JP2021141358A - Image processing device, method, and program - Google Patents

Abstract

To match the colors of outputs of both adjusters even when the number of patches is not the same in the chart output from a target machine and the adjuster.SOLUTION: An image processing device includes first determination means, second determination means, and generation means. The first determination means determines a first color gamut reproduced by a first image formation device on the basis of a first chart including a patch formed by the first image formation device. The second determination means determines a second color gamut reproduced by a second image formation device on the basis of image formation information of the second image formation device and a second chart including patches formed by the second image formation device, which is a smaller number than the number of patches included in the first chart. The generation means associates the first color gamut with the second color gamut, and generates a color adjustment table that adjusts the color reproduced by the second image formation device according to the color reproduced by the first image formation device.SELECTED DRAWING: Figure 4

Description

The present invention relates to an image processing technique for performing color adjustment between models.

An inter-model color matching technique is known in which the color characteristics are adjusted by the same model or a different model of the image forming apparatus to match the color of the output (printed matter) of the image forming apparatus regardless of the model.

Patent Document 1 displays on the display device the average value and the maximum value of the color difference between the two models, which are derived based on the color measurement data of the color chart in which a plurality of patches are formed and output from the target machine and the adjuster. The technology is disclosed.

Japanese Unexamined Patent Publication No. 2011-10231

However, in Patent Document 1, there is a problem that the colors of the output products of both models cannot be matched unless the number of patches (reference images) is the same in the color charts of the target machine and the adjuster. Similar problems have been encountered in image display devices such as monitors and projectors that perform color adjustment based on a display or projection pattern that includes a reference image.

The present invention provides a technique capable of matching the colors of the output products of both models even if the number of patches is not the same in the charts output from the target machine and the adjuster.

The image processing apparatus according to one aspect of the present invention has a first color gamut reproduced by the first image forming apparatus based on a first chart including a patch formed by the first image forming apparatus. A first determining means for determining, a second chart which is a patch formed by the second image forming apparatus and includes a smaller number of patches than the number of patches included in the first chart, and a second chart. Based on the image formation information of the second image forming apparatus, the second determining means for determining the second color gamut reproduced by the second image forming apparatus, the first color gamut and the said A generation means for generating a color adjustment table that adjusts the color reproduced by the second image forming apparatus according to the color reproduced by the first image forming apparatus by associating with the second color gamut. It is characterized by having.

According to the present invention, even if the number of patches is not the same in the charts output from the target machine and the adjuster, it is possible to match the colors of the output products of both models.

Explanatory drawing of an image processing apparatus. The block diagram which shows the hardware configuration example of the image forming apparatus. The functional block diagram which shows the internal structure example of an image processing apparatus. The flowchart which shows the processing flow of an image processing apparatus. The flowchart which shows the flow of the generation process of the color conversion table for a regulator. The figure which shows the example of the color chart for an adjuster. The figure which shows the correction gradation curve example. A flowchart showing the flow of the generation process of the color conversion table for the target machine. The figure which shows the example of the color chart for a target machine. The flowchart which shows the processing flow of an image processing apparatus. The figure which shows the UI screen example. The flowchart which shows the flow of the generation process of the color conversion table for a regulator. The figure which shows the example of the color chart for an adjuster.

Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. However, the components described in this embodiment are merely examples, and are not intended to limit the scope of the present invention to them. Moreover, not all of the combinations of components described in the embodiments are essential for the means for solving the problem, and various modifications and changes are possible. In addition, as a supplement, the same configuration will be described with the same reference numerals.

<< Embodiment 1 >>
As an image processing technology for color adjustment between models, a color chart that is output from the adjuster and the target machine and has a patch showing color reproduction characteristics is measured and converted based on the color measurement result Look Up Table (LUT). ) Is created. The conversion LUT is a table that converts the output value of the adjuster so that the output value is color-reproduced by the target machine. By applying the conversion LUT created by the color matching process to the Color Management System (CMS), the adjuster can reproduce the color of the target machine. That is, it is possible to match the colors of the output products of both models.

<Outline of image processing device that adjusts colors between models>
The outline of the image processing apparatus for performing color adjustment between models according to the present embodiment will be described with reference to FIG. That is, a case where the color of the output of the regulator is matched with the color of the output of the target machine and the image processing device of the present embodiment is applied to the regulator will be described. In addition, as a supplement, it is assumed that the adjuster holds the color characteristic information (image formation characteristic information) in advance, and the target machine does not hold the color characteristic information (image formation characteristic information) in advance. The target machine is not limited to this, and may hold color characteristic information (image formation characteristic information) in advance. The color characteristic information (image formation characteristic information) is, for example, the gradation characteristic information of the color material that can be output by the target device, which is indicated by the gradation curve, which will be described in detail later. 1A and 1B are explanatory views of an image processing apparatus according to the present embodiment, FIG. 1A shows an outline of the image processing apparatus, and FIG. 1B shows an example of color characteristic information held in advance by the adjuster. Therefore, an example of a gradation curve representing gradation characteristic information of a color material that can be output (used) is shown. The application target of the image processing apparatus of this embodiment is not limited to the adjuster. The image processing device of the present embodiment may be applied to a target machine capable of color management of the adjuster, or may be applied to a device other than the adjuster and the target machine and capable of color management of the adjuster. You may.

As shown in FIG. 1A, the adjuster 1 includes a generator color conversion table generation unit (second LUT generation unit) 11 and a target machine color conversion table generation unit (first LUT generation unit). Section) 12 and a color adjustment table generation section 13.

The second LUT generation unit 11 outputs the color measurement data of the chart 21 output by printing (forming) a single color patch by the adjuster 1, the gradation curve 22 showing the color characteristic information of the adjuster 1, and the LUT of devRGBtoCMYeK. Based on this, a color conversion table for the adjuster is generated. By using the color conversion table for the adjuster generated by the second LUT generation unit 11, the second grid point for color reproduction by the output product of the adjuster 1 is determined. It can be said that the color (color gamut) of the output product formed and output by the adjuster 1, more specifically, the color value is determined. The number of monochromatic patches is a predetermined number corresponding to the type of coloring material that can be formed by the adjusting machine 1, and is smaller than the number of patches formed on the chart 31 of the target machine 2, which will be described later. To evaluate the color reproducibility of the output of the adjuster 1 by measuring the color measurement data of the chart 21, that is, the monochromatic patch formed on the chart 21 and acquiring the color measurement data (color measurement result). Can be done. The gradation curve can be said to be data indicating print characteristic information (image formation characteristic information) of the adjuster 1, and is held in advance by the adjuster 1, for example, the adjuster 1 outputs each color ink of CMYeK to a recording medium. In the case of an image forming apparatus, the data is as follows. That is, assuming that the color material has an input value of 255 and the maximum density is DM, the gradation curve is a curve as shown in FIG. 1 (b). The devRGBtoCMYeK LUT is a color conversion table that converts the RGB value of the RGB color space of the input image data into the CMYeK value of the CMYeK color space, which is a device-dependent color space, by the adjuster 1. The color conversion table for the adjuster is a table that converts the RGB value of the input image data into a CMYeK value, corrects it, and converts the correction result into a Lab value, and is also referred to as a devRGBtoLab LUT. The correction is a correction for matching the color measurement result of the monochromatic patch formed on the chart 21 with the gradation curve 22.

The first LUT generation unit 12 generates a color conversion table for the target machine by associating the color measurement data of the chart 31 output by printing (forming) the patch with the target machine 2 with the LUT of tgtRGBtoCMYeK. By using the color conversion table for the target machine generated by the first LUT generation unit 12, the first lattice point to be reproduced by the output product of the target machine 2 is determined. It can be said that the color (color gamut) of the output product formed and output by the target machine 2, more specifically, the color value is determined. The color reproducibility of the output of the target machine 2 can be evaluated by measuring the color measurement data of the chart 31, that is, the patch formed on the chart 31 and acquiring the color measurement data (color measurement result). can. The tgtRGBtoCMYeK LUT is a color conversion table that converts the RGB value of the RGB color space of the input image data into the CMYeK value of the CMYeK color space, which is a device-dependent color space, on the target machine 2.

The color adjustment table generation unit 13 associates the color conversion table for the adjuster with the color conversion table for the target machine to match the color of the output product of the adjuster 1 with the color of the output product of the target machine 2. The color adjustment table 23 is generated. By using the color adjustment table 23 between the models, it is possible to match the colors of the output objects of the adjuster 1 and the target machine 2.

By holding the image formation characteristic information of the adjuster 1 in advance, even if the number of patches is not the same in the charts output from the adjuster 1 and the target machine 2, the colors of the outputs of both models can be matched. Is possible. Hereinafter, the details of the image processing apparatus of this embodiment will be described.

<Application target of image processing equipment>
In the present embodiment, an MFP (Multifunction Peripheral) having a scanning function, a printing function, a copying function, a transmitting function, and the like, which is an image forming apparatus for forming an image on a recording medium such as paper according to an input image, will be described as an example. Shall be done. However, the scope of application of this embodiment is not limited to the MFP, and can be widely applied to all devices that output an image according to an input image. That is, in addition to other types of image forming devices such as copiers, laser printers, and inkjet printers, it is also applied to image display devices such as monitors and projectors that perform color adjustment based on a display or projection pattern including a reference image. It is possible.

<Hardware configuration of image forming device>
FIG. 2 is a block diagram showing a hardware configuration example of the MFP 100 to which the adjuster 1 is applied. The target machine 2 may be applied to the MFP 100. The MFP 100 includes a CPU 101, a ROM 102, a RAM 103, a large-capacity storage device 104, a display unit 105, an operation unit 106, an engine interface (hereinafter referred to as I / F) 107, a network I / F 108, a scanner I / F 109, and an image processing unit 110. To be equipped with. Each of these parts is connected to each other via the system bus 113 so as to be able to transmit and receive data. The MFP 100 further includes a printer engine 111 and a scanner unit 112. The printer engine 111 and the scanner unit 112 are connected to the system bus 113 via the engine I / F 107 and the scanner I / F 109, respectively. The image processing unit 110 may be configured as an image processing device independent of the MFP 100.

The CPU (Central Processing Unit) 101 controls the operation of the entire MFP 100. The CPU 101 executes various processes described later by reading the program stored in the ROM 102 into the RAM 103 and executing the program. The ROM (Read Only Memory) 102 is a read-only memory, and stores a system startup program, a program for controlling a printer engine, character data, character code information, and the like. The RAM (Random Access Memory) 103 is a volatile random access memory, which is used as a work area of the CPU 101 and a temporary storage area of various data. For example, the RAM 103 is used as a storage area for storing font data additionally registered by downloading, an image file received from an external device, and the like. The large-capacity storage device 104 is, for example, an HDD (Hard Disk Drive) or an SSD (Solid State Drive), and various data are spooled and used for storing programs, information files, image data, and the like, or as a work area. ..

The display unit 105 is composed of, for example, a liquid crystal display (LCD) and is used for displaying the setting state of the MFP 100, the status of processing being executed, the error status, and the like. The operation unit 106 is composed of an input device such as a hard key and a touch panel provided on the display unit 105, and receives an input (instruction) by a user operation. The operation unit 106 is used to change the setting of the MFP 100, reset the setting, and the like, and is used to execute the color adjustment processing mode of the MFP 100 when executing the color adjustment processing.

The engine I / F 107 functions as an interface for controlling the printer engine 111 in response to an instruction from the CPU 101 when printing is executed. Engine control commands and the like are transmitted and received between the CPU 101 and the printer engine 111 via the engine I / F 107. The network I / F 108 functions as an interface for connecting the MFP 100 to the network 114. The network 114 may be, for example, a LAN or a telephone line network (PSTN). The printer engine 111 prints a multicolor image using a developer (toner) of a plurality of colors (here, four colors of CMYeK) on a recording medium such as paper based on the print image data received via the system bus 113. To form. The scanner I / F 109 functions as an interface for controlling the scanner unit 112 in response to an instruction from the CPU 101 when the scanner unit 112 reads a document. Scanner unit control commands and the like are transmitted and received between the CPU 101 and the scanner unit 112 via the scanner I / F 109. The scanner unit 112 reads the image of the original and generates the scanned image data under the control of the CPU 101, and transmits the generated scanned image data to the RAM 103 or the large-capacity storage device 104 via the scanner I / F 109.

The image processing unit 110 performs predetermined image processing on the print image data input from an external device such as the host PC 115 to generate image data that can be processed by the printer engine 111. The details of the image processing unit 110 will be described later.

<Structure of image processing unit>
FIG. 3 is a functional block diagram showing the internal configuration of the image processing unit 110. The image processing unit 110 includes an image input unit 301, a control command generation unit 302, a RIP (Raster Image Processor) unit 303, a color conversion processing unit 304, a halftone processing unit 305, an image output unit 306, and a color adjustment table generation unit 307. Be prepared. Each of these functional units is realized by the CPU 101 reading the program stored in the ROM 102 into the RAM 103 and executing the program.

The image input unit 301 accepts input of image data to be printed. The image data to be input is, for example, image data input from the host PC 115 via the network 113 and the network I / F 108. Alternatively, the input image data may be image data stored in the large-capacity storage device 104. The input image data is, for example, three layers of data expressing each RGB signal corresponding to sRGB, which is an RGB color space independent of the printer engine 111, with 256 gradations. In addition, sRGB in this embodiment refers to the standard of RGB color space defined by IEC (International Electrotechnical Commission).

The control command generation unit 302 controls the color adjustment table generation unit 307 and the color conversion processing unit 304, which will be described later, and generates control commands for the RIP unit 303, based on the input image data input to the image input unit 301. The RIP unit control command generated by controlling the color adjustment table generation unit 307 and the color conversion processing unit 304 is sent to the RIP unit 303.

The RIP unit 303 analyzes the RIP unit control command generated by the control command generation unit 302 to generate a CMYeK raster image.

The color conversion processing unit 304 performs color conversion processing to a device-independent color space or a device-dependent color space. The color conversion processing unit 304 uses the color adjustment table and the color conversion table generated by the color adjustment table generation unit 307, which will be described later, to color-convert the RGB values acquired from the control command generation unit 302 into the color values in the CMYeK color space. Perform color conversion processing. The color conversion table is stored in the RAM 103 or the large-capacity storage device 104. Specifically, the color conversion processing unit 304 performs a process of color-converting sRGB into an RGB color space (hereinafter, referred to as a devRGB color space) depending on the printer engine 111 using a color adjustment table. Further, the color conversion processing unit 304 performs color conversion processing by a LUT for color conversion from the devRGB color space to the CMYeK color space (hereinafter, referred to as a LUT of devRGBtoCMYeK). Then, the color conversion processing unit 304 performs color conversion processing by a LUT (hereinafter, referred to as a LUT of CMYeKtoLab) that performs color conversion from the CMYeK color space to the Lab color space. As described above, the color conversion processing unit 304 performs conversion processing for converting the sRGB value into a color value in the CMYeK color space or a Lab value in the Lab color space. The Lab shown in the present embodiment refers to a three-dimensional visual uniform color space defined by the CIE (International Commission on Illumination) that is independent of the printer engine 111 in consideration of human visual characteristics. Here, in the present embodiment, the target machine is used by using the color adjustment table generated by the color adjustment table generation unit 307 to convert the RGB color space (hereinafter referred to as tgtRGB color space) depending on the target machine into the devRGB color space. Simulates the color reproduction of.

The halftone processing unit 305 performs halftone processing on the CMYeK raster image generated by the RIP unit 303.

It is possible to apply various methods such as a density pattern method, a systematic dither method, and an error diffusion method to the halftone processing by the halftone processing unit 305. Through these processes, print image data, which is image data that can be processed by the printer engine 111, is generated.

When the image output unit 306 receives the print image data from the halftone processing unit 305, the image output unit 306 transmits the received print image data to the printer engine 111 via the engine I / F 107.

The color adjustment table generation unit 307 performs an arbitrary color adjustment according to the instruction of the operation unit 106, and then provides a color adjustment table between models for color conversion from the tgtRGB color space to the devRGB color space using the input image data. Generate. In the present embodiment, the color adjustment table between the above-mentioned models is adjusted so as to simulate the color reproduction characteristics of the target machine in the adjuster, thereby realizing color reproduction close to the color intended by the user. Here, it is assumed that the LUT of devRGBtoCMYeK and the LUT of CMYeKtoLab are held in the ROM 102 or the large-capacity storage device 104. However, the output quality of the printed matter based on the output signal value of CMYeK is highly dependent on the image formation state of the machine body, and is not necessarily the same quality. Therefore, it is necessary to convert CMYeK to C'M'Ye'K'matched to the actual output (hereinafter, referred to as CMYKtoC'M'Ye'K'). The LUT of devRGBtoCMYeK, the LUT of CMYeKtoC'M'Y'K', the LUT of CMYeKtoLab, and the LUT of C'M'Ye'K'toLab described later are combined. As a result, the LUT of devRGBtoLab, which takes into account the image formation state of the current aircraft (adjuster), is compared with the LUT of tgtRGBtoLab corresponding to the unknown aircraft (target aircraft), and the number of patches included in the chart is smaller. Can be generated with a patch. The color adjustment table generation unit 307 in the present embodiment is characterized by a process of generating a LUT (color conversion table for an adjuster) of the above devRGBtoLab.

In the present embodiment, the above-mentioned discrete points in the color space are defined as lattice points (lattice points) in the color space. A grid point refers to one element such as tgtRGB or Lab that constitutes a LUT that represents a color space. A detailed example of the LUT will be described later.

<Processing flow of color adjustment table generator>
The process of generating the color adjustment table between models according to the present embodiment will be described with reference to FIG. FIG. 4 is a flowchart showing a processing flow in the color adjustment table generation unit 307. The series of processes shown in the flow of FIG. 4 is realized by the CPU 101 reading the program stored in the ROM 102 into the RAM 103 and executing it, and the data generated during the process is temporarily stored in the RAM 103. do. The symbol "S" in the description of the flowchart represents a step. The same applies to the description of the following flowchart. An image forming apparatus that outputs an output product in which a target color is formed is defined as a target machine (first image forming apparatus). An image forming apparatus to be adjusted according to the color of the output of the target machine is defined as an adjusting device (second image forming apparatus). The image processing device does not hold the print characteristic information (image formation characteristic information) of the target machine which is the image formation information, but holds the print characteristic information (image formation characteristic information) of the adjuster which is the image formation information. .. That is, it is assumed that the print characteristic information of the target machine is unknown, but the print characteristic information (image formation characteristic information) of the adjuster is known.

In S401, the color adjustment table generation unit 307 reads the chart output by the adjuster using the scanner unit 112, acquires the color measurement data, and associates the devRGB value and the Lab value as shown in Table 1 with the devRGBtoLab. Create a LUT. That is, a color conversion table for an adjuster is generated, which is data showing a correspondence relationship between an RGB value in an RGB color space that depends on an adjuster and a Lab value in a Lab color space that does not depend on an adjuster. The chart is a patch for evaluating the color of the output of the adjuster, such as checking the color reproducibility of the output of the adjuster, and is a color material formed with the maximum density (halftone dot area ratio 100%). Includes every patch. The data for outputting the chart is stored in advance in, for example, the large-capacity storage device 104 of the MFP 100, which is a regulator. The detailed flow of S401 will be described later with reference to FIGS. 5, 6 and 7.

In S402, the color adjustment table generation unit 307 reads the chart output by the target machine using the scanner unit 112, acquires the color measurement data, and associates the tgtRGB value and the Lab value as shown in Table 2 with the tgtRGBtoLab. Create a LUT. That is, a color conversion table for the target machine is generated, which is data showing the correspondence between the RGB value of the RGB color space that depends on the target machine and the Lab value of the Lab color space that does not depend on the target machine. The chart is a patch for evaluating the color of the output product of the target machine, such as checking the color reproducibility of the output product of the target machine, and is used for each color material formed in the density range from the minimum density to the maximum density. Includes patches for. The data for outputting the chart is stored in advance in, for example, the large-capacity storage device 104 of the MFP 100, which is the target machine. The detailed flow of S402 will be described later with reference to FIG.

In S403, the color adjustment table generation unit 307 associates the LUT of devRGBtoLab shown in Table 1 generated in S401 with the LUT of tgtRGBtoLab shown in Table 2 generated in S402, thereby providing a color adjustment table between models. To generate. That is, the color adjustment table generation unit 307 generates a color adjustment table (tgtRGBtodevRGB color adjustment table) between models by associating the color conversion table for the adjuster with the color conversion table for the target machine. The association is made by the signal search process. In the signal search process, first, all combinations of signal values from 0 to 255 of the devRGB values are input, and tetrahedral interpolation is performed using the table in Table 1 as a calculation table. Among all Lab values calculated by tetrahedral interpolation, L _N a _N b _N value corresponding to the tgtRGB and color difference extracting the smallest Lab value. The tgtRGB value corresponding to the extracted Lab value and the devRGB value are associated with each other. By performing this signal search process for all the grid points, a color adjustment table from tgtRGB to devRGB is generated. In the present embodiment, the signal search process is used, but the present invention is not limited to this. It suffices if tgtRGB and Lab are associated with each other, and devRGB may be estimated from Lab to determine the Lab corresponding to devRGB.

<Generation process of color conversion table for adjuster>
FIG. 5 is a flowchart showing a detailed flow of the generation process of the color conversion table for the adjuster (LUT of devRGBtoLab) of S401. The series of processes shown in the flow of FIG. 5 is realized by the CPU 101 reading the program stored in the ROM 102 into the RAM 103 and executing the program. The data generated during the process is temporarily stored in the RAM 103.

First, in S501, the color adjustment table generation unit 307 converts the brightness value of the patch in the color chart printed (output) by the adjuster into a density value read by the scanner unit 112, and converts the converted density value of the patch into a density value. Perform the acquisition process (concentration value acquisition process). FIG. 6 is a diagram showing an example of a color chart for an adjuster according to the present embodiment. The color chart 600 includes patches 601 to 604 constituting the patch group, and includes patches 601 to 604 output from the regulator and printed (formed) with each CMYeK color at the maximum density (halftone dot area ratio 100%). .. That is, the color chart 600 includes a single color patch for each color material that can be used in the adjuster. The color adjustment table generation unit 307 converts the brightness value Y of each read patch into a density value D based on Equation 1. That is, the color adjustment table generation unit 307 acquires the density value D of each CMYeK color based on the chart output by the adjuster.

After the processing of S501 is executed, the subsequent processing of S502 to S507 is performed on the density value of the patch of each CMYeK color acquired in S501.

In S502, the color adjustment table generation unit 307 determines whether or not the density value of the patch of each CMYeK color acquired in S501 is larger than the preset maximum density value (threshold value). Here, the predetermined maximum density value set in advance is a value assumed when determining the LUT of the known devRGBtoCMYeK described later, and is held by the ROM 102 or the large-capacity storage device 104. When it is determined that the density value of the patch acquired in S501 is equal to or less than the preset maximum density value and is not larger than the specified maximum density value (NO in S502), the color adjustment table generation unit 307 Shifts the process to S503. On the other hand, when the determination result that the density value of the patch acquired in S501 is larger than the predetermined maximum density value set in advance is obtained (YES in S502), the color adjustment table generation unit 307 shifts the processing to S504. do. The preset maximum density value of the color material may be set within a predetermined range in consideration of an error of the scanner device or the like. When the predetermined range is set, in S502, the determination is made based on the upper limit value of the predetermined range, and in S503 described later, the determination is made based on the lower limit value of the predetermined range.

In S503, the color adjustment table generation unit 307 determines whether or not the density value of the patch of each CMYeK color acquired in S501 is less than the preset maximum density value (threshold value). When the determination result that the density value of the patch acquired in S501 is less than the predetermined maximum density value set in advance is obtained (YES in S503), the color adjustment table generation unit 307 shifts the process to S505. .. On the other hand, when the determination result that the density of the patch acquired in S503 is not less than the predetermined maximum density value set in advance is obtained (NO in S503), the color adjustment table generation unit 307 shifts the processing to S506. do. That is, when the determination result that the density value of the patch acquired in S501 matches the specified maximum density value is obtained in S503 (NO in S503), the color adjustment table generation unit 307 performs the process in S506. Move to. When S503 is NO, the color adjustment table generation unit 307 does not perform the processes of S506 to S508, and uses the LUT of devRGBtoLab held in advance as it is, and generates the color conversion table for the adjuster. You may end it.

In S504, the color adjustment table generation unit 307 generates a correction table for adjusting the gradation value of the color material to the actual output for the color material determined in S502 to be larger than the specified maximum density value. I do. Here, the density value of the patch acquired in S501 is set to DR, the specified maximum density value of the preset color material is set to DM, and when it is determined that DR is larger than DM, cyan is taken as an example before correction. The derivation of the corrected gradation value C'based on the gradation value C of the above will be described. Color adjustment table generation unit 307, first, by using the density value DR _C and the prescribed maximum density value DM _C of cyan patch acquired in S501, obtains the corrected tone values C 'by the operation of Equation 2.

Then, the color adjustment table generation unit 307 generates a correction table (CtoC'LUT) by repeating the process for the number of lattice points of the CMYeKtoLab LUT held in advance. By using this correction table, for example, as shown in FIG. 7A, the gradation curve starting from DR is corrected to obtain a corrected gradation curve starting from DM. Here, the DR _C and 2.0 show an example of a case in which the 1.5 DM _C in Table 3.

By performing the same flow for generating the CtoC'LUT for M, Ye, and K, the CMYeKtoC'M'Ye'K' LUT as shown in Table 4 is generated. However, the density value DR _M patch acquired in S501, DR _Ye, the DR _K and 2.0, the prescribed maximum density value DM _M, the DR _Ye and 2.0, the prescribed maximum density value DM _K 1.9 And. That is, in S504, the color adjustment table generation unit 307 generates a correction table (CMYeKtoC'M'Ye'K'LUT) for deriving the correction gradation value based on the gradation value before correction for each CMYeK color. ..

In S505, the color adjustment table generation unit 307 generates a correction table for adjusting the gradation value of the color material to the actual output for the color material determined to be less than the specified maximum density value in S503. conduct. Here, the density value of the patch acquired in S501 is set to DR, the specified maximum density value of the preset color material is set to DM, and when it is determined that DR is smaller than DM, cyan is taken as an example before correction. The derivation of the corrected gradation value C'after the correction based on the gradation value C of the above will be described. Color adjustment table generation unit 307, first, by using the density value DR _C and the prescribed maximum density value DM _C of the patch of the coloring material obtained in S501, obtains the corrected tone values C 'by the operation of Equation 3.

Then, the color adjustment table generation unit 307 generates a correction table (CtoC'LUT) by repeating the process for the number of lattice points of the CMYeKtoLab LUT held in advance. By using this correction table, for example, as shown in FIG. 7B, the gradation curve starting from DR is corrected to obtain a corrected gradation curve starting from DM.

By performing the same flow for generating the CtoC'LUT for M, Ye, and K, the CToC'M'Ye'K' LUT is generated. That is, in S505, the color adjustment table generation unit 307 generates a correction table (CMYeKtoC'M'Ye'K'LUT) for deriving the correction gradation value based on the gradation value before correction for each CMYeK color. ..

In S506, the color adjustment table generation unit 307 corrects the gradation value before correction as it is for the color material that is not less than the specified maximum density value of the color material preset in S503. Generate a LUT to be adjusted. That is, when the color material is each color of CMYeK, the color adjustment table generation unit 307 generates a LUT of CMYeKtoC'M'Ye'K'.

In S507, the color adjustment table generation unit 307 uses the C'M of the CMYeKtoC'M'Ye'K'generated and acquired in S504, S505 or S506 and the C'M of the CMYeKtoLab held in advance. Generate a LUT for'Ye'K'toLab. For the LUT of C'M'Ye'K'toLab, the signal value is searched for the LUT of CMYeKtoC'M'Ye'K' and the LUT of CMYeKtoLab acquired in S504, S505, and S506 in the same manner as in S503. Is required by.

In S508, the color adjustment table generation unit 307 is a color conversion table for the adjuster based on the color conversion table (LUT of devRGBtoCMYeK), the correction table, and the color conversion table (LUT of C'M'Ye'K'toLab). To generate. The color conversion table (LUT of devRGBtoCMYeK) is a color conversion table stored in advance. The correction table (LUT of CMYeKtoC'M'Ye'K') is a correction table generated in S504, S505 or S506. The color conversion table (LUT of C'M'Ye'K'toLab) is a color conversion table generated in S507. The color adjustment table generation unit 307 combines these tables and generates a color conversion table for an adjuster (LUT of devRGBtoLab) as a result of the combination.

<Generation process of color conversion table for target machine>
FIG. 8 is a flowchart showing a detailed flow of the generation process of the color conversion table for the target machine (LUT of tgtRGBtoLab) of S402. The series of processes shown in the flow of FIG. 8 is realized by the CPU 101 reading the program stored in the ROM 102 into the RAM 103 and executing the program. The data generated during the process is temporarily stored in the RAM 103.

First, in S801, the color adjustment table generation unit 307 reads the color chart printed (output) by the target machine by the scanner unit 112, and acquires the RGB values (color values) of the patches formed on the color chart. Here, it is desirable that the color chart has as many grid points as the color conversion table for the target machine. FIG. 9 is a diagram showing an example of a color chart for a target machine for measuring the color characteristics of the target machine. FIG. 9 shows an example in which the grid points of the color conversion table for the target machine are arranged in increments of 16 and 729 patches are arranged. The number of grid points in the color conversion table for the target machine is not limited to this. If higher accuracy is required, the number of grid points may be changed in increments of 8.

In S802, the color adjustment table generation unit 307 generates a color conversion table for the target machine. The RGB values of each patch acquired in S801 are written in the corresponding color conversion table for the target machine. For example, when the number of grid points is 16, a table in which the RGB values are set in 16 increments is prepared as shown in Table 5. Then, when the Lab value of the patch corresponding to the RGB value (0, 0, 16) is (0, 2, -6), the process of writing to the table is executed as shown in Table 6. By repeating such a writing process for the number of lattice points of tgtRGB, the blanks in the table are filled.

By executing the above processing, it is possible to match the colors of the output products of both models even if the number of patches is not the same in the charts output from the target machine and the adjuster.

Even if the number of patches formed on the chart by the adjuster is reduced as compared with the conventional one, it is possible to simulate the color reproduction characteristics maintaining the same accuracy as the conventional one. In other words, by using not only the color measurement data of the patches formed on the chart by the adjuster but also the print characteristic information of the adjuster held in advance, even if the number of patches is smaller than the conventional one, it is about the same as the conventional one. , It is possible to simulate color reproduction without degrading the accuracy of color reproduction. Moreover, the printing cost can be reduced.

In this embodiment, a color chart in which only single color patches of each CMYeK color are formed at the maximum density (halftone dot area ratio 100%) is used. In addition, as a supplement, more preferably, a single color patch for each color material of CMYeK, which is a color material that can be used in the adjuster, and a single color patch in which the density (halftone dot area ratio) is changed for each color material. , Color charts with white patches that do not form an image may be used.

In the present embodiment, the case where the number of charts on which the patch is formed is one has been described. In addition, as a supplement, more preferably, in consideration of unevenness at the time of printing, a plurality of charts in which patches of each color are formed are output from the adjuster, and for each color, the color measurement of the patches formed in the plurality of charts is performed. The average of the results may be used.

In addition, in the present embodiment, the case where the patch of each color of CMYeK is arranged in one place has been described. In addition, as a supplement, more preferably, in consideration of an error at the time of scanning, the patches of each color of CMYeK may be arranged at a plurality of locations, and the average of the color measurement results of the plurality of locations may be used for each color of CMYeK.

<< Embodiment 2 >>
In the first embodiment, it corresponds to the color conversion table for the adjuster rewritten based on the color measurement result and the print characteristic information of the patch in which each CMYeK color is printed at the maximum density (halftone dot area ratio 100%) output from the adjuster. The process of generating a color adjustment table between models was explained. In the present embodiment, the processing when a paper type that is not considered in designing the color conversion table for the adjuster (LUT of devRGBtoLab) is selected will be described.

The differences from the first embodiment regarding the processing flow of the color adjustment table generation unit 307 in the present embodiment will be described. In the first embodiment, in S401, a method of generating a color conversion table for an adjuster (LUT of devRGBtoLab) based on the color measurement result of a single color patch of each color of CMYeK having the maximum density is shown. In this embodiment, not only a single color patch but also a mixed color patch is output at the maximum density, and a method of estimating an intermediate color which is a color reproduction range is shown. FIG. 10 is a flowchart showing a processing flow in the color adjustment table generation unit 307 according to the present embodiment. As shown in FIG. 10, S1011 to S1013 are added to the process shown in FIG. 4 described in the first embodiment. In the present embodiment, by estimating the intermediate color based on the maximum density patch of the color mixture (also referred to as the color mixture patch of the maximum density), it becomes easy to correspond to various papers.

First, in S1011, the color adjustment table generation unit 307 displays a screen prompting the user to select a paper type on the display unit 105 (FIG. 1), and acquires the paper type selected by the user. FIG. 11 is an example of a paper type selection screen displayed on the display unit 105, and is a diagram showing an example of a UI screen. The UI screen 1100 shown in FIG. 11 is an initial screen that simulates color reproduction characteristics. The UI screen 1100 is a UI screen showing the overall configuration, and includes a paper type selection box 1101, a paper type determination button 1102, and a back button 1103. The paper type selection box 1101 can select a paper type other than the preset paper type and the preset paper type (other paper types). In FIG. 11, the paper type selection box 1101 is displayed by a pull-down menu, and non-glossy paper, glossy paper, and other papers can be selected. It is assumed that the color conversion table for the adjuster (LUT of devRGBtoLab) corresponding to the preset paper type is held in the ROM 102 or the large-capacity storage device 104. That is, the color conversion table for the adjuster (devRGBtoLab LUT) corresponding to the non-glossy paper and the color conversion table for the adjuster (devRGBtoLab LUT) corresponding to the glossy paper are held by the ROM 102 or the large-capacity storage device 104. It is assumed that it is. The paper type determination button 1102 is a button pressed when the user finishes setting the paper type. The back button 1103 is a button pressed by the user when shifting from the paper type selection screen 1100 to the screen before the screen 1100. That is, in S1011, the color adjustment table generation unit 307 selects the paper type in the paper type selection box 1101 by the user operation, and the paper type determination button 1102 is pressed to select the paper type by the user. To get.

In S1012, the color adjustment table generation unit 307 determines whether or not the selected paper type (paper type selected by the user) acquired in S1011 is standard paper. When a preset paper type (non-glossy paper, glossy paper in FIG. 11) is selected in S1011, the color adjustment table generation unit 307 acquires a determination result that standard paper is selected ( YES in S1012), the process shifts to S401. On the other hand, when another paper type is selected in S1011, the color adjustment table generation unit 307 acquires a determination result that the standard paper is not selected (NO in S1012), and shifts the process to S1013.

In S1013, the color adjustment table generation unit 307 generates (creates) a color conversion table for an adjuster (LUT of devRGBtoLab) corresponding to other paper types. The color conversion table for the adjuster generated in S1013 can be said to be the second color conversion table for the adjuster because the paper type to be processed is different from the color conversion table for the adjuster generated in S1012. The detailed flow of S1013 will be described later with reference to FIGS. 12 and 13. When the generation of the color conversion table for the adjuster (color conversion table for the second adjuster) corresponding to other paper types is completed, the color adjustment table generation unit 307 shifts the processing to S402.

<Generation process of color conversion table for other paper type adjusters>
FIG. 12 is a flowchart showing a detailed flow of the generation process of the color conversion table (LUT of devRGBtoLab) for the adjuster of other paper types of S1013. The series of processes shown in the flow of FIG. 12 is realized by the CPU 101 reading the program stored in the ROM 102 into the RAM 103 and executing the program.

First, in S1201, the color adjustment table generation unit 307 reads the color chart printed (output) by the adjuster by the scanner unit 112, and acquires the RGB values (color values) of the patches formed on the color chart. FIG. 13 is a diagram showing an example of a color chart for the adjuster according to the present embodiment. The color chart 1300 is a plurality of (15) patches 1301 to 1315 constituting the patch group, and the patches 1301 to 1315 which are solid printing of the primary color to the fourth color of CMYeK output from the adjuster are each. It is printed. It can be said that the patches 1301 to 1315 are the maximum density single color patch or the maximum density mixed color patch.

In S1202, the color adjustment table generation unit 307 converts the devRGB value of each patch acquired in S1201 to calculate the XYZ value, and acquires the calculated XYZ value. A 3 × 3 matrix as shown in Equation 4 below can be applied to the conversion from the devRGB value to the XYZ value.

In S1203, the color adjustment table generation unit 307 estimates the intermediate color based on the XYZ value of each patch acquired in S1202. In this embodiment, the Neugebauer equation is used for estimating the neutral color. In the Neugebauer formula, the neutral color is estimated from the halftone dot area ratio of each plate and the reflectance of solid printing from the primary color to the fourth color. Here, the halftone dot area ratios c, m, y, and k (devRGBtocmyk) LUTs corresponding to the grid points of devRGB as shown in Table 7, which are the image formation information of the adjuster, are held by the ROM 102 or the large-capacity storage device 104. I will do it. (The N paper white, primary color to quaternary color) average appearance ratio A _N per unit area of the print area is expressed as Equation 5 below.

In S1204, the color adjustment table generation unit 307 generates a second color conversion table (LUT of devRGBtoXYZ). Using the LUT of devRGBtocmyk in Table 7, the X value corresponding to the grid points of devRGB was obtained by Equation 4 and the X value X _M of the patch 1300 (M corresponds to paper white and the primary to fourth colors). it can be expressed by equation 6 below using a _N obtained by equation 5.

The derivation process of the above formula 6 is performed in the same manner for the Y value and the Z value, and the LUT of devRGBtoXYZ as shown in Table 8 is created by repeating the process for the number of grid points.

In the present embodiment, the neutral color is estimated using the Neugebauer equation, but the present invention is not limited to this. Anything can be used as long as the intermediate color can be estimated from a limited number of patches formed in a specific number in the color chart.

In S1205, the color adjustment table generation unit 307 generates a color adjustment table of devRGBtoLab. DevRGBtoLab is obtained by converting XYZ to Lab from the table of devRGBtoXYZ obtained in S1204. The following equation 7 can be applied to the conversion from XYZ to Lab.

Then, by associating the obtained XYZtoLab with the devRGBtoXYZ used in S1202, a color conversion table for the adjuster (LUT of the devRGBtoLab) is generated.

By executing the above processing, the color reproduction characteristics are simulated even for paper types that are not considered in designing the color conversion table for the adjuster when creating the color conversion table for the adjuster (LUT of devRGBtoLab). Can be done. In other words, by using not only the color measurement data of the patches formed on the chart by the adjuster but also the halftone dot area ratio of each version of the adjuster held in advance, even if the number of patches is smaller than before, It is possible to simulate color reproduction without degrading the accuracy of color reproduction, which is about the same as the conventional one. Moreover, the printing cost can be reduced.

[Other Embodiments]
The present invention supplies a program that realizes one or more functions of the above-described embodiment to a system or device via a network or storage medium, and one or more processors in the computer of the system or device reads and executes the program. It can also be realized by processing. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

Claims (11)

Based on the first chart containing the patch formed by the first image forming apparatus, the first determining means for determining the first color gamut reproduced by the first image forming apparatus, and the first determining means.
A second chart containing a number of patches formed by the second image forming apparatus, which is smaller than the number of patches included in the first chart, and an image of the second image forming apparatus. A second determining means for determining a second color gamut reproduced by the second image forming apparatus based on the formation information, and
By associating the first color gamut with the second color gamut, a color adjustment that adjusts the color reproduced by the second image forming apparatus according to the color reproduced by the first image forming apparatus. The generation method to generate the table and
An image processing apparatus comprising. The second determination means according to claim 1, wherein the second color gamut is determined based on the gradation characteristic information of the second image forming apparatus as the image forming information. Image processing device. The second chart is a claim, wherein the patch is a color material that can be used in the second image forming apparatus, and has at least a single color patch in which the halftone dot area ratio of each color material is 100%. Item 2. The image processing apparatus according to item 1 or 2. The second chart is a monochromatic patch possessed as the patch, which is a color material that can be used in the second image forming apparatus, and includes a monochromatic patch in which the halftone dot area ratio is changed for each color material and an image. The image processing apparatus according to claim 1 or 2, wherein the image processing apparatus includes a white patch that is not formed. The second determining means determines the second color gamut based on the image forming state of the second image forming apparatus specified based on the second chart and the image forming information. The image processing apparatus according to claim 1 or 2. The second determining means is characterized in that the second color gamut is determined as the image forming information based on the color reproduction range estimated from the gradation characteristic information of the second image forming apparatus. The image processing apparatus according to claim 1. The image processing according to claim 1 or 6, wherein the second chart includes a patch in which a color material that can be used in the second image forming apparatus is combined and a white paper patch on which an image is not formed. Device. The second determination means determines the second color gamut by estimating based on the second chart and the halftone dot area ratio of each color material that reproduces the patch included in the second chart. The image processing apparatus according to claim 1 or 6. The image processing apparatus according to any one of claims 1 to 8, wherein the image forming information of the second image forming apparatus is held in advance. A first determination step of determining a first color gamut reproduced by the first image forming apparatus based on a first chart including a patch formed by the first image forming apparatus, and a first determination step.
A second chart containing a number of patches formed by the second image forming apparatus, which is smaller than the number of patches included in the first chart, and an image of the second image forming apparatus. A second determination step of determining a second color gamut reproduced by the second image forming apparatus based on the formation information, and a second determination step.
By associating the first color gamut with the second color gamut, a color adjustment that adjusts the color reproduced by the second image forming apparatus according to the color reproduced by the first image forming apparatus. The generation process to generate the table and
An image processing method comprising. A program for causing a computer to function as the image processing device according to any one of claims 1 to 9.

Images