JP2015062281A - Control device, calibration data creation method, and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control device that creates accurate data for calibration with a small number of patches.SOLUTION: A control device includes a storage unit that stores reference data representing the density characteristics with respect to input gradation values when ink droplets are discharged to a recording medium at a reference discharge amount for each type of the recording medium; records patch images corresponding to the input gradation values less than the values of the reference data in a new type of recording medium in two or more pieces of the stored reference data, and reads the density of the patch images; and specifies, of the pieces of stored reference data, the reference data with the density value having the highest correlation with the density of the patch images, and calculates, from the specified reference data, the reference data representing density characteristics corresponding to the new type of recording medium.

Description

The present invention relates to a control device that generates calibration data for each recording medium, a calibration data generation method, and a program.

  In an image forming apparatus such as an ink jet recording apparatus, a laser printer, or a copying machine, output characteristics such as printing may change as the printing environment changes or the apparatus changes over time. For example, in an ink jet recording apparatus, when a recording head that ejects ink is replaced, the ink ejection amount changes due to individual differences in the recording head, and the output characteristics of printing change. Such a change in the output characteristics not only changes the color of the printed matter of the image forming apparatus itself, but also causes a problem that the colors of each other are not uniform in an environment composed of a plurality of image forming apparatuses. End up.

  In order to solve problems associated with changes in output characteristics, color calibration (also simply referred to as calibration) is generally performed. As one of the calibration methods, a color material is printed on a recording medium (medium) that receives a color material such as ink, and the printed image is colorimetrically measured. Specifically, first, a plurality of patches whose gradation values are changed are printed on a recording medium for each color material color. Next, the printed patch is read by a sensor such as a densitometer or a colorimeter. The correction value is calculated by comparing the read value with the target color value (calibration target) of the corresponding recording medium stored in the image forming apparatus in advance for each color material. Then, printing is performed by controlling the ink discharge amount by the correction parameter.

  Further, as a procedure of image processing at the time of printing, RGB or CMYK contone image signals are converted into color material color contone image signals for each color material. The color material color contone image signal is converted into a contone signal capable of printing the same density as the calibration target by a one-dimensional lookup table (1DLUT) in which correction parameters for calibration are set for each color material color. A print control process is performed on the converted signal, and the color material is transferred onto the recording medium to perform printing. As described above, the same density as the calibration target can be reproduced.

  In the case of an ink jet recording apparatus, a color material density value for an input data value printed with a reference discharge amount by a recording head is defined as a calibration target. Here, the color material density value can be converted from the measured value optically read by the reading sensor. The calibration target has different characteristics depending on the recording medium. This is because the fixing state of the ink, which is the color material, to the recording medium differs depending on the recording medium, and is affected by the state in which the coloring material penetrates from the surface of the recording medium. In addition, it is also affected by changes in the recording dot diameter and density distribution due to the bleeding state of the color material on the surface of the recording medium.

  As a result, the calibration target hardly changes linearly with respect to the maximum density of printing, and changes nonlinearly (so-called dot gain). Here, there is also a method in which a calibration target is a value obtained by connecting a measurement value of the reading sensor at the minimum value of the input data and a measurement value of the reading sensor at the maximum value of the input data with a straight line. However, in this case, since the nonlinear characteristic data is converted into the linear characteristic data, data skipping occurs due to a quantization error, which affects the print gradation characteristics. That is, in the calibration executed when a recording head having a different discharge amount is mounted or when the discharge amount fluctuates due to aging of the nozzles, the quantization error is required to be small.

  As described above, calibration requires a calibration target depending on the recording medium. Conventionally, manufacturers have provided calibration targets for recording media to customers. On the other hand, calibration may be performed using a recording medium other than that provided by the manufacturer. However, in that case, a calibration target must be generated on the customer side and registered in the printing system.

  Patent Document 1 describes a method of creating a calibration target for each recording medium. According to Patent Document 1, a patch is color-measured for all input values to generate a calibration target. In addition, a calibration target is generated by measuring colors corresponding to a plurality of gradations and performing an interpolation calculation between the patches. A method for creating a calibration target by the user is also described.

JP 09-116768 A

  As described in Patent Document 1, when creating a calibration target, a patch corresponding to a plurality of gradations is used for each color material color. In general, as the number of gradations (number of patches) increases, interpolation calculation between gradation values can be reduced. By reducing the number of interpolation calculations, the dot gain characteristics can be accurately reproduced even if the linearity of the gradation values (density and colorimetric values) of the calibration target is low. However, as the number of gradations (number of patches) increases, the number of patches to be printed at the time of calibration target creation increases, so the amount of ink and paper used also increases. In addition, since the time for printing and the time for measurement increase, the time for creating the calibration target also increases.

  Conversely, if the number of gradations (number of patches) is reduced, the amount of ink and paper consumed when creating a calibration target is reduced, and the time for creating a calibration target is also reduced. However, the dot gain characteristics cannot be accurately reproduced.

  An object of the present invention is to solve such conventional problems. An object of the present invention is to provide a control device, a calibration data generation method, and a program that create highly accurate calibration data with a small number of patches.

  In order to solve the above problems, the control device according to the present invention stores, for each type of recording medium, reference data representing density characteristics with respect to an input gradation value when ink droplets are ejected onto a recording medium with a reference ejection amount. Storage means; recording control means for recording patch images corresponding to at least two gradation values among the input gradation values of the reference data stored in the storage means on a new type of recording medium; and the recording Read control means for controlling the reading unit to read the densities of the at least two patch images recorded by the control means, and at least two of the reference data stored in the storage means read by the read control means Specifying means for specifying reference data having a density value having the highest correlation with the density of two patch images; and from the reference data specified by the specifying means, A calculation means for calculating a reference data representative of the density characteristic corresponding to the Tana type of recording medium, characterized in that it comprises a.

  According to the present invention, highly accurate calibration data can be created with a small number of patches.

It is a block diagram which shows the flow of a color conversion process. It is a figure which shows an example of a patch chart. It is a figure for demonstrating 1DLUT of a calibration process part. 1 is a diagram illustrating an example of a printing system including an image forming apparatus. It is a figure which shows the structure of a printing part and a sensor part. It is a figure which shows the other structural example of a printing system. It is a block diagram which shows the structure of the part which concerns on this embodiment of an image process part. It is a figure for demonstrating calibration target data. It is a figure for demonstrating selection of a calibration target. It is another figure for demonstrating selection of a calibration target. It is a figure which shows schematic structure of a measuring device. It is a figure which shows the procedure of the production | generation process of calibration target data. It is a figure which shows the procedure of the process of S1204 of FIG.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following embodiments do not limit the present invention according to the claims, and all combinations of features described in the embodiments are not necessarily essential to the solution means of the present invention. . The same constituent elements are denoted by the same reference numerals, and the description thereof is omitted.

[overall structure]
The printing system according to the present embodiment includes an image forming apparatus such as an ink jet recording apparatus, and a colorimeter for optically reading a printed patch chart. In this printing system, a user can print an arbitrary patch chart including a plurality of patch images (patches) to optically read the density and the like, and can also create documents and images created by various application software. Can also be printed. The ink jet recording apparatus has Lc (light cyan) diluted with C (cyan), M (magenta), Y (yellow), K (black), and C (cyan) as coloring materials, and Lm with diluted M (magenta). (Light magenta) 6 color inks are provided. The combination of inks as color materials is not limited to this, and may further include special color inks such as R (red), G (green), B (blue), and Gy (gray). Only C, M, Y, C, M, Y, K may be used.

  FIG. 1 is a block diagram showing the flow of color conversion processing executed as image processing in the image forming apparatus. The image forming apparatus has an RGB printer function for inputting and printing RGB signals and a CMYK printer function for inputting and printing CMYK signals. For the sake of explanation, it is assumed that the quantization number in image data and image processing is 8 bits for each color. However, it may be 10 bits, 12 bits, 16 bits, etc. instead of 8 bits. An image signal interface (I / F) 101 inputs image data to be printed, which is RGB data or CMYK data. The color matching processing unit 102 converts the input device-independent RGB data into device-dependent RGB data. The color matching processing unit 103 converts device-independent CMYK data into device-dependent CMYK data. The color separation processing unit 104 converts device-dependent RGB data into color material color data. The color separation processing unit 105 converts device-dependent CMYK data into color material color data. Here, the color material color data is data on C, M, Y, K, Lc, and Lm corresponding to the color material used in the image forming apparatus. The gradation correction processing unit 106 performs gradation correction on the color material color data in accordance with output characteristics of the image forming apparatus and a user instruction.

  Each of the color matching processing units 102 and 103 and the color separation processing units 104 and 105 performs color conversion processing (hereinafter simply referred to as conversion processing) on the input data using a dedicated look-up table (LUT). Here, each lookup table is prepared for each recording medium (media) and for each printing mode such as high-speed printing / low-speed high-quality printing. The color matching processing units 102 and 103 and the color separation processing units 104 and 105 perform conversion processing using a three-dimensional LUT (3DLUT) or a four-dimensional LUT (4DLUT), and the tone correction processing unit 106 performs a one-dimensional LUT. Conversion processing is performed using (1DLUT). The 3DLUT has 16 grids with 17 count intervals on each color space coordinate axis, and is composed of a total of 16 × 16 × 16 = 4096 grids. Similarly, the 4DLUT is composed of a total of 16 × 16 × 16 × 16 = 65,536 lattices. Note that generation of each LUT and conversion processing using each LUT are performed by a generally known method.

  The calibration processing unit 107 is a reference image forming apparatus (reference machine) for variations in color and density of a printing result caused by individual differences in media, color materials, and ejection amount fluctuations due to changes in the nozzles of the recording head. ) To achieve the quality achieved in step (1). The calibration processing unit 107 performs conversion processing by 1DLUT for each color material color. The calibration processing unit 107 uses the correction parameter for the density value printed with respect to the input data value by the image forming apparatus using the 1DLUT. Correction target).

  FIG. 2A is a diagram showing a calibration execution patch chart for measuring a density value with respect to an input data value. The patch chart shown in FIG. 2A is used for calculating correction parameters used in calibration executed by the calibration processing unit 107 for image data to be printed. That is, the correction parameter is calculated from the density reading result of the patch chart shown in FIG. 2A and the predetermined calibration target.

  The calibration execution patch chart is used to print patches in which the color material color input signal (tone) is changed in increments of 10% for each of the C, M, Y, K, Lc, and Lm color materials. A group of patches. In particular, in an ink jet recording apparatus, due to the characteristics of the ink and the medium, a cockling phenomenon occurs in which the medium expands due to ejected ink droplets and causes undulations. If the cockling amount is large, the distance between the sensor that performs reading and the reading surface of the medium changes according to the reading position of the medium, resulting in measurement variations depending on the reading position.

  Therefore, in this embodiment, in order to reduce the cockling amount, a paper white area where ink is not ejected is provided between the patches, and the printing positions of the patches are shifted so that the upper and lower patches are not arranged in a line. By disposing the paper white area between the patches, the cockling amount can be reduced due to the rigidity of the paper. Furthermore, since a cockling amount increases when a high density patch concentrates on a part of the calibration execution patch chart, each patch is arranged so that a high density patch does not concentrate on a part of the chart. For example, the patches are arranged such that the total of the gradation values of four adjacent gradation patches is 190% or 200%.

  FIG. 2B shows a calibration target creation patch chart for creating calibration target data of unregistered media. Unlike the calibration execution patch chart of FIG. 2A, each color material color is composed of only two types of patches of 30% and 80%. The consumption amount of media and the consumption amount of ink used for printing are smaller than the calibration execution patch chart of FIG. 2A, and as a result, the printing time and the measurement time can be shortened. The calibration target creation process using the patch chart of FIG. 2B will be described later. In FIG. 2B, 30% and 80% patches are shown. However, in the gradation range corresponding to the medium to low density range, other values may be used instead of 30% as long as the influence of the dot gain tends to be large due to the characteristics of the ink and the medium. Further, in the gradation range corresponding to the high density region, other values may be used instead of 80% as long as the dot gain has a relatively small influence on the variation in the ejection amount. Further, the value may be different depending on the color material color. Further, the patch chart of FIG. 2B uses two patches of 30% and 80%, but this case can be applied if the number of patches is smaller than that of the calibration execution patch chart of FIG. is there.

  FIG. 3 is a diagram for explaining the 1DLUT of the calibration processing unit 107 in FIG. FIG. 3 shows one color material color, and the horizontal axis represents an input data value (input gradation value) when the patch is printed. The vertical axis represents the print density value read by the reading sensor. A graph 301 shows print density values with respect to input data values in the reference machine. The data of the graph 301 is stored in advance as reference data in the image forming apparatus 100 in the case of media that can be handled by the printer manufacturer. A graph 302 shows a print density value with respect to an input data value in an actual machine, that is, an image forming apparatus that prints image data to be printed. A graph 302 is data obtained by printing the calibration execution patch chart of FIG. P1 to P11 on the graph 302 correspond to patches of 0% to 100% in the calibration execution patch chart. The graph 302 is obtained by performing arithmetic processing from each reading measurement value of P1 to P11 by a generally known method. The calibration processing unit 107 corrects the contone color material signal for each color material color using the correction parameter so as to obtain the printing density (graph 301) of the reference machine. The description in FIG. 3 is a case where calibration is performed for media that can be handled by the manufacturer. However, in this embodiment, calibration target data (reference data) can be created for new unregistered media. .

  FIG. 4 is a diagram illustrating an example of a printing system including an image forming apparatus. The printing system according to the present embodiment includes an information processing apparatus 401 such as a general-purpose PC and an image forming apparatus 407. Each device is connected to be communicable with each other via a network or an interface such as a USB or a local bus. The information processing apparatus 401 functions as a control apparatus that performs recording control and reading control of the image forming apparatus 407 such as printing and colorimetry by executing various programs. The storage device 405 stores a system program, an application software program, a control program for executing the operation of the present embodiment, various parameters, image data to be printed created by the information processing device 401, and the like. The storage device 405 is, for example, a hard disk or a flash ROM.

  The CPU 403 executes a program for generating an LUT for normal printing and calibration, and for creating and registering calibration target data in this embodiment, stored in the storage device 405. The storage device 405 also stores existing calibration target data, measured print density values, and patch data shown in FIG. The work memory 404 is used as a work area when the CPU 403 executes various programs. The data input / output device 406 is, for example, a portable storage device such as a CD, a DVD, or a USB memory, or a data communication device such as a LAN card. The data input / output device 406 is used as an interface for inputting image data to be printed and input / output of patch measurement values. An operation unit (UI) 402 serving as a user interface can accept various instructions from the user via a keyboard, a pointing device, or the like, and can display various setting contents to the user via a display or the like. .

  The image forming apparatus 407 includes a data transfer unit 408, a printer control unit 409, an image processing unit 410, a printing unit (recording unit) 411, and a sensor unit 412. Based on the print data transmitted from the information processing device 401, the image forming apparatus 407 Print. The print data includes control data for reading and controlling the sensor unit 412. The data transfer unit 408 extracts image data and image processing parameters to be printed from the print data transmitted from the information processing apparatus 401 and sends them to the image processing unit 410, and mechanical parameters, printer control data, and sensor unit control data. Is extracted and sent to the printer control unit 409. The printer control unit 409 controls the printing operation of the printer 407 according to the printer control data sent from the data transfer unit 408. In addition, the printer control unit 409 performs measurement control on the sensor unit 412 in conjunction with the print control. The measurement value read by the sensor unit 412 is transferred to and stored in the storage device 405 of the information processing device 401.

  FIG. 5 is a diagram illustrating the structure of the printing unit 411 and the sensor unit 412. FIG. 5 illustrates an example in which the image forming apparatus 407 is a serial scanning type inkjet recording apparatus that performs printing by scanning the recording head in a direction intersecting the medium conveyance direction. A carriage mounted with a recording head 503 for ejecting ink droplets reciprocates on the guide rail 505 in the scanning direction. The medium 501 is transported in the transport direction by a transport mechanism (not shown). The patch 502 can be printed on the medium 501 by scanning the carriage and conveying the medium 501. The sensor unit 504 that optically reads the printed patch 502 is mounted on the recording head 503. Similarly to the above, the patch 502 is moved by moving the recording head 503 in the scanning direction and the medium 501 in the transport direction. Can be read.

  The image processing unit 410 in FIG. 4 performs color conversion processing, gradation correction processing, and calibration processing as shown in FIG. 1 using the image data and image processing parameters sent from the data transfer unit 408. The image processing unit 410 performs halftoning processing on the data on which these various types of processing are executed, generates nozzle driving data for nozzle driving for each color material color, and sends the nozzle driving data to the printing unit 411. The printing unit 411 performs printing based on the nozzle drive data sent from the image processing unit 410.

  FIG. 6 is a diagram illustrating another configuration example of the printing system. FIG. 6 is an example in which the information processing apparatus 401 in FIG. 4 is configured in the image forming apparatus 420 as the calculation unit 421. In this example, the calculation unit 421 also controls the image processing unit 428, the printing unit 429, and the sensor unit 430 in place of the printer control unit 409 in FIG. The data input / output device 426 is, for example, a portable storage device such as a CD, a DVD, or a USB memory, or a data communication device such as a LAN card. The data input / output device 426 is used as an interface for receiving image data to be printed such as a document or an image from the information processing device 427. In addition, image data to be printed is input to the image forming apparatus 420 via a portable storage device, and a correction parameter calculation process for measured values, an execution instruction for normal printing, and the like can be specified via the UI 422. You may comprise. In this case, since all processing can be performed within the image forming apparatus 420, the information processing apparatus 427 is not necessary. The UI 422, CPU 423, work memory 424, storage device 425, image processing unit 428, printing unit 429, and sensor unit 430 are the UI 402, CPU 403, work memory 404, storage device 405, image processing unit 410, printing unit 411, FIG. This corresponds to the sensor unit 412.

  FIG. 7 is a diagram illustrating each block configuration of a calibration target generation / registration unit and a calibration execution unit that executes calibration in the image processing unit 410. The calibration target generation / registration unit newly generates calibration target data of unregistered media and registers it in the calibration target database (DB).

  The calibration target generation / registration unit includes a measurement value information reading unit 701, a density conversion unit 702, a calibration target selection determination unit 703, a correction adjustment unit 704, a registration unit 705, and a calibration target data storage unit 706. Including. The measurement value information reading unit 701 acquires calibration media information and measurement value information of unregistered media. The calibration media information is for identifying the type of media and is required when registering in the calibration target group DB. The media type is classified according to the material of the media and the coating layer on the surface, such as glossy paper or coated paper. In the present embodiment, for example, the density characteristics resulting from dot gain when ink droplets are ejected onto a medium are classified in a similar range. When the calibration processing unit 107 executes calibration, the medium is designated based on the calibration medium information, and calibration target data corresponding to the medium is used.

  The measured value information is measured values stored in the storage devices 405 and 425 by reading the patch portion and the paper white portion of the calibration target creation patch chart shown in FIG. is there. The measured value varies depending on the optical reading method of the sensor units 412 and 430. For example, when the sensor units 412 and 430 are spectrocolorimeters, they are L * a * b * values that are equal color difference spaces, and when they are optical densitometers, they are stored as optical density values. Further, when the reflection luminance is measured by a light source (tungsten, LED, etc.) and a light receiving sensor (photodiode, etc.), it is stored as a reflection luminance value. In addition, when RGB LEDs are used as the light source, reading results with a wide measurement range can be obtained by irradiating the patch with a light source complementary to the colorant color and measuring it. That is, the G LED is irradiated to measure magenta, light magenta, and black, and the R LED is irradiated to measure cyan and light cyan. Further, the yellow LED is irradiated with the B LED.

  The density converter 702 converts the measurement value into a one-dimensional density signal based on paper white. As described above, since the calibration target data is related to the medium and the dot gain of the color material, it is necessary to pay attention to the density variation in which the value from the paper white of the medium is canceled. Further, since the calibration target data is a print density value with respect to an input value in the reference machine, the density of the paper white portion where the color material is not fixed must be normalized as 0. When the measured value is any of an L * a * b * value, an optical density value, and a reflected luminance value, it can be converted into a paper white reference density value by a generally known method.

  The calibration target selection determination unit 703 selects calibration target data having the highest correlation from the existing calibration target data group using the patch density information of FIG. 2B corresponding to each color material color. Details regarding the selection method will be described later. The correction adjustment unit 704 newly generates calibration target data for unregistered media by correcting and adjusting the selected calibration target data. Details of the correction adjustment unit 704 will be described later. The calibration registration unit 705 stores the generated calibration target data in the calibration target data storage unit 706 in association with the new unregistered media name.

  FIG. 8 is a diagram for explaining calibration target data (reference data) corresponding to each medium stored in the calibration target data storage unit 706. As media types, media A to G and newly added media X are shown. As the stored information, for each medium for each color material, a density value based on paper white with respect to an input value (input gradation value) of image data is stored as a target density value. Further, a density value having a large influence (30% in the present embodiment) of the dot gain in the middle / low density area and a density value having a small influence (80% in the present embodiment) of the dot gain in the high density area. Is remembered. These density values correspond to the input values (30% and 80%) of the calibration target creation patch chart described in FIG. The value is stored together with other input values, but only 30% and 80% are shown in FIG. In the following description, the density value is expressed as D (media type, input value (%), color material color). That is, the density value of cyan (C) ink corresponding to an input value of 30% for medium A is expressed as D (A, 30, C). In the above, the influence of the dot gain in the middle / low density region is large, in other words, the variation in the density change of the density characteristic represented by each of the plurality of calibration target data is large. Further, the influence of the dot gain in the high density region is small, in other words, the variation in density change of the density characteristic represented by each of the plurality of calibration target data is small. Variation in density conversion of each calibration target data stored in the calibration target data storage unit 706 may be obtained in advance within a predetermined gradation range. Then, the user sets arbitrary gradation values (30%, 80%) by the user for each of the gradation range where the variation is larger than a predetermined value (30% to less than 80%, etc.) and the small gradation range (80% or more, etc.). You may make it select.

  Next, processing at the time of executing calibration will be described. The media name for executing calibration is input to the calibration target data selection unit 707 as calibration media information. The calibration target data selection unit 707 selects a target density value of a desired color material color shown in FIG. 8 from the calibration target data storage unit 706 and sets it as calibration target data 708. On the other hand, the parameter generation unit 710 generates correction parameters used in the calibration processing unit 107 in FIG. 1 together with the actual machine print density data 709 (graph 302 in FIG. 3) indicating the already measured print density characteristics in the actual machine. The actual printing density data is also in the form of density value data with respect to the input value of the image data, similarly to the target density value of FIG. As described with reference to FIG. 3, the parameter generation unit 710 generates a correction parameter for converting the density value of the actual printing density data 709 into the density value of the calibration target data in the form of an input / output table. Then, the generated input / output table is set in the calibration processing unit 107 via the parameter setting unit 711.

  Hereinafter, the method of the calibration target selection determination unit 703 will be described with reference to FIGS. 9 and 10. The name of the unregistered medium to be added is medium XX, and the cyan color material will be described. However, other color materials can be obtained by the same method.

  In FIG. 9, the horizontal axis indicates the input value of the image data, and the vertical axis indicates the density value that is the output of the density conversion unit 702 in FIG. A method of calculating the correlation coefficient K for selecting the medium having the highest correlation from the calibration target data storage unit 706 will be described as an example for comparison with the medium A. Here, the density values of the patches of 30% and 80% in FIG. 2B are represented as D (XX, 30, C) and D (XX, 80, C). A graph 901 represents the target density value of the medium A in cyan, and is represented as D (A, x, C). Here, the target density value D (A, x, C) of the medium A is normalized so that the 80% density value D (XX, 80, C) and D (A, 80, C) are the same value. Turn into. When the linear ratio is α, α = D (XX, 80, C) / D (A, 80, C). According to the ratio, the density value in the medium A of 30% is normalized to D (A, 30, C) × α. The normalized position is Q1, while the 30% patch density D (XX, 30, C) is Q0. Here, if Q0 and Q1 match, it can be said that the correlation is the highest, and conversely, the larger the difference, the lower the correlation. That is, the determination is made based on the distance between Q1 and Q0, which is the difference between D (XX, 30, C) and D (A, 30, C) × α. In the present embodiment, the correlation coefficient K is defined as the expression (1) as representing the distance between Q1 and Q0.

K = ABS (D (XX, 30, C) -D (A, 30, C) × D (XX, 80, C) / D (A, 80, C)) (1)
The correlation coefficient K is calculated for each medium, a medium having the smallest K or a medium having a threshold value or less is determined as having high correlation, and a target density value is determined. As described above, in this embodiment, the correlation coefficient K of the media A to G is calculated from the target density value for each media in FIG. In the above description, cyan is described, but each color material is similarly processed, and a target density value used in the next correction adjustment unit 704 is determined.

  Further, in the above, normalization was performed for the density value of 80% and correlation was obtained for the density value of 30%. Conversely, normalization was performed for the density value of 30% and the density value was 80%. Alternatively, the correlation may be obtained. In the calibration target data selection unit 707, the density values of two patches are used, but three or more patches are also applicable. For example, in the case of density values of 30%, 50%, and 80%, after normalizing the density value of 80% by the above method, the correlation coefficient K2 is defined as in equation (2).

K2 = ABS (D (XX, 30, C) −D (A, 30, C) × D (XX, 80, C) / D (A, 80, C) + D (XX, 50, C) −D ( A, 50, C) × D (XX, 80, C) / D (A, 80, C)) (2)
Then, the medium having the smallest correlation coefficient K2 is selected, and the target density value is determined. Moreover, you may define like (3) as a correlation coefficient K3 instead of (2).

K3 = ABS ((D (XX, 30, C) −D (A, 30, C) × D (XX, 80, C) / D (A, 80, C)) + ABS (D (XX, 50, C) ) -D (A, 50, C) × D (XX, 80, C) / D (A, 80, C)) (3)
As described above, in the present embodiment, the medium having the highest correlation is selected from the calibration target data storage unit 706 based on several density values.

  Next, a specific correction method by the correction adjustment unit 704 will be described with reference to FIGS. This correction corrects the distance between Q1 and Q0 described above. Here, the selected medium with high correlation is defined as medium A. A graph 901 in FIG. 10 corresponds to the graph 901 in FIG. 9 and is a target density value D (A, x, C). The curve obtained by normalizing the graph 901 with the density value of 80% as described above is the graph 902 expressed as D (A, x, C) × α. Here, when Q0 and Q1 match, a graph 902 of D (A, x, C) × α is the target density value of the media XX. However, as shown in FIG. 10, since Q0 and Q1 are different, D (XX, 30, C) and D (XX, 80, C) are based on D (A, x, C) which is the graph 901. ) To generate a target density value D ′ (XX, x, C).

  As shown in FIG. 10, the linear ratio at the input value of 80% image data is α = (D (XX, 80, C) / D (A, 80, C)), and 30% image data is input. Let β = (D (XX, 30, C) / D (A, 30, C)) be the linear ratio in terms of value. Then, the input value of the image data is divided into three areas (gradation ranges) with 30% and 80% of the input value of the image data as a boundary. A region from 0% to 30% is a region A, a region from 30% to 80% is a region B, and a region from 80% to 100% is a region C. The target density value in the region A is obtained by changing the linear ratio of the target density value D (A, x, C) in the graph 901 from α to β continuously, and is expressed by Expression (4). It is.

D ′ of region A (XX, x, C) = D (A, x, C) × ((β−α) × x / 30 + α) (4)
Further, the target density value in the region B is obtained by changing the linear ratio from β to α continuously with respect to the target density value D (A, x, C) in the graph 901, and is expressed by the equation (5). It is represented by

D ′ (XX, x, C) of region B = D (A, x, C) × ((α−β) × x / (80-30) + (80 × β−30 × α) / (80− 30)) (5)
Further, the target density value in the region C becomes a linear ratio α with respect to the target density value D (A, x, C) of the graph 901 and is expressed by Expression (6).

D ′ of region C (XX, x, C) = D (A, x, C) × α (6)
In the present embodiment, calibration target data for the unregistered medium XX can be generated as described above. The created graph 903 is registered in the calibration target data storage unit 706 as calibration target data of the media XX.

  Hereinafter, other methods will be described. In the above, calibration target data is created by selecting a highly correlated medium and performing correction by the correction adjustment unit 704. Here, a method may be used in which a medium having a high degree of similarity is selected from the existing calibration target group and is directly registered as calibration target data of an unregistered medium. In this case, as a similarity calculation method, for example, a measurement value of an unregistered medium is compared with a measurement value of a patch of a calibration target group, and a medium whose difference is smaller than a predetermined threshold is set as a medium having a high similarity. select. For example, the similarity KK with respect to the medium A in FIG. 9 is calculated from the equation (7).

KK = ABS ((D (A, 80, C) -D (XX, 80, C)) + (D (A, 30, C) -D (XX, 30, C))) (7)
The similarity KK is calculated for each medium, and the medium with the smallest KK is registered as calibration target data for unregistered media.

  In the above description, the target density value of the same color material is targeted for the medium to be selected. This is because, in different color materials, the blurring state with respect to the medium and the density distribution state in the dot differ depending on the solvent contained in the color material, and it is considered that the dot gain characteristics have peculiarities. However, if the solvent condition of the color material does not particularly affect the dot gain characteristics, the target density value of another color material may be selected. In other words, according to the color material condition, the target density value of the calibration target data storage unit 706 for the color material cyan may be selected as the medium having the highest correlation for the density values of different color materials. .

  In the present embodiment, as the sensor units 412 and 430, measuring instruments constituted by RGB LEDs and photodiodes are used. FIG. 11 is a diagram showing an outline of the configuration. The measuring instrument includes a red LED 1101, a green LED 1102, a blue LED 1103, and a light receiving element 1104. Light is emitted from the red LED 1101, the green LED 1102, and the blue LED 1103, and the light receiving element 1104 receives the light reflected by the medium 1105. As the emission color of each LED, a color having a complementary color relationship is selected and measured so that the density identification range is widened depending on the color material to be measured. For example, the red LED 1101 is selected for cyan and light cyan. A green LED 1102 is selected for magenta, light magenta, and black. For yellow, the blue LED 1103 is selected. When the dot gain characteristic is measured by such a measuring instrument, it is influenced by the spectral light receiving sensitivity characteristic of the sensor. That is, even when no specificity occurs in the dot gain characteristics of the color material, the specificity may occur due to the RGB emission characteristics of the sensor. In such a case, the target density value of the color material color corresponding to the emission color of the LED may be selected. For example, in the case of the example of FIG. 9, since measurement is performed with a red LED, light cyan target density value information may be used as a target density value to be selected in addition to a cyan color material.

[Calibration target data generation / registration process]
FIG. 12 is a flowchart showing a procedure of calibration data generation processing for a newly registered medium to be newly registered and a procedure of processing for registration in the calibration target DB. Hereinafter, FIG. 12 will be described using the system configuration of FIG. 4 in FIGS. 4 and 6 as a representative. Each process of FIG. 12 is realized by the CPU 403 executing a calibration target generation / registration program for unregistered media stored in the storage device 405, for example.

  In step S <b> 1201, the user sets a newly registered media name and printing conditions as unregistered media information via the UI 402. Here, the printing condition is a printing control parameter corresponding to the type of medium, for example, a parameter indicating a conveyance speed, a carriage speed, the number of passes in multi-pass printing, a distance between the recording head and the medium, and the like. .

  In S1202, the patch chart of FIG. 2B is printed based on the patch data stored in advance in the storage device 405 based on the printing conditions set in S1201. The patch data in FIG. 2B is RGB data, and is composed of 13 types of values including a portion that is not printed. Parameters are set in the color separation processing unit 104 of FIG. 1 so that each color material color is output with respect to 30% and 80% input data. For example, if the 3DLUT grid points of the color separation processing unit 104 are configured with 17-value intervals, (R, G, B) = (0, 17, 0) is set for a 30% cyan patch. . The color separation processing unit 104 then selects (C, M, Y, K, lc, lm) = (77, 0) with respect to the grid point input value (R, G, B) = (0, 17, 0). , 0, 0, 0, 0).

  In step S1203, the printed patch chart is measured. The image forming apparatus 407 receives a control command from the information processing apparatus 401 and optically reads and measures the patch chart by the sensor unit 412. A measurement value which is a measurement result is transferred to the information processing apparatus 401 via the data transfer unit 408 and stored in the storage device 405. The measurement value output from the sensor unit 412 is, for example, a Lab value, an optical density value, or a reflection luminance value by an LED.

  In step S1204, based on the measurement values measured in step S1203 and the target density values for a plurality of media stored in advance in the storage device 405, target density values for unregistered media are generated for each color material color. Here, when the target density value of the unregistered medium cannot be generated because the highly correlated medium cannot be selected or the like, an error may be displayed on the UI 402 and the process of FIG. 12 may be terminated. . In step S1205, the target density value generated in step S1204 is stored in the calibration target data storage unit 706 configured in the storage device 405 together with the media name.

  FIG. 13 is a flowchart showing a detailed processing procedure of the target density value generation processing of the unregistered medium in S1204 of FIG.

  In step S1301, it is determined whether or not the processing in FIG. 13 has been performed for all the color material colors C, M, Y, K, Lc, and Lm. Here, when it is determined that the processing has been performed for all the color material colors, the target density value and the generation completion information for each color material color, together with the media name, calibration target data configured in the storage device 405 Store in the storage unit 706. On the other hand, when it is determined that the processing has not been performed for all the color material colors, the color material color to be processed in S1302 and subsequent steps is specified.

  In S1302, the media name, the measured value measured in S1203, and the measured value of the unprinted white paper portion are read from the storage device 405 for the color material color specified in S1301. In step S <b> 1303, the density conversion unit 702 converts the measurement value into a paper white portion reference density value based on the paper white portion measurement value. In S1304, based on the density value converted in S1303, among the plurality of target density values stored in advance in the storage device 405, as shown in FIG. Select the target density value for the media. Here, if all of the target density values to be selected do not fall within the predetermined threshold value, an error signal indicating that selection is impossible is output, and the process of FIG. 13 ends. In step S1305, based on the target density value selected in step S1304 and the density value calculated in step S1303, correction processing is performed as described with reference to FIGS. Generate. When an error signal is output in step S1304, a density value printed for the input data values of 11 patches P1 to P11 in FIG. 3 is newly generated as a target density value and stored in the calibration target data storage unit 706. It doesn't matter.

  As described above, in the present embodiment, the number of patches for generating calibration target data of unregistered media can be reduced compared to the number of patches for executing calibration. As a result, it is possible to reduce calibration creation time and consumption of ink and paper while reducing quantization errors.

  The present invention is also realized by executing the following processing. That is, software (program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various storage media, and a computer (or CPU, MPU, or the like) of the system or apparatus reads the program. It is a process to be executed.

Claims (9)

Storage means for storing, for each type of recording medium, reference data representing density characteristics with respect to an input gradation value when ink droplets are ejected to a recording medium with a reference ejection amount;
Recording control means for recording a patch image corresponding to at least two gradation values among the input gradation values of the reference data stored in the storage means on a new type of recording medium;
Reading control means for controlling the reading unit to read the densities of the at least two patch images recorded by the recording control means;
A specifying unit that specifies reference data having a density value that is most correlated with the density of the at least two patch images read by the reading control unit among the reference data stored in the storage unit;
Calculating means for calculating reference data representing density characteristics corresponding to the new type of recording medium from the reference data specified by the specifying means;
A control device comprising:   2. The control apparatus according to claim 1, wherein the number of patch images to be recorded on a new type of recording medium of the recording control means is two or more and less than the number of input gradation values of reference data. At least two gradation values of the recording control means are defined as a first gradation value and a second gradation value, respectively.
The first gradation value is a gradation range in which the variation in density change of the reference data stored in the storage means is smaller than a predetermined value, and the second gradation value is stored in the storage means 3. The control apparatus according to claim 1, wherein the variation in the density change of the reference data is in a gradation range larger than a predetermined value.   The calculating means is specified by the specifying means so as to pass the density values of the at least two patch images read by the reading control means while leaving the density characteristics of the reference data specified by the specifying means. The control device according to claim 1, wherein the reference data is deformed.   5. The control device according to claim 1, wherein the storage unit stores the reference data calculated by the calculation unit in association with the new type of storage medium.   The control device according to claim 1, wherein the first gradation value is larger than the second gradation value.   The control apparatus according to claim 1, wherein the control apparatus is an ink jet recording apparatus. Calibration data generation method executed in a control device having storage means for storing, for each type of recording medium, reference data representing density characteristics with respect to an input gradation value when ink droplets are discharged onto a recording medium with a reference discharge amount Because
A recording control step of controlling the recording unit so as to record a patch image corresponding to at least two gradation values among the input gradation values of the reference data stored in the storage means, on a new type of recording medium;
A reading control step for controlling the reading unit to read the densities of at least two patch images recorded in the recording control step;
A specifying step of specifying reference data having a density value most correlated with the densities of the at least two patch images read in the reading control step among the reference data stored in the storage unit;
A calculation step of calculating reference data representing density characteristics corresponding to the new type of recording medium from the reference data specified in the specifying step;
A calibration data generation method characterized by comprising:   The program for making a computer perform each process of the calibration data generation method of Claim 8.