JP2007074531A - Method and device for color processing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and a device for color processing to perform color reproduction adjustment easily and efficiently. <P>SOLUTION: An initial color correction LUT is created, a variable for adjusting the initial color correction LUT is selected, and a plurality of color correction LUTs adjusted according to the variable are created with the initial color correction LUT as the center. From the plurality of color correction LUTs, a thumbnail image arrangement is printed and the most desirable image is selected from the printed thumbnail image arrangement. Taking a color correction LUT corresponding to the selected thumbnail image as an initial color correction LUT, the above-mentioned steps are repeated until a user's requirements are met, and a selected thumbnail image is printed in an appropriate size. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a color processing method and a color processing apparatus for adjusting color reproduction.

  In recent years, with the spread of personal computers / workstations, desktop publishing (DTP) and CAD are widely used. Under such circumstances, a color reproduction technique for matching a color expressed on a monitor by a computer with a color reproduced on an output medium is important. For example, in DTP, a workflow is performed in which a color image is created / edited / processed on a monitor and an image is output as a product by a color printer. (Patent Document 1) In this workflow, the user strongly desires that the color image on the monitor and the printer output image coincide perceptually.

  However, in the color reproduction technique, it is difficult to achieve such perceptual coincidence between the color image on the monitor and the printer output image. This difficulty is due to the following reasons.

  In a color monitor, a color image is expressed by emitting light of a specific wavelength using a phosphor. On the other hand, in a color printer, light of a specific wavelength is absorbed using ink or the like, and a color image is expressed by the remaining reflected light.

As described above, since various characteristics are different between the monitor and the printer, it is necessary to perform fine adjustment by the color correction LUT in order to match the color appearance of the monitor display image and the printed matter.
Japanese Patent Laid-Open No. 9-138742

  However, since the appearance of the color of the printed material cannot be easily predicted, it is necessary to repeat printing → adjustment → printing to obtain the desired color reproduction, which wastes time and resources. There was a problem.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a color processing method and apparatus for easily and efficiently performing color reproduction adjustment.

In the color reproduction adjustment of the printer,
Creating an initial color correction LUT;
Selecting a variable for adjusting the initial color correction LUT;
Creating a plurality of color correction LUTs centered on the initial color correction LUT and adjusted according to the variables;
Printing a thumbnail image array from the plurality of color correction LUTs;
Selecting the most preferred image from the printed thumbnail image array;
A step of repeating each of the steps until a user's request is satisfied, using a color correction LUT corresponding to the selected thumbnail image as an initial color correction LUT;
And a final image printing step of printing the selected thumbnail image in an appropriate size.

  When the user selects a variable for adjusting the color correction LUT and prints the thumbnail image array, the color reproduction adjustment desired by the user can be easily and efficiently performed.

<Embodiment 1>
FIG. 1 is a block diagram of a color processing apparatus according to the present invention. In the above configuration, 101 is a CPU, 102 is a main memory, 103 is a SCSI interface, 104 is a network interface, 105 is an HDD, 106 is a graphic accelerator, 107 is a color monitor, 108 is a USB controller, 109 is a color printer, and 110 is a keyboard. / Mouse controller, 111 is a keyboard, 112 is a mouse, 113 is a local area network, and 114 is a PCI bus.

  A digital image printer output operation in the above configuration will be described. First, an image application stored in the HDD 105 is activated by the CPU 101 based on an OS program that has received a user instruction. Subsequently, the digital image data and representative color data stored in the HDD 105 are transferred to the main memory 102 via the PCI bus 114 via the SCSII / F 103 based on a command from the CPU 101 in accordance with the processing in the image application according to the user's instruction. Transferred. Alternatively, image data stored in a server connected to the LAN or digital image data on the Internet is transferred to the main memory 102 via the PCI bus 114 via the network I / F 104 according to a command from the CPU 101. Hereinafter, an embodiment will be described on the assumption that the digital image data held in the main memory 102 is image data in which each RGB color signal is represented by 8 bits without a sign. The digital image data held in the main memory 102 is transferred to the graphic accelerator 106 via the PCI bus 114 in response to a command from the CPU 101. The graphic accelerator 106 performs D / A conversion on the digital image data and then displays the color monitor through the display cable. To 107. As a result, an image is displayed on the color monitor 107. When the user instructs the image application to output the digital image stored in the main memory 102 from the printer 109, the image application transfers the digital image data to the printer driver. The CPU 101 converts the digital image data into CMYK digital image data based on a process flowchart described later of the printer driver, and transmits the CMYK image data to the printer 109 via the USB controller 108. As a result of the series of operations described above, a CMYK image is printed by the printer 109.

  Hereinafter, the printer driver operation in the above configuration will be described with reference to the user interface of FIG. 2 and the flowchart of FIG.

  First, in step S <b> 301, RGB 24-bit image data (each color signal is unsigned 8-bit image data) transferred from the image application is stored in the main memory 102.

  In step S302, an initial color correction LUT is created based on the processing described later. The color correction LUT has a data structure as shown in FIG. 4 showing the correspondence between the color coordinate data of the grid points in the RGB color space and the coordinate values of the L * a * b * color space reproduced by the grid points. Is done. The R / G / B value step is described at the head of the data structure, and thereafter, the color coordinates corresponding to each grid point are L * value, a * value, and b * value are R, G, and B, respectively. Nested in order. In the following, the color correction LUT is also referred to as color distribution data because the data structure indicates a color distribution.

  In step S303, the matrix size and step width are designated from the user interface, and the matrix size colors are shifted vertically, horizontally, and diagonally by the step width designated in the chromaticity direction based on the initial color correction LUT. A correction LUT is created. For example, when the matrix size 3 × 3 and the step width 1 are selected, [Δa *, Δb *] = [− 1, +1], [0, +1], [+1, +1], [ -1, 0], [0, 0], [+1, 0], [-1, -1], [0, -1], [+1, -1] Create a color correction LUT. At this time, the grid points that are outside the color reproduction range of the printer are mapped based on the SGCK technique described later.

  In step S304, RGB 24-bit image data is converted into L * a * b * fixed-point data based on a plurality of color correction LUTs, and stored again in the main memory 102. Tetrahedral interpolation is used for the conversion.

  In step S305, the previous L * a * b * fixed-point data is converted into CMYK 32-bit image data (CMYK color signals are unsigned 8-bit image data) in accordance with a predetermined color conversion LUT, and again stored in the main memory 102. Store.

  In step S306, thumbnail images of CMYK 32-bit image data stored in the main memory are created and arranged two-dimensionally in the order of chromaticity variation. This thumbnail image array is sent to the user interface and printer 109 for printing. The size of the thumbnail image is reduced so that the image arrangement is printed on one sheet of paper.

  In step S307, the user selects the most preferable thumbnail image arrangement from the printed thumbnail image arrangements, and selects from the arrangement displayed on the user interface.

  In step S308, it is determined whether the image selected in step S307 is sufficiently adjusted, and it is selected whether final printing is performed or adjustment is performed again. When the final printing is selected, the process proceeds to step S309, and when readjustment is selected, the process proceeds to step S303 and readjustment is performed.

  In step S309, the image selected in step S307 is transmitted to the printer 109 via the USB controller 108 with an appropriate size and printed.

  Hereinafter, the initial color correction LUT creation processing in step S302 will be described with reference to the flowchart of FIG.

  In step S501, mapping source color reproduction information and mapping destination color reproduction information determined by a method not shown are acquired. These color reproduction information may be, for example, sRGB conversion formulas or device color reproduction characteristics measured in advance. As an example, FIG. 6 shows a schematic diagram of printer color reproduction.

  In step S502, mapping source color gamut information and mapping destination color gamut information are generated in the L * a * b * color space from the acquired mapping source color reproduction information and mapping destination color reproduction information. As an example, FIG. 7 shows color gamut information. Note that the color gamut information is expressed by a combination of a plurality of polygons.

  In step S503, based on the SGCK technique recommended in TC8-03 of the International Commission on Illumination (CIE) for the mapping operation in step 504, the color gamut information of the mapping source is converted to L * a * as described later. Scale in b * color space.

  In step S504, color gamut mapping is performed in the L * a * b * color space, as will be described later, based on the SGCK technique.

  In step S505, the mapping result in step S504 is converted from L * a * b * values to RGB values using the color reproduction information of the mapping destination to generate a color correction LUT.

  Hereinafter, the gamut scaling processing based on the SGCK technique for the gamut information generated in step 502 in step S503 will be described with reference to the flowchart of FIG.

  In step S801, the color gamut information generated in step 502 is acquired.

  In step S802, the lightness value is scaled to normalize the lightness range for each vertex of the line segment constituting the color gamut information as in step S1302.

  In step S803, the brightness value is scaled using the sigmoid function for each vertex of the line segment constituting the color gamut information, as in step S1303.

  In step S804, the lightness value is corrected based on the saturation value for each vertex of the line segment constituting the color gamut information, as in step S1304.

  In step S805, the color gamut information subjected to the processing in steps S802 to S804 is stored in the main memory 102.

  Below, the outline of the mapping process by SGCK technique in step S504 is demonstrated according to the flowchart of FIG. Details of the process are described in the TC8-03 document of the International Commission on Illumination.

  In step S901, the color to be mapped necessary for generating the LUT in step 502 is acquired.

  In step S902, the brightness value is scaled so as to normalize the brightness range. An example of the change in color reproduction due to this processing is shown in FIG. Here, the dashed line represents the color reproduction of the mapping source, the solid line represents the color reproduction after processing, and the dotted line represents the color gamut of the mapping destination.

  In step S903, the brightness value is scaled using a sigmoid function. An example of the change in color reproduction by this processing is shown in FIG. Here, the one-dot broken line represents the color reproduction that is the processing result of step S902, the solid line represents the color reproduction after processing, and the dotted line represents the color gamut of the mapping destination.

  In step S904, the lightness value is corrected based on the saturation value. An example of a change in color reproduction due to this processing is shown in FIG. Here, the one-dot broken line represents the color reproduction that is the processing result of step S903, the solid line represents the color reproduction after the processing, and the dotted line represents the color gamut of the mapping destination.

  In step S905, brightness and saturation are mapped while the hue value is preserved. This mapping will be described with reference to FIG. In the figure, the solid line represents the color gamut of the mapping source scaled in step S503, and the broken line represents the color gamut of the mapping destination. When mapping the color M, first, the equal hue section information closest to the hue of the color M is acquired from the scaled equal hue section information and the mapped destination hue section information. Subsequently, a lightness value having the maximum saturation with the same hue as M is calculated from the equi-hue cross-section information of the mapping destination, and the color on the L * axis having the lightness is defined as F. Then, the intersection Bsrc of the line connecting F and M and the scaled uniform color gamut section information is calculated, and the intersection of the line connecting F and M and the uniform color gamut sectional information of the mapping destination is calculated. Calculate Bdst. Subsequently, a point C that internally divides Bdst and F into 1: 9 is calculated. Here, if the distance between M and F is less than the distance between Bdst and C, no mapping is performed for the color M. On the other hand, if it exceeds, M is the value that internally divides Bsrc and C, and the color that internally divides between Bdst and C is the mapped value of M.

It is a block diagram which shows the system configuration | structure of the color reproduction editing apparatus of this invention. It is a figure showing the interface of the color reproduction editing apparatus of this invention. 6 is a flowchart illustrating processing of a printer driver in the color reproduction editing apparatus of the present invention. It is a figure explaining the data structure of a color correction LUT. It is a flowchart which shows the creation process of a color correction LUT. It is a figure which shows an example of color reproduction information. It is a figure which shows an example of color gamut information. It is a flowchart which shows the scaling of the color gamut information using SGCK technique. It is a flowchart which shows the SGCK technique as a color gamut mapping. It is a figure which shows the change of the color reproduction by SGCK technique. It is a figure explaining the color gamut mapping by SGCK technique.

Explanation of symbols

101 CPU
102 Main memory
103 SCSI I / F
104 Network I / F
105 HDD
106 graphics accelerator
107 color monitor
108 USB controller
109 Color printer
110 Keyboard / Mouse Controller
111 keyboard
112 mice
113 LAN
114 PCI bus
115 scanner

Claims (4)

In the color reproduction adjustment of the printer,
Creating an initial color correction LUT;
Selecting a variable for adjusting the initial color correction LUT;
Creating a plurality of color correction LUTs centered on the initial color correction LUT and adjusted according to the variables;
Printing a thumbnail image array from the plurality of color correction LUTs;
Selecting the most preferred image from the printed thumbnail image array;
Using the color correction LUT corresponding to the selected thumbnail image as an initial color correction LUT, repeating the steps until a user request is satisfied, and a final image printing step of printing the selected thumbnail image with an appropriate size A color reproduction adjustment method characterized by comprising:   2. The color reproduction adjustment method according to claim 1, wherein the variables are a size of an image array for adjusting the initial color correction LUT and a step width between adjacent images of the image array.   3. The color reproduction adjustment method according to claim 2, wherein the step width is based on a color difference.   2. The color reproduction adjustment method according to claim 1, wherein the adjustment to the initial color correction LUT is performed by shifting the grid points of the initial color correction LUT vertically, horizontally, and diagonally in the chromaticity direction by a selected step width.

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