JP2018101948A - Color conversion profile creation method, color conversion profile creation device, and color conversion profile creation program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technology that can improve the accuracy in color reproduction in the vicinity of a surface of a color reproduction area while substantially maintaining the accuracy in color reproduction inside the color reproduction area.SOLUTION: A color conversion profile creation method includes: an expansion range setting step of setting an expansion range in which a color reproduction area of a device is expanded outward on the basis of the interval between first lattice points arranged in a first color space; an extrapolation step of creating extrapolation data for extrapolating color reproduction characteristics of the device in the expansion range on the basis of characteristic data indicating the color reproduction characteristics of the device in the color reproduction area; and an association step of associating a first coordinate value with a second coordinate value in a second color space depending on the device on the basis of the characteristic data and the extrapolation data, for the plurality of first lattice points arranged in the first color space beyond the color reproduction area.SELECTED DRAWING: Figure 7

Description

  The present invention relates to a color conversion profile generation method, a color conversion profile generation apparatus, and a color conversion profile generation program.

In order to obtain good color reproducibility by a device such as a printer, a color conversion profile such as an ICC (International Color Consortium) profile describing the color reproduction characteristics of the device is used. The ICC profile includes, for example, CIE (International Lighting Commission) L ^* a ^* b ^* color space coordinate values, which are device independent color spaces, device-dependent color space coordinate values, Are associated. The ICC profile includes a so-called A2B table and a so-called B2A table. If the device is a printer that uses color materials of C (cyan), M (magenta), Y (yellow), and K (black), the B2A table contains Lab values (L ^* values, a ^* values, and , B ^* value) are converted into CMYK values (C value, M value, Y value, and K value). The B2A table has a plurality of lattice points arranged in the L ^* a ^* b ^* color space so as to be substantially equally spaced in the L ^* axis direction, the a ^* axis direction, and the b ^* axis direction. Each grid point is associated with a CMYK value. For high-speed computation, the Lab value and CMYK value are usually computed with 8 bits (for example, integer values 0 to 255) or 16 bits (for example, integer values 0 to 65535).
In the following description, the description of “ ^* ” may be omitted.

  The device has a color gamut that is a color reproducible range. In the B2A table, CMYK values that reproduce colors of Lab values (L ′ value, a ′ value, and b ′ value) on the surface of the color gamut are usually stored at grid points outside the color gamut. The For this reason, the Lab value of the input color near the surface of the color gamut where a grid point outside the color gamut is referred to for interpolation of the CMYK value is the CMYK value of the output color whose saturation is lower than the target input color. As a result, the color reproduction accuracy near the surface of the color gamut is lowered. Here, the color reproduction accuracy refers to the degree of accurate color reproduction.

  Patent Document 1 discloses a color conversion table in which a conversion result exceeds a predetermined color reproducible range with a device and is described by color signal values that cannot be reproduced by the device. The CMY values (C value, M value, and Y value) of this color conversion table are an integer value of 0 to 255 that represents the inside of the color gamut and an integer value that is less than 0 or greater than 255 that represents the outside of the color gamut. It is represented. The range outside the color gamut is not limited.

JP-A-11-55536

If the range of CMY values is expanded from integer values 0 to 255, the data size of the color conversion table increases and the time required for color conversion calculation also increases. Here, when the CMY values including the numerical range representing the outside of the color gamut are compressed within the range of integer values 0 to 255, the numerical range representing the inside of the color gamut is greatly increased if the range outside the color gamut is not limited. As a result, the color reproduction accuracy within the color gamut is reduced accordingly.
Note that the above-described problem exists not only in the color conversion table for converting Lab values into CMY values, but also in various color conversion profiles.

  One object of the present invention is to provide a technique capable of improving the color reproduction accuracy near the surface of the color gamut while substantially maintaining the color reproduction accuracy inside the color gamut.

In order to achieve one of the above objects, the present invention relates to a first coordinate value of the first color space and a second depending on the device for a plurality of first grid points arranged in the first color space. A color conversion profile generation method for associating the second coordinate value of the color space with
An extension range setting step for setting an extension range for extending the color reproduction range of the device to the outside based on an interval between the first grid points arranged in the first color space;
An extrapolation step of generating extrapolation data for extrapolating the color reproduction characteristics of the device in the extended range, based on characteristic data representing the color reproduction characteristics of the device in the color gamut;
For the plurality of first grid points arranged beyond the color reproduction range with respect to the first color space, the first coordinate value and the second coordinate value based on the characteristic data and the extrapolation data. And an associating step.

The present invention also provides a first coordinate value of the first color space and a second coordinate value of the second color space depending on the device for a plurality of first grid points arranged in the first color space. And a color conversion profile generation device that associates
An extended range setting unit for setting an extended range for extending the color reproduction range of the device to the outside based on an interval between the first grid points arranged in the first color space;
An extrapolation unit that generates extrapolation data for extrapolating the color reproduction characteristics of the device in the extended range based on characteristic data representing the color reproduction characteristics of the device in the color reproduction range;
For the plurality of first grid points arranged beyond the color reproduction range with respect to the first color space, the first coordinate value and the second coordinate value based on the characteristic data and the extrapolation data. And an associating unit for associating with each other.

Furthermore, the present invention provides a first coordinate value of the first color space and a second coordinate value of the second color space depending on the device for a plurality of first grid points arranged in the first color space. And a color conversion profile generation program for associating
An extended range setting function for setting an extended range for extending the color reproduction range of the device to the outside based on the interval between the first grid points arranged in the first color space;
An extrapolation function for generating extrapolation data for extrapolating the color reproduction characteristics of the device in the extended range based on characteristic data representing the color reproduction characteristics of the device in the color reproduction range;
For the plurality of first grid points arranged beyond the color reproduction range with respect to the first color space, the first coordinate value and the second coordinate value based on the characteristic data and the extrapolation data. And an associating function for associating with each other.

  The above-described aspect can provide a technique capable of improving the color reproduction accuracy near the surface of the color gamut while substantially maintaining the color reproduction accuracy inside the color gamut.

FIG. 2 is a block diagram schematically illustrating a configuration example of a color conversion profile generation device. The flowchart which shows the example of a 1st gamut mapping process. The figure which shows typically the example which produces | generates characteristic data from original data and produces | generates three-dimensional LUT. The figure which shows typically the example of the virtual CMY space showing the color reproduction range of a virtual CMY printer. The figure which shows typically the cause for which the color reproduction precision of the color reproduction area surface vicinity falls. The figure which shows the example of extended virtual CMY space typically. The flowchart which shows the example of a 2nd gamut mapping process. The figure which shows typically the example of the extended virtual CMY space which expanded the color reproduction range of the virtual CMY printer. The figure which shows typically the example which produces | generates three-dimensional LUT from extended data. 6 is a flowchart illustrating an example of color conversion profile generation processing. The figure which shows the structural example of a color conversion profile typically. The flowchart which shows the example of a brightness direction expansion range setting process. The figure which shows typically the example which determines the lightness expansion amount of virtual CMY space. The figure which shows typically the example which calculates the lightness expansion amount of virtual CMY space. The figure which shows typically the example which determines the CMY expansion amount corresponding to the lightness expansion amount. The figure which shows typically the example which calculates the lightness expansion amount of virtual CMY space. The flowchart which shows the example of a saturation direction expansion range setting process. The figure which shows typically the example which calculates the saturation expansion amount of virtual CMY space. The flowchart which shows the example of an extended range setting process. The flowchart which shows the example of an extrapolation data generation process. The figure which shows typically the example which expands the surface of virtual CMY space in CMY color space. The figure which shows typically the example which sets multiple combinations of a specific grid point and a specific point. The figure which shows typically the example which selects the combination used for extrapolation calculation among the combination of a specific grid point and a specific point. The figure which shows typically the example which expands the ridgeline of virtual CMY space in CMY color space. The figure which shows typically the example which expands the vertex of virtual CMY space in CMY color space.

  Embodiments of the present invention will be described below. Of course, the following embodiments are merely examples of the present invention, and all the features shown in the embodiments are not necessarily essential to the means for solving the invention.

(1) Summary of technology included in the present invention:
First, the outline | summary of the technique included in this invention is demonstrated with reference to the example shown by FIGS. In addition, the figure of this application is a figure which shows an example typically, The expansion ratio of each direction shown by these figures may differ, and each figure may not match. Of course, each element of the present technology is not limited to the specific example indicated by the reference numeral.

[Aspect 1]
A color conversion profile generation method according to an aspect of the present technology includes an extended range setting step ST1, an extrapolation step ST2, and an association step ST3, and is arranged in a first color space (for example, the Lab color space CS1). For a plurality of first grid points GD1, a first coordinate value (for example, Lab value) of the first color space (CS1) and a second color space (for example, CMYK color space CS2) depending on the device (for example, the printer 200). ) With the second coordinate value (for example, CMYK value). In the extended range setting step ST1, as illustrated in FIG. 12 and the like, the device is based on the interval (for example, gL, gAB) between the first grid points GD1 arranged in the first color space (CS1). An extended range AR1 for extending the color reproduction range (GMT) of the printer 200 (for example, the printer 200) is set. In the extrapolation step ST2, as illustrated in FIG. 7 and the like, the color reproduction characteristics of the device in the extended range AR1 based on the characteristic data 520 representing the color reproduction characteristics of the device in the color gamut (GMT). Extrapolation data 600 for extrapolating is generated. In the associating step ST3, the characteristic data 520 and the extrapolation for the plurality of first grid points GD1 arranged beyond the color reproduction range (GMT) with respect to the first color space (CS1). Based on the data 600, the first coordinate value is associated with the second coordinate value.

  In aspect 1, the color reproduction range (GMT) of the device (200) is extended to the outside based on the spacing (gL, gAB) of the first grid points GD1 arranged in the first color space (CS1). A range AR1 is set. Extrapolation data 600 for extrapolating the color reproduction characteristics of the device is generated in the extended range AR1, and the first coordinate value (Lab value) for the first grid point GD1 is calculated based on the extrapolation data 600 and the characteristic data 520. The second coordinate value (CMYK value) is associated. Therefore, this aspect can provide a color conversion profile generation method capable of improving the color reproduction accuracy near the surface of the color gamut while substantially maintaining the color reproduction accuracy inside the color gamut.

Here, the first color space includes a device independent color space such as a CIE L ^* a ^* b ^* color space, a CIE L ^* u ^* v ^* color space, and the like.
The second color space includes a CMYK color space, a CMY color space, an RGB color space, a CMYKLcLm color space, and the like. Note that R means red, G means green, B means blue, Lc means light cyan with a lower density than C, and Lm means light magenta with a lower density than M. Yes.
A device-dependent color space is also called a device-dependent color space, and even if the coordinate value is determined, the color perceived by humans cannot be specified, and depends on the color reproduction characteristics of the device. This is a color space where colors are determined.

[Aspect 2]
In the extended range setting step ST1, as illustrated in FIG. 12 and the like, the slope of the surface of the device color reproduction region (for example, gamut GMT) in the first color space (CS1) (for example, Slope illustrated in FIG. 13). And an extended range AR1 for extending the color reproduction range (GMT) based on the interval (for example, gL, gAB) between the first grid points GD1 arranged in the first color space (CS1). May be set.

In the aspect 2, the slope (Slope) of the surface of the color gamut (GMT) in the first color space (CS1) and the interval (gL) between the first grid points GD1 arranged in the first color space (CS1). , GAB), an extended range AR1 that extends the color reproduction range (GMT) to the outside is set. Extrapolation data 600 for extrapolating the color reproduction characteristics of the device is generated in the extended range AR1, and the first coordinate value (Lab value) for the first grid point GD1 is calculated based on the extrapolation data 600 and the characteristic data 520. The second coordinate value (CMYK value) is associated. Therefore, this aspect can provide a color conversion profile generation method capable of improving the color reproduction accuracy near the surface of the color gamut while substantially maintaining the color reproduction accuracy inside the color gamut.
Although not included in the above-described aspect 2, the extended range is determined based on the interval between the first grid points arranged in the first color space without being based on the inclination of the surface of the color gamut in the first color space. This setting is also included in the present technology.

[Aspect 3]
As illustrated in FIG. 13 and the like, the slope (for example, Slope) of the surface of the color gamut (GMT) in the first color space (for example, Lab color space CS1) is the ratio of the brightness difference dL to the saturation difference dC. It may be represented by In the extended range setting step ST1, the inclinations of a plurality of locations on the surface of the color gamut (GMT) in the first color space (CS1) may be acquired based on the characteristic data 520. In the extended range setting step ST1, the maximum inclination (for example, Slope_max) among the inclinations of the plurality of places and the interval (for example, gL, gAB) between the first grid points GD1 arranged in the first color space (CS1). ), A brightness extension amount (for example, Ext_L0) for extending the color reproduction range (GMT) in the brightness direction in the first color space (CS1) may be acquired. In the extended range setting step ST1, the extended range AR1 may be set based at least on the brightness extension amount. This aspect can provide a more suitable method for generating a color conversion profile.

[Aspect 4]
As illustrated in FIGS. 17 and 18 and the like, in the extended range setting step ST1, the minimum inclination (for example, Slope_min) among the inclinations of the plurality of locations and the first color space (for example, the Lab color space CS1). The color reproduction range (GMT) is expanded in the direction of saturation in the first color space (CS1) based on the interval (for example, gL, gAB) between the first grid points GD1 arranged in A saturation expansion amount (for example, Ext_C0) may be acquired. In the extended range setting step ST1, the extended range AR1 may be set based at least on the saturation expansion amount. This aspect can also provide a more preferable method for generating a color conversion profile.
Further, as illustrated in FIG. 19, in the extension range setting step ST1, a first extension range based on the brightness extension amount (for example, CMY extension amounts Ext_CMY0L, Ext_CMY1L) and a second extension range based on the saturation extension amount. The wider one of (for example, CMY extension amount Ext_CMY0C, Ext_CMY1C) may be set as the extension range AR1. This aspect can provide a more suitable method for generating a color conversion profile.
Although not included in the above aspects 3 and 4, the present technology also includes a case where the slope of the surface of the color gamut is not the ratio of the brightness difference to the saturation difference.

[Aspect 5]
As illustrated in FIG. 3 and the like, the characteristic data 520 is for the second grid point GD2 arranged in the color gamut (GMT) in a third color space (for example, CMY color space CS3) depending on the device. The third coordinate value (for example, CMY value) of the third color space (CS3) and the first coordinate value (for example, Lab value) may be associated with each other. As illustrated in FIG. 9 and the like, the extrapolated data 600 is the third coordinate value (CMY value) of the third grid point GD3 arranged in the extended range AR1 in the third color space (CS3). And the first coordinate value (Lab value) may be associated with each other. This aspect can provide a suitable method for generating a color conversion profile.
Here, the third color space may be the same color space as the second color space, or may be a color space different from the second color space.

[Aspect 6]
The third color space (for example, CMY color space CS3) may be a color space in which the dimensions of the second color space (for example, CMYK color space CS2) are reduced. As illustrated in FIG. 3 and the like, the present color conversion profile generation method associates the second coordinate value (for example, CMYK value) and the first coordinate value (for example, Lab value) in the second color space (CS2). A characteristic data generation step ST4 for generating the characteristic data 520 based on the attached original data (for example, colorimetric data 500) may be included. This aspect can provide a more suitable method for generating a color conversion profile.
Here, for example, when the second color space is a CMYK color space or a CMYKLcLm color space, the third color space can be a CMY color space.

[Aspect 7]
As exemplified in FIG. 21 and the like, the third color space (for example, CMY color space CS3) is a first axis (for example, C axis) that intersects each other for defining the third coordinate value (for example, CMY value). , A second axis (for example, M axis), and a third axis (for example, Y axis). Here, in the third color space (CS3), the second grid point GD2 within the predetermined range AR2 from the third grid point GD3 among the second grid points GD2 on the surface of the color gamut (GMT). Is a specific grid point GD4. Further, in the third color space (CS3), the point in the direction connecting the third grid point GD3 to the specific grid point GD4 in the color gamut (GMT), the first axis, More than ½ of the size of the color gamut (GMT) in the direction of either the second axis or the third axis, the depth (Ref_Depth, for example) from the surface of the color gamut (GMT) ) Is designated as a specific point P0. In the extrapolation step ST2, the extrapolation data 600 may be generated based on the data of the specific grid point GD4 and the specific point P0 in the characteristic data 520 in the third color space (CS3).

In the aspect 7, the specific point P0 for generating the extrapolation data 600 is at least 1/2 the size of the color gamut (GMT) in the axial direction and is located behind the surface of the color gamut (GMT). Therefore, it is difficult to be affected by the irregular shape of the surface of the color gamut (GMT). Therefore, this aspect can provide a technique capable of further improving the color reproduction accuracy near the surface of the color gamut.
Although not included in the above-described aspect 7, the present technology also includes setting the specific point to a point having a depth less than ½ of the size of the color gamut in the axial direction.

[Aspect 8]
As illustrated in FIG. 22 and the like, a plurality of combinations of the specific grid point GD4 and the specific point P0 may be set. In the extrapolation step ST2, in the third color space (for example, CMY color space CS3), the characteristic data 520 is based on the data of the specific grid point GD4 and the specific point P0 included in the plurality of combinations. Extrapolation data 600 may be generated. This aspect is not easily affected by the error in the coordinate values at the individual specific grid points GD4 and the individual specific points P0. Therefore, this aspect can provide a technique capable of further improving the color reproduction accuracy near the surface of the color gamut.

[Aspect 9]
As illustrated in FIGS. 10 and 11, the present color conversion profile generation method is a correspondence data generation step for generating first correspondence data (for example, three-dimensional LUT 700) and second correspondence data (for example, output table 800). ST5 may be included. Here, the first correspondence data (700) includes the first coordinate value (for example, Lab value) and the second coordinate value (for example, C3M3Y3K3 value) that are at least partially associated in the association step ST3. This data represents the first correspondence relationship. In the second correspondence data (800), the second coordinate value (C3M3Y3K3 value) obtained from the first coordinate value (Lab value) according to the first correspondence relationship is not included in the color gamut (GMT). In the case of a value, the second coordinate value is data representing a second correspondence relationship for converting the second coordinate value into a value (for example, a C4M4Y4K4 value) included in the color gamut (GMT). In this aspect, when the second coordinate value obtained from the first coordinate value according to the first correspondence relationship is a value that is not included in the color gamut (GMT), the second coordinate value is included in the color gamut (GMT). Therefore, a suitable color conversion profile generation method can be provided.

[Aspect 10]
By the way, the color conversion profile generation device (for example, the host device 100) according to an aspect of the present technology includes an extended range setting unit U1 corresponding to the extended range setting step ST1, an extrapolation unit U2 corresponding to the extrapolation step ST2, and An association unit U3 corresponding to the association step ST3 is provided. This aspect can provide a color conversion profile generation device capable of improving the color reproduction accuracy near the surface of the color gamut while substantially maintaining the color reproduction accuracy inside the color gamut. The color conversion profile generation apparatus (100) may further include a characteristic data generation unit U4 corresponding to the characteristic data generation step ST4 and a correspondence relationship data generation unit U5 corresponding to the correspondence relationship data generation step ST5.

[Aspect 11]
In addition, the color conversion profile generation program PR0 according to an aspect of the present technology performs the extended range setting function FU1 corresponding to the extended range setting step ST1, the extrapolation function FU2 corresponding to the extrapolation step ST2, and the association step ST3. A corresponding matching function FU3 is realized on the computer. This aspect can provide a color conversion profile generation program capable of improving the color reproduction accuracy near the surface of the color gamut while substantially maintaining the color reproduction accuracy inside the color gamut. The color conversion profile generation program PR0 may cause the computer to realize the characteristic data generation function FU4 corresponding to the characteristic data generation step ST4 and the correspondence data generation function FU5 corresponding to the correspondence data generation step ST5.

  Furthermore, the present technology can be applied to a composite device including a color conversion profile generation device, a control method for the composite device, a control program for the composite device, a color conversion profile generation program, a computer-readable medium storing the control program, and the like. It is. The aforementioned apparatus may be composed of a plurality of distributed parts.

(2) Specific example of the configuration of the color conversion profile generation device:
FIG. 1 schematically shows a host device 100 as a configuration example of a color conversion profile generation device. The host device 100 includes a CPU (Central Processing Unit) 111, a ROM (Read Only Memory) 112, a RAM (Random Access Memory) 113, a storage device 114, a display device 115, an input device 116, a color measuring device 117, a communication I / O. F (interface) 118 and the like are connected to enable input / output of information.

  The storage device 114 stores an OS (operating system) (not shown), a color conversion profile generation program PR0, and the like. These are read out to the RAM 113 as appropriate, and are used for generating a color conversion profile 400 (for example, an ICC profile). At least one of the RAM 113 and the storage device 114 includes various information such as colorimetric data 500, K (black) generation function 510, characteristic data 520, three-dimensional LUT (look-up table) 530, extrapolated data 600, three-dimensional. An LUT 610, a three-dimensional LUT 700 (example of first correspondence data) included in the color conversion profile 400, an output table 800 (example of second correspondence data) included in the color conversion profile 400, and the like are stored. As the storage device 114, a non-volatile semiconductor memory such as a flash memory, a magnetic storage device such as a hard disk, or the like can be used.

A liquid crystal display panel or the like can be used for the display device 115. As the input device 116, a pointing device, a hard key including a keyboard, a touch panel attached to the surface of the display panel, or the like can be used. The color measuring device 117 can measure each color patch formed on a print substrate, which is an example of a medium on which a color chart is formed, and output a color measurement value. The patch is also called a color chart. The colorimetric value is, for example, a value representing lightness L ^* and chromaticity coordinates a ^* and b ^* in the CIE L ^* a ^* b ^* color space. The color measuring device 117 may be provided outside the host device 100. The host device 100 acquires color measurement data including a plurality of color measurement values from the color measurement device 117 and performs various processes. The communication I / F 118 is connected to the communication I / F 210 of the printer 200 and inputs / outputs information such as print data to the printer 200. USB (Universal Serial Bus), near field communication standard, etc. can be used for the standard of communication I / F 118,210. Communication of the communication I / Fs 118 and 210 may be wired, wireless, or network communication such as a LAN (Local Area Network) or the Internet.

  The color conversion profile generation program PR0 illustrated in FIG. 1 causes the host apparatus 100 to realize the extended range setting function FU1, the extrapolation function FU2, the association function FU3, the characteristic data generation function FU4, and the correspondence relationship data generation function FU5.

  The host device 100 includes a computer such as a personal computer (including a tablet terminal). The host device 100 may have all the components 111 to 118 in one housing, but may be composed of a plurality of devices divided so as to communicate with each other. Even if the printer is in the host device 100, the present technology can be implemented.

  A printer 200 shown in FIG. 1 is an ink jet printer that discharges (jets) C ink, M ink, Y ink, and K ink as color materials from a recording head 220 to form an output image IM0 corresponding to print data. Shall. The recording head 220 is supplied with CMYK (cyan, magenta, yellow, and black) ink from the ink cartridges Cc, Cm, Cy, and Ck, respectively, and receives CMYK ink droplets 280 from the nozzles Nc, Nm, Ny, and Nk, respectively. Discharge. When the ink droplet 280 lands on the substrate ME1, ink dots are formed on the substrate ME1. As a result, a printed material having an output image IM0 on the substrate ME1 is obtained.

(3) Specific example of the first gamut mapping process performed by the color conversion profile generation device:
FIG. 2 shows an example of the first gamut mapping process performed by the host device 100 shown in FIG. Gamut mapping (Colorimetric intent) is to associate Lab values with device color values (for example, CMYK values) in a color reproduction range (for example, gamut GMT shown in FIG. 5). The first gamut mapping process shown in FIG. 2 is an example of gamut mapping that has been performed conventionally, and depends on the device (for example, the printer 200) from the Lab value (example of the first coordinate value) of the device independent color space. This is a process of generating a three-dimensional LUT 530 that is the source of the B2A table to be converted into CMYK values (example of second coordinate values) of the color space CS2 (example of the second color space). FIG. 3 schematically shows an example in which the LUT 530 is generated by the first gamut mapping process. The host device 100 executes a plurality of processes in parallel by multitasking. Here, steps S102 to S104 in FIG. 2 correspond to the characteristic data generation unit U4, the characteristic data generation step ST4, and the characteristic data generation function FU4. Hereinafter, the description of “step” is omitted.

  Before the gamut mapping process is performed on each grid point (first grid point GD1 illustrated in FIG. 3) of the LUT 530 that converts Lab values into CMYK values, the CMY color space CS3 (third) in the gamut GMT of the virtual CMY printer. The characteristic data 520 for converting the CMY value (example of the third coordinate value) of the color space CS1 (example of the third color value) into the Lab value of the Lab color space CS1 (example of the first color space) is generated. The CMY color space CS3 includes a C axis (an example of a first axis), an M axis (an example of a second axis), and a Y axis (an example of a third axis) that intersect with each other to define CMY values. It is a color space in which the dimensions of the four-dimensional CMYK color space CS2 are reduced. The characteristic data 520 is created based on the colorimetric data 500 (example of original data) of the plurality of color patches PA1 formed by the printer 200, and the color reproduction characteristics of the printer 200 are expressed in the gamut GMT. The colorimetric data 500 shown in FIG. 3 is data in which the Lab value (Lp, ap, bp) is associated with the CMYK value (Cp, Mp, Yp, Kp) for each patch PA1 in the CMYK color space CS2. The variable p here is a variable for identifying the patch PA1.

  Since the CMYK color space CS2 is four-dimensional, there are a plurality of CMYK values that reproduce a certain Lab value. For this reason, after the K (black) generation function 510 is determined in advance, the CMYK values are converted into the CMY values of the three-dimensional CMY color space CS3. A K generation function 510 shown in FIG. 3 is a function representing a correspondence relationship between a K value (Kj) and a CMY value (Cj, Mj, Yj) for reproducing the color of the K value, and may be a one-dimensional LUT. The variable j here is a variable for identifying the K value (for example, a gradation value of integers 0 to 255). In the present application, “Min to Max” means a minimum value Min or more and a maximum value Max or less.

  When the first gamut mapping process shown in FIG. 2 is started, the host apparatus 100 acquires colorimetric data 500 in which Lab values are associated with CMYK values (S102). In S <b> 104, characteristic data 520 is generated from the colorimetric data 500 using the K generation function 510. The characteristic data 520 shown in FIG. 3 has CMY values (Cq, Mq, Yq) for Cn × Mn × Yn second grid points GD2 arranged in the color gamut of the CMY color space CS3 depending on the printer 200. This is data in which Lab values (Lq, aq, bq) are associated with each other. The variable q here is a variable for identifying the second grid point GD2. The characteristic data 520 also has CMYK values (C0q, M0q, Y0q, K0q) corresponding to the CMY values (Cq, Mq, Yq). Note that a grid point means a virtual point arranged in the input color space, and it is assumed that an output coordinate value corresponding to the position of the grid point in the input color space is stored in the grid point. I have to.

  FIG. 4 schematically illustrates an example of a virtual CMY space 300 that represents a color reproduction range of the virtual CMY printer in the CMY color space CS3. The characteristic data 520 is data defining a correspondence relationship between the CMY values (Cq, Mq, Yq) that are the grid point coordinate values and the Lab values (Lq, aq, bq) that are the output coordinate values in the virtual CMY space 300. . The characteristic data 520 shown in FIG. 4 includes Cn pieces in the C axis direction (Cn is an integer of 2 or more), Mn pieces in the M axis direction (Mn is an integer of 2 or more), and Yn pieces in the Y axis direction (Yn is 2), the second grid point GD2. The number of lattice points Cn, Mn, Yn in the axial direction is not particularly limited, and can be 17, 32, 64, or the like.

  After the generation of the characteristic data 520, gamut mapping processing is performed in which clipping processing is performed as necessary for each first grid point in the Lab color space CS1. The gamut mapping process calculates CMYK values (Ci, Mi, Yi, Ki) that reproduce the color of the Lab value (Li, ai, bi) of the first grid point GD1 for each first grid point GD1 in the Lab color space CS1. It is processing to do. The variable i here is a variable for identifying the first grid point GD1. In the clipping process, Lab values (Li, ai, bi) that cannot be reproduced by the printer are converted into Lab values (L′ i, a′i, b′i) with low saturation that can be reproduced by the printer. It is processing. In the case of Colorimetric, a point (Li, a′i, b′i that intersects the surface of the virtual CMY space 300 in the Lab color space CS1 when a line is extended from the first grid point to the achromatic color axis in the Lab color space CS1. ).

  First, the host device 100 sets the position (Li, ai, bi) of the first grid point GD1 to be processed from among the plurality of first grid points GD1 arranged in the Lab color space CS1 (S106). In S108, based on the characteristic data 520, the virtual CMY space 300 is divided into small tetrahedrons whose vertices are the lattice points of the characteristic data 520 in the Lab color space CS1, and lattice point coordinate values ( Search for a tetrahedron containing Li, ai, bi). In S110, the process is branched depending on whether or not a tetrahedron including grid point coordinate values (Li, ai, bi) is found.

  When the tetrahedron is found, the host device 100 acquires the CMYK values (C0q, M0q, Y0q, K0q) of the four vertices of the found tetrahedron from the characteristic data 520 (S112), and the first lattice point GD1 is obtained by interpolation calculation. The CMYK values (Ci, Mi, Yi, Ki) are calculated and associated with the Lab values (Li, ai, bi) of the first grid point GD1 (S114), and the process proceeds to S120.

  When the tetrahedron is not found, the grid point coordinate values (Li, ai, bi) cannot be reproduced by the printer 200, so the host device 100 can reproduce colors by the printer 200 and have low saturation coordinates. Clipping processing is performed to convert the values (L′ i, a′i, b′i) (S116 to S118). For example, in the Lab color space CS1, based on the characteristic data 520, the surface of the virtual CMY space 300 is divided into small triangles having the lattice points of the characteristic data 520 as vertices, and first lattice points (coordinate values Li, ai, When a line is extended from a) to an achromatic color axis, a triangle that intersects with this line is searched, and CMYK values (C0q, M0q, Y0q, K0q) of three vertices of the found triangle are acquired from the characteristic data 520 ( S116). In S118, a CMYK value (Ci, Mi, Yi, Ki) is calculated from the CMYK values of the three vertices by interpolation, and is associated with the Lab value (Li, ai, bi) of the first grid point GD1, and the processing is performed in S120. Proceed.

In S120, it is determined whether or not all the first grid points GD1 for generating the LUT 530 have been set. When the first grid point GD1 that has not been set remains, the host device 100 repeats the association processing of S106 to S120. When all the first grid points GD1 are set, the host device 100 ends the first gamut mapping process. As a result, the LUT 530 that is the source of the B2A table in which the correspondence relationship between the Lab value and the CMYK value is defined in the color gamut of the printer 200 is generated. The output coordinate value of the LUT 530 is also expressed as a C1M1Y1K1 value (C1, M1, Y1, K1). The C1M1Y1K1 value (C1, M1, Y1, K1) represents the amount of CMYK ink used in the printer 200 when used as it is for print data. The LUT 530 illustrated in FIG. 3 defines a correspondence relationship between Lab values (Ls, as, bs) that are grid point coordinate values and C1M1Y1K1 values (Cs, Ms, Ys, Ks) that are output coordinate values in the Lab color space CS1. Data. The variable s here is a variable for identifying the first grid point GD1.
If each component value of the CMYK value is called a color coordinate value, the C value is an example of the first color coordinate value, the M value is an example of the second color coordinate value, and the Y value is the first color coordinate value. It is an example of the three color coordinate values. These first, second, and third color coordinate values are component values of the three primary colors.

(4) Causes and solutions to decrease the color reproduction accuracy near the surface of the color reproduction area:
When converting to a Lab value and a CMYK value with reference to the LUT 530 which is a B2A table, there are the following problems.
FIG. 5 schematically shows the reason why the color reproduction accuracy near the surface of the gamut GMT is lowered when the LUT 530 is referred to. Here, the upper side of FIG. 5 shows the gamut GMT in the Lab color space CS1, and the lower side of FIG. 5 shows a graph showing the C value with respect to the a value. Among the plurality of first lattice points GD1, lattice points on the gamut GMT of the printer 200 are indicated by white circles, and lattice points outside the gamut GMT are hatched.

As shown in FIG. 5, when the point e (coordinate values Le, ae, be) is on the surface of the printer gamut GMT, the L value Le and the b value be exactly coincide with the position of the first grid point GD1. To do. Also, let the first grid points on both sides adjacent to the point e in the a-axis direction be points d and f, respectively. The CMYK value at the point e is obtained by linear interpolation of the CMYK values stored at the lattice points d and f. For example, the C value of the point e is calculated from the C values of the points d and f using linear interpolation. Here, as in the graph shown in the lower side of FIG. 5, the C value at the point e is expected to be ideally the minimum value 0 (an example of a value indicating that no color is used) on the broken line. Actually, since the C value at the point f is clipped to the minimum value 0, a slight C is generated at the point e. Therefore, the point e does not become the color of the target Lab value, and the saturation is lowered. This is the cause of the decrease in color reproduction accuracy on the gamut surface.
The above is a description of the surface where C is the minimum value 0 in the gamut GMT, but the same applies to the surface where C is the 8-bit maximum value 255 of the gradation value (an example of a value indicating the maximum use of color). The same applies to the surfaces where M and Y have a minimum value of 0 and a maximum value of 255. Hereinafter, the description will be made assuming that the gradation value is an 8-bit value of 0 to 255 unless otherwise noted.

  In other words, the above-described mapping can be said to be a process in which the CMY value expected to be outside the range of 0 to 255 is clipped within the range of 0 to 255. On the other hand, a negative value smaller than 0 or a value exceeding 255 cannot be input to an actual printer, so the above-described mapping process is performed.

In this specific example, as the CMYK value of the three-dimensional LUT 700 of the color conversion profile 400, when the first grid point GD1 is outside the gamut GMT, a negative value or a value exceeding 255 can be set. Yes. For example, the C value of the grid point f outside the gamut described with reference to FIG. 5 is set to a negative value such as “−20” instead of “0”. In this specific example, an output table 800 as illustrated in FIG. 11 is prepared in the subsequent stage of the three-dimensional LUT 700, and the CMYK value converted from the Lab value by referring to the three-dimensional LUT 700 exceeds a negative value or 255. When the value is reached, the output table 800 is referred to within the range of 0 to 255.
As described above, the above problems can be solved.

  In this specific example, by assuming the extended virtual CMY space 310 illustrated in FIG. 6, a negative value or a CMY value exceeding 255 is generated. FIG. 6 schematically illustrates the extended virtual CMY space 310 in the Lab color space CS1. The extended virtual CMY space 310 is obtained by extending the range of the virtual CMY space 300 obtained from the colorimetric data 500 in the minus direction and in the direction exceeding 255 to make the space size one size larger. As will be described in detail later, extrapolation calculation is used to expand the virtual CMY space 300. FIG. 6 shows an example in which the C value is expanded to “−40” and “275”. In this case, a range satisfying −40 ≦ C <0 and 255 <C ≦ 275 is an expanded range AR1 obtained by extending the gamut GMT outward, and the expanded virtual CMY space 310 is combined with the virtual CMY space 300 and the expanded range AR1. It becomes. By obtaining the CMYK value for the Lab value of each first grid point GD1 using the extended virtual CMY space 310, the CMYK value of the grid point outside the original virtual CMY space 300 is set to a negative value or a value exceeding 255. can do.

(5) Outline of second gamut mapping processing performed by the color conversion profile generation device:
FIG. 7 shows an example of the second gamut mapping process performed by the host device 100 shown in FIG. In this process, the Lab value and the CMYK value are associated with each other in the extended virtual CMY space 310 that exceeds the gamut GMT. The second gamut mapping process shown in FIG. 7 is a process for generating a three-dimensional LUT 610 that is the source of the B2A table for converting Lab values into CMYK values. FIG. 8 schematically illustrates an extended virtual CMY space 310 in which the gamut GMT of the virtual CMY printer is expanded in the CMY color space CS3. FIG. 9 schematically shows an example in which the LUT 610 is generated by the second gamut mapping process. Here, S204 in FIG. 7 corresponds to the extended range setting unit U1, the extended range setting step ST1, and the extended range setting function FU1. S202 and S206 correspond to the extrapolation unit U2, the extrapolation step ST2, and the extrapolation function FU2. S208 to S222 in FIG. 7 correspond to the association unit U3, the association step ST3, and the association function FU3.

  When the process is started, the host device 100 acquires the characteristic data 520 generated in S104 of FIG. 2 (S202). As described above, the characteristic data 520 includes the CMY value (Cq, Mq, Yq) and the Lab value (Lq, aq, bq) for the Cn × Mn × Yn second grid points GD2 in the CMY color space CS3. This data defines the correspondence. The characteristic data 520 also has CMYK values (C0q, M0q, Y0q, K0q) corresponding to the CMY values (Cq, Mq, Yq). In S204, an expansion range AR1 for expanding the gamut GMT of the printer 200 to the outside is set. Details of the extended range setting process of S204 will be described later. In the example shown in FIG. 6, it is shown that the extended range AR1 is set to −40 ≦ C <0 and 255 <C ≦ 275. In S206, extrapolation data 600 for extrapolating the color reproduction characteristics of the printer 200 in the extended range AR1 in the CMY color space CS3 is generated based on the characteristic data 520 representing the color reproduction characteristics of the printer 200 in the gamut GMT. As shown in FIG. 8, the extrapolated data 600 is obtained for the third grid point GD3 arranged on the surface (extended range AR1) of the extended virtual CMY space 310 that is slightly larger than the virtual CMY space 300 in the CMY color space CS3. This is data in which a value and a Lab value are associated with each other. In FIG. 8, the second grid point GD2 in the virtual CMY space 300 is indicated by a white circle, and the third grid point GD3 in the extended range AR1 is hatched. As shown in FIGS. 8 and 9, the CMY value (Cq) for the (Cn + 2) × (Mn + 2) × (Yn + 2) grid points GD2 and GD3 in the CMY color space CS3 by combining the characteristic data 520 and the extrapolated data 600. , Mq, Yq) is associated with Lab values (Lq, aq, bq). The variable q here is a variable for identifying the grid points GD2 and GD3. The characteristic data 520 and the extrapolation data 600 also have CMYK values (C0q, M0q, Y0q, K0q) corresponding to the CMY values (Cq, Mq, Yq). Details of the extrapolation data generation processing in S206 will be described later.

  Thereafter, the Lab value and the CMYK value are associated with each other for the plurality of first grid points GD1 arranged beyond the gamut GMT with respect to the Lab color space CS1 based on the characteristic data 520 and the extrapolation data 600. The association process of S208 to S222 is the same as the association process of S106 to S120 of FIG. First, the host device 100 sets the position (Li, ai, bi) of the first grid point GD1 to be processed from among the plurality of first grid points GD1 arranged in the Lab color space CS1 (S208). In S210, the extended virtual CMY space 310 is divided into small tetrahedrons having the lattice points of the characteristic data 520 and the extrapolated data 600 as vertices in the Lab color space CS1 based on the characteristic data 520 and the extrapolated data 600, and the expanded virtual CMY. A tetrahedron including lattice point coordinate values (Li, ai, bi) is searched from the tetrahedron group in the space 310. In S212, the process is branched depending on whether or not a tetrahedron including grid point coordinate values (Li, ai, bi) has been found.

  When the tetrahedron is found, the host device 100 acquires the CMYK values (C0q, M0q, Y0q, K0q) of the four vertices of the found tetrahedron from the characteristic data 520 and the extrapolation data 600 (S214), and performs interpolation calculation. The CMYK value (Ci, Mi, Yi, Ki) of the first grid point GD1 is calculated and associated with the Lab value (Li, ai, bi) of the first grid point GD1 (S216), and the process proceeds to S222.

  When the tetrahedron is not found, the host device 100 performs a clipping process for converting into coordinate values (L′ i, a′i, b′i) representing the surface of the extended virtual CMY space 310 (S218 to S220). For example, in the Lab color space CS1, based on the characteristic data 520 and extrapolation data 600, the surface of the extended virtual CMY space 310 is divided into small triangles having the lattice points of the characteristic data 520 as vertices, and the first lattice point ( When a line is extended from the coordinate value Li, ai, bi) to the achromatic axis, a triangle that intersects with this line is searched, and the CMYK values (C0q, M0q, Y0q, K0q) of the three vertices of the found triangle are characteristic. Obtained from the data 520 and extrapolation data 600 (S218). In S220, a CMYK value (Ci, Mi, Yi, Ki) is calculated from the CMYK values of the three vertices by interpolation, and is associated with the Lab value (Li, ai, bi) of the first grid point GD1, and the process proceeds to S222. Proceed.

  In S222, it is determined whether or not all the first grid points GD1 for generating the LUT 610 have been set. When the first grid point GD1 that has not been set remains, the host device 100 repeats the association processing of S208 to S222. When all the first grid points GD1 are set, the host device 100 ends the second gamut mapping process. As a result, the LUT 610 that is the source of the B2A table in which the correspondence relationship between the Lab value and the CMYK value is defined beyond the color reproduction range of the printer 200 is generated. The output coordinate value of this LUT 610 is also expressed as a C2M2Y2K2 value (C2, M2, Y2, K2). The C2M2Y2K2 values (C2, M2, Y2, K2) respectively represent the amount of CMYK ink used in the printer 200 when used as it is for print data. The LUT 610 illustrated in FIG. 9 defines a correspondence relationship between Lab values (Ls, as, bs) that are grid point coordinate values and C2M2Y2K2 values (Cs, Ms, Ys, Ks) that are output coordinate values in the Lab color space CS1. Data. The variable s here is a variable for identifying the first grid point GD1.

(6) Outline of color conversion profile generation processing performed by the color conversion profile generation device:
The LUT 610 in which Lab values and C2M2Y2K2 values are associated with each other using the extended virtual CMY space 310 can be used as the three-dimensional LUT 700 of the color conversion profile 400 as it is. However, if there is a portion in the vicinity of the gamut surface where gradation is more important than color reproduction accuracy, an LUT 530 in which Lab values and C1M1Y1K1 values are associated with each other using the virtual CMY space 300, or A combination of LUTs 530 and 610 may be applied.

  FIG. 10 shows an example of color conversion profile generation processing performed by the host device 100. FIG. 11 schematically illustrates the structure of a color conversion profile 400 including a three-dimensional LUT 700 (example of first correspondence data) and an output table 800 (example of second correspondence data). Here, S306 to S308 in FIG. 10 correspond to the correspondence relationship data generation unit U5, the correspondence relationship data generation step ST5, and the correspondence relationship data generation function FU5.

  When the process is started, the host device 100 performs the first gamut mapping process shown in FIG. 2 (S302) and the second gamut mapping process shown in FIG. 7 (S304). In S306, the C3M3Y3K3 value (C3, M3, Y3, K3) of the three-dimensional LUT 700 is determined based on the C1M1Y1K1 value of the LUT 530 based on the virtual CMY space 300 and the C2M2Y2K2 value of the LUT 610 based on the extended virtual CMY space 310. . The LUT 700 illustrated in FIG. 11 includes Lab values (Ls, as, bs) that are grid point coordinate values and C3M3Y3K3 values that are output coordinate values for a plurality of first grid points GD1 arranged beyond the color gamut of the printer 200. This data defines the first correspondence relationship with (Cs, Ms, Ys, Ks). The variable s here is a variable for identifying the first grid point GD1.

For example, if the LUT 610 is directly used as the three-dimensional LUT 700, (C3, M3, Y3, K3) = (C2, M2, Y2, K2). If the C1 value (example of the first color coordinate value) is applied to a part of the three-dimensional LUT 700, the C3 value of that part becomes the C1 value. The same applies when the M1 value (example of second color coordinate value), Y1 value (example of third color coordinate value), and K1 value are applied. If an average value of C1 value and C2 value (for example, (C1 + C2) / 2) is applied to a part of the three-dimensional LUT 700, the C3 value of that part becomes the average value of the C1 value and the C2 value. The same applies when the average value of the M1 value and the M2 value, the average value of the Y1 value and the Y2 value, and the average value of the K1 value and the K2 value are applied. Therefore, for example, all or part of the C2M2Y2K2 values (C2, M2, Y2, K2) are associated with Lab values in a portion of the color space where color reproduction accuracy is more important than gradation, If the part of or the entire C1M1Y1K1 value (C1, M1, Y1, K1) is associated with the Lab value in the part where the gradation is more important than the color reproduction accuracy, the gradation is improved as a whole in the vicinity of the gamut surface. Saturation, that is, color reproduction accuracy can be improved without sacrificing.
As described above, the three-dimensional LUT 700 represents the correspondence between Lab values and CMYK values that are at least partially associated in the association processing of S208 to S222 in FIG.

After generating the three-dimensional LUT 700, the host device 100 converts the C3M3Y3K3 value into the C4M4Y4K4 value included in the gamut GMT when the C3M3Y3K3 value obtained from the Lab value according to the three-dimensional LUT 700 is not included in the gamut GMT. An output table 800, which is a one-dimensional LUT representing the correspondence relationship, is generated (S308), and the color conversion profile generation process is terminated. The output table 800 shown in FIG. 11 is provided for each color of CMYK, and 16 C3M3Y3K3 values (C3, M3, Y3, K3) as input values and 16 C4M4Y4K4 values (C4, M4, Y4, K4) as output values. It is expressed by a gradation value with a bit value of 0 to 65535. A lower limit value Ft and an upper limit value Rf are set as the input value. When the input value is less than or equal to the lower limit value Ft, the input value is converted to a minimum value 0, and when the input value is greater than or equal to the upper limit value Rf, the maximum value 65535 When the input value is Ft to Rf after conversion, the output value has a linear correspondence. Details of the output table generation processing in S308 will be described later.
Through the above processing, the color conversion profile 400 is generated.

(7) Specific example of extended range setting processing performed by the color conversion profile generation device:
Next, details of the extended range setting process performed in S204 of FIG. 7 will be described.
The characteristic data 520 shown in FIG. 4 is a data in which the CMYK printer is virtually a CMY three-channel input printer, and the PCS (profile connection space) Lab value for the printer input CMY and the actual output CMYK value are held. Is a set. The original characteristic data 520 has Cn pieces in the C-axis direction, Mn pieces in the M-axis direction, and Yn pieces of second lattice points GD2 in the Y-axis direction, and a total of Cn × Mn × Yn pieces of second lattice points GD2. Two lattice points GD2 are arranged in a three-dimensional manner.

  In this specific example, by extending the virtual CMY space 300 as shown in FIGS. 6 and 8, one point on the side of less than 0 in each of the C-axis direction, the M-axis direction, and the Y-axis direction, and One third lattice point GD3 is increased on the side exceeding 255. Therefore, the number of grid points GD2 and GD3 in the extended virtual CMY space 310 is (Cn + 2) × (Mn + 2) × (Yn + 2).

In this specific example, the CMY value and Lab value of the increased third grid point GD3 are calculated by the following procedure.
Procedure 1. Determination of the CMY expansion amount of the virtual CMY space 300.
Procedure 2. Creation of an expanded surface (six surfaces) to be an expanded virtual CMY space 310 (hexahedron).
Procedure 3. Creation of extended ridgelines (12 lines) to be the extended virtual CMY space 310 (hexahedral).
Procedure 4. Creation of extended vertices (8 points) to be the extended virtual CMY space 310 (hexahedron).
The procedure 1 is performed in the extended range setting process, and the procedures 2 to 4 are performed in the extrapolation data generation process. First, an example of determining the amount of CMY expansion in Procedure 1 will be described.

  FIG. 12 shows a specific example of the extended range setting process performed in S204 of FIG. In this example, the extension amounts Ext_L0 and Ext_L1 in the brightness direction of the extension range AR1 are set, and then the extension amounts Ext_CMY0 and Ext_CMY1 in the CMY color space CS3 are set. FIG. 13 schematically illustrates how the brightness extension amount Ext_L0 of the virtual CMY space 300 is determined in the Lab color space CS1. FIG. 14 schematically illustrates how the brightness extension amount Ext_L0 of the virtual CMY space 300 is calculated. Among the plurality of first lattice points GD1 shown in FIGS. 13 and 14, the lattice point GD1a in the gamut is indicated by a white circle, and the lattice point GD1b outside the gamut is hatched. FIG. 15 schematically illustrates how the CMY extension amount Ext_CMY0 corresponding to the brightness extension amount Ext_L0 is determined. FIG. 16 schematically illustrates how the brightness extension amount Ext_L1 of the virtual CMY space 300 is calculated. Here, the brightness extension amount Ext_L0 is an extension amount in the direction in which the brightness L is larger than the white point W as shown in FIG. 13 and the like, and the brightness extension amount Ext_L1 is the brightness L from the black point K as shown in FIG. Is the amount of expansion in the direction of decreasing. The CMY extension amount Ext_CMY0 is an extension amount corresponding to the brightness extension amount Ext_L0 in the CMY color space CS3, and the CMY extension amount Ext_CMY1 is an extension amount corresponding to the brightness extension amount Ext_L1 in the CMY color space CS3.

The basic idea for determining the extended range AR1 of the virtual CMY space 300 is that the first grid point GD1 (referred to in the interpolation process for calculating the CMYK value for the Lab value of the gamut surface in the Lab color space CS1 ( The expansion amount is determined so that one unit cuboid having eight vertices as shown in FIG. Thereby, the numerical range Ft to Rf representing the inside of the gamut GMT is sufficiently secured for the CMYK output values of the three-dimensional LUT 700 of the color conversion profile 400, and the color reproduction accuracy inside the gamut is sufficiently maintained. Note that the expansion amounts of C, M, and Y are the same.
Although it is possible to calculate the expansion amount strictly in consideration of the position of the first grid point GD1 in the Lab color space CS1, the processing becomes very complicated. Therefore, for the sake of simplicity, the minimum expansion amount in which the unit rectangular parallelepiped can be calculated without considering the position of the first grid point GD1. This method is considered to have little effect on accuracy.

The brightness extension amount Ext_L0 on the negative side of the CMY value can be determined as follows, for example.
First, as shown in FIG. 13, in the Lab color space CS1, the interval between the first lattice points GD1 in the L-axis direction of the three-dimensional LUT 700 is gL, and the first lattice points in the a-axis direction and the b-axis direction of the three-dimensional LUT 700 The interval of GD1 is gAB. Here, the lattice point interval in the a-axis direction and the lattice point interval in the b-axis direction are set to the same interval bAB.

ただし、ｄＬ＝（Ｌｗ−Ｌｐ）、ｄＡ＝（ａｗ−ａｐ）、ｄＢ＝（ｂｗ−ｂｐ）である。
すなわち、Ｌａｂ色空間ＣＳ１におけるガマットＧＭＴの表面の傾きSlopeは、彩度差ｄＣに対する明度差ｄＬの比で表される。 As can be seen in FIGS. 13 and 14, the steep slope of the gamut surface requires a larger amount of expansion in the lightness direction to include the unit rectangular parallelepiped. Therefore, secondary colors of R (Y and M are equal), G (C and Y are equal), and B (C and M are equal) on the surface of the gamut GMT of the printer 200 are increased. The slopes Slope_W-R, Slope_W-G, and Slope_W-B are calculated for, and the maximum slope Slope_max is used from these to be used for later calculations. Here, the slopes Slope_W-R, Slope_W-G, and Slope_W-B are collectively referred to as slopes Slope. The slope Slope of R, G, B is the RGB minimum density grid point P1 having the lowest density of R, G, B among the second grid points GD2 of the characteristic data 520, and RGB in the Lab color space CS1. The slope of the line connecting the minimum density grid point P1 (coordinate values Lp, ap, bp) and the white point W (coordinate values Lw, aw, bw) is used.

However, dL = (Lw−Lp), dA = (aw−ap), and dB = (bw−bp).
That is, the slope Slope of the surface of the gamut GMT in the Lab color space CS1 is represented by the ratio of the brightness difference dL to the saturation difference dC.

Based on the above considerations, when the brightness direction expansion range setting process shown in FIG. 12 is started, the host device 100 determines the slopes Slope_W-R, Slope_W-G, and Slope_W-B of the low density portions of R, G, and B. Are calculated according to the above equation (1) (S402). In S404, the maximum slope Slope_max is selected from the slopes Slope_W-R, Slope_W-G, and Slope_W-B at a plurality of locations. In S406, the brightness extension amount Ext_L0 is calculated based on the maximum gradient Slope_max and the intervals gL and gAB between the first grid points GD1.

  In S408, the CMY extension amount Ext_CMY0 that realizes the brightness extension amount Ext_L0 in the negative direction of the CMY value is acquired. As shown in FIG. 15, the CMY extension amount Ext_CMY0 is the CMY at the point where the L value decreases from the white point W by the brightness extension amount Ext_L0 on the line (on the gray axis) where C = M = Y in the virtual CMY space 300. It is obtained from the values (Ext_CMY0, Ext_CMY0, Ext_CMY0). Therefore, by referring to the characteristic data 520, CMY expansion is performed by obtaining CMY values (Ext_CMY0, Ext_CMY0, Ext_CMY0) corresponding to the Lab values at the point where the L value is lowered by the brightness extension amount Ext_L0 from the white point W by interpolation. The quantity Ext_CMY0 is determined.

Also, the brightness extension amount Ext_L1 on the side exceeding the CMY value of 255 can be basically determined in the same way as the minus side brightness extension amount Ext_L0. In the dark part of the gamut GMT, since the ridge line from the maximum density of C, M, and Y to the black point K has the maximum inclination, the inclination of these lines is calculated. However, since the gamut shape in the vicinity of the black point K is unstable, for example, the slopes Slope_C-K, Slope_M-K, and Slope_Y-K of the three straight lines connecting the following two points are calculated and the maximum value is calculated. We will use Slope_max1.
Line from C to K: A straight line connecting CMY values (255, 0, 0) and (255, 127, 127) Line from M to K: CMY values (0, 255, 0) and (127, Line connecting 255, 127) Line from Y to K ... Line connecting CMY values (0, 0, 255) and (127, 127, 255)

Based on the above thinking, in S410 of the brightness direction expansion range setting process shown in FIG. 12, the host device 100 sets the slopes Slope_C-K, Slope_M-K, and Slope_Y-K from C, M, Y to K, respectively. It calculates according to Formula (1). In S412, the maximum slope Slope_max1 is selected from the slopes Slope_C-K, Slope_M-K, and Slope_Y-K at a plurality of locations. In S414, the brightness extension amount Ext_L1 is calculated based on the maximum gradient Slope_max1 and the intervals gL and gAB between the first grid points GD1.

  Finally, the host device 100 acquires the CMY extension amount Ext_CMY1 that realizes the brightness extension amount Ext_L1 in the direction exceeding the CMY value 255 (S416), and ends the brightness direction extension range setting process. As shown in FIG. 16, the CMY extension amount Ext_CMY1 is the CMY at the point where the L value increases from the black point K by the brightness extension amount Ext_L1 on the line where C = M = Y in the virtual CMY space 300 (on the gray axis). It is obtained from the values (255−Ext_CMY0, 255−Ext_CMY0, 255−Ext_CMY0). Therefore, by referring to the characteristic data 520, CMY values (255−Ext_CMY0, 255−Ext_CMY0, 255−Ext_CMY0) corresponding to the Lab value at the point where the L value is increased by the brightness extension amount Ext_L1 from the black point K are interpolated. As a result, the CMY extension amount Ext_CMY1 is determined.

  As described above, the expansion range AR1 is set so that the lightness expansion amounts Ext_L0 and Ext_L1 are based on the maximum inclinations Slope_max and Slope_max1 among the inclinations at a plurality of locations on the gamut surface and the intervals gL and gAB of the first grid points GD1. The

In the above description, the expansion amount for including the unit rectangular parallelepiped of the three-dimensional LUT 700 is obtained from the viewpoint of the lightness expansion amount. However, the expansion amount can be determined from the viewpoint of the saturation expansion amount.
FIG. 17 shows another specific example of the extended range setting process performed in S204 of FIG. In this example, the extension amounts Ext_C0 and Ext_C1 in the saturation direction of the extension range AR1 are set, and then the extension amounts Ext_CMY0 and Ext_CMY1 in the CMY color space CS3 are set. FIG. 18 schematically illustrates how the saturation extension amount Ext_C0 of the virtual CMY space 300 is calculated in the Lab color space CS1. Here, as shown in FIG. 18, the saturation extension amount Ext_C0 is higher than the maximum saturation point a of each of C, M, Y on the higher lightness side than the maximum saturation point a of C, M, Y. The saturation extension amount Ext_C1 is greater than the maximum saturation point a for each of C, M, and Y on the lower lightness side than the maximum saturation point a for each of C, M, and Y. The amount of expansion in the direction of increasing. The CMY extension amount Ext_CMY0 is an extension amount corresponding to the saturation extension amount Ext_C0 in the CMY color space CS3, and the CMY extension amount Ext_CMY1 is an extension amount corresponding to the saturation extension amount Ext_C1 in the CMY color space CS3.

The saturation extension amount Ext_C0 on the negative side of the CMY value can be determined as follows, for example.
As can be seen in FIG. 18, the gradual inclination of the gamut surface requires a larger amount of expansion in the saturation direction to include the unit rectangular parallelepiped. Therefore, the slopes Slope_C-W, Slope_M-W, and Slope_Y-W are calculated for the primary colors of C, M, and Y, where the slope Slope becomes small on the surface of the gamut GMT of the printer 200, and the minimum slope Slope_min is selected from these. Will be used for later calculations. Here, the slopes Slope_C-W, Slope_M-W, and Slope_Y-W are collectively referred to as a slope Slope. The slope Slope of C, M, and Y has the maximum saturation point a of C, M, and Y in the second grid point GD2 of the characteristic data 520, and the density of C, M, and Y is greater than the maximum saturation point. Using the data of the second grid point P2 that is one step lower, the slope dL / dC of the line connecting the maximum saturation point a and the second grid point P2 in the Lab color space CS1.

Based on the above considerations, when the saturation direction expansion range setting process shown in FIG. 17 is started, the host apparatus 100 determines the slopes Slope_C-W, Slope_M-W, Slope_Y-W from C, M, Y to W. Are calculated respectively (S422). In S424, the minimum slope Slope_min is selected from the slopes Slope_C-W, Slope_M-W, and Slope_Y-W at a plurality of locations. In S426, the saturation extension amount Ext_C0 is calculated based on the minimum slope Slope_min and the intervals gL and gAB between the first grid points GD1.

  In S428, the CMY extension amount Ext_CMY0 that realizes the saturation extension amount Ext_C0 in the negative direction of the CMY value is acquired. As shown in FIG. 18, the CMY extension amount Ext_CMY0 from the maximum saturation point a to the point c in the virtual CMY space 300 is the point b where the saturation is the same brightness from the maximum saturation point a and the saturation is decreased by the saturation extension amount Ext_C0. From the CMY values at Here, if the CMY value of the maximum saturation point a is (255, 0, 0), the CMY value of the point b is (255−Ext_CMY0, 0, 0), and the CMY value of the maximum saturation point a is ( CMY value of the point b is (0, 255-Ext_CMY0, 0) if it is 0, 255, 0), and CMY of the point b if the CMY value of the maximum saturation point a is (0, 0, 255). The value is (0, 0, 255−Ext_CMY0). Accordingly, the CMY extension amount Ext_CMY0 is obtained by interpolating the CMY value corresponding to the Lab value of the point b where the saturation is decreased from the maximum saturation point a by the saturation extension amount Ext_C0 with reference to the characteristic data 520. It is determined.

Further, the saturation extension amount Ext_C1 on the side exceeding the CMY value of 255 can basically be determined in the same way as the minus side saturation extension amount Ext_C0. For example, the dark part of gamut GMT calculates the slopes Slope_R-K, Slope_G-K, and Slope_B-K of the three straight lines connecting the following two points, and uses the minimum value Slope_min1.
Line from R to K: Line connecting CMY values (0, 255, 255) and (127, 255, 255) Line from G to K: CMY values (255, 0, 255) and (255, Line connecting 127, 255) Line from B to K ... Line connecting CMY values (255, 255, 0) and (255, 255, 127)

Based on the above thinking, in S430 of the saturation direction expansion range setting process shown in FIG. 17, the host device 100 sets the slopes Slope_R-K, Slope_G-K, and Slope_B-K from R, G, B to K, respectively. calculate. In S432, the minimum slope Slope_min1 is selected from the slopes Slope_R-K, Slope_G-K, and Slope_B-K at a plurality of locations. In S434, the saturation extension amount Ext_C1 is calculated based on the minimum gradient Slope_min1 and the intervals gL and gAB between the first grid points GD1.

  Finally, the host device 100 acquires the CMY extension amount Ext_CMY1 that realizes the saturation extension amount Ext_C1 in the direction in which the CMY value exceeds 255 (S436), and ends the saturation direction extension range setting process. With reference to the characteristic data 520, the CMY extension amount Ext_CMY1 is determined by interpolating the CMY value corresponding to the Lab value at the point b where the saturation is lowered by the saturation extension amount Ext_C1 from the maximum saturation point. .

  As described above, the extension range AR1 is set so that the saturation extension amounts Ext_C0 and Ext_C1 are based on the minimum slopes Slope_min and Slope_min1 of the slopes at a plurality of locations on the gamut surface and the intervals gL and gAB of the first grid points GD1. Is done.

In the above description, the expansion amount for including the unit rectangular parallelepiped of the three-dimensional LUT 700 is obtained from the viewpoint of the lightness expansion amount or the saturation expansion amount. However, the expansion amount is determined from the viewpoint of both the lightness expansion amount and the saturation expansion amount. It is also possible to decide.
FIG. 19 shows another specific example of the extended range setting process performed in S204 of FIG. When the processing is started, the host device 100 first performs brightness direction expansion range setting processing shown in FIG. 12 (S442). Temporary CMY extension amounts Ext_CMY0 and Ext_CMY1 obtained by this processing are set as CMY extension amounts Ext_CMY0L and Ext_CMY1L (example of first extension range). In S444, the saturation direction expansion range setting process shown in FIG. 17 is performed. Temporary CMY extension amounts Ext_CMY0 and Ext_CMY1 obtained by this processing are set as CMY extension amounts Ext_CMY0C and Ext_CMY1C (example of second extension range).

In S446, the larger CMY extension amount Ext_CMY0L, Ext_CMY0C is set as the final CMY extension amount Ext_CMY0. Finally, the host device 100 sets the larger of the CMY extension amounts Ext_CMY1L and Ext_CMY1C as the final CMY extension amount Ext_CMY1 (S448), and ends the extension range setting process.
As described above, the extension range AR1 is set based on both the brightness extension amounts Ext_L0 and Ext_L1 and the saturation extension amounts Ext_C0 and Ext_C1. Therefore, the accuracy of determining the expansion amount is improved so that one unit rectangular parallelepiped having the first grid point GD1 as a vertex is completely included.

(8) Specific example of extrapolation data generation processing performed by the color conversion profile generation device:
Next, details of the extrapolation data generation process performed in S206 of FIG. 7 will be described.
FIG. 20 shows a specific example of extrapolation data generation processing performed in S206 of FIG. In this example, the procedure 2 described above is performed in S502 to S508, the procedure 3 described above is performed in S510 to S516, and the procedure 4 described above is performed in S518 to S524.

In the procedure 2 described above, the Lab value and the CMYK value at the third lattice point GD3 of the extended surface (ridge line is not included) obtained by expanding the six surfaces of the virtual CMY space 300 (hexahedron) in the CMY color space CS3 are used as the characteristic data. Extrapolate based on 520.
When the extrapolation data generation process is started, the host device 100 selects a third grid point to be extrapolated from among a plurality of third grid points GD3 arranged on the expansion plane of the virtual CMY space 300 in the CMY color space CS3. Setting is made (S502). For example, the C value of the third grid point GD3 arranged on the minus side expansion plane in the C-axis direction is −Ext_CMY0, and the M value and the Y value of the third grid point GD3 are respectively the second grid of the virtual CMY space 300. Assume that the M value and the Y value of the point GD2. The C value of the third grid point GD3 arranged on the extended surface on the side exceeding 255 in the C-axis direction is 255 + Ext_CMY0, and the M value and Y value of the third grid point GD3 are the second grid points of the virtual CMY space 300, respectively. The M value and Y value of GD2. The same applies to the expansion surfaces in the M-axis direction and the Y-axis direction.

FIG. 21 schematically illustrates how the surface of the virtual CMY space 300 is expanded in the CMY color space CS3. The C-axis, M-axis, and Y-axis shown in FIG. 21 are different from the CMY color space CS3 shown in FIG. 8 and the like, and the lightness L becomes higher as it goes upward with respect to the gray axis of C = Y = M. I have to. The same applies to FIGS. 24 and 25 described later. A point a (hatched lattice point) shown in FIG. 21 indicates a third lattice point GD3 set on the expanded surface.
After setting the third grid point, the host device 100 is within the predetermined range AR2 from the point a (the set third grid point) among the second grid points GD2 on the surface of the virtual CMY space 300 (gamut GMT). A specific grid point GD4 is set (S504). A point b (a grid point with a + mark) illustrated in FIG. 21 indicates a specific grid point GD4 set on the surface of the virtual CMY space 300. A point b illustrated in FIG. 21 is a point closest to the point a and is located in the C-axis direction from the point a. Of course, depending on the position of the extended surface, the point b may be a point in the M-axis direction from the point a or a point in the Y-axis direction from the point a.

  In S506, in the CMY color space CS3, the specific point P0 in the direction connecting the point a (set third grid point) to the point b (specific grid point GD4) in the virtual CMY space 300 (gamut GMT). 50% of the size of the virtual CMY space 300 in the C-axis direction (example of the first axis), the M-axis direction (example of the second axis), or the Y-axis direction (example of the third axis) (1 / 2) As described above, the specific point P0 that is behind the surface of the virtual CMY space 300 is set. A point c (white circle) shown in FIG. 21 indicates a specific point P0 set inside the virtual CMY space 300. The depth Ref_Depth of the point c with respect to the size of the virtual CMY space 300 in the direction connecting the point a to the point b is set to 50 to 100% (more preferably 60 to 90%) as a preferable range. A point c illustrated in FIG. 21 is located at a depth Ref_Depth from the point b in the virtual CMY space 300 in the C-axis direction connecting the point a to the point b.

  In S508, the Lab and CMYK values of the third grid point GD3 in the extrapolated data 600 are extrapolated based on the Lab and CMYK values of the specific grid point GD4 and the specific point P0 in the characteristic data 520 in the CMY color space CS3. To do. For example, when the point a is a point extended to the negative side of C, the M value and Y value of the points b and c are made the same as the point a. The C value at the point c is Ref_Depth. Since the point c does not necessarily overlap with the second grid point GD2, linear interpolation is performed based on the C values of the plurality of second grid points GD2 in the characteristic data 520. When the CMY value of the point a is (−Ext_CMY0, M, Y), the CMY value of the point b is (0, M, Y), and the CMY value of the point c is (Ref_Depth, M, Y).

Here, the Lab value of the point a to be obtained is (La, aa, ba), the CMYK value of the point a to be obtained is (Ca, Ma, Ya, Ka), and the Lab value of the point b is (Lb, ab, bb). And the CMYK value at point b is (Cb, Mb, Yb, Kb), the Lab value at point c is (Lc, ac, bc), and the CMYK value at point c is (Cc, Mc, Yc, Kc). To do. The Lab value and CMYK value of the point a can be calculated by, for example, the following equations.
La = Lb + (Ext_CMY0 / Ref_Depth) × (Lb−Lc)
aa = ab + (Ext_CMY0 / Ref_Depth) × (ab−ac)
ba = bb + (Ext_CMY0 / Ref_Depth) × (bb−bc)
Ca = Cb + (Ext_CMY0 / Ref_Depth) × (Cb−Cc)
Ma = Mb + (Ext_CMY0 / Ref_Depth) × (Mb−Mc)
Ya = Yb + (Ext_CMY0 / Ref_Depth) × (Yb−Yc)
Ka = Kb + (Ext_CMY0 / Ref_Depth) × (Kb−Kc) (6)
The same applies when the point a is on the side of M exceeding 255, or when the point a is on the negative side of C and Y and beyond 255.

  When the depth Ref_Depth of the specific point P0 is 50 to 100%, it is difficult to be affected by the irregular shape of the gamut surface when extrapolating the Lab value and CMYK value of the third grid point GD3. Therefore, the color reproduction accuracy near the gamut surface is further improved.

  In this specific example, in order to further improve the color reproduction accuracy in the vicinity of the gamut surface, a plurality of combinations of specific grid points GD4 and specific points P0 are set as shown in FIG. FIG. 22 schematically illustrates a state in which a plurality of combinations of the specific grid point GD4 and the specific point P0 are set in the CMY color space CS3. FIG. 23 schematically illustrates a state in which a combination used for extrapolation calculation is selected from the combination of the specific grid point GD4 and the specific point P0. For ease of understanding, FIG. 23 schematically illustrates the CMY color space CS3 viewed from the Y-axis direction.

  In the example shown in FIGS. 22 and 23, nine points b0 to b8 are set as the specific grid point GD4 within the predetermined range AR2 from the third grid point GD3 (point a) among the second grid points GD2 on the gamut surface. ing. Here, the point b4 is a lattice point closest to the point a, the points b1, b3, b5, and b7 are lattice points adjacent to the point b4 in the axial direction, and the point b0 is a lattice point adjacent to the points b1 and b3. , Point b2 is a lattice point adjacent to points b1 and b5, point b6 is a lattice point adjacent to points b3 and b7, and point b8 is a lattice point adjacent to points b5 and b7. The points c0 to c8 are specific points P0 in the direction connecting the points a to b0 to b8, respectively, and the virtual CMY space 300 in the axial direction (C-axis direction in FIG. 23) intersecting the surface where the points b0 to b8 are present. The depth of the virtual CMY space 300 is at least 1/2 of the size of the virtual CMY space 300. Depth Ref_Depth means the depth in the axial direction as shown in FIG. Here, a point that goes out of the virtual CMY space 300 among the points c0 to c8, such as a point c1 shown in FIG. 23, is not used as an excluded point in the extrapolation calculation.

  For points a, b0, c0, points a, b1, c1,..., Points a, b8, c8, except for the combinations including the excluded points, the Lab values and CMYK values of the points a are calculated, respectively. When the arithmetic average of the values is obtained, the obtained arithmetic average value can be used as the final Lab value and CMYK value of the point a.

The above-described processing of S502 to S508 is repeated until the Lab values and CMYK values of all the third grid points GD3 on the expansion plane are extrapolated.
In the procedure 3 thereafter, the Lab value and the CMYK value at the third lattice point GD3 of the extended ridge line (excluding vertices) obtained by extending the 12 ridge lines of the virtual CMY space 300 (hexahedron) in the CMY color space CS3 are obtained. Extrapolation is performed based on the characteristic data 520. First, in S510 of FIG. 20, the host device 100 sets a third grid point to be extrapolated from among a plurality of third grid points GD3 on the extended ridge line of the virtual CMY space 300 in the CMY color space CS3.

FIG. 24 schematically illustrates a state in which the ridge line of the virtual CMY space 300 is expanded in the CMY color space CS3. A point a illustrated in FIG. 24 indicates the third grid point GD3 set in the extended ridge line.
After setting the third grid point, the host device 100 is within the predetermined range AR2 from the point a (the set third grid point) among the second grid points GD2 on the ridgeline on the surface of the virtual CMY space 300 (gamut GMT). A specific grid point GD4 is set (S512). A point b illustrated in FIG. 24 indicates a specific lattice point GD4 set on a ridgeline on the surface of the virtual CMY space 300. A point b shown in FIG. 24 is a point closest to the point a and has the same M value as the point a. Of course, depending on the position of the extended ridgeline, the point b may be a point having the same C value as the point a, or a point having the same Y value as the point a.

  In S514, in the CMY color space CS3, the specific point P0 in the direction connecting the point a (set third grid point) to the point b (specific grid point GD4) in the virtual CMY space 300 (gamut GMT). 50% of the size of the virtual CMY space 300 in the C-axis direction (example of the first axis), the M-axis direction (example of the second axis), or the Y-axis direction (example of the third axis) (1 / 2) As described above, the specific point P0 that is behind the surface of the virtual CMY space 300 is set. A point c illustrated in FIG. 24 indicates a specific point P0 set in the virtual CMY space 300. A point c illustrated in FIG. 24 is located at a depth Ref_Depth from the point b in the virtual CMY space 300 in the C-axis direction and the Y-axis direction.

  In S516, in the CMY color space CS3, the Lab value and the CMYK value of the third grid point GD3 in the extrapolated data 600 are extrapolated based on the Lab value and the CMYK value of the specific grid point GD4 and the specific point P0 in the characteristic data 520. To do. For example, when the point a is a point extended to the negative side of C and Y, the M values of the points b and c are the same as the point a. Further, the C value and the Y value at the point c are Ref_Depth. Since the point c does not necessarily overlap with the second grid point GD2, linear interpolation is performed based on the C values of the plurality of second grid points GD2 in the characteristic data 520. When the CMY value of the point a is (−Ext_CMY0, M, −Ext_CMY0), the CMY value of the point b is (0, M, 0), and the CMY value of the point c is (Ref_Depth, M, Ref_Depth).

The Lab value (La, aa, ba) and CMYK value (Ca, Ma, Ya, Ka) of the point a to be obtained can be calculated by the above-described equation (6). The same applies when the point a is on another extended ridgeline.
When extrapolating the Lab value and the CMYK value of the third grid point GD3 on the extended ridge line, a plurality of combinations of the specific grid point GD4 and the specific point P0 are set as in the case shown in FIGS. The specific grid point GD4 is not arranged on the same plane. The Lab value and the CMYK value of the third grid point GD3 on the extended ridge line in the extrapolation data 600 are the Lab values of the specific grid point GD4 and the specific point P0 included in the plurality of combinations in the characteristic data 520, as in the case of the extended surface. And extrapolated based on the CMYK values.

The processes of S510 to S516 described above are repeated until the Lab values and CMYK values of all the third grid points GD3 on the extended ridge line are extrapolated.
In the procedure 4 thereafter, the Lab value and the CMYK value at the third lattice point GD3 of the extended vertex obtained by extending the eight vertices of the virtual CMY space 300 (hexahedron) in the CMY color space CS3 are extrapolated based on the characteristic data 520. To do. First, in S518 of FIG. 20, the host device 100 sets a third grid point to be extrapolated from among a plurality of third grid points GD3 at the extended vertex of the virtual CMY space 300 in the CMY color space CS3.

FIG. 25 schematically illustrates how the vertices of the virtual CMY space 300 are expanded in the CMY color space CS3. A point a shown in FIG. 25 indicates the third grid point GD3 set at the extended vertex.
After setting the third grid point, the host device 100 is within the predetermined range AR2 from the point a (the set third grid point) among the second grid points GD2 at the top of the surface of the virtual CMY space 300 (gamut GMT). A specific grid point GD4 is set (S520). A point b illustrated in FIG. 25 indicates the specific lattice point GD4 set at the vertex of the surface of the virtual CMY space 300. A point b shown in FIG. 25 is a point closest to the point a.

  In S522, in the CMY color space CS3, the specific point P0 in the direction connecting the point a (set third grid point) to the point b (specific grid point GD4) in the virtual CMY space 300 (gamut GMT) 50% of the size of the virtual CMY space 300 in the C-axis direction (example of the first axis), the M-axis direction (example of the second axis), or the Y-axis direction (example of the third axis) (1 / 2) As described above, the specific point P0 that is behind the surface of the virtual CMY space 300 is set. A point c illustrated in FIG. 25 indicates the specific point P0 set inside the virtual CMY space 300. A point c illustrated in FIG. 25 is located at a depth Ref_Depth from the point b in the virtual CMY space 300 in the C-axis direction, the M-axis direction, and the Y-axis direction.

  In S524, the Lab and CMYK values of the third grid point GD3 in the extrapolated data 600 are extrapolated based on the Lab and CMYK values of the specific grid point GD4 and the specific point P0 in the characteristic data 520 in the CMY color space CS3. To do. For example, when the point a is a point extended to the negative side of C, M, Y, the C, M, Y value at the point c is Ref_Depth. Since the point c does not necessarily overlap with the second grid point GD2, linear interpolation is performed based on the C values of the plurality of second grid points GD2 in the characteristic data 520. When the CMY value of the point a is (−Ext_CMY0, −Ext_CMY0, −Ext_CMY0), the CMY value of the point b is (0, 0, 0), and the CMY value of the point c is (Ref_Depth, Ref_Depth, Ref_Depth). .

The Lab value (La, aa, ba) and CMYK value (Ca, Ma, Ya, Ka) of the point a to be obtained can be calculated by the above-described equation (6). The same applies when the point a is at another extended vertex.
Also when extrapolating the Lab value and CMYK value of the third grid point GD3 at the extended vertex, a plurality of combinations of the specific grid point GD4 and the specific point P0 are set as in the case shown in FIGS. For example, seven specific grid points GD4 are set and are not arranged on the same plane. The Lab value and the CMYK value of the third grid point GD3 on the extended ridge line in the extrapolation data 600 are the Lab values of the specific grid point GD4 and the specific point P0 included in the plurality of combinations in the characteristic data 520, as in the case of the extended surface. And extrapolated based on the CMYK values.

  The processes of S518 to S524 described above are repeated until the Lab values and CMYK values of all the third grid points GD3 on the extended ridge line are extrapolated.

  When the generation of the extrapolated data 600 is completed, in the association processing of S208 to S222 shown in FIG. 7, the host device 100 has a plurality of first grid points arranged beyond the gamut GMT with respect to the Lab color space CS1. For GD1, the Lab value (Ls, as, bs) and the C2M2Y2K2 value (Cs, Ms, Ys, Ks) are associated with each other based on the characteristic data 520 and the extrapolation data 600. As a result, the LUT 610 in which the Lab value and the C2M2Y2K2 value are associated with each other beyond the color gamut of the printer 200 is generated. Thereafter, in the process of S306 shown in FIG. 10, based on the C1M1Y1K1 value of the LUT 530 based on the virtual CMY space 300 and the C2M2Y2K2 value of the LUT 610 based on the extended virtual CMY space 310, the C3M3Y3K3 value (C3M3 M3, Y3, K3) are determined. In this determination process, at least the C2M2Y2K2 value of the LUT 610 is used, and this C2M2Y2K2 value may become the C3M3Y3K3 value of the three-dimensional LUT 700 as it is.

(9) Specific example of output table generation processing performed by the color conversion profile generation device:
The C3M3Y3K3 value that is the output value of the three-dimensional LUT 700 is based on the characteristic data 520 and extrapolation data 600 of the extended virtual CMY space 310, and may be outside the range of 0 to 255. On the other hand, since the subsequent processing can handle only the range of 0 to 255, the C3M3Y3K3 value is set within the range of 0 to 255 by the output table 800 shown in FIG.

For the input values (C3, M3, Y3, K3) of the output table 800, the lower limit value Ft and the upper limit value Rf can be determined by the following equations, for example.
Ft = 255 × {Ext_CMY0 / (255 + Ext_CMY0 + Ext_CMY1) × 257} (7)
Rf = 255 × {(255 + Ext_CMY0) / (255 + Ext_CMY0 + Ext_CMY1) × 257} (8)
When the input value (C3, M3, Y3, K3) is less than or equal to the lower limit value Ft by referring to the output table 800 in which the second correspondence relationship determined by the above equations (7) and (8) is defined, the minimum When the input value (C3, M3, Y3, K3) is greater than or equal to the upper limit value Rf, the value is converted to the maximum value 65535. When the input values (C3, M3, Y3, K3) are Ft to Rf, the range is widened so that the output values (C4, M4, Y4, K4) are 0 to 65535, and as the input value increases, the linearity increases. The output value increases. Thus, when the C3M3Y3K3 value obtained from the Lab value according to the three-dimensional LUT 700 is a value not included in the gamut GMT, the output table 800 representing the second correspondence relationship for converting the C3M3Y3K3 value into the C4M4Y4K4 value included in the gamut GMT. Generated.

(10) Actions and effects of specific examples:
As described above, in this specific example, the gamut GMT is calculated based on the slope Slope of the gamut surface in the Lab color space CS1 and the intervals gL and gAB of the first grid points GD1 arranged in the Lab color space CS1. An expansion range AR1 that extends outside is set. Extrapolation data 600 for extrapolating the color reproduction characteristics of the device is generated in the extended range AR1, and the Lab value and the CMYK value are associated with each other for the first grid point GD1 based on the extrapolation data 600 and the characteristic data 520. It is done. Therefore, this specific example can improve the color reproduction accuracy in the vicinity of the gamut surface while substantially maintaining the color reproduction accuracy inside the gamut.

(11) Modification:
Various modifications can be considered for the present invention.
For example, the device is not limited to an ink jet printer, and may be an electrophotographic printer such as a laser printer, a three-dimensional printer, a display device, or the like.
The types of color materials that form an image are not limited to C, M, Y, and K. In addition to C, M, Y, and K, Dy (dark yellow) and Or having a higher density than Lc, Lm, and Y are used. (Orange), Gr (green), Lk (light black) having a lower density than K, and an uncolored colorant for improving image quality may be included.
The above-described processing can be changed as appropriate, for example, by changing the order. For example, in the process of FIG. 12, the processes of S410 to S416 can be performed before any of the processes of S402, S404, S406, and S408.
The gamut mapping process shown in FIGS. 2 and 7 divides the virtual CMY space 300 and the extended virtual CMY space 310 into four-vertex tetrahedrons and interpolates CMYK values. The space division is a unit of a triangular prism having six vertices. , A hexahedral unit having eight vertices, and the like. Further, the unit of clipping processing is not limited to a triangle.
In the calculation of the brightness extension amounts Ext_L0 and Ext_L1, the slopes Slope_max and Slope_max1 in the equations (2) and (3) may be replaced with predetermined positive constants. Further, in the calculation of the saturation expansion amounts Ext_C0 and Ext_C1, the slopes Slope_min and Slope_min1 in the above equations (4) and (5) may be replaced with predetermined positive constants.

(12) Conclusion:
As described above, according to the present invention, there are provided various techniques that can improve the color reproduction accuracy near the surface of the color gamut while maintaining the color reproduction accuracy inside the color gamut. be able to. Needless to say, the above-described basic functions and effects can be obtained even with the technology consisting only of the constituent elements according to the independent claims.
In addition, the configurations disclosed in the above-described examples are mutually replaced or the combination is changed, the known technology and the configurations disclosed in the above-described examples are mutually replaced or the combinations are changed. The configuration described above can also be implemented. The present invention includes these configurations and the like.

DESCRIPTION OF SYMBOLS 100 ... Host device (example of color conversion profile generation device), 114 ... Storage device, 115 ... Display device, 116 ... Input device, 200 ... Printer (example of device), 300 ... Virtual CMY space, 310 ... Extended virtual CMY space , 400 ... color conversion profile, 500 ... colorimetric data (example of original data), 510 ... K generation function, 520 ... characteristic data, 530 ... LUT, 600 ... extrapolation data, 610 ... LUT, 700 ... LUT (first) Example of correspondence data), 800 ... Output table (example of second correspondence data), AR1 ... Extended range, AR2 ... Predetermined range, CS1 ... Lab color space (example of first color space), CS2 ... CMYK colors Space (example of second color space), CS3 ... CMY color space (example of third color space), GD1 ... first grid point, GD2 ... second grid point, GD3 ... third grid point, D4: specific grid point, GMT: gamut (color gamut), IM0 ... output image, P0 ... specific point, P1 ... RGB minimum density grid point, PA1 ... patch, PR0 ... color conversion profile generation program, ST1 ... extended range setting Step, ST2 ... Extrapolation step, ST3 ... Association step, ST4 ... Characteristic data generation step, ST5 ... Correlation relationship data generation step.

Claims (11)

Color conversion that associates the first coordinate value of the first color space with the second coordinate value of the second color space depending on the device for a plurality of first grid points arranged in the first color space. A profile generation method,
An extension range setting step for setting an extension range for extending the color reproduction range of the device to the outside based on an interval between the first grid points arranged in the first color space;
An extrapolation step of generating extrapolation data for extrapolating the color reproduction characteristics of the device in the extended range, based on characteristic data representing the color reproduction characteristics of the device in the color gamut;
For the plurality of first grid points arranged beyond the color reproduction range with respect to the first color space, the first coordinate value and the second coordinate value based on the characteristic data and the extrapolation data. A color conversion profile generation method including an associating step.   In the extended range setting step, based on the inclination of the surface of the color gamut in the first color space and the interval between the first grid points arranged in the first color space, the extended range. The color conversion profile generation method according to claim 1, wherein: The slope of the surface of the color gamut in the first color space is represented by the ratio of the brightness difference to the saturation difference,
In the extended range setting step, a plurality of slopes on the surface of the color gamut in the first color space are acquired based on the characteristic data, and the maximum slope among the slopes of the plurality of places and the first A lightness expansion amount for expanding the color reproduction area in the lightness direction in the first color space based on the interval between the first grid points arranged in the color space, and the lightness expansion amount The color conversion profile generation method according to claim 2, wherein the extended range is set based on at least. The slope of the surface of the color gamut in the first color space is represented by the ratio of the brightness difference to the saturation difference,
In the extended range setting step, a plurality of slopes on the surface of the color gamut in the first color space are acquired based on the characteristic data, and a minimum slope among the slopes of the plurality of places is obtained. A saturation expansion amount for extending the color reproduction range in the first color space in the direction of the saturation based on the interval between the first grid points arranged in the color space of The color conversion profile generation method according to claim 2, wherein the extension range is set based on at least a degree extension amount. The characteristic data is a third coordinate value of the third color space, a first coordinate value of the second grid point arranged in the color gamut in a third color space depending on the device, Is the associated data,
The extrapolated data is data in which the third coordinate value and the first coordinate value are associated with each other with respect to a third grid point arranged in the extended range in the third color space. The color conversion profile generation method according to claim 4. The third color space is a color space in which the dimension of the second color space is reduced,
The color conversion profile according to claim 5, further comprising a characteristic data generation step of generating the characteristic data based on original data in which the second coordinate value and the first coordinate value are associated with each other in the second color space. Generation method. The third color space has a first axis, a second axis, and a third axis that intersect with each other to define the third coordinate value,
In the third color space, out of the second grid points on the surface of the color gamut, a second grid point within a predetermined range from the third grid point is a specific grid point,
In the third color space, the first axis, the second axis, and the third axis are points in a direction connecting the specific grid point from the third grid point in the color gamut. As a specific point, a point that is at least 1/2 the size of the color gamut in the direction of any of the axes and that is behind the surface of the color gamut,
The color conversion profile generation method according to claim 6, wherein, in the extrapolation step, the extrapolation data is generated based on the specific grid points and the data of the specific points in the characteristic data in the third color space. . A plurality of combinations of the specific grid points and the specific points are set,
In the extrapolation step, in the third color space, the extrapolation data is generated based on data of the specific grid points and the specific points included in the plurality of combinations in the characteristic data. The color conversion profile generation method described.   First correspondence data representing a first correspondence between the first coordinate value and the second coordinate value, at least a part of which are associated in the association step, and the first correspondence from the first coordinate value. Second correspondence data representing a second correspondence relationship for converting the second coordinate value into a value included in the color gamut when the second coordinate value obtained according to the above is a value not included in the color gamut The color conversion profile generation method according to claim 1, further comprising: a correspondence data generation step for generating. Color conversion that associates the first coordinate value of the first color space with the second coordinate value of the second color space depending on the device for a plurality of first grid points arranged in the first color space. A profile generator,
An extended range setting unit for setting an extended range for extending the color reproduction range of the device to the outside based on an interval between the first grid points arranged in the first color space;
An extrapolation unit that generates extrapolation data for extrapolating the color reproduction characteristics of the device in the extended range based on characteristic data representing the color reproduction characteristics of the device in the color reproduction range;
For the plurality of first grid points arranged beyond the color reproduction range with respect to the first color space, the first coordinate value and the second coordinate value based on the characteristic data and the extrapolation data. A color conversion profile generation device comprising: For associating the first coordinate value of the first color space with the second coordinate value of the second color space depending on the device, for a plurality of first grid points arranged in the first color space. A color conversion profile generation program,
An extended range setting function for setting an extended range for extending the color reproduction range of the device to the outside based on the interval between the first grid points arranged in the first color space;
An extrapolation function for generating extrapolation data for extrapolating the color reproduction characteristics of the device in the extended range based on characteristic data representing the color reproduction characteristics of the device in the color reproduction range;
For the plurality of first grid points arranged beyond the color reproduction range with respect to the first color space, the first coordinate value and the second coordinate value based on the characteristic data and the extrapolation data. A color conversion profile generation program that causes a computer to realize a mapping function for mapping the.

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