JP6794818B2 - Color conversion profile generation method, color conversion profile generation device, and color conversion profile generation program - Google Patents

Description

The present invention relates to a color conversion profile generation method, a color conversion profile generation device, 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 that describes the color reproduction characteristics of the device is used. The ICC profile includes, for example, the coordinate values of the CIE (International Commission on Illumination) L ^* a ^* b ^* color space, which is the device independent color space, and the coordinate values of the color space depending on the device. Are associated with each other. The ICC profile includes a so-called A2B table and a so-called B2A table. If the device is a printer that uses C (cyan), M (magenta), Y (yellow), and K (black) colorants, the B2A table will show the Lab values (L ^* value, a ^* value, and , B ^* value) is an information table for converting CMYK values (C value, M value, Y value, and K value). The B2A table has a plurality of lattice points arranged at substantially equal intervals in the L ^* a ^* b ^* color space in the L ^* axial direction, the a ^* axial direction, and the b ^* axial direction. A CMYK value is associated with each grid point. For high-speed calculation, the Lab value and CMYK value are usually calculated with 8 bits (for example, integer value 0 to 255) or 16 bits (for example, integer value 0 to 65535).
In the following description, the description of " ^* " may be omitted.

The device has a color gamut, which is a color reproducible range. In the B2A table, CMYK values that reproduce the colors of the Lab values (L'value, a'value, and b'value) on the surface of the color reproduction region are usually stored in the grid points outside the color reproduction region. To. Therefore, the Lab value of the input color near the surface of the color reproduction area where the lattice points outside the color reproduction area are referred to in the interpolation of the CMYK value becomes the CMYK value of the output color whose saturation is lower than that of the target input color. It is converted and the color reproduction accuracy near the surface of the color reproduction area is lowered. Here, the color reproduction accuracy refers to the degree of accurate reproduction of colors.

Patent Document 1 discloses a color conversion table in which a range in which the conversion result exceeds a predetermined color reproducible range in the device is described by a color signal value that cannot be reproduced in 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 representing the inside of the color reproduction range and an integer value less than 0 or larger than 255 representing the outside of the color reproduction range. It is represented. The range outside the color reproduction range is not limited.

Japanese Unexamined Patent Publication No. 11-55536

When the range of CMY values is expanded from the integer values 0 to 255, the data size of the color conversion table increases, and the time required for the color conversion calculation also increases. Here, when the CMY value is compressed within the range of the integer value 0 to 255 including the numerical range representing the outside of the color reproduction range, the numerical range representing the inside of the color reproduction range is significantly large unless the range outside the color reproduction range is restricted. The color reproduction accuracy inside the color reproduction range is reduced accordingly.
It should be noted that the above-mentioned problem exists not only in the color conversion table for converting the Lab value into the CMY value but also in various color conversion profiles.

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

In order to achieve one of the above objects, the present invention relates to a plurality of first lattice points arranged in the first color space with respect to the first coordinate value of the first color space and the device-dependent second. It is a color conversion profile generation method that associates the second coordinate value of the color space of.
The inclination of the surface of the color gamut of the device in the first color space, the a first interval placed the first grid point in the color space, based on, outside the front Symbol gamut The expansion range setting process for setting the expansion range to be expanded and the expansion range setting process
An extrapolation step of generating extrapolated data that extrapolates the color reproduction characteristics of the device in the extended range based on the characteristic data representing the color reproduction characteristics of the device in the color reproduction range.
The first coordinate value and the second coordinate value of the plurality of first lattice points arranged beyond the color reproduction range with respect to the first color space based on the characteristic data and the extrapolation data. It has an aspect including the associating step of associating with.

Further, the present invention relates to a plurality of first lattice points arranged in the first color space, the first coordinate value of the first color space and the second coordinate value of the second color space depending on the device. It is a color conversion profile generator that associates with and
The inclination of the surface of the color gamut of the device in the first color space, the a first interval placed the first grid point in the color space, based on, outside the front Symbol gamut An extended range setting unit that sets the extended range to be expanded, and
An extrapolation unit that generates extrapolated data that extrapolates the color reproduction characteristics of the device in the extended range based on the characteristic data representing the color reproduction characteristics of the device in the color reproduction range.
The first coordinate value and the second coordinate value of the plurality of first lattice points arranged beyond the color reproduction range with respect to the first color space based on the characteristic data and the extrapolation data. It has an aspect including an associating unit for associating with.

Further, the present invention relates to a plurality of first lattice points arranged in the first color space, the first coordinate value of the first color space and the second coordinate value of the second color space depending on the device. Is a color conversion profile generation program for associating with
The inclination of the surface of the color gamut of the device in the first color space, the a first interval placed the first grid point in the color space, based on, outside the front Symbol gamut The extended range setting function that sets the extended range to be expanded, and the extended range setting function
An extrapolation function that generates extrapolated data that extrapolates the color reproduction characteristics of the device in the extended range based on the characteristic data representing the color reproduction characteristics of the device in the color reproduction range.
The first coordinate value and the second coordinate value of the plurality of first lattice points arranged beyond the color reproduction range with respect to the first color space based on the characteristic data and the extrapolation data. It has an aspect of realizing a computer with an associating function for associating with.

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

The block diagram which shows the structural example of the color conversion profile generator schematically. The flowchart which shows the example of the 1st gamut mapping process. The figure which shows typically the example which generates characteristic data from the original data and generates 3D LUT. The figure which shows typically the example of the virtual CMY space which represents the color reproduction area of a virtual CMY printer. The figure which shows typically the cause that the color reproduction accuracy near the surface of a color reproduction area decreases. The figure which shows the example of the extended virtual CMY space schematically. The flowchart which shows the example of the 2nd gamut mapping processing. The figure which shows typically the example of the extended virtual CMY space which expanded the color reproduction range of a virtual CMY printer. The figure which shows typically the example of generating 3D LUT from extended data. The flowchart which shows the example of the color conversion profile generation processing. The figure which shows the structural example of the color conversion profile schematically. The flowchart which shows the example of the brightness direction extension range setting processing. The figure which shows typically the example which determines the brightness expansion amount of a virtual CMY space. The figure which shows typically the example of calculating the brightness expansion amount of a virtual CMY space. The figure which shows typically the example which determines the CMY expansion amount corresponding to the brightness expansion amount. The figure which shows typically the example of calculating the brightness expansion amount of a virtual CMY space. The flowchart which shows the example of the saturation direction extension range setting processing. The figure which shows typically the example of calculating the saturation expansion amount of the virtual CMY space. The flowchart which shows the example of the extended range setting process. A flowchart showing an example of extrapolation data generation processing. The figure which shows typically the example which expands the surface of the virtual CMY space in the CMY color space. The figure which shows typically the example of setting a plurality of 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 from the combination of a specific lattice point and a specific point. The figure which shows typically the example which extends the ridge line of a virtual CMY space in a CMY color space. The figure which shows typically the example which expands the vertex of the virtual CMY space in the CMY color space.

Hereinafter, embodiments of the present invention will be described. Of course, the following embodiments merely exemplify the present invention, and not all of the features shown in the embodiments are essential for the means for solving the invention.

(1) Outline of the technique included in the present invention:
First, an outline of the technique included in the present invention will be described with reference to the examples shown in FIGS. 1 to 25. It should be noted that the figures of the present application are diagrams schematically showing examples, and the enlargement ratios in each direction shown in these figures may be different, and the figures may not be consistent. Of course, each element of the present technology is not limited to the specific example indicated by the reference numeral.

[Aspect 1]
The color conversion profile generation method according to one aspect of the present technology includes the extended range setting step ST1, the extrapolation step ST2, and the associating step ST3, and is arranged in the first color space (for example, Lab color space CS1). For a plurality of first lattice points GD1, the first coordinate value (for example, Lab value) of the first color space (CS1) and the second color space (for example, CMYK color space CS2) depending on the device (for example, printer 200) ) With the second coordinate value (for example, CMYK value). In the extended range setting step ST1, as illustrated in FIG. 12, the device is based on the interval (for example, gL, gAB) of the first grid points GD1 arranged in the first color space (CS1). An extended range AR1 that extends the color reproduction range (GMT) of (for example, the printer 200) to the outside is set. In the extrapolation step ST2, as illustrated in FIG. 7, the color reproduction characteristic of the device in the extended range AR1 is based on the characteristic data 520 representing the color reproduction characteristic of the device in the color reproduction region (GMT). Extrapolate data 600 is generated. In the associating step ST3, the characteristic data 520 and the extrapolation of the plurality of first lattice points GD1 arranged beyond the color reproduction range (GMT) with respect to the first color space (CS1). The first coordinate value and the second coordinate value are associated with each other based on the data 600.

In the first aspect, 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). The range AR1 is set. Extrapolation data 600 for extrapolating the color reproduction characteristics of the device is generated in this extended range AR1, and based on the extrapolation data 600 and the characteristic data 520, the first coordinate value (Lab value) for the first lattice point GD1 It is associated with the second coordinate value (CMYK value). Therefore, this aspect can provide a color conversion profile generation method capable of improving the color reproduction accuracy near the surface of the color reproduction area while substantially maintaining the color reproduction accuracy inside the color reproduction area.

Here, the first color space includes a device-independent color space such as a CIE L ^* a ^* b ^* color space and a CIE L ^* u ^* v ^* color space.
The second color space includes a CMYK color space, a CMY color space, an RGB color space, a CMYKLcLm color space, and the like. In addition, R means red, G means green, B means blue, Lc means light cyan having a lower concentration than C, and Lm means light magenta having a lower concentration than M. There is.
The device-dependent color space is also called the device-dependent color space, and even if the coordinate values are determined, the color itself perceived by humans cannot be specified, and it depends on the color reproduction characteristics of the device. It is a color space where the colors are fixed.

[Aspect 2]
In the extended range setting step ST1, as illustrated in FIG. 12, the inclination of the surface of the color gamut (for example, Gamat GMT) of the device in the first color space (CS1) (for example, the slope shown in FIG. 13). And the extended range AR1 that extends the color gamut (GMT) to the outside based on the interval (for example, gL, gAB) of the first lattice point GD1 arranged in the first color space (CS1). May be set.

In the second aspect, the slope of the surface of the color reproduction region (GMT) in the first color space (CS1) and the distance (gL) of the first lattice point GD1 arranged in the first color space (CS1) , GAB), and 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 this extended range AR1, and based on the extrapolation data 600 and the characteristic data 520, the first coordinate value (Lab value) for the first lattice point GD1 It is associated with the second coordinate value (CMYK value). Therefore, this aspect can provide a color conversion profile generation method capable of improving the color reproduction accuracy near the surface of the color reproduction area while substantially maintaining the color reproduction accuracy inside the color reproduction area.
Although not included in the above aspect 2, the extension range is expanded based on the spacing of the first grid points arranged in the first color space, not based on the inclination of the surface of the color reproduction region in the first color space. The setting is also included in this technology.

[Aspect 3]
As illustrated in FIG. 13 and the like, the surface inclination (for example, Slope) of the color reproduction region (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 reproduction region (GMT) in the first color space (CS1) may be acquired based on the characteristic data 520. In the extended range setting step ST1, the distance between the maximum inclination (for example, Slope_max) among the inclinations of the plurality of locations and the first lattice point GD1 arranged in the first color space (CS1) (for example, gL, gAB). ), And the lightness expansion amount (for example, Ext_L0) that expands the color reproduction area (GMT) in the direction of the lightness in the first color space (CS1) may be acquired. In the expansion range setting step ST1, the expansion range AR1 may be set based on at least the brightness expansion amount. This aspect can provide a more preferred method of generating a color conversion profile.

[Aspect 4]
Further, as illustrated in FIGS. 17 and 18, 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, Lab color space CS1) The color reproduction region (GMT) is extended in the direction of the saturation in the first color space (CS1) based on the interval (for example, gL, gAB) of the first lattice point GD1 arranged in. The saturation expansion amount (for example, Ext_C0) may be acquired. In the expansion range setting step ST1, the expansion range AR1 may be set based on at least the saturation expansion amount. This aspect can also provide a more preferred method of generating a color conversion profile.
Further, as illustrated in FIG. 19, in the expansion range setting step ST1, the first expansion range based on the brightness expansion amount (for example, CMY expansion amount Ext_CMY0L, Ext_CMY1L) and the second expansion range based on the saturation expansion amount. (For example, CMY expansion amount Ext_CMY0C, Ext_CMY1C) and the wider one may be set as the expansion range AR1. This aspect can provide a more preferred method of generating a color conversion profile.
Although not included in the above aspects 3 and 4, the present technology also includes a case where the inclination of the surface of the color reproduction region is not the ratio of the difference in brightness to the difference in saturation.

[Aspect 5]
As illustrated in FIG. 3 and the like, the characteristic data 520 relates to a second grid point GD2 arranged in the color reproduction region (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 extrapolation data 600 is the third coordinate value (CMY value) of the third grid point GD3 arranged in the extension range AR1 in the third color space (CS3). The data may be associated with the first coordinate value (Lab value). This aspect can provide a suitable method of 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 having a reduced dimension of the second color space (for example, CMYK color space CS2). As illustrated in FIG. 3 and the like, the present color conversion profile generation method corresponds the second coordinate value (for example, CMYK value) and the first coordinate value (for example, Lab value) in the second color space (CS2). The characteristic data generation step ST4 that generates the characteristic data 520 based on the attached original data (for example, color measurement data 500) may be included. This aspect can provide a more preferred method of generating a color conversion profile.
Here, the third color space can be, for example, a CMY color space when the second color space is a CMYK color space or a CMYKLcLm color space.

[Aspect 7]
As illustrated in FIG. 21 and the like, the third color space (for example, CMY color space CS3) is an intersecting first axis (for example, C axis) for defining the third coordinate value (for example, CMY value). , A second axis (eg, M axis), and a third axis (eg, Y axis). Here, among the second grid points GD2 on the surface of the color reproduction region (GMT) in the third color space (CS3), the second grid point GD2 within a predetermined range AR2 from the third grid point GD3. Is a specific grid point GD4. Further, in the third color space (CS3), a point in the color reproduction region (GMT) in the direction connecting the third grid point GD3 to the specific grid point GD4, and the first axis, said. 1/2 or more of the size of the color reproduction area (GMT) in any direction of the second axis and the third axis, from the surface to the depth (for example, depth Ref_Depth) of the color reproduction area (GMT). ) Is a specific point P0. In the extrapolation step ST2, the extrapolation data 600 may be generated in the third color space (CS3) based on the data of the specific grid point GD4 and the specific point P0 in the characteristic data 520.

In the above aspect 7, the specific point P0 for generating the extrapolation data 600 is ½ or more of the size of the color reproduction area (GMT) in the axial direction, and is deep from the surface of the color reproduction area (GMT). Therefore, it is not easily affected by the irregular shape of the surface of the color reproduction range (GMT). Therefore, this aspect can provide a technique capable of further improving the color reproduction accuracy near the surface of the color reproduction region.
Although not included in the above aspect 7, the present technology also includes setting a specific point to a point having a depth of less than 1/2 of the size of the color reproduction range 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), based on the data of the specific lattice point GD4 and the specific point P0 included in the plurality of combinations in the characteristic data 520, the said Extrapolation data 600 may be generated. This aspect is less susceptible to coordinate value errors 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 reproduction region.

[Aspect 9]
As illustrated in FIGS. 10 and 11, the color conversion profile generation method is a correspondence data generation step of generating first correspondence data (for example, three-dimensional LUT700) 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) to which at least a part is associated in the association step ST3. It is the data showing the first correspondence relationship of. 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 is not included in the color reproduction range (GMT). When it is a value, it is data representing a second correspondence relationship for converting the second coordinate value into a value included in the color reproduction area (GMT) (for example, a C4M4Y4K4 value). In this embodiment, when the second coordinate value obtained from the first coordinate value according to the first correspondence is a value that is not included in the color reproduction area (GMT), the second coordinate value is included in the color reproduction area (GMT). Therefore, it is possible to provide a method for generating a suitable color conversion profile.

[Aspect 10]
By the way, the color conversion profile generation device (for example, the host device 100) according to one aspect of the present technology includes an extension range setting unit U1 corresponding to the extension range setting step ST1, an extrapolation unit U2 corresponding to the extrapolation step ST2, and an extrapolation unit U2. The association unit U3 corresponding to the association process 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 reproduction area while substantially maintaining the color reproduction accuracy inside the color reproduction area. The color conversion profile generation device (100) may further include a characteristic data generation unit U4 corresponding to the characteristic data generation step ST4 and a correspondence data generation unit U5 corresponding to the correspondence data generation step ST5.

[Aspect 11]
Further, the color conversion profile generation program PR0 according to one aspect of the present technology includes 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. The corresponding mapping function FU3 is realized in 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 reproduction area while substantially maintaining the color reproduction accuracy inside the color reproduction area. The color conversion profile generation program PR0 may 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 on the computer.

Further, the present technology can be applied to a composite device including a color conversion profile generator, a control method of the composite device, a control program of the composite device, a color conversion profile generation program, a computer-readable medium on which the control program is recorded, and the like. Is. The above-mentioned device may be composed of a plurality of dispersed parts.

(2) Specific example of the configuration of the color conversion profile generator:
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, and communication I / output. F (interface) 118, etc. are connected so that information can be input and output from each other.

The storage device 114 stores an OS (operating system) (not shown), a color conversion profile generation program PR0, and the like. These are appropriately read into the RAM 113 and used in the generation process of the color conversion profile 400 (for example, ICC profile). At least one of the RAM 113 and the storage device 114 has various information such as color measurement data 500, K (black) generation function 510, characteristic data 520, three-dimensional LUT (look-up table) 530, extrapolation data 600, and three dimensions. The LUT 610, the three-dimensional LUT 700 included in the color conversion profile 400 (example of the first correspondence data), the output table 800 included in the color conversion profile 400 (example of the second correspondence data), 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 as the display device 115. As the input device 116, a pointing device, hard keys including a keyboard, a touch panel attached to the surface of a display panel, and the like can be used. The color measuring device 117 can measure each color patch formed on a printed matter (print substrate), which is an example of a medium on which a color chart is formed, and output a color measuring value. Patches are also called color tags. The colorimetric value is, for example, a value representing the brightness L ^* and the chromaticity coordinates a ^* , 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. As the communication I / F 118, 210 standard, USB (Universal Serial Bus), short-range wireless communication standard, and the like can be used. The communication of the communication I / Fs 118 and 210 may be wired, wireless, or network communication such as LAN (Local Area Network) or the Internet.

The color conversion profile generation program PR0 shown in FIG. 1 realizes the extended range setting function FU1, the extrapolation function FU2, the association function FU3, the characteristic data generation function FU4, and the correspondence data generation function FU5 in the host device 100.

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 be able to communicate with each other. Further, even if the printer is in the host device 100, the present technology can be implemented.

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

(3) Specific example of the first gamut mapping process performed by the color conversion profile generator:
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 a Lab value with a device color value (for example, CMYK value) in a color gamut (for example, Gamut GMT shown in FIG. 5). The first gamut mapping process shown in FIG. 2 is an example of conventional gamut mapping, and CMYK depends on the device (for example, 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 a CMYK value (an example of a second coordinate value) of the color space CS2 (an example of a 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 of 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" will be omitted.

CMY color space CS3 (third) in the virtual CMY printer Gamut GMT before performing the gamut mapping process for each grid point (first grid point GD1 illustrated in FIG. 3) of the LUT 530 that converts the Lab value into a CMYK value. The characteristic data 520 for converting the CMY value (example of the third coordinate value) of the color space of (1) to the Lab value of the Lab color space CS1 (example of the first color space) is generated. The CMY color space CS3 has C-axis (example of first axis), M-axis (example of second axis), and Y-axis (example of third axis) that intersect each other to define CMY values. It is a four-dimensional CMYK color space, which is a color space in which the dimensions of CS2 are reduced. The characteristic data 520 is created based on the color measurement data 500 (example of the original data) of the plurality of color patches PA1 formed by the printer 200, and the color reproduction characteristics of the printer 200 are represented in the Gamut GMT. The color measurement data 500 shown in FIG. 3 is data in which CMYK values (Cp, Mp, Yp, Kp) are associated with Lab values (Lp, ap, bp) for each patch PA1 in the CMYK color space CS2. The variable p here is a variable that identifies patch PA1.

Since the CMYK color space CS2 is four-dimensional, there will be a plurality of CMYK values that reproduce a certain Lab value. Therefore, after determining the K (black) generation function 510 in advance, the CMYK value is converted into the CMY value of the three-dimensional CMY color space CS3. The K generation function 510 shown in FIG. 3 is a function representing the correspondence between the K value (Kj) and the CMY value (Cj, Mj, Yj) that reproduces the color of the K value, and may be a one-dimensional LUT. The variable j here is a variable that identifies the K value (for example, a gradation value of an integer 0 to 255). In the present application, "Min to Max" means a minimum value of Min or more and a maximum value of Max or less.

When the first gamut mapping process shown in FIG. 2 is started, the host device 100 acquires the colorimetric data 500 in which the CMYK value is associated with the Lab value (S102). In S104, the characteristic data 520 is generated from the colorimetric data 500 by using the K generation function 510. The characteristic data 520 shown in FIG. 3 has CMY values (Cq, Mq, Yq) for the Cn × Mn × Yn second lattice points GD2 arranged in the color reproduction range of the CMY color space CS3 depending on the printer 200. It is the data associated with the Lab values (Lq, aq, bq). The variable q here is a variable that identifies the second grid point GD2. The characteristic data 520 also has CMYK values (C0q, M0q, Y0q, K0q) corresponding to CMY values (Cq, Mq, Yq). Note that the grid point means a virtual point arranged in the input color space, and it is assumed that the 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 shows an example of a virtual CMY space 300 representing a color reproduction range of a virtual CMY printer in the CMY color space CS3. The characteristic data 520 is data that defines the correspondence between the CMY values (Cq, Mq, Yq), which are the grid point coordinate values, and the Lab values (Lq, aq, bq), which 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 an integer of 2 or more). It has a second grid point GD2 of (an integer greater than or equal to 2). The number of grid points Cn, Mn, Yn in the axial direction is not particularly limited and may be 17, 32, 64, or the like.

After the characteristic data 520 is generated, the gamut mapping process of performing the clipping process as necessary for each first lattice point of the Lab color space CS1 is performed. The gamut mapping process calculates CMYK values (Ci, Mi, Yi, Ki) that reproduce the colors of the Lab values (Li, ai, bi) of the first grid point GD1 for each first grid point GD1 in the Lab color space CS1. It is a process to do. The variable i here is a variable that identifies the first grid point GD1. The clipping process converts a Lab value (Li, ai, bi) that cannot be reproduced by a printer into a low-saturation Lab value (L'i, a'i, bi) that can be reproduced by a printer. It is a process. In the case of Colorimetric, when a line is extended from the first lattice point to the achromatic axis in the Lab color space CS1, the points (Li, a'i, b'i) that intersect the surface of the virtual CMY space 300 in the Lab color space CS1. ).

First, the host device 100 sets the positions (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, the virtual CMY space 300 is divided into small tetrahedrons having the lattice points of the characteristic data 520 as vertices in the Lab color space CS1 based on the characteristic data 520, and the grid point coordinate values (lattice point coordinate values) from the tetrahedron group of the virtual CMY space 300 ( Search for tetrahedrons containing Li, ai, bi). In S110, the process is branched depending on whether or not a tetrahedron containing the 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 performs the first lattice point GD1 by the interpolation calculation. CMYK values (Ci, Mi, Yi, Ki) are calculated and associated with the Lab values (Li, ai, bi) of the first lattice point GD1 (S114), and the process proceeds to S120.

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

In S120, it is determined whether or not all the first grid points GD1 for generating the LUT 530 are set. When the first grid point GD1 that has not been set remains, the host device 100 repeats the associating process 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, which is the source of the B2A table in which the correspondence between the Lab value and the CMYK value is defined in the color reproduction range 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 values (C1, M1, Y1, K1) each represent the amount of CMYK ink used in the printer 200 when used as is for print data. The LUT 530 shown in FIG. 3 defines the correspondence between the Lab value (Ls, as, bs) which is a grid point coordinate value and the C1M1Y1K1 value (Cs, Ms, Ys, Ks) which is an output coordinate value in the Lab color space CS1. It is the data that was done. The variable s here is a variable that identifies 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 second. This is an example of three color coordinate values. These first, second, and third color coordinate values are component values of the three primary colors.

(4) Causes and solutions for reduced 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 LUT530 which is a B2A table, there are the following problems.
FIG. 5 schematically shows the cause of the decrease in color reproduction accuracy near the surface of the Gamut GMT 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. Of the plurality of first grid points GD1, the grid points in the gamut GMT of the printer 200 are indicated by white circles, and the grid 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 Gamut GMT of the printer, the L value Le and the b value be exactly coincide with the position of the first grid point GD1. To do. Further, let the first lattice points on both sides adjacent to the point e in the a-axis direction be points d and f, respectively. The CMYK values at the point e are obtained by linearly interpolating the CMYK values stored at the grid 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 by using linear interpolation. Here, as shown in the graph shown on the lower side of FIG. 5, the C value at the point e is ideally expected to have a minimum value of 0 on the broken line (an example of a value indicating that no color is used). 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 deterioration of the color reproduction accuracy of the gamut surface.
The above is the description of the surface where C is the minimum value 0 in Gamut GMT, but the same is true for the surface where C is the 8-bit maximum value 255 (an example of a value indicating that the color is used maximum) of the gradation value. The same applies to the aspects in which M and Y have a minimum value of 0 and a maximum value of 255. Hereinafter, unless otherwise specified, the gradation value will be described as having an 8-bit value of 0 to 255.

In other words, the above-mentioned 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, since a negative value whose CMY value is smaller than 0 or a value exceeding 255 cannot be input to the actual printer, the above-mentioned mapping process is performed.

In this specific example, when the first grid point GD1 is outside the Gamut GMT, a negative value or a value exceeding 255 can be set as the CMYK value of the three-dimensional LUT 700 of the color conversion profile 400. There is. For example, the C value of the grid point f outside the gamut described in FIG. 5 is set to a negative value such as "-20" instead of "0". Further, in this specific example, an output table 800 as illustrated in FIG. 11 is prepared after the three-dimensional LUT 700, and the CMYK value converted from the Lab value by reference to the three-dimensional LUT 700 is a negative value or exceeds 255. When it becomes a value, it is set to be in the range of 0 to 255 by referring to the output table 800.
As described above, the above-mentioned problem 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 having a 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 expands the range of the virtual CMY space 300 obtained from the color measurement 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, the range in which −40 ≦ C <0 and 255 <C ≦ 275 is the extended range AR1 that extends the Gamut GMT to the outside, and the virtual CMY space 300 and the extended range AR1 are combined to form the extended virtual CMY space 310. 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 points outside the original virtual CMY space 300 becomes a negative value or a value exceeding 255. can do.

(5) Outline of the second gamut mapping process performed by the color conversion profile generator:
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 beyond the Gamut GMT. The second gamut mapping process shown in FIG. 7 is a process for generating a three-dimensional LUT610 that is the source of the B2A table that converts the Lab value into the CMYK value. 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 of FIG. 7 corresponds to the extended range setting unit U1, the extended range setting process ST1, and the extended range setting function FU1. S202 and S206 correspond to the extrapolation portion U2, the extrapolation step ST2, and the extrapolation function FU2. S208 to S222 of FIG. 7 correspond to the association unit U3, the association process 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 contains CMY values (Cq, Mq, Yq) and Lab values (Lq, aq, bq) for the Cn × Mn × Yn second lattice points GD2 in the CMY color space CS3. This is the data that defines the correspondence. The characteristic data 520 also has CMYK values (C0q, M0q, Y0q, K0q) corresponding to CMY values (Cq, Mq, Yq). In S204, an extension range AR1 that extends 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, external data 600 for extrapolating the color reproduction characteristics of the printer 200 in the extended gamut 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 CMY for the third lattice point GD3 arranged on the surface (extended range AR1) of the extended virtual CMY space 310 in which the virtual CMY space 300 is slightly enlarged in the CMY color space CS3. It is the data in which the value and the 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 extension range AR1 is hatched. As shown in FIGS. 8 and 9, the CMY values (Cq) are combined for the (Cn + 2) × (Mn + 2) × (Yn + 2) lattice points GD2 and GD3 of the CMY color space CS3 by combining the characteristic data 520 and the extrapolation data 600. , Mq, Yq) and the Lab value (Lq, aq, bq). The variable q here is a variable that identifies the grid points GD2 and GD3. The characteristic data 520 and the extrapolated data 600 also have CMYK values (C0q, M0q, Y0q, K0q) corresponding to the CMY values (Cq, Mq, Yq). Details of the extrapolation data generation process of S206 will be described later.

After that, the Lab value and the CMYK value are associated with each other for the plurality of first lattice 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 associative processing of S208 to S222 is the same as the associative processing of S106 to S120 of FIG. First, the host device 100 sets the positions (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 extended virtual CMY space 310 is divided. A tetrahedron including lattice point coordinate values (Li, ai, bi) is searched from the tetrahedron group in space 310. In S212, the process is branched depending on whether or not a tetrahedron containing the 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 and the extrapolation data 600 (S214), and performs an interpolation calculation. The CMYK values (Ci, Mi, Yi, Ki) of the first grid point GD1 are calculated and associated with the Lab values (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 clipping processing 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, 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 based on the characteristic data 520 and the extrapolation data 600, and the first lattice points ( When a line is extended from the coordinate values Li, ai, bi) to the achromatic axis, the triangle that intersects this line is searched for, and the CMYK values (C0q, M0q, Y0q, K0q) of the three vertices of the found triangle are characteristic. Obtained from data 520 and extrapolated data 600 (S218). In S220, the CMYK values (Ci, Mi, Yi, Ki) are calculated from the CMYK values of the three vertices by interpolation calculation and associated with the Lab values (Li, ai, bi) of the first grid point GD1, and the processing is performed in S222. Proceed.

In S222, it is determined whether or not all the first grid points GD1 for generating the LUT 610 are set. If the first grid point GD1 that has not been set remains, the host device 100 repeats the associating process 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, which is the source of the B2A table in which the correspondence 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 the LUT 610 is also expressed as a C2M2Y2K2 value (C2, M2, Y2, K2). The C2M2Y2K2 values (C2, M2, Y2, K2) each represent the amount of CMYK ink used in the printer 200 when used as is for print data. The LUT 610 shown in FIG. 9 defines the correspondence between the Lab value (Ls, as, bs) which is a grid point coordinate value and the C2M2Y2K2 value (Cs, Ms, Ys, Ks) which is an output coordinate value in the Lab color space CS1. It is the data that was done. The variable s here is a variable that identifies the first grid point GD1.

(6) Outline of the color conversion profile generation process performed by the color conversion profile generation device:
The LUT 610 in which the Lab value and the C2M2Y2K2 value are associated with each other using the extended virtual CMY space 310 can be directly used as the three-dimensional LUT 700 of the color conversion profile 400. However, if there is a part near the surface of the gamut where gradation is more important than color reproduction accuracy, the LUT530 or C1M1Y1K1 value in which the Lab value and the C1M1Y1K1 value are associated with each other using the virtual CMY space 300, or A combination of LUT 530 and 610 may be applied.

FIG. 10 shows an example of the color conversion profile generation process performed by the host device 100. FIG. 11 schematically illustrates the structure of the color conversion profile 400 including the three-dimensional LUT 700 (example of first correspondence data) and the output table 800 (example of second correspondence data). Here, S306 to S308 in FIG. 10 correspond to the correspondence data generation unit U5, the correspondence data generation process ST5, and the correspondence 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 shown in FIG. 11 is a Lab value (Ls, as, bs) which is a grid point coordinate value and a C3M3Y3K3 value which is an output coordinate value for a plurality of first grid points GD1 arranged beyond the color reproduction range of the printer 200. This is data that defines the first correspondence with (Cs, Ms, Ys, Ks). The variable s here is a variable that identifies the first grid point GD1.

For example, if the LUT 610 is to be a three-dimensional LUT 700 as it is, (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 to the case where the M1 value (example of the second color coordinate value), the Y1 value (example of the third color coordinate value), and the K1 value are applied. If the average value of the C1 value and the 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 applying 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. Therefore, for example, all or part of the C2M2Y2K2 value (C2, M2, Y2, K2) is associated with the Lab value in the part of the color space where the color reproduction accuracy is more important than the gradation, and the color space is included. By associating a part or all of the C1M1Y1K1 value (C1, M1, Y1, K1) 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.
From the above, the three-dimensional LUT 700 represents the correspondence between the Lab value and the CMYK value that are at least partially associated with each other in the association processing of S208 to S222 of FIG.

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

(7) Specific example of extended range setting processing performed by the color conversion profile generator:
Next, the 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 data in which the CMYK printer is virtually used as a CMY 3-channel input printer, and the Lab value of the PCS (profile connection space) with respect to the input CMY of the printer and the actual output CMYK value are held. It is a set. The original characteristic data 520 has Cn in the C-axis direction, Mn in the M-axis direction, and Yn second lattice points GD2 in the Y-axis direction, and has a total of Cn × Mn × Ynth. The two grid points GD2 are arranged three-dimensionally.

In this specific example, by expanding the virtual CMY space 300 as shown in FIGS. 6 and 8, one point is set on the side less than 0 in each of the C-axis direction, the M-axis direction, and the Y-axis direction, and One third grid point GD3 is added to 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).

Further, in this specific example, the CMY value and the Lab value of the increased third grid point GD3 are calculated by the following procedure.
Step 1. Determining the amount of CMY expansion of the virtual CMY space 300.
Step 2. Creation of extended faces (6 faces) that will be the extended virtual CMY space 310 (hexahedron).
Step 3. Creation of extended ridge lines (12 lines) that will be the extended virtual CMY space 310 (hexahedron).
Step 4. Creation of extended vertices (8 points) that will be the extended virtual CMY space 310 (hexahedron).
The above procedure 1 is performed in the extended range setting process, and the above steps 2 to 4 are performed in the extrapolation data generation process. First, an example of determining the expansion amount of CMY in the above procedure 1 will be described.

FIG. 12 shows a specific example of the extended range setting process performed in S204 of FIG. 7. In this example, the expansion amounts Ext_L0 and Ext_L1 in the lightness direction of the expansion range AR1 are set, and then the expansion amounts Ext_CMY0 and Ext_CMY1 in the CMY color space CS3 are set. FIG. 13 schematically illustrates how the brightness expansion amount Ext_L0 of the virtual CMY space 300 is determined in the Lab color space CS1. FIG. 14 schematically illustrates how to calculate the brightness expansion amount Ext_L0 of the virtual CMY space 300. Of the plurality of first grid points GD1 shown in FIGS. 13 and 14, the grid points GD1a inside the gamut are indicated by white circles, and the grid points GD1b outside the gamut are hatched. FIG. 15 schematically illustrates how the CMY expansion amount Ext_CMY0 corresponding to the brightness expansion amount Ext_L0 is determined. FIG. 16 schematically illustrates how to calculate the brightness expansion amount Ext_L1 of the virtual CMY space 300. Here, the lightness expansion amount Ext_L0 is the expansion amount in the direction in which the lightness L becomes larger than the white point W as shown in FIG. 13, and the lightness expansion amount Ext_L1 is the expansion amount in the direction in which the lightness L is larger than the black point K as shown in FIG. Is also the amount of expansion in the direction of becoming smaller. Further, the CMY expansion amount Ext_CMY0 is an expansion amount corresponding to the lightness expansion amount Ext_L0 in the CMY color space CS3, and the CMY expansion amount Ext_CMY1 is an expansion amount corresponding to the lightness expansion amount Ext_L1 in the CMY color space CS3.

The basic idea of determining the extended gamut AR1 of the virtual CMY space 300 is that in the Lab color space CS1, the first lattice point GD1 (referred to in the interpolation process for calculating the CMYK value with respect to the Lab value of the gamut surface) ( The expansion amount is determined so that one unit rectangular body having eight vertices (see FIG. 13) is completely contained. As a result, the numerical gamut Ft to Rf representing the inside of the Gamut GMT is sufficiently secured for the CMYK output value of the three-dimensional LUT 700 of the color conversion profile 400, and the color reproduction accuracy inside the Gamut is sufficiently maintained. 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, simply, the minimum expansion amount in which the unit rectangular parallelepiped fits is calculated without considering the position of the first grid point GD1. It is considered that this method also has a small effect on accuracy.

The brightness expansion amount Ext_L0, which is on the negative side of the CMY value, can be determined, for example, as follows.
First, as shown in FIG. 13, in the Lab color space CS1, the distance between the first grid points GD1 in the L-axis direction of the three-dimensional LUT 700 is gL, and the first grid points in the a-axis direction and the b-axis direction of the three-dimensional LUT 700. Let the interval of GD1 be gAB. Here, the grid point spacing in the a-axis direction and the grid point spacing in the b-axis direction are the same spacing 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 steeper the slope of the surface of the gamut, the larger the amount of expansion in the lightness direction for including the unit rectangular parallelepiped is required. Therefore, the secondary colors of R (Y and M are equal amounts), G (C and Y are equal amounts), and B (C and M are equal amounts) in which the slope slope becomes large on the surface of the Gamat GMT of the printer 200. Slope_W-R, Slope_W-G, and Slope_W-B are calculated for, and the maximum slope Slope_max is used for later calculation. Here, the slopes Slope_W-R, Slope_W-G, and Slope_W-B are collectively referred to as the slopes. The slope slope of R, G, and B uses the data of the RGB minimum density lattice point P1 having the lowest density of R, G, and B in the second lattice point GD2 of the characteristic data 520, and RGB in the Lab color space CS1. Let it be the slope of the line connecting the minimum density lattice point P1 (coordinate values Lp, ap, bp) and the white point W (coordinate values Lw, aw, bw).

However, dL = (Lw-Lp), dA = (aw-ap), 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 idea, when the brightness direction extension range setting process shown in FIG. 12 is started, the host device 100 tilts the low density portions of R, G, and B Slope_W-R, Slope_W-G, and Slope_W-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 expansion amount Ext_L0 is calculated based on the maximum slope Slope_max and the intervals gL and gAB of the first grid point GD1.

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

Further, the brightness expansion amount Ext_L1 on the side where the CMY value exceeds 255 can be basically determined in the same way as the brightness expansion amount Ext_L0 on the minus side. In the dark part of Gamut GMT, the slopes of the ridges from the maximum concentrations of C, M, and Y to the black point K have the maximum slopes, so the slopes of these lines will be calculated. However, since the shape of the gamut near the black point K is unstable, for example, the slopes of the three straight lines connecting the following two points, Slope_C-K, Slope_M-K, and Slope_Y-K, are calculated and their maximum values are 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, Straight line connecting 255, 127) ・ Line from Y to K ... Straight line connecting CMY values (0, 0, 255) and (127, 127, 255)

Based on the above idea, in S410 of the brightness direction extension 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, and Y to K, respectively. Calculate according to equation (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 expansion amount Ext_L1 is calculated based on the distance gL and gAB between the maximum slope Slope_max1 and the first grid point GD1.

Finally, the host device 100 acquires the CMY expansion amount Ext_CMY1 that realizes the brightness expansion amount Ext_L1 in the direction exceeding the CMY value of 255 (S416), and ends the brightness direction expansion range setting process. As shown in FIG. 16, the CMY expansion amount Ext_CMY1 is the CMY at the point where the L value increases by 1 minute from the black point K on the line (on the gray axis) where C = M = Y in the virtual CMY space 300. It can be obtained from the values (255-Ext_CMY0, 255-Ext_CMY0, 255-Ext_CMY0). Therefore, referring to the characteristic data 520, the CMY values (255-Ext_CMY0, 255-Ext_CMY0, 255-Ext_CMY0) corresponding to the Lab value of the point where the L value is increased by 1 minute of the brightness expansion amount Ext_L from the black point K are interpolated. By obtaining, the CMY expansion amount Ext_CMY1 is determined.

As described above, the extension range AR1 is set so that the brightness expansion amount Ext_L0 and Ext_L1 are obtained based on the maximum inclinations Slope_max and Slope_max1 among the inclinations of the plurality of points on the surface of the gamut and the intervals gL and gAB of the first lattice point GD1. To.

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 brightness expansion amount, but the expansion amount can also 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. 7. In this example, the expansion amounts Ext_C0 and Ext_C1 in the saturation direction of the expansion range AR1 are set, and then the expansion amounts Ext_CMY0 and Ext_CMY1 in the CMY color space CS3 are set. FIG. 18 schematically illustrates how to calculate the saturation expansion amount Ext_C0 of the virtual CMY space 300 in the Lab color space CS1. Here, as shown in FIG. 18, the saturation expansion amount Ext_C0 has a saturation higher than the maximum saturation point a of each of C, M, and Y on the higher brightness side than the maximum saturation point a of each of C, M, and Y. It is an expansion amount in the increasing direction, and the saturation expansion amount Ext_C1 has a saturation higher than the maximum saturation point a of each of C, M, and Y on the lower brightness side than the maximum saturation point a of each of C, M, and Y. The amount of expansion in the increasing direction. Further, the CMY expansion amount Ext_CMY0 is an expansion amount corresponding to the saturation expansion amount Ext_C0 in the CMY color space CS3, and the CMY expansion amount Ext_CMY1 is an expansion amount corresponding to the saturation expansion amount Ext_C1 in the CMY color space CS3.

The saturation expansion amount Ext_C0 on the negative side of the CMY value can be determined, for example, as follows.
As can be seen in FIG. 18, the gentler the inclination of the surface of the gamut, the larger the amount of expansion in the saturation direction for including the unit rectangular parallelepiped is required. Therefore, the slopes Slope_C-W, Slope_M-W, and Slope_Y-W are calculated for each of the primary colors C, M, and Y whose slope slope becomes smaller on the surface of the Gamat GMT of the printer 200, and the minimum slope Slope_min is calculated 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 the slopes. The slopes of the slopes of C, M, and Y have the maximum saturation points a of C, M, and Y in the second lattice point GD2 of the characteristic data 520, and the concentrations of C, M, and Y are higher than the maximum saturation points. Using the data of the second lattice point P2, which is one step lower, the slope dL / dC of the line connecting the maximum saturation point a and the second lattice point P2 in the Lab color space CS1 is used.

Based on the above idea, when the saturation direction extension range setting process shown in FIG. 17 is started, the host device 100 tilts from C, M, Y to W Slope_C-W, Slope_M-W, Slope_Y-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 expansion amount Ext_C0 is calculated based on the minimum slope Slope_min and the intervals gL and gAB of the first grid point GD1.

In S428, the CMY extension amount Ext_CMY0 that realizes the saturation expansion 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 of the virtual CMY space 300 is a point b in which the saturation is reduced by the saturation extension amount Ext_C0 minutes from the maximum saturation point a at the same brightness. It can be obtained from the CMY value in. 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 (255-Ext_CMY0,0,0). If it is 0,255,0), the CMY value of point b is (0,255-Ext_CMY0,0), and if the CMY value of maximum saturation point a is (0,0,255), the CMY value of point b is. The value is (0,0,255−Ext_CMY0). Therefore, by referring to the characteristic data 520 and obtaining the CMY value corresponding to the Lab value of the point b whose saturation is decreased by the saturation expansion amount Ext_C0 minutes from the maximum saturation point a by the interpolation calculation, the CMY expansion amount Ext_CMY0 can be obtained. It is determined.

Further, the saturation expansion amount Ext_C1 on the side where the CMY value exceeds 255 can be basically determined in the same way as the saturation expansion amount Ext_C0 on the minus side. For example, for the dark part of Gamut GMT, the slopes of three straight lines connecting the following two points, Slope_R-K, Slope_G-K, and Slope_B-K, are calculated and the minimum value Slope_min1 is used.
・ Line from R to K… A straight line connecting CMY values (0,255,255) and (127,255,255) ・ Line from G to K… CMY values (255,0,255) and (255, Straight line connecting 127, 255) ・ Line from B to K ... Straight line connecting CMY values (255, 255, 0) and (255, 255, 127)

Based on the above idea, in S430 of the saturation direction extended 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, and 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 expansion amount Ext_C1 is calculated based on the intervals gL and gAB between the minimum slope Slope_min1 and the first grid point GD1.

Finally, the host device 100 acquires the CMY expansion amount Ext_CMY1 that realizes the saturation expansion amount Ext_C1 in the direction exceeding the CMY value of 255 (S436), and ends the saturation direction expansion range setting process. The CMY extension amount Ext_CMY1 is determined by obtaining the CMY value corresponding to the Lab value of the point b whose saturation is decreased by the saturation extension amount Ext_C1 minutes from the maximum saturation point by the interpolation calculation with reference to the characteristic data 520. ..

Based on the above, the extension range AR1 is set so that the saturation expansion amounts Ext_C0 and Ext_C1 are set based on the minimum inclinations Slope_min and Slope_min1 among the inclinations of the plurality of locations on the surface of the gamut and the intervals gL and gAB of the first lattice point GD1. Will be 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 brightness expansion amount or the saturation expansion amount, but the expansion amount is calculated from the viewpoint of both the brightness 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. 7. When the process is started, the host device 100 first performs the brightness direction extension range setting process shown in FIG. 12 (S442). Let the temporary CMY expansion amounts Ext_CMY0 and Ext_CMY1 obtained by this process be CMY expansion amounts Ext_CMY0L and Ext_CMY1L (examples of the first expansion range). In S444, the saturation direction extension range setting process shown in FIG. 17 is performed. Let the temporary CMY expansion amounts Ext_CMY0 and Ext_CMY1 obtained by this process be CMY expansion amounts Ext_CMY0C and Ext_CMY1C (example of the second expansion range).

In S446, the larger of the CMY expansion amounts Ext_CMY0L and Ext_CMY0C is set as the final CMY expansion amount Ext_CMY0. Finally, the host device 100 sets the larger of the CMY expansion amounts Ext_CMY1L and Ext_CMY1C as the final CMY expansion amount Ext_CMY1 (S448), and ends the expansion 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 expansion 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 lattice point GD1 as the apex is completely included.

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

In step 2 described above, in the CMY color space CS3, the Lab value and the CMYK value at the third lattice point GD3 of the extended surface (the ridge line is not included) obtained by expanding the six surfaces of the virtual CMY space 300 (hexahedron) are characteristic data. Externalize based on 520.
When the extrapolation data generation process is started, the host device 100 selects the third lattice point to be extrapolated from among the plurality of third lattice points GD3 arranged on the expansion surface of the virtual CMY space 300 in the CMY color space CS3. Set (S502). For example, the C value of the third grid point GD3 arranged on the extension surface on the minus side in the C-axis direction is −Ext_CMY0, and the M value and Y value of the third grid point GD3 are the second grids of the virtual CMY space 300, respectively. Let it be the M value and the Y value of the point GD2. The C value of the third grid point GD3 arranged on the expansion 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. Let it be the M value and the 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 direction in which the brightness L becomes higher as the upper side is based on the gray axis of C = Y = M. I have to. The same applies to FIGS. 24 and 25 described later. The point a (hatched grid point) shown in FIG. 21 indicates the third grid point GD3 set on the expansion surface.
After setting the third grid point, the host device 100 is within a predetermined range AR2 from the point a (set third grid point) of the second grid points GD2 on the surface of the virtual CMY space 300 (Gamat GMT). The specific grid point GD4 is set (S504). The point b (the grid point marked with +) shown in FIG. 21 indicates the specific grid point GD4 set on the surface of the virtual CMY space 300. The point b shown in FIG. 21 is the point closest to the point a and is a point in the C-axis direction from the point a. Of course, depending on the position of the expansion 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 lattice point) to the point b (specific lattice point GD4) in the virtual CMY space 300 (Gamat GMT). 50% (1) 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). / 2) As described above, the specific point P0 behind the surface of the virtual CMY space 300 is set. The 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 points a to b is set to 50 to 100% (more preferably 60 to 90%) as a preferable range. The point c shown in FIG. 21 is located at a position where the depth is Ref_Depth from the point b in the virtual CMY space 300 in the C-axis direction connecting the points a to b.

In S508, in the CMY color space CS3, the Lab value and the CMYK value of the third grid point GD3 in the extrapolation 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 minus side of C, the M value and the Y value of the points b and c are set to be the same as the point a. The C value at 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 desired point a is (La, aa, ba), the CMYK value of the desired point a is (Ca, Ma, Ya, Ka), and the Lab value of the point b is (Lb, ab, bb). Let the CMYK value of the point b be (Cb, Mb, Yb, Kb), the Lab value of the point c be (Lc, ac, bc), and the CMYK value of the point c be (Cc, Mc, Yc, Kc). To do. The Lab value and CMYK value of the point a can be calculated by, for example, the following formula.
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 exceeding 255 of M, or on the minus side of C and Y and on the side exceeding 255.

Since the depth Ref_Depth of the specific point P0 is 50 to 100%, it is not easily affected by the irregular shape of the gamut surface when extrapolating the Lab value and the CMYK value of the third lattice point GD3. Therefore, the color reproduction accuracy near the surface of the gamut is further improved.

In this specific example, in order to further improve the color reproduction accuracy near the surface of the gamut, a plurality of combinations of the specific grid point GD4 and the specific point P0 are set as shown in FIG. FIG. 22 schematically illustrates how 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 how to select the combination used for the extrapolation calculation from the combinations of the specific grid point GD4 and the specific point P0. For the sake of clarity, FIG. 23 schematically illustrates the CMY color space CS3 viewed from the Y-axis direction.

In the examples shown in FIGS. 22 and 23, nine points b0 to b8 are set as specific grid points GD4 within a predetermined range AR2 from the third grid point GD3 (point a) among the second grid points GD2 on the surface of the gamut. ing. Here, the point b4 is the grid point closest to the point a, the points b1, b3, b5 and b7 are the grid points adjacent to the point b4 in the axial direction, and the point b0 is the grid point adjacent to the points b1 and b3. , Point b2 is a grid point adjacent to points b1 and b5, point b6 is a grid point adjacent to points b3 and b7, and point b8 is a grid point adjacent to points b5 and b7. The points c0 to c8 are specific points P0 in the direction connecting the points b0 to b8 from the point a, respectively, and the virtual CMY space 300 is in the axial direction (C-axis direction in FIG. 23) intersecting the surface of the points b0 to b8. It is more than half the size of the virtual CMY space 300 from the surface to the back. Depth Ref_Depth means the depth in the axial direction, as shown in FIG. Here, like the point c1 shown in FIG. 23, the points c0 to c8 that go out of the virtual CMY space 300 are not used in the extrapolation calculation as exclusion points.

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

The processing of S502 to S508 described above is repeated until the Lab values and CMYK values of all the third lattice points GD3 on the expansion surface are extrapolated.
In the subsequent procedure 3, the Lab value and the CMYK value at the third lattice point GD3 of the extended ridge line (the vertices are not included) obtained by extending the 12 ridge lines of the virtual CMY space 300 (hexahedron) in the CMY color space CS3 are obtained. Extrapolate based on 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 ridgeline of the virtual CMY space 300 in the CMY color space CS3.

FIG. 24 schematically illustrates how the ridgeline of the virtual CMY space 300 is expanded in the CMY color space CS3. The point a shown in FIG. 24 indicates the third grid point GD3 set at the extended ridgeline.
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) of the second grid points GD2 on the ridgeline of the surface of the virtual CMY space 300 (Gamat GMT). The specific grid point GD4 in is set (S512). Point b shown in FIG. 24 indicates a specific grid point GD4 set on the ridgeline of the surface of the virtual CMY space 300. The point b shown in FIG. 24 is the point closest to the point a, and the point a and the M value are the same. Of course, depending on the position of the extended ridgeline, the point b may be a point where the points a and C have the same value, or a point where the points a and Y have the same value.

In S514, in the CMY color space CS3, the specific point P0 in the direction connecting the point a (the set third lattice point) to the point b (specific lattice point GD4) in the virtual CMY space 300 (Gamat GMT). 50% (1) 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). / 2) As described above, the specific point P0 behind the surface of the virtual CMY space 300 is set. The point c shown in FIG. 24 indicates a specific point P0 set inside the virtual CMY space 300. The point c shown in FIG. 24 is located at a position at a depth Ref_Depth from the point b of 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 extrapolation 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 minus side of C and Y, the M value of the points b and c is 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-mentioned formula (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 cases shown in FIGS. 22 and 23. The specific grid point GD4 is not arranged on the same plane. The Lab value and CMYK value of the third grid point GD3 on the extended ridge line in the extrapolated 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 CMYK values.

The processing of S510 to S516 described above is repeated until the Lab values and CMYK values of all the third grid points GD3 on the extended ridgeline are extrapolated.
In the subsequent procedure 4, the Lab value and the CMYK value at the third lattice point GD3 of the extended vertices 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 vertices 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. The 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 (set third grid point) of the second grid points GD2 at the apex of the surface of the virtual CMY space 300 (Gamat GMT). The specific grid point GD4 in is set (S520). Point b shown in FIG. 25 indicates a specific grid point GD4 set at the apex of the surface of the virtual CMY space 300. The point b shown in FIG. 25 is the 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 (the set third lattice point) to the point b (specific lattice point GD4) in the virtual CMY space 300 (Gamat GMT). 50% (1) 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). / 2) As described above, the specific point P0 behind the surface of the virtual CMY space 300 is set. The point c shown in FIG. 25 indicates a specific point P0 set inside the virtual CMY space 300. The point c shown in FIG. 25 is located at a position at a depth Ref_Depth from the point b of the virtual CMY space 300 in the C-axis direction, the M-axis direction, and the Y-axis direction.

In S524, in the CMY color space CS3, the Lab value and the CMYK value of the third grid point GD3 in the extrapolation 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 minus side of C, M, Y, the C, M, Y values 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 point a is (-Ext_CMY0, -Ext_CMY0, -Ext_CMY0), the CMY value of point b is (0,0,0) and the CMY value of 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-mentioned formula (6). The same applies when the point a is at another extended vertex.
When extrapolating the Lab value and the 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 cases shown in FIGS. 22 and 23. For example, 7 specific grid points GD4 are set and are not arranged on the same plane. The Lab value and CMYK value of the third grid point GD3 on the extended ridge line in the extrapolated 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 CMYK values.

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

When the generation of the extrapolation 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 lattice 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 reproduction range of the printer 200 is generated. Then, in the process of S306 shown in FIG. 10, based on the C1M1Y1K1 value of the LUT530 based on the virtual CMY space 300 and the C2M2Y2K2 value of the LUT610 based on the augmented virtual CMY space 310, the C3M3Y3K3 value (C3) of the three-dimensional LUT700. M3, Y3, K3) are determined. At least the C2M2Y2K2 value of the LUT610 is used for this determination process, and the C2M2Y2K2 value may be used as it is as the C3M3Y3K3 value of the three-dimensional LUT700.

(9) Specific example of output table generation processing performed by the color conversion profile generator:
The C3M3Y3K3 value, which is the output value of the three-dimensional LUT 700, may be out of the range of 0 to 255 because it is based on the characteristic data 520 and the extrapolation data 600 of the extended virtual CMY space 310. On the other hand, since the subsequent processing can handle only the range of 0 to 255, the output table 800 shown in FIG. 11 is used to keep the C3M3Y3K3 value within the range of 0 to 255.

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, for example, the following equations.
Ft = 255 × {Ext_CMY0 / (255 ＋ Ext_CMY0 ＋ Ext_CMY1) × 257}… (7)
Rf = 255 × {(255 + Ext_CMY0) / (255 + Ext_CMY0 ＋ Ext_CMY1) × 257}… (8)
By referring to the output table 800 in which the second correspondence determined by the above equations (7) and (8) is defined, the minimum value when the input value (C3, M3, Y3, K3) is equal to or less than the lower limit value Ft. It is converted to a value of 0, and when the input value (C3, M3, Y3, K3) is equal to or higher than the upper limit value Rf, it is converted to a maximum value of 65535. When the input value (C3, M3, Y3, K3) is Ft to Rf, the range is widened so that the output value (C4, M4, Y4, K4) is 0 to 65535, and the larger the input value, the more linear the line. The output value becomes large. As described above, 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 is provided. Will be generated.

(10) Actions and effects of specific examples:
As described above, in this specific example, the gamut GMT is set based on the inclination slope of the gamut surface in the Lab color space CS1 and the intervals gL and gAB of the first lattice points GD1 arranged in the Lab color space CS1. An extension range AR1 that extends outward is set. Extrapolated data 600 that extrapolates the color reproduction characteristics of the device is generated in this extended range AR1, and the Lab value and the CMYK value are associated with each other for the first lattice point GD1 based on the extrapolated data 600 and the characteristic data 520. Be done. Therefore, in this specific example, it is possible to improve the color reproduction accuracy in the vicinity of the gamut surface while maintaining the color reproduction accuracy inside the gamut.

(11) Modification example:
Various modifications of the present invention can be considered.
For example, the device is not limited to an inkjet 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 colorants that form images are not limited to C, M, Y, and K, and in addition to C, M, Y, and K, Dy (dark yellow) and Or, which have higher concentrations than Lc, Lm, and Y, It may contain (orange), Gr (green), Lk (light black) having a concentration lower than K, a non-colored coloring material for improving image quality, and the like.
The above-mentioned processing can be changed as appropriate, such as changing the order. For example, in the process of FIG. 12, the process of S410 to S416 can be performed before any of the processes of S402, S404, S406, and S408.
In the Gamat mapping process shown in FIGS. 2 and 7, the virtual CMY space 300 and the extended virtual CMY space 310 are divided into tetrahedrons having four vertices to interpolate the CMYK values, but 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 the triangle.
In the calculation of the brightness expansion amounts Ext_L0 and Ext_L1, the slopes Slope_max and Slope_max1 in the above 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 is provided a technique capable of improving the color reproduction accuracy in the vicinity of the surface of the color reproduction area while substantially maintaining the color reproduction accuracy inside the color reproduction area according to various aspects. be able to. Of course, the above-mentioned basic actions and effects can be obtained even with a technique consisting of only the constituent requirements according to the independent claims.
In addition, the configurations disclosed in the above-mentioned examples are mutually replaced or the combinations are changed, the known techniques and the configurations disclosed in the above-mentioned examples are mutually replaced or the combinations are changed. It is also possible to implement the above-mentioned configuration. The present invention also includes these configurations and the like.

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 ... color measurement data (example of original data), 510 ... K generation function, 520 ... characteristic data, 530 ... LUT, 600 ... extrapolation data, 610 ... LUT, 700 ... LT (first) Correspondence data example), 800 ... Output table (second correspondence data example), AR1 ... expansion range, AR2 ... predetermined range, CS1 ... Lab color space (example of first color space), CS2 ... CMYK color 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, GD4 ... specific Lattice point, GMT ... Gamat (color reproduction range), IM0 ... Output image, P0 ... Specific point, P1 ... RGB minimum density grid point, PA1 ... Patch, PR0 ... Color conversion profile generation program, ST1 ... Extended range setting process, ST2 ... Externalization process, ST3 ... Correspondence process, ST4 ... Characteristic data generation process, ST5 ... Correspondence relationship data generation process.

Claims (10)

A 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 lattice points arranged in the first color space. It is a profile generation method
The inclination of the surface of the color gamut of the device in the first color space, the a first interval placed the first grid point in the color space, based on, outside the front Symbol gamut The expansion range setting process for setting the expansion range to be expanded and the expansion range setting process
An extrapolation step of generating extrapolated data that extrapolates the color reproduction characteristics of the device in the extended range based on the characteristic data representing the color reproduction characteristics of the device in the color reproduction range.
The first coordinate value and the second coordinate value of the plurality of first lattice points arranged beyond the color reproduction range with respect to the first color space based on the characteristic data and the extrapolation data. A color conversion profile generation method including a mapping process for associating with. The inclination of the surface of the color reproduction region in the first color space is represented by the ratio of the difference in brightness to the difference in saturation.
In the extended range setting step, the inclinations of a plurality of locations on the surface of the color reproduction region in the first color space are acquired based on the characteristic data, and the maximum inclination among the inclinations of the plurality of locations and the first inclination are obtained. based the spacing arranged the first grid point in the color space, to a acquires the lightness extension amount for extending the color gamut in the direction of the light of the said first color space,該明degree extension amount The color conversion profile generation method according to claim 1 , wherein the extended range is set based on at least. The inclination of the surface of the color reproduction region in the first color space is represented by the ratio of the difference in brightness to the difference in saturation.
In the extended range setting step, the inclinations of a plurality of locations on the surface of the color reproduction region in the first color space are acquired based on the characteristic data, and the minimum inclination among the inclinations of the plurality of locations and the first inclination are obtained. of the spacing of the first grid points arranged in the color space, based on, obtains the saturation amount of expansion for expanding the color gamut in the direction of the saturation in the first color space,該彩degree The color conversion profile generation method according to claim 1 or 2 , wherein the expansion range is set based on at least the expansion amount. A 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 lattice points arranged in the first color space. It is a profile generation method
An extension range setting step of setting an extension range for extending the color reproduction range of the device to the outside based on the distance between the first lattice points arranged in the first color space, and
An extrapolation step of generating extrapolated data that extrapolates the color reproduction characteristics of the device in the extended range based on the characteristic data representing the color reproduction characteristics of the device in the color reproduction range.
The first coordinate value and the second coordinate value of the plurality of first lattice points arranged beyond the color reproduction range with respect to the first color space based on the characteristic data and the extrapolation data. Including the mapping process of associating with
The characteristic data includes the third coordinate value of the third color space, the first coordinate value, and the second coordinate value of the second lattice point arranged in the color reproduction region in the third color space depending on the device. Is the associated data,
The extrapolation data is a color conversion profile in which the third coordinate value and the first coordinate value are associated with each other for the third lattice point arranged in the extension range in the third color space. Generation method. The third color space is a color space in which the dimensions of the second color space are reduced.
The color conversion profile according to claim 4 , further comprising a characteristic data generation step of generating the characteristic data based on the 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 each other to define the third coordinate value.
Of the second grid points on the surface of the color reproduction region in the third color space, the second grid point within a predetermined range from the third grid point is designated as a specific grid point.
In the third color space, points in the color reproduction region in the direction connecting the third grid point to the specific grid point, the first axis, the second axis, and the third. A point that is at least 1/2 of the size of the color reproduction area in any direction of the axis and is deep from the surface of the color reproduction area is set as a specific point.
The color conversion profile generation method according to claim 5 , 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 the specific grid points and the data of the specific points included in the plurality of combinations in the characteristic data, according to claim 6 . The described color conversion profile generation method. A 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 lattice points arranged in the first color space. It is a profile generation method
An extension range setting step of setting an extension range for extending the color reproduction range of the device to the outside based on the distance between the first lattice points arranged in the first color space, and
An extrapolation step of generating extrapolated data that extrapolates the color reproduction characteristics of the device in the extended range based on the characteristic data representing the color reproduction characteristics of the device in the color reproduction range.
The first coordinate value and the second coordinate value of the plurality of first lattice points arranged beyond the color reproduction range with respect to the first color space based on the characteristic data and the extrapolation data. And the mapping process that associates with
The first correspondence data representing the first correspondence between the first coordinate value and the second coordinate value, which is at least partially associated in the association step, and the first correspondence from the first coordinate value. Second correspondence data representing the second correspondence that converts the second coordinate value into the value included in the color reproduction region when the second coordinate value obtained according to the above is a value not included in the color reproduction region. A color conversion profile generation method , including , and a correspondence data generation step to generate. A 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 lattice points arranged in the first color space. It is a profile generator
The inclination of the surface of the color gamut of the device in the first color space, the a first interval placed the first grid point in the color space, based on, outside the front Symbol gamut An extended range setting unit that sets the extended range to be expanded, and
An extrapolation unit that generates extrapolated data that extrapolates the color reproduction characteristics of the device in the extended range based on the characteristic data representing the color reproduction characteristics of the device in the color reproduction range.
The first coordinate value and the second coordinate value of the plurality of first lattice points arranged beyond the color reproduction range with respect to the first color space based on the characteristic data and the extrapolation data. A color conversion profile generator including a mapping unit that associates with. For associating a plurality of first lattice points arranged in the first color space with the first coordinate value of the first color space and the second coordinate value of the second color space depending on the device. A color conversion profile generator
The inclination of the surface of the color gamut of the device in the first color space, the a first interval placed the first grid point in the color space, based on, outside the front Symbol gamut The extended range setting function that sets the extended range to be expanded, and the extended range setting function
An extrapolation function that generates extrapolated data that extrapolates the color reproduction characteristics of the device in the extended range based on the characteristic data representing the color reproduction characteristics of the device in the color reproduction range.
The first coordinate value and the second coordinate value of the plurality of first lattice points arranged beyond the color reproduction range with respect to the first color space based on the characteristic data and the extrapolation data. A color conversion profile generation program that realizes a computer-based mapping function that associates with.

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