Color conversion apparatus and method, color conversion table creation apparatus, and storage medium

Abstract

The invention discloses a color conversion apparatus and method, a color conversion table creation apparatus, and a storage medium, the color conversion apparatus includes a processor that creates a first color conversion table, the input signal value of the first color space is converted into a signal value of a second color space by using a second color conversion table which converts the signal value of the first color space into the signal value of the second color space and is predetermined according to the printing device, and the first color conversion table, and the input signal value of the first color space is converted into the signal value of the second color space. The first color conversion table indicates an input value independent of the first color space of the printing apparatus and a color measurement value of the first color space, which is the result of color measurement of a printed image that is converted into a signal value dependent on the second color space of the printing apparatus and printed by the printing apparatus and obtaining a corresponding relation.

Description

Technical Field

[0001] The invention relates to a color conversion device, a color conversion method, a color conversion table creation device and a computer readable medium. Background Art

[0002] As a prior art, there is a method of converting L into * a * b * A technique for converting an input signal such as a color signal into a color signal including a color signal of a common color such as YMCK and a color signal of a special color such as PG used in an image output device. For example, in the Kueppers method, L * a * b * After the color signal is converted into a CMY signal or an RGB signal, the color signal is subjected to UCR processing of the achromatic component and UCR processing of the color difference component. * a * b * The color signal is converted into a color signal composed of YMCK+PG.

[0003] In addition, as a prior art, Japanese Patent No. 4206743 discloses the following technology: * a * b * The color signal determines the ink amount K and the special color amount O, and according to L * a * b * The color signal and KO color signal determine the L input under the condition that the ink volume is the K color signal and the special color volume is the O color signal. * a * b * The color signal is the YMC color signal of the image output device that is consistent with the color measurement, so that L * a * b * The process of converting the color signal into the image recording signal YMCKO which is input to the image output device. Summary of the invention

[0004] When converting a signal value of a first color space that is independent of a printing device into a signal value of a second color space that is dependent on the printing device, if the colorimetric consistency between the signal value of the first color space and the signal value of the second color space is not considered as in the Kueppers method, the color reproducibility in the printing device is likely to be reduced.

[0005] On the other hand, from the perspective of improving color reproducibility, in order to make the signal values ​​of the first color space and the signal values ​​of the second color space consistent in colorimetry, if a color conversion table that converts the signal values ​​of the first color space into the signal values ​​of the second color space is created by numerically solving conversion conditions such as a printer model that is created based on the colorimetric results of the printed image printed by the printing device and represents the correspondence between the first color space and the second color space, the time required for color conversion is likely to be prolonged.

[0006] An object of the present invention is to shorten the time required for conversion from a signal value in a first color space that is not dependent on a printing device to a signal value in a second color space that is dependent on a printing device, compared to a case in which a color conversion table is created by numerically solving conversion conditions that are created based on color measurement results of a print image printed by a printing device.

[0007] According to a first aspect of the present invention, a color conversion device is provided, which has a processor, which creates a first color conversion table, the first color conversion table indicating a correspondence between an input value of a first color space that is independent of a printing device and a result of colorimetric measurement of a printed image that is obtained by converting the input value into a signal value of a second color space that is dependent on the printing device and printed by the printing device, i.e., a colorimetric value of the first color space, and uses a second color conversion table that is predetermined according to the printing device and converts the signal value of the first color space into a signal value of the second color space, and the first color conversion table to convert the signal value of the first color space input into a signal value of the second color space.

[0008] According to a second aspect of the present invention, in the color conversion device of the first aspect, the processor acquires paper information related to the type of paper on which the image is printed by the printing device, and creates the first color conversion table based on the paper information.

[0009] According to the third aspect of the present invention, based on the color conversion device of the second aspect, the second color conversion table is determined based on a predetermined standard paper, and when the color difference between the paper on which the 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 the signal value of the first color space into the signal value of the second color space.

[0010] According to the fourth aspect of the present invention, based on the color conversion device of the second aspect, the second color conversion table is determined according to the type of paper, and the processor creates the first color conversion table based on the paper information and using the colorimetric value of the printed image printed based on the signal value of the second color space, and the signal value of the second color space is obtained by converting the input value according to the second color conversion table corresponding to the type of paper.

[0011] According to the fifth aspect of the present invention, based on the color conversion device of any one of the first to fourth aspects, the processor creates the first color conversion table that converts the colorimetric value of the first color space into a signal value of the first color space corresponding to the input value.

[0012] According to the sixth aspect of the present invention, based on the color conversion device of the fifth aspect, the processor creates the first color conversion table by creating a first correspondence relationship that converts the input value of the first color space into the color measurement value of the first color space, and inversely converting the first correspondence relationship.

[0013] According to the seventh aspect of the present invention, based on the color conversion device of any one of the first to sixth aspects, the processor converts the signal value of the first color space composed of three variables into the signal value of the second color space composed of five or more variables including signal values ​​of commonly used colors, i.e., normal colors, and signal values ​​of colors other than normal colors, i.e., special colors.

[0014] According to the eighth aspect of the present invention, based on the color conversion device of any one of the first to seventh aspects, the processor synthesizes the first color conversion table and the second color conversion table, creates an output profile that converts the signal value of the first color space to be input into the signal value of the second color space and outputs it, and converts the signal value of the first color space converted from the signal value of the third color space dependent on the input device according to the input profile into the signal value of the second color space according to the output profile.

[0015] According to the ninth aspect of the present invention, there is provided a color conversion table creation device, which comprises a processor, wherein the processor creates a first color conversion table, wherein the first color conversion table represents a correspondence between an input value of a first color space that is independent of a printing device and a result of colorimetric measurement of a printed image that is obtained by converting the input value into a signal value of a second color space that is dependent on the printing device and printed by the printing device, namely, a colorimetric value of the first color space, and synthesizes a second color conversion table that is predetermined according to the printing device and converts the signal value of the first color space into a signal value of the second color space, and the first color conversion table, to create a third color conversion table that converts the input signal value of the first color space into a signal value of the second color space.

[0016] According to a tenth aspect of the present invention, there is provided a computer-readable medium storing a program causing a computer to execute processing, wherein the processing comprises: the steps of creating a first color conversion table, the first color conversion table representing a correspondence between an input value of a first color space that is independent of a printing device and a result of colorimetric measurement of a printed image that is obtained by converting the input value into a signal value of a second color space that is dependent on the printing device and printed by the printing device, namely, a colorimetric value of the first color space; and the steps of synthesizing a second color conversion table that is predetermined according to the printing device and converts the signal value of the first color space into a signal value of the second color space, and the first color conversion table, and converting the input signal value of the first color space into a signal value of the second color space.

[0017] According to the eleventh aspect of the present invention, there is provided a color conversion method, comprising: a step of creating a first color conversion table, the first color conversion table representing a correspondence between an input value of a first color space that is independent of a printing device and a result of colorimetric measurement of a printed image that is obtained by converting the input value into a signal value of a second color space that is dependent on the printing device and printed by the printing device, i.e., a colorimetric value of the first color space; and a step of converting the input signal value of the first color space into a signal value of the second color space using a second color conversion table that is predetermined according to the printing device and converts the signal value of the first color space into a signal value of the second color space.

[0018] (Effect)

[0019] According to the first aspect, compared to a case where a color conversion table is created by numerically solving a conversion condition created based on a color measurement result of a print image printed by a printing device, the time required for conversion from a signal value in a first color space that is not dependent on the printing device to a signal value in a second color space that is dependent on the printing device can be shortened.

[0020] According to the second aspect, the color reproducibility of an image printed on paper can be improved compared to a case where the first color conversion table is not created based on paper information.

[0021] According to the third aspect, the time required for conversion from 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 is created when the color difference between the paper and the standard paper is within a predetermined range.

[0022] According to the fourth aspect, the color reproducibility of an image printed on paper can be improved compared to a case where the second color conversion table is not determined according to the type of paper.

[0023] According to the fifth aspect, compared with a case where a color conversion table is created by numerically solving conversion conditions created based on color measurement results of a print image printed by a printing device, the time required for conversion from a signal value in a first color space to a signal value in a second color space can be shortened.

[0024] According to the sixth aspect, compared with a case where a color conversion table is created by numerically solving conversion conditions created based on color measurement results of a printed image printed by a printing device, the time required for conversion from a signal value in a first color space to a signal value in a second color space can be shortened.

[0025] According to the seventh aspect, it is possible to shorten the time required for conversion from the signal value of the first color space to the signal value of the five or more second color spaces including normal colors and special colors.

[0026] According to the eighth aspect, the time required for conversion from the signal value of the first color space to the signal value of 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 synthesized to create an output profile.

[0027] According to the ninth aspect, compared with a case where a color conversion table is created by numerically solving a conversion condition created based on a color measurement result of a print image printed by a printing device, the time required for conversion from a signal value in a first color space that is not dependent on the printing device to a signal value in a second color space that is dependent on the printing device can be shortened.

[0028] According to the tenth aspect, compared with a case where a color conversion table is created by numerically solving a conversion condition created based on a color measurement result of a print image printed by a printing device, the time required for conversion from a signal value in a first color space that is not dependent on the printing device to a signal value in a second color space that is dependent on the printing device can be shortened.

[0029] According to the eleventh aspect, compared with a case where a color conversion table is created by numerically solving a conversion condition created based on a color measurement result of a print image printed by a printing device, the time required for conversion from a signal value in a first color space that is not dependent on the printing device to a signal value in a second color space that is dependent on the printing device can be shortened. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is a diagram illustrating the structure of a printing system to which this embodiment is applied;

[0031] Figure 2 is a functional block diagram of a color conversion device;

[0032] Figure 3 is a diagram showing an example of color conversion processing performed by a color conversion section using an output profile created by a profile creation section;

[0033] Figure 4 is a flowchart showing an example of a process for creating a reference output profile;

[0034] Figure 5 This is a flowchart showing an example of the process of creating an output profile. DETAILED DESCRIPTION

[0035] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0036] Figure 1 This is a diagram for explaining the configuration of a printing system 100 to which this embodiment is applied.

[0037] 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 communicable.

[0038] The network connecting the input device 10, the printing device 20, and the color conversion device 30 uses, for example, a LAN (Local Area Network) or the Internet. Of course, the network may be a composite structure of a LAN and the Internet.

[0039] The input device 10 is constituted by a computer device and inputs image data for printing in the printing device 20 to the color conversion device 30 .

[0040] The printing device 20 prints an image on paper as an example of a recording medium based on image data input by the input device 10 and color-converted by the color conversion device 30. The printing device 20 includes a printing unit 21 for printing and a print control unit 22 for controlling the operation of the printing unit 21.

[0041] The printing unit 21 prints an image on a sheet of paper, for example, by means of an electrophotographic method. The printing unit 21 of the present embodiment uses toners of yellow (Y), magenta (M), cyan (C), and black (K) (hereinafter, these colors are sometimes referred to as normal colors) and toners of special colors different from the normal colors to print an image on a sheet of paper. A toner is an example of a colorant used to form an image. Here, a special color refers to a color different from the normal color, for example, a color that is difficult to achieve using toners of the normal colors of yellow, magenta, cyan, and black. As such special colors, in addition to fluorescent pink, fluorescent yellow, white, bright cyan, orange, purple, green, etc., metallic colors such as gold or silver colored with metallic pigments can also be cited, but are not limited thereto. In the present embodiment, the case where 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 is described as an example.

[0042] In addition, the printing unit 21 forms an image on paper using colorants of common colors, i.e., yellow (Y), magenta (M), cyan (C), and black (K) and one or more special colorants, and the printing form and the type of colorants are not particularly limited. The printing unit 21 may print an image on paper by inkjet printing, thermal transfer printing, offset printing, etc., in addition to the above-mentioned electrophotography.

[0043] In the following description, the normal colors of yellow (Y), magenta (M), cyan (C), and black (K) are sometimes referred to as YMCK colors. In addition, the YMCK colors used for printing in the printing device 20 and the special colors of fluorescent pink (P) and green (G) are sometimes referred to as YMCKPG colors.

[0044] The color conversion device 30 is an example of a color conversion device or a color conversion table creation device, and is composed of a computer device. The color conversion device 30 may be physically a single computer, or may be implemented by distributed processing performed by multiple computers. In addition, the color conversion device 30 may be configured as a shared server that provides a so-called cloud service, or may be configured as a pre-installed server.

[0045] Alternatively, the color conversion device 30 may be built into the printing device 20 as a part of the printing device 20 .

[0046] Here, in the printing system 100 of the present embodiment, image data represented by signal values ​​in 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 ​​in the RGB color space into signal values ​​in the YMCKPG color space used by the printing device 20. Incidentally, the color conversion device 30 converts the signal values ​​in the RGB color space into signal values ​​in the YMCKPG color space using an input profile and an output profile described later.

[0047] Then, the color conversion device 30 outputs the image data represented by the signal value of the YMCKPG color space to the printing device 20. In the printing device 20, based on the image data acquired from the color conversion device 30, an image is printed on paper using toners of Y, M, C, K, P, and G colors.

[0048] The signal value of the YMCKPG color space includes the signal value of the YMCK colors corresponding to the usage amount of the YMCK color toners and the signal values ​​of the special colors P and G. The signal value of each color in the YMCKPG color space is associated with the usage amount of the color toners in the printing unit 21 of the printing device 20.

[0049] Figure 2 is a functional block diagram of the color conversion device 30 .

[0050] The color conversion device 30 includes a color conversion unit 31 that performs color conversion processing on image data input from the input device 10, and a profile creation unit 32 that creates an output profile for the color conversion processing performed by the color conversion unit 31. In addition, the color conversion device 30 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 receives input of information through the user's operation. In addition, the color conversion device 30 includes a storage unit 35 that stores information such as the output profile created by the profile creation unit 32.

[0051] Here, the functions of the color conversion unit 31 and the profile creation unit 32 in the color conversion device 30 are implemented by a CPU 30A as an example of a processor. The CPU 30A reads the program stored in a ROM (Read Only Memory) 30B and executes the program using a RAM (Random Access Memory) 30C as a work area. The program executed by the CPU 30A can be provided to the color conversion device 30 in a state stored in a computer-readable recording medium such as a magnetic recording medium (a magnetic tape, a magnetic disk, etc.), an optical recording medium (an optical disk, etc.), an optical magnetic recording medium, a semiconductor memory, etc. In addition, the program executed by the CPU 30A can also be downloaded to the color conversion device 30 using a communication method such as the Internet.

[0052] In the present embodiment, the functions of the color conversion unit 31 and the profile creation unit 32 in the color conversion device 30 are implemented by software, but the present invention is not limited thereto and may be implemented by, for example, an ASIC (Application Specific IC).

[0053] The color conversion unit 31 converts the signal value in the RGB color space representing the image data input from the input device 10 into the signal value in the YMCKPG color space used by the printing device 20 , using the input profile and the output profile stored in the storage unit 35 .

[0054] In the present embodiment, a profile refers to a color conversion condition when performing color conversion between data composed of signal values ​​in different color spaces.

[0055] The input profile converts the signal value of the RGB color space representing the image data input from the input device 10 into a signal value of a color space that is independent of the input device 10 or the printing device 20. In the present embodiment, the input profile converts the signal value of the RGB color space into the RGB color space that is independent of the device. * a * b * Signal value in color space. L * a * b * The color space is an example of the first color space, which is used to represent the lightness L * 、Chroma a * and chromaticity b * The rectangular coordinates of the axes are represented in color space.

[0056] In addition, the output profile is L converted from the input profile. * a * b * The signal value of the color space is converted into the signal value of the YMCKPG color space used by the printing device 20. Incidentally, the output profile is L consisting of three variables: * a * b * The signal value of the color space is converted into the signal value of the YMCKPG color space composed 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.

[0057] The profile creation section 32 creates an output profile used for the color conversion process performed by the color conversion section 31. The output profile creation process performed by the profile creation section 32 will be described in detail in the following section.

[0058] The color measuring unit 33 measures the color of the image printed on the paper by the printing device 20, and obtains the color of the image. * a * b * The colorimetric value represented by the signal value in the color space.

[0059] The structure of the colorimetric unit 33 is not particularly limited, and for example, a structure that performs colorimetric measurement based on a user's operation of moving a colorimetric device on an image printed on paper by the printing device 20 may be cited. Alternatively, the colorimetric unit 33 may be a component that is provided inside the printing device 20 and that reads an image printed on paper by the printing device 20 and performs colorimetric measurement.

[0060] The operation display unit 34 displays a display screen for providing information to the user. In addition, the operation display unit 34 receives input of information through the user's operation on the display screen.

[0061] When the profile creation unit 32 creates an output profile, the operation display unit 34 of the present embodiment displays, as a display screen, an input screen for accepting input of the type of paper used for printing an image in the printing device 20 .

[0062] The storage section 35 stores an input profile and an output profile used for the color conversion process performed by the color conversion section 31 .

[0063] In addition, the storage section 35 stores a reference output profile and a K amount / special color amount determination model used for creation of an output profile by the profile creation section 32 .

[0064] Here, in the color space L that does not depend on the printing device 20, * a * b * When the signal value of the color space is converted into the signal value of the YMCKPG color space that depends on the color space of the printing device 20 and the image is printed by the printing device 20, if L * a * b * If the signal value of the color space and the signal value of the converted YMCKPG color space are colorimetrically identical, the reproducibility of the color in the image is likely to be reduced.

[0065] On the other hand, from the viewpoint of improving color reproducibility, there is a case where the colorimetric value representing L is numerically solved based on the color measurement result of the image printed by the printing device 20. * a * b * The printer model that corresponds to the color space and the YMCKPG color space is created to convert L * a * b* An output profile that converts a signal value in a color space into a signal value in a YMCKPG color space. In this case, the time required for creating an output profile and a color conversion process using the created output profile is likely to be long.

[0066] Figure 3 1 is a diagram showing an example of color conversion processing performed by the color conversion section 31 using the output profile created by the profile creation section 32 .

[0067] In the color conversion device 30 of the present embodiment, the profile creation unit 32 creates a color conversion profile that converts L into color using a previously determined reference output profile and a color conversion condition, namely a 3DLUT (three-dimensional lookup table), obtained from a color measurement result of a color measurement image printed by the printing device 20. * a * b * An output profile that converts a signal value in a color space into a signal value in a YMCKPG color space. 3DLUT is an example of a first color conversion table, and the reference output profile is an example of a second color conversion table.

[0068] The color conversion section 31 of the color conversion device 30 converts the image data represented by the signal value of the RGB color space input from the input device 10 into an RGB color space that does not depend on the printing device 20 using the input profile. * a * b * Then, the color conversion section 31 converts the signal value of the L*a*b* color space into the signal value of the YMCKPG color space using the output profile created by the profile creation section 32 .

[0069] Next, the output profile creation process performed by the profile creation section 32 of the color conversion device 30 will be described.

[0070] First, a reference output profile used in the output profile creation process performed by the profile creation unit 32 will be described.

[0071] The reference output profile is L as an example of the first color space. * a * b * The color conversion condition for converting the signal value of the color space into the signal value of the YMCKPG color space. In the present embodiment, the reference output profile is determined in advance for each of the types of the printing device 20 and the paper used for printing the image by the printing device 20. And each reference output profile is stored in the storage unit 35 in association with the printing device 20 and the type of paper.

[0072] Figure 4 : is a flowchart showing an example of a process of creating a reference output profile.

[0073] The reference output profile can be created, for example, by the following process. The reference output profile may be created by the profile creation unit 32 of the color conversion device 30 and stored in the storage unit 35, or may be created by a device other than the color conversion device 30 and stored in the storage unit 35. The following description will be made of a case where the reference output profile is created by a profile creation device (not shown) other than the color conversion device 30.

[0074] The profile creation device uses the printing device 20 to print the color measurement image on a predetermined type of paper (step S101). The type of paper refers to the type of paper on which the color of the image printed is different due to the different colors of the surface of the paper. Examples of such types of paper include glossy paper, matte paper, and high-grade paper, but are not particularly limited.

[0075] The profile creation device inputs the image data representing the colorimetric image, that is, the colorimetric image data, into the printing device 20. In this example, the colorimetric image data is represented by the signal value of the YMCKPG color space. Then, the printing device 20 prints the colorimetric image on the selected type of paper using the colorimetric image data input from the profile creation device. The colorimetric image is an image in which a plurality of small blocks (e.g., a rectangular image) having colors that include the entire color gamut that can be printed in the printing device 20 are arranged. Here, the colorimetric image is an image in which a plurality of small blocks of image data represented by the signal value of the YMCKPG color signal with a predetermined step size are arranged to be printed.

[0076] Next, the profile creation device obtains the color measurement value obtained by colorimetrically measuring the colorimetric image formed on the paper (step S102). Incidentally, the profile creation device obtains information obtained by reading each small block of the colorimetric image with a colorimetric device (not shown) as the colorimetric value. In this example, the profile creation device obtains the colorimetric value using a color space that does not depend on the device such as the printer 20, that is, L * a * b * Colorimetric values ​​expressed in a color space.

[0077] Next, the profile creation device determines a printer model using the colorimetric values ​​acquired in step S102 (step S103). The printer model is a colorimetric prediction of the image to be printed by the printing device 20 based on the signal values ​​of each color in the YMCKPG color space. * a * b * The printer model can also be said to be a signal value of each color in the YMCKPG color space and the L * a * b* The printer model determined in step S103 is represented by function f1 of equation (1).

[0078] (L * 、a * , b * )=f1(Y, M, C, K, P, G)...(1)

[0079] Next, the profile creation device creates a * a * b * The color space sets the input grid points. Then, the profile creation device will * a * b * The input grid points of the color space setting are mapped to the L that can be printed by the printing device 20. * a * b * The color gamut of the color space (step S104). * a * b * Each input grid point of the color space setting uses a predetermined step size L * a * b * The color space is represented by the signal value.

[0080] Next, the profile creation device determines the L mapped in step S104. * a * b * The signal values ​​of the input grid points in the color space correspond to the signal values ​​of the K color in the YMCKPG color space and the signal values ​​of the special colors, namely, the P color and the G color (step S105). Incidentally, the profile creation device determines the signal values ​​of the K color, the P color, and the G color using the K amount / special color amount determination model determined in advance and stored in the storage unit 35. * a * b * The K amount / special color amount determination model can be said to be a model that represents the K, P, and G color signal values ​​and L * a * b * The function of the relationship between the signal value of the color space is shown as a in equation (2).

[0081] (K, P, G) = a(L * 、a * , b * )…(2)

[0082] The K quantity / special color quantity determination model is based on L *a * b * The signal value of the color space calculates the color conversion conditions of the signal values ​​of K color as the normal color and P color and G color as the special colors. As the K amount / special color amount determination model, a conventionally known model can be used.

[0083] The K amount / special color amount determination model is created, for example, by the following process and stored in the storage unit 35. Here, a case where the profile creation device creates the K amount / special color amount determination model will be described.

[0084] First, the profile creation device prints a colorimetric image on paper using the printing device 20, and obtains the signal value of each color in the YMCKPG color space used for printing the colorimetric image and the L value obtained by colorimetrically measuring the colorimetric image. * a * b * Then, the profile creation device converts L * a * b * The signal value of the color space and the signal values ​​of K, P and G colors in the YMCKPG color space are combined as input, and the conversion function is numerically solved, thereby calculating the remaining signal values ​​of Y, M and C colors in the YMCKPG color space that are consistent in colorimetry.

[0085] Next, the profile creation device determines the colorimetric value of the image reproduced based on the combination of the signal values ​​of K, P, and G in the YMCKPG color space and the calculated signal values ​​of Y, M, and C, and the input L * a * b * Then, the profile creation device determines the color difference of the signal value of the color space based on the determination of the color difference relative to the input L * a * b * The profile creation device determines the K color conversion ratio of the signal value of the color space, and determines the signal value of the K color. Further, the profile creation device determines the K color conversion ratio of the signal value of the input L color space based on the determination of the color difference and the determined K color signal value. * a * b * The P color conversion ratio and the G color conversion ratio of the signal value of the color space determine the signal values ​​of the P color and the G color. The K color conversion ratio, the P color conversion ratio and the G color conversion ratio are respectively the L * a * b * The conversion ratio into the signal values ​​of K color, P color, and G color when the signal value of the color space is converted into the signal value of the YMCKPG color space.

[0086] Through the above steps, the profile creation device can create a * a * b * The K amount / special color amount determination model obtains the signal values ​​of K color, P color, and G color by using the signal values ​​of the color space.

[0087] Next, the profile creation apparatus 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 S103 (step S106). Incidentally, the profile creation apparatus determines the signal values ​​of Y, M, and C colors in the YMCKPG color space by inverse conversion of the function f1 representing the printer model, based on the signal values ​​of K, P, and G colors determined in step S105 and the L mapped in step S104. * a * b * The signal value of each input grid point in the color space determines the signal value of the Y color, M color, and C color in the YMCKPG color space. The inverse conversion of the printer model means performing a color conversion opposite to the color conversion performed by the printer model. The inverse conversion of the printer model in step S106 is represented by the inverse conversion function f1 of the function f1 -1 , as shown in formula (3).

[0088] (Y, M, C) = f1 -1 (L * 、a * 、b * , K, P, G)…(3)

[0089] The profile creation device maps the L in step S104. * a * b * All input grid points in the color space are processed in steps S105 and S106 to determine the signal value of each color in the YMCKPG color space.

[0090] Then, the profile creation device is based on the L * a * b * The signal value of each color in the YMCKPG color space determined by each input grid point in the color space is created by L * a * b * The signal value of the color space is converted into a reference output profile of the signal value of the YMCKPG color space (step S107). Then, the profile creation device stores the created reference output profile in the storage unit 35 of the color conversion device 30 in association with the information related to the printing device 20 and the type of paper (step S108). Through the above steps, the profile creation device ends a series of processes for creating the reference output profile.

[0091] Next, the output profile creation process performed by the profile creation unit 32 of the color conversion device 30 of this embodiment is described. As described above, the profile creation unit 32 creates an output profile using a previously determined reference output profile and a 3DLUT obtained from the color measurement results of an image printed by the printing device 20.

[0092] Figure 5 This is a flowchart showing an example of the process of creating an output profile.

[0093] The profile creation unit 32 acquires paper information, which is information on the type of paper used for printing an image by the printing device 20 (step S201). The profile creation unit 32 displays, for example, an input screen for receiving input of the type of paper on the operation display unit 34 of the color conversion device 30. Then, the profile creation unit 32 acquires paper information, which is information on the type of paper, based on the user's operation on the input screen of the operation display unit 34. Alternatively, the profile creation unit 32 may acquire paper information based on a detection result of a paper sensor or the like that detects the type of paper provided in the printing device 20, for example.

[0094] Next, the profile creation unit 32 uses the reference output profile corresponding to the type of paper to print the color measurement image on the type of paper acquired in step S201 using the printing device 20 (step S202 ).

[0095] Specifically, the profile creation unit 32 first sets L * a * b * Grid points in color space. * a * b * Each grid point in the color space setting uses a predetermined step size L * a * b * Hereinafter, the profile creation unit 32 may express the signal value of the color space. * a * b * The signal value of the grid point set in the color space is expressed as (L * ′、a * ′、b * ′).

[0096] Then, the profile creation unit 32 uses the reference output profile corresponding to the type of paper to generate the L * a * b * The signal value of the grid point set in the color space (L * ′、a * ′、b *′) is converted into a signal value in the YMCKPG color space. In this embodiment, the pair L input to the reference output profile * a * b * The signal value of the grid point set in the color space (L * ′、a * ′、b * ′) is an example of an input value of the first color space.

[0097] Furthermore, when there is no paper type that matches the paper type acquired in step S201 among the paper types associated with the reference output profiles stored in the storage unit 35, the profile creation unit 32 uses the reference output profile associated with the paper type that is closest to the type acquired in step S201. Alternatively, the profile creation unit 32 may use a reference output profile that is determined in advance among a plurality of reference output profiles stored in the storage unit 35.

[0098] Then, the profile creation unit 32 inputs the colorimetric image data represented by the signal value of the YMCKPG color space converted by the reference output profile to the printing device 20. Then, the printing device 20 uses the colorimetric image data input by the profile creation unit 32 to print the colorimetric image on the type of paper acquired in step S201.

[0099] The color measurement image that the profile creation unit 32 causes the printer 20 to print in step S202 is an example of a print image. * a * b * The signal value of each grid point in the color space (L * ′、a * ′、b * An image in which a plurality of small blocks are arranged is an image data represented by the signal value of the YMCKPG color signal obtained by conversion.

[0100] Next, the profile creation unit 32 acquires the color measurement value (step S203), which is the result of the color measurement of the color measurement image formed on the paper by the color measurement unit 33. Incidentally, the profile creation unit 32 acquires information obtained by reading each small block of the color measurement image by the color measurement unit 33 as the color measurement value. In this example, the profile creation unit 32 acquires the color measurement value for L * a * b * The colorimetric value represented by the signal value in the color space.

[0101] Next, the profile creation unit 32 determines a color prediction model using the colorimetric values ​​acquired in step S203 (step S204 ).

[0102] Here, the profile creation unit 32 generates a reference output profile based on the L input to the reference output profile. * a * b * The signal value of each grid point in the color space (L * ′、a * ′、b * ′), determine the L of the image predicted to be printed by the printing device 20 * a * b * Color prediction model of signal value in color space: The color prediction model determined in step S204 is shown as function f2 in equation (4).

[0103] (L * 、a * , b * )=f2(L * ′、a * ′、b * ′)…(4)

[0104] The color prediction model is an example of a first correspondence relationship that converts an input value in a first color space into a colorimetric value in the first color space.

[0105] Next, the profile creation unit 32 generates a profile based on the L color of the image to be printed by the printing device 20 by inverse conversion of the color prediction model determined in step S204. * a * b * The signal value in the color space determines the L input to the reference output profile. * a * b * The signal value of the color space (L *′ 、a *′ , b *′ ) (step S205). The inverse conversion of the color prediction model means performing a color conversion opposite to the color conversion performed by the color prediction model. The inverse conversion of the color prediction model in step S205 is represented by the inverse conversion function f2 of function f2 -1 , as shown in formula (5).

[0106] (L * ′、a * ′、b * ′)=f2 -1 (L * 、a * , b * )…(5)

[0107] Next, the profile creation unit 32 determines the L color of the image to be printed by the printing device 20 based on the result of the inverse conversion of the color prediction model in step S205. * a* b * The signal value of the color space is converted into the L input of the reference output profile * a * b * The signal value of the color space (L * ′、a * ′、b * In this embodiment, the profile creation unit 32 creates a color conversion condition for L * a * b * The signal value of the color space (L * 、a * , b * ) is converted to L * a * b * The signal value of the color space (L * ′、a * ′、b * ′) as the color conversion condition.

[0108] Next, the profile creation section 32 synthesizes the 3DLUT created in step S206 and the reference output profile. Thus, the profile creation section 32 creates a profile that will not depend on the LUT of the printing device 20. * a * b * The signal value of the color space is converted into an output profile of the signal value of the YMCKPG color space that can be printed by the printing device 20 (step S207).

[0109] Then, the profile creation unit 32 stores the output profile created in step S207 in the storage unit 35 (step S208 ), and ends the series of processing.

[0110] As described above, in the color conversion device 30 , the color conversion section 31 performs color conversion processing of image data input from the input device 10 using the output profile created by the profile creation section 32 .

[0111] Specifically, the color conversion unit 31 converts the signal value in the RGB color space representing the image data input from the input device 10 into the L color space using the input profile stored in the storage unit 35. * a * b * Next, the color conversion section 31 uses the output profile created by the profile creation section 32 to convert L * a * b * The signal value of the color space is converted into the signal value of the YMCKPG color space.

[0112] As described above, in this embodiment, the profile creation unit 32 of the color conversion device 30 acquires L * a * b * The color value of the color space, the L * a * b * The colorimetric value of the color space is independent of the L of the printing device 20. * a * b * The result obtained by converting the signal value of the color space into the signal value of the YMCKPG color space depending on the printing device 20 and measuring the color of the color measurement image printed by the printing device 20. Then, the profile creation unit 32 creates a 3DLUT indicating the L input to the printing device 20. * a * b * The signal value of the color space is related to L * a * b * The corresponding relationship between the color measurement values ​​in the color space, the L * a * b * The colorimetric value of the color space is a result obtained by colorimetrically measuring the colorimetric image printed by the printing device 20 .

[0113] The profile creation unit 32 also compares the 3DLUT and the L * a * b * The reference output profile is synthesized by converting the signal value of the color space into the signal value of the YMCKPG color space, and creating an L image to be input to the printing device 20. * a * b * An output profile that converts a signal value in a color space into a signal value in a YMCKPG color space.

[0114] Then, the color conversion section 31 of the color conversion device 30 converts the signal value of the RGB color space representing the image data input from the input device 10 or the like into the signal value of the YMCKPG color space using the output profile created by the profile creation section 32 and the input profile determined in advance.

[0115] As a result, for example, the color reproducibility of the image printed by the printing device 20 can be improved compared to a case where color conversion of image data input from an input device 10, etc. is performed using a uniform output profile determined in advance based on the printing device 20, etc. instead of using the result obtained by colorimetrically measuring the colorimetric image.

[0116] In addition, in the color conversion device 30 of the present embodiment, the output profile is created by synthesizing the 3DLUT and a previously determined reference output profile, for example, the output profile represented by L is created by numerically solving the color measurement result based on the color measurement image. * a * b * Compared with the case where an output profile is created based on a color conversion condition based on the correspondence relationship between a color space and a YMCKPG color space, the time required for creating an output profile can be shortened.

[0117] Thus, when the color conversion device 30 performs color conversion on image data input from the input device 10 or the like using the output profile, it is possible to shorten the time required for color conversion.

[0118] Here, in the color conversion device 30 described above, the reference output profile is determined in advance for each of the plurality of types of paper used for printing an image by the printing device 20, and is stored in the storage unit 35 in association with the type of paper. However, in the color conversion device 30, the reference output profile may be determined based on a type of paper determined in advance, that is, standard paper (e.g., high-quality paper).

[0119] In this case, the profile creation section 32 may create an output profile using a reference output profile determined based on standard paper regardless of the paper information acquired in the above-described step S201 .

[0120] In addition, in the color conversion device 30, when the color difference between the paper used for printing the image performed 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 use the reference output profile instead of creating an output profile to convert the signal value of the RGB color space representing the image data input from the input device 10, etc. into the signal value of the YMCKPG color space.

[0121] When the color difference between the paper used for printing the image by the printing device 20 and the standard paper is within a predetermined range, the color reproducibility of the image printed by the printing device 20 is unlikely to be reduced by using the reference output profile for color conversion. Furthermore, when the color difference between the paper used for printing the image by the printing device 20 and the standard paper is within a predetermined range, the reference output profile is used for color conversion without creating an output profile, thereby eliminating the time required for creating an output profile and shortening the time required for color conversion.

[0122] Here, the case where the color difference between the paper used for printing the image performed by the printing device 20 and the standard paper associated with the reference output profile is within a predetermined range may include the case where the paper used for printing the image performed by the printing device 20 is consistent with the standard paper, the case where the color of the paper detected by a paper sensor provided in the printing device 20 is consistent with the standard paper, etc.

[0123] In addition, as the signal value representing the image data input from the input device 10 to the color conversion device 30, the signal value of the RGB color space is exemplified, but the present invention is not limited thereto. For example, the signal value representing the image data input from the input device 10 to the color conversion device 30 may be a signal value represented by a color space such as YMCK or YMCKRGB in addition to the RGB color space.

[0124] In addition, the output profile created by the color conversion device 30 will not depend on the color space of the device, i.e., L * a * b * The signal value of the color space is converted into the signal value of the YMCKPG color space, but the color space is not limited to L depending on the device * a * b * Color space. For example, it can also be XYZ color space, Yxy color space, L * u * v * Color space, HLS color space, etc.

[0125] In the above-described embodiment, the output profile created by the profile creation unit 32 of the color conversion device 30 is L consisting of three variables. * a * b * The signal value of the color space is converted into the signal value of the YMCKPG color space consisting of six variables including the normal color and two special colors. However, as long as the output profile converts the L consisting of three variables * a * b * The signal value of the color space is converted into the signal value of the color space composed of five or more variables including normal colors and special colors, and the special color can be one color or three or more colors.

[0126] In general, the more special colors there are, in other words, the more variables there are in the converted color space, the longer it takes to create an output profile. * a * b *When the signal value of the color space is converted into the signal value of the color space with more variables, the color conversion device 30 of this embodiment can be used more effectively.

[0127] As described above, the embodiments of the present invention have been described, but the technical scope of the present invention is not limited to the scope described in the above embodiments. According to the description of the claims, various changes or improvements to the above embodiments are also included in the technical scope of the present invention.

[0128] The processor in the above-mentioned embodiment refers to a processor in a broad sense, which includes, in addition to general-purpose processors (such as CPU (=Central Processing Unit)), special-purpose processors (such as GPU (=Graphical Processing Unit), ASIC (=Application Specific Integrated Circuit), FPGA (=Field Programmable Gate Array), programmable logic devices, etc.).

[0129] In addition, the operation of the processor in this embodiment can be performed by a single processor alone, or can be performed collaboratively by multiple processors located in physically separate locations. In addition, the execution order of each operation in the processor is not limited to the order described in the above-mentioned embodiment, and can also be changed individually.

[0130] <Note> (((1)))

[0132] A color conversion device,

[0133] It has a processor,

[0134] The processor

[0135] A first color conversion table is created, wherein the first color conversion table represents a correspondence between an input value in a first color space that is independent of a printing device and a color measurement result of a printed image that is converted from the input value into a signal value in a second color space that is dependent on the printing device and printed by the printing device, namely, a color measurement value in the first color space.

[0136] The input signal value of the first color space is converted into a signal value of the second color space using the second color conversion table and the first color conversion table, which is predetermined according to the printing apparatus and converts the signal value of the first color space into a signal value of the second color space. (((2)))

[0138] The color conversion device according to (((1))), wherein:

[0139] The processor acquires paper information which is information related to a type of paper on which an image is printed by the printing device, and creates the first color conversion table based on the paper information. (((3)))

[0141] The color conversion device according to (((2))), wherein:

[0142] The second color conversion table is determined based on a predetermined standard paper.

[0143] The processor converts the signal value of the first color space into the signal value of the second color space using the second color conversion table when the color difference between the paper on which the image is printed by the printing device and the standard paper is within a predetermined range. (((4)))

[0145] The color conversion device according to (((2))), wherein:

[0146] The second color conversion table is determined according to the type of paper.

[0147] The processor creates the first color conversion table based on the paper information and using the colorimetric values ​​of the printed image printed based on the signal values ​​of the second color space, wherein the signal values ​​of the second color space are obtained by converting the input values ​​according to the second color conversion table corresponding to the type of paper. (((5)))

[0149] The color conversion device according to any one of (((1))) to (((4))), wherein:

[0150] The processor creates the first color conversion table that converts the colorimetric value of the first color space into a signal value of the first color space corresponding to the input value. (((6)))

[0152] The color conversion device according to (((5))), wherein:

[0153] The processor creates the first color conversion table by creating a first correspondence relationship that converts the input value of the first color space into the colorimetric value of the first color space, and performing an inverse conversion on the first correspondence relationship. (((7)))

[0155] The color conversion device according to any one of (((1))) to (((6))), wherein:

[0156] The processor converts the signal value of the first color space composed of three variables into the signal value of the second color space composed of five or more variables including the signal value of the normal color, which is the color usually used, and the signal value of the special color, which is the color other than the normal color. (((8)))

[0158] The color conversion device according to any one of (((1))) to (((7))), wherein:

[0159] The processor

[0160] synthesizing the first color conversion table and the second color conversion table to create an output profile that converts an input signal value of the first color space into a signal value of the second color space and outputs the converted signal value,

[0161] The signal value of the first color space converted from the signal value of the third color space depending on the input device according to the input profile is converted into the signal value of the second color space according to the output profile. (((9)))

[0163] A color conversion table creation device,

[0164] It has a processor,

[0165] The processor

[0166] A first color conversion table is created, wherein the first color conversion table represents a correspondence between an input value in a first color space that is independent of a printing device and a color measurement result of a printed image that is converted from the input value into a signal value in a second color space that is dependent on the printing device and printed by the printing device, namely, a color measurement value in the first color space.

[0167] A second color conversion table that is predetermined according to the printing device and converts the signal value of the first color space into the signal value of the second color space is synthesized with the first color conversion table to create a third color conversion table that converts the input signal value of the first color space into the signal value of the second color space. (((10)))

[0169] A procedure,

[0170] It enables computers to:

[0171] A function of creating a first color conversion table, the first color conversion table indicating a correspondence between an input value in a first color space that is independent of a printing device and a color measurement result of a printed image that is converted from the input value into a signal value in a second color space that is dependent on the printing device and printed by the printing device, i.e., a color measurement value in the first color space; and

[0172] A function of synthesizing a second color conversion table predetermined according to the printing device and converting a signal value of the first color space into a signal value of the second color space, and converting the input signal value of the first color space into a signal value of the second color space.

[0173] According to the color conversion device of (((1))), compared with a case where a color conversion table is created by numerically solving a conversion condition created based on a color measurement result of a print image printed by a printing device, the time required for conversion from a signal value in a first color space that is not dependent on the printing device to a signal value in a second color space that is dependent on the printing device can be shortened.

[0174] According to the color conversion device of (((2))), the color reproducibility of the image printed on the paper can be improved compared with the case where the first color conversion table is not created based on the paper information.

[0175] According to the color conversion device of (((3))), the time required for converting the signal value of the first color space to the signal value of the second color space can be shortened compared to the case where the first color conversion table is created when the color difference between the paper and the standard paper is within a predetermined range.

[0176] According to the color conversion device of (((4))), the color reproducibility of the image printed on the paper can be improved compared to the case where the second color conversion table is not determined according to the type of paper.

[0177] According to the color conversion device of (((5))), the time required for conversion from the signal value of the first color space to the signal value of the second color space can be shortened compared to the case where a color conversion table is created by numerically solving the conversion conditions created based on the color measurement results of the print image printed by the printing device.

[0178] According to the color conversion device of (((6))), the time required for conversion from the signal value of the first color space to the signal value of the second color space can be shortened compared to the case where a color conversion table is created by numerically solving the conversion conditions created based on the color measurement results of the print image printed by the printing device.

[0179] According to the color conversion device of (((7))), it is possible to shorten the time required for conversion from the signal value of the first color space to the signal value of the second color space of five or more including normal colors and special colors.

[0180] According to the color conversion device of (((8))), the time required for conversion from the signal value of the first color space to the signal value of 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 synthesized to create an output profile.

[0181] According to the color conversion table creation device of (((9))), the time required for conversion from a signal value in a first color space that is not dependent on the printing device to a signal value in a second color space that is dependent on the printing device can be shortened compared to a case in which a color conversion table is created by numerically solving a conversion condition created based on a color measurement result of a print image printed by a printing device.

[0182] According to the procedure of (((10))), compared with a case where a color conversion table is created by numerically solving a conversion condition created based on a color measurement result of a print image printed by a printing device, the time required for conversion from a signal value in a first color space that is not dependent on the printing device to a signal value in a second color space that is dependent on the printing device can be shortened.

Claims

1. A color conversion device, characterized in that: With processor, The processor A first color conversion table is created, wherein the first color conversion table represents a correspondence between an input value in a first color space that is independent of a printing device and a color measurement result of a printed image that is converted from the input value into a signal value in a second color space that is dependent on the printing device and printed by the printing device, namely, a color measurement value in the first color space. The input signal value of the first color space is converted into a signal value of the second color space using the second color conversion table and the first color conversion table, which is predetermined according to the printing apparatus and converts the signal value of the first color space into a signal value of the second color space.

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

3. The color conversion device according to claim 2, wherein: The second color conversion table is determined based on a predetermined standard paper. The processor converts the signal value of the first color space into the signal value of the second color space using the second color conversion table when the color difference between the paper on which the image is printed by the printing device and the standard paper is within a predetermined range.

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

5. The color conversion device according to any one of claims 1 to 4, wherein: The processor creates the first color conversion table that converts the colorimetric value of the first color space into a signal value of the first color space corresponding to the input value.

6. The color conversion device according to claim 5, wherein: The processor creates the first color conversion table by creating a first correspondence relationship that converts the input value of the first color space into the colorimetric value of the first color space, and performing an inverse conversion on the first correspondence relationship.

7. The color conversion device according to any one of claims 1 to 6, wherein: The processor converts the signal value of the first color space composed of three variables into the signal value of the second color space composed of five or more variables including the signal value of the normal color, which is the color usually used, and the signal value of the special color, which is the color other than the normal color.

8. The color conversion device according to any one of claims 1 to 7, wherein: The processor synthesizing the first color conversion table and the second color conversion table to create an output profile that converts an input signal value of the first color space into a signal value of the second color space and outputs the converted signal value, The signal value of the first color space converted from the signal value of the third color space depending on the input device according to the input profile is converted into the signal value of the second color space according to the output profile.

9. A color conversion table creation device, characterized in that: With processor, The processor A first color conversion table is created, wherein the first color conversion table represents a correspondence between an input value in a first color space that is independent of a printing device and a color measurement result of a printed image that is converted from the input value into a signal value in a second color space that is dependent on the printing device and printed by the printing device, namely, a color measurement value in the first color space. A second color conversion table that is predetermined according to the printing device and converts the signal value of the first color space into the signal value of the second color space is synthesized with the first color conversion table to create a third color conversion table that converts the input signal value of the first color space into the signal value of the second color space.

10. A storage medium, which is a computer-readable medium and stores a program for causing a computer to execute a process, characterized in that: The process has: A step of creating a first color conversion table, wherein the first color conversion table represents a correspondence between an input value in a first color space that is independent of a printing device and a color measurement result of a printed image that is converted from the input value into a signal value in a second color space that is dependent on the printing device and printed by the printing device, namely, a color measurement value in the first color space; as well as A step of synthesizing a second color conversion table predetermined according to the printing device and converting a signal value of the first color space into a signal value of the second color space, and the first color conversion table, and converting an input signal value of the first color space into a signal value of the second color space.

11. A color conversion method, characterized in that: have: A step of creating a first color conversion table, wherein the first color conversion table represents a correspondence between an input value in a first color space that is independent of a printing device and a color measurement result of a printed image that is converted from the input value into a signal value in a second color space that is dependent on the printing device and printed by the printing device, namely, a color measurement value in the first color space; as well as The step of converting the input signal value of the first color space into the signal value of the second color space using the second color conversion table determined in advance according to the printing device and the first color conversion table for converting the signal value of the first color space into the signal value of the second color space.

Images