JP2012178737A - Profile creation method, profile creation apparatus, image processing apparatus for performing color conversion using profile, and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform more natural color reproduction with excellent gradation with respect to data outside an output color gamut irrespective of the color gamut shape of an output device.SOLUTION: An area in a color space in which lattice points of a profile are to be defined is divided, and a moving range of a focal color defined for each divided area is switched. Then, the moving ranges of at least two defined focal colors are set so as not to match each other and so as to have a part in which the ranges overlap each other. This enables data outside an output color gamut to be mapped so that intended color reproduction is realized irrespective of the color gamut shape of an output device.

Description

  The present invention relates to a profile creation method, a profile creation apparatus, an image processing apparatus and an image processing system that perform color conversion using a profile, and more specifically, color processing that performs gamut mapping for converting a color gamut of an input device to a color gamut of an output device. It is about.

  In recent years, networks such as the Internet have become widespread, and many users are connected to various devices. And in environments with diverse input / output environments such as digital cameras, image scanners, and ink jet printers, for example, when hard-copying color image signals from a monitor with a certain color reproduction range using a printer with a narrower color reproduction range As described above, input / output of color image data is performed between devices having different color reproduction ranges.

  Therefore, there has been a demand for a device-independent color reproduction technique for reproducing colors with different colors between different devices. A system that realizes this device-independent color reproduction technology is generally called a color management system (CMS).

  FIG. 1 is a diagram showing an outline of this CMS, and shows a CMS using a device-independent color space (referred to as a device-independent color space). When connecting an image input device (camera, scanner, etc.) and an image output device (printer, monitor, etc.), in the configuration shown in FIG. 1, conversion from a color signal of a certain device to a color signal of an output device is performed for each device. This is realized by interposing a device-independent color space (CIE-XYZ, CIE-L * a * b *, etc.) according to the above profile. A profile is a conversion formula that links a device-dependent space (referred to as device-dependent color space or device color) of each device and a device-independent color space, or mapping between a device-dependent color space and a device-independent color space. This is realized by a look-up table (conversion table) in which is described. Such a color management system has an advantage that a system with different input / output devices to be connected can be easily replaced.

  As a device-independent color space (hereinafter also referred to as a standard color space or an equipment independent space) used in the CMS, for example, in the profile proposed by the International Color Consortium (ICC) widely spread as an industry standard, a D50 light source The CIE-XYZ color space and the CIE-L * a * b * color space below are defined. Furthermore, in recent years, sRGB color space, AdobeRGB (proposed by Adobe) color space, and the like may be used in input devices such as digital cameras. A color space having these color gamuts may be a standard color space. By using the standard color space which is such a device-independent color space, it is possible to perform color reproduction independent of the device.

    As a method for converting the color signal defined in the standard color space to the color signal of the printer, a method is well known in which conversion for connecting color spaces is performed using a profile created as a lookup table in advance. FIG. 2A is a perspective view showing the Adobe RGB color space 200 as the input color space, the printer color gamut 202 as the output color gamut, and the CIE-L * a * b * color space 201 as the standard color space. It is. The profile that connects the standard color space and the color signal of the printer is, for example, a device-dependent color corresponding to a color having the L * a * b * value of the lattice point at a plurality of lattice points in the L * a * b * color space. It is a three-dimensional lookup table that associates spatial data. The device-dependent color space data is, for example, RGB data. In the case of a printer, an example of a profile is a lookup table in which RGB data for outputting the color of a certain grid point in the L * a * b * color space by the printer is stored in association with the grid point. FIG. 2B is a cross-sectional view of the a * b * plane at a certain lightness on the L * axis where the lattice points of FIG. 2A exist. The input color space, standard color space, and printer color gamut are viewed from above the L axis, and the black dots indicate the coordinates of lattice points defined on the standard color space.

  When performing color reproduction with each device in the CMS described above, colors that can be reproduced with a certain input device can be reproduced with other output devices having different color reproduction ranges. Gamut mapping technology that absorbs differences in the reproduction range is realized with color profiles. In addition, printer manufacturers absorb colors between input and output devices using unique color parameters in the provided printer driver. These color profiles and color parameters are created by a printer manufacturer through trial and error and provided to the user. However, in recent years, with the advent of printers with built-in colorimeters, there has been an increasing demand for technologies that allow printer users to automatically generate color profiles for various additional papers.

  As a conventional gamut mapping method realized by a color profile, Japanese Patent Application Laid-Open No. 2004-228561 requires a user who emphasizes saturation and lightness when mapping an input image to an output color gamut using a colorimetric method. There has been disclosed a technique for performing mapping by controlling a moving range of a focal color according to a mapping characteristic and further moving a focal color according to lightness of an input value. This is a mapping method that reflects the user's request by being able to select importance on saturation, importance on lightness, and the like.

FIG. 3 is a cross-sectional view represented by a lightness (L *) axis and a saturation (C *) axis in a certain hue in FIG. FIG. 3 shows a fixed focus color range (upper limit value L_max, lower limit value L_min) on the L axis set with emphasis on saturation and lightness in data Pin of grid points of a certain lightness defined in the standard color space. It is the figure which illustrated the result mapped by the method of patent document 1 toward (1). The focal color is calculated by the following equation (1) that adaptively sets the focal color according to the brightness of the grid points. Ls is the brightness value of the focus color. L_in is a lightness value of a grid point (referred to as an input point) in the standard color space to which the input color data corresponds, Lt is the highest lightness value of the input color space, and Lb is the lowest lightness value of the input color space. .
Ls = (L_max−L_min) · L_in / (Lt−Lb) + L_min (1)
From the above formula, the lightness value Ls of the focus color is given as a value obtained by mapping the lightness value L_in of the input point to the lightness range of the focus color. In the conventional method, the focal color (Ls, 0, 0) on the achromatic color axis moves between L_min and L_max according to the lightness L_in of the input point. According to the equation (1), if the difference between L_min and L_max is small, the focus color moves in a narrow range on the achromatic color axis, and the saturation-oriented mapping is performed as shown in FIG. On the other hand, if the difference between L_min and L_max is large, the focus color moves in a wide range on the achromatic color axis, resulting in mapping with emphasis on brightness as shown in FIG.

JP 2007-274484 A

  FIG. 4 is a cross-sectional view represented by a lightness (L *) axis and a saturation (C *) axis in the hue 203 of FIG. This is a result of mapping using the focus color range with emphasis on saturation in the input color gamut 200 and the output color gamut 202 by the method described above. In the conventional method, when the output color gamut 202 is as shown in FIG. 4, the grid point data P2in on the high lightness side is mapped to the data P2out of the output color gamut, and the saturation-oriented mapping is performed. On the other hand, the grid point data P3in on the low brightness side is mapped to the output color gamut data P3out. The saturation of the mapped data P3out is considerably lower than the saturation of the input data P3in. When the actual print result is observed, it is preferable to map to the point moved in the direction of the arrow 400 on the output color gamut 202. I understand that. In creating a normal color profile, if such a color separation before and after mapping is large, partial correction is performed after the color profile is created for that portion.

  Not only in the above-mentioned mapping with emphasis on saturation, but also in mapping with emphasis on the balance between lightness and saturation, when the focus color range is set by the conventional method, depending on the shape of the output color gamut, There was a problem that the data could not be mapped to achieve the intended color reproduction. Therefore, in color profile creation, it is necessary to repeat creation, printing, subjective evaluation, and partial correction, and it is difficult to automatically generate an optimum color profile (reducing labor).

The present invention has been made in view of the above problems, and a profile mapped so as to realize intended color reproduction with respect to data outside the output color gamut, regardless of the color gamut shape of the output device. To provide a profile creation method, a profile creation device, an image processing device and an image processing system that perform color conversion using a profile, which can be generated with reduced labor.

    As a technique for solving the above problems, the present invention has the following features.

A profile creation device that creates a profile that defines color conversion from a first color space to a second color space that does not cover the entire first color space,
Gamut information acquisition means for acquiring second gamut information in which the second color space is associated with a standard color space;
Area dividing means for dividing the standard color space into two areas, with the brightness corresponding to the maximum saturation in the standard color space of the second color space as a boundary;
Profile creation means for creating a profile for converting a color in a standard color space corresponding to the first color space into a color in the second color space for each of the divided areas.

According to the present invention, the region of the color space where the lattice points of the profile are defined is divided, and the focus color movement range defined for each divided region is switched. Then, the defined movement ranges of at least two focal colors are set so as not to coincide with each other and there are portions where the ranges overlap. Thereby, it is possible to perform mapping so as to realize intended color reproduction for data outside the output color gamut, regardless of the color gamut shape of the output device.

It is a figure which shows the outline | summary of a color management system. It is a figure which shows an input color gamut, a standard color space, and an output color gamut. It is a figure for demonstrating the conventional gamut mapping method of emphasis on saturation and lightness. It is a figure explaining the gamut mapping method which sets the upper limit and lower limit of a focus color on a brightness axis. 1 is a block diagram illustrating a schematic configuration of an image processing system according to an embodiment of the present invention. It is a figure which shows the outline of the image processing structure for printing using the profile produced | generated by this invention. 6 is a flowchart illustrating color profile creation processing according to an embodiment of the present invention. It is a figure explaining the gamut mapping method of this invention. It is a figure which illustrates the gamut mapping by the profile produced by one Embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

<Embodiment 1>
In the first embodiment, an apparatus and a process for generating a profile for converting image data of a first color space into image data of a second color space according to the present invention will be described.

[Configuration of image processing apparatus]
FIG. 5 is a block diagram illustrating a schematic configuration of the image processing device 5000 according to the present embodiment. The image processing apparatus of the present embodiment is realized by executing a program on a host computer. The host computer includes a CPU 500, a RAM 501, an operation unit 502, an information storage unit 503, an external interface 504, an image processing unit 505, and a display unit 506, and the CPU 500 controls them according to various information data and various programs. The function performed by the program executed by the computer can be realized by hardware having the same function.

  In FIG. 5, a CPU 500 performs various controls of a RAM 501, an operation unit 502, an image processing unit 505, and an image output device 507 in accordance with information data and a program. The information storage unit 503 includes a hard disk and a non-volatile memory, and is a storage unit that stores and reads out information and data to be described later that are necessary for the invention according to the present embodiment. The information storage unit 503 also stores image data digitized by an input device such as a scanner or a digital camera. Although these input devices are not shown in FIG. 5, they may of course be included. The colorimeter 508 measures the color of the patch chart printed by the image output device 507 in order to acquire information necessary for generating the output color reproduction region and profile. In this embodiment, a configuration is shown in which colorimetry is performed under the control of the CPU 500 and the colorimetric information is stored in the information storage unit 503. However, a colorimeter incorporated in the image output device 507 can provide the same effect. The image output device 507 is realized by a monitor, an inkjet printer, a thermal transfer printer, a dot printer, or the like. In this embodiment, an image is output by an inkjet printer apparatus using six colors of ink of cyan, light cyan, magenta, light magenta, yellow, and black.

  The RAM 501 is used as a work area and a temporary save area for various control programs and data input from the operation unit 502. The operation unit 502 sets the image output device 507 and inputs data based on a user operation. The image processing unit 505 performs predetermined image processing such as profile creation processing and color conversion processing using a profile described in the following embodiment.

  Note that the present invention is not limited to this mode, and a part or all of the image processing apparatus may be executed by a printing apparatus such as a printer. For example, in an embodiment in which an image captured by a digital camera is directly input to a printer and printed out, an image processing apparatus is configured in the printer. The image output device 507 can be a printing device such as a printer or a monitor.

  The profile creation described in each embodiment described later can be performed by a host computer as the image processing apparatus, and the created profile is a predetermined information such as a host computer or a printer as the image processing apparatus. It can be used by storing in the memory.

  In this embodiment, a system using an inkjet printer as the image output apparatus 507 will be described. The color space used in the embodiment is the input RGB color space (that is, the first color space) is the AdobeRGB color space. The standard color space is assumed to be represented by the CIE-L * a * b * color space, but the J * C * H * color space, sRGB, AdobeRGB, PCS (profile connection space), input device, and image output device Other color spaces such as a color space uniquely determined by the manufacturer and a device-independent color space may be used. The profile generated by the image processing device 5000 is a profile for converting the CIE-L * a * b * color space into a device RGB value that is an output color space of the printer (ie, the second color space).

  In the following embodiment, an example of colorimetric processing is shown as a color gamut mapping method. In the colorimetric processing, the color gamut common to the input device and the output device is expressed as it is, and the color of the input device is mapped to the surface of the output gamut for the non-common region that cannot be reproduced by the image output apparatus 507.

  In this example, the device RGB, which is a device-dependent color space, is a color range that can be expressed by the above-described six inks on the paper, for example, but of course depends on the device, such as the type of device and the type of ink. The profile indicating the correspondence between the device-dependent color space and the standard color space can be measured by a user using a colorimeter, for example, or may be provided by a device vendor. In this embodiment, it is obtained by measuring with a colorimeter possessed by the output device. In any case, the gamut conversion is not considered in the output profile that is originally given. For example, the output profile is given in the form of a table in which the corresponding values of the device-dependent color space are stored at the grid points of the standard color space. It is done. When color conversion is performed using this table, if a color in the input standard color space is on a grid point, the value corresponding to that grid point is the converted output color value. If it is not a grid point, for example, it is obtained by linear interpolation using the values of 4 grid points in the vicinity of the input color. The same applies to profiles including color gamut conversion. In the present embodiment, the output color gamut is described as being narrower than the input color gamut. This is because, in the opposite case, color gamut conversion is not required in colorimetric processing.

[Functional configuration of image processing apparatus]
FIG. 6 is a schematic diagram of an image processing configuration for printing using a profile generated by the invention according to the present embodiment. Input image data to be input is RGB image data defined in the device-dependent color space of the input device, in this example, the Adobe RGB color space, and is input to the image data I / F unit 601. The RGB image data is converted by the input space conversion processing unit 602 into output image data in the color space of the standard color space (in this example, CIE-L * a * b *) according to the attributes of the RGB image data. The device-dependent color space of the input device is called the input color space or the first color space, the device-dependent color space of the output device is called the output color space or the second color space, and the extension of the color space is the color gamut or reproducible range. Call it.

《Input space conversion unit》
In this example, the input space conversion processing unit 602 performs conversion by 3D-LUT processing. The processing parameters there are converted into parameters for the input space conversion processing unit by the input coefficient conversion unit 603 based on information from the input profile 604 and set. The parameter setting is, for example, storing parameters in a predetermined format in a predetermined location so that the input space conversion processing unit can access them. The 3D-LUT process uses, for example, a table that stores color data (for example, (R, G, B)) of the input color space in association with predetermined grid points (L * a * b *) in the standard color space. Conversion process. In this case, the input coefficient conversion unit 603 performs 3D-LUT conversion of the input profile in this format.

《Output space conversion unit》
The output space conversion processing unit 605 receives the result from the input space conversion processing unit 602 and converts the image data in the standard color space into image data in the RGB space depending on the output device. The processing here is also performed by 3D-LUT processing. Based on the information from the output profile 607, the output coefficient conversion unit 606 sets parameters for the output space conversion unit 605, and the output space conversion unit 605 performs conversion processing. The output profile 607 is a color profile generated by the profile creation process according to the present embodiment.

《Color material color development processing unit》
The device-dependent RGB image data that is the result of the output space conversion processing unit 605 is input to the color material color development processing unit 608. The color material color development processing unit 608 converts the RGB signal in the device-dependent color space into a signal for each color corresponding to the color material of the image output device 507. This conversion is performed by a known 3D-LUT process, and is called a color material color development process. In this example, the color material is cyan, light cyan, magenta, light magenta, yellow, and black ink, and is converted into data indicating the density of each color. Of course, the color after development varies depending on the output device. Parameters used in the color material color development processing unit 608 are set by the color material coefficient conversion unit 609 based on information in the print information DB 613. The print information DB 613 stores various parameters for processing by the color material color development processing unit 608, the halftoning processing unit 610, and the print control unit 611. Although description of various parameters is omitted, various parameter information corresponding to the type of media, print mode, printing purpose, etc. is managed, and is selected and set as necessary. The data developed on the color material is then input to the halftoning processing unit 610 for each color. In the halftoning processing unit 610, it is converted into binary data by processing such as an error diffusion processing method and a dither method, and is input to the printing control unit 611 and output by performing printing control according to the number of printing passes. Detailed description here is omitted. The printing pass is a concept applied to a serial printer, and is not applied to a printer having a line head or a display device. If the output device is a display device, the image data in the RGB color space, which is the output color space, can be used for processing that has been subjected to gamma correction. Is also unnecessary.

  The input color space and the output color space have been described as the RGB color spaces of the input device and the output device, respectively, and the standard color space has been described as the L * a * b * color space. However, any color space is not limited to this example. In addition, each device color space can be applied to various color spaces such as CMYK color space.

[Create profile according to the present invention]
Hereinafter, a method of creating a profile parameter used in the output space conversion processing unit 605 of FIG. 6 will be described. The parameters of the profile created in the present embodiment are 729 grid points (9 slices), and the profile proposed by the above-mentioned ICC (standard color space is CIE-L * a * b *). Further, in this embodiment, for easy understanding, the color reproduction area of the printing apparatus as an output device is expressed as the output color gamut 202 with respect to the input color space 200 and the standard color space 201 shown in FIG. We will show how to create a profile based on an example. The process of calculating output data for each lattice point of the profile will be described in detail below.

    FIG. 7 is a flowchart illustrating a process for creating a color profile. FIG. 8 is a schematic diagram for explaining a method of gamut mapping (color gamut conversion) described in this embodiment, and shows a mapping method for data P (x) in of lattice points.

    First, when the start of profile creation is instructed by the operation unit 502 of FIG. 5, the following process is performed by the profile creation software by the operation of each unit on the host computer.

  Step S700 is a step of setting information of grid point data of the color profile to be generated. In the output color profile, the correspondence between L * a * b * values and device RGB values is generally described as a three-dimensional correspondence with 17 or 33 grid points. However, in the present embodiment, the description will be made on the premise that a color profile is created with nine grid points in order to simplify the description. Accordingly, although not shown, the number of grid points is set to 9 in accordance with instructions from the operation unit 503 and the display unit 506. The number of grid points refers to the number of grid points per axis in the standard color space, and the number of grid points in the entire color space is the third power. In the present embodiment, the number of grid points defined in the CIE-L * a * b * color space is 729 (9 × 9 × 9) grid points, and the L * a * b * value of the grid points is expressed as L_in (i ), A_in (j), b_in (k) (where i, j, k are 0 to 8).

    Step S701 is a step of acquiring information on an output color gamut that is a color reproduction range of the output device by printing patch chart image data stored in advance and measuring the color of the patch part. In the present embodiment, since there are nine grid points, each color component of the RGB image data is combined in 17 steps in increments of 16 counts in order to obtain a colorimetric value of the intermediate color in consideration of data interpolation processing described later. 17 × 17 × 17 = 4913 color patches are generated. Then, the generated patch chart image data is output by the image output device 507, and the colorimetric data (L * a * b * value) measured by the colorimeter 508 is stored in the information storage unit 503. Each stored measurement value is associated with a corresponding RGB value. As a result, a table is obtained in which each L * a * b * value of the color is associated with each 17 × 17 × 17 grid point in the RGB color space of the output device. Based on this table, a table of RGB values in the L * a * b * color space is created. Details are described below.

  Specifically, in step S701, patch chart image data is first input to the image data I / F unit 601 in FIG. Here, the input space conversion processing unit 602 and the output space conversion processing unit 605 do not perform processing, and the RGB signals are input to the color material color development processing unit 608 as they are. In the color material color development processing unit 608, inks of six colors, cyan, light cyan, magenta, light magenta, yellow, and black, which are the parameters for the target paper by the print information DB 613 and the color material coefficient conversion unit 609, are used. Expanded to Then, based on the print information DB 613 and the print coefficient conversion unit 612, a patch chart image is printed via the halftoning processing unit 610 and the print control unit 611.

  Each color of the printed patch chart image is measured by the colorimeter 508, and the colorimetric value is associated with the input RGB value and stored in the information storage unit 503. The stored colorimetric values are converted into the following two output color gamut information and stored in the information storage unit 503. The output color gamut information in the first format is information in which RGB values that can be reproduced as the closest color (the smallest color difference) are associated with the L * a * b * values of the lattice points of the profile. Since the stored colorimetric value is a measured value of L * a * b * for a given RGB value, the L * a * b * value that is a lattice point is obtained by reverse interpolation processing that is a known technique. Convert to RGB values and store the values in association with the corresponding L * a * b * values. That is, the output color gamut information in the first format is a primitive output profile that is not corrected at all. Similarly, the output color gamut information of the second format is stored as output color gamut information that is easy to discriminate the output color gamut range in a later-described step by a known technique based on the colorimetric values. In this embodiment, the output gamut information is managed by storing the a * b * value of the gamut boundary region for each L * value in the range of 0 to 100. That is, a pair of values (a *, b *) corresponding to the boundary of the output color gamut 202 in FIG. 2B is created for each L * value. Moreover, although the example which memorize | stores separately as 1st and 2nd information was shown, even if these 2 information is memorize | stored as one memory | storage information, the same effect is acquired. Note that the output color gamut information indicated by the output color gamut information in the first format or the second format may be referred to as second color gamut information.

    In step S702, a target grid point is set, and it is determined whether the L * a * b * value of the grid point exists in the output color gamut or is out of the color gamut and needs to be compressed. If it is determined in steps S702 to S707 that initial values 0 are given to i, j, and k for all the grid points (729 points in this example) set in step S700, and it is not completed in step S707. Processing is performed for all grid points by nesting in order. Here, the target lattice point (also referred to as a target lattice point) is described below as i = x, j = y, and k = z. Therefore, in step S702, whether the grid points (L_in (x), a_in (y), b_in (z)) are within the output color gamut range or out of range is stored in the second format stored in step S701. Judgment is based on the output color gamut information. If it is within the output color gamut, the process proceeds to step S703. If it is out of the range, the process proceeds to step S704.

  If the values of all grid points are initialized to (0, 0, 0) before creating the output color gamut information in the first format, the grid points of interest in the first output color gamut information are set. When the corresponding device RGB value is not (0, 0, 0), it can be determined that the target lattice point is within the output color gamut. On the other hand, if the device RGB value corresponding to the target grid point is (0, 0, 0), the target grid point may be outside the range of the output color gamut. When the colorimetric value of the patch with the device RGB value = (0, 0, 0) happens to be located at a grid point, the grid point is also within the color gamut. Therefore, when the first output color gamut information is created, the RGB origin information indicating whether or not the colorimetric value of the device RGB value is (0, 0, 0) is on the grid point, and if so, which grid point. Are attached to the first output color gamut information. If the device RGB value corresponding to the target grid point is (0, 0, 0), the RGB origin information is referred to. If not, the target grid point is determined to be out of the output color gamut. Of course, this is just one way.

    In step S703, color conversion is performed within the output color gamut. Here, since the target grid point can be reproduced within the output color gamut, the target grid point (L_in (x), a_in (y), b_in) is directly determined based on the first output color gamut information obtained in step S701. The device RGB value corresponding to (z)) is duplicated as a value corresponding to the target grid point of the output profile to be created. That is, the output profile to be created matches the first output color gamut information with respect to the output color gamut.

    Step S704 is a step of calculating an output color reproduction region on the hue plane of the target lattice point. The hue plane is a lightness-saturation plane in a predetermined hue. In the L * a * b * space, for example, in the standard color space of FIG. 2A, the lightness (or luminance) axis is set as one coordinate axis. It is a plane to do. Here, based on the (a *, b *) value of the gamut area corresponding to the divided L * value stored as the second output color gamut information in step S701, an output as shown in FIG. Calculate the color reproduction area. That is, the calculated output color reproduction region is defined by, for example, a lightness value-saturation value pair (L *, c *) on the hue plane around the lightness axis. The saturation c * is calculated from (a *, b *) that forms the outline of the color gamut of the hue plane. Since the number of grids on the lightness axis is the same as that acquired in step S700, the output color reproduction area of a certain hue plane, for example, obtains the saturation value that becomes the outline of the color gamut corresponding to each lightness of the grid. Are stored in association with each other. The hue plane on which the output color reproduction area is calculated may be selected so as to include, for example, grid points, or may be selected at predetermined angles around the brightness axis. In the latter case, it is desirable that a hue plane including the a * axis and the b * axis is also included.

  P (x) in in FIG. 8 is a target lattice point to be processed. Here, in the present embodiment, the solid line 200 indicates the boundary of the input color space region (input color gamut or first color gamut), and the solid line 201 indicates the boundary of the standard color space region (CIE-L * a * b * space). The broken line 202 indicates the boundary of the output color reproduction area (output color gamut or second color gamut). Since the target is the output color, the contour of the output color gamut 202 in FIG. 8 may be calculated as the output color reproduction region.

  Step S705 is a step of dividing the standard color space region on the hue plane of the target lattice point of interest. In the present embodiment, an example in which the image is divided into two regions based on the maximum saturation point of the output color reproduction region is shown. The maximum saturation point is a point having the maximum distance from the brightness axis on the contour surface of the output color gamut. The processing is switched in the next step depending on the positional relationship between the divided area and the target lattice point to be processed. This is a feature of the color profile created in this embodiment. The maximum saturation point of the output color reproduction region is C, the region having a lightness value higher than the lightness value Lc of the C point is the first region 800, and the other region is the second region 801. Eventually, the area division in step S705 is a process of determining the lightness value Lc (also referred to as boundary lightness) of the maximum saturation point C. The determined boundary brightness Lc is stored in a predetermined storage area.

  In the present embodiment, an example of dividing into two regions based on the maximum saturation point of the output reproduction region is shown, but depending on the shape of the input reproduction region and the output reproduction region, based on the maximum saturation point of the input reproduction region. It may be divided into two regions, or may be divided into three regions based on the maximum saturation point of the input reproduction region and the maximum saturation point of the output reproduction region. For the input color gamut, for example, if the input color gamut information in the first format is given by the device vendor, it is sufficient to create the input color gamut information in the second format. Information representing the input color gamut is referred to as input color gamut information or first color gamut information.

  In step S706, depending on whether the target grid point to be processed exists in the first area 800 and the second area 801 divided in step S705, the focus color movement range (focus color of the focus color) is determined. This is a step of performing gamut mapping processing by switching the range. The focal color is achromatic and has only a brightness component. In determining which region the target lattice point belongs to, the value of the lightness component of the target lattice point is compared with the boundary lightness Lc, and if it is larger, it is determined that it belongs to the first region 800, and if smaller, it belongs to the second region 801. Is done. If the value of the lightness component at the grid point of interest is equal to the boundary lightness Lc, it may be set to one of predetermined regions.

With reference to FIG. 8A, a process when the target lattice point is in the first area will be described. The brightness L1s (x) of the first focal color on the achromatic color axis corresponding to the data P (x) in of the target grid point in the first region is calculated by the following equation (2). As shown in FIG. 8A, Lt is the highest lightness value of the input space, and Lc is the lightness value of the maximum saturation point C. That is, in this embodiment, the brightness of the focus color is calculated according to the brightness of the data of the grid points from the information on the moving range of the first focus color (upper limit value L1_max, lower limit value L1_min). In addition, the moving range of the first focus (upper limit value L1_max, lower limit value L1_min) is set so that the grid points on the first region 800 are mapped with emphasis on saturation, and the setting method is the same as the conventional method. is there.

L1s (x) = (L1_max−L1_min) · L_in (x) / (Lt−Lc) + L1_min (2)

The L * a * b * value of the intersection point P (x) out between the straight line connecting the data P (x) in of the target grid point and the calculated focal color L1s (x) and the contour of the output color gamut 202. Certain L_out (x), a_out (y), and b_out (z) are calculated. Device-dependent color data (this example) corresponding to the position (L_out (x), a_out (y), b_out (z)) in the standard color space represented by the L * a * b * value of this intersection P (x) out , Device RGB) is the output color for the grid point of interest P (x) in. That is, in the profile to be created, device-dependent color data corresponding to P (x) out is stored as device-dependent color data corresponding to the target lattice point. Since P (x) out is not necessarily a lattice point, in that case, a value is calculated by interpolation. In other words, the intersection point P (x) out is the color at the shortest distance from the target grid point among the device-dependent colors (second color space) on the line connecting the target grid point and the focus. It is a close color.

Next, processing when the lattice point is in the second region will be described with reference to FIG. Although the focal color movement range is different, the processing is basically the same as in the first area. The brightness L2s (x) of the focal color on the achromatic color axis corresponding to the data P (x) in of the target lattice point is calculated by the following equation (3). As shown in FIG. 8B, Lb is the lowest lightness value of the input space, and Lc is the lightness value of the maximum saturation point C. That is, in this embodiment, the brightness of the focus color is calculated according to the brightness of the data of the grid points from the information on the movement range of the second focus color (upper limit value L2_max, lower limit value L2_min). The second focus movement range (upper limit value L2_max, lower limit value L2_min) is set so that the grid points on the second region 801 are mapped with emphasis on brightness, and the setting method is the same as the conventional method. .

L2s (x) = (L2_max−L2_min) · L_in (x) / (Lc−Lb) + L2_min (3)

The L * a * b * value of the intersection point P (x) out between the straight line connecting the data P (x) in of the target grid point and the calculated focal color L2s (x) and the contour of the output color gamut 202. Certain L_out (x), a_out (y), and b_out (z) are calculated. Device-dependent color data (this example) corresponding to the position (L_out (x), a_out (y), b_out (z)) in the standard color space represented by the L * a * b * value of this intersection P (x) out , Device RGB) is the output color for the grid point of interest P (x) in. That is, in the profile to be created, device-dependent color data corresponding to P (x) out is stored as device-dependent color data corresponding to the target lattice point. Since P (x) out is not necessarily a lattice point, in that case, a value is calculated by interpolation.

  Note that the focal range and the second focal range of the first region are determined in advance, for example. However, since the range of each area is unknown until the area is divided, for example, the focus movement range with respect to the first area is determined relative to the brightness range of the first area, and the second area It is only necessary to determine the movement range of the focal point relative to the relative movement range of the focal point of the first region.

  As described above, the output device RGB value corresponding to the target grid point is obtained and stored in the output color profile. In step S707, it is determined whether processing for determining parameters (that is, image data expressed in the output device-dependent color space corresponding to the grid points) is completed for all grid points of the output color profile created in the present embodiment. To do. If completed, the process proceeds to the next step S708. If not completed, the indices i, j, and k of the coordinate components of the grid points are incremented in a nested manner, the next grid point is advanced, and the process branches to S702. Note that incrementing the index i, j, k of the coordinate component means incrementing each component by the difference between the grid points. In this example, i = j = k = 9 is completed.

  In step S708, the determined color profile parameters are converted into a format that can be used as the output profile 607 in FIG. Of course, if the color profile created up to step S707 can be used as it is, nothing is performed in step S708.

  In this way, an output profile subjected to color gamut conversion is generated. This output profile is referred to when the standard color space is converted into the output device-dependent color space by the output space conversion processing unit 605 in FIG. As a result, the input data converted from the input device-dependent color space is subjected to color conversion in accordance with the output color gamut. The output is subjected to color material color development and halftoning, and is printed.

  As described above, the feature of the present invention is that the color space region in which the grid points of the profile are defined is divided, the focal color movement range is switched for each divided region, and the movement of at least two defined focal colors is performed. The range is set so that there is a portion where the ranges do not coincide with each other and the ranges overlap.

  In the present embodiment, the focus movement ranges corresponding to the two defined areas (in this embodiment, the focus color movement ranges of the first and second areas) are matched with each other as shown in FIG. It is characterized by setting so that there is a portion where the ranges overlap. By setting the focus movement range in this way, it becomes possible to control the points to be gamut mapped in more detail according to the shape of the output color gamut.

  The mapping result when the profile created in this embodiment is applied is shown in FIG. Compared with the conventional example, as shown in FIG. 4, in the past, when mapping was performed by setting the focus movement range with emphasis on saturation, depending on the shape of the output color gamut, the result with emphasis on saturation was not necessarily obtained. Could not get. However, by applying the output profile according to the present embodiment, it is possible to perform mapping that places importance on chroma on both the low brightness side and the high brightness side. Further, in this embodiment, mapping with emphasis on saturation has been described as an example, but mapping as intended is also possible in mapping with emphasis on lightness and a balance between the two.

  In this way, by applying the method of the present invention, it is possible to set and map the focus color in more detail for the data outside the output color gamut, and to achieve a good gradation and natural color reproduction. Become. As a result, it has become possible for the user to automatically generate a color profile that has been created by repeating the operations of color profile creation, printing, subjective evaluation, and partial correction.

  The present invention is not limited to these embodiments, and can be implemented in various forms without departing from the scope of the invention. For example, the sRGB color space is exemplified as the input color space, but the present invention is not limited to this, and other color spaces such as AdobeRGB, WideGamutRGB may be used. In addition, the CIE-L * a * b * color space is exemplified as the standard color space, but the color space is not limited to this, and a color space similar to the XYZ color space, J * C * H * color space, or the like. Needless to say, this is feasible. In this embodiment, an example of colorimetric processing is shown, but perceptual and saturation processing may also be used. In this embodiment, the number of grid points of the LUT to be created is 729 grid points. However, the present invention is not limited to this, and any number of slices that can express the output color gamut may be used. Further, the formulas (2) and (3) for calculating the focus color are not limited to the formulas exemplified in this embodiment, and any formula may be used as long as the mapping can be performed as intended.

  In the present embodiment, the color gamut conversion in the case where the lightness corresponding to the maximum saturation of the output color gamut is lower than the lightness corresponding to the maximum saturation of the input color gamut as shown in FIG. This is because the relationship between the color gamut of an input device such as a scanner or a digital camera and the color gamut of an output device such as a printer is often such a relationship. In such a case, the color gamut conversion is performed as described in the present embodiment for the following reason. Normally, the output color gamut cannot cover the entire input color gamut. Further, when the lightness corresponding to the maximum saturation of the output color gamut deviates from the lightness corresponding to the maximum saturation of the input color gamut, the first region described above with the lightness corresponding to the maximum saturation of the output color gamut When the image is divided into the second regions, in a region to which the lightness corresponding to the maximum saturation of the input color gamut belongs, when attention is paid to a certain lightness, a difference in saturation corresponding to each of the input color gamut and the output color gamut becomes large. . In contrast, in a region where the brightness corresponding to the maximum saturation of the input color gamut does not belong, the difference in saturation corresponding to each of the input color gamut and the output color gamut is small. For this reason, ideal color gamut conversion can be realized by performing color gamut conversion with emphasis on saturation for areas to which lightness corresponding to the maximum saturation of the input color gamut belongs, and with emphasis on lightness for other areas.

  Therefore, in the above example, based on the relationship between the input color gamut and the output color gamut in many cases, an area having a brightness higher than the brightness corresponding to the maximum saturation of the output color gamut is set as the first area, and the output color A region having a lightness lower than the lightness corresponding to the maximum saturation of the region was defined as the second region. However, generally speaking, when the lightness corresponding to the maximum saturation of the output color gamut is divided into two regions, the region to which the lightness corresponding to the maximum saturation of the input color gamut belongs is the first region, It is desirable to apply the above-described example by replacing the other region, that is, the region to which the lightness corresponding to the maximum saturation of the input color gamut does not belong, with the second region.

  Also, an output profile that emphasizes saturation is created in the present embodiment. However, such fixed processing is not performed. For example, when creating an output profile, the operator specifies the attribute to be emphasized, and when the saturation is specified, the procedure of FIG. 7 is applied and the brightness is specified. A conventional lightness-oriented procedure may be applied.

  In the present embodiment, the creation of an output profile has been described. However, the present embodiment is applied to the creation of a profile that involves color gamut conversion from a certain color gamut to another color gamut that does not cover the whole. Is possible.

[Other Examples]
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 (7)

A profile creation device for creating a profile defining color conversion from a first color space to a second color space different from the first color space,
Gamut information acquisition means for acquiring second gamut information in which the second color space is associated with a standard color space;
Area dividing means for dividing the standard color space into two areas, with the brightness corresponding to the maximum saturation in the standard color space of the second color space as a boundary;
Profile division means for creating a profile for converting a color in a standard color space corresponding to the first color space into a color in the second color space for each of the divided areas. Profile creation device. For each of the two divided areas, the profile creation means sets the range of the focus color of each area corresponding to the brightness of the color in the standard color space so that the ranges do not coincide with each other and overlap each other. Means to set
The profile creating means associates the color in the standard color space with the color at the shortest distance in the second color space with the focal color corresponding to the color as a focus.
The profile creating apparatus according to claim 1, wherein the profile is created.   The profile creation means includes the first region as the region to which the lightness corresponding to the maximum saturation in the standard color space of the first color space belongs to the first region, and the other as the second region. As the second region, the focal color range of the second region is set within the brightness range of the second region, and the focal color range of the first region is set to the second region. The profile creation apparatus according to claim 2, wherein the profile creation apparatus is set so as to overlap within the range of the focal color of the area.   4. The table according to claim 1, wherein the profile is a table in which color values in the corresponding second color space are associated and stored for each color of a predetermined grid point in the standard color space. The profile creation device according to claim 1.   The program for functioning a computer as a profile creation apparatus as described in any one of Claims 1 thru | or 4. A profile creation method executed by a profile creation device for creating a profile that defines color conversion from a first color space to a second color space different from the first color space,
Obtaining color gamut information for obtaining second color gamut information in which the second color space is associated with a standard color space;
A region dividing step of dividing the second color space into two regions with a brightness corresponding to the maximum saturation in the standard color space as a boundary;
A profile creating step of creating a profile for converting a color in a standard color space corresponding to the first color space into a color in the second color space for each of the divided areas. Profile creation method. A profile created by the profile creation device according to any one of claims 1 to 4 is provided as an output profile,
The input image data in the first color space converted into a color in the standard color space is converted into output image data in the second color space using the output profile and output. Image processing device.

Images