JP2006086969A - Image processing apparatus, method thereof and storage medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable selection and composition of an optimum color separation table in accordance with the image quality (granularity and color reproduction gamut) desired by a user when color material colors of new high saturation inks are provided in addition to key four colors of cyan, magenta, yellow and black, and light color inks. <P>SOLUTION: In an ink system consisting of key four colors (cyan, magenta, yellow and black), light color inks and a high saturation inks, four color separation tables of only the key four colors, key four colors and light color inks, key four colors and high saturation inks, and key four colors and light color inks and high saturation inks are prepared. In this system, UI is used and image quality (granularity and color reproduction gamut) can be adjusted in accordance with the preference of the user. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image processing apparatus and method for a color printer. In particular, the present invention relates to a calibration technique for suppressing variation in color reproduction characteristics of a color printer.

  Conventionally, a color printer calibration technique is configured as shown in the block diagram of FIG. In FIG. 9, reference numeral 901 denotes an ink color separation processing unit, 902 denotes a calibration CMYK one-dimensional LUT unit, 903 denotes a halftone processing unit, 904 denotes a color printer engine unit, 905 denotes a CMYK one-dimensional LUT creation unit, and 906 denotes a sensor unit. Reference numeral 907 denotes an ink color separation table unit. Reference numeral 901 denotes cyan which is a color material color (hereinafter referred to as ink color) of a color printer by performing interpolation processing such as tetrahedral interpolation on the input multi-value RGB image data based on the table information of the ink color separation table unit 907. Ink color separation processing is performed on C, magenta M, yellow Y, and black K. The multivalued CMYK data output from the ink color separation processing unit 901 is corrected by the CMYK one-dimensional LUT unit 902 for calibration using the CMYK one-dimensional LUT corresponding to the color reproduction characteristics of the printer. Then, multi-value C′M′Y′K ′ is output. This process realizes calibration according to the characteristics of the color printer. The halftone processing unit 903 performs halftone processing for binarizing the corrected multilevel C′M′Y′K ′ data to the number of gradations that can be printed by a color printer, for example, a binary printer. The C "M" Y "K" binary data is output. The color printer engine unit 904 performs printing based on the input C "M" Y "K" binary data. Here, the sensor unit 906 is a sensor unit for examining the color reproduction characteristics of the color printer engine unit 904, and the CMYK one-dimensional LUT creation unit 905 is based on the color reproduction characteristics for each color of CMYK from the sensor unit 905. A CMYK one-dimensional LUT is created so as to achieve target color reproduction characteristics for each color, and the result is written to the CMYK one-dimensional LUT unit 902.

Further, as a method of calibrating secondary colors such as Red, Green, and Blue, and tertiary colors and quaternary colors constituting a gray line, the contents of the ink color separation table section 907 are recreated to regenerate the secondary colors. There is a method for calibrating colors that are equal to or greater than colors (Patent Document 1).
JP 2001-136401 A

  However, in the conventional example using the above one-dimensional LUT, since calibration is performed independently for each color of CMYK, high-precision calibration can be realized for the primary color. However, secondary colors such as Red, Green, Blue, etc. There is a problem that high-precision calibration cannot be realized for colors other than the primary color such as a tertiary color and a quaternary color constituting the gray line.

  Also, in the case of the conventional example in which the color of the secondary color or more is calibrated by recreating the contents of the ink color separation table section, the ink color separation table that observes the total ink amount limit allowable for the printing paper is recreated. There was a problem that was difficult. Furthermore, recent inkjet printers employ a six-color ink system that uses light cyan or light magenta ink in addition to cyan, magenta, yellow, and black as the color material color. There is a problem that it becomes complicated.

  Accordingly, an object of the first invention according to the present application is to propose an image processing apparatus and method capable of calibrating a secondary color or higher without directly recreating an ink color separation table. is there.

In order to achieve the above object, an image processing apparatus according to the first aspect of the present invention comprises the following arrangement.
Means for printing a patch corresponding to the color signal value of the gray line; means for measuring the color of the printed patch; and the gray line based on the target color of the color signal value of the gray line and the color measurement value. Means for calibrating the color signal value of the image,-means for creating a multi-dimensional LUT for calibration from the color signal value of the calibrated gray line-and means for color conversion based on the multi-dimensional LUT It is characterized by that.

  In the above configuration, the means for creating a multi-dimensional LUT for calibration and the means for color conversion based on the multi-dimensional LUT perform multi-dimensional LUT processing before the color separation processing means. Compared to the method of re-creating and executing calibration, it is easy to stabilize the color tone of the printed material of the secondary color or more without complicated control of the total ink amount limiting process and 6-color ink system. Can be realized.

  According to the present invention, it is possible to easily correct the secondary color or higher without directly complicating the color separation table and performing complicated control such as a total ink amount restriction process or a six-color ink system, which is difficult to compare with the calibration method. Stabilization of color of printed matter can be realized.

  The best mode for carrying out the present invention will be described below based on examples.

(First embodiment)
FIG. 1 is a diagram best representing the features of the present invention, and the configuration of the present invention is shown in a block diagram. In FIG. 1, 101 is a color matching processing unit, 102 is a 3D calibration processing unit, 103 is a color separation processing unit, 104 is an output γ correction processing unit, and 105 is a halftone processing unit. 106 is a color printer engine unit, 107 is a color matching table unit, 108 is a 3D calibration table unit, 109 is a color separation table unit, 110 is a CPU unit, and 111 is a ROM unit. Yes, 112 is a RAM section, and 113 is a reference table section. A color matching processing unit 101 matches the color reproduction characteristics of the input image data RGB and the printer color. Based on the contents of the color matching table unit 107, the RGB image data is subjected to tetrahedral interpolation processing, cube interpolation processing, and the like. Color matching processing is executed by three-dimensional interpolation processing, and color conversion is performed to R′G′B ′. Reference numeral 102 denotes a 3D calibration processing unit, which performs calibration processing on R′G′B ′ data based on the contents of the 3D calibration table unit 108 by three-dimensional interpolation processing such as tetrahedral interpolation processing and cube interpolation processing. And color conversion to R "G" B ". 103 is a color separation processing unit, and R" G "B" data is converted into tetrahedral interpolation processing and cube based on the contents of the color separation table unit 109. Color separation processing for converting the color material color (ink color) of the printer into C (cyan), M (magenta), Y (yellow), and K (black) is executed by three-dimensional interpolation processing such as interpolation processing. Reference numeral 104 denotes an output γ correction processing unit for correcting CMYK color material color data for γ characteristics due to the combination of the processing content of the halftone processing unit 105 and the color printer engine unit 106. A halftone processing unit 105 is a halftone process for converting the C′M′Y′K ′ multi-value data from the output γ correction processing unit 104 into the number of gradations that can be expressed by the color printer engine unit 106. Part. A color printer engine unit 106 performs development printing processing based on C "M" Y "K" from the halftone processing unit 105. Reference numeral 110 denotes a control CPU unit of the image processing apparatus, and the update process of the 3D calibration table unit 108 for executing calibration, and the execution of the image process using the updated 3D calibration table unit 108. To control. Reference numeral 111 denotes a ROM unit that stores operation content data of the CPU unit 110. The RAM unit 112 is a work work area for the CPU unit 110. Reference numeral 113 denotes a reference table section that stores the relationship between the value of R "G" B "and the actual color of printed matter.

  In this embodiment, the contents of the 3D calibration table unit 108 are updated, so that the total ink amount limitation such as changing the contents of the color separation table is not required, and complicated control such as a six-color ink system is not required. In addition, it is possible to achieve stabilization of the color of the printed matter of the secondary color or higher. Hereinafter, a method for re-creating the 3D calibration table unit 108 for realizing stabilization of the color printer will be described in detail with reference to FIG.

  FIG. 2 shows a system configuration example including a color printer in which the present invention is implemented. In FIG. 2, 201 is a computer for controlling the color printer 203 and the colorimeter 204, and 202 is a computer 201. A monitor 203 for displaying data and the like held in the printer, 203 is a color printer for printing image data, and 204 is a colorimeter for measuring colors of patches printed by the color printer 203. Reference numeral 205 denotes a patch printed by the color printer 203. The present embodiment shown in FIG. 1 is implemented in the color printer 203 in FIG.

  FIG. 3 is a flowchart for executing calibration. In FIG. 3, S301 is a start step. S302 is a gray line patch pattern generation step, and image data R "G" B "corresponding to the gray line patch pattern is generated by the CPU 110 in Fig. 1. S303 is a gray line patch printing process step. The image data R "G" B "generated in step S302 is sent to the color separation processing unit 103, and the image processing from the output γ correction processing unit 104 to the color printer engine unit 106 is performed, and the patch Printing processing is performed. The printed result is shown in the print patch 205 in FIG. S 304 is a gray line patch colorimetric processing step. The print patch 205 in FIG. 2 is color-measured using the colorimeter 204, and the result is transmitted to the computer 201. In the computer 201, the color measurement result is transferred to the image processing apparatus in the color printer 203. S305 is a step of determining whether or not the color difference from the target value is within an allowable value. The color difference ΔE between the target color of the predetermined gray line and the value measured in step S304 is calculated. If it is greater than or equal to the allowable value ε (No), the process proceeds to step S306. S306 is a gray line correction processing step, which will be described in detail with reference to FIGS.

  4 shows an initial state of data corresponding to a gray line of the 3D calibration table unit 108 of input R′G′B ′ and output R ″ G ″ B ″. The signal and the B signal are all overlapped, and the data of R "G" B "corresponding to the data α1, α2, and α3 of the input R'G'B 'are α1, α2, and α3, respectively. FIG. 5 shows the result of the gray line correction processing executed in step S306 in order to suppress the variation in the color reproduction characteristics of the color printer 203. As is apparent from FIG. 5, the value of the R signal is emphasized from the initial value, and the G signal and the B signal are weakened. For example, the value of (R ′, G ′, B ′) = (α2, α2, α2) is (R ″, G ″, B ″) = (β2r, β2b, β2g). As a result, the gray line color reproduction characteristics of the color printer 203 can be stabilized.

  FIG. 6 is a diagram for explaining the gray line correction processing algorithm from FIG. 4 to FIG. 5. P0 to P7 are printed in the L * a * b * space of the CIE by preliminarily printing and measuring the target color of the gray line for the R "G" B "signal stored in the reference table unit 113 and its neighboring color. P8 is a gray line colorimetric value (L8) obtained as a result of the processing in steps S302 to S304, with the gray line signal value (R ″, G ″, B ″) = (α2, α2, α2). , A8, b8) are plotted. For each point, a value of L * a * b * indicating the color of the point and a signal value of R ″, G ″, B ″ constituting the point are shown. For example, P0 is the CIE L * Indicates L0, CIE a * is a0, CIE b * is b0, R "signal value is R" 0, G "signal value is G" 0, B "signal value is B" 0 However, the elements (R ″ 8, G ″ 8, B ″ 8) of P8 are obtained by interpolation from the signal values of the surrounding P0 to P7 based on (L8, a8, b8).

  FIG. 7 is a diagram for explaining the reference table unit 113. Although the reference table unit 113 is a three-dimensional table, in order to simplify the description, the gray line from White to Black is represented by a two-dimensional cross section passing through Red and Cyan. As is clear from the figure, the table is held in the vicinity of the gray line by making the lattice spacing close, and by making the lattice point spacing in the region far from the gray line sparse. Distribution is performed so that color reproduction accuracy is improved.

Here, when the target value of the color measurement result P8 of the gray line signal values (R ″, G ″, B ″) = (α2, α2, α2) is P0, the color difference ΔE is
ΔE = sqrt ((L0−L8) ^ 2 + (a0−a8) ^ 2 + (b0−b8) ^ 2)
In step S305, it is determined whether or not the error ΔE is within ε. When ε or more, (R ", G", B ") = ([beta] 2r, [beta] 2b, [beta] 2g) is the R" G "B" signal value based on the R "G" B "signal value of the target color and the measured value Is corrected using the following equation.

β2r = α2 + (R ″ 0−R ″ 8)
β2g = α2 + (G "0-G" 8)
β2b = α2 + (G "0-G" 8)
Similarly, the gray line signal value can be corrected for α1 and α3.

  Thereafter, the process from step S302 to step S306 is executed using the corrected value of R "G" B ", and is repeated until the color difference from the target value in step S305 is within an allowable value. If the color difference from the target value is within the allowable value, the process proceeds to step S307, where step S307 is a 3D calibration table generation step, and correction of the gray line corrected by the processing from step S302 to S306 is performed. Using the value, a 3D calibration table is obtained by a three-dimensional interpolation process.

  With the above processing, the gray line color reproduction characteristic can stably reproduce the target color even when the printing characteristic of the color printer 203 changes. Further, since the peripheral colors other than the gray line are re-created by the three-dimensional interpolation processing based on the calibrated gray line, it is possible to realize good color reproduction characteristics.

  In this embodiment, since the calibration process is performed in which a three-dimensional LUT is arranged between the color matching process and the color separation process, it is difficult to control the total ink required when changing the contents of the color separation table. Stabilization of the color of the printed matter of the secondary color or more can be easily realized without performing complicated control such as a quantity limiting process or a six-color ink system.

(Second embodiment)
In the first embodiment, a 3D calibration processing unit 102 is provided between the color matching processing unit 101 and the color separation processing 103, and three-dimensional calibration is executed based on the contents of the 3D calibration table unit 108. However, the 3D calibration processing method using the 3D calibration table is not limited to this, and the color matching processing unit 101 and the color separation processing unit 103 are directly connected as shown in FIG. Can also be realized. In this case, the color matching table unit 107 and the 3D calibration table unit 108 are combined and newly written in the color matching table unit 107. Alternatively, by synthesizing the 3D calibration table unit 108 and the color separation table unit 109 and newly writing to the color separation table unit 109, processing equivalent to that in the first embodiment can be realized.

  In addition, a three-dimensional table is created by synthesizing three three-dimensional tables of the color matching table unit 107, the 3D calibration table unit 108, and the color separation table unit 109, and a three-dimensional table is created using the one three-dimensional table. A process equivalent to that of the first embodiment can also be realized in the interpolation process.

(Third embodiment)
In the first embodiment, after correcting the value of the gray line, the 3D calibration table is created based on the corrected gray line. However, the method of creating the 3D calibration table is not limited to this. For example, a white-red-black line other than the gray line, or a target color to be calibrated such as skin color may be corrected, and a 3D calibration table may be created based on the corrected color.

(Fourth embodiment)
In the first embodiment, as shown in FIG. 2, the colorimeter 204 is used as an apparatus for measuring the color of the print patch. However, the apparatus for measuring the color of the print patch is not limited to this, and a commercially available flat color is used. Any device that can measure color, such as a bed scanner, is acceptable.

It is a figure which best represents the characteristic of 1st Example, and is a block diagram which shows the structure of the calibration proposed in an Example. 1 is a diagram showing a system configuration including a color printer in which the present invention is implemented. It is a flowchart for performing calibration. FIG. 10 is a diagram illustrating an initial state of data corresponding to a gray line in the 3D calibration table unit 108 of an input R′G′B ′ and an output R ″ G ″ B ″. It is a figure which shows the result by which the correction process of the gray line was performed. It is a figure for demonstrating the correction process algorithm of a gray line. 4 is a diagram for explaining a reference table unit 113. FIG. It is a figure which shows the structure of 2nd Example. It is a figure for demonstrating a prior art.

Explanation of symbols

101 Color Matching Processing Unit 102 3D Calibration Processing Unit 103 Color Separation Processing Unit 104 Output Gamma Correction Processing Unit 105 Halftone Processing Unit 106 Color Printer Engine Unit 107 Color Matching Table Unit 108 3D Calibration Table Unit 109 Color Separation Table Unit 110 CPU Section 111 ROM section 112 RAM section 113 Reference table section 201 Computer 202 Monitor 203 Color printer 204 Colorimeter 205 Print patch 901 Ink color separation processing section 902 Calibration CMYK one-dimensional LUT section 903 Halftone processing section 904 Color printer engine 905 CMYK One-dimensional LUT creation unit 906 sensor unit 907 ink color separation table unit

Claims (14)

An image processing apparatus for color calibration for stabilizing the color of printed matter in a color printer,
Means for printing a patch corresponding to a color signal value to be stabilized; means for measuring the color of the printed patch; means for creating a multidimensional LUT for calibration based on the colorimetric value; An image processing apparatus comprising: means for color conversion based on the multidimensional LUT. An image processing apparatus for color calibration for stabilizing the color of printed matter in a color printer,
A means for printing a patch corresponding to a color signal value to be stabilized; a means for measuring the color of the printed patch; a target color of the color signal value to be stabilized; and the colorimetric value And means for calibrating the color signal value to be stabilized, and means for creating a multidimensional LUT for calibration from the calibrated color signal value to be stabilized. An image processing apparatus comprising: means for color conversion based on an LUT.   3. The image processing apparatus according to claim 2, wherein the calibration multi-dimensional LUT is created by multi-dimensional interpolation processing from the calibrated color signal value to be stabilized. .   3. The image processing apparatus according to claim 2, wherein the means for calibrating the color signal value to be stabilized is created using a reference table created in advance.   The reference table according to claim 4 is characterized in that the lattice spacing near the color signal value to be stabilized is dense and the lattice spacing apart from the color signal value to be stabilized is sparse. An image processing apparatus. An image processing apparatus related to color calibration for stabilizing the color of printed matter in a color printer is
Means for printing a patch corresponding to the color signal value of the gray line; means for measuring the color of the printed patch; and the gray line based on the target color of the color signal value of the gray line and the color measurement value. Means for calibrating the color signal value of the image,-means for creating a multi-dimensional LUT for calibration from the color signal value of the calibrated gray line-and means for color conversion based on the multi-dimensional LUT An image processing apparatus.   7. The image processing apparatus according to claim 6, wherein the means for creating a multi-dimensional LUT for calibration is created by multi-dimensional interpolation processing from the color signal values of the calibrated gray line.   7. The image processing apparatus according to claim 6, wherein the means for calibrating the color signal value of the gray line is created using a reference table created in advance.   9. The image processing according to claim 8, wherein the grid intervals near the gray line color signal values are dense, and the grid intervals at grid points far from the gray line color signal values are sparse. apparatus. A color printer image processing apparatus that performs color conversion from a color signal value representing color image data to a color material color of a color printer, wherein the image processing apparatus includes:
A multi-dimensional LUT processing unit that performs color matching, a multi-dimensional LUT processing unit that performs calibration, and a multi-dimensional LUT processing unit that performs color separation into color material colors of the color printer. An image processing apparatus. A color printer image processing apparatus that performs color conversion from a color signal value representing color image data to a color material color of a color printer, wherein the image processing apparatus includes:
・ Multi-dimensional LUT means for color matching ・ Multi-dimensional LUT means for calibration ・ Multi-dimensional LUT means for color separation into color material colors of the color printer In actual processing, an image processing apparatus is characterized in that color conversion processing is performed using one of these multidimensional LUTs or a combination of two multidimensional LUTs. A color printer image processing method for performing color conversion from a color signal value representing color image data to a color material color of a color printer, the image processing method comprising:
A multi-dimensional LUT processing step for performing color matching, a multi-dimensional LUT processing step for performing calibration, and a multi-dimensional LUT processing step for performing color separation into color material colors of the color printer. An image processing method. A color printer image processing method for performing color conversion from a color signal value representing color image data to a color material color of a color printer, the image processing method comprising:
Multi-dimensional LUT means for performing color matching, Multi-dimensional LUT means for performing calibration, Multi-dimensional LUT means for performing color separation into color material colors of the color printer, and the three multi-dimensional LUT means Combining into one or two multidimensional LUT means;
An image processing method characterized by performing color conversion processing using the synthesized one or two multidimensional LUT means. In a recording medium for recording a program for realizing a color calibration method for stabilizing the color of a printed matter in a color printer,
A method of printing a patch corresponding to a color signal value to be stabilized; a method of measuring the color of the printed patch; a target color of the color signal value to be stabilized; and the colorimetric value A method for calibrating the color signal value to be stabilized, a method for creating a multidimensional LUT for calibration from the calibrated color signal value to be stabilized, and the multidimensional A recording medium comprising: a color conversion method based on an LUT.

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