Color conversion device, color conversion table creation device, and program

Abstract

To shorten the time required for conversion from a signal value of a first color space not depending on a printer into a signal value of a second color space depending on the printer, compared with a case where a conversion condition created on the basis of a result of color measurement of a print image created by a printer is numerically resolved to create a color conversion table.SOLUTION: A color conversion device comprises a processor. The processor creates a first color conversion table representing the correspondence between an input value of a first color space not depending on a printer and a colorimetric value of the first color space that is a result of color measurement of a print image printed by the printer while converting the input value into a signal value of a second color space depending on the printer, and uses the first color conversion table and a second color conversion table converting the signal value of the first color space into the signal value of the second color space and predetermined according to the printer, to convert the input signal value of the first color space into the signal value of the second color space.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a color conversion device, a color conversion table creation device, and a program. [Background technology]

[0002] As a conventional technique, L * a * b * There is a technology that converts input signals such as color signals into color signals that include normal color signals such as YMCK used in image output devices and special color signals such as PG, using the so-called Kueppers method. For example, in the Kueppers method, * a * b * After converting the color signal to a CMY signal or RGB signal, etc., the achromatic component UCR processing and the chromatic component UCR processing are performed on this color signal to obtain the L * a * b * The color signal is converted into a color signal consisting of YMCK+PG.

[0003] In addition, as a conventional technique, Patent Document 1 discloses that the input L * a * b * The amount of black K and the amount of special color O are determined from the color signal, and L * a * b * From the color signal and KO color signal, the amount of black is input under the condition of the K color signal and the amount of special color is input under the condition of the O color signal. * a * b * By determining the YMC color signals of the image output device that match the colorimetric signal of the L * a * b * A technique is disclosed for converting a color signal into an image recording signal YMCKO that is input to an image output device. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 4206743 Summary of the Invention [Problem to be solved by the invention]

[0005] When converting signal values ​​in a first color space that is independent of the printing device into signal values ​​in a second color space that is dependent on the printing device, if the colorimetric match between the signal values ​​in the first color space and the signal values ​​in the second color space is not taken into consideration, as in the Kueppers method, the color reproducibility on the printing device is likely to be poor. On the other hand, if a color conversion table is created to convert signal values ​​in the first color space to signal values ​​in the second color space by numerically solving conversion conditions such as a printer model that shows the correspondence between the first and second color spaces and is created based on the colorimetric results of an image printed by a printing device so that the signal values ​​in the first color space and the signal values ​​in the second color space match colorimetrically from the perspective of improving color reproducibility, the time required for color conversion can be long.

[0006] The present invention aims to shorten the time required to convert signal values ​​in a first color space that is independent of the printing device to signal values ​​in a second color space that is dependent on the printing device, compared to creating a color conversion table by numerically solving conversion conditions created based on the colorimetric results of an image printed by a printing device. [Means for solving the problem]

[0007] The invention described in claim 1 is a color conversion device that includes a processor, which creates a first color conversion table that represents a correspondence between input values ​​of a first color space that is independent of a printing device and colorimetric values ​​of the first color space that are the result of converting the input values ​​into signal values ​​of a second color space that is dependent on the printing device and measuring the colorimetric values ​​of the first color space, and converts the signal values ​​of the first color space into the second color space using a second color conversion table that is predetermined according to the printing device and the first color conversion table. The invention described in claim 2 is a color conversion device described in claim 1, in which the processor acquires paper information, which is information regarding the type of paper on which an image is printed by the printing device, and creates the first color conversion table in accordance with the paper information. The invention described in claim 3 is the color conversion device described in claim 2, wherein the second color conversion table is determined based on a predetermined standard paper, and when the color difference between the paper on which an image is printed by the printing device and the standard paper is within a predetermined range, the processor uses the second color conversion table to convert signal values ​​of the first color space into signal values ​​of the second color space. The invention described in claim 4 is the color conversion device described in claim 2, wherein the second color conversion table is determined according to the type of paper, and the processor creates the first color conversion table using the colorimetric values ​​of the printed image printed based on the signal values ​​of the second color space obtained by converting the input values ​​using the second color conversion table according to the type of paper, based on the paper information. The invention described in claim 5 is a color conversion device described in claim 1, in which the processor creates the first color conversion table that converts the colorimetric values ​​of the first color space into signal values ​​of the first color space corresponding to the input values. The invention described in claim 6 is a color conversion device described in claim 5, in which the processor creates a first correspondence relationship that converts the input values ​​in the first color space to the colorimetric values ​​in the first color space, and creates the first color conversion table by inversely converting the first correspondence relationship. The invention described in claim 7 is a color conversion device described in claim 1, in which the processor converts signal values ​​of the first color space consisting of three variables into signal values ​​of the second color space consisting of five or more variables including signal values ​​of normal colors, which are colors that are commonly used, and signal values ​​of special colors, which are colors other than the normal colors. The invention described in claim 8 is the color conversion device described in claim 1, in which the processor combines the first color conversion table and the second color conversion table to create an output profile that converts input signal values ​​of the first color space into signal values ​​of the second color space and outputs them, and converts the signal values ​​of the first color space converted from signal values ​​of a third color space dependent on the input device by the input profile into the second color space by the output profile. The invention described in claim 9 is a color conversion table creation device that includes a processor, which creates a first color conversion table that represents a correspondence between input values ​​in a first color space that is independent of a printing device and colorimetric values ​​of the first color space that are the result of converting the input values ​​into signal values ​​in a second color space that is dependent on the printing device and measuring the colorimetric values ​​of the first color space that are the result of converting the input values ​​into signal values ​​in a second color space that is dependent on the printing device, and creates a third color conversion table that converts the signal values ​​of the first color space into signal values ​​of the second color space by combining the first color conversion table with a second color conversion table that is predetermined according to the printing device and converts the signal values ​​of the first color space into signal values ​​of the second color space. The invention described in claim 10 is a program that provides a computer with the following functions: creating a first color conversion table that represents the correspondence between input values ​​in a first color space that is independent of a printing device and colorimetric values ​​of the first color space that are the result of converting the input values ​​into signal values ​​of a second color space that is dependent on the printing device and measuring the colorimetric values ​​of the first color space that are the result of converting the input values ​​into signal values ​​of a second color space that is dependent on the printing device; and combining the first color conversion table with a second color conversion table that is predetermined according to the printing device and converts the signal values ​​of the first color space into signal values ​​of the second color space. Effect of the Invention

[0008] According to the invention described in claim 1, the time required to convert signal values ​​in a first color space that is independent of the printing device to signal values ​​in a second color space that is dependent on the printing device can be shortened compared to the case where a color conversion table is created by numerically solving conversion conditions created based on the colorimetric results of a printed image by a printing device. According to the invention as recited in claim 2, it is possible to improve the color reproducibility of an image printed on paper, compared to a case in which the first color conversion table is not created according to paper information. According to the invention described in claim 3, the time required to convert signal values ​​in the first color space to signal values ​​in the second color space can be shortened compared to the case where a first color conversion table is created when the color difference between the paper and standard paper is within a predetermined range. According to the invention as recited in claim 4, it is possible to improve the color reproducibility of an image printed on paper, compared to a case in which the second color conversion table is not determined according to the type of paper. According to the invention described in claim 5, the time required to convert signal values ​​in a first color space to signal values ​​in a second color space can be shortened compared to the case where a color conversion table is created by numerically solving conversion conditions created based on the colorimetric results of a printed image by a printing device. According to the invention described in claim 6, the time required to convert signal values ​​in a first color space to signal values ​​in a second color space can be shortened compared to the case where a color conversion table is created by numerically solving conversion conditions created based on the colorimetric results of a printed image by a printing device. According to the invention described in claim 7, it is possible to reduce the time required to convert signal values ​​in a first color space into signal values ​​in five or more second color spaces including normal colors and special colors. According to the invention described in claim 8, the time required to convert signal values ​​in the first color space to signal values ​​in the second color space can be shortened compared to the case where the first color conversion table and the second color conversion table are not combined to create an output profile. According to the invention described in claim 9, the time required to convert signal values ​​in a first color space that is independent of the printing device to signal values ​​in a second color space that is dependent on the printing device can be shortened compared to the case where a color conversion table is created by numerically solving conversion conditions created based on the colorimetric results of a printed image by a printing device. According to the invention described in claim 10, the time required to convert signal values ​​in a first color space that is independent of the printing device to signal values ​​in a second color space that is dependent on the printing device can be shortened compared to the case where a color conversion table is created by numerically solving conversion conditions created based on the colorimetric results of an image printed by a printing device. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram illustrating a configuration of a printing system to which the present embodiment is applied. [Diagram 2] FIG. 2 is a functional block diagram of a color conversion device. [Diagram 3] 13A and 13B are diagrams showing an example of color conversion processing performed by a color conversion unit using an output profile created by a profile creation unit. [Figure 4] 11 is a flowchart showing an example of a process for creating a reference output profile. [Diagram 5] 11 is a flowchart showing an example of a process for creating an output profile. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a diagram illustrating the configuration of a printing system 100 to which this embodiment is applied. The printing system 100 shown in the figure includes an input device 10, a printing device 20, and a color conversion device 30. The input device 10, the printing device 20, and the color conversion device 30 are connected to each other so as to be able to communicate with each other. A LAN (Local Area Network) or the Internet, for example, is used as the network connecting the input device 10, the printing device 20, and the color conversion device 30. However, the network may also be a combination of a LAN and the Internet.

[0011] The input device 10 is configured by a computer device. The input device 10 inputs image data to be used for printing by the printing device 20 to the color conversion device 30.

[0012] The printing device 20 prints an image on paper, which is an example of a recording medium, based on image data that has been input by the input device 10 and has been color converted by the color conversion device 30. The printing device 20 includes a printing unit 21 that performs the printing operation, and a print control unit 22 that controls the operation of the printing unit 21.

[0013] The printing unit 21 prints an image on a sheet by, for example, an electrophotographic method. The printing unit 21 of this embodiment prints an image on a sheet using toners of yellow (Y), magenta (M), cyan (C), and black (K) (hereinafter, these colors may be referred to as normal colors) and toners of special colors different from the normal colors. The toners are an example of color materials used in forming an image. Here, the special colors are colors different from the normal colors, and examples of the special colors include colors that are difficult to achieve using toners of normal colors such as yellow, magenta, cyan, and black. Examples of such special colors include, but are not limited to, fluorescent pink, fluorescent yellow, white, light cyan, orange, violet, and green, as well as metallic colors such as gold and silver colored using metal pigments. In this embodiment, an example will be described in which the printing unit 21 forms an image using toners of fluorescent pink (P) and green (G) as special colors in addition to the normal colors.

[0014] The printing format and type of color material of the printing unit 21 are not particularly limited as long as the printing unit 21 forms an image on paper using color materials of normal colors, yellow (Y), magenta (M), cyan (C), and black (K), and one or more special color materials. The printing unit 21 may print an image on paper by the above-mentioned electrophotographic method, as well as by inkjet method, thermal transfer method, offset printing, etc. In the following description, the normal colors yellow (Y), magenta (M), cyan (C), and black (K) may be referred to as YMCK colors. Also, the YMCK colors and the special colors fluorescent pink (P) and green (G) used in printing by the printing device 20 may be collectively referred to as YMCKPG colors.

[0015] The color conversion device 30 is an example of a color conversion device or a color conversion table creation device, and is configured by a computer device. The color conversion device 30 may be a single physical computer, or may be realized by distributed processing using multiple computers. The color conversion device 30 may be configured as a shared server that provides a so-called cloud service, or may be configured as an on-premise server. Furthermore, the color conversion device 30 may be built into the printing device 20 as a part of the printing device 20 .

[0016] In the printing system 100 of this embodiment, image data expressed in signal values ​​of the RGB color space is input from the input device 10 to the color conversion device 30. The color conversion device 30 converts the input signal values ​​of the RGB color space into signal values ​​of the YMCKPG color space used by the printing device 20. In addition, the color conversion device 30 converts the signal values ​​of the RGB color space into signal values ​​of the YMCKPG color space using an input profile and an output profile described below. Then, the color conversion device 30 outputs the image data represented by signal values ​​in the YMCKPG color space to the printing device 20. The printing device 20 prints an image on paper using Y, M, C, K, P, and G toners based on the image data acquired from the color conversion device 30. The signal values ​​in the YMCKPG color space include signal values ​​of YMCK colors corresponding to the amounts of YMCK toner used, and signal values ​​of the special colors P and G. The signal values ​​of each color in the YMCKPG color space correspond to the amount of toner used of each color in the printing unit 21 of the printing device 20.

[0017] FIG. 2 is a functional block diagram of the color conversion device 30. As shown in FIG. The color conversion device 30 includes a color conversion unit 31 that performs color conversion processing of image data input from the input device 10, and a profile creation unit 32 that creates an output profile used in the color conversion processing by the color conversion unit 31. The color conversion device 30 also includes a color measurement unit 33 that measures the color of an image printed on paper by the printing device 20, and an operation display unit 34 that displays information to the user and accepts information input by the user's operation. The color conversion device 30 also includes a storage unit 35 that stores information such as the output profile created by the profile creation unit 32.

[0018] Here, the functions of the color conversion unit 31 and the profile creation unit 32 in the color conversion device 30 are realized by a CPU 30A as an example of a processor. The CPU 30A reads out a program stored in a ROM (Read Only Memory) 30B, and executes the program using a RAM (Random Access Memory) 30C as a working area. The program executed by the CPU 30A may be provided to the color conversion device 30 in a state where it is stored in a computer-readable recording medium such as a magnetic recording medium (magnetic tape, magnetic disk, etc.), an optical recording medium (optical disk, etc.), a magneto-optical recording medium, or a semiconductor memory. The program executed by the CPU 30A may also be downloaded to the color conversion device 30 using a communication means such as the Internet. In addition, in this embodiment, the functions of the color conversion unit 31 and the profile creation unit 32 in the color conversion device 30 are realized by software, but this is not limited to this and may be realized by, for example, an ASIC (Application Specific IC).

[0019] The color conversion unit 31 converts signal values ​​in the RGB color space representing the image data input from the input device 10 into signal values ​​in the YMCKPG color space used by the printing device 20 using the input profile and output profile stored in the memory unit 35. In this embodiment, a profile means color conversion conditions when converting colors between data made up of signal values ​​in different color spaces.

[0020] The input profile converts signal values ​​in the RGB color space that represent image data input from the input device 10 into signal values ​​in a color space that is independent of devices such as the input device 10 and the printing device 20. In this embodiment, the input profile converts signal values ​​in the RGB color space into signal values ​​in a color space that is independent of devices such as the input device 10 and the printing device 20. * a * b * Converts the signal value into a color space. * a * b * The color space is an example of a first color space, and is a lightness L * and chromaticity a * and chromaticity b * It is expressed in a Cartesian coordinate color space with axes and . The output profile is the L converted from the input profile. * a * b * The signal values ​​of the color space are converted to signal values ​​of the YMCKPG color space used by the printing device 20. In addition, the output profile is a L * a * b * The signal values ​​of the color space are converted into signal values ​​of the YMCKPG color space consisting of six variables including normal colors and special colors. The YMCKPG color space is an example of the second color space. The output profile is an example of the third color conversion table.

[0021] The profile creation unit 32 creates an output profile used in the color conversion process by the color conversion unit 31. The process of creating the output profile by the profile creation unit 32 will be described in detail later.

[0022] The color measurement unit 33 measures the color of an image printed on a sheet by the printing device 20, and * a * b * Colorimetric values ​​expressed as signal values ​​in a color space are obtained. The configuration of the color measurement unit 33 is not particularly limited, but for example, it can be a unit that performs color measurement in response to a user's operation of moving a colorimeter over an image printed on paper by the printing device 20. In addition, the color measurement unit 33 may be provided inside the printing device 20 and may read and measure the color of an image printed on paper by the printing device 20.

[0023] The operation display unit 34 displays a display screen for providing information to the user, and also accepts information input by the user's operation on the display screen. In this embodiment, the operation display unit 34 displays, as a display screen, an input screen for receiving input of the type of paper to be used for printing an image in the printing device 20 when the profile creation unit 32 creates an output profile.

[0024] The storage unit 35 stores the input profile and the output profile used in the color conversion process by the color conversion unit 31 . The storage unit 35 also stores a reference output profile and a black color / spot color amount determination model used when the profile creation unit 32 creates an output profile.

[0025] Here, L, which is a color space independent of the printing device 20, * a * b * When the signal values ​​of the color space are converted into signal values ​​of the YMCKPG color space, which is a color space that depends on the printing device 20, and an image is printed by the printing device 20, L * a * b * If the colorimetric match between the signal values ​​in the color space and the signal values ​​in the YMCKPG color space after conversion is not taken into consideration, the color reproducibility in the image is likely to be poor. On the other hand, in order to improve color reproducibility, the L * a * b * A printer model showing the correspondence between the color space and the YMCKPG color space is numerically solved to obtain the L * a * b *In some cases, an output profile is created to convert signal values ​​in a color space into signal values ​​in a YMCKPG color space. In such cases, the time required to create the output profile and to perform color conversion processing using the created output profile can be long.

[0026] FIG. 3 is a diagram showing an example of color conversion processing performed by the color conversion unit 31 using the output profile created by the profile creation unit 32. As shown in FIG. In the color conversion device 30 of this embodiment, a profile creation unit 32 creates a L * a * b * An output profile is created that converts signal values ​​in the color space into signal values ​​in the YMCKPG color space. The 3DLUT is an example of a first color conversion table, and the reference output profile is an example of a second color conversion table. The color conversion unit 31 of the color conversion device 30 converts the image data input from the input device 10, which is expressed by signal values ​​in the RGB color space, into a L color space that is independent of the printing device 20, using the input profile. * a * b * Then, the color conversion unit 31 converts the L * a * b * The signal values ​​in the color space are converted into signal values ​​in the YMCKPG color space.

[0027] Next, the output profile creation process performed by the profile creation unit 32 of the color conversion device 30 will be described. First, a reference output profile used in the process of creating an output profile by the profile creating unit 32 will be described. The reference output profile is an example of a first color space, L * a * b *These are color conversion conditions for converting signal values ​​in a color space into signal values ​​in a YMCKPG color space. In this embodiment, a reference output profile is determined in advance for each printing device 20 and each type of paper used to print an image by the printing device 20. Each reference output profile is stored in the storage unit 35 in association with the printing device 20 and the type of paper.

[0028] FIG. 4 is a flowchart showing an example of a process for creating a reference output profile. The reference output profile can be created, for example, by the following process. The reference output profile may be created by the profile creation section 32 of the color conversion device 30 and stored in the storage section 35, or may be created by a device other than the color conversion device 30 and stored in the storage section 35. In the following, it is assumed that the reference output profile is created by a profile creation device (not shown), which is a device other than the color conversion device 30.

[0029] The profile creation device uses the printing device 20 to print a color measurement image on a predetermined type of paper (step 101). The type of paper refers to a type of paper on which the colors of images printed on the paper differ due to differences in the color tone of the paper surface. Examples of such paper types include gloss coated paper, matte coated paper, and fine paper, but are not limited thereto. The profile creation device inputs color measurement image data, which is image data representing a color measurement image, to the printing device 20. In this example, the color measurement image data is expressed by signal values ​​in the YMCKPG color space. The printing device 20 then prints the color measurement image on a selected type of paper using the color measurement image data input from the profile creation device. The color measurement image is an image in which a plurality of patches (e.g., rectangular images) having colors that cover the entire color gamut printable by the printing device 20 are arranged. Here, the color measurement image is an image in which a plurality of patches are arranged on which image data expressed by signal values ​​of YMCKPG color signals with a predetermined interval is printed.

[0030] Next, the profile creation device obtains colorimetric values ​​that are the result of measuring the colorimetric image formed on the paper (step 102). In addition, the profile creation device obtains information obtained by reading each patch of the colorimetric image with a colorimeter (not shown) as the colorimetric values. In this example, the profile creation device uses L * a * b * Obtain colorimetry values ​​expressed in a color space.

[0031] Next, the profile creation device uses the colorimetric values ​​acquired in step 102 to determine a printer model (step 103). The printer model determines the L of an image printed by the printing device 20 from the signal values ​​of each color in the YMCKPG color space. * a * b * The printer model is a conversion condition that predicts the signal values ​​of the YMCKPG color space. * a * b * The printer model determined in step 103 is a function of the function f in equation (1). 1 It can be expressed as follows. (L * , a * , b * )=f 1 (Y, M, C, K, P, G) …(1)

[0032] The profile creation device then * a * b * Set the input grid points in the color space. Then, the profile creation device creates the L * a * b * The input grid points set in the color space are converted into L * a * b * The color space is mapped to the gamut (step 104). * a * b *Each input lattice point set in the color space is a predetermined step size L * a * b * It is expressed as a signal value in a color space.

[0033] The profile creator then performs the mapping in step 104. * a * b * The signal value of K color in the YMCKPG color space and the signal values ​​of P color and G color, which are spot colors, corresponding to the signal values ​​of each input lattice point in the color space are determined (step 105). In addition, the profile creation device determines the signal values ​​of K color, P color, and G color using a K amount / spot color amount determination model that is predetermined and stored in the storage unit 35. * a * b * The K amount / feature amount determination model, which obtains the signal values ​​of K, P, and G colors from the signal values ​​of the color space, is as shown in equation (2a) by dividing the signal values ​​of K, P, and G colors by the L * a * b * It can also be said to be a function that represents the relationship with signal values ​​in the color space. (K, P, G)=a(L * , a * , b * ) …(2)

[0034] The K amount / feature amount determination model is L * a * b * These are color conversion conditions for calculating the signal values ​​of K, which is a normal color, and P and G, which are special colors, from the signal values ​​in the color space. As the K amount / special color amount determination model, a conventionally known one can be used. The K amount / special color amount determination model is created, for example, by the following process and stored in the storage unit 35. Here, the description will be given assuming that the profile creation device creates the K amount / special color amount determination model.

[0035] First, the profile creation device prints a color measurement image on paper using the printing device 20, and records the signal values ​​of each color in the YMCKPG color space used to print the color measurement image and the L * a *b * A conversion function that expresses the relationship between the color space and the color measurement value is obtained. Then, the profile creation device uses the L * a * b * The signal values ​​of the remaining Y, M, and C colors in the YMCKPG color space that match colorimetrically are calculated by numerically solving the conversion function using a combination of the signal values ​​of the color space and the signal values ​​of K, P, and G colors in the YMCKPG color space as input.

[0036] Next, the profile creation device calculates the colorimetric values ​​of an image reproduced by a combination of the K, P, and G signal values ​​in the YMCKPG color space and the calculated Y, M, and C signal values, and calculates the colorimetric values ​​of the image reproduced by the combination of the K, P, and G signal values ​​in the YMCKPG color space and the calculated Y, M, and C signal values. * a * b * The profile creation device then determines the color difference between the input L * a * b * The profile creation device determines a K color conversion ratio for the signal value of the color space, and determines the signal value of the K color. Furthermore, the profile creation device determines the K color conversion ratio for the input L based on the color difference judgment and the determined signal value of the K color. * a * b * The P color conversion ratio and the G color conversion ratio for the signal value of the color space are determined, and the signal values ​​of P and G colors are determined. The K color conversion ratio, the P color conversion ratio, and the G color conversion ratio are respectively * a * b * This is the conversion ratio for the signal values ​​of K, P, and G colors when converting signal values ​​in a color space into signal values ​​in the YMCKPG color space. As a result, the profile creation device * a * b * It is possible to create a K amount / special color amount determination model that obtains the signal values ​​of K color, P color, and G color from the signal values ​​in the color space.

[0037] Next, the profile creation device determines the signal values ​​of Y, M, and C colors in the YMCKPG color space by inverse conversion of the printer model determined in step 103 (step 106). 1 By inversely converting the signal values ​​of K, P, and G determined in step 105 and the L * a * b * The signal values ​​of Y, M and C in the YMCKPG color space are determined from the signal values ​​of each input grid point in the color space. The inverse conversion of the printer model means performing a color conversion that is the reverse of the color conversion performed by the printer model. The inverse conversion of the printer model in step 106 is performed by using a function f 1 The inverse transformation function f 1 -1 It is expressed as: (Y, M, C)=f 1 -1 (L * , a * , b * , K, P, G) … (3)

[0038] The profile creation device performs the L mapping in step 104. * a * b * The processes of steps 105 and 106 are carried out for all input lattice points in the color space, and the signal values ​​of each color in the YMCKPG color space are determined. And the profile creation device is L * a * b * Based on the signal values ​​of each color in the YMCKPG color space determined for each input grid point in the color space, L * a * b *A reference output profile is created that converts the signal values ​​in the color space into signal values ​​in the YMCKPG color space (step 107). The profile creation device then stores the created reference output profile in the storage unit 35 of the color conversion device 30 in association with information related to the printing device 20 and the type of paper (step 108). With this, the profile creation device completes the series of processes for creating the reference output profile.

[0039] Next, a description will be given of the output profile creation process performed by the profile creation unit 32 of the color conversion device 30 of this embodiment. As described above, the profile creation unit 32 creates an output profile using a predetermined reference output profile and a 3DLUT obtained from the colorimetric result of an image printed by the printing device 20. FIG. 5 is a flowchart showing an example of a process for creating an output profile.

[0040] The profile creation unit 32 acquires paper information, which is information about the type of paper used to print an image by the printing device 20 (step 201). The profile creation unit 32, for example, causes the operation display unit 34 of the color conversion device 30 to display an input screen for receiving input of the paper type. Then, the profile creation unit 32 acquires the paper information, which is information about the paper type, in response to a user's operation on the input screen of the operation display unit 34. The profile creation unit 32 may also acquire the paper information based on the detection result of a paper sensor or the like provided in the printing device 20 that detects the type of paper.

[0041] Next, the profile creation unit 32 causes the printing device 20 to print a color measurement image for the type of paper acquired in step 201, using a reference output profile that corresponds to the type of paper (step 202). Specifically, the profile creation unit 32 first * a * b * Sets the grid points in the color space. * a * b *Each lattice point set in the color space is a predetermined step size L * a * b * In the following, the profile creation unit 32 uses the L * a * b * The signal value of the grid point set in the color space is (L * ´、a * ´、b * It may be written as ´).

[0042] Then, the profile creation unit 32 creates the L * a * b * The signal value of the grid point set in the color space (L * ´、a * ´、b * In this embodiment, the L * a * b * The signal value of the grid point set in the color space is (L * ´、a * ´、b * ´) is an example of an input value in the first color space. If there is no paper type associated with the reference output profile stored in the storage unit 35 that matches the paper type acquired in step 201, the profile creation unit 32 uses the reference output profile associated with the paper type that is closest to the type acquired in step 201. Alternatively, the profile creation unit 32 may use a predetermined reference output profile from among the multiple reference output profiles stored in the storage unit 35.

[0043] Then, the profile creation unit 32 inputs the color-measurement image data, which is expressed by signal values ​​in the YMCKPG color space converted by the reference output profile, to the printing device 20. Then, the printing device 20 uses the color-measurement image data input by the profile creation unit 32 to print an image for color measurement on the type of paper acquired in step 201. The color measurement image that the profile creation unit 32 causes the printing device 20 to print in step 202 is an example of a print image. * a * b * The signal value of each grid point in the color space (L * ´、a * ´、b * This is an image in which multiple patches are printed with image data represented by signal values ​​of YMCKPG color signals converted from the YMCKPG color signal.

[0044] Next, the profile creation unit 32 obtains colorimetric values ​​that are the results of the colorimetric measurement unit 33 measuring the colorimetric image formed on the paper (step 203). In addition, the profile creation unit 32 obtains information obtained by reading each patch of the colorimetric image by the colorimetric measurement unit 33 as the colorimetric values. In this example, the profile creation unit 32 obtains the colorimetric values ​​by the L * a * b * Colorimetric values ​​expressed as signal values ​​in a color space are obtained.

[0045] Next, the profile creation unit 32 uses the colorimetric values ​​acquired in step 203 to determine a color prediction model (step 204). Here, the profile creation unit 32 creates the L * a * b * The signal value of each grid point in the color space (L * ´、a * ´、b * ´) to obtain the L of the image printed by the printing device 20. * a * b * A color prediction model for predicting signal values ​​in the color space is determined. The color prediction model determined in step 204 is a function f 2 It can be expressed as follows. (L * , a * , b * )=f 2 (L * ´、a * ´、b * ´) …(4) The color prediction model is an example of a first correspondence that converts input values ​​in a first color space to colorimetric values ​​in the first color space.

[0046] Next, the profile creation unit 32 performs inverse conversion of the color prediction model determined in step 204 to obtain the L of the image to be printed by the printing device 20. * a * b * From the signal values ​​in the color space, the L input to the reference output profile * a * b * Color space signal value (L * ´、a * ´、b * The inverse transformation of the color prediction model means performing a color transformation that is the opposite of the color transformation performed by the color prediction model. The inverse transformation of the color prediction model in step 205 is performed by using a function f 2 The inverse transformation function f 2 -1 It is expressed as: (L * ´、a * ´、b * ´)=f 2 -1 (L * , a * , b * ) …(5)

[0047] Next, the profile creation unit 32 calculates the L of the image to be printed by the printing device 20 from the result of the inverse conversion of the color prediction model in step 205. * a * b * The signal values ​​of the color space are input to the reference output profile. * a * b * Color space signal value (L * ´、a * ´、b * In this embodiment, the profile creation unit 32 determines the color conversion conditions for converting the L * a * b * Color space signal value (L * , a * , b* ) to L * a * b * Color space signal value (L * ´、a * ´、b * Create a 3DLUT (3D lookup table) to convert the

[0048] Next, the profile creation unit 32 synthesizes the 3DLUT created in step 206 with the reference output profile. * a * b * An output profile is created that converts the signal values ​​of the color space into signal values ​​of the YMCKPG color space printable by the printing device 20 (step 207). Then, the profile creation unit 32 stores the output profile created in step 207 in the storage unit 35 (step 208), and ends the series of processes.

[0049] As described above, in the color conversion device 30, the color conversion section 31 performs color conversion processing on the image data input from the input device 10 using the output profile created by the profile creation section 32. Specifically, the color conversion unit 31 converts the signal values ​​in the RGB color space representing the image data input from the input device 10 into L, * a * b * Next, the color conversion unit 31 converts the L * a * b * The signal values ​​in the color space are converted into signal values ​​in the YMCKPG color space using the output profile created by the profile creation unit 32.

[0050] As described above, in this embodiment, the profile creation unit 32 of the color conversion device 30 creates a L * a * b *The signal values ​​of the color space are converted into signal values ​​of the YMCKPG color space that depends on the printing device 20, and the color measurement image is printed by the printing device 20. * a * b * The profile creation unit 32 then acquires colorimetric values ​​of the color space. * a * b * The signal values ​​in the color space and the result of measuring the color measurement image printed by the printing device 20 are * a * b * A 3DLUT is created that represents the correspondence between the color space and the colorimetric values. Furthermore, the profile creation unit 32 creates a profile based on the 3DLUT and a L * a * b * The L input to the printing device 20 is synthesized with a reference output profile that converts the signal values ​​of the color space into signal values ​​of the YMCKPG color space. * a * b * An output profile is created to convert signal values ​​in the color space into signal values ​​in the YMCKPG color space.

[0051] Then, the color conversion unit 31 of the color conversion device 30 converts the signal values ​​in the RGB color space representing the image data input from the input device 10, etc., into signal values ​​in the YMCKPG color space using the output profile created by the profile creation unit 32 and a predetermined input profile. This makes it possible to improve the color reproducibility of an image printed by the printing device 20 compared to, for example, performing color conversion on image data input from an input device 10, etc., using a uniform output profile predetermined in accordance with the printing device 20, etc., without using the results of measuring the colorimetric image.

[0052] In addition, in the color conversion device 30 of this embodiment, the 3DLUT and a predetermined reference output profile are combined to create an output profile, so that, for example, a L * a * b* The time required to create an output profile can be reduced compared to when an output profile is created by numerically solving color conversion conditions that indicate the correspondence between the color space and the YMCKPG color space. As a result, in the color conversion device 30, when performing color conversion of image data input from the input device 10 or the like using the output profile, the time required for color conversion can be shortened.

[0053] Here, in the above-described color conversion device 30, a reference output profile is predetermined for each of a plurality of paper types used for printing images by the printing device 20, and is stored in association with the paper type in the storage unit 35. However, in the color conversion device 30, the reference output profile may be determined based on standard paper (e.g., fine paper), which is a predetermined type of paper. In this case, the profile creation unit 32 may create an output profile using a reference output profile determined based on the standard paper, without relying on the paper information acquired in step 201 described above.

[0054] In addition, in the color conversion device 30, if the color difference between the paper used to print an image by the printing device 20 and the standard paper associated with the reference output profile is within a predetermined range, the color conversion unit 31 may convert the signal values ​​in the RGB color space representing the image data input from the input device 10, etc., into signal values ​​in the YMCKPG color space using the reference output profile without creating an output profile.

[0055] When the color difference between the paper used to print an image by the printing device 20 and the standard paper is within a predetermined range, performing color conversion using the reference output profile is unlikely to result in a decrease in the color reproducibility of the image printed by the printing device 20. Furthermore, when the color difference between the paper used to print an image by the printing device 20 and the standard paper is within a predetermined range, performing color conversion using the reference output profile without creating an output profile eliminates the time required to create an output profile and can shorten the time required for color conversion. Here, cases in which the color difference between the paper used to print an image by the printing device 20 and the standard paper associated with the reference output profile is within a predetermined range include cases in which the paper used to print an image by the printing device 20 and the standard paper match, or cases in which the color of the paper detected by a paper sensor or the like provided in the printing device 20 matches the standard paper.

[0056] Although the signal values ​​representing the image data input from the input device 10 to the color conversion device 30 are exemplified as signal values ​​in the RGB color space, the present invention is not limited to this. The signal values ​​representing the image data input from the input device 10 to the color conversion device 30 may be signal values ​​represented in a color space such as YMCK or YMCKRGB in addition to the RGB color space. In addition, the output profile created by the color conversion device 30 is in a device-independent color space called L * a * b * Converts the signal values ​​of the color space to signal values ​​of the YMCKPG color space, but the device-independent color space is L * a * b * Not limited to color spaces. For example, XYZ color space, Yxy color space, L * u * v * It may be a color space, an HLS color space, etc.

[0057] In the above embodiment, the output profile created by the profile creation unit 32 of the color conversion device 30 is a L * a * b * The signal values ​​of the color space are converted to signal values ​​of the YMCKPG color space consisting of six variables including normal colors and two special colors. However, the output profile is a three-variable L * a * b * If the signal values ​​in the color space are converted into signal values ​​in a color space consisting of five or more variables including normal colors and special colors, the special colors may be one color or three or more colors. Generally, the more spot colors there are, in other words, the more variables there are in the converted color space, the longer the time required to create an output profile. * a * b * It is more effectively used when converting signal values ​​of a color space into signal values ​​of a color space with more variables.

[0058] Although the embodiment of the present invention has been described above, the technical scope of the present invention is not limited to the scope described in the above embodiment. It is clear from the claims that various modifications and improvements to the above embodiment are also included in the technical scope of the present invention.

[0059] The processor in the above-described embodiments refers to a processor in a broad sense, and includes general-purpose processors (e.g., CPU (=Central Processing Unit)) as well as dedicated processors (e.g., GPU (=Graphical Processing Unit), ASIC (=Application Specific Integrated Circuit), FPGA (=Field Programmable Gate Array), programmable logic devices, etc.). In addition, the operations of the processor in this embodiment may be executed by one processor alone, or may be executed by multiple processors located at physically separate locations in cooperation with each other. Furthermore, the order of execution of each operation in the processor is not limited to the order described in the above embodiment, and may be changed individually.

[0060] <Additional Notes> (((1))) A processor is provided. The processor, creating a first color conversion table that represents a correspondence relationship between input values ​​in a first color space that is independent of a printing device and colorimetric values ​​in the first color space that are the result of converting the input values ​​into signal values ​​in a second color space that is dependent on the printing device and measuring the color of a print image printed by the printing device; A signal value of the first color space is converted into a signal value of the second color space by using a second color conversion table predetermined according to the printing device and the first color conversion table. Color conversion device. (((2))) The processor acquires paper information, which is information regarding the type of paper on which an image is printed by the printing device, and creates the first color conversion table in accordance with the paper information (((1))). (((3))) the second color conversion table is determined based on a predetermined standard paper; The processor, when the color difference between the paper on which an image is printed by the printing device and the standard paper is within a predetermined range, uses the second color conversion table to convert the signal values ​​of the first color space into signal values ​​of the second color space. (((4))) the second color conversion table is determined according to a type of paper, The processor creates the first color conversion table using the colorimetric values ​​of the printed image printed based on the signal values ​​of the second color space obtained by converting the input values ​​using the second color conversion table corresponding to the type of paper based on the paper information. (((5))) The processor creates the first color conversion table that converts the colorimetric values ​​in the first color space into signal values ​​in the first color space corresponding to the input values. (((6))) The processor creates a first correspondence relationship that converts the input values ​​in the first color space to the colorimetric values ​​in the first color space, and creates the first color conversion table by inversely converting the first correspondence relationship. (((7))) The processor converts signal values ​​of the first color space consisting of three variables into signal values ​​of the second color space consisting of five or more variables including signal values ​​of normal colors, which are colors that are normally used, and signal values ​​of special colors, which are colors other than the normal colors. (((8))) The processor, creating an output profile that combines the first color conversion table and the second color conversion table to convert the input signal values ​​in the first color space into signal values ​​in the second color space and output the converted signal values; A color conversion device according to any one of ((1))) to (((7))), which converts signal values ​​of the first color space, which have been converted from signal values ​​of a third color space that depends on an input device using an input profile, into the second color space using the output profile. (((9))) A processor is provided. The processor, creating a first color conversion table that represents a correspondence relationship between input values ​​in a first color space that is independent of a printing device and colorimetric values ​​in the first color space that are the result of converting the input values ​​into signal values ​​in a second color space that is dependent on the printing device and measuring the color of a print image printed by the printing device; A color conversion table creation device that combines a second color conversion table, which is predetermined according to the printing device and converts signal values ​​of the first color space into the second color space, with the first color conversion table to create a third color conversion table that converts input signal values ​​of the first color space into signal values ​​of the second color space. (((10))) On the computer, a function for creating a first color conversion table that represents a correspondence relationship between input values ​​in a first color space that is independent of a printing device and colorimetric values ​​in the first color space that are the result of converting the input values ​​into signal values ​​in a second color space that is dependent on the printing device and measuring the color of a printed image printed by the printing device; a function of converting signal values ​​of the first color space into signal values ​​of the second color space by combining a second color conversion table, which is predetermined according to the printing device, with the first color conversion table, and converting input signal values ​​of the first color space into signal values ​​of the second color space; A program to achieve this.

[0061] According to the color conversion device of (((1))), the time required to convert signal values ​​in a first color space that is independent of the printing device to signal values ​​in a second color space that is dependent on the printing device can be reduced, compared to the case where a color conversion table is created by numerically solving conversion conditions that are created based on the colorimetric results of an image printed by a printing device. According to the color conversion device in accordance with (((2))), it is possible to improve the color reproducibility of an image printed on paper, compared to a case in which the first color conversion table is not created according to paper information. According to the color conversion device of (((3))), the time required to convert signal values ​​in the first color space to signal values ​​in the second color space can be shortened compared to the case where a first color conversion table is created when the color difference between the paper and standard paper is within a predetermined range. According to the color conversion device of (((4))), it is possible to improve the color reproducibility of an image printed on paper, compared to a case in which the second color conversion table is not determined according to the type of paper. According to the color conversion device of (((5))), the time required to convert signal values ​​in a first color space to signal values ​​in a second color space can be reduced compared to the case where a color conversion table is created by numerically solving conversion conditions created based on the colorimetric results of a printed image by a printing device. According to the color conversion device of (((6))), the time required to convert signal values ​​in a first color space to signal values ​​in a second color space can be reduced, compared to the case where a color conversion table is created by numerically solving conversion conditions created based on the colorimetric results of a printed image by a printing device. According to the color conversion device of (((7))), it is possible to reduce the time required to convert signal values ​​in a first color space into signal values ​​in five or more second color spaces including normal colors and special colors. According to the color conversion device of (((8))), the time required to convert signal values ​​in the first color space to signal values ​​in the second color space can be reduced compared to a case in which the first color conversion table and the second color conversion table are not combined to create an output profile. According to the color conversion table creation device of (((9))), the time required to convert signal values ​​in a first color space that is independent of the printing device to signal values ​​in a second color space that is dependent on the printing device can be reduced, compared to the case where a color conversion table is created by numerically solving conversion conditions that are created based on the colorimetric results of an image printed by a printing device. According to the program pertaining to (((10))), the time required to convert signal values ​​in a first color space that is independent of the printing device to signal values ​​in a second color space that is dependent on the printing device can be reduced compared to the case in which a color conversion table is created by numerically solving conversion conditions that are created based on the colorimetric results of an image printed by a printing device. [Explanation of symbols]

[0062] 10...input device, 20...printing device, 21...printing section, 22...printing control section, 30...color conversion device, 31...color conversion section, 32...profile creation section, 33...colorimetry section, 34...operation display section, 35...storage section

Claims

1. A processor is provided. The processor, creating a first color conversion table that represents a correspondence relationship between input values ​​in a first color space that is independent of a printing device and colorimetric values ​​in the first color space that are the result of converting the input values ​​into signal values ​​in a second color space that is dependent on the printing device and measuring the color of a print image printed by the printing device; A signal value of the first color space is converted into a signal value of the second color space by using a second color conversion table predetermined according to the printing device and the first color conversion table. Color conversion device.

2. 2. The color conversion device according to claim 1, wherein the processor acquires paper information that is information about a type of paper on which an image is printed by the printing device, and creates the first color conversion table in accordance with the paper information.

3. the second color conversion table is determined based on a predetermined standard paper; The color conversion device described in claim 2, wherein the processor uses the second color conversion table to convert signal values ​​of the first color space into signal values ​​of the second color space when the color difference between the paper on which an image is printed by the printing device and the standard paper is within a predetermined range.

4. the second color conversion table is determined according to a type of paper, The color conversion device described in claim 2, wherein the processor creates the first color conversion table using the colorimetric values ​​of the printed image printed based on the signal values ​​of the second color space obtained by converting the input values ​​using the second color conversion table corresponding to the type of paper based on the paper information.

5. The color conversion device according to claim 1 , wherein the processor creates the first color conversion table that converts the colorimetric values ​​in the first color space into signal values ​​in the first color space that correspond to the input values.

6. The color conversion device described in claim 5, wherein the processor creates a first correspondence relationship that converts the input values ​​in the first color space to the colorimetric values ​​in the first color space, and creates the first color conversion table by inversely converting the first correspondence relationship.

7. 2. The color conversion device according to claim 1, wherein the processor converts signal values ​​of the first color space consisting of three variables into signal values ​​of the second color space consisting of five or more variables including signal values ​​of normal colors, which are colors that are normally used, and signal values ​​of special colors, which are colors other than the normal colors.

8. The processor, creating an output profile by combining the first color conversion table and the second color conversion table to convert input signal values ​​in the first color space into signal values ​​in the second color space and outputting the converted signal values; 2. The color conversion device according to claim 1, wherein the signal values ​​of the first color space converted from signal values ​​of a third color space dependent on an input device by an input profile are converted into the second color space by the output profile.

9. A processor is provided. The processor, creating a first color conversion table that represents a correspondence relationship between input values ​​in a first color space that is independent of a printing device and colorimetric values ​​in the first color space that are the result of converting the input values ​​into signal values ​​in a second color space that is dependent on the printing device and measuring the color of a print image printed by the printing device; A color conversion table creation device that combines a second color conversion table, which is predetermined according to the printing device and converts signal values ​​of the first color space into signal values ​​of the second color space, with the first color conversion table to create a third color conversion table that converts input signal values ​​of the first color space into signal values ​​of the second color space.

10. On the computer, a function for creating a first color conversion table that represents a correspondence relationship between input values ​​in a first color space that is independent of a printing device and colorimetric values ​​in the first color space that are the result of converting the input values ​​into signal values ​​in a second color space that is dependent on the printing device and measuring the color of a print image printed by the printing device; a function of converting signal values ​​of the first color space into signal values ​​of the second color space by combining a second color conversion table, which is predetermined according to the printing device, with the first color conversion table, and converting input signal values ​​of the first color space into signal values ​​of the second color space; A program to achieve this.

Images