defined as "color values", A step of outputting the pre-application color value, which is the color value in the device-independent color space before the application of the color conversion option, from the pre-application ink amount, (e) With respect to the amount of ink associated with a target grid point in the profile that represents the input value and is the grid point that represents the input value to which the color conversion option is applied, A step of outputting the amount of ink after application, which is the amount of ink after the color conversion option has been applied, by performing an optimization process using a color prediction model that takes the amount of ink as input and outputs the spectral reflectance that is the basis for calculating the color value, under constraints determined according to the specified color conversion option, using the amount of ink before application and the color value before application, (f) A step of outputting the applied color value, which is the color value after the color conversion option has been applied, from the applied ink amount, (g) A step of outputting a color difference, which is the difference between the pre-application color value and the post-application color value, for the target grid point. (h) A step of outputting a post-propagation ink amount, which is the ink amount after performing propagation correction to propagate the application of the color conversion option using the ink amount corresponding to propagation grid points that exist in a predetermined range around the target grid point among the grid points representing the input value in the profile, and the color difference, (i) A step of modifying the profile using the amount of ink after application and the amount of ink after propagation, A method for creating color conversion data, including the creation of color conversion data.

2. A method for creating color conversion data according to claim 1, The aforementioned color conversion option is: This is for the purpose of reflecting the intention set in the input value in the ink quantity when converting the input value, which was intentionally set in the input color space, into the ink quantity in the output color space. When the input value contains only one color component, pure color preservation corrects it so that only the color component in the output color space corresponding to the one color component is included in the output value. Non-input color removal corrects the output value to zero the value of the color component in the output color space corresponding to the color component not included in the input value, When the multiple color components included in the input value are values ​​that indicate the maximum density of each of them, the output value is corrected to make the multiple color components in the output color space corresponding to the multiple color components included in the input value have the maximum density by holding the darkest area, A method for creating color conversion data, including the creation of color conversion data.

3. A method for creating color conversion data according to claim 2, The aforementioned color prediction model is a neural network model generated by machine learning using the spectral reflectance of a printed color chart and the amount of ink used when printing the color chart as training data, and outputs the spectral reflectance when the amount of ink is input. In step (d) above, The amount of ink before application is input to the color prediction model to obtain the spectral reflectance before the color conversion option is applied. The pre-application color value is calculated based on the spectral reflectance before the application of the color conversion option. How to create color conversion data.

4. A method for creating color conversion data according to claim 3, In step (e) above, Under the aforementioned constraints, the amount of ink after application is obtained by performing the optimization process that determines the amount of ink in the output color space that minimizes the difference between the color value calculated from the spectral reflectance output by the color prediction model and the pre-application color value. How to create color conversion data.

5. A method for creating color conversion data according to claim 4, In the above step (h), The aforementioned propagation grid points are located within a predetermined range around at least one color axis in which at least one of the target grid points representing the input value in the profile exists. The color difference is multiplied by a coefficient that decreases as the distance between the color axis containing at least one of the target grid points and the propagation grid point increases, and this value is added to the pre-application color value corresponding to the amount of ink associated with the propagation grid point to obtain the propagation color value. With respect to the amount of ink associated with the propagation grid points, the amount of ink after propagation is output by performing an optimization process using the color prediction model with the propagation color value. How to create color conversion data.

6. A method for creating color conversion data according to claim 5, In the above step (h), If the propagation grid point is subject to the propagation correction by applying the color conversion option to two or more target grid points for the application of at least one of the color conversion options, The color difference corresponding to the closest target grid point is multiplied by a coefficient that corresponds to the distance between the target grid point closest to the propagation grid point and the propagation grid point, and which decreases as the distance increases, and this value is added to the pre-application color value corresponding to the ink amount associated with the propagation grid point, thereby obtaining the post-propagation color value. With respect to the amount of ink associated with the propagation grid points, the amount of ink after propagation is output by performing an optimization process using the color prediction model with the propagation color value. How to create color conversion data.

7. A method for creating color conversion data according to claim 6, In the above step (h), If the propagation grid point is subject to the propagation correction by applying the color conversion option to two target grid points for which at least one of the color conversion options is applied, and the distance from the propagation grid point to the two target grid points is the same, A first value is calculated by adding to the pre-application color value corresponding to the amount of ink associated with the spreading grid point a coefficient corresponding to the distance between one of the target grid points and the spreading grid point, which decreases as the distance increases, multiplied by the color difference applied to one of the target grid points, A second value is calculated by adding to the pre-application color value corresponding to the ink amount associated with the aforementioned spreading grid point a coefficient corresponding to the distance between the other target grid point and the spreading grid point, which decreases as the distance increases, multiplied by the color difference relating to the other target grid point, By calculating the average of the first value and the second value, the ripple effect color value is obtained. With respect to the amount of ink associated with the propagation grid points, the amount of ink after propagation is output by performing an optimization process using the color prediction model with the propagation color value. How to create color conversion data.

8. A method for creating color conversion data according to claim 7, In step (f) above, The amount of ink after application is input to the color prediction model to obtain the spectral reflectance after the color conversion option has been applied. The post-application color value is calculated based on the spectral reflectance after the application of the color conversion option. How to create color conversion data.

9. A color conversion data creation device, A process for obtaining a profile that defines the correspondence between input values ​​in the input color space of image data and the ink amounts of multiple ink colors as output values ​​in the output color space of a printing device that prints the image data, The process of accepting the specification of color conversion options, Using the profile, a process is performed to convert the input value of the input color space in the image data into the ink amount of the output color space as the ink amount before application, When the three attribute values ​​of the device-independent color space are defined as "color values", the process outputs the pre-application color values, which are the color values ​​of the device-independent color space before the application of the color conversion option, from the pre-application ink amount. In the profile, with respect to the amount of ink associated with the target grid point, which is a grid point representing the input value to which the color conversion option is applied, among the grid points representing the input value, Using the aforementioned pre-application ink amount and the pre-application color value, an optimization process is performed using a color prediction model that takes the ink amount as input and outputs the spectral reflectance that forms the basis for calculating the color value, under constraints determined according to the specified color conversion option, thereby outputting the post-application ink amount, which is the ink amount after the color conversion option has been applied. A process to output the applied color value, which is the color value after the color conversion option has been applied, from the amount of ink after application, For the aforementioned target grid point, a process is performed to output the color difference, which is the difference between the pre-application color value and the post-application color value. A process to output a post-propagation ink amount, which is the ink amount after performing propagation correction to propagate the application of the color conversion option using the ink amount associated with propagation grid points located within a predetermined range around the target grid point among the grid points representing the input value in the profile, and the color difference; A process to modify the profile using the amount of ink after application and the amount of ink after propagation, A color conversion data creation device that performs this operation.

10. A program that is executed by a computer, A function to acquire a profile that defines the correspondence between the input values ​​of the input color space in image data and the ink amounts of multiple ink colors as output values ​​in the output color space of a printing device that prints the image data, A function that accepts the specification of color conversion options, A function that uses the profile to convert the input value of the input color space in the image data into the ink amount of the output color space as the ink amount before application, When the three attribute values ​​of the device-independent color space are defined as "color values," the function outputs the pre-application color value, which is the color value of the device-independent color space before the application of the color conversion option, from the pre-application ink amount. In the profile, with respect to the amount of ink associated with the target grid point, which is a grid point representing the input value to which the color conversion option is applied, among the grid points representing the input value, The function outputs the amount of ink after application, which is the amount of ink after the color conversion option has been applied, by performing an optimization process using a color prediction model that takes the amount of ink as input and outputs the spectral reflectance that forms the basis for calculating the color value, under constraints determined according to the specified color conversion option, using the amount of ink before application and the color value before application. A function to output the applied color value, which is the color value after the color conversion option has been applied, from the applied ink amount, The function outputs the color difference, which is the difference between the pre-application color value and the post-application color value, for the aforementioned target grid point. A function to output a post-propagation ink amount, which is the ink amount after performing propagation correction that propagates the application of the color conversion option using the ink amount corresponding to propagation grid points located within a predetermined range around the target grid point among the grid points representing the input value in the profile, and the color difference, A function to modify the profile using the amount of ink after application and the amount of ink after propagation. A program that enables a computer to perform this task.

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