JP2006303918A - Image processing apparatus and image processing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image processing apparatus capable of executing a plurality of times of color correction having different contents without changing a color correction parameter by utilizing a parameter to be used in dimension conversion in color correction conversion. <P>SOLUTION: In color correction conversion, a UCR quantity of 100×ucr% according to a parameter ucr value is used to convert an RGB value into a cmyk value and a dimension is added by one. Then, the color correction conversion is performed by an operation using a color correction parameter for colors in a CMYK space having the incremented dimension. In this case, the ucr value to be used in incrementing the dimension by one, as described above, is associated with a color correction mode. In this way, correction based on the plurality of color correction modes having different contents can each be realized without executing processing of changing or processing of generating the color correction parameter. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image processing apparatus and an image processing method, and more particularly to color correction for realizing desired color reproduction.

  In recent years, with the spread of personal computers and workstations, color document creation using DTP (desktop publishing) and CAD (computer-aided design) using these has become widely performed. In such an environment, a color reproduction technique in printing a color document is important. In the case where various color printers can be used, a highly accurate color reproduction management technique is required in order to always maintain color reproduction of color printing by these printers, for example. Specifically, there is a need for a color reproduction management technique that realizes a constant color reproduction that does not depend on the characteristics of the printing device and a stable color reproduction that does not depend on a change in the printing device over time or an environmental change.

  The characteristics of the printing device vary depending on the printing mechanism, color materials such as toner and ink, the type of printing medium such as paper used for printing, and the color reproduction characteristics change accordingly. For example, a change in color reproduction characteristics depending on the type of color material or print medium itself directly affects color reproduction. Even if the printing mechanism is the same model, a difference in color reproduction occurs due to a difference in the amount of color material applied to the paper, a subtle shift in the CMYK plate due to machine accuracy, and the like. Even if the same printing device is used, the color reproduction characteristics change due to changes over time, and the amount of color material attached to paper also changes depending on environmental conditions such as temperature and humidity.

  In commercial printing, CMS (color management system), which is a color reproduction management technique between printing devices, is generally used as a technique for suppressing the difference in color reproduction and maintaining the same color reproduction characteristics. In addition, calibration is used as a color reproduction management technique with respect to changes over time and environmental fluctuations, and thereby, for example, management is performed so that the amount of color material attached is constant.

  However, many of these calibration techniques manage color reproduction for each primary color of CMYK, and color reproduction focusing on intermediate colors such as secondary colors and tertiary colors is often out of scope. As a result, although color reproduction can be roughly maintained against changes with time and environmental fluctuations, the effect is limited. On the other hand, according to CMS using an ICC profile, which is a conventional color reproduction management method, color reproduction management between printing devices by managing a destination profile, or color reproduction management with respect to a change with time and environmental variation. Is possible. In addition, the present applicant has proposed another color reproduction management method in Japanese Patent Application No. 2004-024844. According to this method, color reproduction management that realizes desired color reproduction is automatically generated, and color reproduction management is realized by performing image output through the color conversion. All of the above CMS techniques realize color reproduction management by color conversion using a high-order function. In such a CMS technique, it is conceivable to increase the order of a high-order function as one method for improving the management accuracy of color reproduction. However, in this case, the pseudo contour in the printed image that is finally obtained when the solution unnecessarily vibrates with respect to the change in the color correction parameter, such as including an inappropriate solution due to the higher order. In some cases, the failure that occurs is more problematic than the effect obtained by increasing the order of the higher-order function.

  The present applicant has proposed a technique that further improves the above problem in Japanese Patent Application No. 2004-311377. In this technique, when a color correction is converted for a three-dimensional color signal value such as RGB, it is once converted into a four-dimensional signal such as YMCK, and this four-dimensional signal is converted for color correction. After that, the original three-dimensional color signal is converted. According to this, it is possible to improve the color reproduction management accuracy without causing a problem including an inappropriate solution as in the case of increasing the order. In this technique, first, dimension conversion is performed to convert a three-dimensional color signal into a four-dimensional color signal, and then color correction conversion is performed on the four-dimensional color signal using a color correction parameter. In order to perform appropriate or preferable color correction conversion, the color correction parameter is a color correction parameter that provides a target color reproduction target that realizes the color correction conversion in advance, and satisfies this color better. Generate.

JP 09-326938 A

  By the way, in the technique disclosed in the above-mentioned Japanese Patent Application No. 2004-311377, when a color correction parameter is set, the color correction conversion can realize only one conversion corresponding to the parameter, and the content of correction is changed. In this case, it is necessary to regenerate the color correction parameter. For example, the content of color correction may be changed depending on the type of image to be printed and the type of printing paper to be used. In addition, the content of color correction may be changed in order to obtain a more appropriate printing result in accordance with the specifications of the printing apparatus used for printing. In such a case, if the color correction parameter is generated each time, there is a problem that it is troublesome for the user.

  The present invention has been made to solve the above-described problems. The object of the present invention is to change the color correction parameters by using the parameters used in the dimension conversion in the color correction conversion. An object of the present invention is to provide an image processing apparatus and an image processing method capable of executing a plurality of color corrections having different contents without performing a process to be generated again.

  Therefore, in the present invention, the color correction conversion is performed to correct the color signal. After the color signal is converted into a color signal having an increased dimension, the color correction parameter is set to the color signal having the increased dimension. An image processing apparatus that performs color correction conversion using the correction parameters and then returns the original color signal to the original color signal, and the conversion parameters used for the conversion that increases the dimension of the color signal are different in the correction content of the color correction conversion. Parameter holding means for holding a plurality of color correction modes, correction mode acquisition means for acquiring a set color correction mode, and conversion parameters corresponding to the color correction mode acquired by the correction mode acquisition means are stored as parameters. A parameter acquisition means acquired from the means, and conversion for increasing the dimension of the color signal using the conversion parameter acquired by the parameter acquisition means, and a color signal having the increased dimension Conversion means for performing correction using the color correction parameter and then performing color correction conversion for returning to the original dimensional color signal, and the color correction parameter is a color obtained by conversion using the conversion parameter. The present invention is characterized in that the color difference between the target color and the estimated color represented by a predetermined color system of the signal is reduced.

  In another embodiment, the color correction conversion is performed to correct the color signal, and after the color signal is converted into a color signal having an increased dimension, the color correction parameter is used for the color signal having the increased dimension. In the color correction conversion for correcting the color signal and then returning to the original dimension color signal, the image processing apparatus performs the process of generating the color correction parameter, and the conversion parameter used for the conversion to increase the dimension of the color signal , Parameter holding means for holding a plurality of color correction modes with different correction contents of color correction conversion, and conversion using a conversion parameter corresponding to the color correction mode for one color correction mode held by the parameter holding means Target color acquisition means for obtaining a target color in a predetermined color system for the color signal obtained by the above, and the conversion parameter for the one color correction mode. Estimated color acquisition means for obtaining an estimated color in the predetermined color system of a color signal obtained by conversion using a color correction parameter for the color signal obtained by conversion, and the target color and the one color for the one color correction mode Parameter determining means for determining a color correction parameter so as to reduce the color difference from the estimated color, and a plurality of color correction modes in which the parameter holding means holds the processing by the target color acquisition means, the estimated color acquisition means, and the parameter determination means And a control means to be executed for each.

  Also, color correction conversion for correcting the color signal, after converting the color signal to a color signal having an increased dimension, the color signal having the increased dimension is corrected using a color correction parameter. An image processing method for performing color correction conversion to be performed and then returning to a color signal of the original dimension, wherein a plurality of conversion parameters used for conversion to increase the dimension of the color signal are different in the correction contents of the color correction conversion Prepared for each color correction mode, acquires the set color correction mode, acquires conversion parameters corresponding to the acquired color correction mode from the prepared conversion parameters, and uses the acquired conversion parameters to convert the color Performing conversion to increase the dimension of the signal, performing correction using the color correction parameter for the color signal having the increased dimension, and then performing color correction conversion to restore the original color signal. color Positive parameters, characterized in that it is obtained so as to reduce the color difference in each target color and the estimated color is represented by a predetermined color system of the color signal obtained by the conversion using the conversion parameter.

  In another embodiment, the color correction conversion is performed to correct the color signal, and after the color signal is converted into a color signal having an increased dimension, the color correction parameter is used for the color signal having the increased dimension. An image processing method for performing the process of generating the color correction parameter in color correction conversion for correcting the color signal and then returning to the original dimension color signal, the conversion being used for conversion to increase the dimension of the color signal A parameter is stored for each of a plurality of color correction modes having different correction contents of color correction conversion, and the color signal obtained by conversion using the conversion parameter corresponding to the color correction mode for the one color correction mode held. A target color in a predetermined color system is obtained, and color correction parameters for color signals obtained by conversion using the conversion parameters are used for the one color correction mode. Obtaining an estimated color of the color signal obtained by the conversion in the predetermined color system, determining a color correction parameter for the one color correction mode so as to reduce a color difference between the target color and the estimated color, The method includes a step of acquiring a color, acquiring the estimated color, and determining the color correction parameter for each of the plurality of color correction modes.

  According to the above configuration, when the dimension is increased by one, the conversion parameter is used, and this conversion parameter is associated with the color correction mode, so that each color correction in a plurality of color correction modes having different contents can be performed with the color correction parameter. This can be realized without executing again the process of changing or generating.

  According to another embodiment, the color correction mode and the conversion parameter are associated with each other in advance, thereby performing color conversion that increases the dimension from RGB to CMYK, for example, using the conversion parameter according to the color correction mode. In addition, by obtaining the estimated color in color conversion parameter generation, an appropriate color conversion parameter corresponding to the color correction mode can be obtained in association with the conversion parameter.

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

  FIG. 1 is a block diagram showing an image processing apparatus according to the first embodiment of the present invention. Specifically, the image processing apparatus of the present embodiment is configured by a personal computer connected to a printer through a communication line. In FIG. 1, 101 indicates a CPU, and 102 indicates a main memory. Reference numeral 103 denotes a SCSI interface that controls data exchange with the HDD 105. Reference numeral 104 denotes a network interface that controls transmission and reception of signals and data with a server on the local area network 113. A graphic accelerator 106 controls display on the color monitor 107. Reference numeral 108 denotes a USB controller that controls communication with the color printer 109. A keyboard / mouse controller 110 controls input / output between the keyboard 111 and the mouse 112. Reference numeral 114 denotes a PCI bus.

  An operation of printing out an image by the printer 109 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 stored in the HDD 105 is transferred to the main memory 102 via the PCI bus 114 via the SCSII / F 103 in accordance with the processing in the image application according to the user's instruction. 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 network I / F 104 and the PCI bus 114 in response to a command from the CPU 101.

  The digital image data held in the main memory 102 as described above is, for example, image data expressed by unsigned 8 bits of each color signal of RGB, and this image data is transmitted through the PCI bus 114 by a command from the CPU 101. The graphic accelerator 106 transmits the image data to the color monitor 107 through a display cable after D / A conversion. As a result, an image is displayed on the color monitor 107. Here, when the user designates the color correction mode and instructs the image application to output the digital image stored in the main memory 102 from the printer 109, the image application performs the color correction designated as digital image data. Transfer the mode to the printer driver. In the present embodiment, this color correction mode is predetermined according to the combination of the type of image to be printed and the type of printing paper to be used. The CPU 101 converts the digital image data into CMYK digital image data based on processing described later with reference to FIG. 2 of the printer driver, and transmits this data to the printer 109 via the USB controller 108.

  The printer 109 prints an image using CMYK toner based on the transmitted image data. In this embodiment, the printer 109 is an electrophotographic system using a laser beam, but the printer configuration is of course not limited to such a system. For example, an ink jet printer may be used.

  FIG. 2 is a flowchart showing creation of print data by color conversion processing by the printer driver. The printer driver according to the present embodiment corrects RGB values to obtain a desired color reproduction according to color gamut conversion using a lookup table (LUT) for color gamut conversion, and instructed color correction mode. In order to convert the color correction conversion and RGB color signals into CMYK color signals, three color conversions of color separation conversion using an LUT are executed to convert RGB 24-bit image data into CMYK 32-bit image data.

  First, in step 201, in order to obtain a pointer to RGB 24-bit image data (color signal RGB each of which is unsigned 8-bit image data) held in the main memory 102, and to hold the image data after CMYK conversion Initialize processing such as securing the memory area. In step 202, the color correction parameters used in the color correction conversion in step 206 are acquired from the HDD 105. The color correction parameter is created or updated in advance by a user operation, as will be described later with reference to FIG. In this operation, the color correction parameter is set for each color correction mode. In applying the present invention, the timing of creating or updating the color correction parameter does not necessarily have to be made according to the user's instruction operation. For example, every time the printer usage time elapses. Alternatively, the parameter may be created or updated for color correction each time the printing amount in the printer reaches a predetermined amount.

  In step 203, the color correction mode designated by the user is acquired, and the LUT (lookup table) shown in FIG. 11 is referred to by the acquired color correction mode, and the ucr value corresponding to each color correction mode is acquired. .

  In step 204, one RGB value, which is a pixel value, is acquired from the RGB 24-bit image data in the main memory 102 in the raster scan order.

  In step 205, color gamut conversion is performed. That is, RGB 24-bit → RGB 24-bit conversion is performed by tetrahedral interpolation calculation using LUT. The LUT describes the correspondence between the coordinate data of the grid points defined in the RGB color space and the RGB coordinate values corresponding to each grid point, and has a data structure as shown in FIG. It is configured. As shown in the figure, RGB coordinate steps are described at the head of the data structure, and lattice points are defined by a combination of these steps. Along with these coordinate steps, RGB coordinate values corresponding to each grid point specified by these coordinate steps are described in a nested manner in the order of R, G, and B. When this data structure is schematically represented in the RGB color space, it is represented as shown in FIG. In tetrahedral interpolation, a hexahedron region surrounded by adjacent eight lattice points is divided into six tetrahedron regions as shown in FIG. 4, and four lattices constituting each divided region are formed. The coordinate value of the point is read from the above LUT and interpolation calculation is performed.

  In step 206, color correction conversion is performed. That is, in accordance with the equations shown in FIGS. 5A to 5D, dimensional conversion, nonlinear conversion, γ conversion, and dimensional conversion are sequentially performed, and color correction for correcting the RGB values obtained in step 204 is performed. In this conversion, first, as shown in FIG. 5A, an RGB three-dimensional signal is converted into a CMYK four-dimensional signal, and nonlinear conversion (FIG. 5B), γ conversion is performed on the four-dimensional signal. (FIG. 5C) is performed, and finally, as shown in FIG. 5D, the RGB three-dimensional signal is restored.

  Specifically, using a UCR amount of 100 × ucr% according to the ucr value acquired in step 203, an RGB value is converted into a cmyk value and one dimension is added by the arithmetic expression shown in FIG. . Thus, in this embodiment, a plurality of colors having different contents are used by using the ucr value used when adding one dimension and associating this ucr value with the color correction mode as described later in FIG. Each correction in the correction mode can be realized without executing again the process of changing or generating the color correction parameter.

  Next, a quadratic transformation using a matrix is performed as a non-linear transformation for the cmyk value by an operation according to the equation of FIG. 5B, and then the cmyk is calculated by an operation according to the equation of FIG. Gamma transformation is applied to each component independently. Finally, the calculation according to the equation of FIG. 5D is used to convert the cmyk value to the RGB value using the same UCR amount as that of the calculation of FIG. Here, the matrix element mij in the equation of FIG. 5B and the γ conversion coefficient γi in the equation of FIG. 5C are color correction parameters. As described above, these color correction parameters are generated for each color correction mode. The calculation is performed by a floating point calculation. After the conversion according to the equation of FIG. 5D is completed, each color signal is rounded to unsigned 8-bit data. At this time, a value exceeding 255 is clipped to 255, and a value below 0 is clipped to 0.

  In step 207, color separation conversion is performed. That is, by performing a tetrahedral interpolation operation using an LUT, RGB 24-bit data is converted to CMYK 32-bit image data (CMYK color signals are unsigned 8-bit image data). In the following description, this RGB color space before conversion is particularly called Private RGB. That is, the color correction calculation in step 205 after RGB 24-bit → RGB 24-bit conversion in step 205 is a calculation on Private RGB.

  In step 208, the CMYK 32-bit value obtained in step 206 is written into the memory at the address corresponding to the pixel position of the color signal. Then, in the next step 209, it is determined whether or not conversion has been performed for all necessary pixels. If so, the process jumps to step 210. If not, the process jumps to step 204. In step 210, the CMYK 32-bit image data stored in the main memory is transmitted to the printer 109 via the USB controller 108. In step 211, this process is terminated.

  Next, the creation or update of color correction parameters used in the calculation of step 206 will be described.

  First, a color correction parameter creation application stored in the HDD 105 is activated by the CPU 101 based on an OS program that receives a user instruction. When the color correction parameter creation application is activated, a dialog window shown in FIG. 6 is displayed.

In FIG. 6, reference numeral 601 denotes a pull-down list, which displays or selects a private RGB value to be set for target color reproduction information. Reference numeral 602 denotes a private RGB value addition button. When this button is pressed, an addition dialog shown in FIG. 7A is displayed. The user can input and add a private RGB value to be set as target color reproduction information via the addition dialog. Reference numeral 603 denotes a private RGB value deletion button that is a target for setting target color reproduction information. By pressing this button, the private RGB value displayed in the pull-down list 601 is deleted from the target for setting target color reproduction information. . Reference numeral 604 denotes a window that displays a list of target color reproduction information for the private RGB values displayed in the pull-down list 601. The target color correction mode is displayed on the left side of the window, and the color reproduction target when an image is displayed on the right side. The L ^* a ^* b ^* value is displayed. Further, the selected target color reproduction information is displayed in reverse video. Reference numeral 605 denotes a slider bar. By controlling this bar, it is possible to scroll and select target color reproduction information of each mode for the Private RGB values displayed in the pull-down list 601.

  Reference numeral 606 denotes a reproduction color designation button. When this button is pressed, a designation dialog shown in FIG. 7B is displayed. The user designates the target color to be reproduced when the image is displayed for the Private RGB value, that is, the target color reproduction information, through the designation dialog. Reference numeral 607 denotes a parameter creation button. When this button is pressed, a color correction parameter is generated as will be described later with reference to FIG. 9 and thereafter, and the result is stored in the HDD 105. Reference numeral 608 denotes an end button. When this button is pressed, the color correction parameter creation application is ended.

  FIG. 8 is a diagram for explaining state transitions in the operation of the color correction parameter creation application.

  In FIG. 8, a state 801 is a state in which an initialization operation is performed such as reading an initial setting value of target color reproduction information. A state 802 is a user operation determination waiting state for the window shown in FIG. When the add button 602 is pressed, the process proceeds to the setting color addition of the state 804. When the slider bar 605 is operated, the display scrolls to the display of the state 803. When the reproduction color designation button 606 is pressed, the state 805 changes. When the process proceeds to setting update and the parameter creation button 607 is pressed, the process proceeds to color correction parameter creation in the state 806, and when the end button 608 is pressed, the process proceeds to the end process in the state 807.

  In the display scroll in the state 803, the display of the target color reproduction information window 601 is scrolled and the selected target color reproduction information is changed according to the control amount of the slider bar. In the setting color addition in the state 804, the dialog shown in FIG. 7A is displayed, and the target color reproduction information is entered. Here, in the edit box 701, a private RGB value to be added as a target for setting target color reproduction information is input. Then, by pressing an add button 702, the input in the box window 701 is confirmed and the dialog is closed.

In the reproduction color designation in the state 805, the dialog shown in FIG. 7B is displayed, and the target color reproduction information is entered. Here, an L ^* a ^* b ^* value which is a color reproduction target is input in the edit box 703. In the edit box 704, the importance of the color to be edited is set as an integer. This value is used as a weight when calculating the evaluation value in the evaluation value calculation process described later with reference to FIG. Further, when the designation button 705 is pressed, the inputted L ^* a ^* b ^* value is stored as target color reproduction information, and this dialog is closed.

  A state 806 is a state in which color correction parameters are created according to the color correction parameter creation process described later with reference to FIG. A state 807 is a state in which the color correction parameter creation application operation is terminated after performing a termination operation such as memory release.

  FIG. 9 is a flowchart showing color correction parameter creation processing in the state 806.

  In FIG. 9, first, in step 901, initialization such as initial setting of the color correction parameters (matrix elements mij and γ conversion coefficients γi of the equations shown in FIGS. 5B and 5C) and securing of a memory area is performed. Do.

Next, in step 902, a target color reproduction in the CMYK color space is generated as will be described later with reference to FIG. 14 based on a set of L ^* a ^* b ^* values for each private RGB value given as target color reproduction information. To do.

  In step 903, an evaluation value sum for the current color correction parameter is calculated. Details thereof will be described later with reference to FIG. Next, in step 904, it is determined whether or not the calculated evaluation value sum is equal to or smaller than a predetermined value. If it is equal to or smaller than the predetermined value, the process jumps to step 907, and if larger than the predetermined value, the process jumps to step 905.

  In step 905, the number of times that the loop calculation from step 906 to step 904 has been performed is acquired, and if this number is greater than the predetermined number, the process jumps to step 907;

  In step 906, the color correction parameter is updated based on an algorithm described later with reference to FIG. In step 907, the current color correction parameter by update or the like is stored in the memory, and the color correction parameter creation process is terminated.

  FIG. 10 is a flowchart showing the target color reproduction generation process in the CMYK space in step 902.

In FIG. 10, first, in step 1401, initialization such as securing a memory area is performed. Next, in step 1402, target color reproduction information defined in the RGB space, which is composed of a set of L ^* a ^* b ^* values corresponding to each color correction mode for each private RGB value, is read from the memory.

  In step 1403, one private RGB value is obtained in a predetermined order from the read target color reproduction information. In step 1404, one color correction mode is selected according to a predetermined order.

In step 1405, the L ^* a ^* b ^* value corresponding to the set of the acquired PrivateRGB value and the selected color correction mode, that is, the L ^* a that becomes the color reproduction target is the PrivateRGB value acquired in the selected color correction mode. ^* B ^* value is acquired from the read target color reproduction information. At the same time, the ucr value is acquired with reference to the LUT shown in FIG. 11 based on the selected color correction mode. Also, the corresponding weight w is acquired at the same time. In step 1406, a cmyk value is calculated by the equation shown in FIG. 5A using the acquired ucr value and the private RGB value acquired in step 1403. In step 1407, the set of the L ^* a ^* b ^* value acquired in step 1405 and the calculated cmyk value is stored as one set of color reproduction targets defined on CMYK. That is, the color reproduction target for the calculated cmyk value is the acquired L ^* a ^* b ^* value. Furthermore, the acquired weight w and the calculated ucr are stored in association with each other at the same time. The weights w and ucr values stored here are used in the processing described later in FIG.

As described above, the color correction mode and the ucr value are associated with each other in advance, thereby using the ucr value corresponding to the color correction mode to perform color conversion to increase the dimension from RGB to cmyk, and in FIG. As will be described later, an L ^* a ^* b ^* value is estimated when an evaluation value for color conversion parameter generation is obtained. Thereby, an appropriate color conversion parameter corresponding to the color correction mode can be obtained in association with the ucr value.

  Next, in step 1408, it is determined whether or not the processing in steps 1404 to 1407 has been performed for all the set color correction modes. If processing has been completed, the processing proceeds to step 1409 for processing for all color correction modes. If is not completed, the process jumps to step 1404.

  In step 1409, for the target color reproduction information defined in the RGB color space, it is determined whether or not the processing in steps 1403 to 1408 has been executed for all the private RGB values for which the target color reproduction is set. When the execution is finished, the process jumps to step 1410, and when not finished, the process jumps to step 1403. In step 1410, the color reproduction target defined in the CMYK color space generated by the above-described processing is stored in the memory, and in step 1411 this processing ends.

  FIG. 12 is a flowchart showing details of the evaluation value calculation processing in step 903 shown in FIG. In this process, an evaluation value fi for the i-th color reproduction target color and an evaluation value sum based on the sum of the fi are calculated.

In FIG. 12, first, in step 1001, the color correction parameters to be evaluated (mij and γi shown in FIGS. 5B and 5C) are acquired and set. Next, in step 1002, i, which is a variable indicating the number of loops, is set to 1 as an initialization operation. Also, the color estimation LUT necessary for color estimation in step 1006 is read. This LUT has a data structure as shown in FIG. 13B. When this data structure is schematically represented in the RGB color space, it is represented as shown in FIG. Since this configuration has the same format as the data structure shown in FIGS. 3A and 3B described in step 205 in FIG. 2, detailed description thereof will be omitted. This LUT stores the values of the L ^* a ^* b ^* color system obtained by measuring the private RGB values obtained by actually printing out the colors as patches, etc. Prepared.

Next, in step 1003, the set of correspondence between the cmyk value obtained by the processing described with reference to FIG. 10 and the L ^* a ^* b ^* value that is a color reproduction target when an image is printed with this cmyk value. The i-th target color reproduction information is read from the memory.

In step 1004, a pair of correspondences between the Cmyk value Corg and the corresponding L ^* a ^* b ^* value Drep is obtained from the target color reproduction information read from the memory. Also, the weight w for the acquired color is acquired at the same time. Next, in step 1005, the cmyk value Corg is converted into the cmyk value Ccmp using the same equations in FIGS. 5B and 5C as the equation used in step 206. In step 1006, a private RGB value is calculated by performing the calculation of the equation shown in FIG. 5D using the ucr value corresponding to the color reproduction target for the current process with respect to the cmyk value Ccmp. The L ^* a ^* b ^* value Dcal is estimated by referring to the color estimation LUT read in step 1002 based on the calculated RGB values. For this estimation, tetrahedral interpolation is used, and interpolation calculation is performed for the tetrahedral region divided into six shown in FIG. Next, in step 1007, the color difference between the L ^* a ^* b ^* value Drep, which is the value of the target color reproduction color, and the estimated L ^* a ^* b ^* value Dcal obtained in step 1006 is calculated according to CIEΔE94. An evaluation value fi is obtained by multiplying the weight w.

In step 1008, it is determined whether or not the processing from steps 1004 to 1007 has been performed on the correspondence relationship between all the cmyk values Corg of the target color reproduction information and the value Drep of L ^* a ^* b ^* . If there is, the process goes to step 1009. If not yet applied, 1 is added to the variable i indicating the number of loops, and the process jumps to step 1004.

  In step 1009, an evaluation value sum, which is the sum of the evaluation values fi, is obtained. In step 1010, the evaluation value calculation process ends.

  FIG. 14 is a flowchart showing details of the color correction parameter update processing shown in step 906 of FIG. In this processing, the D.D. L. S. The color correction parameter is updated based on the method (damped least square method). In the following description, matrix elements mij and γ conversion coefficients γi, which are color correction parameters, are arranged in a line and treated as a vector x, and each element of the color correction parameter is represented by a vector element xk (k = 0 to l). Further, a change amount to be updated of the color correction parameter k-th parameter xk is represented by Δxk.

  In FIG. 14, first, in step 1201, the color correction parameter to be updated, the evaluation values of all target color reproduction information based on this, the minute fluctuation width necessary for calculating the evaluation value space and the gradient of the column vector x, Obtain and set the damping factor (ρ). The damping factor is defined by the following formula 5.

  Next, in step 1202, each element of the color correction parameter to be updated is converted into a vector element xi according to the following expression 2, and a vector x is set.

  Here, the column vector x existing at this step is set as the initial value of the vector. Further, s, which is a variable indicating the number of loops, is set to 1 as an initialization operation.

  In step 1203, the minute fluctuation width set in step 1201 is added to the l-th parameter xl of the column vector x to change it. Next, in step 1204, an evaluation value is calculated for the column vector x changed in step 1203 using the process described in FIG. In step 1205, the column vector x changed in step 1203 is restored as the initial value of the vector. Further, in step 1206, the initial evaluation value and the fluctuation range of all the target color reproduction information set in step 1201 and the evaluation value after change calculated in step 1204 are used, and the evaluation is performed based on the following Expression 3. Compute the gradient of the value space and column vector x.

  The gradient is calculated for the target color reproduction information n (n = 0 to p) and stored in the memory as akn. Here, the minute fluctuation width corresponds to a variable difference in partial differentiation.

  In step 1207, it is determined whether or not the processing from step 1203 to step 1206 has been performed on all the parameters of the column vector x. If so, the process proceeds to step 1208. If not, the loop count is set. After adding 1 to the indicated variable i, the process jumps to step 1203.

  In step 1208, the damping factor and initial evaluation value set in step 1201 and the gradient calculated in step 1206 are set to D.E. L. S. By applying the method, a variation amount Δxi of xi that is a parameter of the column vector x is calculated from Equation 4 below.

  In step 1209, the color correction parameters are updated by the following formulas 5 and 6.

  Finally, in step 1210, an end operation of the color processing parameter update process is performed.

  In the present invention, the RGB color space signal is converted into the CMYK color space signal to perform color correction. However, the same effect can be obtained by converting the RGB signal into the RGBW color space signal. Further, when the signal to be color-corrected is a color signal in the CMY space, it can be converted into a CMYK signal or an RGBW signal to perform the same processing.

<Other embodiments>
Color Correction Conversion In the above embodiment, a discrete color correction mode is prepared in order to change the content of the color correction conversion. However, as is apparent from the fact that the ucr value is a continuous value, the content of the color correction conversion can be continuously changed.

Types of color correction conversion In the above-described embodiment, the second-order nonlinear conversion is used as the color correction conversion. However, it is also possible to use a third-order or higher-order nonlinear conversion. Further, linear transformation can be used, and γ transformation and logarithmic transformation can be used in combination.

Dimensions of color correction conversion In the above - described embodiment, a color correction conversion is performed by converting a three-dimensional signal into a four-dimensional signal. However, in other cases, for example, in order to improve accuracy for each hue, it is also possible to perform color correction conversion by converting into a six-dimensional signal such as a signal in the RGBCMY color space. Furthermore, it is possible to perform color correction conversion by converting the dimension of a color signal of fourth order or higher, such as a CMYK signal or an RGBW signal.

Parameter Update In the above example, D.D. L. S. Although the method is used, other optimization methods such as an orthogonalization method and a quasi-Newton method can be applied.

<Still another embodiment>
As described above, the present invention can be applied to a system composed of a plurality of devices (for example, a host computer, an interface device, a reader, a printer, etc.) but also to an apparatus composed of a single device (for example, a copying machine, a facsimile machine). May be.

  In addition, FIG. 2, FIG. 9, FIG. 10, FIG. 14 and FIG. 14 are connected to an apparatus or a computer in the system connected to the various devices to operate the various devices so as to realize the functions of the above-described embodiments. A program implemented by operating the various devices according to a program stored in a computer (CPU or MPU) of the system or apparatus is provided. It is included in the category of the invention.

  Further, in this case, the program code of the software itself realizes the functions of the above-described embodiments, and the program code itself and means for supplying the program code to the computer, for example, a storage storing the program code The medium constitutes the present invention.

  As a storage medium for storing the program code, for example, a floppy (registered trademark) disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, a magnetic tape, a nonvolatile memory card, a ROM, or the like can be used.

  Further, by executing the program code supplied by the computer, not only the functions of the above-described embodiments are realized, but also the OS (operating system) in which the program code is running on the computer, or other application software, etc. It goes without saying that the program code is also included in the embodiment of the present invention even when the functions of the above-described embodiment are realized in cooperation with the embodiment.

  Further, after the supplied program code is stored in a memory provided in a function expansion board of a computer or a function expansion unit connected to the computer, a CPU provided in the function expansion board or function storage unit based on an instruction of the program code However, it is needless to say that the present invention also includes a case where the function of the above-described embodiment is realized by performing part or all of the actual processing.

1 is a block diagram illustrating a configuration of an image processing apparatus according to an embodiment of the present invention. It is a flowchart figure which shows the image output process by the printer driver which concerns on one implementation of this invention. (A) RGB is a schematic diagram showing a grid point arrangement in a color space, and (b) is a diagram showing a data structure of an LUT. It is a schematic diagram explaining the area division | segmentation in the tetrahedral interpolation using LUT. (A)-(d) is a figure which shows the computing equation of the color correction conversion which concerns on one Embodiment of this invention. It is a figure which shows the user interface of the color correction parameter creation application which concerns on one Embodiment of this invention. (A) is a diagram showing a user interface for addition in creating the color correction parameter, and (b) is a diagram showing a user interface for designating reproduction colors. It is a state figure showing operation of the above-mentioned color correction parameter creation application. It is a flowchart figure which shows the color correction parameter calculation process in the said color correction parameter preparation. 10 is a flowchart showing target color reproduction generation processing in the CMYK space shown in step 902 of FIG. 9. It is a figure which shows the table which shows a response | compatibility with the color correction mode and ucr value which concern on one Embodiment of this invention. It is a flowchart figure which shows the process of evaluation value calculation in the said color correction parameter preparation. (A) is a schematic diagram showing a grid point arrangement in the RGB color space, and (b) is a diagram showing a data structure of the LUT. It is a flowchart figure which shows the color correction parameter update process using DLS method in the said color correction parameter preparation.

Explanation of symbols

101 CPU
102 Main memory 105 HDD
107 Color Monitor 109 Color Printer 111 Keyboard 112 Mouse

Claims (8)

Color correction conversion for correcting the color signal, after converting the color signal to a color signal with an increased dimension of the color signal, performing correction using the color correction parameter for the color signal with the increased dimension, An image processing apparatus that performs color correction conversion to return to the original dimension color signal,
Parameter holding means for holding a conversion parameter used for conversion for increasing the dimension of the color signal for each of a plurality of color correction modes having different correction contents of color correction conversion;
Correction mode acquisition means for acquiring a set color correction mode;
Parameter acquisition means for acquiring a conversion parameter corresponding to the color correction mode acquired by the correction mode acquisition means from the parameter holding means;
Conversion that increases the dimension of the color signal using the conversion parameter acquired by the parameter acquisition means, correction using the color correction parameter for the color signal with the increased dimension, and then the color signal of the original dimension Conversion means for performing color correction conversion to return to
The color correction parameter is obtained by reducing a color difference between a target color and an estimated color represented by a predetermined color system of a color signal obtained by conversion using the conversion parameter. Image processing device. Color correction conversion for correcting the color signal, after converting the color signal to a color signal having an increased dimension of the color signal, performing correction using the color correction parameter for the color signal having the increased dimension, An image processing apparatus that performs processing for generating the color correction parameter in color correction conversion to return to the original dimension color signal,
Parameter holding means for holding a conversion parameter used for conversion for increasing the dimension of the color signal for each of a plurality of color correction modes having different correction contents of color correction conversion;
Target color acquisition means for obtaining a target color in a predetermined color system for a color signal obtained by conversion using a conversion parameter corresponding to the color correction mode for one color correction mode held by the parameter holding means;
Estimated color acquisition means for obtaining an estimated color in the predetermined color system of a color signal obtained by conversion using a color correction parameter with respect to a color signal obtained by conversion using the conversion parameter for the one color correction mode; ,
Parameter determining means for determining a color correction parameter so as to reduce a color difference between the target color and the estimated color for the one color correction mode;
Control means for executing the processing by the target color acquisition means, the estimated color acquisition means and the parameter determination means for each of a plurality of color correction modes held by a parameter holding means;
An image processing apparatus comprising:   The color signal color system before increasing the dimension is an RGB color system or a CMYK color system, and the color system after increasing the dimension is a CMYK color system or an RGBW color system. The image processing apparatus according to claim 1, wherein the parameter is a UCR processing parameter. Color correction conversion for correcting the color signal, after converting the color signal to a color signal with an increased dimension of the color signal, performing correction using the color correction parameter for the color signal with the increased dimension, An image processing method for performing color correction conversion to return to the original dimensional color signal,
A conversion parameter used for conversion for increasing the dimension of the color signal is prepared for each of a plurality of color correction modes having different correction contents of color correction conversion,
Get the set color correction mode,
Obtaining a conversion parameter corresponding to the acquired color correction mode from the prepared conversion parameter;
Color conversion that increases the dimension of the color signal using the acquired conversion parameter, correction using the color correction parameter for the color signal with the increased dimension, and then returning to the color signal of the original dimension Do the conversion, have steps,
The color correction parameter is obtained by reducing a color difference between a target color and an estimated color represented by a predetermined color system of a color signal obtained by conversion using the conversion parameter. Image processing method. Color correction conversion for correcting the color signal, after converting the color signal to a color signal having an increased dimension of the color signal, performing correction using the color correction parameter for the color signal having the increased dimension, An image processing method for performing processing for generating the color correction parameter in color correction conversion to return to the original dimension color signal,
A conversion parameter used for conversion for increasing the dimension of the color signal is held for each of a plurality of color correction modes having different correction contents of color correction conversion,
For the one color correction mode to be held, a target color in a predetermined color system is obtained for a color signal obtained by conversion using a conversion parameter corresponding to the color correction mode,
For the one color correction mode, an estimated color in the predetermined color system of a color signal obtained by conversion using a color correction parameter for a color signal obtained by conversion using the conversion parameter is obtained,
For the one color correction mode, a color correction parameter is determined so that a color difference between the target color and the estimated color is reduced,
Obtaining the target color, obtaining the estimated color and determining the color correction parameter for each of the plurality of color correction modes;
An image processing method comprising steps.   The color signal color system before increasing the dimension is an RGB color system or a CMYK color system, and the color system after increasing the dimension is a CMYK color system or an RGBW color system. 6. The image processing method according to claim 4, wherein the parameter is a UCR processing parameter. Color correction conversion for correcting a color signal by a computer, converting the color signal to a color signal having an increased dimension, and correcting the color signal having the increased dimension using a color correction parameter Is a program that functions as an image processing device that performs color correction conversion that returns to the original dimensional color signal.
Parameter holding means for holding a conversion parameter used for conversion for increasing the dimension of the color signal for each of a plurality of color correction modes having different correction contents of color correction conversion;
Correction mode acquisition means for acquiring a set color correction mode;
Parameter acquisition means for acquiring a conversion parameter corresponding to the color correction mode acquired by the correction mode acquisition means from the parameter holding means;
Conversion that increases the dimension of the color signal using the conversion parameter acquired by the parameter acquisition means, correction using the color correction parameter for the color signal with the increased dimension, and then the color signal of the original dimension Conversion means for performing color correction conversion to return to
The color correction parameter is obtained by reducing a color difference between a target color and an estimated color represented by a predetermined color system of a color signal obtained by conversion using the conversion parameter. program. Color correction conversion for correcting a color signal by a computer, converting the color signal to a color signal having an increased dimension, and correcting the color signal having the increased dimension using a color correction parameter Is a program that functions as an image processing device that performs the process of generating the color correction parameter in color correction conversion that returns to the original dimensional color signal.
Parameter holding means for holding a conversion parameter used for conversion for increasing the dimension of the color signal for each of a plurality of color correction modes having different correction contents of color correction conversion;
Target color acquisition means for obtaining a target color in a predetermined color system for a color signal obtained by conversion using a conversion parameter corresponding to the color correction mode for one color correction mode held by the parameter holding means;
Estimated color acquisition means for obtaining an estimated color in the predetermined color system of a color signal obtained by conversion using a color correction parameter with respect to a color signal obtained by conversion using the conversion parameter for the one color correction mode; ,
Parameter determining means for determining a color correction parameter so as to reduce a color difference between the target color and the estimated color for the one color correction mode;
Control means for executing the processing by the target color acquisition means, the estimated color acquisition means and the parameter determination means for each of a plurality of color correction modes held by a parameter holding means;
The program characterized by having.

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