JP2014075666A - Image processor, and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform calibration at a higher speed in an image processor.SOLUTION: A color conversion storage part 14 stores a LUT for CMS for converting an input color signal into an output color signal composed of color components adaptable to an initial printing engine characteristic. A calibration information creation part 16 creates a LUT for calibration to be used in calibration to the output color signal as compensation for compensating characteristic fluctuation for a printing engine characteristic from the initial printing engine characteristic. A synthesis processing part 18 creates an integrated LUT for converting an input color signal into a calibrated output color signal by synthesis processing using the LUT for CMS and the LUT for calibration.

Description

  The present invention relates to an image processing apparatus and a program.

  In an image forming apparatus that forms an image by applying an electrophotographic process using a color material (recording material) such as toner or ink, the characteristics of the image density fluctuate depending on the use environment or use conditions, and the gradation is unnatural. Or an outline may occur. For this reason, a change over time in color reproduction characteristics is compensated by performing calibration based on a predetermined timing such as a certain time interval or when the power is turned on or a user instruction.

  For example, Patent Documents 1 and 2 disclose a one-dimensional lookup table (one-dimensional LUT) for each color component in an image forming apparatus using toners of six colors of dark cyan, light cyan, dark magenta, light magenta, yellow, and black. ) Is used to perform gradation correction for each color component.

  Also, cited document 3 discloses gradation correction when at least one of light color toner and dark color toner is used.

JP 2006-163000 A JP 2006-93957 A Japanese Patent No. 3903401

  By the way, when the input color signal to be printed is converted into a signal in a color space depending on the image forming apparatus and the converted signal is calibrated, signal conversion and calibration are performed separately. The total time for generating the calibrated signal may increase.

  An object of the present invention is to provide an image processing apparatus and program capable of performing calibration at higher speed.

  According to a first aspect of the present invention, there is provided an information storage means for storing color conversion information for converting an input color signal into an output color signal composed of n (where n> 4) color components adapted to the initial print engine characteristics. The basic color that is a part of the n color components constituting the output color signal is included as information for compensating the characteristic variation from the initial print engine characteristic to the print engine characteristic at the time of calibration. The input color signal is generated by combining the information generation means for generating multidimensional calibration information for calibrating the color component group and the color conversion information and the multidimensional calibration information. Synthesis processing means for generating calibration-compatible color conversion information for conversion to a calibrated output color signal comprising the color components of It is an image processing apparatus according to claim.

  The invention according to claim 2 is the image processing apparatus according to claim 1, wherein a plurality of out-group color components other than the color component group out of the n color components constituting the output color signal. One-dimensional calibration information generating means for generating a plurality of one-dimensional calibration information for individually performing gradation correction, and the multi-dimensional calibration information includes the color component group and the gradation correction. This is information for generating a color component group after calibration from a plurality of later color components outside the group.

  The invention according to claim 3 is the image processing apparatus according to claim 1, wherein the color conversion information constitutes a color conversion table, the multidimensional calibration information constitutes one or a plurality of calibration tables, The synthesis processing unit is configured to input a table sequence including a unit that sequentially generates a test input color signal while changing the content of the input color signal, and the color conversion table and the one or more calibration tables. Means for sequentially providing the test input color signal generated in succession, means for sequentially obtaining a calibrated output color signal as a test result from the output of the table sequence, and the test input color signal generated sequentially Based on the correspondence with the calibrated output color signal sequentially obtained as the test result, Characterized in that it comprises means for generating a calibration corresponding color conversion table as emissions corresponding color conversion information.

  According to a fourth aspect of the present invention, the computer obtains color conversion information for converting the input color signal into an output color signal composed of n (where n> 4) color components conforming to the initial print engine characteristics. And a basic color that is a part of the n color components constituting the output color signal as information for compensating the characteristic variation from the initial print engine characteristic to the print engine characteristic during calibration. The step of generating multi-dimensional calibration information for calibrating the included color component group, and the combining color processing information and the multi-dimensional calibration information are used to combine the input color signal with the n pieces of color signals. Generating calibration-compatible conversion information for conversion to a calibrated output color signal composed of color components. Is a program for causing the.

  According to the first and fourth aspects of the invention, it is possible to perform calibration at a higher speed than when the configuration of the present invention is not provided.

  According to the second aspect of the present invention, it is possible to improve the accuracy of calibration as compared with the case where the configuration of the present invention is not provided.

  According to the third aspect of the present invention, it is possible to create a table capable of simultaneously executing calibration and color conversion.

It is a block diagram which shows an example of the image processing apparatus which concerns on embodiment of this invention. It is a block diagram which shows an example of the calibration information preparation part which concerns on this embodiment. It is a flowchart which shows an example of the preparation procedure of CMS LUT. It is a flowchart which shows an example of the preparation procedure of the LUT for calibration. It is a flowchart which shows an example of the preparation procedure of the LUT for calibration. It is a conceptual diagram which shows an example of integrated LUT. 10 is a block diagram illustrating an example of a calibration information creation unit according to Modification 1. FIG. 10 is a block diagram illustrating an example of a procedure for creating a calibration LUT according to Modification 1. FIG. 10 is a flowchart illustrating an example of a procedure for creating a calibration LUT according to Modification 1. FIG. 10 is a block diagram illustrating an example of a calibration information creation unit according to Modification 2. FIG. 10 is a block diagram illustrating an example of a procedure for creating a calibration LUT according to Modification 2. 14 is a flowchart illustrating an example of a procedure for creating a calibration LUT according to Modification 2. It is a conceptual diagram which shows an example of the integrated LUT which concerns on the modification 3. It is a conceptual diagram which shows an example of the integrated LUT which concerns on the modification 4.

  FIG. 1 shows an example of an image processing apparatus according to an embodiment of the present invention. The image processing apparatus 10 receives the image data, performs image processing, and outputs the image data subjected to the image processing to the image forming apparatus 30.

  The image forming apparatus 30 has a function of forming and outputting an image corresponding to image data on a recording medium such as recording paper using a color material (recording material) such as toner or ink. For example, the image forming apparatus 30 forms an image by applying an electrophotographic process using five or more toners including basic colors and special colors. For example, cyan (C), magenta (M), yellow (Y), and black (K) are used as basic colors, and special colors such as orange (O), green (G), and violet (V) are used. At least one of them is used. As an example, the image forming apparatus 30 uses toner of each color of cyan (C), magenta (M), yellow (Y), black (K), orange (O), green (G), and violet (V). Form an image. Specifically, the image forming apparatus 30 receives the data of each color component of CMYOGVK as print data, and scans and exposes the photosensitive drum, which is an image carrier, according to each data. Then, an electrostatic latent image is formed and developed using each color toner of CMYOGVK to form each color toner image. Then, the image forming apparatus 30 transfers the toner image while superimposing the toner image on the recording medium, and melts and fixes the toner image on the recording medium by performing heating and pressurizing processes. As a result, an image corresponding to the image data is formed on the recording medium. In this embodiment, as an example, a case of using CMYOGVK seven-color toner will be described. For example, seven-color toner (CMYKRGB) or CMYKOV using red (R), green (G), and blue (B) is used. For example, a 6-color toner or a 5-color toner may be used.

  The color conversion unit 12 receives image data to be printed and converts the image data into device color space data that depends on the image forming apparatus 30. As an example, when the device color space of the image forming apparatus 30 is a CMYOGVK color space, the color conversion unit 12 converts the image data into data in the CMYOGVK color space (hereinafter referred to as a CMYOGVK color signal). For example, when the color conversion unit 12 receives CMYK color space data (CMYK color signal) or RGB color space data (RGB color signal), the color conversion unit 12 performs a multidimensional lookup table (CMYK color signal or RGB color signal). By applying the multi-dimensional LUT), it is converted into a CMYOGVK color signal that is data in the device color space.

  When calibration (compensation for change in color reproduction characteristics over time) described later is not performed, the color conversion unit 12 is an initial stage of the image forming apparatus 30 (image forming apparatus) as an LUT for a color management system (CMS), for example. By applying the CMS LUT created at the time of 30 design or shipping inspection) to the image data, the image data is converted into device color space data. On the other hand, as will be described in detail later, when an integrated LUT is created by combining a calibration LUT and a CMS LUT created by calibration, the color conversion unit 12 converts the integrated LUT into image data. By applying, the image data is converted into device color space data. Note that the image forming characteristic of the image forming apparatus 30 in the initial stage corresponds to an example of the initial print engine characteristic, and the image forming characteristic of the image forming apparatus 30 at the time of calibration is an example of the print engine characteristic at the time of performing calibration. Equivalent to.

  The color conversion information storage unit 14 stores a CMS LUT. This CMS LUT is an LUT for converting image data to be printed into data in the device color space of the image forming apparatus 30. As an example, the CMS LUT is an LUT that converts a CMYK color signal or an RGB color signal into a CMYOGVK color signal that is data in the device color space of the image forming apparatus 30. The color conversion information storage unit 14 corresponds to an example of an information storage unit.

  The calibration information creation unit 16 performs a multi-dimensional lookup table (calibration LUT) for performing calibration (compensation for change in color reproduction characteristics over time) on device color space data converted by the CMS LUT. ). The calibration LUT is an LUT for compensating for a characteristic variation from the initial print engine characteristic to the print engine characteristic at the time of executing calibration. As an example, the calibration LUT is an LUT for performing calibration on CMYKOGV color signals that are data in the device color space. The calibration information creation unit 16 corresponds to an example of an information generation unit, and the output signal after calibration corresponds to an example of a calibrated output color signal.

  The combination processing unit 18 combines the two LUTs by combining the CMS LUT stored in the color conversion information storage unit 14 and the calibration LUT created by the calibration information creation unit 16. Create an integrated LUT. The CMS LUT corresponds to an example of color conversion information, the calibration LUT corresponds to an example of multidimensional calibration information, and the integrated LUT corresponds to an example of calibration-compatible color conversion information.

  As shown in FIG. 2, the calibration information creation unit 16 includes an input signal generation unit 20, a color conversion unit 22, a device independent color space conversion unit 24, and a CMY determination unit 26.

  The input signal generator 20 outputs CMYK color signals corresponding to each grid (each grid point) of the CMS LUT to the color converter 22. For each input color signal value (for example, CMYK value) corresponding to each of these grids, an output color signal value (for example, CMYOGVK) value corresponding to the input color signal is registered in the CMS LUT.

  The color conversion unit 22 uses the CMS LUT to convert the CMYK color signal received from the input signal generation unit 20 into C′M′Y′O′G, which is data in the device color space depending on the image forming apparatus 30. Convert to 'V'K' color signal. Specifically, the color conversion unit 22 reads the C′M′Y′O′G′V′K ′ color signal corresponding to the CMYK color signal from the CMS LUT and outputs it. The device independent color space conversion unit 24 converts the C′M′Y′O′G′V′K ′ color signal into a device independent color space (for example, L * a * b * color space) signal (L * A * b * color signal).

  The CMY determination unit 26 uses the same values as the O′G′V′K ′ color signal output from the color conversion unit 22 for the orange, green, violet, and black color signals supplied to the image forming apparatus 30. When the image forming apparatus 30 forms an image under a certain condition, the colorimetric value of the image and the color represented by the L * a * b * color signal output from the device independent color space conversion unit 24 are colorimetric. The C ″ M ″ Y ″ color signal is determined so that the same color is obtained.

In the CMY determination unit 26, a function F ₂ (color) representing the relationship between the CMYOGVK color signal input to the image forming apparatus 30 and the colorimetric value L * a * b * when an image is formed based on the CMYOGVK color signal. Conversion model) is obtained in advance. Then, the CMY determination unit 26 performs color conversion from the L * a * b * color signal received from the device independent color space conversion unit 24 and the O′G′V′K ′ color signal received from the color conversion unit 22. By solving the model numerically, the orange, green, violet and black color signals input to the image forming apparatus 30 are O′G′V′K ′ color signals, and L * a * b * color signals. The remaining three C ″ M ″ Y ″ color signals of the image forming apparatus 30 that match colorimetrically are determined.

  Next, detailed processing in each unit will be described. First, referring to the flowchart shown in FIG. 3, for example, a procedure for creating the color conversion parameters and CMS LUT of the device-independent color space conversion unit 24 in the initial stage (design time or shipping time) of the image forming apparatus 30. explain.

  First, the patch data generation unit 40 outputs patch data indicating an arbitrary combination of CMYOGVK color signals to the image forming apparatus 30, and the image forming apparatus 30 converts the CMYOGVK color signals into an arbitrary combination based on the patch data. The corresponding patch image 32 is printed (S01).

  Then, the colorimeter L * a * b * of each patch image 32 is measured using the colorimeter 42 (S02). Thereby, a pair of a plurality of CMYOGVK color signals and the colorimetric values L * a * b * at the time of creating the CMS LUT is obtained.

  The number of combinations of CMYOGVK color signals (number of patches) may be arbitrary, but the accuracy of color conversion improves as the number increases. In addition to the L * a * b * color space, an XYZ color space may be used.

Next, the calculation unit 44 receives the patch data from the patch data generation unit 40, receives the colorimetric values L * a * b * from the colorimeter 42, and measures the colorimetric values for the CMYOGVK color signal when the CMS LUT is created. A function F ₁ (color conversion model) indicating the conversion characteristics of L * a * b * is obtained (S03). A high-order polynomial or a neural network is used for the color conversion model. For example, the calculation unit 44 causes a neural network to learn a data set of a plurality of CMYOGVK color signals and colorimetric values L * a * b * as teacher data, and obtains a color conversion model.

Relationship between CMYOGVK color signals and colorimetric values L * a * b * is expressed by the following function _{F 1.}
(L *, a *, b *) = F ₁ (C, M, Y, O, G, V, K) (1)
Here, when the expression (1) is decomposed into the respective color components, the following is obtained.
L * = F _1L (C, M, Y, O, G, V, K) (2)
a * = F _1a (C, M, Y, O, G, V, K) (3)
b * = F _1b (C, M, Y, O, G, V, K) (4)
The function F ₁ is stored in the color conversion information storage unit 14 and set in the device independent color space conversion unit 24.

  As the neural network, for example, the document “High-precision color conversion by flexible UCR -High-precision printer model by neural network-”, Kazumasa Murai, Japan Hard Copy '94, pp. Learning is performed by the back-propagation method using the neural network shown in 181 to 184. In addition to using a neural network as the color conversion model, other polynomial models and conversion table type color conversion models may be applied.

  Then, the calculation unit 44 converts the CMYK color signal, which is an input color signal, into an L * a * b * color signal using a conversion parameter based on, for example, the specification of ICC (International Color Course), and depends on the image forming apparatus 30. Based on the correspondence between the CMYOGVK color signal, which is device color space data, and the colorimetric value L * a * b *, the input color signal (CMYK color signal) and the device color space data depending on the image forming apparatus 30 A CMS LUT indicating a correspondence relationship with a certain output color signal (C′M′Y′O′G′V′K ′ color signal) is created (S04). The CMS LUT is stored in the color conversion information storage unit 14 and set in the color conversion unit 22.

As described above, the CMS LUT and the color conversion model (function F ₁ ) in the initial stage of the image forming apparatus 30 are obtained in advance. Thus, by using the CMYOGVK color signals and functions _{F 1, L * a * b} * color signals corresponding to CMYOGVK color signal at the LUT creation for the CMS is obtained.

Next, a procedure for obtaining a color conversion model (function F ₂ ) at the time of calibration will be described with reference to the flowchart shown in FIG. For example, the calibration is executed based on a predetermined timing such as a certain time interval or when the power is turned on, or a user instruction.

  First, the patch data generation unit 40 outputs patch data indicating an arbitrary combination of CMYOGVK color signals to the image forming apparatus 30, and the image forming apparatus 30 converts the CMYOGVK color signals into an arbitrary combination based on the patch data. The corresponding patch image 32 is printed (S10).

  Then, the colorimeter L * a * b * of each patch image 32 is measured using the colorimeter 42 (S11). Thereby, a pair of a plurality of CMYOGVK color signals and colorimetric values L * a * b * at the time of calibration is obtained.

Next, the calculation unit 44 receives the patch data from the patch data generation unit 40, receives the colorimetric value L * a * b * from the colorimeter 42, and measures the colorimetric value L * a for the CMYOGVK color signal at the time of calibration. A function F ₂ (color conversion model) indicating the conversion characteristics of * b * is obtained (S12). For example, the calculation unit 44 causes a neural network to learn a data set of a plurality of CMYOGVK color signals and colorimetric values L * a * b * as teacher data, and obtains a color conversion model.

Relationship between CMYOGVK color signals and colorimetric values L * a * b * is expressed by the following function _{F 2.}
(L *, a *, b *) = F ₂ (C, M, Y, O, G, V, K) (5)
Here, when Expression (5) is decomposed into the respective color components, the following is obtained.
L * = F _2L (C, M, Y, O, G, V, K) (6)
a * = F _2a (C, M, Y, O, G, V, K) (7)
b * = F _2b (C, M, Y, O, G, V, K) (8)
Thus, the color conversion model (function F ₂ ) at the time of calibration is obtained. Function _{F 2} is set to CMY determination unit 26.

  Next, processing of each unit at the time of calibration will be described with reference to the flowchart shown in FIG.

  First, the input signal generator 20 outputs an input color signal (CMYK color signal) corresponding to each grid (each grid point) of the CMS LUT to the color converter 22 (S20).

  The color conversion unit 22 uses the CMS LUT to convert the input color signal (CMYK color signal) received from the input signal generation unit 20 into C′M ′, which is device color space data depending on the image forming apparatus 30. Y'O'G'V'K 'color signals are converted (S21).

The device-independent color space conversion unit 24 uses the function F ₁ obtained when the CMS LUT is generated, so that the C′M′Y′O′G′V′K ′ color signal received from the color conversion unit 22 is obtained. , L * a * b * color signals are converted (S22). This L * a * b * color signal corresponds to a color (target value) to be reproduced when an image based on the input color signal (CMYK color signal) is formed on the recording medium.

The CMY determination unit 26 receives the L * a * b * color signal from the device-independent color space conversion unit 24, and receives a part of the C′M′Y′O′G′V′K ′ color signal (O 'G'V'K' color signal) is received from the color conversion unit 22. Then, the CMY determining unit 26 inputs to the image forming apparatus 30 based on the L * a * b * color signal, the O′G′V′K ′ color signal, and the function F ₂ obtained at the time of calibration. The orange, green, violet, and black color signals that are generated are O'G'V'K 'color signals and are colorimetric to L * a * b * color signals that are colors (target values) to be reproduced. The remaining three C ″ M ″ Y ″ color signals of the image forming apparatus 30 are determined so as to coincide with (S23). That is, the color (L * a * b *) ′ when an image is formed based on the C ″ M ″ Y ″ O′G′V′K ′ color signal is the color to be reproduced (L * a * B *), C''M''Y '' color signal is obtained. In other words, for the O′G′V′K ′ color signal, the color (L * a * b *) ′ when the image is formed is to be reproduced while maintaining the output value from the color conversion unit 22. The C ″ M ″ Y ″ color signal is adjusted so that (L * a * b *).

Here, the inverse function of the function F ₂ (color conversion model) represented by the above formula (5) is not uniquely obtained. Therefore, if an L * a * b * color signal that does not depend on the image forming apparatus 30 is given and the four variables in the C′M′Y′O′G′V′K ′ color signal are appropriately determined, Expression (5) ) To obtain the remaining three variables. For example, the remaining C ″ M ″ Y ″ color signals are obtained by giving L * a * b * color signals and O′G′V′K ′ color signals.

The color to be reproduced is L * a * b *, the color signal to be given is O'G'V'K 'color signal, and the image is C''M''Y''O'G'V'K' color signal. The color difference between the color to be reproduced (L * a * b *) and the color to be formed (L * a * b *) 'is assumed to be the color (L * a * b *)' ΔE * ab is defined by the following equation (9) as a function of the C ″ M ″ Y ″ color signal.
ΔE * ab (C ″, M ″, Y ″)
= [{L * -F _2L (C ″, M ″, Y ″, O ′, G ′, V ′, K ′)} ²
+ {A * -F _2a (C ″, M ″, Y ″, O ′, G ′, V ′, K ′)} ²
+ {B * −F _2b (C ″, M ″, Y ″, O ′, G ′, V ′, K ′)} ² ] ^1/2
... (9)
As described above, L * a * b * indicates a color (target value) to be reproduced. Further, since the function F ₂ indicates the conversion characteristic at the time of calibration, F _2L (C ″, M ″, Y ″, O ′, G ′, V ′, K ′), F _2a (C ″, M ″, Y ″, O ′, G ′, V ′, K ′) and F _2b (C ″, M ″, Y ″, O ′, G ′, V ′, K ′). ) Corresponds to the color (L * a * b *) ′ at the time of calibration.

  Solving color (5), which is a nonlinear equation, is the same as finding a C ″ M ″ Y ″ color signal in which the color difference ΔE * ab is zero, so the problem of solving equation (5) Can be reinterpreted as a nonlinear optimization problem of obtaining a C ″ M ″ Y ″ color signal that minimizes the objective function ΔE * ab by using the color difference ΔE * ab as an objective function. Therefore, Equation (5) can be solved by a nonlinear optimization method such as the simplex method. That is, the target value (L * a * b *) and the O′G′V′K ′ color signal are input to the equation (9), and C ″ M ″ Y ′ that minimizes ΔE * ab is obtained. 'Get the color signal. As for the simplex method, see, for example, “Nonlinear Programming”, Hiroshi Konno, Nikka Giren Publisher, pp. The algorithm is introduced in 284-287. The simplex method is a method suitable for optimizing such a multivariable function, and an optimum value is obtained at high speed.

  Here, the simplex method capable of optimizing multivariable functions at high speed was applied as the nonlinear optimization method, but any method can be applied as long as it is a nonlinear optimization method. Other nonlinear optimization methods such as the method may be applied. Further, the color conversion model may be solved by applying a numerical solution of a nonlinear equation such as Newton's method.

  As described above, the CMY determination unit 26 solves the color conversion model, whereby orange, which is input to the image forming apparatus 30 from the L * a * b * color signal and the O′G′V′K ′ color signal. The remaining three colors C of the image forming apparatus 30 in which the color signals of green, violet, and black are O′G′V′K ′ color signals and colorimetrically match the L * a * b * color signals. The “M” Y ”color signal is determined.

  As described above, the C′M′Y′O′G′V′K ′ color signal after color conversion by the CMS LUT and the C ″ M ″ Y after calibration in step S23. A calibration LUT indicating the correspondence with the “O′G′V′K” color signal is obtained. This calibration LUT calibrates the C′M′Y′O′G′V′K ′ color signal, thereby converting the C′M′Y′O′G′V′K ′ color signal into the colorimetric measurement. This is an LUT for converting to a C ″ M ″ Y ″ O′G′V′K ′ color signal whose value is a target value (L * a * b *). Note that the C ′ ″ M ″ Y ″ O′G′V′K ′ color signal after calibration corresponds to an example of a calibrated output color signal.

  1 synthesizes the CMS LUT and the calibration LUT, so that the CMYK color signal and the C ″ M ″ Y ″ O′G′V′K ′ color signal are synthesized. An integrated LUT indicating the correspondence relationship is created (S24). For example, as conceptually shown in FIG. 6, the synthesis processing unit 18 synthesizes the CMYK color signal with C ″ M ″ Y ″ O′G ′ by synthesizing the CMS LUT 50 and the calibration LUT 52. An integrated LUT 54 that converts to a V′K ′ color signal is created.

  For example, the composition processing unit 18 outputs the CMS LUT output side (C′M′Y′O′G′V′K ′ color signal) and the calibration LUT input side (C′M′Y′O ′). G'V'K 'color signal) is created to create an integrated LUT that converts CMYK color signals into C "M" Y "O'G'V'K' color signals.

  The specific processing will be described. The composition processing unit 18 sequentially generates test input color signals (CMYK color signals) while changing the contents of the m color components, and uses the CMS LUT and the calibration LUT. And a calibrated output color signal (C ″ M ″ Y ″ O′G′V′K ′ color signal) as a test result is sequentially obtained from the output of the table column. The synthesis processing unit 18 then sequentially generates the test input color signal (CMYK color signal) and the calibrated output color signal (C ″ M ″ Y ″ O′G) sequentially acquired as the test result. Based on the correspondence relationship with “V′K” color signal), an integrated LUT is created as calibration-compatible color conversion information.

  As described above, an integrated LUT as a multi-function look-up table that simultaneously performs calibration and color conversion is created by a simple process of sequentially inputting test input color signals and sequentially acquiring test results.

  When an input color signal (CMYK color signal) is input to the image processing apparatus 10 after calibration, the color conversion unit 12 illustrated in FIG. 1 applies an input by applying the integrated LUT 54 to the input color signal (CMYK color signal). The color signal (CMYK color signal) is output from the device color space (CMYOGVK color space) depending on the image forming apparatus 30 and the output color signal (C ″ M ″ Y ″ O) which is calibrated data. 'G'V'K' color signal). The image forming apparatus 30 forms an image on a recording medium in accordance with the calibrated output color signal (C ′ ″ M ″ ″ Y ″ O′G′V′K ′ color signal). When an arbitrary CMYK color signal is input, C ″ M ″ Y ″ O′G′V′K ′ color signal corresponding to one or a plurality of grid points of the integrated LUT is read and interpolation processing is performed. Then, the C ″ M ″ Y ″ O′G′V′K ′ color signal corresponding to the CMYK color signal may be obtained.

  As described above, by combining the CMS LUT and the calibration LUT to create an integrated LUT, conversion to device color space data and calibration are executed by one integrated LUT during image formation. The Thus, by performing color conversion and calibration by one integrated LUT, the CMS LUT is applied to the input color signal (CMYK color signal), and the device color space data (C'M'Y'O'G The processing time for obtaining a calibrated signal is shortened and less compared to the case where the calibration is performed by applying the calibration LUT and then performing the calibration. Color conversion and calibration are performed by hardware. That is, calibration is performed at a higher speed. Further, since the calibration LUT included in the integrated LUT performs multi-color calibration, the accuracy of multi-color calibration is improved. That is, in the gradation correction for each color component (for each single color), calibration of multiple colors formed by superimposing toners of a plurality of color components is not sufficient, and calibration is performed as the number of toners used increases. There is a risk that the accuracy of the lowering. On the other hand, in this embodiment, since multiple color calibration is performed, a decrease in calibration accuracy is suppressed even when the number of toners used is increased.

  In the above example, the case where the input color signal is the CMYK color signal has been described. However, the integrated LUT is similarly created when the input color signal is the RGB color signal. In this case, an integrated LUT for converting the RGB color signals into C ″ M ″ Y ″ O′G′V′K ′ color signals is created.

  When the input color signal is composed of four color signals (CMYK color signals), the integrated LUT converts the CMYK color signals into C ″ M ″ Y ″ O′G′V′K ′ color signals. A four-dimensional LUT for performing When the input color signal is composed of three color signals (RGB color signal), the integrated LUT changes from the RGB color signal to the C ″ M ″ Y ″ O′G′V′K ′ color signal. This is a three-dimensional LUT that performs the conversion. Although the order of the integrated LUT is less than 7 dimensions, the integrated LUT includes a calibration LUT corresponding to the 7-dimensional LUT, so that the calibration is performed substantially in the same manner as when the 7-dimensional LUT is applied. . Therefore, by applying the integrated LUT, the same calibration accuracy as when the 7-dimensional LUT is applied can be obtained. As described above, the integrated LUT according to the present embodiment is a three-dimensional LUT or a four-dimensional LUT even though the calibration accuracy similar to that of the seven-dimensional LUT can be obtained. Requires less memory capacity.

  In step S23 described above, the case where the CMY determination unit 26 solves the color conversion model to obtain the C "M" Y "color signal has been described. However, calibration is performed by obtaining a color signal other than the CMY color signal. May be created. That is, four arbitrary color signals can be selected from the seven CMYOGVK color signals, and the remaining three variables (color signals) can be obtained by the processing in step S23. For example, cyan, magenta, yellow, and black color signals input to the image forming apparatus 30 are C′M′Y′K ′ color signals after being converted by the color conversion unit 22 and should be reproduced. The remaining three O ″ G ″ V ″ color signals of the image forming apparatus 30 may be determined so as to match the color (L * a * b *) colorimetrically.

  Note that the color gamut expressed by the basic colors CMY is wider than the color gamut expressed by the spot color OGV. Therefore, calibration by adjusting the CMY color signal and performing calibration by adjusting the OGV color signal and performing calibration corresponding to a wider color gamut is performed. That is, while maintaining the output value from the color conversion unit 22 for the CMYK color signal, the output value from the color conversion unit 22 for the OGVK color signal is maintained rather than performing calibration by adjusting the OGV color signal. When calibration is performed by adjusting the CMY color signals, calibration is performed corresponding to a wider color gamut.

  Further, the color conversion unit 22 and the device independent color space conversion unit 24 are combined into one means, and the input color signal (CMYK color signal) is converted into an L * a * b * color signal and an O′G′V′K ′ color. You may make it convert into a signal.

(Modification 1)
Next, an image processing apparatus according to Modification 1 will be described with reference to FIGS. In the first modification, gradation correction for each single color is performed by applying a one-dimensional LUT to orange (O), green (G), violet (V), and black (K).

  For example, as illustrated in FIG. 7, the image processing apparatus according to the first modification includes a calibration information creation unit 16 </ b> A including one-dimensional LUTs 70 to 76 instead of the calibration information creation unit 16. The one-dimensional LUTs 70 to 76 are LUTs created at the time of calibration, and are LUTs that respectively perform gradation correction (individually) for the corresponding O′G′V′K ′ color signals for each single color. For example, the one-dimensional LUT 70 is an LUT that converts an O ′ color signal output from the color converter 22 into an O ″ color signal so that the density or brightness when an image is formed becomes a target value. The one-dimensional LUTs 72 to 76 also convert the corresponding G′V′K ′ color signals into G ″ V ″ K ″ color signals so that the density or brightness when the image is formed becomes the target value. LUT.

  Here, an example of a procedure for creating the one-dimensional LUTs 70 to 72 will be described with reference to FIG.

  The storage unit 60 stores colorimetric values (L * a * b *) corresponding to each patch image measured when the CMS LUT is created. The measurement value stored in the storage unit 60 is the target value.

  For example, when obtaining the one-dimensional LUT 70 for orange (O), the halftone dot area ratio (density) of six colors (CMYGVK) other than orange (O) is set to zero and the halftone dot area ratio of only orange (O) is changed. Several patch images 32 are printed, and the colorimeter (L * a * b *) of each patch image 32 is measured by the colorimeter 42.

  The gradation correction information creating unit 62 measures the orange (O) colorimetric value (L * a * b *) measured from the patch image 32 of each halftone dot area ratio at the time of calibration and the CMS LUT. A one-dimensional LUT 70 that obtains a difference from the colorimetric value (target value) of orange (O) corresponding to each halftone dot area ratio stored in the storage unit 60 and corrects the input color signal so as to cancel the difference. Create The gradation correction information creation unit 62 corresponds to an example of a one-dimensional calibration information generation unit.

  Similarly, for green (G), violet (V), and black (K), the difference between the colorimetric value at the time of calibration and the colorimetric value at the time of creation of the CMS LUT is obtained. Dimension LUTs 72-76 are created.

In addition to the patch image for creating the one-dimensional LUT shown above, a patch image of a secondary color or higher color is also created and measured, and the same processing as in the above-described embodiment is performed. A color conversion model (function F ₂ ) at the time of calibration is obtained.

  Next, processing of each unit at the time of calibration will be described with reference to the flowchart shown in FIG.

  First, the input signal generation unit 20 outputs an input color signal (CMYK color signal) to the color conversion unit 22 using the CMS LUT (S30), and the color conversion unit 22 uses the CMS LUT, so that CMYK. The color signal is converted into a C′M′Y′O′G′V′K ′ color signal (S31).

  Then, by using the one-dimensional LUTs 70 to 76 created at the time of calibration, gradation correction for each single color is performed on the corresponding O′G′V′K ′ color signal, so that O′G′V ′. The K ′ color signal is converted into an O ″ G ″ V ″ K ″ color signal (S32).

On the other hand, the device-independent color space conversion unit 24 uses the function F ₁ obtained when generating the CMS LUT, so that the C′M′Y′O′G′V′K ′ color received from the color conversion unit 22 is used. The signal is converted into an L * a * b * color signal (S33).

The CMY determination unit 26 receives the L * a * b * color signal from the device independent color space conversion unit 24 and the O ″ G ″ V ″ K ″ color signal from each of the one-dimensional LUTs 70 to 76. Then, the CMY determination unit 26 forms an image based on the L * a * b * color signal, the O ″ G ″ V ″ K ″ color signal, and the function F ₂ obtained at the time of calibration. The orange, green, violet, and black color signals input to the device 30 are O "G" V "K" color signals, and L * a *, which is a color (target value) to be reproduced. The remaining three C ″ M ″ Y ″ color signals of the image forming apparatus 30 that colorimetrically match the b * color signal are determined (S34). For example, a target value (L * a * b *) and an O ″ G ″ V ″ K ″ color signal are input to the above equation (9), and C ′ such that ΔE * ab is minimized. The “M” Y ”color signal is obtained by the simplex method or the like.

  As described above, in step S34, the C′M′Y′O′G′V′K ′ color signal after being converted by the CMS LUT and the C ″ M ″ Y ′ after calibration. A calibration LUT indicating the correspondence with the “O” G ”V” K ”color signal is obtained.

  Then, the composition processing unit 18 synthesizes the CMYK color signal and the C ″ M ″ Y ″ O ″ G ″ V ′ by synthesizing the CMS LUT, the calibration LUT, and the one-dimensional LUTs 70 to 76. An integrated LUT indicating the correspondence with the “K” color signal is created (S35).

  The specific processing will be described. The composition processing unit 18 sequentially generates and applies test input color signals (CMYK color signals) to the CMS LUT while changing the contents of the m color components. Partial color signals (O′G′V′K ′ color signals) of the output color signals (C′M′Y′O′G′V′K ′ color signals) are individually processed by the one-dimensional LUTs 70 to 76. By performing tone correction, the color signal after the tone correction (O ″ G ″ V ″ K ″ color signal) is obtained. Then, the composition processing unit 18 gives the color signal (C′M′Y′O ″ G ″ V ″ K ″ color signal) to the calibration LUT, and outputs the calibrated output color signal (C ″). M ″ Y ″ O ″ G ″ V ″ K ″ color signals) are sequentially acquired. The synthesis processing unit 18 sequentially generates test input color signals (CMYK color signals) and calibrated output color signals (C ″ M ″ Y ″ O ″ G ′) sequentially acquired as test results. An integrated LUT is created based on the correspondence relationship with the “V” K ”color signal).

  According to the first modification, the same effect as that of the image processing apparatus 10 according to the above-described embodiment can be obtained, and the O′G′V′K ′ color signal is tone-corrected for each single color by the one-dimensional LUTs 70 to 76. This further improves the accuracy of calibration.

(Modification 2)
Next, an image processing apparatus according to Modification 2 will be described with reference to FIGS. 10 to 12. In the second modification, gradation correction for each single color is performed by applying a one-dimensional LUT to the CMYOGVK color signal.

  For example, as illustrated in FIG. 10, the image processing apparatus according to the second modification includes a calibration information creation unit 16 </ b> B including one-dimensional LUTs 80 to 92 instead of the calibration information creation unit 16. The one-dimensional LUTs 80 to 92 are LUTs created at the time of calibration. For example, as illustrated in FIG. 11, the one-dimensional LUTs 80 to 92 are LUTs that perform gradation correction for each corresponding CMYOGVK color signal.

  Here, an example of a procedure for creating the one-dimensional LUTs 80 to 92 will be described with reference to FIG.

  For example, when obtaining the one-dimensional LUT 80 for cyan (C), the patch area 32 of six colors (MYOGVK) other than cyan (C) is set to zero, and the dot area ratio of only cyan (C) is changed. And the colorimetric value (L * a * b *) is measured by the colorimeter 42.

  The gradation correction information creating unit 62 stores the cyan (C) colorimetric value (L * a * b *) measured at the time of calibration and the CMS LUT at the time of creating the CMS LUT. A difference from the colorimetric value (target value) of cyan (C) is obtained, and a one-dimensional LUT 80 for correcting the input color signal so as to cancel the difference is created.

  Similarly, for magenta (M), yellow (Y), orange (O), green (G), violet (V) and black (K), the colorimetric values during calibration and the CMS LUT By obtaining the difference from the colorimetric value, one-dimensional LUTs 82 to 92 for each color are created.

Next, a procedure for obtaining a color conversion model (function F ₂ ) at the time of calibration and processing of each unit at the time of calibration will be described with reference to FIG.

  First, the patch data generation unit 40 outputs patchac data indicating an arbitrary combination of CMYOGVK color signals, and corrects the gradations of the corresponding CMYOGVK color signals for each single color using the one-dimensional LUTs 80 to 92 (S40). The image forming apparatus 30 prints a patch image 32 corresponding to the CMYOGVK color signal whose gradation is corrected for each single color (S41). Then, the colorimeter L * a * b * of each patch image 32 is measured using the colorimeter 42 (S42).

Next, the calculation unit 44 performs a function F ₂ (conversion model) indicating conversion characteristics of the colorimetric values L * a * b * with respect to the CMYOGVK color signal subjected to gradation correction for each single color by the same processing as in the above-described embodiment. ) Is obtained (S43). Function _{F 2} is set to CMY determination unit 26.

  Then, the input signal generation unit 20 outputs the input color signal (CMYK color signal) to the color conversion unit 22 using the CMS LUT (S44), and the color conversion unit 22 uses the CMS LUT, thereby The color signal is converted into a C′M′Y′O′G′V′K ′ color signal (S45).

On the other hand, the device-independent color space conversion unit 24 uses the function F ₁ obtained when generating the CMS LUT, so that the C′M′Y′O′G′V′K ′ color received from the color conversion unit 22 is used. The signal is converted into an L * a * b * color signal (S46).

Then, the CMY determining unit 26 inputs to the image forming apparatus 30 based on the L * a * b * color signal, the O′G′V′K ′ color signal, and the function F ₂ obtained at the time of calibration. The orange, green, violet, and black color signals that are generated are O'G'V'K 'color signals and are colorimetric to L * a * b * color signals that are colors (target values) to be reproduced. The remaining three color C ″ M ″ Y ″ color signals of the image forming apparatus 30 that match the above are determined (S47).

  As described above, in step S47, the C′M′Y′O′G′V′K ′ color signal after being converted by the CMS LUT and the C ″ M ″ Y ′ after calibration. A calibration LUT indicating the correspondence with the “O′G” V′K ”color signal is obtained.

  Then, the synthesis processing unit 18 synthesizes the CMYK color signal and C ′ ″ M ′ ″ Y ′ ″ O ″ G ′ by synthesizing the CMS LUT, the calibration LUT, and the one-dimensional LUTs 80 to 92. An integrated LUT indicating the correspondence with the “V” K ”color signal is created (S48).

  When an input color signal (CMYK color signal) is input to the image processing apparatus 10 after calibration, the color conversion unit 12 illustrated in FIG. 1 applies the integrated LUT to the input color signal (CMYK color signal), thereby inputting the input color signal. A color signal (CMYK color signal) is converted into an output color signal (C ′ ″ M ′ ″ Y ′ ″ O ″ G ″ V ″ K ″ color signal). The image forming apparatus 30 forms an image on a recording medium in accordance with the output color signal (C ′ ″ M ″ ″ Y ″ ″ O ″ ″ G ″ V ″ ″ color signal).

  According to the second modification, the same effect as that of the image processing apparatus 10 according to the above-described embodiment can be obtained, and further, the calibration accuracy can be further improved by correcting the gradation for each single color using the one-dimensional LUTs 80 to 92. .

(Modifications 3 and 4)
FIG. 13 shows an image processing apparatus according to the third modification. In the third modification, the CMS LUT 50, the four-dimensional LUT 100 that performs calibration for the combination of CMYK color signals, and the one-dimensional LUTs 102 to 106 that perform gradation correction for each OGV color signal are synthesized. The integrated LUT 110 is created. The four-dimensional LUT 100 converts the C′M′Y′K ′ color signal into C ″ M ″ Y ″ so that the colorimetric value (L * a * b *) when the image is formed becomes the target value. This is an LUT for converting to a K ″ color signal. For example, a colorimetric value (L * a * b *) corresponding to each patch image measured when creating the CMS LUT is used as the target value. The one-dimensional LUTs 102 to 106 convert the corresponding O′G′V ′ color signals into O ″ G ″ V ″ color signals so that the density or brightness when an image is formed becomes a target value. LUT.

  FIG. 14 shows an image processing apparatus according to Modification 4. In the fourth modification, an integrated LUT 130 is created by synthesizing the CMS LUT 50 and a 7-dimensional LUT 120 that performs calibration for a combination of C′M′Y′O′G′V′K ′ color signals. To do. The 7-dimensional LUT 120 converts the C′M′Y′O′G′V′K ′ color signal to C ″ so that the colorimetric value (L * a * b *) when the image is formed becomes the target value. This is an LUT for converting to M ″ Y ″ O ″ G ″ V ″ K ″ color signals.

  Even when the integrated LUTs 110 and 130 are used, the processing time for obtaining a calibrated signal is shortened and less hardware compared to the case where the CMS LUT and the calibration LUT are applied separately. The color conversion and calibration are performed by. In addition, since multiple color calibration is performed, the accuracy of calibration is improved. Since the integrated LUTs 110 and 130 are three-dimensional or four-dimensional LUTs, the memory capacity for the LUT can be reduced.

  In the above-described embodiment and modification, the case where toner of seven colors (CMYOGVK) is used has been described, but the same effect as in the above-described embodiment and modification can also be obtained when toner of five or more colors is used. Further, the patch data generation unit 40, the calculation unit 44, the storage unit 60, and the gradation correction information creation unit 62 may be included in the image processing apparatus 10, and the image processing apparatus 10 is included in the image forming apparatus 30. May be.

  The image processing apparatus 10 described above is realized by cooperation of hardware resources and software as an example. Specifically, the image processing apparatus 10 includes a processor such as a CPU (not shown). The processor reads out and executes a program stored in a storage device (not shown), thereby executing the functions of the color conversion unit 12, the calibration information creation unit 16, and the synthesis processing unit 18 described above. The program is stored in a storage device such as a hard disk drive (HDD) via a recording medium such as a CD or DVD, or via communication means such as a network. Note that the program may be stored in advance in a storage device such as a hard disk drive. A program stored in a storage device such as a hard disk drive is read into a memory such as a RAM and executed by a processor, whereby each of the color conversion unit 12, the calibration information creation unit 16, and the synthesis processing unit 18 described above is performed. The function is realized. The functions of the color conversion unit 12, the calibration information creation unit 16, and the synthesis processing unit 18 may be realized only by hardware. In addition, the patch data generation unit 40, the calculation unit 44, and the gradation correction information creation unit 62 are also realized by cooperation of hardware resources and software, for example. For example, a processor (not shown) reads and executes a program stored in a storage device (not shown), thereby executing the functions of the patch data generation unit 40, the calculation unit 44, and the gradation correction information creation unit 62. Note that the patch data generation unit 40, the calculation unit 44, and the gradation correction information creation unit 62 may be realized only by hardware.

DESCRIPTION OF SYMBOLS 10 Image processing apparatus, 12, 22 color conversion part, 14 color conversion information storage part, 16, 16A, 16B Calibration information creation part, 18 composition processing part, 20 input signal generation part, 24 apparatus independent color space conversion part, 26 CMY determination unit, 30 image forming apparatus, 32 patch image, 40 patch data generation unit, 42 colorimeter, 44 calculation unit, 50 CMS LUT, 52 calibration LUT, 54, 110, 130 integrated LUT, 60 storage unit 62 gradation correction information creation unit, 70-76, 80-92, 102-106 1-dimensional LUT, 100 4-dimensional LUT, 120 7-dimensional LUT.

Claims (4)

Information storage means for storing color conversion information for converting an input color signal into an output color signal composed of n (where n> 4) color components conforming to the initial print engine characteristics;
Information for compensating for a characteristic variation from the initial print engine characteristic to the print engine characteristic at the time of calibration includes a basic color that is a part of n color components constituting the output color signal. Information generating means for generating multidimensional calibration information for calibrating the color component group;
Calibration-compatible color conversion information for converting the input color signal into a calibrated output color signal composed of the n color components by combining processing using the color conversion information and the multidimensional calibration information. Synthesis processing means for generating
An image processing apparatus comprising: The image processing apparatus according to claim 1,
A plurality of one-dimensional calibration information for individually performing gradation correction on a plurality of out-group color components other than the color component group among n color components constituting the output color signal is generated. A one-dimensional calibration information generating means for
The multidimensional calibration information is information for generating a color component group after calibration from the color component group and a plurality of color components outside the group after gradation correction.
An image processing apparatus. The image processing apparatus according to claim 1,
The color conversion information constitutes a color conversion table,
The multidimensional calibration information constitutes one or a plurality of calibration tables,
The synthesis processing means includes
Means for sequentially generating test input color signals while changing the contents of the input color signals;
Means for providing the test input color signal generated sequentially with respect to an input of a table row composed of the color conversion table and the one or more calibration tables;
Means for sequentially obtaining a calibrated output color signal as a test result from the output of the table sequence;
Based on the correspondence between the sequentially generated test input color signal and the calibrated output color signal sequentially acquired as the test result, a calibration-compatible color conversion table is used as the calibration-compatible color conversion information. Means for generating;
An image processing apparatus comprising: On the computer,
Obtaining color conversion information for converting an input color signal into an output color signal composed of n (where n> 4) color components conforming to the initial print engine characteristics;
Information for compensating for a characteristic variation from the initial print engine characteristic to the print engine characteristic at the time of calibration includes a basic color that is a part of n color components constituting the output color signal. Generating multidimensional calibration information for calibrating color component groups;
Calibration-compatible conversion information for converting the input color signal into a calibrated output color signal composed of the n color components by combining processing using the color conversion information and the multidimensional calibration information. Generating step;
A program characterized by having executed.

Images