JP2012175253A - Profile generation device, profile generation method, and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To generate a profile of which color reproduction is improved, while restricting the decrease of a gamut in a device.SOLUTION: A profile generation device generates a profile for converting a first color in a first color space into a second color in a second color space. A multi-dimensional look-up table (LUT) generation part 104 generates a multi-dimensional LUT for allowing the first color to be a value on the input lattice point of the multi-dimensional LUT. A profile output part 105 generates a profile by using the multi-dimensional LUT and outputs it.

Description

  The present invention relates to a technique for generating a profile for converting a first color in a first color space into a second color in a second color space.

  In general color matching between different devices, input data that is RGB data or CMYK data is converted into XYZ data in a color space (hereinafter referred to as PCS) that does not depend on the input device. Since colors outside the color reproduction range of the output device are not represented by the output device, the input data is converted to data in a color space independent of the input device so that all the colors fall within the color reproduction range of the output device. On the other hand, color space compression is performed. After color space compression is performed, the input data is converted from a color space that does not depend on the input device to CMYK data in a color space that depends on the output device. In this way, for example, color matching between different devices can be realized by passing through XYZ values (or Lab values) that do not depend on the input device.

  As a general color matching technique, for example, a technique disclosed in Non-Patent Document 1 is known. In the technology disclosed in Non-Patent Document 1, AToBxTag and BToAxTag are stored in the printer profile in order to perform mutual conversion between PCS and device-dependent colors. AToBxTag is a tag that describes color conversion from a device-dependent color space to a PCS using an LUT or the like, and BToAxTag is a tag that describes color conversion from a PCS to a device-dependent color space using an LUT or the like. AToBxTag and BtoATag are composed of a combination of a matrix, a one-dimensional LUT, and a multi-dimensional LUT, and the color conversion module performs color conversion with reference to these tags.

International Color Consortium, Specification ICC. 1: 2004-10, (Profile Version 4.2.0.0)

  The multidimensional LUT is a table storing device-dependent color values corresponding to the thinned Lab grid points. For this reason, when a Lab value between grid points is input, an interpolation process is performed, and a desired value may not be obtained. For example, there is a problem that the color gamut of the printer that can actually be used is reduced in the multidimensional LUT interpolation processing using the Lab value as an input.

  In FIG. 10, the grid represents a Lab grid of a multi-dimensional LUT of BtoAxTag, and the circles correspond to the yellow solid value (C, M, Y, K) = (0, 0, 255, 0) of the printer. The Lab value 1001 and the solid line represent the color gamut of the printer. Originally, when the Lab value 1001 is input to the multidimensional LUT, it is expected that (C, M, Y, K) = (0, 0, 255, 0) as the device-dependent color value to be output. Is done. However, since the device-dependent color value for the Lab value 1001 is actually interpolated by the grid points 1002 and 1003 outside the printer gamut and the grid points 1006 and 1007 within the printer gamut, (C, M, Y, K) = (0, 0, 255, 0). This is because there are no device-dependent color values corresponding to the grid points 1002 and 1003 outside the printer gamut, so the grid points 1002 and 1003 are once mapped to the outermost values 1004 and 1005 (♦ points) in the printer gamut. This is because the value of the device dependent color corresponding to that point is stored. For this reason, the result of the interpolation calculation when the Lab value 1001 at the point O is input becomes a point ▲, and the color gamut decreases as shown by the broken line.

  Even in corporate color output where accurate single color output is required, if the important color (Lab value) specified in the NamedColor profile is input, the output value is approximated by interpolation of the multidimensional LUT. There is a problem that it is difficult to reproduce colors. Also, in creating a profile, the color space of the input device is limited to sRGB, and R, G, B, C, M, Y solid values, RGB values such as sky and skin color, and corresponding Lab values Color design is done with the important color. However, even when the above important colors are input, there is a problem in that accurate color reproduction cannot be performed because the output value becomes an approximate value by interpolation of the multidimensional LUT.

  Therefore, an object of the present invention is to create a profile that improves color reproduction while suppressing a decrease in the color gamut of the device.

  A profile generation apparatus according to the present invention is a profile generation apparatus that generates a profile for converting a first color in a first color space into a second color in a second color space, wherein the first color is the first color. A multi-dimensional LUT generating means for generating the multi-dimensional LUT such that the value becomes a value on an input lattice point of the multi-dimensional LUT, and a profile generating means for generating the profile using the multi-dimensional LUT. And

  According to the present invention, it is possible to create a profile with improved color reproduction while suppressing a decrease in the color gamut of the device.

It is a figure which shows the structure of the profile production apparatus which concerns on 1st-3rd embodiment. 6 is a flowchart illustrating color conversion profile creation processing according to the first embodiment. It is a figure which shows the colorimetric value (Lab value) of the RGB value showing the outermost point of a printer. It is a figure which shows the relationship between the input value and output value in a one-dimensional LUT. It is a flowchart which shows the detail of step S203 of FIG. It is a flowchart which shows the detail of step S204 of FIG. It is a figure which shows the example of the Lab value designated with a NamedColor profile. It is a figure which shows the example of the Lab value corresponding to sRGB value and AdobeRGB. It is a figure which shows the structure of the profile creation apparatus which concerns on 4th Embodiment. It is a figure which shows the example of the Lab lattice of the multidimensional LUT of BtoAxTag.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments to which the invention is applied will be described in detail with reference to the accompanying drawings.

  First, the first embodiment will be described. In the first embodiment, a method for creating a BToAxTag of an ICC profile whose PCS is Lab will be described as an example of a general profile. Here, the multi-dimensional LUT (look-up table) of the ICC profile has a structure in which the input grid points are evenly arranged for each dimension. In this embodiment, in order to suppress a decrease in the printer color gamut, the one-dimensional LUT is set so that the colorimetric values of the outermost points of the printer color gamut become values on the input grid points of the multidimensional LUT. Generate.

  FIG. 1 is a diagram illustrating a configuration of a profile creation device according to the first embodiment. The important color input unit 101 inputs an important color such as the outermost point (outermost value) of the printer color gamut. The lattice point information input unit 102 inputs lattice point information such as the number of lattice points of the one-dimensional LUT or multidimensional LUT of the ICC profile to be created. The one-dimensional LUT generation unit 103 generates a one-dimensional LUT such that the value of the important color becomes a value on the input grid point of the multidimensional LUT based on the input important color and grid point information. The multidimensional LUT generation unit 104 calculates a device-dependent color value of the printer corresponding to the input grid point of the multidimensional LUT and generates a multidimensional LUT. The profile output unit 105 stores the generated one-dimensional LUT and multi-dimensional LUT in an ICC profile format and outputs them as a color conversion profile. Note that the profile creation apparatus according to the present embodiment has a configuration that is an application example of the profile generation apparatus. The important color is an example of the first color in the first color space, and the device-dependent color value of the printer is an example of the second color in the second color space.

  Next, color conversion profile creation processing in the first embodiment will be described with reference to FIG. FIG. 2 is a flowchart showing color conversion profile creation processing in the first embodiment.

  In step S <b> 201, the important color input unit 101 inputs an important color such as the outermost point of a printer that creates a color conversion profile in accordance with a user operation. For example, when the printer is an RGB printer, colorimetric values (Lab values) of RGB values representing important colors are input as shown in FIG. FIG. 3 is a diagram showing colorimetric values (Lab values) of RGB values representing the outermost points of the printer. In FIG. 3, colorimetric values (Lab values) for two RGB values are shown in FIGS. 3 (a) and 3 (b). In the following description, it is assumed that a Lab value is input as an important color in step S201. Note that the number of important color input points is arbitrary. In step S202, the grid point information input unit 102 inputs the number of grid points M of the one-dimensional LUT and the number of grid points N of the multidimensional LUT of the ICC profile to be created in accordance with a user operation.

  In step S203, the one-dimensional LUT generation unit 103 calculates the input Lab value from the input Lab value, the number of lattice points M of the one-dimensional LUT, and the number of lattice points N of the multidimensional LUT on the input lattice point of the multidimensional LUT. Three one-dimensional LUTs that become values are generated for L value conversion, a value conversion, and b value conversion. Hereinafter, the process of step S203 will be described in detail with reference to FIGS. Here, a case where a one-dimensional LUT for L value conversion is generated will be described.

  FIG. 4 is a diagram showing the relationship between the input value and the output value in the one-dimensional LUT. The horizontal axis shows the input value of the one-dimensional LUT, and the vertical axis shows the output value of the one-dimensional LUT. Both the input value and the output value range from 0 to 1. The vertical grid represents the input grid points of the one-dimensional LUT, and there are M at intervals of 1 / (M−1). The horizontal grid represents the values on the input grid points of the multidimensional LUT, and there are N grids with an interval of 1 / (N−1). FIG. 5 is a flowchart showing details of step S203. In step S501 in FIG. 5, the one-dimensional LUT generation unit 103 normalizes the L value of the input Lab value from 0 to 1, and then uses the following equation 1 to calculate the input value on the input lattice point of the multidimensional LUT. To the value of.

  Here, INT () is a function that returns a value rounded to an integer close to 0, P is a normalized L value (the x point in FIG. 4), and P ′ is a value on an input lattice point of the multidimensional LUT. (A point in FIG. 4). In step S502, the one-dimensional LUT generation unit 103 calculates an output value (dots in FIG. 4) corresponding to the input lattice points of the one-dimensional LUT that sandwich the P value. Here, the intersection of the straight line with the inclination 1 passing through the ▲ point in FIG. 4 and the input grid point sandwiching the P value is calculated, and this value is set as the output value corresponding to the input grid point sandwiching the P value. Here, in the case of a straight line passing through a ▲ point, the slope value may be the slope of a straight line connecting adjacent X points, or may be the slope of a straight line connecting adjacent ▲ points, and is arbitrary.

  In step S503, the one-dimensional LUT generation unit 103 determines whether or not the processing in steps S501 and S502 has been executed for all important color points (here, all L value points). If the processes in steps S501 and S502 are not executed for all L values, the process returns to step S501. On the other hand, when the processes of steps S501 and S502 are executed for all L values, the process proceeds to step S504.

  In step S504, the one-dimensional LUT generation unit 103 calculates an output value (a point in FIG. 4) corresponding to the input grid point of the other one-dimensional LUT. Here, the intersection point between the straight line connecting the dots ● calculated in step S503 (dotted line in FIG. 4) and the input grid point for which the output value is not calculated is calculated, and this value is set as the output value. Here, the ● points at both ends are straight lines connecting the maximum and minimum values (□ points in FIG. 4) of the input grid points. By performing the above processing, it is possible to generate a one-dimensional LUT such that the input Lab value becomes a value on an input lattice point of the multidimensional LUT. The one-dimensional LUT generation unit 103 generates the one-dimensional LUT by performing the above processing for the a value and the b value.

  Returning to the description of FIG. In step S204, the multidimensional LUT generation unit 104 generates a multidimensional LUT from the created one-dimensional LUT and the color reproduction data of the printer that is stored in advance. Here, step S204 will be described in detail with reference to FIG. FIG. 6 is a flowchart showing details of step S204.

  In step S601, the multidimensional LUT generation unit 104 inputs uniform grid points (L1, a1, b1). Here, since the number of grid points of the multi-dimensional LUT is N points, the L value is a value obtained by evenly cutting a value from 0 to 100 at the N point, and the a value and the b value are equally cut from -128 to 127 at the N point. Value grid points (N × N × N points) are input. In step S602, the multidimensional LUT generation unit 104 converts the input uniform grid points (L1, a1, b1) using the inverse function of the one-dimensional LUT generated in step S203 (L2, a2, b2). ) Is calculated.

  In step S603, the multidimensional LUT generation unit 104 performs color space compression on (L2, a2, b2) calculated in step S602, and the device-dependent color values (R, G, B) of the printer corresponding to the values. Is calculated from the color reproduction data of the printer. In step S604, the multidimensional LUT generation unit 104 determines whether steps S601 to S603 have been executed for all grid points. If steps S601 to S603 have been executed for all grid points, the process ends. On the other hand, when steps S601 to S603 have not been executed for all grid points, the process returns to step S602. A multidimensional LUT is generated by the above processing.

  Returning to the description of FIG. In step S205, the profile output unit 105 stores the one-dimensional LUT and the multidimensional LUT in the ICC profile format and outputs them as a color conversion profile.

  As described above, it is possible to create a color conversion profile with improved color reproduction while suppressing a decrease in the color gamut of the printer. In the present embodiment, the Lab value is used for the PCS, but the same result can be obtained even with the XYZ value.

  Next, a second embodiment will be described. Even in corporate color output where accurate single color output is required, when the important color (Lab value) specified in the NamedColor profile is input, the output value is approximated by interpolation of the multidimensional LUT. There is a problem that color reproduction is impossible. In the second embodiment, in order to solve the above problem, the user inputs a Lab value specified by the NamedColor profile, and the Lab value becomes a value on the input grid point of the multidimensional LUT. An example of creating a color conversion profile in which the color reproduction of the Lab value specified by the NamedColor profile is improved by generating a dimension LUT will be described.

  Since the profile creation apparatus according to the second embodiment has the same configuration as that shown in FIG. 1, the following description will be made using the same reference numerals as those in FIG. The processing of the profile creation device according to the second embodiment is the same as that of the first embodiment except for step S201 in the flowchart of FIG. In step S201 in the second embodiment, the important color input unit 101 inputs a Lab value specified by the NamedColor profile in accordance with a user operation. Here, for example, as shown in FIG. 7, the Lab value specified by the NamedColor profile is input.

  As described above, in the second embodiment, it is possible to create a color conversion profile that improves the color reproduction of the Lab value specified by the NamedColor profile.

  Next, a third embodiment will be described. Conventionally, when creating a color conversion profile, the input color space is limited to sRGB, and R, G, B, C, M, Y solid values, RGB values such as sky and skin color, and corresponding Lab values are set. Color design is performed as an important color. However, even when the above important colors are input, there is a problem that accurate color reproduction cannot be performed because the output value becomes an approximate value by interpolation of the multidimensional LUT. In the third embodiment, in order to solve the above problem, a one-dimensional LUT is generated so that a user inputs an important color and the important color becomes a value on an input grid point of the multi-dimensional LUT. Thus, an example of creating a color conversion profile with improved color reproduction of important colors will be described.

  Since the profile creation apparatus according to the third embodiment has the same configuration as that shown in FIG. 1, the following description will be given using the same reference numerals as those in FIG. 1. The processing of the profile creation device according to the second embodiment is the same as that of the first embodiment except for step S201 in the flowchart of FIG. In step S201 in the third embodiment, the important color input unit 101 inputs Lab values corresponding to a plurality of sRGB values in accordance with a user operation. For example, the Lab value corresponding to the sRGB value as shown in FIG. The solid values of R, G, B, C, M, and Y, the color of the sky and skin that are important in printing, and the like. Other processes are the same as those in the first embodiment.

  As described above, in the third embodiment, it is possible to create a color conversion profile with improved color reproduction of important colors. In this embodiment, an example of sRGB is used, but a standard color space that is generally used such as Adobe RGB as shown in FIG. 8B may be used.

  Next, a fourth embodiment will be described. In the first to third embodiments, the case where the color conversion profile in which the input grid points of the multidimensional LUT are uniform has been described. However, the first to third embodiments are configured by non-uniform multidimensional LUTs that do not include the one-dimensional LUT. It may be a color conversion profile.

  FIG. 9 is a diagram illustrating a configuration of a profile creation device according to the fourth embodiment. The important color input unit 901 inputs an important color such as the outermost point of the printer color gamut. The grid point information input unit 902 inputs non-uniform input grid point information of the multidimensional LUT. The multi-dimensional LUT creation unit 903 performs non-uniform multi-dimensional such that the value of the important color becomes the value on the input grid point of the multi-dimensional LUT based on the input important color and the input grid point information of the multi-dimensional LUT. LUT input lattice points are generated. Then, the multidimensional LUT creation unit 903 calculates a device-dependent color value of the printer corresponding to the input lattice point of the multidimensional LUT and generates a multidimensional LUT. The profile output unit 905 stores the generated multidimensional LUT in a profile format and outputs it as a color conversion profile.

  In the first to fourth embodiments, the method for creating the BToAxTag of the ICC profile has been described as an example of a general profile. In addition to the ICC profile, the same effect can be obtained as long as the color conversion profile format has at least a one-dimensional LUT followed by a multidimensional LUT.

  The present invention can also be realized by executing the following processing. That is, software (program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various storage media, and a computer (or CPU, MPU, or the like) of the system or apparatus reads the program. It is a process to be executed.

Claims (11)

A profile generation device that generates a profile for converting a first color in a first color space into a second color in a second color space,
Multidimensional LUT generation means for generating the multidimensional LUT such that the first color becomes a value on an input lattice point of the multidimensional LUT;
And a profile generation unit configured to generate the profile using the multidimensional LUT. One-dimensional LUT generation means for generating a one-dimensional LUT for converting the first color into a value on an input grid point of the multi-dimensional LUT;
The multidimensional LUT generation unit generates the multidimensional LUT by converting lattice points of the multidimensional LUT based on the one-dimensional LUT, and the profile generation unit includes the one-dimensional LUT and the multidimensional LUT. The profile generation apparatus according to claim 1, wherein the profile is generated using an LUT.   The profile generation apparatus according to claim 2, wherein the input grid points of the multidimensional LUT are evenly arranged.   The profile generation apparatus according to claim 1, wherein the input grid points of the multidimensional LUT are non-uniformly arranged.   The profile generation apparatus according to claim 2, wherein the one-dimensional LUT generation unit calculates an output value corresponding to an input lattice point of the one-dimensional LUT that sandwiches the first color.   6. The profile generation apparatus according to claim 1, wherein the first color is an outermost value of a color gamut of a device for which the profile is to be created.   The profile generation apparatus according to claim 1, wherein the first color is a value specified by a NamedColor profile.   The profile generation apparatus according to claim 1, wherein the first color is a value designated in a standard color space.   9. The profile generation apparatus according to claim 8, wherein the standard color space is sRGB or AdobeRGB. A profile generation method executed by a profile generation device that generates a profile for converting a first color in a first color space to a second color in a second color space,
A multidimensional LUT generation step for generating the multidimensional LUT such that the first color becomes a value on an input lattice point of the multidimensional LUT;
And a profile generation step of generating the profile using the multidimensional LUT. A program for causing a computer to execute a profile generation method executed by a profile generation apparatus that generates a profile for converting a first color in a first color space into a second color in a second color space. And
A multidimensional LUT generation step for generating the multidimensional LUT such that the first color becomes a value on an input lattice point of the multidimensional LUT;
A program for causing a computer to execute a profile generation step of generating the profile using the multidimensional LUT.

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