JP2006197457A - Color chart creating method, device, and program, and color conversion definition correcting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a color chart creating method, etc. which create a color chart arranged with a patch group which comprises a plurality of color patches and create the color chart which can correct a color conversion definition efficiently. <P>SOLUTION: A color chart 500 is created to be arranged with a fixing patch group 505 which comprises color patches of respective predetermined colors, and an image depending patch group 506 which comprises the color patch of each color which represents each area selected preferentially from a high frequency in which a color of each part of an obtained color image appears in each of a plurality of areas on a color space. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a color chart creation method for creating a color chart in which a plurality of color patches are arranged, a color chart creation apparatus for creating such a color chart, and a color for causing a computer to create such a color chart. A first device color space that depends on a first device that outputs a color image based on a chart creation program and image data; and a second device color space that depends on a second device that outputs a color image based on the image data The present invention relates to a color conversion definition correction method for correcting a color conversion definition that defines a color conversion relationship between the two.

  Conventionally, an image (hereinafter referred to as an original image) is acquired by an input device such as a color scanner or an electronic still camera, and image data is obtained. Based on the image data, a printer, a printer, or a display screen is now used. A reproduction image in which the original image is reproduced by an output device such as is obtained. In this case, the color conversion definition (input profile) that associates the color on the original image with the color representation in the image data according to the input device, and the color representation in the image data and the color on the reproduced image according to the output device. A color conversion definition (output profile) that associates the image data obtained from the original image with the input device, and a color conversion definition (device) that combines both color conversion definitions (input profile and output profile) The image data is converted into image data suitable for the output device based on the link profile, and a reproduced image is output based on the image data for the output device. By doing so, it is possible to obtain a reproduced image that is as similar in color as possible to the original document image.

  The same is true between output devices. For example, when printing a color image using a printing press, create a proof image that resembles the color of the image printed by the printing press using a color printer or the like before printing. To be done. When creating a proof image with a printer, for example, C (Cyan), M (Magenta), Y (Yellow: Yellow), K (Black) corresponding to the printing press to be printed. A color conversion definition (printing profile) that defines the correspondence between the image data for printing that represents each half of the image and the colorimetric value that represents the color of the actual printed matter that is output based on the image data for printing, Corresponding to the printer that is going to output a proof image, for example, image data for a printer that represents each CMYK half-net, and colorimetry that represents the color of the proof image that is actually printed out based on the image data for that printer Know the color conversion definition (printer profile) that defines the correspondence with the values, and connect these print profiles and printer profiles. Image data for printing based on one of the color conversion definition (the device link profile) obtained by converting into image data for the printer, creating a proof image based on the image data for the converted printer. By doing so, it is possible to create a proof image that is similar in color to the actual printed matter as much as possible.

  In order to obtain images with matching colors as described above, color conversion definitions (input profiles) for input devices such as color scanners and electronic still cameras, and color conversion definitions for output devices such as printing machines and printers ( Output profile) must be determined accurately.

In determining the color conversion definition such as the input profile and the output profile, for example, in the case of an input device, a color chart in which color patches are arranged is read by the input device and converted into image data, for example, C, M, Y, CMYK color space consisting of four K colors, or an RGB color space consisting of three colors R (Red: Red), G (Green: Green), and B (Blue: Blue), etc. In addition, the coordinate value (device value such as CMYK value or RGB value) of such color space is referred to as a device-dependent color space), and each color patch constituting the same color chart is measured with a spectrocolorimeter. to, for example, L ^* a ^* b ^*, such as color space or XYZ color space, the independent to the device color space ( Under such color space is referred to as device independent color space) coordinate values (L ^* a ^* b ^* values or colorimetric values such as XYZ values) determined for a plurality of device values of those device-dependent color space An input profile can be obtained by associating a plurality of colorimetric values in the device-independent color space on a one-to-one basis.

  In the case of an output device, for example, color patches corresponding to each of a plurality of types of halftone dot area ratios obtained by sequentially changing the halftone for each of the four colors of CMYK, such as 0%, 10%,. Create chart data corresponding to the arranged color chart, output the color chart with the output device based on the chart data, and measure the color patches that make up the output color chart with the spectrocolorimeter The output profile can be obtained by associating a plurality of device values in the device-dependent color space thus obtained and a plurality of colorimetric values in the device-independent color space in a one-to-one relationship.

  Basically, color conversion definitions such as an input profile and an output profile are obtained in this way, but the correspondence as described above is a correspondence corresponding to sparse coordinate values that are rather coarse in the color space. The color conversion definition used for color conversion is too rough. Therefore, based on the one-to-one correspondence obtained as described above, the number of one-to-one correspondence between the device value and the colorimetric value is increased by interpolation or the like. Desired color conversion definition.

  However, even if color conversion definitions such as input profile and output profile are obtained in this way and image data is converted based on the color conversion definition, measurement errors by the spectrocolorimeter and attempts to create the color conversion definition Depending on various errors and fluctuation factors such as color error of color patch due to output characteristics in target device, color error of adding color patch of practically important color typified by skin color to color chart, etc. There is a possibility that a phenomenon in which colors slightly differ between the original image and the reproduced image or between the printed matter and the proof image may occur.

  Here, in order to cope with such a phenomenon, it is conceivable to correct a color conversion definition such as an input profile, an output profile, or a device link profile obtained by combining an input profile and an output profile. Hereinafter, a method for correcting a color conversion definition will be described using a device link profile as an example.

  First, a color chart is output by a printing machine based on print chart data representing a color chart in which color patches corresponding to each of the CMYK four colors for printing are arranged, and the output color chart is configured. Measure each color patch with a spectrophotometer.

  Next, the chart data for printing is converted into chart data for the printer using the device link profile, and the color chart is printed out by the printer based on the chart data for the printer, and the color chart printed out The color patches constituting the color are measured with a spectrocolorimeter.

It is obtained by measuring the colorimetric values obtained by measuring the color patches constituting the color chart output by the printing press and the color patches constituting the color chart printed by the printer. By correcting the color conversion definition based on the color difference from the measured color value, it is possible to obtain a device link profile with further improved practical color matching accuracy (see, for example, Patent Document 1).
JP 2000-278547 A

  According to the correction method proposed in Patent Document 1 described above, the color patch color difference is reduced based on an objective colorimetric value obtained by measuring the color patch with a spectrocolorimeter. Since the device link profile is corrected, the accuracy of the device link profile is improved, and a proof image whose color matches the actual printed matter is created. By repeating such correction, the accuracy of the device link profile can be gradually increased. Further, when a color chart having a large number of color patches is used for correcting the color conversion definition, the number of measurement points increases, so that the accuracy of the device link profile can be further improved. However, when a color chart with a large number of color patches is used to correct the color conversion definition, the measurement time for measuring the color patch becomes long, and as a result, it takes a lot of time to correct the device link profile. However, there is a problem that the efficiency of correcting the color conversion definition is poor.

  In addition, when the average value of the colorimetric value difference representing the color patch color difference is smaller than 3, when the correction by the correction method proposed in Patent Document 1 is repeated, the average value of the difference is repeated. However, it is known that the difference in color perceived by the observer is not improved when the actual printed product and the proof image are compared visually.

  In view of the above circumstances, the present invention provides a color chart creation method for creating a color chart capable of efficiently correcting a color conversion definition, a color chart creation apparatus for creating such a color chart, and such a color in a computer. It is an object of the present invention to provide a color chart creation program for creating a chart and a color conversion definition correction method for correcting a color conversion definition using such a color chart.

The color chart creating method of the present invention that achieves the above object is as follows.
An image acquisition process for acquiring a color image;
An area selection process in which the color of each part of the color image acquired in the image acquisition process is selected preferentially from the higher frequency of appearance in each of a plurality of areas on the color space;
A chart creation process for creating a color chart in which a first patch group composed of color patches of each predetermined color and a second patch group composed of color patches of each color representing each area selected in the area selection process; It is characterized by having.

  Note that the color chart created by the color chart creation method of the present invention may be chart data representing a color chart, or an image actually output based on chart data representing a color chart. Good.

  In the color chart creation method of the present invention, priority is given to the first patch group consisting of color patches of each predetermined color and the one in which the color of each part of the acquired color image appears in each of a plurality of regions on the color space. Color that is considered important by the user as a color image to be acquired in the image acquisition process, because a color chart in which a second patch group including color patches of each color representing each region selected by the user is aligned is created. By preparing a color image including the color image and acquiring the prepared color image in the image acquisition process, a suitable color chart based on the color image is created. Therefore, when such a color chart is used for correcting the color conversion definition, it is possible to efficiently obtain a color conversion definition that has been corrected and improved in practical color matching accuracy, in which the colors that are considered important by the user are more closely matched. Can do.

  Here, in the color chart creation method of the present invention, the color creation patches representing the respective areas selected in the area selection process are arranged in the order of the frequency as the second patch group in the chart creation process. It is preferable that the process uses a patch group.

  According to such a preferred form, a convenient color chart can be obtained, for example, when the user manually selects a color patch from the patch group and applies it to correction of the color conversion definition.

In addition, the color chart creating apparatus of the present invention that achieves the above object is as follows.
An image acquisition unit for acquiring a color image;
A region selection unit that preferentially selects the region from the higher frequency in which the color of each part of the color image acquired by the image acquisition unit appears in each of a plurality of regions on the color space;
A chart creation unit for creating a color chart in which a first patch group composed of color patches of each predetermined color and a second patch group composed of color patches of each color representing each region selected by the region selection unit; It is provided with.

  The color chart creating apparatus of the present invention includes all modes corresponding to the respective modes of the color chart creating method of the present invention.

In addition, the color chart creating program of the present invention that achieves the above object is
Built into the computer, on this computer,
An image acquisition unit for acquiring a color image;
A region selection unit that preferentially selects the region from the higher frequency in which the color of each part of the color image acquired by the image acquisition unit appears in each of a plurality of regions on the color space;
A chart creation unit for creating a color chart in which a first patch group composed of color patches of each predetermined color and a second patch group composed of color patches of each color representing each region selected by the region selection unit; It is characterized by constructing.

  According to the color chart creating program of the present invention, the components of the color chart creating apparatus of the present invention can be easily constructed by a computer.

  In addition, the constituent elements such as the image acquisition unit constructed by the color chart creating program of the present invention may be one constituent element constructed by one program part, and one constituent element may be composed of a plurality of programs. It may be constructed by parts, or a plurality of components may be constructed by one program part. In addition, these components may execute such actions themselves, or may be executed by giving instructions to other programs and program components incorporated in the computer. Also good.

  It should be noted that the color chart creation program of the present invention includes all modes corresponding to the respective modes of the color chart creation method of the present invention.

In addition, the color conversion definition correcting method of the present invention that achieves the above object is as follows.
Color conversion between a first device color space dependent on a first device that outputs a color image based on image data and a second device color space dependent on a second device that outputs a color image based on image data In the color conversion definition correction method for correcting the color conversion definition that defines the relationship between
The first patch group composed of the color patches of each predetermined color and the respective areas preferentially selected from the ones having a higher frequency of appearance of the colors of the respective parts of the predetermined color image in each of the plurality of areas on the color space. A first color chart is output by the first device based on the first chart data representing the color chart in which the second patch group composed of the color patches of each color is arranged in the first device color space. Chart output process,
A color conversion process of converting the first chart data into second chart data representing colors in the second device color space based on the color conversion definition;
A second chart output process for outputting the color chart by the second device based on the second chart data obtained in the color conversion process;
By measuring each color patch of the color chart output in the first chart output process and each color patch of the color chart output in the second chart output process, between the color charts A difference measurement process for obtaining a color difference between color patches corresponding to each other;
A definition correction process for correcting the color conversion definition by focusing on the difference in the color patch of the second patch group among the differences obtained in the difference measurement process, rather than the difference in the color patch of the first patch group; It is characterized by having.

  The color conversion definition correcting method according to the present invention corrects the difference in the color patch of the second patch group more than the difference in the color patch of the first patch group when the color chart is used for correcting the color conversion definition. Therefore, when the color chart is created, a color image including colors that the user thinks important is prepared, and if the prepared color image is acquired and the color chart is created, the present invention By the color conversion definition correcting method, it is possible to efficiently obtain a color conversion definition that can further improve the practical color matching accuracy that further matches the colors that the user considers important.

  According to the present invention, a color chart creating method for creating a color chart capable of efficiently correcting a color conversion definition, a color chart creating apparatus for creating such a color chart, and a computer for such a color chart creating apparatus And a color conversion definition correcting method for correcting a color conversion definition using such a color chart.

  Embodiments of the present invention will be described below with reference to the drawings.

  In this embodiment, a color chart corresponding to an example of a color chart according to the present invention is created, and a device link profile corresponding to an example of a color conversion definition according to the present invention is modified using the created color chart. I will explain it. Note that this device link profile is obtained by printing a color on a proof image printed by a printer corresponding to an example of the second device according to the present invention on a printing machine corresponding to an example of the first device according to the present invention. This is for matching or sufficiently approximating the color on the obtained printed matter.

  FIG. 1 is an overall configuration diagram of a printing and proof image creation system to which an embodiment of the present invention is applied. Here, first, the positioning of the present invention will be described with reference to FIG.

  In the color scanner 10, the document image 11 is read, and from C (Cyan), M (Magenta), Y (Yellow: yellow), and K (Black: black) representing the read document image 11. The four color separation image data is generated. The CMYK four-color image data is input to the workstation 20. The CMYK four-color image data is referred to a color conversion definition (profile) having a LUT (Look Up Table) format inside the workstation 20, and is converted into CMYK four-color color separation image data suitable for the printing press 40. Color conversion is performed. In the workstation 20, the operator performs electronic plate collection based on the color-converted image data to generate image data representing an image for printing. The image data for printing is input to the film printer 30 when printing is performed, and the film printer 30 creates CMYK printing film originals corresponding to the input image data.

  A printing plate is produced from the printing film original plate, and the produced printing plate is mounted on a printing machine 40 corresponding to an example of a first device according to the present invention. Ink is applied to the printing plate mounted on the printing machine 40, and the applied ink is transferred onto a printing sheet to form a printed image 41 on the sheet.

  A series of operations in which a film original plate is prepared by the film printer 30, a printing plate is further prepared and mounted on the printing machine 40, ink is applied to the printing plate, and printing is performed on paper is a large-scale operation. Cost too. For this reason, before the actual printing operation is performed, a proof image 61 is created as follows by the printer 60 corresponding to an example of the second device according to the present invention, and the finished prediction of the printed image 41 is predicted in advance. Done.

  In creating a proof image, image data created by electronic plate collection on the workstation 20 is input to the personal computer 50. Here, the image data input to the personal computer 50 is description language data described in so-called PDL (Page Description Language). In the personal computer 50, the image data is developed into a bitmap by a so-called RIP (Raster Image Processor). The converted CMYK four-color image data. The CMYK four-color image data is substantially the same as the image data for printing input to the film printer 30.

  The spectrocolorimeter 70 and the personal computer 80 shown in FIG. 1 are related to the creation of a color chart, the creation of a profile, and the modification of a profile. The personal computer 80 is a color chart creating apparatus according to the present invention. This corresponds to an example. The spectrocolorimeter 70 is an auxiliary device for creating and modifying a profile, and the personal computer 80 is a profile creating device and a profile modifying for realizing the color conversion definition modifying method according to the present invention. It is also a device. The personal computer 50 stores a device link profile having a LUT (Look Up Table) format created and modified in advance using the personal computer 80. The image data expressing the color in the above-mentioned CMYK color space for printing is an image in which the color is expressed in the CMYK color space for a printer suitable for the printer 60 with reference to the device link profile inside the personal computer 50. Converted to data. The printer 60 receives image data for the printer, and the printer 60 creates a proof image 61 based on the input image data for the printer.

  Here, the degree of color matching between the image 41 obtained by printing by the printer 40 and the proof image obtained by the printer 60 is determined by the device link profile in the personal computer 50. This device link profile is created for each print condition for each printer.

  Further, FIG. 1 shows only one printing machine, but there may be a plurality of printing machines, or even a single printing machine may have a plurality of different printing conditions. Often, the device link profile is created in accordance with each of a plurality of printing conditions including differences in printing presses. That is, the device link profile is created in accordance with a combination of each printing condition and each printer (each printing condition when a plurality of printing conditions exist in one printer). A method for creating the device link profile will be described later.

  Thus, by creating a proof image and confirming the proof image, it is possible to predict the print finish in advance.

  Here, the feature of the printing and proof image creation system shown in FIG. 1 as an embodiment of the present invention relates to the processing contents executed in the personal computer 80. First, the personal computer will be described below. 80 will be described.

  2 is an external perspective view of the spectrocolorimeter 70 and the personal computer 80 shown as blocks in FIG. 1, and FIG. 3 is a hardware configuration diagram of the personal computer 80. As shown in FIG.

  Here, the hardware and OS (Operation System) of the personal computer 80 and the color chart creation program installed and executed on the personal computer 80 constitute one embodiment of the color chart creation device according to the present invention. Has been. The color conversion definition correction method according to the present invention is realized by a profile correction apparatus configured by the hardware and OS of the personal computer 80 and a profile correction program installed and executed on the personal computer 80. .

A spectrocolorimeter 70 shown in FIG. 2 is mounted with a color chart 90 in which a plurality of color patches are arranged, and the color of each of the plurality of color patches constituting the color chart 90 is measured. A colorimetric value representing the color of each color patch obtained by the colorimetry by the spectrocolorimeter 70 (here, L ^* a ^* b ^* value as an example of the colorimetric value) passes through the cable 91. And input to the personal computer 80.

  The color chart 90 is created by printing on the printing machine 40 shown as one block in FIG. 1 or by printing output on the printer 60. The personal computer 80 is configured by each of the color charts 90 constituting the color chart 90. The color data (coordinates in the device color space; each value of CMYK or RGB) corresponding to the color patch is known. In this personal computer 80, the color data of each color patch in the color chart 90 and the spectrocolorimeter 70 are measured. A print profile and a printer profile are created based on the colorimetric values obtained in the above. A detailed description of this point will be given later. Here, the hardware configuration of the personal computer 80 will be described next.

  As shown in FIG. 2, the personal computer 80 includes a main body device 81, an image display device 82 that displays an image on a display screen 82 a according to an instruction from the main body device 81, and the main body device 81. By specifying an arbitrary position on the display screen 82a and a keyboard 83 for inputting various information according to key operations, an instruction corresponding to, for example, an icon or the like displayed at that position at the time of the specification is input. A mouse 84 is provided. The main unit 81 has an FD loading port 81a for loading a flexible disk (FD) and a CD-ROM loading port 81b for loading a CD-ROM.

  As shown in FIG. 3, the main body 81 includes a CPU 811 that executes various programs, a main memory 812 that reads programs stored in the hard disk device 813 and develops them for execution by the CPU 811, and various programs. , A hard disk device 813 storing data and the like, an FD drive 814 loaded with the FD 100 and accessing the loaded FD 100, a CD-ROM 110 loaded with the CD-ROM 110, and a CD-ROM drive 815 accessing the loaded CD-ROM 110 An I / O interface 816 that is connected to the spectrocolorimeter 70 shown in FIGS. 1 and 2 and receives colorimetric values from the spectrophotometer 70 is built-in. The image display device 82, the keyboard 83, and the mouse 84 are connected to each other via the bus 85. It is.

  Here, the CD-ROM 110 stores a color chart creation program for operating the personal computer 80 as a color chart creation device. The CD-ROM 110 is loaded in the CD-ROM drive 815 and the CD-ROM 110 is loaded. The color chart creation program stored in the ROM 110 is uploaded to the personal computer 80 and stored in the hard disk device 813.

  It is assumed that a program or the like necessary for realizing a profile creation function and a profile correction function, which will be described later, built in the personal computer 80 is already installed in the personal computer 80.

  As described above, since the personal computer 80 has a color chart creation function, a profile creation function, and a profile correction function, each function in the personal computer 80 will be described separately below.

  First, a color chart creation function built in the personal computer 80 will be described with reference to FIGS.

  FIG. 4 is a flowchart showing an embodiment of the color chart creation method of the present invention.

  This color chart creation method creates a color chart in which a fixed patch group corresponding to an example of the first patch group according to the present invention and an image dependent patch group corresponding to an example of the second patch group according to the present invention are arranged. The color chart creating method includes an image acquisition process (step S11), a thinning process process (step S12), an area selection process (step S13), and a chart creation process (step S14).

  Details of each step of the color chart creation method shown in FIG. 4 will be described later.

  FIG. 5 is a diagram showing an embodiment of the color chart creation program of the present invention.

  The color chart creation program 210 shown in FIG. 5 is stored in the CD-ROM 110 shown in FIG.

  The color chart creation program 210 is executed in the personal computer 80 shown in FIGS. 1, 2, and 3, and causes the personal computer 80 to operate as an embodiment of the color chart creation apparatus according to the present invention. . The color chart creation program 210 includes an image acquisition unit 211, a thinning processing unit 212, an area selection unit 213, and a chart creation unit 214.

  Each element of the image acquisition unit 211, the thinning processing unit 212, the region selection unit 213, and the chart creation unit 214 constructed by the color chart creation program 210 is the same as the color chart creation program 210 shown in FIGS. When installed and executed in the personal computer 80 shown in FIG. 3, the image acquisition process (step S11), the thinning process (step S12), the region selection process (step S13) of the color chart creation method shown in FIG. And it is a program part which performs each step of a chart preparation process (step S14).

  Detailed description of each element of the color chart creation program 210 will be given later.

  FIG. 6 is a functional block diagram showing an embodiment of the color chart creating apparatus of the present invention.

  In the color chart creating apparatus 300 shown in FIG. 6, the color chart creating program 210 shown in FIG. 5 is installed in the personal computer 80 shown in FIGS. 1, 2, and 3, and the color chart creating program 210 is installed in the personal computer. This is realized by being executed within 80.

  The color chart creating apparatus 300 shown in FIG. 6 includes a fixed patch group corresponding to an example of a first patch group according to the present invention and an image-dependent patch group corresponding to an example of a second patch group according to the present invention. The color chart creation apparatus 300 includes an image acquisition unit 311, a thinning processing unit 312, a region selection unit 313, and a chart creation unit 314.

  Each element of the image acquisition unit 311, the thinning processing unit 312, the region selection unit 313, and the chart creation unit 314 included in the color chart creation apparatus 300 constitutes a color chart creation program 210 shown in FIG. 5. The elements of the image acquisition unit 211, the thinning processing unit 212, the region selection unit 213, and the chart creation unit 214 as program parts are shown in FIG. 1, FIG. It is constructed by combining the hardware of the personal computer 80 shown in FIG. 3 with the OS and application programs.

  Next, each step of the color chart creation method shown in FIG. 4, each program part of the color chart creation program 210 shown in FIG. 5, and each element of the color chart creation apparatus 300 shown in FIG. 6 will be described.

  Note that each program component of the color chart creation program 210 shown in FIG. 5 and each element of the color chart creation apparatus 300 shown in FIG. 6 correspond one-to-one to each step of the color chart creation method shown in FIG. Here, each step of the color chart creation method shown in FIG. 4 is taken up and explained, so that each program part of the color chart creation program 210 shown in FIG. 5 and each element of the color chart creation apparatus 300 shown in FIG. It shall also serve as an explanation.

  First, in the image acquisition process (step S11) of the color chart creating method shown in FIG. 4, the CD-ROM on which the color image is recorded functions as the color chart creating apparatus 300 shown in FIG. The CD-ROM loading slot 81b of the personal computer 80 shown in FIG. 3 is loaded, and when the loaded CD-ROM is accessed by the CD-ROM drive 815, the color image is acquired.

  FIG. 7 is a diagram showing an example of a color image acquired in the image acquisition process (step S12) of the color chart creation method shown in FIG.

  FIG. 7 shows an evaluation image 400 as an example of a color image acquired in the image acquisition process (step S12). The evaluation image 400 is a CMYK for printing corresponding to the printing machine 40. It is a color image expressing colors in a CMYK color space for printing, which is represented by evaluation image data expressing colors in a color space. Originally, the evaluation image 400 is output as a printed matter by the printing machine 40 (see FIG. 1), and is also output as a proof image by the personal computer 50 (see FIG. 1) and the printer 60 (see FIG. 1). By comparing the color of the printed material and the color of the proof image, it is used for the reproducibility evaluation of the printer 60 by the user, and five color images 401, 402, 403, 404 desirable for such reproducibility evaluation. , 405 are combined images.

  Next, in the thinning process step (step S12) shown in FIG. 4, the human visual frequency is compared with the color image (here, the evaluation image 400; see FIG. 7) acquired in the image acquisition step (step S11). By applying a Gaussian filter that approximates the characteristics and the output resolution is about 25 to 120 dpi, thinning processing is performed on the color image.

  Next, in the region selection process (step S13) shown in FIG. 4, first, statistical processing of the appearance frequency is executed for the color of each pixel of the evaluation image subjected to the thinning process in the thinning process (step S12). An appearance frequency is obtained for each of a plurality of regions obtained by dividing a CMYK color space for printing, which will be described later, and regions are extracted from the one with the highest frequency. Next, an area is selected from the extracted areas by a selection procedure described later. In the present embodiment, an area obtained by dividing the CMYK color space for printing in 10% steps and a color distribution that requires accuracy are captured with high accuracy in order to widely capture the color distribution tendency of the entire evaluation image. Therefore, the color appearance frequency is calculated for an area obtained by dividing the CMYK color space for printing in 5% steps, and the area is preferentially selected from the higher frequency.

  8 to 11 are explanatory diagrams for explaining the region selection procedure in the region selection process (step S13) shown in FIG.

FIG. 8 shows a 10% patch group 501 in which color patches of respective colors representing areas obtained by dividing the CMYK color space for printing in 10% steps are arranged in the order of frequencies obtained by statistical processing. In this case, the color corresponding to the center point of each region is employed as the color representing the region. Here, for convenience of illustration, a limited number of color patches are shown, but at this stage, selection priority is given to all areas, and no area is selected. Also, below the 10% patch group 501, a table of CMYK values expressing the color of each color patch is shown. Among the color patches composing the 10% patch group 501 shown in FIG. 8, colors that overlap in color with the color patches constituting the fixed patch group represented by the halftone data shown in FIG. Since patches may exist, color patches with overlapping colors are deleted from the 10% patch group 501. In the CMYK color space for printing, L ^* <30
The dark color included in the area corresponding to the area has a small effect of improving practical color matching accuracy when the color chart created by the color chart creation method of the present embodiment is used for correcting the device link profile described later. To the 10% patch group 501. Further, the color frequency statistic based on the region where the color space is divided in 10% steps is for reflecting the overall color tendency of the image in the profile, so that C ^* <30 in the CMYK color space for printing. However, C ^* = √ ((a ^* ) ² + (b ^* ) ² )
A color patch of a low saturation color included in the area corresponding to is also deleted from the 10% patch group 501. Such deletion of the color patch is a selection of a color patch that remains without being deleted if it is reversed.

  FIG. 9 shows a color patch after the color patches of the 10% patch group 501 shown in FIG. 8 that overlap with the color of the fixed patch group described above, the dark color, and the low-saturation color patch are deleted. A 10% patch group 502 is shown in which a predetermined number is selected and arranged in the order of frequencies obtained by statistical processing. That is, each color patch constituting the 10% patch group 502 shown in FIG. 9 represents each area selected with priority in the area selection process (step S13).

FIG. 10 shows a 5% patch group 503 in which color patches of respective colors representing areas obtained by dividing the CMYK color space for printing in 5% steps are arranged in the order of frequencies obtained by statistical processing. In this case as well, the color corresponding to the center point of each region is adopted as the color representing the region. Also, below the 5% patch group 503, a table of CMYK values expressing the color of each color patch is shown. Among the color patches constituting the 5% patch group 503 shown in FIG. 10, colors whose colors overlap with those of the color patches constituting the fixed patch group represented by halftone data shown in FIG. 12 described later. Since patches may exist, color patches with overlapping colors are deleted from the 5% patch group 503. In the CMYK color space for printing, L ^* <30
As described above, the dark color included in the region corresponding to is a practical color matching accuracy when the color chart created by the color chart creation method of the present embodiment is used for correcting the device link profile described later. Since the effect of enhancing is small, the 5% patch group 503 is deleted. In addition, the color frequency statistic by the area where the color space is divided in 5% steps is intended to reflect the tendency of light colors with high human eye sensitivity in the profile, so in the CMYK color space for printing, ^* > 35, provided that C ^* = √ ((a ^* ) ² + (b ^* ) ² )
A color patch having a high saturation color included in the area corresponding to is also deleted from the 5% patch group 503. Further, for each color patch whose color overlaps with the 10% patch group 502 selected from the color patches of each color representing each area obtained by dividing the CMYK color space for printing in 10% steps shown in FIG. It is deleted from the patch group 503.

  FIG. 11 shows a color that overlaps the color of the fixed patch group described above from the 5% patch group 503 shown in FIG. 10, a dark color, a highly saturated color, and a 10% patch group 502 shown in FIG. A 5% patch group 504 is shown in which a predetermined number of color patches after the deletion of each color patch of the color overlapping with the color are selected and arranged in the order of the frequency obtained by the statistical processing. Each color patch constituting the 5% patch group 504 shown in FIG. 11 also represents each area selected with priority in the area selection process (step S13).

  Next, in the chart creation process (step S14) shown in FIG. 4, a fixed patch group composed of color patches of each predetermined color, and color patches of each color representing each area selected in the area selection process (step S13). Chart data expressing colors in the CMYK color space for printing is generated, which represents a color chart in which image-dependent patch groups arranged in the order of the frequencies are arranged.

  FIG. 12 is an explanatory diagram illustrating a specific example of halftone data expressing colors in the CMYK color space for printing applied to the fixed patch group in the chart creation process (step S14) shown in FIG.

  As shown in FIG. 12, the colors constituting the fixed patch group are obtained by regularly changing the halftone% for each of the four CMYK colors for printing.

  FIG. 13 is a diagram showing an example of a color chart represented by the chart data created in the chart creation process (step S14) shown in FIG.

  FIG. 13 shows a color chart 500 actually output based on the chart data representing the color chart created in the chart creation process (step S14). In the upper part of the color chart 500, a fixed patch group 505 composed of color patches of colors represented by halftone data shown in FIG. 12, in which the halftone percentage is regularly changed for each of the four CMYK colors for printing, is arranged. ing. Further, an image-dependent patch group 506 including a 10% patch group 502 shown in FIG. 9 and a 5% patch group 504 shown in FIG.

  As described above, the fixed patch group composed of the color patches of each predetermined color and the color of each part of the acquired color image are preferentially selected from the ones having a higher frequency of appearance in each of a plurality of regions on the color space. According to the color chart creation method for creating a color chart in which image-dependent patch groups composed of color patches of respective colors representing each region are arranged, the color image acquired in the image acquisition process (step S12) is shown in FIG. A color image including a color that the user considers important, such as the evaluation image 400 shown, is prepared, and the prepared color image is acquired in the image acquisition process (step S12). A color chart suitable for a profile correction function to be described later is created.

  In the description of the present embodiment, the chart creation process according to the present invention is an image in which color patches representing each color representing each area selected in the area selection process are arranged in the order of the frequency as the second patch group. Although an example using the dependency patch group has been given, the chart creation process according to the present invention uses a patch group composed of color patches of each color representing each area selected in the area selection process as the second patch group. There may be.

  In the description of the present embodiment, an example in which the chart creation process according to the present invention creates chart data representing a color chart has been described. However, the chart creation process according to the present invention is based on chart data representing a color chart. It is also possible to create an actually output image.

  Next, a profile creation function built in the personal computer 80 will be described.

  First, a printing profile creation method using this creation function will be described.

Chart data representing colors in a CMYK color space for printing, representing a color chart in which fixed patch groups and image-dependent patch groups are arranged, created by the color chart creating method described with reference to FIGS. 1 is output by the printing machine 40 shown in FIG. 1 according to the printing procedure in the printing and proof image creation system shown in FIG. 1, and is a color chart as a printed matter (here, color chart 500; see FIG. 13). Create Each color patch of the fixed patch group 505 and the image-dependent patch group 506 constituting the color chart 500 is measured by the spectrocolorimeter 70 shown in FIGS. By doing so, obtain the CMYK values of the CMYK color space for printing, the correspondence between the L ^* a ^* b ^* values of the L ^* a ^* b ^* color space.

Since the correspondence obtained in this way is limited in the number of color patches constituting the color chart, the CMYK values and the L ^* a ^* b ^* values for coordinate points with a rather coarse interval in the CMYK color space for printing are used ^. Correspondence with value. For this reason, after obtaining this correspondence relationship, an interpolation operation or the like is applied to this correspondence relationship to create a print profile in which the correspondence relationship with respect to coordinate points of desired fine intervals in the CMYK space for printing is defined. . In applying an interpolation operation or the like to this correspondence relationship, for example, an operation in a profile creation method disclosed in Japanese Patent Laid-Open No. 2003-289446 that creates a profile using a color chart including an arbitrary color patch. A desired print profile can be created by applying a method or the like.

  Next, a printer profile creation method will be described.

In the personal computer 50 shown in FIG. 1, halftone data represented by four colors of CMYK is sequentially changed to 0%, 10%,..., 100% for each color, and the halftone data generated in this way is sequentially sent to the printer 60. The printer 60 prints out a color chart based on the halftone data. Each color patch constituting this color chart is measured by the spectrocolorimeter 70 shown in FIGS. Thereby, obtained about the printer 60, the CMYK values of the CMYK color space for a printer, the relationship between L ^* a ^* b ^* values of the L ^* a ^* b ^* color space.

Since the correspondence obtained in this way is limited in the number of color patches constituting the color chart as in the case of creating the print profile described above, the coordinate points of the CMYK color space for the printer are fairly coarse. Is a correspondence relationship between the CMYK value and the L ^* a ^* b ^* value, and an interpolation operation or the like is applied to this correspondence relationship to define a correspondence relationship with respect to coordinate points at a desired fine interval in the CMYK space for the printer. The created printer profile is created.

  By combining the print profile created in this way and the inverse conversion printer profile in which the inverse conversion of the printer profile is defined, the image data expressing the color in the CMYK color space for printing is converted into the CMYK color for the printer. A device link profile for conversion to image data expressing colors in space is obtained.

  When the device link profile is thus created in the personal computer 80 constituting the printing and proof image creation system shown in FIG. 1, the created device link profile is installed in the personal computer 50 shown in FIG. . In the personal computer 50, as described above, the image data described in PDL input from the workstation 20 is converted into image data expressing colors in the CMYK color space for printing. The image data for printing is converted into image data expressing colors in the CMYK color space for the printer using the device link profile installed in the personal computer 50, and is converted into image data for the printer by the printer 60. A base image is printed out. As a result, a proof image that is similar in color to the image printed by the printer 40 shown in FIG. 1 is created as much as possible.

  However, as described in the “Background Art” section, the measurement error by the spectrocolorimeter 70, the color error of the color patch due to the output characteristics of the target device for which the profile is to be created, and the skin color are representative. Various errors such as color errors caused by adding color patches of practically important colors to the color chart and fluctuation factors may cause a phenomenon in which colors slightly differ between the printed material and the proof image. In order to cope with such a phenomenon, it is desirable to appropriately correct a color conversion definition such as a print profile, a printer profile, or a device link profile obtained by combining a print profile and a printer profile.

  In the following, the profile correction function built in the personal computer 80 will be described with reference to FIG. Here, a method for correcting a profile will be described using a device link profile as an example.

  FIG. 14 is a flowchart showing an embodiment of the color conversion definition correcting method of the present invention.

  This color conversion definition correction method outputs a color image based on image data, and is a CMYK color space for printing that depends on the printer 40 corresponding to an example of the first device according to the present invention (the first color according to the present invention). An example of a device color space) and a CMYK color space for a printer that depends on the printer 60 corresponding to an example of a second device according to the present invention that outputs a color image based on image data (second device color according to the present invention) A device link profile correction method for correcting a device link profile that defines a color conversion relationship with an example of a space, a first chart output process (step S21), a color conversion process (step S22), It consists of a second chart output process (step S23), a difference measurement process (step S24), and a definition correction process (step S25). There.

  The first chart output process (step S21) of the device link profile correction method shown in FIG. 14 is a fixed patch group and an image dependent patch group created by the color chart creation method described with reference to FIGS. Represents a color chart in which colors are expressed in a CMYK color space for printing (this chart data corresponds to an example of the first chart data according to the present invention. Is referred to as the first chart data), the color chart is output by the printing machine 40 shown in FIG. 1, and the processing in the first chart output process (step S21) is performed by the printing profile described above. Same as part of the creation method that was executed when creating the print profile It is a process. Therefore, here, the color chart as the printed matter (here, the color chart 500; see FIG. 13) created when creating the print profile without executing the first chart output process (step S21), The color chart obtained in the first chart output process (step S21) is used.

  In the color conversion process (step S22) of the device link profile correction method shown in FIG. 14, the first chart data is converted into a CMYK color space for a printer based on the device link profile installed in the personal computer 50 shown in FIG. To convert to the second chart data expressing the color. This second chart data corresponds to an example of the second chart data referred to in the present invention.

  Next, in the second chart output process (step S23) of the device link profile correction method shown in FIG. 14, the color chart is shown in FIG. 1 based on the second chart data obtained in the color conversion process (step S22). Is output by the printer 60 shown.

  Next, in the difference measurement process (step S24) of the device link profile correction method shown in FIG. 14, each color patch of the color chart output in the first chart output process (step S21) and the second chart output process The color patches in the color chart output in (Step S23) are measured by the spectrocolorimeter 70 shown in FIGS. 1 and 2, and the colors in the color patches corresponding to each other between the color charts are measured. Find the difference.

  Next, in the definition correction process (step S25) of the device link profile correction method shown in FIG. 14, among the differences obtained in the difference measurement process (step S24), the differences in the color patches of the image-dependent patch group 506 are fixed. The device link profile installed in the personal computer 50 shown in FIG. 1 is corrected with emphasis on the difference in the color patches of the patch group 505 as described later.

  As a specific method for correcting the device link profile, for example, the correction method disclosed in Japanese Patent Laid-Open No. 2000-278547 can be applied, and the device link profile can be corrected by such a correction method. it can.

  The accuracy of the device link profile is gradually improved by repeatedly executing the device link profile correction method shown in FIG. In repeating the device link profile correction method, in the first correction, the difference in the color patch of the fixed patch group 505 and the difference in the color patch of the image-dependent patch group 506 obtained in the difference measurement process (step S24). The device link profile is modified using the difference between the two. In the second and subsequent corrections, the image dependence created based on the evaluation image 400 (see FIG. 7) that is desirable for the reproducibility evaluation of the printer 60 by the user out of the difference measurement process (step S24). Emphasizing differences in the color patches of the patch group 506, the device link profile is corrected using only these differences.

  The image-dependent patch group 506 has a smaller number of color patches than the number of color patches of the fixed patch group 505, but reflects the color tendency of the evaluation image 400 (see FIG. 7). The profile is efficiently corrected by the correction that emphasizes the difference in the color patch of the dependent patch group 506. In addition, since the image-dependent patch group 506 is formed by arranging color patches in the order of the color frequency, when the profile is corrected in the definition correction process (step S25), for example, a color having a higher frequency is used. An application in which a user manually selects a patch and applies it to profile correction is also possible.

  In the description of the present embodiment, the definition correction process according to the present invention is based on the difference between the color patch of the fixed patch group 505 and the color patch of the image dependent patch group 506 in the first correction. In the second and subsequent corrections, the device link profile is corrected using only the differences in the color patches of the image-dependent patch group 506. However, the definition correction process referred to in the present invention is as follows. For example, the device link profile may be corrected using only the difference in the color patch of the image-dependent patch group 506, or the difference in the color patch of the image-dependent patch group 506 may be corrected by weighting. Focus on device links rather than differences in 505 color patches. It may be intended to correct the file.

1 is an overall configuration diagram of a printing and proof image creation system to which an embodiment of the present invention is applied. FIG. 2 is an external perspective view of a spectrocolorimeter and a personal computer indicated by blocks in FIG. 1. FIG. 3 is a hardware configuration diagram of the personal computer shown in FIG. 2. It is a flowchart which shows one Embodiment of the color chart production method of this invention. It is the figure which showed one Embodiment of the color chart preparation program of this invention. It is a functional block diagram which shows one Embodiment of the color chart production apparatus of this invention. FIG. 5 is a diagram showing an example of a color image acquired in an image acquisition process (step S12) of the color chart creation method shown in FIG. It is explanatory drawing explaining the 1st procedure of the area | region selection in the area | region selection process (step S13) shown in FIG. It is a figure showing the area | region selected by the 1st procedure of the area | region selection in the area | region selection process (step S13) shown in FIG. It is explanatory drawing explaining the 2nd procedure of the area | region selection in the area | region selection process (step S13) shown in FIG. It is a figure showing the area | region selected by the 2nd procedure of the area | region selection in the area | region selection process (step S13) shown in FIG. FIG. 5 is an explanatory diagram illustrating a specific example of halftone data expressing colors in a CMYK color space for printing applied to a fixed patch group in the chart creation process (step S14) shown in FIG. It is a figure which shows an example of the color chart which the chart data produced in the chart production process (step S14) shown in FIG. 4 represents. It is a flowchart which shows one Embodiment of the color conversion definition correction method of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Color scanner 11 Original image 20 Workstation 30 Film printer 40 Printing machine 41 Print image 50 Personal computer 60 Printer 61 Proof image 70 Spectrocolorimeter 80 Personal computer 81 Main body apparatus 81a FD loading port 81b CD-ROM loading port 811 CPU
812 Main memory 813 Hard disk device 814 FD drive 815 CD-ROM drive 816 I / O interface 82 Image display device 82a Display screen 83 Keyboard 84 Mouse 85 Bus 90 Color chart 91 Cable 100 FD
110 CD-ROM
210 Color chart creation program 211 Image acquisition unit 212 Thinning processing unit 213 Area selection unit 214 Chart creation unit 300 Color chart creation device 311 Image acquisition unit 312 Thinning processing unit 313 Area selection unit 314 Chart creation unit 400 Evaluation image 401, 402, 403, 404, 405 Image 500 Color chart 501 10% patch group 502 10% patch group 503 5% patch group 504 5% patch group 505 Fixed patch group 506 Image dependent patch group

Claims (5)

An image acquisition process for acquiring a color image;
A region selection step in which the color of each part of the color image acquired in the image acquisition step preferentially selects the region from the higher frequency of appearance in each of a plurality of regions on the color space;
A chart creation process for creating a color chart in which a first patch group composed of color patches of each predetermined color and a second patch group composed of color patches of each color representing each area selected in the area selection process; A method for creating a color chart, comprising:   The chart creation process is a process of using a patch group in which color patches of each color representing each area selected in the area selection process are arranged in the order of the frequency as the second patch group. The color chart creation method according to claim 1. An image acquisition unit for acquiring a color image;
A region selection unit that preferentially selects the region from the higher frequency that the color of each part of the color image acquired by the image acquisition unit appears in each of a plurality of regions on a color space;
A chart creation unit for creating a color chart in which a first patch group composed of color patches of each predetermined color and a second patch group composed of color patches of each color representing each region selected by the region selection unit; A color chart creating apparatus comprising: Embedded in a computer, on the computer,
An image acquisition unit for acquiring a color image;
A region selection unit that preferentially selects the region from the higher frequency that the color of each part of the color image acquired by the image acquisition unit appears in each of a plurality of regions on a color space;
A chart creation unit for creating a color chart in which a first patch group composed of color patches of each predetermined color and a second patch group composed of color patches of each color representing each region selected by the region selection unit; A color chart creation program characterized by building Color conversion between a first device color space dependent on a first device that outputs a color image based on image data and a second device color space dependent on a second device that outputs a color image based on image data In the color conversion definition correction method for correcting the color conversion definition that defines the relationship between
The first patch group composed of the color patches of each predetermined color and the respective areas preferentially selected from the ones having a higher frequency of appearance of the colors of the respective parts of the predetermined color image in each of the plurality of areas on the color space. A color chart in which a second patch group composed of color patches of each color is arranged is output based on first chart data representing colors in the first device color space, and the color chart is output by the first device. Chart output process,
A color conversion process for converting the first chart data into second chart data representing colors in the second device color space based on the color conversion definition;
A second chart output process of outputting the color chart by the second device based on the second chart data obtained in the color conversion process;
By measuring each color patch of the color chart output in the first chart output process and each color patch of the color chart output in the second chart output process, between the color charts A difference measurement process for obtaining a color difference between color patches corresponding to each other;
A definition correction step of correcting the color conversion definition by focusing on the difference in the color patch of the second patch group among the differences obtained in the difference measurement process, rather than the difference in the color patch of the first patch group; A color conversion definition correction method comprising:

Images