Image processing apparatus, image processing method, and storage medium

Abstract

The present invention relates to an image processing apparatus, an image processing method, and a storage medium. An object of the present invention is to realize high-precision color calibration in a printing apparatus that performs printing using fluorescent ink at low cost. One embodiment of the present invention is an image processing apparatus including a processing unit configured to perform processing relating to color calibration in a printing apparatus that performs printing of an image on a print medium using a fluorescent print material, and an execution unit configured to perform calibration processing of the printing apparatus based on a measurement value obtained by measuring a patch chart used to obtain information relating to an application amount of the fluorescent print material in the printing apparatus, wherein a patch included in the patch chart is printed with the fluorescent print material and a subtractive mixed-color print material, and at least one dot of the subtractive mixed-color print material covers a dot of the fluorescent print material.

Description

Technical Field

[0001] This invention relates to a technique for unifying the color tone of prints across multiple printing devices in a system having multiple printing devices. Background Technology

[0002] Traditionally, color calibration is known in which a measuring device is used to read the printed halftone patches, and the color density of the printing equipment is made uniform across devices by changing the amount of ink to be ejected.

[0003] Attempts to obtain color density and color values ​​(e.g., CIE L*a*b* or tristimulus values ​​XYZ, etc.) using a diffraction grating filter in the measuring device would make the measuring device expensive. On the other hand, when obtaining density characteristics by using a light source (e.g., an LED, etc.) with bandwidth in a predetermined wavelength and a light-receiving element (e.g., a photodiode, etc.) to obtain the reflectance coefficient, there is a possibility of malfunction when measuring fluorescent inks. This is because, due to the characteristic of emitting light at a wavelength longer than the wavelength region of the incident light, the difference in reflectance coefficients between halftone patches becomes smaller.

[0004] Therefore, in order to introduce color management with high-precision calibration into a printing system with multiple printing devices, expensive measuring devices are required that can separate the wavelength range of the received light into small regions, thus increasing the cost of introducing the printing system.

[0005] Japanese Patent Application Publication No. 2014-136413 discloses a method as a technique related to the color calibration of fluorescent inks. This method creates a color shift correction table based on concentration characteristics that conform to visual perception by correcting the measured concentration detected by an optical sensor according to fluorescence information related to the ink. Specifically, a correction is performed that weights the measured concentration according to visual perception. Summary of the Invention

[0006] However, when the difference between the sensor's readings of concentration differences decreases due to fluorescence light emission, the sensor's reading error (S / N ratio) becomes more significant. As a result, even assigning visually appropriate weights to the sensor's readings, as described in Japanese Patent Application Laid-Open No. 2014-136413, cannot improve the sensor's reading accuracy, leading to a decrease in calibration accuracy. Furthermore, improving the sensor's S / N ratio requires a highly sensitive sensor, thus increasing the cost of the sensor device.

[0007] Therefore, in view of the above problems, one embodiment of the present invention aims to achieve high-precision color calibration in a printing device that uses fluorescent ink for printing at low cost.

[0008] One embodiment of the present invention is an image processing apparatus, comprising: a processing unit configured to perform processing related to color calibration in a printing apparatus for printing an image on a printing medium using a fluorescent printing material; and an execution unit configured to perform calibration processing of the printing apparatus based on measurements obtained by measuring a block map, the block map being used to obtain information related to the amount of fluorescent printing material applied in the printing apparatus, wherein the blocks included in the block map are printed using the fluorescent printing material and a subtractive color mixing printing material, and at least one point of the subtractive color mixing printing material covers a point of the fluorescent printing material.

[0009] An image processing apparatus includes: a processing unit configured to perform processing related to color calibration in a printing apparatus for printing an image on a printing medium using a fluorescent printing material; and a measurement unit including a light source and a light-receiving element, and configured to measure a block map for obtaining information related to the amount of fluorescent printing material applied in the printing apparatus, wherein, when the measurement unit illuminates the block map with light from the light source, the light-receiving element receives reflected light from the illuminated light and light emitted due to the fluorescence of the fluorescent printing material, and the measurement unit further includes an optical filter for blocking a portion of the light emitted by the fluorescent printing material.

[0010] An image processing apparatus includes: a processing unit configured to perform processing related to color calibration in a printing apparatus for printing an image on a printing medium using a fluorescent printing material; and a measurement unit including a light source and a light-receiving element, and configured to measure a block map for obtaining information related to the amount of fluorescent printing material applied in the printing apparatus, wherein, when the measurement unit illuminates the block map with light from the light source, the light-receiving element receives reflected light from the illuminated light and light emitted due to the fluorescence of the fluorescent printing material, and the measurement unit further includes an optical filter for cutting off a portion of the light of the excitation wavelength of the fluorescent printing material.

[0011] An image processing method, performed by an image processing device, includes the following steps: performing a color calibration-related process in a printing device for printing an image on a printing medium using a fluorescent printing material; and performing a calibration process for the printing device based on measurements obtained by measuring a block map, the block map being used to obtain information related to the amount of fluorescent printing material applied in the printing device, wherein the blocks included in the block map are printed using the fluorescent printing material and a subtractive color mixing printing material, and at least one point of the subtractive color mixing printing material covers a point of the fluorescent printing material.

[0012] A non-transitory computer-readable storage medium storing a program for causing a computer to perform an image processing method performed by an image processing device, the image processing method comprising the steps of: performing processing related to color calibration in a printing device for printing an image on a printing medium using a fluorescent printing material; and performing calibration processing of the printing device based on measurements obtained by measuring a block map, the block map being used to obtain information related to the amount of fluorescent printing material applied in the printing device, wherein the blocks included in the block map are printed using the fluorescent printing material and a subtractive color mixing printing material, and at least one point of the subtractive color mixing printing material covers a point of the fluorescent printing material.

[0013] Further features of the invention will become apparent from the following description of typical embodiments with reference to the accompanying drawings. Attached Figure Description

[0014] Figure 1 This is a block diagram showing the structure related to the color conversion processing of the image processing unit;

[0015] Figure 2 It is a diagram showing a patch chart.

[0016] Figures 3A to 3C This is a diagram illustrating 1D-LUT data;

[0017] Figure 4 This is a structural diagram of the printing system;

[0018] Figure 5 This is a diagram illustrating the readings using a block diagram of a sensor unit;

[0019] Figure 6A and Figure 6B This is a diagram illustrating the sensor unit;

[0020] Figure 7It is a graph showing the activation wavelength and emission wavelength of fluorescent ink, as well as the spectral reflectance of subtractive color mixture ink.

[0021] Figures 8A to 8E Each is a graph of spectral reflectance;

[0022] Figure 9A and Figure 9B Each figure shows the results of measuring the halftone patches used for calibration with a color sensor;

[0023] Figure 10A and Figure 10B Each is a schematic diagram illustrating the relationship between reflected light and emitted light due to fluorescence when measuring ink ejected onto a sheet using a color sensor;

[0024] Figure 11A and Figure 11B Each is a schematic diagram illustrating the relationship between reflected light and emitted light due to fluorescence when a color sensor equipped with an optical filter (green filter) measures the phosphory pink ink emitted onto a thin film.

[0025] Figure 12A and Figure 12B A flowchart illustrating the calibration process;

[0026] Figure 13 This is a diagram showing a block diagram.

[0027] Figures 14A to 14D Each is a graph of spectral reflectance;

[0028] Figure 15A and Figure 15B Each describes the density characteristics of a block printed by mixing 80% green ink with fluorescent pink ink, achieved by varying the amount of fluorescent pink ink applied; and...

[0029] Figure 16 This is a flowchart of the process for selectively using measurements of the fluorescent pink blocks used in the generation of 1D-LUT data. Detailed Implementation

[0030] The embodiments of the present invention will be described below using the accompanying drawings.

[0031] [First Embodiment]

[0032] <Image processing unit of printing equipment>

[0033] The following describes the printing device with an image processing unit in this embodiment. Specifically, an inkjet printer (hereinafter also simply referred to as "printer") is assumed to be the printing device. Internally, the printer includes an RGB LED light source for measuring the printed block image and a color sensor composed of a light-receiving element that is a photodiode. The printer prints any block image, and the printed block image can be measured using this color sensor. Furthermore, the printer can also be simply used as a printing device, and printing processing can be performed based on printable object data such as documents and images processed by various software.

[0034] The printer uses six ink colors as colorants: C (cyan), M (magenta), Y (yellow), K (black), FP (fluorescent pink), and G (green). Ink combinations are not limited to these. For example, combinations of specific color inks such as R (red), Or (orange), B (blue), and Gy (gray) are acceptable, and these combinations can have Lc (light cyan) obtained by diluting C (cyan) and Lm (light magenta) obtained by diluting M (magenta). Furthermore, FB (fluorescent blue) and FY (fluorescent yellow) can be used instead of FP (fluorescent pink).

[0035] <About the structure related to color conversion processing>

[0036] Figure 1 This is a block diagram illustrating the structure related to the color conversion processing of the image processing unit in this embodiment. It is assumed that the printer in this embodiment has both the function of an RGB printer that receives RGB signals and the function of a CMYK printer that receives CMYK signals. Furthermore, for ease of explanation, it is assumed that the image data is processed as signal values ​​where each color is represented by 8 bits. However, needless to say, the same effect can be obtained when the pixel values ​​of each pixel in the image data are represented by 10 bits, 12 bits, or 16 bits.

[0037] Image signal I / F 101 is an I / F unit for input image data, and in this embodiment, it inputs image data in both RGB and CMYK signals. For the RGB signal image data, a conversion process is performed using color matching processing unit 102, which converts color data in device-independent color space into color data in device-dependent color space. Similarly, for the CMYK signal image data, a conversion process is performed using color matching processing unit 103, which converts color data in device-independent color space into color data in device-dependent color space.

[0038] For image data output from color matching processing unit 102, color separation processing unit 104 performs color separation processing to convert color data in the device-related space into color material color data. Similarly, for image data output from color matching processing unit 103, color separation processing unit 105 performs color separation processing to convert color data in the device-related space into color material color data.

[0039] For the color data of the pigment output from the color separation processing units 104 and 105, the hue correction processing unit 106 performs hue correction processing to match the color data of the pigment with the output characteristics of the printer.

[0040] For each of the color matching processing units 102 and 103 and the color separation processing units 104 and 105, the desired color conversion for the input image data can be performed by setting a dedicated lookup table (hereinafter described as LUT). The LUT used here is provided and managed for each printing medium and for each printing mode such as high-speed printing and low-speed high-quality printing.

[0041] Regarding the aforementioned processing units, color matching processing unit 102 and color separation processing unit 104 each perform color conversion processing using a 3D-LUT. Color matching processing unit 103 and color separation processing unit 105 each perform color conversion processing using a 4D-LUT. Hue correction processing unit 106 performs color conversion processing using a 1D-LUT. The 3D-LUT used by color matching processing unit 102 and color separation processing unit 104 is specifically a 3D-LUT consisting of 16 cells spaced at 17 intervals for each color (that is, consisting of 16×16×16=4096 cells).

[0042] like Figure 1 As shown, the image processing unit includes a calibration processing unit 107. The calibration processing unit 107 corrects color variations in the printed result caused by individual differences in the devices constituting the printer, the printing media, and the pigments, as well as variations in the ejection volume caused by changes in these devices over time. Specifically, the calibration processing unit 107 performs 1D-LUT processing on the color signals of each pigment. This processing is performed to match the density values ​​in the printing unit against the input data values ​​of the actual printing device with a calibration target value, which is the density value in the printing unit against the input values ​​of a reference device.

[0043] In this embodiment, a structure in which the printing device has an image processing unit is described. However, an image processing unit that is separate from the printing device can also be provided. For example, an information processing device such as a personal computer can also perform the function of the image processing unit.

[0044] <About Block Diagrams>

[0045] Figure 2 This diagram shows a block diagram of the actual printing results from the actual printing equipment used to perform calibration, based on the concentration values ​​measured for predetermined input data values ​​during actual printing. The block diagram has multiple blocks for each ink.

[0046] In the cyan, magenta, yellow, black, and green blocks, the input signal for each color ink is changed at 20% intervals, and the ejection amount corresponding to each color ink in the printer can be estimated by measuring the color of the printed block image. For example, cyan block P20 is printed with only cyan ink, block P201 is printed with cyan ink with an application amount of 0%, block P202 is printed with cyan ink with an application amount of 20%, and block P203 is printed with cyan ink with an application amount of 120%.

[0047] In contrast, fluorescent pink ink is used to print fluorescent pink blocks by using a fluorescent pink ink with an input signal that changes at 20% intervals and a green ink with an input signal that is fixed at a constant 80%. That is, fluorescent pink block P21 is printed using fluorescent pink ink and green ink. Specifically, block P211 is printed with 0% fluorescent pink ink and 80% green ink, block P212 is printed with 20% fluorescent pink ink and 80% green ink, and block P213 is printed with 120% fluorescent pink ink and 80% green ink.

[0048] <Regarding the execution of calibration>

[0049] Figure 3A It is used to explain in Figure 1 A graph of the 1D-LUT data used in the calibration processing unit 107. Figure 3A An example of an ink type using a certain medium is shown, with the vertical axis representing the print density value of the print cell read by a sensor, and the horizontal axis representing the amount applied (%) in the case of a print block.

[0050] The amount applied refers to the proportion of ink dots to be printed on the paper. Here, we will illustrate this using an inkjet printer with a resolution of 1200 dpi × 1200 dpi as an example. If we define an area where a single dot of 1200 dpi × 1200 dpi is printed as a grid, 100% means printing one dot at each of all the grids. Furthermore, 200% means printing two dots at each of the 1200 dpi × 1200 dpi grids (a state where the number of dots is twice the number of dots for 100%). The printed dot does not necessarily need to be in the center of the grid, and dots can be printed between grids.

[0051] By setting the reflectance coefficient output by the sensor as P(X), the concentration value when the applied amount is X% can be defined as follows.

[0052] D(X)=-log(P(X) / P(0))…Formula 1

[0053] Here, P(0) is the reflectance coefficient of the block in the paper white area.

[0054] Furthermore, when printing with ink mixed with ink of a predetermined constant amount of C%, the concentration value can be defined as follows.

[0055] D(X)=-log(P(X) / P(C))…Formula 2

[0056] Here, P(C) is the reflectance coefficient of ink applied at a predetermined constant of C%.

[0057] Figure 3B The curve represented by the dashed line 301 in the figure represents the print density value of the pigment in the reference device against the input data value, which represents the calibration target value. The reference device is a printer used as a reference, and refers to a printer whose output is located at the center of the deviation from the output of the actual device. Information related to calibration target values, such as this calibration target value, is pre-stored in the storage unit of each printer within the system.

[0058] Furthermore, the curve represented by the solid line 302 indicates the print density value of the pigment on the actual device. The actual device refers to a calibrated printer. This information is obtained through printing. Figure 2 The block diagram is obtained by reading the printed block diagram using a sensor. D0 to D6 each represent the concentration (calculated using Formula 1) corresponding to each block in the block diagram at 20% intervals from 0% to 120%. The solid line 302 is derived by interpolation and approximate curves based on the measured values ​​D0 to D6.

[0059] like Figure 3A As shown in the actual printing status of the device, the overall output of the pigment in the actual device is greater than that of the reference device, and especially in the intermediate density region, the printing is denser compared to the reference device. The calibration processing unit 107 performs calibration by converting and correcting the continuous hue pigment signals of each pigment color, so that the printing density becomes the same as that of the reference device, and the calibration processing unit 107 performs the calibration process using calibration parameters. Figure 3B This will explain the calculation of the correction parameter.

[0060] Figure 3BThe plotted point D2 in the image represents the point printed by the actual equipment. Figure 2 The concentration value in the block diagram is the case where the applied amount is 40%. This value is higher than the target concentration value represented by plotted point T2 corresponding to the same applied amount. Therefore, it is necessary to match the actual device concentration value with the target concentration value by reducing the applied amount. Specifically, a point DY is found on the solid line 302 to find the concentration value at T2 that corresponds to the applied amount of the actual device. That is, when using the actual device, under the condition of printing with an applied amount 303 represented by point DY, the printed concentration value becomes substantially equal to the target concentration value.

[0061] After performing the processing described above for plotted point D2 on all plotted points D0 to D6, interpolation and approximate curves are used. Therefore, it is possible to generate curves such as... Figure 3C The 1D-LUT data shown represents the relationship between the applied amount (%) of the output and the applied amount (%) of the input. A 1D-LUT is a correction parameter that can be defined by discrete values ​​(such as 256 points or 1024 points) or by a mathematical expression defined by a curve.

[0062] <About the structure of the printing system>

[0063] Figure 4 This is a block diagram illustrating the structure of the printing system in this embodiment. The printing system has a personal computer (hereinafter also simply referred to as "PC") 401 as an information processing device and a printer 407 as a printing device. The PC 401 and the printer 407 are connected via a network and interfaces such as USB and local bus.

[0064] PC 401 performs control-related processing of printer 407 as described below, according to various software programs. Storage unit 405 stores system programs, application software programs, software programs required for printing operations, and software programs required for the processing described below. Furthermore, storage unit 405 stores various image processing parameters, mechanism parameters, printer control data, sensor unit control data, required programs, various data, and print object data created on PC 401. Storage unit 405 is represented by a hard disk and flash ROM. CPU 403 performs predetermined processing using the working area of ​​working memory 404 based on the various programs and data stored in storage unit 405.

[0065] The data input / output unit 406 is a portable storage device represented by a CD, DVD, or USB memory, or a data communication device represented by a LAN card and serves as an interface to the outside.

[0066] The user interface (hereinafter also referred to as "UI") unit 402, which serves as an operating unit for the user, performs processing related to user input and output to the user (such as display), and includes input devices such as keyboards and mice, and display devices such as displays.

[0067] Printer 407 includes a data transmission unit 408, a printer control unit 409, an image processing unit 410, a printing unit 411, and a sensor unit 412, and performs printing processing based on printing data sent from PC 401. This printing data also includes control data from sensor unit 412, and printer 407 uses this control data to measure the printed matter. Data transmission unit 408 extracts image data and image processing parameters from the printing data sent from PC 401 and sends both to image processing unit 410, and extracts mechanism parameters, printer control data, and sensor unit control data and sends both to printer control unit 409. Furthermore, data transmission unit 408 reads information related to printing results and sensor measurements stored in the printer's internal storage unit from the storage unit and sends the read information to PC 401. Printer control unit 409 includes a CPU, ROM, and RAM, and controls the printing operation of printer 407 according to the printer control data sent from data transmission unit 408. Furthermore, printer control unit 409 performs control based on measurements from sensor unit 412 and control of the printing operation.

[0068] <About Color Sensors>

[0069] Figure 5 An example of the structure of the sensor unit 412 in printer 407 is shown. The carriage 503 forms a block image 502 by expelling ink while scanning left and right on a sheet 501. A sensor component 504 is mounted on the side of the carriage 503.

[0070] <Regarding the LED light source of the color sensor>

[0071] Figure 6AThe schematic structure of the sensor unit is shown. The sensor unit has a red LED 601, a green LED 602, a blue LED 603, and a light-receiving element 604. Light is emitted from the red LED 601, green LED 602, and blue LED 603, and the light reflected from the printed material 605 is received by the light-receiving element 604. The color of the light emitted from the LEDs is selected based on the colorant being measured, choosing a complementary color with a wide concentration recognition range. That is, measurements are performed by selecting a red LED for cyan and green, a green LED for magenta, fluorescent pink, and black, and a blue LED for yellow. The red LED is also referred to as a red LED, the green LED as a green LED, and the blue LED as a blue LED.

[0072] Figure 6B The spectral intensity distribution is shown as the spectral light emission characteristics of each LED. Symbol 611 represents the spectral intensity distribution of the blue LED, symbol 612 represents the spectral intensity distribution of the green LED, and symbol 613 represents the spectral intensity distribution of the red LED.

[0073] <Properties of Fluorescent Ink and Subtractive Mixing Ink>

[0074] Fluorescent pigments are pigments that exhibit color by absorbing light with an excitation wavelength from the ground state to enter the excited state and emitting light with an emission wavelength back to the ground state. Figure 7 The image shows the intensity of excitation 701 and the intensity of light emission 702 when printed with fluorescent pink ink on a thin sheet surface, with the horizontal axis representing the wavelength of light and the vertical axis representing reflectivity (intensity). Figure 7 The graph shown illustrates the light intensity when detection is performed by changing the wavelength of the light projected onto the printed sample and the wavelength of the light received from the sample, respectively.

[0075] Light emission 702 refers to the intensity of light received from the printed sample for each wavelength when the printed sample is irradiated with light of a wavelength that causes excitation. Figure 7 The graph shown in this embodiment illustrates the case where a fluorescent pink sample is irradiated with light at a wavelength of 480 nm.

[0076] Excitation 701 refers to the intensity of the received light when the wavelength of the light to be received is fixed and the wavelength of the light used to illuminate the printed sample is changed. Figure 7 The graph shown in this embodiment is for the case where the wavelength of the light to be received is fixed at 600 nm for fluorescent pink.

[0077] from Figure 7It was also observed that the wavelength region of the fluorescent ink discharged onto the surface of the sheet overlapped with the emission wavelength region while being on the shorter wavelength side. Furthermore, the excitation 701 intensified or weakened depending on the wavelength, and had wavelengths where light was emitted efficiently and wavelengths where light was not emitted efficiently. Moreover, since the fluorescent material emits light, in many cases, the reflectance at the emission wavelength exceeds 1. In this embodiment, a material possessing the above characteristics is defined as a fluorescent material.

[0078] The excitation and light emission of fluorescent pink ink have been explained above. However, in this embodiment, fluorescent ink that emits light with a different wavelength can also be used. Examples of fluorescent inks such as this one include fluorescent blue, which emits light in the blue region (from 450 nm to 500 nm), and fluorescent green, which emits light in the green region (from 500 nm to 560 nm). Furthermore, fluorescent yellow, which emits light in the yellow region (from 565 nm to 590 nm), fluorescent orange, or fluorescent red, which emits light in the red region (from 590 nm to 780 nm), can also be used. Additionally, fluorescent inks obtained by combining the fluorescent inks described above can also be used. Furthermore, fluorescent inks with different intensities causing excitation wavelengths can be combined and the color hue adjusted. For example, fluorescent pink, which exhibits weak excitation in the blue region, strong excitation in the green region, and emits light in the orange region, is mentioned.

[0079] In this embodiment, subtractive color-mixing ink is defined as an ink containing a colorant that absorbs light of a specific wavelength from the projected light and does not emit light. For example, subtractive color-mixing ink refers to basic color inks such as cyan, magenta, and yellow. The spectral reflectance of subtractive color-mixing ink is, for example,... Figure 7 The spectral reflectance of cyan (C) 703, magenta (M) 704, and yellow (Y) 705 are shown. Unlike fluorescent inks, subtractive mixed inks only absorb light, therefore their reflectance does not exceed 1.

[0080] <About Fluorescent Ink>

[0081] Next, the fluorescent ink used in this embodiment will be explained. In this embodiment, a fluorescent ink produced by mixing a dispersion having fluorescent properties, a solvent, and a surfactant is used. The fluorescent dispersion used in this embodiment is a dispersion having fluorescent properties. For example, NKW-3207E (fluorescent pink aqueous dispersion: NIHON KEIKOHKAGAKU) and NKW-3205E (fluorescent yellow aqueous dispersion: NIHON KEIKOHKAGAKU) are mentioned, but any dispersion having fluorescent properties can be used.

[0082] Ink is produced by combining a known solvent and a known surfactant with the aforementioned fluorescent dispersion and dispersing the fluorescent dispersion. There are no particular limitations on the dispersion method of the fluorescent dispersion. For example, fluorescent dispersions obtained by dispersion with a surfactant, and fluorescent dispersions obtained by dispersion with a dispersing resin, can be used. Of course, combinations of fluorescent dispersions with different dispersion methods can also be used. As surfactants, anionic, nonionic, cationic, and biomimetic surfactants can be used. As dispersing resins, any resin having water solubility or water dispersibility can be used, but preferably a dispersing resin with a weight average molecular weight of not less than 1000 and not more than 100,000, and further not less than 3000 and not more than 50,000. As solvents, an aqueous solvent, for example, containing water or a water-soluble organic solvent, is preferred.

[0083] <About Printing Media>

[0084] In this embodiment, the printing medium to which the ink is ejected (also referred to as the printed medium) has a substrate and at least one ink receiving layer. Preferably, the printing medium is an inkjet printing medium used in inkjet image printing methods.

[0085] (Surface roughness of the printing medium)

[0086] It is sufficient to appropriately adjust the surface roughness of the printing medium according to the desired gloss level. As a method for adjusting the surface roughness of the printing medium, for example, a method is mentioned in which the surface of a substrate or similar material with a specific texture is pressed against the surface of the printing medium by a roller with a specific texture, and the textured surface is coated with an ink receiving layer coating liquid. Furthermore, a method is mentioned in which, after forming an ink receiving layer by applying an ink receiving layer coating liquid, a roller with a specific texture is pressed against the surface of the ink receiving layer, thereby providing the texture. In addition, the surface roughness can be controlled according to the particle size of the inorganic particles to be included in the ink receiving layer; by further providing a layer including inorganic particles on the surface of the ink receiving layer and controlling the surface roughness based on the particle size of the inorganic particles in the layer and the coverage of the layer; and so on. The preferred surface roughness of a representative printing medium is described below.

[0087] (1) Glossy paper

[0088] When using glossy paper as the printing medium, the arithmetic mean surface roughness Ra of the printing medium as specified in JIS B 0601:2001 is preferably 0.13 μm or less. More preferably, Ra is not less than 0.05 μm and not more than 0.13 μm, and particularly preferably, Ra is not less than 0.10 μm and not more than 0.13 μm.

[0089] (2) Matte paper

[0090] When using matte paper as the printing medium, the arithmetic mean surface roughness Ra of the printing medium as specified in JIS B 0601:2001 is preferably not less than 1.0 μm and not more than 10.0 μm, and more preferably not less than 1.0 μm and not more than 5.0 μm. Furthermore, when using matte paper as the printing medium, the root mean square slope RΔq of the surface roughness curve element of the printing medium as specified in JIS B 0601:2001 is preferably 0.3 μm or greater, and more preferably 0.5 μm or greater.

[0091] <About Block Printing and Measurement>

[0092] In this embodiment, the utilization is carried out. Figure 6A The readings of the color sensor block shown.

[0093] First, let's illustrate an example of reading the magenta halftone block. Figure 8A This illustrates the spectral reflectance of ink obtained by measuring a magenta patch printed on paper using a spectrophotometer. Figures 8A to 8E In the various graphs, the horizontal axis represents wavelength λ, and the vertical axis represents reflectance. Figure 8A The symbol 801 in the figure represents the reflectance of the paper white, and the symbols 802 to 807 each represent the reflectance of the calibration block when the applied amount is changed at 20% intervals.

[0094] As described above, in this embodiment, the color sensor illuminates one of the LEDs for R, G, and B and receives light in the visible light region (400 to 700 nm). In the case of measuring a magenta patch, the color sensor illuminates a green LED. The reflectance changes significantly around 540 nm as the amount of magenta ink changes; therefore, using a green LED as the illuminated LED allows for efficient detection of changes in ink amount using the sensor. Figure 9A The symbol 905 in the figure shows an example of the results of measuring seven blocks printed with red ink using a color sensor.

[0095] like Figure 6B As shown, each LED has a bandwidth of a predetermined wavelength. For example, a green LED has a light emission spectrum in the wavelength region around 500 to 600 nm, and as... Figure 6AAs shown, a sensor receives the reflected light from the illuminated light. In the case of subtractive mixing inks, the increase in ink volume reduces the reflected light, thus decreasing the sensor's output value (reflectance coefficient). Based on this reduction, the change in discharge volume is estimated. Specifically, the target concentration is compared with the actual device concentration calculated using Formula 1 or Formula 2 based on the sensor's output value (reflectance coefficient). Then, if the actual device concentration is lower than the target concentration, the discharge volume of the actual device is estimated to be less than the discharge volume of the reference device. On the other hand, if the actual device concentration is higher than the target concentration, the discharge volume of the actual device is estimated to be greater than the discharge volume of the reference device.

[0096] Here, for reference Figure 9A . Figure 9A The symbol 905 in the equation represents the relationship between the amount of magenta ink applied and the reflectance calculated according to Formula 1. In the relationship represented by symbol 905, for the discharge difference 902 (=20%) that is expected to be corrected by color calibration, the reflectance difference 907 (=0.2) is sufficiently greater than the sensor reading error 901 (=0.1), and therefore can be ignored. Therefore, the discharge difference that is expected to be corrected using the sensor can be detected with high precision. Strictly speaking, the discharge difference and the applied difference are different, but here, the discharge difference is approximated as the applied difference, and this applies equally below.

[0097] Next, an example of reading the fluorescent pink halftone block will be explained. Figure 8B The diagram shows the ink spectral reflectance obtained by measuring a block printed on paper using only fluorescent pink ink with a spectrophotometer. Figure 8B The symbol 811 in the figure represents the reflectance of the paper white, and the symbols 812 to 817 each represent the spectral reflectance of the calibration block when the applied amount is changed at 20% intervals.

[0098] When measured with a color sensor, similar to the case of magenta, the reflectance variation is large around 540nm, therefore, when illuminating a green LED... However, regarding phosphor pink ink, as... Figure 8B As shown, with increasing ink volume, the reflectivity near λ = 540 nm decreases, while on the other hand, light emission occurs near λ = 600 nm due to fluorescence. Therefore, compared to the case where there is no light emission due to fluorescence, the amount of light received by the sensor increases with increasing ink volume.

[0099] Therefore, as from Figure 9A The symbol 904 in the figure represents an example of the results of measuring seven fluorescent pink patches using a color sensor. The slope of the relationship between the amount of fluorescent pink ink applied and the reflectance calculated according to Formula 1 is compared with the slope of magenta. Figure 9AThe symbol 905 in the original text becomes flatter. As a result, the color sensor's calibration error (=0.1) increases for the reflectance difference 906 (=0.05) corresponding to the discharge difference 902 (=20%) that is expected to be corrected by color calibration, and therefore the discharge difference cannot be detected with high accuracy.

[0100] Next, we will describe the case of printing by mixing the fluorescent pink ink specified by the fluorescent pink halftone block with green ink applied at 80%. In the "printing by mixing inks" in this embodiment, the two inks are discharged from separate outlets, but are applied to the same area on the paper in a mixed state. Figure 8D An example of the spectral reflectance of a fluorescent ink halftone patch is shown with an application of 80% green ink. (Compared to...) Figure 8C The same applies to the symbol 821 in the text. Figure 8D The symbol 831 indicates the spectral reflectance of the calibration block with 80% green ink applied. Furthermore, symbols 832 to 837 each indicate the spectral reflectance of the calibration block when the application amount of fluorescent pink ink is varied at 20% intervals for an 80% application amount of green ink. The 80% application amount of green ink is an example of a value used when covering the paper surface with ink, taking into account the ink bleeding onto the sheet, and this is not limited by the sheet or the ink. The optimal application amount is determined using the conditional formula described later in <Regarding the Selection of Subtractive Mixing Inks for Block Printing>.

[0101] Figure 10A and Figure 10B Each is used to illustrate the use Figure 6A The graph shows the measurements of a printed sample of the sensor unit. In detail, Figure 10A This demonstrates the case of printing using only fluorescent pink ink, and Figure 10B This illustrates a printing process where fluorescent pink ink is mixed with green ink, which is used as a subtractive mixing ink.

[0102] To explain Figure 10A As described above, the fluorescent pink ink 1004 absorbs the incident light and reflects light in the wavelength region that is not absorbed (indicated by arrow 1001), and further adds the emitted light of the fluorescent pink ink 1004 (indicated by arrow 1002).

[0103] On the other hand, such as Figure 10B As shown, when printing is performed by mixing fluorescent pink ink with green ink, the light emitted from the fluorescent pink ink 1004 (indicated by arrow 1002) is absorbed by the green ink layer 1005 as it passes through. Consequently, the amount of light to be emitted is reduced (indicated by arrow 1003). Therefore, compared to printing without mixing green ink... Figure 9B Compared to symbol 904 in the text, in the case of printing by mixing green ink, such as Figure 9B As indicated by symbol 909, the slope of the relationship between the applied amount and the reflection coefficient calculated by Equation 2 becomes steep.

[0104] As a result, the reflectance difference 908 (=0.2) corresponding to the expected ejection difference 902 (=20%) corrected by color calibration becomes greater than the correction error difference 901 (=0.1) of the color sensor. Therefore, the ejection difference can be detected with high accuracy. In this embodiment, when printing by mixing green ink, at least one green ink dot covers the fluorescent pink ink dot. For example, by controlling the order in which the inks are applied to the same area, such that green ink is applied to the position where fluorescent pink ink has been applied, the green ink dot can cover the fluorescent pink ink dot. Furthermore, the amount of application of the green ink dot covering the fluorescent pink ink dot to the desired degree can be achieved by adjusting the application timing of each ink.

[0105] Furthermore, as mentioned earlier, in order for light with the excitation wavelength to be absorbed, green ink needs to be applied until the coverage on the paper surface becomes a predetermined percentage (80% in this example) or higher. Moreover, to avoid the effects caused by deviations in the amount of green ink applied, when calculating according to Formula 2, it is best to treat the reading value of the block printed by the actual device using only 80% applied green ink as P(C).

[0106] Next, an example of printing by mixing yellow ink instead of green ink will be given. Figure 8E The spectral reflectance is shown when printing is performed by mixing fluorescent pink ink with yellow ink. Figure 8E Symbol 841 indicates the spectral reflectance of a calibration block with 80% yellow ink applied. Furthermore, symbols 842 to 847 each indicate the spectral reflectance of the calibration block when the applied amount of yellow ink and fluorescent pink ink is varied at 20% intervals.

[0107] like Figure 8E As shown, the yellow ink has the effect of absorbing the excitation wavelength, but it cannot absorb the emission wavelength. Specifically, it cannot suppress reflected light caused by light emission around 600nm, therefore the effect of the yellow ink is insufficient.

[0108] Based on the above, when the wavelength at the point where the spectral reflectance of the fluorescent ink intersects with the spectral reflectance of white paper is defined as the "reference wavelength," the characteristic of the subtractive color-mixing ink that mixes fluorescent ink during printing is that the reflectance on the wavelength side longer than the reference wavelength is relatively lower than the reflectance on the shorter wavelength side. In the preceding description, green ink was used as the ink mixed during printing, but other inks such as cyan ink can be used as long as this characteristic is met.

[0109] <Regarding the selection of subtractive inks for block printing>

[0110] The following describes the conditions that the subtractive color mixing ink in this embodiment should meet.

[0111] With the reflection spectrum set as S(λ), the light emission spectrum set as α(λ), the excitation spectrum set as β(λ), and the light source spectrum set as E(λ), the intensity Y of light at a certain wavelength (λ) in the fluorescent ink can be defined as the following formula 3.

[0112] Y(λ) 荧光 =S(λ)E(λ)+α(λ)∫ λ β(λ 激发 )E(λ 激发 )dλ 激发 …Formula 3

[0113] (Source: Journal of the Japan Society for Imaging Studies, 2018, Vol. 57, No. 2, pp. 207-213)

[0114] Here, in Equation 3, λ ranges from 400 to 700 nm. Furthermore, λ... 激发 λ is the excitation wavelength of the fluorescent ink, and for the fluorescent pink ink used in this embodiment, λ 激发 The range is from 400nm to 630nm.

[0115] On the other hand, since there is no light emission caused by fluorescence, the light intensity at a certain wavelength λ in the subtractive color mixing ink can be defined by the following formula 4.

[0116] Y(λ) 减法 =S(λ)E(λ)…Formula 4

[0117] Then, the light intensity of the fluorescent ink with a small discharge amount (denoted as Vd) is set as Y(λ). 荧光Vd小 Furthermore, the light intensity of the fluorescent ink with a large discharge volume is set as Y(λ). 荧光Vd大 Then, assume that the light intensity of the secondary color generated by the fluorescent ink and the subtractive mixing ink is Y(λ). 荧光 ×Y(λ) 减法 .

[0118] Then, with the interval of n of Σ set to 10 of λ from 400 to 700, the intensity of the light received by the sensor can be defined as Equation 5 below.

[0119]

[0120] Therefore, for the discharge difference Vd large – Vd small (=20%) that is expected to be corrected by calibration as described above, the subtractive mixing ink needs to be an ink that meets the following condition (Formula 6).

[0121] Sensor reading error <|Σ n (Y(λ) 荧光Vd小 ×Y(λ) 减法 )-Σ n (Y(λ) 荧光Vd大 ×Y(λ) 减法 )|

[0122] …·Formula 6

[0123] From the subtractive mixing inks assembled in the printer in a manner that meets the above conditions, select the optimal ink type, and find the optimal application amount by changing the application amount of the selected ink type.

[0124] <Regarding the calibration process>

[0125] The following uses Figure 12A and Figure 12B The calibration process in this embodiment will be explained below. Each calibration process is performed by the CPU 403, etc., based on the storage unit 405 (see...). Figure 4 The calibration process is performed using the calibration procedure stored in the UI unit 402. The parameters required for the calibration process are input by the user via the UI unit 402.

[0126] First, let me explain how to print. Figure 2 The process of calibrating the block diagram shown (steps S1201 to S1205) is as follows: First, in S1201, the CPU 403 determines whether the target block to be created is a fluorescent ink block. If the determination result of this step is affirmative, the process proceeds to step S1202. On the other hand, if the determination result of this step is negative, the process proceeds to S1203. Hereinafter, "step S-" will be abbreviated as "S-".

[0127] In S1202, CPU 403 creates block image data for estimating the discharge volume, wherein a subtractive color mixing ink with high reflectivity at the excitation wavelength of the fluorescent ink and low reflectivity in the emission wavelength region of the fluorescent ink is mixed with the block image data. Specifically, the subtractive color mixing ink to be mixed with the fluorescent ink during printing is selected by the method described in the previous section "Regarding the selection of subtractive color mixing inks during printing".

[0128] In S1203, CPU 403 creates block image data for estimating the discharge amount, wherein the applied amount varies from 0% to 120% in 20% intervals in the block image data. In this embodiment, blocks in which the ink applied amount varies from 0% to 120% in 20% intervals are used, but the intervals can be other predetermined intervals besides 20%. Furthermore, the minimum applied amount can be anything other than 0%, and the maximum applied amount can be anything other than 120%.

[0129] In S1204, CPU 403 determines the image data of all created object ink color block maps ( Figure 2 The process checks whether the creation of the image data of the block diagram shown is complete. If the result of this step is positive, the process proceeds to S1205 after storing the image data of the created block diagram in storage unit 405. On the other hand, if the result of this step is negative, the process returns to S1201.

[0130] In S1205, CPU 403 reads information related to printing on the printing medium from storage unit 405 and sends this information to printer 407. Similarly, CPU 403 also reads block diagram data from storage unit 405. Figure 2 The image data of the block diagram shown is transmitted to printer 407. This block diagram data is transmitted via image signal I / F101 of printer 407 (see image signal I / F101). Figure 1 The data is input to a halftone processing unit (not shown) next to the calibration processing unit 107, and halftone processing is performed directly on the block image data. Afterwards, the printing unit 411 performs printing based on the halftone processed block image data.

[0131] In this embodiment, image data for the calibration block map is created during the calibration process, but it is also possible not to create image data during the calibration process. For example, pre-created block map data can be stored in storage unit 405 and read and used during calibration processing.

[0132] Next, the process of measuring each block included in the printed block diagram will be explained (S1206 to S1209). First, in S1206, the printer control unit 409 determines whether the block to be measured is a fluorescent ink block. If the determination result of this step is affirmative, the process proceeds to S1207. On the other hand, if the determination result of this step is negative, the process proceeds to S1208.

[0133] In S1207, the printer control unit 409 reads the reflection intensity using the sensor unit 412 by projecting light, whose spectral distribution exists in a wavelength region including the excitation wavelength of ink, onto the block. Specifically, the printer control unit 409 reads the reflection intensity of the block using the method described in <About Block Printing and Measurement>.

[0134] <About Block Printing and Measurement>

[0135] In S1208, the printer control unit 409 uses the sensor unit 412 to read the reflection intensity by projecting light with a spectral distribution that exists in a wavelength region where the spectral reflectance of the ink changes greatly with the change in the amount of ink dispensed.

[0136] In this embodiment, the calibration process selects to illuminate the calibration block with light during the measurement of the calibration block, but the measurement can also be performed by using the conditions related to the illumination light that are pre-stored in the storage unit 405.

[0137] In S1209, the printer control unit 409 determines whether the measurement of all ink color blocks has been completed. If the determination result of this step is positive, the process proceeds to S1210 for calibration. On the other hand, if the determination result of this step is negative, the process returns to S1206.

[0138] Next, the actual calibration process (S1210 to S1212) will be explained. First, in S1210, the printer control unit 409 estimates the discharge volume based on the reflection intensity read by the block measurement.

[0139] At S1211, the printer control unit 409 corrects the amount of ink applied based on the estimation result of S1210. Specifically, the printer control unit 409 performs the correction by the method described in the previous section on <Execution of Calibration>, and performs the correction process using the 1D-LUT stored in the calibration processing unit 107. Alternatively, the correction process can be performed based on the target concentration value and the concentration value calculated from the read reflection intensity without estimating the ejection amount based on the reflection intensity read by the block measurement (i.e., without performing S1210).

[0140] In S1212, the printer control unit 409 determines whether the calibration for all ink colors has been completed. If the determination result of this step is positive, the process terminates. On the other hand, if the determination result of this step is negative, the process returns to S1210.

[0141] In this embodiment, the tone correction processing unit 106 performs processing using a 1D-LUT different from the 1D-LUT used by the calibration processing unit 107. However, the tone correction processing unit 106 and the calibration processing unit 107 can also perform processing using a single 1D-LUT obtained by combining these 1D-LUTs. Furthermore, it is also possible to... Figure 1 The image processing shown generates 1D-LUT data.

[0142] <Effects of this embodiment>

[0143] According to this embodiment, high-precision color calibration in printing devices that use fluorescent ink can be achieved at low cost.

[0144] [Second Embodiment]

[0145] In the first embodiment, the aspect of printing calibration block diagrams by mixing fluorescent ink and subtractive color mixing ink is described. In this embodiment, the printing order of the fluorescent ink and subtractive color mixing ink for the blocks used for calibration varies depending on the printing medium. This is because the light emission and absorption efficiency of the fluorescent ink varies depending on the printing medium and the printing order.

[0146] As a printing medium for printing blocks, matte paper with high surface roughness (i.e., rough) and glossy paper with low surface roughness (i.e., smooth) are mainly mentioned.

[0147] Figure 14A and Figure 14B This shows the case of printing halftone blocks on matte paper.

[0148] Figure 14A An example of spectral reflectance is shown when a fluorescent pink halftone patch is printed on matte paper by mixing the fluorescent pink ink specified by the fluorescent pink halftone patch with green ink applied at 80% of its amount, without any green ink being expelled after the fluorescent pink ink. In detail, Figure 14A The symbol 1401 indicates the spectral reflectance of the calibration block with 80% green ink applied. In addition, symbols 1402 to 1407 each indicate the spectral reflectance of the calibration block when the application amount of green ink and fluorescent pink ink is varied at 20% intervals.

[0149] Unlike Figure 14A , Figure 14B This illustrates an example of spectral reflectance when a fluorescent pink halftone patch is printed on matte paper by mixing the fluorescent pink ink specified by the fluorescent pink halftone patch with green ink applied at 80% of its amount, with the green ink expelled after the fluorescent pink ink. In detail, Figure 14BThe symbol 1411 indicates the spectral reflectance of the calibration block with 80% green ink applied. In addition, symbols 1412 to 1417 each indicate the spectral reflectance of the calibration block when the amount of green ink and fluorescent pink ink applied is varied at 20% intervals.

[0150] on the other hand, Figure 14C and Figure 14D This shows the case of printing halftone blocks on glossy paper.

[0151] Figure 14C An example of spectral reflectance is shown when a fluorescent pink halftone patch is printed on glossy paper by mixing the fluorescent pink ink specified by the fluorescent pink halftone patch with green ink applied at 80% of its amount, without any green ink being expelled after the fluorescent pink ink. In detail, Figure 14C The symbol 1421 indicates the spectral reflectance of the calibration block with 80% green ink applied. In addition, symbols 1422 to 1427 each indicate the spectral reflectance of the calibration block when the amount of green ink and fluorescent pink ink applied is varied at 20% intervals.

[0152] Unlike Figure 14C , Figure 14D This illustrates an example of spectral reflectance when a fluorescent pink halftone patch is printed on glossy paper by mixing the fluorescent pink ink specified by the fluorescent pink halftone patch with green ink applied at 80% of its amount, with the green ink being expelled after the fluorescent pink ink. In detail, Figure 14D The symbol 1431 indicates the spectral reflectance of the calibration block with 80% green ink applied. In addition, symbols 1432 to 1437 each indicate the spectral reflectance of the calibration block when the amount of green ink and fluorescent pink ink applied is varied at 20% intervals.

[0153] Figure 15A and Figure 15B Each graph shows the concentration characteristics calculated using measurements of halftone blocks of fluorescent pink ink.

[0154] Figure 15A An example is shown of calculating a concentration value using the measured value of a block according to Formula 2, wherein the measured value of the block is obtained by printing a fluorescent pink halftone block on matte paper by mixing the fluorescent pink ink specified by the fluorescent pink halftone block with green ink. Figure 15A The solid line 1501 shows the concentration value calculated based on the block measurements when no green ink is expelled after the fluorescent pink ink. In contrast, the dashed line 1502 shows the concentration value calculated based on the block measurements when green ink is expelled after the fluorescent pink ink.

[0155] Figure 15B An example is shown of calculating a concentration value using the measured value of a block according to Formula 2, wherein the measured value of the block is obtained by printing a fluorescent pink halftone block on glossy paper by mixing the fluorescent pink ink specified by the fluorescent pink halftone block with green ink. Figure 15B The solid line 1511 shows the concentration value calculated based on the block measurements when no green ink is expelled after the fluorescent pink ink. In contrast, the dashed line 1512 shows the concentration value calculated based on the block measurements when green ink is expelled after the fluorescent pink ink.

[0156] Regarding matte paper, such as Figure 14A and Figure 14B As shown, the spectral reflectance near λ = 600 nm indicates that, compared to the case where green ink is emitted after the fluorescent pink ink, the emission wavelength of the fluorescent pink ink is absorbed more when no green ink is emitted after the fluorescent pink ink.

[0157] On the other hand, regarding glossy paper, such as Figure 14C and Figure 14D As shown, based on the spectral reflectance near λ = 600 nm, the absorption efficiency at the emission wavelength appears to be the same, but... Figure 15A and Figure 15B As shown, the concentration values ​​are different. That is to say, in the case of glossy paper, it can be seen that when green ink is emitted after fluorescent pink ink, the emission wavelength of fluorescent pink is absorbed more than when no green ink is emitted after fluorescent pink ink, compared to when green ink is emitted after fluorescent pink ink.

[0158] Therefore, when printing blocks on matte paper, it can be determined that the sensor's S / N ratio increases when green ink is not expelled after the fluorescent pink ink. Furthermore, when printing blocks on glossy paper, it can be determined that the sensor's S / N ratio increases when green ink is expelled after the fluorescent pink ink.

[0159] <About Block Diagrams>

[0160] Figure 13 An example of a block diagram in this embodiment is shown. In this embodiment, fluorescent pink colorant with an input signal that changes at 20% intervals and green colorant with an input signal that is fixed at a predetermined constant application amount of 80% are used to print fluorescent pink blocks.

[0161] Figure 13 In the fluorescent pink 1 block group P22 is a block group that does not expel green ink after the fluorescent pink ink. P221 is printed with 0% fluorescent pink and 80% green, P222 is printed with 20% fluorescent pink and 80% green, and P223 is printed with 120% fluorescent pink and 80% green.

[0162] In contrast, block group P23 of fluorescent pink 2 is a block group that discharges green ink after fluorescent pink ink. P231 was printed with 0% fluorescent pink and 80% green ink, P232 was printed with 20% fluorescent pink and 80% green ink, and P233 was printed with 120% fluorescent pink and 80% green ink.

[0163] Any method can be used to control the printing order of ink. One method for controlling the printing order in a so-called serial inkjet printer, which prints by scanning the ink-discharging printhead in a direction intersecting with the printing medium, is as follows.

[0164] For example, when printing is completed by performing 16 scans with the print head, green ink can be expelled after the fluorescent pink ink by expelling the fluorescent pink ink in the first eight scans and then expelling green ink in the following eight scans. Alternatively, by expelling both fluorescent pink and green ink simultaneously during the 16 scans, green ink can be expelled without following the fluorescent pink ink. The number of scans is not limited to 8 or 16, and other numbers of scans can also be performed.

[0165] Even when green ink is ejected after fluorescent pink ink, scans may still involve the ejection of both green and fluorescent pink ink. Furthermore, even when green ink is not ejected after fluorescent pink ink, scans may still involve the ejection of neither green nor fluorescent pink ink.

[0166] The printing sequence of inks can also be controlled by changing the outlets for the fluorescent pink ink and green ink in the printhead, or by altering the position of the printing media through ink ejection. Additionally, the printing sequence can be controlled using a so-called multi-pass mask.

[0167] Figure 16 It is a flowchart of a process that selectively employs measurements of fluorescent pink blocks used to generate 1D-LUT data for use in calibration processing unit 107. Figure 16 The processes shown can be performed by the CPU 403 of PC 401 or the printer control unit 409 of printer 407.

[0168] First, in S1601, information related to the printing media containing blocks is obtained.

[0169] In S1602, using the information obtained in S1601, it is determined whether the printing medium with the printed blocks is matte paper or glossy paper. If the determination result of this step indicates that the printing medium is matte paper, the process proceeds to S1603; on the other hand, if the determination result indicates that the printing medium is glossy paper, the process proceeds to S1604.

[0170] In S1603, the measurement value is used when green ink is not discharged after the fluorescent pink.

[0171] In S1604, the measurement value of green ink being discharged after fluorescent pink ink is used.

[0172] In this embodiment, the following block pattern example is shown (see Figure 13 In this block image example, there are blocks that do not expel green ink after the fluorescent pink ink and blocks that expel green ink after the fluorescent pink ink. However, it is not necessary to print both blocks, and it is also possible to print only the blocks used for generating the 1D-LUT data, and the number of blocks printed depends on the type of printing medium on which the blocks are printed.

[0173] Furthermore, the type of printing media is not limited to glossy and matte paper, and another type of printing media can be used.

[0174] Furthermore, the surface roughness of the printed medium can be measured, and the block group that adopted the measured value among multiple printed block groups can be determined based on the measured surface roughness, thus identifying the printed block group among multiple block groups, and so on. For example, consider: if the measured surface roughness is greater than a predetermined threshold, the measured value of block group P22 of fluorescent pink 1 is used, and if the surface roughness is less than or equal to the predetermined threshold, the measured value of block group P23 of fluorescent pink 2 is used.

[0175] Furthermore, the type of printing media is not necessarily set based on surface roughness. For example, the type of printing media can be preset based on factors such as the sensor's signal-to-noise ratio (S / N ratio).

[0176] <Effects of this embodiment>

[0177] As described above, in this embodiment, the printing order of the fluorescent ink and subtractive mixing ink when printing blocks used to generate 1D-LUT data for calibration varies depending on the printing medium. Therefore, the sensor's signal-to-noise ratio increases, and calibration accuracy can be improved.

[0178] [Third Embodiment]

[0179] In the first embodiment, printing was described by mixing fluorescent pink ink with green ink. In contrast, in this embodiment, instead of printing by mixing green ink as a subtractive color mixing ink, a light filter is installed on the light-receiving side of the sensor.

[0180] Specifically, such as Figure 11A As shown, an optical filter 1102 is installed at the location where the light used to illuminate the printed surface by the LED is received by the sensor. In the case of the fluorescent pink ink 1101, a green filter can be specified as a candidate for the optical filter, similar to the case of the green ink in the first embodiment. By using the green filter, a portion of the light emitted due to fluorescence (shown by arrow 1104) is cut off (shown by arrow 1105), and changes in the amount of reflected light (shown by arrow 1103) are separated and detected. Then, calibration can be performed by estimating the discharge amount based on the detected change in the amount of reflected light. That is, in this example, the optical filter suppresses changes in the amount of emitted light near λ = 600 nm, which are inconvenient to detect due to changes in the amount of reflected light accompanying changes in discharge amount (see [link to original text]). Figure 8B ).

[0181] Furthermore, when using an optical filter, changes in reflected light can be detected not only by suppressing the amount of emitted light, but also by suppressing changes in reflected light. For example... Figure 11B As shown, the change in the amount of emitted light (shown by arrow 1102) can also be separated and detected by using a red filter as optical filter 1102 to cut off a portion of the reflected light (shown by arrow 1103) in the excitation wavelength region (shown by arrow 1106). Then, calibration can be performed by estimating the emission amount based on the detected change in the amount of emitted light. That is, in this example, the optical filter suppresses the change in the amount of reflected light near λ = 540 nm, which is inconvenient to detect due to changes in the amount of emitted light accompanying changes in emission amount (see [link to original text]). Figure 8B ).

[0182] <Effects of this embodiment>

[0183] According to this embodiment, high-precision color calibration in printing devices that use fluorescent ink can be achieved at low cost.

[0184] [Other Embodiments]

[0185] In the embodiments described above, the printing method of the printing device is an inkjet method, but the printing method of the printing device is not limited to the inkjet method, and other printing methods such as electrophotography and thermal transfer methods can be used.

[0186] In addition, the reflectance coefficient is used to illustrate the sensor's measurements, but concentration or color values ​​(CIE L*a*b* and tristimulus values ​​XYZ, etc.) calculated based on the reflectance coefficient can also be used.

[0187] In the embodiments described above, it is assumed that the block map used for calibration is a halftone block, but a calibration table can also be generated by estimating the amount of a particular hue emitted.

[0188] In the embodiments described above, the light-receiving element of the color sensor is assumed to be a photodiode. However, the light-receiving element of the color sensor can also have a structure such as a phototransistor.

[0189] In the embodiments described above, a structure in which the color sensor is mounted on the side of the carriage was illustrated (see [link]). Figure 5 However, the structure can be one where the color sensor is mounted in a location other than the side of the carriage, or one where the blocks can be measured manually.

[0190] In the embodiments described above, a color sensor with an RGB LED structure was illustrated (see...). Figure 6A and Figure 6B However, the LEDs of the color sensor can be LEDs other than RGB, and the color sensor can also have LEDs of three or more colors or three or fewer colors.

[0191] Other embodiments

[0192] The embodiments of the present invention can also be implemented by providing software (programs) that perform the functions of the above embodiments to a system or device via a network or various storage media, and the computer or central processing unit (CPU) or microprocessor unit (MPU) of the system or device reads out and executes the program.

[0193] According to one embodiment of the present invention, high-precision color calibration in printing equipment using fluorescent ink can be achieved at low cost.

[0194] Although the invention has been described with reference to exemplary embodiments, it should be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the appended claims is to be interpreted in the broadest sense to include all such modifications, equivalent structures, and functions.

Claims

1. An image processing apparatus, comprising: A processing unit configured to perform processing related to color calibration in a printing device used to print images on a printing medium using fluorescent ink; as well as An execution unit is configured to perform calibration processing of the printing device based on measurements obtained through a measurement block diagram, the block diagram being used to obtain information related to the amount of fluorescent ink ejected from the printing device. The blocks included in the block diagram are printed using the fluorescent ink and the subtractive color mixing ink, and the fluorescent ink and the subtractive color mixing ink are discharged such that the dots of the subtractive color mixing ink and the dots of the fluorescent ink exist in the same area on the surface of the printing medium.

2. The image processing apparatus according to claim 1, wherein, The spectral reflectance of the subtractive color mixing ink is as follows: the reflectance of the fluorescent ink is high in the excitation wavelength region and low in the emission wavelength region.

3. The image processing apparatus according to claim 1 or 2, further comprising: A printing unit configured to print the image on the printing medium using the fluorescent ink and the block diagram.

4. The image processing apparatus according to claim 1 or 2, further comprising: A measurement unit, comprising a light-receiving element and one or more light sources, is configured to measure the blocks included in the block diagram.

5. The image processing apparatus according to claim 4, wherein, The light source or each of the multiple light sources emits light with a predetermined wavelength.

6. The image processing apparatus according to claim 4, wherein, In the measurement unit, light is projected from a light source onto the block, wherein the spectral distribution of the light exists in a wavelength region including the excitation wavelength of the fluorescent ink.

7. The image processing apparatus according to claim 1 or 2, wherein, The block diagram includes multiple blocks that contain the block, and The plurality of blocks are blocks in which a predetermined amount of the subtractive mixing ink is discharged, and for these blocks, the amount of fluorescent ink discharged is varied at predetermined intervals.

8. The image processing apparatus according to claim 1 or 2, wherein, The subtractive color mixing ink is an ink in which the reflectance at the point where the spectral reflectance of the fluorescent ink intersects with the spectral reflectance of paper white is defined as the reference wavelength, and the reflectance on the wavelength side that is longer than the reference wavelength is relatively lower than the reflectance on the wavelength side that is shorter than the reference wavelength.

9. The image processing apparatus according to claim 1 or 2, wherein, The coverage of the subtractive mixed ink on the paper surface is higher than or equal to a predetermined value.

10. The image processing apparatus according to claim 1 or 2, wherein, The actuator performs the calibration process based on the concentration characteristics of the fluorescent ink calculated using the measured values.

11. The image processing apparatus according to claim 7, wherein, Among the plurality of blocks are: The first group of subtractive mixed inks is not discharged after the fluorescent ink is discharged; and After the fluorescent ink is discharged, the second group of subtractive mixed inks is discharged.

12. The image processing apparatus according to claim 11, wherein, Each of the first block group and the second block group includes: A block printed using only the subtractive color mixing ink; and Multiple blocks are printed using the subtractive mixing ink and the fluorescent ink, wherein the amount of fluorescent ink discharged from these multiple blocks is varied at predetermined intervals.

13. The image processing apparatus according to claim 11, further comprising: The determination component is configured to determine which of the measurements from the first block group and the second block group to use based on the type of printing media.

14. The image processing apparatus according to claim 11, further comprising: A measurement unit configured to measure the surface roughness of the printing medium; as well as The determining component is configured to determine, based on the surface roughness, which of the measurements from the first block group and the second block group should be used.

15. The image processing apparatus according to claim 14, wherein, The determining component determines that the measurement value of the first block group is used when the surface roughness is greater than a predetermined threshold, and the measurement value of the second block group is used when the surface roughness is less than or equal to the predetermined threshold.

16. The image processing apparatus according to claim 10, further comprising: The determining component is configured to determine, based on the type of printing media, whether to print a first block group or a second block group, wherein for the first block group, the subtractive mixed ink is not discharged after the fluorescent ink is discharged, and for the second block group, the subtractive mixed ink is discharged after the fluorescent ink is discharged.

17. The image processing apparatus according to claim 1, wherein, The fluorescent ink and the subtractive color-mixing ink are discharged into the same area such that at least one point of the subtractive color-mixing ink covers a point of the fluorescent ink.

18. An image processing method performed by an image processing device, the image processing method comprising the following steps: Perform processing related to color calibration in a printing device used to print images on a printing medium using fluorescent ink; as well as The calibration process for the printing device is performed based on measurements obtained through a measurement block diagram, which provides information related to the amount of fluorescent ink ejected from the printing device. The blocks included in the block diagram are printed using the fluorescent ink and the subtractive color mixing ink, and the fluorescent ink and the subtractive color mixing ink are discharged such that the dots of the subtractive color mixing ink and the dots of the fluorescent ink exist in the same area on the surface of the printing medium.

19. A non-transitory computer-readable storage medium storing a program for causing a computer to perform an image processing method performed by an image processing device, the image processing method comprising the following steps: Perform processing related to color calibration in a printing device used to print images on a printing medium using fluorescent ink; as well as The calibration process for the printing device is performed based on measurements obtained through a measurement block diagram, which provides information related to the amount of fluorescent ink ejected from the printing device. The blocks included in the block diagram are printed using the fluorescent ink and the subtractive color mixing ink, and the fluorescent ink and the subtractive color mixing ink are discharged such that the dots of the subtractive color mixing ink and the dots of the fluorescent ink exist in the same area on the surface of the printing medium.

20. A computer program product including a program for causing a computer to perform an image processing method performed by an image processing device, the image processing method comprising the following steps: Perform processing related to color calibration in a printing device used to print images on a printing medium using fluorescent ink; as well as The calibration process for the printing device is performed based on measurements obtained through a measurement block diagram, which provides information related to the amount of fluorescent ink ejected from the printing device. The blocks included in the block diagram are printed using the fluorescent ink and the subtractive color mixing ink, and the fluorescent ink and the subtractive color mixing ink are discharged such that the dots of the subtractive color mixing ink and the dots of the fluorescent ink exist in the same area on the surface of the printing medium.

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