JP5254674B2 - Image processing method and image processing apparatus - Google Patents

Description

  The present invention relates to a technique for adjusting the color tone of printed matter by calibration.

  Printing apparatuses (for example, printers) that perform printing using a recording material such as ink or toner are known. For example, in an ink jet printer, variations in the ink ejection amount occur due to differences in individual models, changes over time, environments such as temperature and humidity, and the like. When such variations occur, the gradation characteristics of the output image become unstable and the color balance is often lost. In the case of the ink jet system, when gray scale printing is performed using only K (black), gradation is lowered and graininess is deteriorated. Therefore, in an inkjet printer, four colors of C (cyan), M (magenta), Y (yellow), and K (black), or six colors obtained by adding Lc (light cyan) and Lm (light magenta) to these. Since printing is performed by this, it is easy to be affected by this.

However, when gray is created by mixing these colors, there is a difference in color due to variations in the density of each color. In order to cope with this, conventionally, various adjustment methods have been proposed. In JP-A No. 2004-133260, the color tone of the gray color that is the N-order color is shifted only by matching the CMY single color density. Therefore, a correction table is created in consideration of the color components related to the other color materials of each color material. The technology to be mentioned is mentioned. Patent Document 2 discloses a calibration by adjusting a multi-dimensional lookup table (hereinafter abbreviated as LUT) or a multi-dimensional LUT + output γ in order to realize not only a single color material color but also gray calibration. The technology to perform
JP 2003-069844 A JP 2003-169219 A

  In general, gray ink is obtained by diluting black ink at a certain ratio. However, since diluted gray ink has uneven spectral reflectance characteristics, a small amount of cyan ink and magenta ink are mixed together to produce spectral reflection. Toning is performed so that the rate characteristic is almost flat. This is called a toning ink or the like, and by using this toning ink, the gray color is stabilized and a gray close to neutral is obtained.

  However, if the blending amounts of cyan ink and magenta ink are slightly different during toning, the spectral reflectance characteristics of the gray ink will vary. Therefore, for example, when the gray ink is replaced, the gray color of the printed material is lost. For example, in the technique of Patent Document 1 described above, since a correction table is created from CMY density components, even a slight difference in spectral reflectance of gray ink cannot be corrected. Further, for example, in the technique of Patent Document 2 described above, a patch in the vicinity of a gray line is printed and L * a * b * is measured to adjust the multidimensional LUT, but the composition of the gray ink itself is taken into consideration. No correction was made. In addition, it is only necessary to make corrections by printing a patch and checking it. However, in order to include all combinations of colors including gray ink in the patch, the procedure is complicated, and the spectral reflectance of the gray ink It is not suitable for correcting the difference in characteristics.

Accordingly, the present invention has been made in view of the above problems, and an object of the present invention is to provide a technique for suppressing variation in the color tone of a printed matter caused by a shift in blending when a toned recording material is generated.

To achieve the above object, according to one embodiment of the present invention, a first ink containing an achromatic color material and a chromatic color material for toning, and a second ink that is a chromatic color ink can be ejected. An image processing method of an image processing apparatus for recording an image on a recording medium using a simple recording head, the recording step of recording a patch image with the first ink ejected from the recording head, and the recording step Based on the colorimetric result of the recorded patch image, the recording data corresponding to the first ink and the second ink is determined from the recording data representing the image recorded using the first ink. And determining the recording data corresponding to the first ink in the determining step .

  According to the present invention, it is possible to suppress variations in spectral reflectance characteristics due to misalignment of the toned recording material, and thus it is possible to suppress variations in the color of printed matter.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, an embodiment of a printing system, a printing apparatus, and a calibration method according to the invention will be described in detail with reference to the accompanying drawings. The configurations shown in the following embodiments are merely examples, and the present invention is not limited to the illustrated configurations.

(Embodiment)
FIG. 1 is a diagram showing an example of the configuration of a printing system configured by arranging a printer to which a printing apparatus according to the present invention is applied. In the present embodiment, as a representative example, an ink jet printer equipped with a spectrometer is used.

  The printing system includes a printer 10 and a host computer (hereinafter abbreviated as host PC) 20.

  The host PC 20 is a computer device handled by the user. For example, the host PC 20 generates print data based on a user instruction, and inputs the print data to the printer 10.

  The printer 10 forms an image on a recording medium such as paper based on the print data and performs printing. The printer 10 includes a calculation unit 110 as a calculation device, a print unit 120 as an output device, and a measurement unit 130 as a measurement device.

  The measurement unit 130 is configured by, for example, a spectrophotometer that measures the spectral characteristics of a reflective original or a transparent original. In general, the measurement unit 130 is often configured to be built in the side surface of the print head, but may be of a type that is connected to the outside of the printer 10 and used.

  The calculation unit 110 includes an operation unit (hereinafter also referred to as UI) 111 serving as a user interface, a CPU 112, a work memory 113, a storage unit 114, and a data input / output unit 115.

  The operation unit 111 inputs various instructions from the user into the apparatus, and displays various information to the user. The CPU 112 controls the print unit 120 and the measurement unit 130 according to a program stored in the storage unit 114. At this time, the work memory 113 is used as a work area.

  Here, a flow when printing is performed by the printer 10 will be briefly described.

  A user operates an application on the host PC 20 to create a document, an image, and the like. Then, print data based on the data is transmitted to the printer 10 and the printer 10 performs printing. At the time of printing, the host PC 20 performs predetermined image processing on a document or image to be printed, and then passes it to the printer driver 21 as input image data. Upon receiving this, the printer driver 21 converts the input image data into CMYK, which is the ink color of the printer 10, and performs halftone processing. Then, the print data that has undergone the halftone process is transmitted to the printer 10. In the printer 10, the printing unit 120 forms an image based on the print data received from the host PC 20 on a sheet and performs printing. In the present embodiment, the case where the printer driver 21 performs color conversion processing and halftone processing will be described. However, these processing may be performed in the printer 10.

  Next, an example of the operation of the printer 10 shown in FIG. 1 will be described with reference to FIG. Here, the calibration process will be described. The calibration process is performed, for example, at the time of ink replacement. By performing the calibration process at the time of ink replacement as described above, lot variation can be suppressed.

  The user first calls a menu from the operation unit 111 and instructs execution of calibration. The execution of calibration may be instructed from the host PC 20 side. When the printer 10 receives this instruction (step S201), the printer 10 displays a screen for selecting a paper feed port and a paper type on the operation unit 111. The paper feed port is selected by default based on the standard selection logic of the printer. The printer 10 includes, for example, a paper feeding unit for feeding roll paper and a paper feeding unit such as a manual feed on the back side. The paper type is also selected by default in the same manner as the paper feed port described above. Note that the operation unit 111 displays only sheets corresponding to calibration execution as the types of sheets that can be selected.

  Here, when the user selects a paper feed port and a paper type via the operation unit 111, the printer 10 that has received the check checks the selected paper. In this check, for example, it is determined whether or not the selected sheet is a calibration execution compatible sheet. After the check, the printer 10 displays a calibration execution confirmation screen on the operation unit 111.

  If cancellation is instructed by the user referring to the calibration execution confirmation screen (NO in step S203), the printer 10 returns to the process of step S201 again. On the other hand, when OK is instructed by the user (YES in step S203), the printer 10 prints a patch chart in the printing unit 120 (step S204). The patch chart has a layout shown in FIG. 3, for example. As shown in FIG. 3, the patch chart 30 includes a plurality of patches 31. The patch 31 is printed by changing the density stepwise with the toning gray ink to be calibrated. The toned gray ink used for printing the patch 31 is a toned recording material in which a plurality of recording materials are blended, and is adjusted so that the color tone has a predetermined chromaticity. For example, a patch having a driving amount of 50%, 100%, or 150% is printed. The patches with 50%, 100%, and 150% driving amount have different ink discharge amounts at the time of patch formation, and have different gray levels. When there are a plurality of toning recording materials to be calibrated, that is, toning inks, it is necessary to print patches corresponding to the number of ink colors. The patch 31 is generated and printed by the arithmetic unit 110 and the print unit 120 in the printer body. Further, the count value of the patch 31, parameters such as resolution conversion and error diffusion, and the image processing table are stored in the storage unit 114 of the printer 10. The printer 10 generates a patch chart based on the count value of the patch 31 and prints it.

  When the patch chart is printed, the printer 10 measures each patch 31 in the patch chart. The patch measurement is performed by the measurement unit 130 according to a predetermined sequence (step S205). In the process of step S205, for example, the spectral reflectance of the patch is measured.

  In the calculation unit 110, the printer 10 converts the output value of the measurement result into a predetermined format, and generates a correction lookup table (hereinafter abbreviated as a correction LUT) based on the converted output value. Then, after the correction LUT is stored in the storage unit 114 (step S206), this process ends. Although details will be described later, in some cases, the correction LUT may not be generated.

  Here, the details of the correction LUT generation processing in step S206 will be described with reference to FIG.

When the correction LUT generation process is started, the printer 10 first determines whether or not correction is necessary (step S301). Here, this determination process will be described with reference to FIG. FIG. 5 shows the spectral reflectance characteristics when measuring a gray patch printed with an implantation amount of 50%. The broken line is an ideal spectral reflectance (hereinafter referred to as ideal spectral reflectance) serving as a reference. The ideal spectral reflectance is stored in the storage unit 114 in advance. The solid line is the spectral reflectance actually measured. In the case of FIG. 5, a deviation from the reference occurs in the range of about 400 nm to 550 nm. Here, the difference ΔD _λ between the ideal spectral reflectance T _{λ of} the patch printed with the reference gray ink (hereinafter referred to as the reference gray ink) and the measured spectral reflectance M _λ is calculated at each wavelength. (Formula 1) Then, the integral value I obtained by “Expression 2” is compared with a predetermined threshold Th. As a result, if the integral value I is equal to or less than the threshold value, it is determined that correction is not necessary, and if not, it is determined that correction is performed. The wavelength λ that can be measured by the measurement unit 130 is min <λ <max, and the resolution is represented by step.

(Λ = min, min + step,..., Max)
If correction is not necessary as a result of the determination in step S301 (NO in step S301), the printer 10 ends this processing as it is. If correction is necessary (YES in step S301), the printer 10 proceeds to the process in step S302.

  Next, the printer 10 determines a color to be corrected (step S302). The correction color is determined by referring to the spectral reflectance characteristic pattern and comparing the patterns. The spectral reflectance characteristic pattern is stored in advance in the storage unit 114.

  Here, the storage unit 114 stores a spectral reflectance characteristic pattern obtained by the following procedure.

The reference gray ink and the toned ink obtained by adding the maximum amount of cyan ink that can vary with respect to the reference gray ink are printed at a predetermined density. The driving amount is 50%. The spectral reflectance M _{λc +} of each ink printed with an applied amount of 50% is measured. At each wavelength, the difference ΔD _{λc +} between the spectral reflectance T _λ of the reference gray ink and the spectral reflectance T _λ of the toning ink is measured _. Is calculated (Equation 3).

In the range of λ = 420nm~720nm, finding the minimum and maximum values [Delta] D _{[lambda] c + max} of [Delta] D _{[lambda] c +} value _ΔD λc _{+ min.} Then, normalization is performed so that the maximum value of ΔD _{λc +} is 1 and the minimum value is 0. Thereby, a spectral reflectance characteristic pattern is obtained. Similarly, the spectral reflectance characteristic pattern when the magenta ink is increased or decreased or when the cyan ink and the magenta ink are increased or decreased is also obtained. FIG. 6 shows a combination example of increase / decrease of cyan ink and magenta ink. +1 to −1 is a range that can vary. 7a and 7b show an example of the spectral reflectance characteristic pattern.

In the printer 10, the color to be corrected is determined using the spectral reflectance characteristic pattern thus created. In this process, first, the difference between the spectral reflectance M _λ of the patch with the 50% implantation amount measured in the above-described process and the ideal spectral reflectance T _{λ serving} as a reference is calculated, and the normalized spectral reflectance characteristics are calculated. A pattern (spectral reflectance characteristic pattern B) is generated. Then, the spectral reflectance characteristic pattern (spectral reflectance characteristic pattern A) stored in advance in the storage unit 114 is referred to and compared with the spectral reflectance characteristic pattern B based on the following “Equation 4”. Specifically, the color to be corrected, strictly speaking, the combination of colors to be corrected is determined to be the color of the characteristic pattern that minimizes Ip calculated by “Expression 4”.

  When the correction color is determined in this way, the printer 10 subsequently generates a correction LUT. The correction LUT is generated based on a correction amount calculation lookup table (hereinafter abbreviated as a correction amount calculation LUT) stored in advance in the storage unit 114.

  Here, the storage unit 114 stores a correction amount calculation LUT generated by the following procedure.

  First, the printer 10 prints a correction amount calculation patch chart using the reference gray ink in the printing unit 120. An example of a correction amount calculation patch chart is shown in FIG. The correction amount calculation patch chart 40 includes a plurality of patches 41 as shown in FIG. The patch 41 has an increased amount of reference gray ink (50%, 100%, 150%) along the vertical direction. In the patch 41, the amount of C (cyan) applied to the reference gray ink increases stepwise along the horizontal direction. In FIG. 8, the amount of C (cyan) implantation is changed in five stages from 0 to 4. The range of the shot amount is set so as to include the range of the spectral reflectance variation due to the ink preparation.

The printer 10 uses the measurement unit 130 to measure the spectral reflectance of each patch of the correction amount calculation patch chart, and obtains a difference ΔD _λ from the reference at each wavelength in the same manner as when determining the correction color described above. The integral value I of the difference is obtained by “Expression 2”. Then, the correction amount calculation LUT shown in FIG. 9 is generated by using the C (cyan) driving amount (in this case, five stages) corresponding to the integral value I as a correction amount.

  When generating the correction LUT, the correction amount corresponding to each reference gray ink placement amount (50%, 100%, 150%) is obtained using the correction amount calculation LUT. The correction amount corresponding to each driving amount is determined based on the integral value I of “Expression 2” obtained from the measured values obtained by measuring the patches of each driving amount (50%, 100%, 150%). Then, two types of correction LUTs for C and M are generated as shown in FIG. The correction amount in the correction LUT varies depending on the combination of the color combinations to be corrected determined in the process in step S302. For example, if the color to be corrected is blended as (C, M) = (+ 1, −0.5), the correction LUT for C (cyan) is generated using the correction amount shown in FIG. 9 as it is. However, the M (magenta) correction LUT is generated by halving the correction amount shown in FIG. Note that when “0” is set as the combination index of C (cyan) and M (magenta), the correction LUT for that color is not generated.

  Next, a case where image processing is performed by applying a correction LUT will be described. At the start of this processing, the host PC 20 needs to hold the correction LUT by transmitting the correction LUT from the printer 10 to the host PC 20 side.

  First, the user instructs printing on the host PC 20. Then, the printer 10 performs printing to which the calibration is applied. The printing to which the calibration is applied is performed, for example, by changing the value of the output signal of the output γ table when the printer driver 21 in the host PC 20 performs image processing. Note that this processing may be performed by the calculation unit 110 of the printer 10.

  Here, a color conversion process performed in the printer driver 21 will be described with reference to FIG. As described above, this color conversion process may be performed on the printer 10 side.

  When the color conversion process is started, a color matching process is first performed (step S501). The color matching process is performed to match the R1G1B1 signal of the input image data with the color of the printer 10. Through this process, the input image data is converted into a device-specific device R2G2B2 signal. The conversion from the input R1G1B1 signal to the device R2G2B2 signal refers to a built-in three-dimensional lookup table (hereinafter abbreviated as 3DLUT), and performs three-dimensional interpolation processing such as tetrahedral interpolation processing and cube interpolation processing. This is done by executing.

  In the color separation process, the input device R2G2B2 signal is color-separated into C1M1Y1K1Gy1 signals corresponding to the ink of the printer 10 (step S502). Here, by way of example, a five-color configuration including Gy ink is used, but it is not limited to this configuration as long as it includes Gy ink. Conversion from the device R2G2B2 signal to the ink C1M1Y1K1Gy1 signal (multi-valued data) is also performed using the 3DLUT. The ink color of the printer 10 is converted by three-dimensional interpolation processing such as tetrahedral interpolation processing or cube interpolation processing.

  In the output γ correction process, the color material color data of the CMYK signal is γ-corrected in order to correct the γ characteristic according to the combination of the processing content of the halftone process and the print unit 120 of the printer 10 (step S503). Specifically, correction processing is performed based on the output γ correction table, and the color material color data of the C1M1Y1K1Gy1 signal is converted into multivalued data of the C2M2Y2K2Gy2 signal and output. Normally, after this processing, the process proceeds to halftone processing. In this embodiment, spectral correction processing by the correction LUT 60 is performed before halftone processing.

  In the spectral correction process, a spectral correction process using the correction LUT 60 is performed (step S504). In this process, first, it is determined whether or not the correction LUT 60 exists. If not, the C2M2Y2K2Gy2 signal is output as it is without performing correction processing. Further, even when the sheet is not subject to correction, the C2M2Y2K2Gy2 signal is output as it is without performing correction processing. On the other hand, when the correction is performed, only the Gy2 signal among the C2M2Y2K2Gy2 signals after the output γ correction processing in step S503 is passed through the correction LUT (two types for C and M) to obtain a correction value CαMα. Then, after the correction value is added or subtracted by executing the correction value application process, the C3M3Y2K2Gy2 signal is output (step S505).

  In the halftone process, a binarization process for converting the C2M2Y2K2Gy2 signal or the C3M3Y2K2Gy2 signal (multi-valued data) into the number of gradations that can be expressed by the print unit 120 of the printer 10 is performed (step S506). This process is performed for each color. The C4M4Y3K3Gy4 signal (binary data) obtained through the halftone process is transferred to the printer 10. As a result, the printer 10 executes printing to which the calibration is applied.

  As described above, according to the present embodiment, since the spectral variation of each color material blended in the gray ink can be suppressed, an image with good gray balance can be obtained in which the spectral variation of the gray ink is suppressed. .

  The above is an example of a typical embodiment of the present invention, but the present invention is not limited to the embodiment described above and shown in the drawings, and can be appropriately modified and implemented without departing from the scope of the present invention. .

  For example, instead of the printer 10 described above, a device having a function such as a scanner unit or a printer unit (referred to as a copier) or a device having a function such as a fax unit added to its configuration (such as a multifunction device) The above-described processing may be performed using the above.

  In the above-described embodiment, the inkjet printer 10 has been described as an example. However, the present invention is not limited to the inkjet method, and other formats such as an electrophotographic method may be employed.

  In the above-described embodiment, the case of adjusting an achromatic color, specifically, a gray tint has been described as an example. However, the present invention is not limited to this, and a color constituted by a combination of a plurality of recording materials. If present, the present invention can be applied as in the case of gray.

  The present invention achieves the functions of the embodiments by supplying a software program directly or remotely to a system or apparatus, and a computer built in the system or apparatus reads and executes the supplied program code. This includes cases where In this case, the supplied program is a computer program corresponding to the flowchart shown in the drawings in the embodiment.

  Accordingly, since the functions of the present invention are implemented by computer, the program code installed in the computer also implements the present invention. In other words, the present invention includes a computer program itself for realizing the functional processing of the present invention. In that case, as long as it has the function of a program, it may be in the form of object code, a program executed by an interpreter, script data supplied to an OS (Operating System), or the like.

  Examples of the computer-readable recording medium for supplying the computer program include the following. For example, floppy (registered trademark) disk, hard disk, optical disk, magneto-optical disk, MO, CD-ROM, CD-R, CD-RW, magnetic tape, nonvolatile memory card, ROM, DVD (DVD-ROM, DVD- R).

  As another program supply method, a client computer browser is used to connect to a homepage on the Internet, and the computer program of the present invention is downloaded from the homepage to a recording medium such as a hard disk. In this case, the downloaded program may be a compressed file including an automatic installation function. It can also be realized by dividing the program code constituting the program of the present invention into a plurality of files and downloading each file from a different homepage. That is, a WWW server that allows a plurality of users to download a program file for realizing the functional processing of the present invention on a computer is also included in the present invention.

  Further, the program of the present invention may be encrypted, stored in a recording medium such as a CD-ROM, and distributed to users. In this case, a user who has cleared a predetermined condition is allowed to download key information for decryption from a homepage via the Internet, execute an encrypted program using the key information, and install the program on the computer. You can also.

  In addition to the functions of the above-described embodiment being realized by the computer executing the read program, the embodiment of the embodiment is implemented in cooperation with an OS or the like running on the computer based on an instruction of the program. A function may be realized. In this case, the OS or the like performs part or all of the actual processing, and the functions of the above-described embodiments are realized by the processing.

  Furthermore, the program read from the recording medium is written in a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer, so that part or all of the functions of the above-described embodiments are realized. May be. In this case, after a program is written to the function expansion board or function expansion unit, the CPU (Central Processing Unit) provided in the function expansion board or function expansion unit is a part of the actual processing or based on the instructions of the program. Do everything.

1 is a diagram illustrating an example of a configuration of a printing system in which a printer to which a printing apparatus according to the present invention is applied is arranged. 3 is a flowchart illustrating an example of an operation in the printer 10 illustrated in FIG. 1. It is a figure which shows an example of the layout of a patch chart. 4 is a flowchart illustrating an example of a correction LUT generation process in step S206 illustrated in FIG. It is a figure which shows an example of a spectral reflectance characteristic. It is a figure which shows an example of the combination of increase / decrease of cyan ink and magenta ink. It is a figure which shows an example of a spectral reflectance characteristic pattern. It is a figure which shows an example of the layout of the patch chart for correction amount calculation. It is a figure which shows an example of LUT for correction amount calculation. It is a figure which shows an example of correction | amendment LUT. It is a figure which shows an example of the flow of a color conversion process.

Explanation of symbols

10 Printer 20 Host PC
21 Printer Driver 110 Operation Unit 111 Operation Unit 112 CPU
113 Working memory 114 Storage unit 115 Data input / output unit 120 Printing unit 130 Measuring unit

Claims (6)

An image for recording an image on a recording medium using a recording head capable of ejecting a first ink containing an achromatic color material and a chromatic color material for toning and a second ink that is a chromatic color ink An image processing method for a processing apparatus,
A recording step of recording a patch image with the first ink ejected from the recording head;
Based on the colorimetric result of the patch image recorded in the recording step, it corresponds to the first ink and the second ink in the recording data representing the image recorded using the first ink. A determination step for determining recording data ;
In the determining step, the recording data corresponding to the first ink is not changed.
An image processing method. The image processing method according to claim 1, wherein the achromatic color material contained in the first ink is a black color material. The chromatic color material contained in the first ink is at least one of cyan and magenta.
The second ink is an ink containing at least one colorant of cyan and magenta.
The image processing method according to claim 2 . The image processing method according to any one of claims 1 to 3, characterized by further comprising an acquisition step of acquiring a color measurement result obtained by measuring the patch image. The recording step, said without using the second ink, the image processing method according to any one of claims 1 to 4, characterized in that recording the patch image by the first ink. An image for recording an image on a recording medium using a recording head capable of ejecting a first ink containing an achromatic color material and a chromatic color material for toning and a second ink that is a chromatic color ink A processing device comprising:
Recording means for recording a patch image with the first ink ejected from the recording head;
Corresponding to the first ink and the second ink in the recording data representing the image recorded using the first ink based on the colorimetric result of the patch image recorded by the recording means. Determining means for determining recorded data ;
The determining means does not change the recording data corresponding to the first ink;
An image processing apparatus.

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